Prius NHW10 (MK1) Hybrids - How to test and resurrect them

Mr. Mik

1 kW
Sep 3, 2008
There will be some updates and edits to the post in this thread as needed, so that the main content of the thread remains concentrated at the beginning.
Hopefully it will get better over time!

Here is a bit of an "Index" for the posts following further down:

External links to sites with information about the identical Honda Insight and Civic "Sticks":

Replacement battery modules are available from (incomplete list):


Anatomy of a single stick and the temperature sensor strip:

Pictures of the Battery-ECU

Changing the inverter coolant:

Getting it into diagnostic mode:

Error codes:

S2000 scanner menu mindmap:

Suggested service summary:

The MAF Sensor and how to clean it:

Results of 3-weeks self-DC test and how to detect a single cell hitting zero V during discharge:

An experimental NHW10 EQ charger design: Special Freddy 8.0

And a later version of the Special Freddy NHW10 EQ charger V10.9:

And the so far latest version of Special Freddy NHW10 EQ charger V15.3:

The Panasonic Patent on how to replace faulty cells in batteries:

Mr. Mik's way of finding the worst capacity cell in a battery:

The DiPoD: A device to tell if you are burning Dino Poop:

My latest "best" method to test a NHW10 battery for faulty sticks: (unless I came up with something better and did not change this link, yet....always working on improvements!)


These batteries are also known as Prius Mk1 or NHW10 traction battery (made by Panasonic).

The Prius Mk1 were apparently only sold in Japan, but are more recently being exported as used cars to other countries.
They are often in good shape, but their weak point is the about 10 year old battery pack.

The NHW10 battery is a 240s NiMH battery consisting of 2 half-packs (HP's) with 20 "sticks" in each of them.
Each stick is made of 6 "D"-sized NiMH cells in serial connection.

The D-cells are firmly welded together to make up a "Stick"and have a female screw connector at each end.

The sticks are therefore 7.2V NiMH batteries and they have a nominal capacity of 6.5Ah.

35mm diameter (at the widest parts)
381mm length (+ screw and connector and temp sensor strip)
400mm total length (approximately, with screws, connectors, BMS tabs, temp sensors etc etc etc)

The form factor is quite different from the better known NHW11 and NHW20 (prismatic) cells from the later Prius models.
These sticks might be far superior to the newer prismatic cells in some applications, particularly because they do not require compression.

The screw connector at each end makes it relatively easy to assemble them into serial or parallel battery packs with very high discharge current capability, voltages and capacity.

There are of course many uses for these batteries other than keeping Prius Mk1 hybrids going for longer.

But selling some sticks to help owners to keep the first hybrids running longer can't be all bad, either!

For applications other than the replacement of defective modules in Prius Mk1 batteries, I suggest to use the following parameters. Sticking to similar parameters is the reason for the phenomenal longevity of the NiMH cells in Toyota Prius and Toyota RAV4-EV cars!

Keep the SOC between 80% and 20% for the vast majority of the batteries life span. Occasional full charges and deep discharges are useful for equalizing and reconditioning, but the longevity of these cells will suffer if they are regularly cycled from full to empty.

Keep them cool whenever possible. They function best at similar ambient temperatures to our human comfort zone: Around 24degrees Celsius!
Use forced air cooling if the battery temperature tends to get high during operation. These batteries can produce very high currents and they can also absorb high currents during regenerative braking, but they need either much time to cool down or active cooling if such high currents are required frequently.

These are the steps before the actual testing can begin:

1) Dis-assembly of the Prius battery pack, so that the dangerous 288V serial connection is reduced to 40 x 7.2V. From then on the modules will be much safer to handle. If you are competent and confident with high voltage DC, it is much faster to cycle an entire pack or two half-packs than to cycle individual sticks. But this is much more dangerous and needs special equipment and safety measures.

2) The modules are then individually removed from the battery, cleaned and inspected for any external damage.

3) Any cracks in the shrink-wrap tubing which covers the modules are repaired with shrink-wrap to prevent accidental shorting between sticks.

4) Both module terminals are then polished to ensure a low resistance electrical connection.

5) The terminals for the temperature sensor strip are then covered with shrink-wrap. This prevents accidental shorting of the module through it's temperature sensors.

After that, the sticks are ready for the testing program. What I have come up with over a month or so of experimenting with these cells is this testing program:
(This keeps changing, of course, hopefully getting better in the process...)

EDIT: The below procedure is too time consuming. I now prefer to charge a half-pack or entire pack and then let it self-discharge for several weeks. Unfortunately this is much more dangerous because the HP remains potentially lethal for the entire resting and testing time.


Systematic Testing Series 1:
CBA2 Capacity test at 6.5A to 6.6V Nr1
CBA2 Capacity test at 0.7A to 5.4V Nr1
CBA2 Capacity test 17A for 1Ah directly after charging
Check Voltage at 1Ah end point.
CBA2 Capacity test at 11.95A to 5.4V directly after 17A test.
CBA2 Capacity test at 0.65A to 5.4V Nr2
100A test; 10seconds (that is about 0.28Ah capacity drained)
Note: Voltage (V): Before: At 10sec point:
60A discharge test to 6.0V: Time to cutoff voltage (s):
Approximate Ah:
Cell temperatures (DegC): Highest: Lowest:
CBA2 Capacity test 6.5A to 5.4V Nr2
Charge and wait 2 weeks.
CBA2 Capacity test 6.5A to 5.4V Nr3; Note open Voltage before test (V):
CBA2 Capacity test at 0.65A to 5.4V
Charge to 2.6Ah @ 3A; Note charger end voltage (V):

This testing schedule might seem a little grueling, and it is...

The worst part was the 2 week holiday (absolutely necessary to keep me away from the sticks during the 2 week self discharge waiting time!)
Mr. Mik said:
There will be many updates and edits to this first post as needed, so that the main content of the thread remains concentrated at the beginning.
When you do update it, please also make a new post so that those (like me) who've subscribed to the thread will be notified that it is updated; otherwise it won't show up that anything has happened in the thread so we'll know to come look. ;)
amberwolf said:
Mr. Mik said:
There will be many updates and edits to this first post as needed, so that the main content of the thread remains concentrated at the beginning.
When you do update it, please also make a new post so that those (like me) who've subscribed to the thread will be notified that it is updated; otherwise it won't show up that anything has happened in the thread so we'll know to come look. ;)
That is a great idea!

I'll drop in a few place-holder replies now so that I keep open some more options to make it more reader-friendly.
I found on other forums that there are massive gaps in the general understanding of the Prius NHW10 (MK1) system, including the battery.

So I decided to take one stick apart to figure out what we are dealing with before I spend too much time guessing.

Of particular interest is the sensor strip
that runs along every stick. The sensor
strips of all 20 sticks in each battery half
are connected in series and
in series with a single 300 Ohm resistor:
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This is the "sacrificial lamb" for this exercise: a stick
that seems to have a weak cell. The cell has show up as
a potential problem in the test procedure described above.
It was reversing during CBA II discharge tests and got hotter
than the other cells during charging and the 100A and 60A discharge
test. It was OK in the 3 week self discharge test, though.
(The blue bit of shrink-wrap was added by myself. Usually it's all orange):
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I marked the cell (in addition to other notes) during
the testing procedures. The photo also shows the
serial number, in case it turns out to be important:
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Here it is without the shrink-wrap, sensor strip still attached:
This is the positive end ot the stick:
And this is the negative end of the stick:

Another view of the sensor strip partially removed from the stick:

Stick and strip separated from each other:
Here is the end of the sensor strip emerging from underneath it's own shink-wrap:

It is covered in a second, clear layer of plastic underneath the black shrink-wrap. The plastic seems a lot like the kind of plastic used to laminate paper.
Together the two layers are quite tough. It is highly unlikely that the layers ever wear through and make contact with the conducting cell walls.
The clear plastic layer is most likely water and chemical-proof. It is definitely not a sensor to detect electrolyte leaks, like some people on other forums have hypothesized.

To be continued .....
The shrink-wrap coming off the sensor strip reveals it's structure: The stainless steel
strip is interrupted six times along it's length, at each cell. A piece of a different
material is sandwiched between the interrupted layers of stainless steel:
This material has temperature dependent resistance, with a very steep rise of resistance around 60degC. See below for measurements.
The print in the sensor strip:
Does anyone know what it means?
Stick and sensor strip:

Here is how I tested the variable, temperature dependent resistance:

I used a copper nut (plumbing leftover) as heat sink/reservoir to achieve some degree of temperature stability;
an aluminium plate to protect the desk from heat, and hot melt glue as a heat transfer device.
A single "Cell sensor sandwich" (CSS, I'll fix this once I know the right term!) was connected
to the copper heat reservoir by hot melt glue, then heated to varying temperatures
with a hot air gun. Both ends of the sensor strip were connected to the probes of an auto-ranging
DMM. The temperature of the hot-melt-glue blob was measured with an IR-thermometer:
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
At around 20degC, the resistance is about 1Ohm.

The resistance rises gradually and slowly with rising temperature, until there is a sudden steep rise at around 60degC. It goes up to 20kOhm (the highest I've seen, maybe more) when the tempeature is around 100degC.


During the slower cooling down phase I took photos of the measurement results during the
rapid drop of resistance around the 60degC mark. The resistance values shown are too low
for the temperatures shown in the same photo (due to the continuing fall of resistance
during the 1-2sec needed to take the temp measurement and take the photo. But it shows
the principle very well, and exact values are not needed. The important point to understand
is that these sensor strips manage to monitor every single cell for overtemperature
without the need for numerous cables!
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mike Dabrowski has done much more accurate measurements, the results can be seen here (in degF): and are explained here:
Click the thumbnails to see larger photos of the Battery-ECU (B-ECU) inside the NHW10 battery housing:

I have not yet have had time to have a close, detailed look at it all in order to figure out what it does (and how it does it).

If anyone is particularly interested and able to analyse this BMS, than I can put in an effort and find the other detail photos which I have taken. I can also take the B-ECU apart again if it helps!
The described procedures involve handling of equipment containing lethal voltages and capable of extremely high discharge currents.

Touching the wrong parts is very likely going to kill you!

Shorting the wrong parts with metal tools will practically explode the tool, or weld it to the battery and cause a fire!

Overcharging can also cause a powerful fire, exploding cells with splattering of caustic electrolyte (which can blind you!) and aggressive toxic fumes!

Only persons experienced in safe electrical working techniques and with appropriate tools and safety equipment should attempt any of this!

You have been warned!

I have two NHW10 half-packs sitting on the bench waiting for their first charge in probably about two or three years.

These half-packs (HPs) are from the battery in the 1998 Prius I bought recently. This battery had been dismantled and was later reassembled incorrectly. I cannot be certain about anything with this battery, because no information is available about what happened to it, especially about what was tried to charge it.


I'll try to assume the worst and the best at the same time!

A) The best, because the car was reportedly running well, possibly without warning symbol, before a 1 month holiday resulted in a non-starting car. Hopefully the battery had simply fallen below 288V, without logging of non-removable EQ-error codes in wherever they get recorded.

B) The worst, because the person/s attempting to fix the battery might have tried to charge it and could have damaged cells by over-charging.

The HP's had been re-installed into the correct sides of the battery housing (contrary to my initial impression), but the plastic board with the System Main Relays (SMRs), pre-charge resistor and Hall-effect sensor had been mounted onto HP1 instead of HP2. As a result, the cooling impeller and ECU did not fit back in and were left in the boot.


I did a thorough inspection of the HPs after removal from the battery housing:
No signs of external heat damage from careless over-charging - good!

No loose screws on the housing, or among the temp sensor strip screws or the bolts securing each stick - good.
I re-tightened all stick bolts with 10Nm, most felt like they had been stuck in the same position and just broke loose to move a few degrees.
So it seems like the sticks were not removed from the assembly, thats also good.
The plastic tubes around the bottom 3 sticks in each HP are also in place - good.

The only damage done by the dis-assembly and incorrect re-assembly seems to be bending of the plastic covers that protect each side of each HP from accidental touching of the stick ends.
One of them has been bent excessively, resulting in white lines appearing in the otherwise transparent plastic sheet.

There might be damage to the wiring harness which is not immediately apparent, but hopefully it is OK.
I'll inspect that visually and with a DMM once I have the wiring diagrams sufficiently advanced to work my way along them for a systematic check (without the batteries attached).


In order to safeguard against the worst scenario I'll do the first few cycles on the bench, rather than charge the entire string and just hope for the best!

The overall idea is to do cycles which exercise the weakest cell gently and progressively, until they have recovered as much as they can.


The things to avoid during the re-awakening of the battery are:

1) Over-charging of cells with full State of Charge (SOC) with currents higher than C/10. The capacity of some cells might initially be severely reduced, so that they might have full SOC long before the rest of the pack. Therefore limit all charging to about 600mA initially.

2) Over-heating of any cells. This can be monitored by measuring the resistance of the thermistor string (PTC Strip) running along all cells. Each cell is monitored, the resistance rises sharply if any cell reaches around 60-70degC. The HP needs to be elevated off the workbench to allow entry of cool air from below. If it is simply placed on a flat surface, it seals very well at the bottom and prevents almost all cooling! If elevated, there is a fair amount of "chimney" effect and cooling works quite well.

3) Reverse charging of any cells for prolonged periods, particularly at high currents. Because capacity is initially unknown this could happen inadvertently and unnoticed during discharging of an entire HP.
Deeply discharging cells (to maybe 0.4V/cell) at very low currents (1A or less) is however likely to result in rejuvenation of the cells.
Best way to prevent this is to use something like the CBA III (Computerized Battery Analyser from West Mountain Radio), but it is time intensive. Maybe I'll set the cutoff voltage to 6V on the first run, unlike with the tests shown at this link:
Some cells were reverse charged with more than 1Ah at 12A, and a 6V cutoff level instead of the 5.4V would have prevented all of the reverse charging!


At this stage I think I'll proceed like this:

1) Mount HP1 on timber rails to allow entry of cooling air at the bottom.
2) Record open voltage of all sticks.
3) 100mA charge of HP1 for 1 hr. (Using timer and temp check via resistance measurement of thermistor chain, recording maximum via min/max function of DMM)
4) 200mA charge of HP1 for 1 hr. (Using timer and temp check via resistance measurement of thermistor chain, recording maximum via min/max function of DMM)
5) 400mA charge of HP1 for 1 hr. (Using timer and temp check via resistance measurement of thermistor chain, recording maximum via min/max function of DMM)
6) Approximately 600mA charge of HP1 for 1 hr. (Using timer and temp check via resistance measurement of thermistor chain, recording maximum via min/max function of DMM)
7) Repeat step 6 up to 15 times as long as there is no unacceptable temperature rise or other problems.
8 ) Discharge all 20 sticks in HP1 at 12A to 6V cutoff level using CBA III.
9) Recharge HP1 at about 600mA to the capacity of the lowest capacity stick. (Using timer and temp check via resistance measurement of thermistor chain, recording maximum via min/max function of DMM)
10) Recharge HP1 at about 600mA for 1 hr. (Using timer and temp check via resistance measurement of thermistor chain, recording maximum via min/max function of DMM)
11) Repeat step 10 until all sticks have been over-charged by at least 50%, without undue temperature rise.
12) Further discharge procedure depends on how closely matched the capacity of all sticks was during the first discharge. If they were wide apart, then I'll probably repeat CBA III tests of all sticks.
If their capacities were closely matched, then I'll consider discharging the entire HP in series through an incandescent light bulb array, with discharge current measured by a clamp meter. I still need to build this resistive load and a timer to safeguard against over-discharging the HP in case I get distracted.


Once the HP1 is balanced and can be discharged and recharged in one step, due to known capacity, I can proceed to HP2.

Depending on how HP1 went, I might go straight to serial discharging; but probably not.

With a known good pack, the exercise cycling could probably be done with both HPs in series, inside the battery container in the car, with the cooling impellers running.

The careful approach outlined above should result in some reliable protocol for cycling a "known to be good" entire NHW10 pack inside the car at specific service intervals.

And maybe it also results in a perfectly working battery without warning symbols for my Prius!


I just completed measuring the open voltage of the two HP's and the 40 sticks.

This is going to be interesting!

The battery is very flat and many would assume that it cannot be restored at all.

But I believe that the NiMH technology will quite likely showcase it's resilience here once again; and that the battery might well be fine once I have pampered and cycled it a few times!

Here are the open voltages:

HP1: Open voltages (mV) : Entire 120s: 11230mV (yes, millivolt!)

HP2: 8060mV

Individual stick results, also all in mV:
1 1862
2 971
3 912
4 512
5 103
6 489
7 421
8 7
9 394
10 551
11 499
12 439
13 491
14 809
15 479
16 109
17 113
18 561
19 935
20 551
21 139mV
22 383mV
23 66mV
24 104mV
25 56mV
26 499
27 840
28 29
29 72
30 70
31 509
32 439
33 135
34 111
35 140
36 136
37 546
38 133
39 1415
40 2219

Best stick 2.2V, worst stick 0.007V - what do you think?

Who wants to hazard a guess if this battery is dead as a dodo, or not?

Very basic schematic of the NHW10 battery is attached.
The below info originates from the Prius MK1 yahoo group:
Thank you for providing the information, I trust you don't mind it being made more accessible by reproducing it here!

I'm just pasting it here as in the original, I hope it is accurate enough to be of some help!

N.B.: All the instructions here are for a 1998 MK1 car for New
Zealand where we use Right Hand drive.

Hi Guys,
I have changed the coolant of my 1998 Prius. I have used Toyota Long
Life Coolant (Pink in Color). Do not use the nasty green color type
Coolants. It is important to buy the recommended coolant so that
Aluminium Engine does not get corroded. I live in Auckland, New
Zealand and temperature never goes below 5 degrees (centigrade) hence
I used a mix as 40% Coolant and 60% Tap water. Please see the
attached pics. These pics are taken when the car was up in the hoist.
There are 3 separate bolts to get all the old coolants out. The user
manual says that total amount of coolant required is 7.5 litre (4.9
litre for Engine and 2.6 for the Inverter unit) however I was only
able to put 5 litre all together. Believe that even when the coolants
are drained there would be good 2 - 2.5 litres still be left in the
system. When you fill in the Inverter Coolant (it's on the passenger
side), make sure to open bleeder caps and attach two plastic pipes
the way it's shown in the pic otherwise it will make a mess.


First we
fill in the Inverter and then the Engine. When the Inverter is filled
in initially, get the ignition on (caution: please do not start the
engine because the engine does not have any coolant left at this
stage) and wait for a couple of seconds. The inverter coolant pump
would start and you will see the coolant level will decrease. Fill in
again and replace the coolant cap. Do not forget to replace the caps
for the bleeders as well. I understand in some models the bleeders
are on the right side of the Hybrid unit. In my case it was in the
left side (as shown in the pic).

Now fill in the engine with coolant. It's on the driver side. After
it's filled in, replace the coolant cap and start the engine when the
car is in the "P" mode. Get the heater dial to Max and Air Flow dial
to the Max. After about 5 mins the radiator pump will start. It helps
if the accelerator is depressed a little. Switch off the car after 10
secs after the radiator pump starts. Wait for 10-15 mins for the
Engine Coolant to cool down. Open the cap and fill in more coolant.
Replace the cap. There is another white coolant top up container at
the driver side. Top it up as well. Drive the car for a little while
and put it in your garage.

Next morning when the car is cold, please check the coolant level.
You may find that the Inverter and the Engine both can take a bit
more coolant (I found that in my car this morning). Top it up

Another post from pasted verbatim.

It explains how to bring the Prius MK1 into diagnostic mode. This is useful for testing the airconditioner, filling coolant and maybe other situations.

I have only tested the second way to bring on the diagnostic mode, it works.

Beginning of quote:
There are no clear description on how to bring MK1 to the equalization
mode. However, I found two ways to bring MK1 to a service mode, which
prohibits the gasoline engine to stop. This may make MK1 continuously
charge the HV battery, but not sure. The two ways below seem to bring
in the same mode with a slight difference. Anyway follow either 1 or 2.

1. Short-circuit the TC pin on DLC3 (OBD-II). TC is pin 13, and CG is
pin 4. (upper-left is pin 1, lower-right is pin 16)

2. Follow the sequence below within 60 seconds
a change IG switch from OFF to ON (not start)
b. with the shift in "P", floor the gas pedal two times
c. with the shift in "N", do the same
d. repeat b
e. you will see the warning lamp begin to flash to let you know that you
are in the service mode
f. switch IG to "Start" to start the engine

Don't drive while in the mode, since the mode also kills the traction
control function. (2 only)

Good luck
Here is a Prius MK1 Service Summary copied (anonymized) from

Incomplete, but a good start!

Start of quote :
I live in Xxxxx Australia, and have helped some of the other Australian owners
on a number of issues. My direct email address is xxxxx@...

As to question of sourcing CV joints - they are from a 1998 Corolla, so easy to
source in Australia. The thing to remember is that many mechanical components
are from Corolla, but the internal combustion engine is from Echo.... it is just
the HV battery that is in a league of its own!

As to your questions about quantity and type of oil etc for service, the
following are my aggregated notes (including info from posts by others on the
group) on this subject, pulled into one document:

Prius Oil Change – used Toyota Echo (all years) filter Toyota#90915-YZZE1 - but
oil still in good shape after 11,000km without a change in interim, so able to
go considerable mileage between changes, due to engine-off in traffic. I used
4.3 litres of "Caltex Havoline 5W40 Fully Synthetic" oil A$58 fm Auto-One; plus
STP (long-chain oil to prevent dry-starts) plus Nulon E10 (teflon
friction-reducer for used petrol engines), both of which I strongly recommend;
Oil plug needs 14mm spanner; Re-use the squash washer on the oil plug, unless
damaged. Need smaller c2.5-inch small-car filter removal tool (normal filter
grips are too large).
Others note Ryco filter Z386 (not specific for 1999 model, but stated as right
one for 2001-3 ones imported to Oz), or via US web site, NPN Toyota Prius Oil
Filter Brand: NPN #423553~A6000174968 Fits: 05/2000 - 07/2003 Toyota Prius
(Echo engine is claimed on motoring web site to have 10k km minor service
interval, but forum purists suggest oil+filter changes every 5k km, with 5W30
per manual but maybe thicker 10W40 if very hot climate – need 3.5 litres for oil

Things to do at other major intervals, see:\

Note slightly different Toyota part numbers for oil filter for Mk2, but maybe
washer numbers and plug bolt is same:
Prius 2001-2005 4CYL (1NZFXE): Engine Oil Filter#:90915-YZZF2 Drain
Plug#:90341-12012 D/P Washer#:90430-12031

There is a 'crush washer' to be replaced on the oil-draining bolt. Rarely, this
gets forgotten and can result in slow leaks later. 5W30 is correct. Synthetic
oil (eg Mobil 1) is popular particularly with Prius drivers who intend to extend
their oil change intervals [up to 10k km], because it resists thermal breakdown
and stays the same viscosity better, through longer periods of use. The Prius
engine is famous for not releasing much 'wear metals. Whether or not you choose
to 'go long' is entirely your decision. Don't forget to change the engine air
filter as well.

Instructions to change Prius Oil and Filter:
Drain from oil pan, drain plug on bottom of engine, oil filter on front side of
engine, access from bottom while draining engine oil.
When removing oil filter, oil flows out. Make sure rubber seal comes away with
filter and discard.
Wet new oil filter rubber seal with engine oil as a light smear.
Only tighten by hand - but not overtight (read instructions).
Refit oil pan plug (14 mm), making sure crush-washer is fitted (else slow
Use funnel to pour new oil into top rocker cover.
Pour very slowly or oil will overflow.
Initially pour 3 litres (rec to use fully-synthetic, 5W30 Mobil 1 SuperSyn or
Castrol R-5w30 Synthetic)
Start engine (to fill oil filter with oil and to check for leaks).
Check level on dipstick, and add oil to 'full' mark.
Don't overfill.

SPARK PLUGS: best rec is to use NGK IFR5A11 (Iridium Type) good for 100,000km,
per 2007:
"Spark Plug for MK1 Prius (NHW10): I would rec using the NGK IFR5A11 (Iridium
Type) every time I get a misfire code it's because the wrong spark plugs are
used. The savings are not worth the trouble it can also ruin the coils if you
use the wrong plugs. You will get another 100,000km with no problems – Xxxx
Xxxxx. Toyota Master/Hybrid Technician, Xxxxx"

TYRES: Recommended tyre pressure is 2.3bar all-around per Toyota, but NHW10
group suggests 2.6bar (and elsewhere 35psi-Front and 33psi-Rear but Xxxxx
Xxxxx goes as far as 38-hot or 40-cold, which is near max allowed pressure).
Recommended tyre upgrade for Prius is "Michelin HydroEdge 185/65R15" $113ea '800
treadware' 90,000 mile warranty, per web, but Xxxxx wonders if maybe 65 too low
a sidewall for alloy rims, so better 70 or 75 is better, to allow for potholes
and driveway edges etc. Xxxxx also thinks that 185 is a bit narrow, so could
tweak to 195 or 205? Peter recs "Bridgestone B391" in 165/65/R15 or "Yokohama
DNA ES 02 - 165/65/R15/81H"

HV BATTERY PROBLEMS: If the Prius HV battery is too weak to use the car:
If Turtle comes on, let car re-charge its battery, do not turn key off while
it is doing that for 5-10mins or longer.
If you do find that a flat HV battery causes car to not start:
A. Connect jumper leads from another car (which you keep running) to your 12 v
battery in the boot.
B. Keep the key OUT of the ignition
C. Press and hold the start button on the HV battery charger in the boot of the
car ( top left hand side above the HV battery) until the charge light comes on.
D. Wait (around 10-15 minutes) until the charged light flashes and beeps a
couple of times.
E. You should now be able to put the key in the ignition and start the car
F: Don't try to start the car while the charger is charging. It will put the
charger in a fault mode (red LED comes on)
LOSS OF POWER: A loss of engine power (ICE) output can be caused by any of the
following basic problems to be checked first:
(a) Air filter element for cleanliness;
(b) Air flow meter for cleanliness of the hot wire (Cleaning of the hot wire
airflow meter sensing wire is a delicate but not technically difficult procedure
and the procedure is posted on the Prius Mark I site using artist brush, not
cotton bud.);
Also see
(c) All vacuum hoses for air leaks (loose hose connections or split hoses); (d).
Ensure that the air intake connections between the air cleaner and the engine
are tight so that all air must enter the engine via the air flow meter. Any
loose connections can allow air to bypass the air flow meter and even very small
air leaks in the induction tract (air cleaner to engine) can cause serious
engine performance problems.

1. Engine oil - 3.4 litres (if no filter change), 3.7 litres (if filter also
2. Coolant - 5.2 liter for engine, 2.6 liter for inverter assy and
motor/generator - Toyota genuine long life coolant, no freezing -12degC @30%,
-35degC @50%
3. Transaxle including differential gear - 3.5 litre - Toyota genuine
auto-fluid, type T-IV. The transaxle filler plug location is very difficult to
tell from the drawing in the manual. It seems it is visible between a couple of
unknown pipes. The fluid level should be 5-10mm below of the filler plug. The
oil drain plug is located on the center of a cover that is connected to
transaxle body by 12 bolts.
4. Brake fluid: Toyota brake fluid 2500H
5. A/C compressor oil: ND-OIL8 (HFC-134a or R134a, scroll compressor type)

Cruise control US$176 (2001-on model which should be same) #08501-47801 fm as at 2007

Regards Xxxxx
End of quote.

Hope it helps!
The Prius NHW10 (MK1) MAF Sensor (Mass Air Flow) is sometimes the cause of baffling performance problems of the entire hybrid system.

If the MAF sensor is too dirty, it measures the amount of air entering the ICE incorrectly, causing poor combustion, poor power, high emissions, and over-use of the electric motor and HV battery to compensate for the loss of power. Soon this may look like a battery problem, when the actual problem is the lack of power generated by the ICE.

The MAF sensor is located on the air filter housing and can be unscrewed by loosening two Phillipshead screws. These are a bit hard to get to, the first time I used an angled screwdriver.

I found it is much easier to remove the entire air filter housing. That also allows inspection and cleaning of the "Butterfly Valve" underneath the air filter.
A few hose clamps and other screws are easily removed to take the whole air filter out. Much easier than removing the MAF sensor when the air filter is still attached to the car. The electrical connector comes off easily if pushed the right way...:


The lower one of the two Phillipshead screws is difficult to remove if the air filter is still mounted to the engine:



The underside of the air filter:


The air filter - old and new - inside the filter housing:

MAF Sensor removed from air filter:



Butterfly valve before cleaning


And after cleaning:


There are three different parts in the MAF sensor that need to be cleaned for normal performance. A temperature sensor on the outside, and two sensor wires deep inside the MAF sensor housing. These two are often overlooked and only the temp sensor is cleaned. But all three need to be clean!

The delicate sensor wires can quite easily be destroyed and it is expensive to replace the MAF sensor!

An artists brush can be used to gently wash the wires, using contact cleaner or other solvents. I'm quite certain you can also destroy the wires by pushing the artists brush in with a little bit of force!

Before cleaning:

Still wet from the solvent:



The air filter also needs to be clean for the entire hybrid system to perform well!

Clicking on the Thumb-nails below will open a large version of pictures showing clean and dirty MAF Sensor parts from a 1998 NHW10 Prius:

Just another place holder to allow later structuring of the thread to make it more organised and readable.

Turns out I will possibly need more placeholders because I can only put 10 pictures into each post.

So I'll drop a few more in, just in case...
Just another place holder to allow later structuring of the thread to make it more organised and readable.
I have posted something new above:

I bought a 1998 Prius MK1 for a very good price, and got it going with one of the traction batteries I bought earlier.

Now I am starting to try to resurrect the battery that came with the car.
Results so far from the test started at

A slight change to the plan due to the unexpectedly low SOC of the entire
battery: Several 1 hr charges at 100mA instead of just one:

Results so far:

11.7V starting voltage, initial charging current 110mA, dropping to between 0.08
and 0.09A as voltage increases.

HP voltages at times after charging start:

1 min: 35V
2min: 44.5V
6min: 82V (0.1A now)
11min: 103V
23min: 117V (0.095A)
51min: 139V
55min: 140.7V; 0.08A ; 320.9Ohm; 27.3degC
1612pm: max: 142.3V at about 60min.

Sticks open Voltages at 1620pm: After about 8 min resting.
(The negative values are just so that I have a way of checking that I did not
miss a stick. Instead of moving the DMM probes from side to side, I just move
them from stick to stick, which results in a negative voltage reading for all
even numbered sticks)

String voltage at start of measurement: 127.3V
1 7.08
2 -6.77
3 6.55
4 -6.18
5 5.77
6 -6.06
7 5.74
8 -5.52
9 6.34
10 -6.26
11 6.63
12 -6.20
13 6.62
14 -6.43
15 6.37
16 -5.83
17 6.21
18 -5.92
19 6.28
20 -6.29
String V at end of measurement: 123.0V

Charging restarted 1621pm, same settings: 1hr with around 0.09A:
120.9V at start. 0.085A
17pm: 149.7V ; 0.08A ; 321.0Ohm
1803pm: 151.8V max; 136.5V actual; 321.2Ohm max; 27.5degC

Stick open voltages 1805pm after 2 hrs of 100mA charging and 45min rest:
1 7.18
2 -7.02
3 6.93
4 -6.61
5 6.47
6 -6.69
7 6.43
8 -6.43
9 7.00
10 -6.76
11 6.97
12 -6.74
13 6.97
14 -6.77
15 6.78
16 - 6.43
17 6.76
18 -6.54
19 6.94
20 -6.99
All: 134.9V

Sticks voltage 2025pm after further 2:20 hrs resting:

All: 118.7
1 6.65
2 -6.38
3 6.15
4 -5.82
5 5.46
6 -5.76
7 5.62
8 -5.35
9 6.10
10 -5.586
11 6.23
12 -5.77
13 6.20
14 -5.91
15 5.93
16 -5.59
17 5.90
18 -5.67
19 6.13
20 -6.21
All at end of measurement: 118.5

Restarted charger at same settings at 2030pm: for 1 hr:
154.1V max; 149.7V actual at 2143pm. ; 321.1Ohm

No voltages measured after charging.

Restarted charger at same settings at 2145pm: for 1 hr:

Sticks voltages whilst charging at 0.09A at 2150pm:
152.4 whole string at start.
1 7.69
2 -7.67
3 7.66
4 -7.58
5 7.56
6 -7.66
7 7.63
8 -7.63
9 7.74
10 -7.65
11 7.70
12 -7.65
13 7.70
14 -7.59
15 7.62
16 -7.57
17 7.63
18 -7.58
19 7.71
20 -7.74
All at end of measurement: 153.0V

That's looking very promising so far!
Here are the voltages following an 8 hr overnight rest following the third 1 hr charge with about 85mA:

Entire HP at start: 143.3V
1 7.31
2 -7.27
3 7.23
4 -7.10
5 7.02
6 -7.21
7 7.13
8 -7.15
9 7.30
10 -7.18
11 7.25
12 -7.15
13 7.23
14 -7.10
15 7.13
16 -7.03
17 7.15
18 -7.08
19 7.27
20 -7.29
Entire HP at end: 143.3

I think it means that there are no completely dead cells in this half-pack; otherwise the voltage of the affected stick would have to be around 6.0V !!!

All good so far!
The initially very flat HP continues to do well during carefully stepped recharging.

After four initial charges at about 85mA I continued as follows:

Charging at 0.17A for one hour: 158.6Vmax ; 320.8Ohm

Ah gone in so far: 0.35Ah + 0.17Ah = 0.52Ah


Stick voltages after 10hrs rest:

Entire HP at start: 148.1
1 7.49
2 -7.47
3 7.44
4 -7.37
5 7.32
6 -7.43
7 7.37
8 -7.39
9 7.49
10 -7.42
11 7.46
12 -7.41
13 7.45
14 -7.38
15 7.39
16 -7.33
17 7.39
18 -7.36
19 7.46
20 -7.47
Entire HP at end: 148.0


Next step done:
Charging at 0.16A for 2 hrs: 321.0Ohm, 27.0degC; 148.7V at start.
At end of 2 hrs: 160.1V ; 320.9Ohm; 26.9degC; 0.16A

Ah gone in: 0.52Ah + 0.32Ah = 0.84Ah

Stick voltages just after charging finished: 2010-01-11, 1925pm:

Entire HP at start: 159.2V
1 7.98
2 -7.96
3 7.97
4 -7.95
5 7.94
6 -7.97
7 7.97
8 -7.97
9 8.00
10 -7.96
11 7.97
12 -7.95
13 7.97
14 -7.93
15 7.95
16 -7.93
17 7.94
18 -7.94
19 7.97
20 -7.98
Entire HP at end: 158.8V


Next step done:

Charging at 0.32A = C/20 for 2 hrs: 163.1V max; 321.1 Ohm; 27.2degC

Ah gone in: 0.84Ah + 0.32 + 0.32 = 1.48Ah

No individual stick voltage test done - they were so balanced in the above test
that it seems not worth the risk and effort to test individual sticks
frequently. I'll test again once the HP is full, both under charge and after
rest. This allows me to leave the protective plastic covers on the sides of the
HP, making it a lot safer on the workbench!


Next step done:

Charging at 0.78A = C/8.333, stopped after 5 min.

Decided to remain cautious and take a smaller step in current.


Next step done:

Charging at 0.47A = C/14 for 1 hr: 164.8Vmax; 321.3Ohm; 27.8degC

Ah gone in: 1.48Ah + 0.47Ah = 1.95Ah


Next step done:
After about 8 hrs rest, with HP 159.4V; 320.9Ohm; 25.4degC (=ambient)

I made some changes to my charger and tested it at the following currents on the

(microF / resulting charge current into HP at about 160V)
4 / 0.16A
8 / 0.34A
12 / 0.48A
16 / 0.64A
20 / 0.82A
24 / 0.97A
28 / 1.1A
30 / 1.3A
34 / 1.4A
38 / 1.6A
42 / 1.7A
46 / 1.9A
50 / 2.0A
54 / 2.16A
58 / 2.3A
These brief tests went well and as expected, no indication that the HP cannot
easily accept these currents by now.

Next steps:
Repeatedly charging at about 0.6A (= C/10) in 1hr installments (timer
controlled) with recording of Vmax and Rmax of thermistor strip.
(Ambient temperature is always around 25degC to 28degC)

1st Charging at C/10 = 0.6A for 1 hr:
164.8V just after start
166.7V max.
321.1Ohm max
Ah gone in: 1.95Ah + 0.6Ah = 2.55Ah

2nd Charging at 0.6A, 1hr timer.
Starting voltage: 162.2V; 321.0Ohm; 26.7degC
167.2Vmax; 321.2Ohm max; 27.3degC.
Ah gone in: 2.55+0.6=3.15Ah total

3rd Charging restarted for 1hr same settings:
166.0V at start
321.3Ohm max
Ah gone in: 3.15+0.6=3.65Ah total

4th Charging restarted for 1hr same settings:
166.1V at start
167.8Vmax; 321.5Ohmmax; 28.0degC
Ah gone in: 3.65+0.6=4.25Ah total.

5th Charging at 0.6A for 1 hr:
168.3Vmax; 321.3Ohm; 0.6A; 28.7degC (3degC elevated)

Ah gone in: 4.25+0.6= 4.85Ah .

After about 8hrs rest period: 164.4V; 321.0Ohm; 25.2degC (=ambient)


And that's where it go to so far!

HP1 has been charged to 75% at C/10 without undue heating of the battery.

When I have time to observe then I'll continue to do C/10 charges for one hour
at a time, until I get a clear temperature rise during the C/10 charge. I might
repeat the C/10 charges a few times, with cooling periods inbetween, until I
think all cells are full to their present capacity level.

Then I'll take the plastic protectors of the HP sides again, check individual
stick voltages under charge and after some rest; and then start to test each
stick with the CBA III (@ 12A to 6.0V cutoff).
The NHW10 HP1 is now fully charged and the sticks are nicely balanced (at least their voltages are)!

I did a total of 13 charges at 0.6A for one hour each (8 further charges since the last update).

During the last few of these "C/10 for 1 hr" charges the HP reached the appropriate voltage for a NIMH string with C/10 charge when full.
This is in my experience 1.44V to 1.445V per cell.
Continuing to charge (after this voltage has been reached) usually results in the ' - delta V ' (negative delta-V) phenomenon, which it also did here.

So far it appears as if the cells in HP1 have all recovered without a hitch!

But of course, only capacity testing can really show what is going on. Voltages alone can be very deceptive with NiMH batteries.

I'll repeat the stick level voltage test once more after a rest period, and then proceed to capacity test each stick individually.

Below are the details of the charges and measurements up to now:


2010-01-13: Charging at 0.6A to 1hr limit: Nr 6

163.7V before start; 321.0Ohm; 27.0degC (=ambient)
169.0Vmax; 321.2Ohm; 28.2degC

Total gone in: 4.85Ah + 0.6Ah = 5.45Ah


Charging at 0.6A for 1 hr Nr. 7:

167.4V start ; 169.3Vmax; 321.5Ohm; 29.7degC (27degC ambient)

Total gone in: 5.45 + 0.6 = 6.05Ah.


Charging at 0.6A for 1 hr Nr. 8:
167.1V at start. Clos to finish: 31.6degC ; 322.0Ohm; 170.1V; 0.61A
convective airflow apparent with incense stick test.

Total Ah gone in: 6.05 + 0.6 = 6.65Ah.


Charging at 0.6A for 1 hr Nr. 9: immediate continuation from charge Nr. 8:
171.4Vmax; 322.9Ohmmax; 34.7degC;

Total gone in: 6.65 + 0.6 = 7.25Ah .


Turned off to let rest overnight.


Next morning: Charging at 0.6A for 1 hr Nr. 10:
Start V: 164.6V; 321.1Ohm; 26.4degC , 25degC ambient
173.6Vmax; 321.9Ohmmax; 30.2degC;

Total gone in: 7.25Ah + 0.6Ah = 7.85Ah


Let rest during the day.


Charging at 0.6A for 1 hr Nr. 11:

Before start: 164.6V ; 28.0degC; 321.0Ohm; 0.6A
At end: 173.7Vmax; 322.6Ohm; 33.3degC

Total gone in: 7.85Ah + 0.6Ah = 8.45Ah


Charging at 0.6A for 1 hr Nr. 12:
171.5V at start.
173.1Vmax sometime before 28min into charge.
172.9V at 28min; 37.4degC; 324.0Ohm; 0.56A;

Stick voltages a few minutes before end of charge during 0.57A charging (with second DMM, reading slightly different):

Entire HP at start: 171.9
1 8.65
2 -8.62
3 8.61
4 -8.60
5 8.59
6 -8.60
7 8.62
8 -8.61
9 8.60
10 -8.58
11 8.58
12 -8.58
13 8.63
14 -8.62
15 8.63
16 -8.60
17 8.59
18 -8.59
19 8.60
20 -8.60
Entire HP at end: 171.8

6 min before charge end: 172.1V; 326.2Ohm; 41.9degC;

Just before finish: 171.9V; 326.3Ohm; 43.1degC;

10min after charge end: 166.2V; 43.7degC; 326.3Ohm.

Total gone in: 8.45Ah + 0.6Ah = 9.05Ah


Let rest and cool overnight.


9 hrs later: 163.2V; 321.7Ohm; 27.9degC

Stick Voltages (again with second DMM):

Entire HP at start: 162.6V
1 8.20
2 -8.16
3 8.15
4 -8.13
5 8.12
6 -8.12
7 8.15
8 -8.13
9 8.11
10 -8.10
11 8.12
12 -8.12
13 8.17
14 -8.18
15 8.20
16 -8.16
17 8.13
18 -8.13
19 8.12
20 -8.12
Entire HP at end: 162.6


Shortly after these measurements:

Charging at 0.6A for 1 hr Nr. 13:

174.2Vmax recorded during the charge; 174.0Vactual at end; 322.6Ohm; 32.8degC;

Total gone in: 9.05Ah + 0.6Ah = 9.65Ah


I declare it "FULL".


Stick voltages 5 min after charge end:

Entire HP at start: 171.6
1 8.63 (second run at end of measurement: 8.60)
2 -8.60 (second run at end of measurement: -8.58)
3 8.59
4 -8.58
5 8.57
6 -8.58
7 8.60
8 -8.58
9 8.58
10 -8.56
11 8.55
12 -8.56
13 8.60
14 -8.58
15 8.60
16 -8.58
17 8.56
18 -8.56
19 8.57
20 -8.56
Entire HP at end: 171.1


The results of measurements after about 10hrs rest, before starting the capacity measurement, were:

322.0Ohm; 29.3degC.

Open voltages:

Entire HP at start: 163.1
1 8.21
2 -8.18
3 8.17
4 -8.16
5 8.15
6 -8.16
7 8.18
8 -8.17
9 8.15
10 -8.14
11 8.15
12 -8.15
13 8.19
14 -8.19
15 8.20
16 -8.18
17 8.15
18 -8.15
19 8.15
20 -8.16
Entire HP at end: 163.1

I don't think it gets much better than that, but my experience comes from working with damaged battery packs; maybe a new pack would be balanced even better?


Now the CBA capacity test are under way.
First 9 sticks done:

NHW10 BlueCar HP1 Stick 01 @ 12A to 6V: 1730pm: 5.83Ah, good curve.
NHW10 BlueCar HP1 Stick 02 @ 12A to 6V: 1812pm: 5.676Ah, good curve.
NHW10 BlueCar HP1 Stick 03 @ 12A to 6V: 1852pm: 5.703Ah, good curve.
NHW10 BlueCar HP1 Stick 04 @ 12A to 6V: 1922pm: 5.746Ah, good curve.
NHW10 BlueCar HP1 Stick 05 @ 12A to 6V: 2000pm: 5.663Ah, good curve.
NHW10 BlueCar HP1 Stick 06 @ 12A to 6V: 2030pm: 5.670Ah, good curve.
NHW10 BlueCar HP1 Stick 07 @ 12A to 6V: 2059pm: 5.761Ah, good curve.
NHW10 BlueCar HP1 Stick 08 @ 12A to 6V: 2134pm: 5.671Ah, good curve.
NHW10 BlueCar HP1 Stick 09 @ 12A to 6V: 2210pm: 5.55Ah, good curve.
All 20 sticks from the NHW10 BlueCar HP1 have now been capacity tested for the first time.

Here are the results:

NHW10 BlueCar HP1 Stick 01 @ 12A to 6V: 1730pm: 5.830Ah, good curve.
NHW10 BlueCar HP1 Stick 02 @ 12A to 6V: 1812pm: 5.676Ah, good curve.
NHW10 BlueCar HP1 Stick 03 @ 12A to 6V: 1852pm: 5.703Ah, good curve.
NHW10 BlueCar HP1 Stick 04 @ 12A to 6V: 1922pm: 5.746Ah, good curve.
NHW10 BlueCar HP1 Stick 05 @ 12A to 6V: 2000pm: 5.663Ah, good curve.
NHW10 BlueCar HP1 Stick 06 @ 12A to 6V: 2030pm: 5.670Ah, good curve.
NHW10 BlueCar HP1 Stick 07 @ 12A to 6V: 2059pm: 5.761Ah, good curve.
NHW10 BlueCar HP1 Stick 08 @ 12A to 6V: 2134pm: 5.671Ah, good curve.
NHW10 BlueCar HP1 Stick 09 @ 12A to 6V: 2210pm: 5.55Ah, good curve.
NHW10 BlueCar HP1 Stick 10 @ 12A to 6V: 2239pm: 5.635Ah, good curve.
NHW10 BlueCar HP1 Stick 11 @ 12A to 6V: 2313pn: 5.572Ah, good curve.
NHW10 BlueCar HP1 Stick 12 @ 12A to 6V: 2343pm: 5.591Ah, good curve.
NHW10 BlueCar HP1 Stick 13 @ 06A to 6V: 0725am: 5.691Ah, good curve. 6A in
NHW10 BlueCar HP1 Stick 14 @ 12.1A to 6V: 0820am: 5.648Ah, good curve. 12.1A
in error.
NHW10 BlueCar HP1 Stick 15 @ 12A to 6V: 0851am: 5.683Ah, good curve.
NHW10 BlueCar HP1 Stick 16 @ 12A to 6V: 0934am: 5.629Ah, good curve.
NHW10 BlueCar HP1 Stick 17 @ 12A to 6V: 1008am: 5.582Ah, good curve.
NHW10 BlueCar HP1 Stick 18 @ 12A to 6V: 1047am: 5.613Ah, good curve.
NHW10 BlueCar HP1 Stick 19 @ 12A to 6V: 1120am: 5.569Ah, good curve.
NHW10 BlueCar HP1 Stick 20 @ 12A to 6V: 1151am: 5.502Ah, good curve.



The one test at 6A was due to operator error. The software had crashed and I was not careful enough when I set it up again!
Same for the 12.1A following it. Never mind...
Mr. Mik said:
The print in the sensor strip:
Does anyone know what it means?
I thought that the PSR might stand for Polyswitch Resettable. It's probably now made by this company:
I didn't do much good searching for 24155 on that site, though there were some reasonable matches to devices with no information available on the website. This might be because they are now obsolete, or because Toyota wanted a paticular design custom made, so the details of that part aren't available to others.

These polyswitches are used in place of fuses, so they are rated by current, not temperature. So maybe these are really just positive coefficient thermistors, or at least should be replaced with PTC thermistors.
I have had an unexpected result: A repeated capacity test after 5 recharge / discharge cycles shows reduced capacity of all sticks in the NHW10 BlueCar HP1 sticks!

The discharge curves with 6V cutoff are from the first capacity test, done after the first recharge from deeply discharged and neglected state.

The discharge curves down to 5.4V are the ones from the capacity test done after a further 5 charges and 4 discharges.


Click thumbnail for better quality picture:

(I have misnamed several of the sticks tests in the overlay and cannot change what the CBAIII puts on the screen. All the tests are in fact the BlueCar HP1 sticks, not the NFG battery sticks.)

What I expected was a capacity increase with a few more cycles, but in fact the capacities of all sticks are reduced by about 5%.

Why is this the case?

Two possible explanations come to mind:

1) The prolonged, almost total discharge was acting as a reconditioning cycle, restoring the maximum capacity which the cells are still capable of. With the further 5 cycles (which were not over-discharging the cells past 0.9V) the capacity returned to the real level and will remain relatively stable there. (When I do reconditioning cycles on NiMH batteries on purpose, I discharge them at about C/50 to 0.4V cutoff with good results during the next discharge. But I have never systematically tested if these results disappear again, at least partially, over the next few cycles!)

2) The "Universal Freddy charger" might be doing some damage to the batteries, possibly due to excessive ripple in the output voltage / current.

I stopped using the Universal Freddy and ordered an oscilloscope to rule out damage due to the charger and/or improve it by adding smoothing measures to it's output and testing what works best. But the scope broke soon after I started to play with it, and the seller tells me that there is some spring festival holiday period going on in China, which stops apparently everything for the next 10 days or so. So it will be a while before I get a result with that broken scope! I might just fork out the money and buy one from Jaycar in the meantime.
I got a USB scope now, and it works somewhat. I cannot really tell if the thing is malfunctioning or not, but it sometimes seems to do strange stuff until the program gets rebooted and the hardware disconnected and reconnected.

And I cannot figure out how to calibrate it and set the zero point...

So all these results might be rubbish!

The thumbnails below lead to screenshots of the USB scope measuring the voltage drop across a 10mOhm shunt. The shunt is in series with the Freddy charger and the HP2 out of the BlueCar NHW10 battery (120s NiMH, 6 or 6.5Ah). Battery is empty, started at around 145V, at end of experimenting it was about 155V.

The title of the scope graphs describe details about them: Charge current, motor run capacitor used to achieve this current, and either 12 Ohm resistor added in series or no resistor added. The resistor should probably be located between the smoothing capacitors, but for this experiment I simply put it in series with the charger output.

The actual zero line should be where 0.01V is, in the next post I will post the graph showing no charge current (the forum software will only allow 10 pictures per post).

If I interpret these graphs correctly, then the Freddy charger without resistor creates so much 100Hz ripple that the charge current becomes negative for a short time each 1/100th of a second. EDIT 2010-03-23: That's rubbish - faulty thinking. The diode in the charger prevents any reverse curent flow, ever. The charger output is ripply, but always directed into the battery.
With a 12 Ohm resistor, there is still a lot of ripple, but the current always goes into the cell.

I have been using the 8microF / 0.64A setting to cycle the HP1 5 times, without smoothing resistor.

Is that likely behind the 5% capacity reduction?
Here is what the scope shows when no current is going through the shunt. It stubbornly claims -0.01V when it should be zero....

Any help with figuring out how to properly use this scope, and what the results mean (if anything), would be greatly appreciated!

The charger used is similar to this one (but has now a 16microF instead of the 20microF motor-run capacitor):

I think it needs some more work! A few extra smoothing resistors, exact values to be determined experimentally as soon as I am more comfortable using the scope.

The scope is a PoScope USB scope similar to this package:
Mr. Mik said:
I have had an unexpected result: A repeated capacity test after 5 recharge / discharge cycles shows reduced capacity of all sticks in the NHW10 BlueCar HP1 sticks!


What I expected was a capacity increase with a few more cycles, but in fact the capacities of all sticks are reduced by about 5%.

Why is this the case?

Two possible explanations come to mind:


It turned out that I fell into the same old self-discharge trap that has gotten me a few times before - I'll learn one day!

It was the same problem that causes the early demise of many Vectrix packs and the destruction of the Prius MK1 batteries: Differential self-discharge rates at different temperatures.

I had tried to control the self discharge between the repeated tests by letting the same number of hours pass between charging fully and beginning capacity testing (about 9hrs).

But the first charge was terminated with a battery temperature of about 34degC, because I was cautious and gave it a top-up after several short charging bursts with frequent observation to rule out possible overheating.

As I got more experienced (and the battery characteristics became known to me), I was able to do a full charge in one relatively fast move. This caused the battery to be about 44degC warm when fully charged.

The self-discharge rate at 44degC is much higher than at 34degC, and although the ambient temperature was similar at about 26degC, the batteries would have spent the 9hr wait at a significantly higher temperature then the first time. That's the cause of the apparent capacity loss after 5 charges.

I have returned to using the charger with good success. The Prius I bought in December ran very well for 2.5 months, then started to show small signs of battery imbalance (ICE running at increased idle speed to charge the battery a few times, and a single "Turtle" on the dash display).

I stopped driving the car and did an EQ charge (with battery remaining in the car) - the cars performance has returned to very good immediately.

An EQ charge done on a friends car has also had a very good effect on the cars performance, time will tell if it lasts several months or just a few days. It depends on many variables, particularly the state of health of the battery.