10s charger measures 42.3v. Bad thing?

I bought a charger to a 10s battery pack and it measures 42.3 volts. Now that will over charge each cell a bit to 4.23v or will a good Bms kick in and stop at 42.0v?
Should I be concerned?

I'm the guy that usually charges to 3.8-4v to extend battery life.

eikido said:

I bought a charger to a 10s battery pack and it measures 42.3 volts. Now that will over charge each cell a bit to 4.23v or will a good Bms kick in and stop at 42.0v?

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The BMS should not kick in at 4.23VPC. Usual design limits are 4.25-4.30VPC. However, since no battery pack is 100% perfectly balanced, a slight imbalance may cause a shutdown.

You are seeing a slightly high charge voltage due to manufacturing tolerances. In most cases it won't be an issue. You might want to lower the voltage a bit. Before you do so, make 100% certain that you are actually measuring the voltage correctly, with a calibrated meter. Some cheap off the shelf DMM's are only guaranteed to have less than a 1% error - and a .7% error would show a good 42 volt charger at 42.3 volts.

Charging **to** a slight overvoltage - immediate stop at that setpoint with no holding CV/Absorb stage at all - will not be too stressful.

You will see Resting OCV drop back to well below.

Otherwise, if you can't get the charger reset, an HVC could cut off its source feed when you hit say 4.05Vpc or whatever your target is.

Keep in mind it is **sitting** at high SoC that is reducing longevity, a lot more than briefly touching it and then immediately applying a heavy load to start pulling it down.

So if not immediately using the bank, you could burn say 2-3% off the top charge to reduce damaging stress.

In your situation, you can use an overvoltage protection relay, between the charger and battery. The overvoltage relay measures battery voltage and will pull relay when your set voltage is reached. You want 42 volts max, set it to 42 volts and thats where it cutsoff, the bms will be extra protection in case of failure. I never trust just 1 method to turnoff charging with lithium, charger can fail,bms can fail, wrong charger connected.

Its how I charge all my lithiums when using a normal charger, not needed when when using a balance charger. You can get a 0-99 volt relay for less then 10 dollars, I have it trigger a larger 30 amp automotive relay. Very cheap insurance for expensive batteries.

Better to charge to ~4.1 / cell. Gives more headroom against imbalance issues reaching over 4.2 / cell. Topping out like that will also disproportionately hurt your pack for no benefit.

You might be able to open it up and adjust it down a notch, using the V adj trimpot. How hard that is depends on the type of charger.

You are looking at a .03v overcharge per cell, assuming a perfect balance. I would not worry about it, possible that you are measuring with a tool not really accurate to .01v anyway. Another thing to consider, as chargers age, they typically start to put out lower voltage anyway.

In any case, balancing with that charger will not harm the pack, the bms will kick in to discharge high charged cells as soon as it should. Just don't store it that way a long time, ride it down to your target full charge voltage asap after you balance charge it.

Another story if you are charging naked cells. Then you might want to turn it down somehow, adjust the pot if possible, or do something with the output to drop its voltage. .3v,, a long cord on the dc end would do er.

Thanks for the response all.
Some of the information is a bit difficult to understand but i'm digesting and learning.
Also, this charger is charging none critical/expensive batteries so it's not the end of the world.
I just need to learn more incase this would happen the day i started charging expensive packs.

I'm leaning towards extending the cable a bit to add resistance. That was a neat idea.