Battery or Charger Issues

[Hirschowl]

I have a Venom 3s 5400mah 20c that I think I am having issues with. I use it in my Traxxas P4de. The battery doesn't charge properly. When charging with an Onyx 235, the charger won't charge at 5.4a. It is set up to charge at 1c. Only goes to 4.1a. Also it will overcharge the battery. Even though the current drops a bit once it hits 4.2ish, but continues to charge cells. I have to shut off charger to stop charge.

Then when using the battery and the LVC cuts in on the esc (hobbywing SC8 wp), the cells are all off balance. Like 3.41, 3.56, and 3.63. Only off balance after LVC cut in. Not off balance after a short run. I know this is not good for the battery and thinking that the battery is the problem. But why would my charger over charge? I have an auto balancer that has saved this batterys' life. Also it is balanced before and after charging.

This is currently the only 3s I own. Waiting for some stock at SPC RacingI have 2 different 2s batteries and they both charge fine and balanced when discharged via LVC.

So wondering should I ditch this battery because it can do damage to charger or ESC? or just continue to use it till I get new batteries? Or worse catch fire..

Your shared knowledge on this matter will be greatly appreciated.

[SilmarilS]

If you didn't measure the cell voltage right after charge, and you are not over 4.2V per cell, how do you claim that you charger overcharged?

It's normal for charger to take a long time in the end of a charge to complete the process. It's where it need time to balance the cells.
The lower the batt quality, the more time the charger needs to balance the cells. I see a good amount of difference in charging time between different batteries, of the same capacity, but different brand/age/"C"

[Hirschowl]

Originally Posted by SilmarilS

If you didn't measure the cell voltage right after charge, and you are not over 4.2V per cell, how do you claim that you charger overcharged?

Originally Posted by Hirschowl

Also it is balanced before and after charging.

The balancer is a seperate device from the charger. When it balances with the balancer after charging, I am able to see the volts per cell on the balancer...

[SilmarilS]

Normally, the charger should balance the cells correctly, no need to balance again, which will only lower the battery charge.
What are your cells voltages after the charge?

Just my opinion, but I don't like Onyx chargers. A friend of mine has a 245 and the charger has trouble charging a battery with too much out off balance cells correctly. So I use mine to correct the offset charge!

[Hirschowl]

Only have to balance this battery after charging. My other 2s batteries charge ok. The one time the charger timed out(i wasn't paying close attention to it) cells were over 4.55v. The next time I caught it before the charger timed out cell were around 4.4. If I stop the charge above 4.2, not all cells are balanced therefore I use the external balancer to get the cells back in check. They are most commonly at 4.22, 4.25 and 4.27. I am not to happy with this charger either. Its was ok when I was just using 1 vehicle. Now I have multilple rides and want to charge more than 1 battery at a time, I will probably upgrade to an external power supply and charger here soon. Just not in the budget right now to drop 200+ bucks.

[SilmarilS]

Over 4.23V you risk to explode the batteries. Li-po doesn't tolerate over-charge very much!
I would stop using that charger before burning something up.
Do you have access to a good quality voltmeter to check the accuracy of the voltage of the charger and balancer?

Quote : "The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination."

[Hirschowl]

Yes I do have a Fluke 116 True RMS meter for work and have checked my voltages with that. The stand alone balancer is the one that is dead on with the Fluke. The charger is off, but not by much. Like .01v to .02v off.

How come the charger doesn't overcharge the other 2s batteries???? and why would the 3s battery be so unbalanced after LVC????

[SilmarilS]

Unbalanced cells after discharging is normal. But the cells should be pretty close together. Your values of 0.2V start to be a little high.

For the charging problem, the way most chargers work is that they push the current through the discharge plug. It monitor the voltage at the charging plug AND at the balance plug through the balance board. When it sense a difference between the cells, it pulls the current from the cell that is higher than the others and pass it through a resistor/heatsink to stabilize the cells. If the charger is not designed correctly (which I think) it can't pull enough current on the balance plug, versus what it deliver on the charging plug. Which will result with a overcharged cell.

You can try some cheap RTR chargers that charge through the balance plug each cell separately.
But it's possible that the battery pack is just not of quality or a construction defect.

Or it could be possible that one of it's voltage sensing circuitry ( one for each cell ) is defective!

[Hirschowl]

Still at a loss here, but really leaning towards battery failure. The cells really shouldn't be that unbalanced after running. Is there anybody else with any kind of opinion?