CellLog 8 hacking

[fechter]

I've heard of some blowing the USB port if they were still connected to the battery, but not when used properly. Mine don't have the logging feature, so won't have an issue there. There is a much longer thread on CellLogs somewhere.

[evtdriver]

Hello,

no I didn't connect the cellog to the battery and to the computer at the same time. No burn, nothing special. USB port is fine.

[ssalbach]

Hallo,
does anybody know, what are the function from Q3,Q4,Q8 and so on???
I'm buiding an BMS and use some Ideas from Cellog 8S..
I don't understand why are there 100K and 75K Resistors?
Normaly I use 100K for all...I think it can compensate the Voltage Drop from Diodes?
For my Design I don't use the Diodes.so i think I can use 100K for all?!
But I think there are to less Resistors...
I need one Resisot vor Every Signal from Batterie and the same vor all negatives..
So I need 14 Resistors...+7 for coupling the output from Opamp and 7for ground for OP-amp (Diferential Amplifier...)

[fechter]

I'm not sure. I couldn't quite figure those out. They appear to be part of the differential amplifier circuits. The bottom two cells go through resistor dividers straight to the MCU. Cells 3 to 8 go through differential amplifiers first to bring them within range of the MCU inputs. Seems like any differential amp circuit should work.

[ssalbach]

the other thing that dislike is that the Power comes from Cell1 and Cell2..alls other Cells giving 0,7V less then Cell 1 and 2 because they are diodes..
If the Cellog are online all the time the Cells will be emptier than cell 3-8...I don't thing, that the Jumper Modifikation can fix that..
I am bouliding a Cellog clone on experemting Pad at this time..but I use an Analog Voltage Regulator for 40V and more..
That is not a good solution, but less parts then a Step Down converter. but with this I use the Voltage from Cell 1 to 8 without the risk of differents..
Then I use an Op Amp LM258 instead an 358, because the temperature Range can go under 0°C
Because My Cellog have to Balance the Cells with the Help from REsistors too

[texaspyro]

I am bouliding a Cellog clone on experemting Pad at this time..but I use an Analog Voltage Regulator for 40V and more..

I am using an LM2936 ultra low standby power regulator on my LED dimmer for the same reason. It drops the power from the 8S - 10S A123 pack down to power an ATtiny13A. The regulator itself draws around 7 uA. You do have to worry about how much current you can draw since it is dropping 40V. There are other low power regulators out there that have inputs up yo 60V and standby currents below 1 uA (but the LM2936 is a drop in replacement on an existing circuit board).

Now I need to come up with a voltage divider circuit that does not waste any power. A 10 megohm divider would work, but the micro's input leakage current is spec'd at +/- 1 uA. That could overwhelm the divider current. I might need a micro-power op amp as a buffer...

[ssalbach]

I'm not shure..but I thing my one goes up to 100V!!! or 150V ?! I don't know
It is Cheap, around 2,5$...
I don't have a better cheaper easier Idea

[Alan B]

Now I need to come up with a voltage divider circuit that does not waste any power. A 10 megohm divider would work, but the micro's input leakage current is spec'd at +/- 1 uA. That could overwhelm the divider current. I might need a micro-power op amp as a buffer...

Since the ADC is a capacitive divider, using a high Z divider with a large enough output capacitor should handle the current input that the ADC requires. I have not tested this yet but it is worth a try as long as the resulting low bandwidth is acceptable.

[texaspyro]

Since the ADC is a capacitive divider, using a high Z divider with a large enough output capacitor should handle the current input that the ADC requires. I have not tested this yet but it is worth a try as long as the resulting low bandwidth is acceptable.

Low bandwidth should be more than OK... I sum 49 samples taken every 16 msec to get a battery reading resolved to millivolts. Battery voltage changes very slowly. But, it appears that I don't need to worry about it. I measured the input current to the ADC and it is under 2 nanoamps!

[Alan B]

... I measured the input current to the ADC and it is under 2 nanoamps!

Dynamically? I would expect it to have transients as they switch capacitive dividers that might need some current, static impedance is not the whole story. Interesting.

[texaspyro]

The ATtyiny13 uses a SAR ADC. The inputs go into an analog mux to select the channel, the output of that goes into a sample/hold then a comparator. The sample/hold cap is 14 pF. The input signal is not directly exposed to any other circuitry/dividers/etc.

I was testing the thing with a string of three battery packs connected in series with Deans "Y" cables. The total length of the leads were about 18". I was getting false HVC cutoffs when the PWM was set low due to spikes getting into the power (it was switching 22V at 2 amps, 140 Hz). I put a 0.1 uF cap across the lower divider resistor and that went away. When I used 2 packs in series, I had no problems.

The HVC cutoff is used to protect the LED incase one connected a bigger pack that the LED was speced at... this thing is direct LED drive (via PWM for dimming) with no regulation. It can be disabled in firmware.

[auraslip]

This is a good thread. I'm about the do the even drain mod. Any tips on what to use as a jumper? I imagine even thin 22awg wire will be tough to stuff in the case.

Also looking at photos like this:

I'm having trouble understand how the alarm output isn't isolated. It's just a transistor that functions as a relay right? Why the need to keep it isolated?

[fechter]

Any skinny wire will be OK for the jumper. I used one strand from a larger stranded wire. Keep it long while soldering so you have something to hold it with. After it's soldered, snip off the end.

The negative side of the CellLog alarm output connects to the pack negative. If you try to put two alarm lines in parallel, it will cause a short. This is only an issue when using more than 8s.

[dumbass]

Anyone know where to but replacement wire/plug for the alarm output? Or maybe what this size is called.

Bob

[auraslip]

Does this look about right for the even drain mod? The original picture is corrupted

[amberwolf]

Does this look about right for the even drain mod? The original picture is corrupted

http://imgur.com/DShwv.jpg
http://imgur.com/a37GC.jpg

The first picture is probably not what you meant to post; it's kind of fuzzy.

DShwv.jpg (41.05 KiB) Viewed 741 times

The second pic probably is right; I'm assuming you're referring to the added wire here?

a37GC.jpg (111.91 KiB) Viewed 775 times

Somebody that's done the mod should chime in, though.

[fechter]

That looks right (but it's a really fat wire!). I think I fixed some of the corrupted images.

[mr.electric]

Does anyone have a recommendation for a relay to connect to the alarm output and pull down a throttle or flip a main power contactor. I am using just one cell log but the fact that the alarm signal is tied to ground seems to be an issue with certain controllers. For example I connected the alarm output to an older brushed controller brake signal and it does not function properly. Im looking for a small mechanical or solid state relay to connect directly to the cell log without the need to create an interface board so hopefully just a relay and associated wiring.

[auraslip]

The first picture I posted got catrupted.

thanks for reuploading the pictures again!

[fechter]

Does anyone have a recommendation for a relay to connect to the alarm output and pull down a throttle or flip a main power contactor. I am using just one cell log but the fact that the alarm signal is tied to ground seems to be an issue with certain controllers. For example I connected the alarm output to an older brushed controller brake signal and it does not function properly. Im looking for a small mechanical or solid state relay to connect directly to the cell log without the need to create an interface board so hopefully just a relay and associated wiring.

This one seems to be good:
http://www.allelectronics.com/make-a-store/item/RLY-212/12-VDC-DPDT-MINIATURE-RELAY/1.html It will need about a 2.2k resistor in series depending on your total voltage, and a diode to go across the coil, something like a 1N4004 or similar. The diode is to prevent a voltage spike when the coil is turned off. This relay draws about 8mA when on. This has DPDT contacts, so can be wired for either NO or NC.

An alternate is something like this: http://www.mouser.com/ProductDetail/Omron-Electronics/G3VM-61B1/?qs=sGAEpiMZZMtHD6BhCPGf2pzm%2flBpqtlmFv2krLQd97c%3d
This is a solid state relay, so only needs a resistor, and can operate with about 2mA of drain. The contacts are only N.O. and can only handle about 500mA max. This would be OK to pull down a throttle line.

[auraslip]

I had no idea those baby relays existed!

[spinningmagnets]

Electronics noob warning...(I apologize in advance)

I am seeing a lot of LiPo users with the CellLog8 and they sound pleased, so I will probably get one. There have been concerns expressed that if left plugged in (example: over winter?) it will drain and damage the pack over time.

Is there a simple on/off switch I can put inline on one of the balance leads so I can turn the cell-log off, without unplugging it? The tiny balance leads concern me if I need to plug and unplug them frequently. Another option I am considering is adding two extra short JST jumpers inline, so that the plug and socket that are plugged-in/un-plugged often, are replaceable when they incur damage from my fat caveman fingers.

[fechter]

If you disconnect the pack negative to the CellLog, the drain drops to around 400uA on the cells other than the first one. This would still be bad for long term storage.

A PC board mounted connector makes it pretty easy to plug and unplug them, but takes a board. Perf board might work for this.

IMG_0006.JPG (124.97 KiB) Viewed 688 times

[mr.electric]

So would you power the relay coil from one of the sense wires and run the coil ground to one of the alarm signal wires. The other alarm signal wire is already grounded so just snip it off?

[fechter]

Here's how I think it should look:

CellLog Isolator_relay.jpg (25.74 KiB) Viewed 692 times

The alarm negative line is redundant, so you could just snip it off.

The diode is not critical, but should be rated for about 1A. It can be soldered directly to the relay pins. Without the diode, the voltage spike from the coil will zap the alarm output transistor.

The resistor value is approximate for a 32v total voltage. It should be 1/2W or more. If you ran the relay off a ~12v tap on the pack, you could eliminate the resistor, but it would unevenly drain the pack if it stayed on for long.

I show the 'typical' throttle cutoff wiring, but you could also use the NC contacts and place the contacts in series with the throttle signal line (and probably not need the 1k resistor on the throttle line). You could also chain multiple CellLogs in series by using this approach.