E-powered Kayak battery charger....

I built a a 3S2P 16AH pack using LIPO cells which powers a 30lb trolling motor. Has been working great for months.
I use a BMS (ebay $8) with 4.2v/cell balance circuit, overcharge protection, and overdischarge protection.
I simply charge it with a lab supply set at 3 amps @ 12.6V.
Is there any reason why I need a charger specific to the pack chemistry&voltage or is the BMS providing the protection already?
I never gave it any thought really (having worked with RC plain LIPOs/chargers for years.

But now that I am in the middle of a 10s2P Lithium-Ion pack build, my lab PS will not work (only goes to 30V).
I can buy another PS (the reason I posted)...or go the cheap route and just get an Ebay 36V charger.

PS: Why do Ebike battery chargers typically rated for about 6v higher voltage than peak-charge (4.2v/cell) of pack? The BMS has very little voltage drop at end of charge, so 37v charge voltage for 36V battery should be fine.

v/r, P

As long as the voltage of each cell doesn't exceed 4.2 V, you can charge it with anything you like. 12.6 V is spot on.
For the 10s pack, most E-bike chargers will deliver 42 V max, so you're safe there too. BMS sounds like it should take care of any excursions.

pullin-gs said:

PS: Why do Ebike battery chargers typically rated for about 6v higher voltage than peak-charge (4.2v/cell) of pack?

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I haven't seen this in any of the chargers I have worked with or owned, including generic stuff that comes wiht batteries, or aftermarket multiprofile charges like the Satiator. I also havent' seen it with correctly specified chargers that people have posted about here on ES.

I *have* see wrong voltages, too high and too low, on varoius chargers people have posted about here on ES, some of which have caused problems with their packs.

One problem that can happen is a BMS FET failure, preventing it from being able to shut off charging, and a too-high-voltage charger then continuing to charge the pack up to whatever it's voltage is. If you have, say, a 36v LiIon pack, it should be around 42v fullly charged, for 10s. If the charger is, say, 48v, then you have 6v extra to be apportioned among 10 cells (assuming they're well balanced and it's even distributed), bringing each up to 4.8v. If some of them are badly unbalanced, the charger could bring them up well over 5v. Could end up with a fire.


What specific chargers have you seen this with?

Thanks for the posts all. I had brain-flatulence. I forgot the 36V pack is actually 42v fully charged (not 36V!).
Lab power supply upgrade from 30v-max to 60v-max will set me back $90+, so will instead go with a new $25 36v lipo charger.
Maybe take the money I save and roll it into a budget tab-tack-welder?

PS: A $200 36V 12AH+ Ebay pack meets my "on paper" requirements.....are they for real or are they garbage? I cant make a pack for that price.

pullin-gs said:

... I cant make a pack for that price.

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Yeah, it's like that.

If you have low expectations they might be fine. I'd be making sure everything is vibration-proof and water-proof, but often with these packs they aren't built to withstand high discharge rates.