PANASONIC ebike battery change

osa57

10 mW
Joined
Feb 14, 2013
Messages
24
Hi experts,
I have a BH pedelec bycicle with a Panasonic motor and a standard battery pack of 26V x 8A.
After 3 and half years of loyal services I guess that very shortly this battery has to retire :)
With the Cycle Analyst I can see that the voltage sag is huge and that capaciity is down at around 70%
Given the unbelievable prices that are charged for a spare new battery (around 300 Euro!) this is what I'd like to do:

- buy 2 batteries from HobbyKing Zippy 5000mAh 8S (8 Cell) 29.6V
(weight: 937g, Dimensions: 160x46x59mm)

- then install them in parallel in the original battery case.

My 2 questions:
- do you think that the BMS would be capable to handle this new battery pack (with a total capacity of 10 A instead of 8A) ? :shock:
- do you think that the Panasonic electric motor (since a couple of years it's only produced on 36V...), would be able to handle those additional 3 V (from 26 to 29) ? :oops:

thanks a lot!
Daniele
 
osa57 said:
Hi experts,
I have a BH pedelec bycicle with a Panasonic motor and a standard battery pack of 26V x 8A.
After 3 and half years of loyal services I guess that very shortly this battery has to retire :)
With the Cycle Analyst I can see that the voltage sag is huge and that capaciity is down at around 70%
Given the unbelievable prices that are charged for a spare new battery (around 300 Euro!) this is what I'd like to do:

- buy 2 batteries from HobbyKing Zippy 5000mAh 8S (8 Cell) 29.6V
(weight: 937g, Dimensions: 160x46x59mm)

- then install them in parallel in the original battery case.

My 2 questions:
- do you think that the BMS would be capable to handle this new battery pack (with a total capacity of 10 A instead of 8A) ? :shock:
- do you think that the Panasonic electric motor (since a couple of years it's only produced on 36V...), would be able to handle those additional 3 V (from 26 to 29) ? :oops:

thanks a lot!
Daniele
you're basically looking at ditching the BMS+charger and building a wiring harness and balancing method (i use quality battery medics) and getting a bulk charger. I suggest staying away from large hobby packs, and go for the 4S1P 5000mah Turnigy hardcase packs (2 in series, limitless parallels). read read read about lipo is always a good suggestion. as for voltage compatibility, they try to give significant tolerances for controllers so the 3V difference in nominal voltage is not significant. Some '36V' controllers go as high as 63V caps, but don't assume that your controller has that. 8S is very safe.
 
Ok, it's clear: now I really need to find out which battery packs configurations out there (essentially HK...) are more suitable for my project.
Yes, I need to buy a good charger+balancer, but this is well worth the investment!
I was wondering if buying 2 x 4S is really safer than 8S: is it to reduce the chance than some cells might be defectives in one only 'big' pack?
 
osa57 said:
Ok, it's clear: now I really need to find out which battery packs configurations out there (essentially HK...) are more suitable for my project.
Yes, I need to buy a good charger+balancer, but this is well worth the investment!
I was wondering if buying 2 x 4S is really safer than 8S: is it to reduce the chance than some cells might be defectives in one only 'big' pack?
yes it is cheaper if you get a dud, plus the 4S hardcases are the best price in 20C lipo on earth. Don't spend good money on two chargers, pick either balance charger or bulk charger with a balancing and monitoring component separate, like my batt medics connected to the paralleled balance connectors.
 
I had a 24V NiMh Panasonic pedelec and IIRC it would shut down above 29V. 8S RC Lipoly will be north of 33V hot off charger. Now, in my situation it didn't seem to hurt anything when I tried but it refused to power up anything above 29V, or thereabouts.

I really like those drives for true pedelec hard to beat. Some Lipoly would be a sweet upgrade but you might need to stick closer to 6S bricks. Test it and see?
 
Yep, 7s charged to 4.1v is closest to 24v nominal. 28.7v.

3s plus 4s packs? with an adapter for the balance plugs, they'd charge on relatively cheap 8s RC chargers.
 
@ Ykick
what you say is that if I want to keep the same Panasonic electronics & BMS, I cannot really go beyond 29 V :-(
The original battery has 7S 2p Lipo , see picture from french bike forum here:
http://cyclurba.fr/forum/53910/batterie-panasonic.html?from=121&discussionID=3814&messageID=158912&rubriqueID=99&pageprec=
In this blog a swiss guy managed to replace the original pack with 2 packs (2S + 5S (5000 mAh)) in parallel: he said that this replacement was absolutely brilliant as opposed to standard Panasonic pack (500 Eur ?!?!?)

So I guess the other option I have is to work on the Ah: I have seen not very expensive Zippy 7S 5800 mAh (72 USD), so if I put 2 of them in the same configuration as the standard Panasonic, I should get an increased range of almost 40 %.

As far as the increase in mAh is concerned (from 8 to 11.6 mAh) I don't think that the BMS should stop anything...
 
I've just put in 2 7S 5800mAh Zippy compacts in my 10Ah Panasonic battery case.

As the Swiss guy writes, if you circumvent the Panasonic BMS, you only get the first LED on the handlebar switch lit.

I have a feeling that the current gets limited too, but thet it stays the same much longer.

I plan to do as him, by connecting the Zippy balance leads to the Panasonic BMS, to retain the original functionality.

The original balance leads are hair thin, but then again the original charger takes 5 or more hours to charge.
I don't know if parallel connections allowing fast charging from a balancing charger would destroy the built-in BMS
 
no, a balance charger would not damage the panasonic BMS unless the voltage you charged up to went too high and provoked the fuse to burn.

the original poster needs to measure the cell voltages when charging and then when it balances she can discharge that pack into a dummy load through a wattmeter to see how much charge is stored when the pack is balanced down to the first cell to hit the LVC.

there may just one cell that is short and causing the BMS to cut off for LVC much too early and she can replace the low cell and restore the original battery capacity.

if those cells are fixed so they will all balance again then she can wire the zippy packs in parallel with the current cells after it is fixed and get even more capacity than with the zippy packs alone. so just a little investigation could double the range when she goes with the zippy packs.
 
hi ErikDK,

thanks for sharing your experiences!
I received a couple of weeks ago 2 7S 5800 mAh Zippy from Hobbyking....
Bad surprise, I cannot perform balancing with the charger I bought (iCharger 208B) since there are 2 plugs (a 3s and a 4S) from each battery and with the standard balance board I cannot plug both of them at the same time :-(
So I bought a new JST-XH single 7S plug and I will have to do some rewiring....couldn't see any other concrete alternative.

I am not planning to rewire the original Panasonic balance leads ....for a couple of reasons:
- not easy job, since the original balance leads are hair thin
- as you said, why keeping the original charger if it still take 5 hours to charge....

My new charger, at 1C, could easily (and safely) recharge 1 pack in one hour.
Then I am going to use a Lipo LOW Voltage alarm, at 3,40 Volts, to tell me when I should stop using the new Zippy back (even without connecting it to the original BMS) :D
 
My reasons for keeping the original Panasonic electronics are, in no particular order:

Retaining the 3 handlebar status LED's
Retaining the 5 battery case LED's
Ease of using the original charger without worrying about connecting balance leads.

I have a feeling that the motor controller goes into some kind of "emergency mode" if the battery state information is omitted, and restricts the current. Fresh off the charger, the Zippy lipos make the motor feel like the tired OEM does after a couple of kilometers, whereas the tired OEM pulls really strong for the first couple of kilometers.
 
do you have a voltmeter so you could measure the cell voltages of the old pack?

i read where you asked about this project on the swiss website last september after reading spy70 and what he did.

if you have no intention of using the old pack anymore by replacing the low cells then it might be best for you just build a new battery using th ehobby king zippys or turnigy lipo packs.

if you can open the controller we can look at the parts and tell you how high a voltage you can use for the battery replacement and then you could buy the packs from hobbyking and use another BMS to control the new pack. just skipping the use of the old panasonic BMS and use a really better BMS from the guys at Bestekpower.com.

instead of 7S you might be able to use 10S or the lipo or even go to 12 or 13S without harming the controller by replacing a few resistors on the input to reduce the input voltage to the controller voltage regulator. then you could use a regular bulk charger and you would then have short circuit protection and over discharge protection as well as over charging protection and balancing from the new BMS but it will allow you to use the battery without having to stop at 3.5V on discharge because of the alarm. the alarms will unbalance your battery if you leave then attached.

i was surprised there was not more informed advice on that swiss website. people could only comment in terms of 4 out of 5 leds and had little idea about how the battery and BMS for the panasonic worked. we already helped one guy from New Zealand who had problems with his panasonic battery and charger and there was no one who could help him by giving advice before he came here.

i was able to walk him through the testing of his BMS until he found the problem. not many people actually do try to follow the methodical isolation of the problem with a BMS but that guy was interested enuff in fixing his bike that he followed through and got his charger and BMS working again. that was the pvdm guy i mentioned.

you should be able to restore most of the capacity of that battery by replacing the bad cells but if you don't do work then you could just replace it altogether with another lipo battery and BMS. that would allow you to go to higher voltage and maintain more control over the battery than having to be limited to using the balancing charger.
 
hi,
"do you have a voltmeter so you could measure the cell voltages of the old pack?"
I have the Cycle Analyst installed: after recharge it goes up to 28,6 V, don't know the voltage of individual cells...
Then Panasonic BMS cuts at 25.5V, I have the feeling that I could use the battery until it goes down to 23,5 ( = 3,35 per cell, assuming they are balanced...)

"if you can open the controller we can look at the parts and tell you how high a voltage you can use for ...."
Sounds great, but probably it requires higher skills than mine :)
Just kidding....another idea I had was to buy a battery higher than 26V (example a 8S) and to set a higher limit with my iCharger to try to find when the Panasonic BMS would cut off.

"instead of 7S you might be able to use 10S or the lipo or even go to 12 or 13S without harming the controller by replacing a few resistors on the input to reduce the input voltage to the controller voltage regulator."
Interesting...any example in this forum where I could see what does it mean 'by replacing few resistors' just to get a better idea ?

"the alarms will unbalance your battery if you leave then attached"
I think that it might (slightly) increase the consumption....but cannot see why this would unbalance the cells.

"you should be able to restore most of the capacity of that battery by replacing the bad cells but if you don't do work then you could just replace it altogether with another lipo battery and BMS. that would allow you to go to higher voltage and maintain more control over the battery than having to be limited to using the balancing charger."
I am not sure it is worth to replace the bad cells (or just old!), I guess that the ZIPPY option is great for me.
It could be done in two steps:
1) with same voltage (7S 26V), this is what I am doing now
2) then try with higher voltage (8S for example) and a different BMS

thanks!
 
your little panasonic BMS will not handle the zippie power so you will need a different BMS so if you want you can just toss the entire thing and get a 8S lipo pack and a 8S BMS from Bestechpower to control it. that will give you short circuit protection and over charge protection too.

the resistor would be in addition to the current input power resistor if you raised the voltage significantly but if you go to 8S then most likely it would not be needed.

i have heard people talk about this over voltage limit but no one has demonstrated it so until then i consider it just yakyak.

i did notice that none of the guys on that thread where spy70 guy talked about this conversion ever measured the cell voltage of any of those batteries. i found that amazing since they are talking about modifying the battery and converting to a pack with no BMS and they have no clue about cell voltages. i would have expected more from the swiss.

he is all happy about how he doesn't have to pay for the panasonic battery and how they are all gouging for money. like is that new? but he does nothing to protect the battery or bike from short circuit or over discharge except for the cellogs. the cellogs take power from the first 6 cells, and the upper cells do not drain down at the same rate so the pack becomes unbalanced while sitting around doing nothing.
 
Do you have any firsthand experience with second-generation Panasonic crank drive motors dnmun?

They are very good at what they do, but from what I've read, tuning them doesn't give good results.

It's not just the BMS, the motor controller receives information from the BMS, and there's all kinds of speed and current limits.

All I want to do is to restore the original battery performance as cheaply as possible, and I don't want to gamble that the Turnigy's are worth their premium price in this low-current application.
 
then demonstrate it and we will figure how to fix it. i would never buy one of those panasonic drives myself but you guys are stuck with them so we are trying to help you overcome the limitations. like i said i did help repair the BMS on one of them and know that the output mosfets on that BMS will not handle the current the zippies can produce. so you will need a different BMS to use the zippies.

if you can show how the 8S voltage prevents the controller from working then i will show you how to fix that too.
 
The Panasonic battery has a full set of balance leads for both 7s packs, 30A fuses for each 7s pack, that goes to separate spade connectors on the BMS with infinite resistance between them.

According to osa57 "Panasonic BMS cuts at 25.5V" - 3.65V/cell, what more do you want for protection.

The original Panasonic pack, which was fully charged before dissektion, had the same voltage on all cells within 0.01V

The BMS is far from crude, it just doesn't support quick charging, but I have lived with it for 5 years, and can do so in the future.
I have the Icharger 208b and a powerful power supply, so I can perform rapid balance charging, but dumping the battery case in the OEM charger is so much easier.

Time will tell how the Zippy's hold up
 
Yes, I have exactly the same feeling as yours...http://endless-sphere.com/forums/images/icons/smile/mrgreen.gif
In the french forum all people tend to talk a lot but then at the end very few guys actually go through facts and measures.
The swiss guy has done a great job and it was great for him to share all what he did...still not clear on his findings about cell voltage, BMS cut off range, actual mAh delivered from the new zippy...
I am also busy doing another project (Cyclone mid drive motor on a recumbent bike...) so I am afraid I will not be able to progress on the Panasonic as quickly as I would like http://endless-sphere.com/forums/posting.php?mode=reply&f=14&t=47779#
 
Here's a better shot of the BMS:

The two extra wires on the right balance plug is a temperature sensor wedged between the two packs.

attachment.php
 
this is a totally different BMS from the other panasonic BMS.

there are two series of 7S cells and the two plugs for the sense wires 1 and 2.

on the top of the one on the right are there 8 sense wires also and do the top two wires, the black and grey run into the battery also? are there 10 wires there?

the charger plug has just the two main pins or is there another set of pins for the white and yellow wire that run up to the plug. i wondered if they provide feedback to the charger and maybe turn it off with an interlock of some sort. or maybe sense the polarity before the battery is allowed to connect to the charger.

i guess the shunts are on the other side of that pcb and the other ICs.

i think they have laid out both plugs for more cells in series since it looks like the left plug has 12 pins but only 8 are used. so maybe it could work up to 11S but the two wires on the top of the #1 plug would keep you from using all of plug #1 even if there are traces for control or balancing.

so there is no mosfet to burn up then. i wonder how it is switched.
 
As I wrote, the two extra leads, grey and black, on the right plug are a to a temperature sensor wedged between the two packs.

My plan is to cut the thin wires and install male/female JST-XH connectors, which will allow me to balance charge and test the original Panasonic pack with my Junsi iCharger, and allow the Zippy packs to operate with the Panasonic BMS during everyday operation, as well as Junsi balance charging.

A weatherproof balance connection outside the battery case would be ideal.

To elaborate on the photo, I can't measure continuity between any combination of B+(1), B+(2) and (+), so there's some kind of power management going on on the other side of the PCB.

Under the black heatshrink on the red wires is a 30A glass fuse, one per cell pack.

There are no components in the connector PCB in the left side of the picture and I currently run both Zippy packs in parallel directly to the connector PCB, bypassing the BMS.
 
i found a good source for JST-XH plugs and sockets, prewired with 300mm leads. i get the 9 pin set for the 8S cellogs and solder them directly to the sense wire plug through hole leads on the underside of the BMS.

sorry i missed it being the thermistor wires.

you could also wire up another 7S BMS in parallel and attach it right there on the B+ and B- spot. maybe even consider using diodes. you could use separate chargers too.

i do think it significant that they did not parallel the cells at the cell level. just parallel the strings. but no separate switch to isolate them it appears. so the fault on one is all that is needed to shut it off i guess.

all this time i was thinking lipo.

i think the switch is a surface mount mosfet on the other side between the two B- leads and the Charger - there. i can almost make out the little pinholes through the pcb. i think
 
dnmun said:
...
i do think it significant that they did not parallel the cells at the cell level. just parallel the strings. but no separate switch to isolate them it appears. so the fault on one is all that is needed to shut it off i guess.

...

I can make a test to see if it will work with one pack alone. Is it to risky to try with one charged and one discharged pack?
 
nope, no need to push it outa balance. just making observations. this is more sophisticated than the other BMS, but here are some links:

7 pin,

http://www.ebay.com/itm/JST-XH-2-5-7-Pin-Connector-Plug-w-Wire-x-10-Sets/181150412657?_trksid=p2047675.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D8488890838506379269%26pid%3D100011%26prg%3D1005%26rk%3D3%26sd%3D251269581310%26

http://www.ebay.com/itm/5-x-JST-2-5-XH-7-Pin-Connector-Extension-Wire-Male-to-Female-Length-200mm/111096175020?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222005%26algo%3DSIC.NUQ%26ao%3D1%26asc%3D16097%26meid%3D8488901210920886480%26pid%3D100005%26prg%3D7683%26rk%3D2%26sd%3D181150412657%26

8 pin,

http://www.ebay.com/itm/Micro-JST-2-5-XH-8-Pin-Connector-Plug-w-Wire-x10-Sets-/111096175029?pt=US_Radio_Control_Control_Line&hash=item19ddd919b5

9 pin,

http://www.ebay.com/itm/JST-2-5-XH-9-Pin-Connector-Plug-w-Wire-x-5-sets-/111093380099?pt=LH_DefaultDomain_0&hash=item19ddae7403
 
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