What you think of this charging method

I’m going to give you a solid “no!” on this one. You’re wasting money and adding tons of complexity.

Use a charger like this: https://www.aliexpress.com/item/Global-Certification-50-4V10A-Charger-44-4V-Li-ion-Battery-Smart-Charger-Used-for-12S-44/32822262578.html

And a tiny resistor board like this: https://www.ebay.com/itm/263384603242

The resistor board I linked isnt for 12S but they do make them for 12S. I’ll try and fine one. Dirt cheap

And there you have it, 10A charging with passive balancing for a FRACTION of the price and far simpler. It’s so small you could even leave that tiny board inside your battery pack. But it will also work just as well outside as an external device. I highly recommend just sticking it inside your board, it will ensure the cells are always balanced.


with 4 in parallel can do 16a and be within manu specs

1 Like

It comes in 2 sizes. There are plastic versions too.

4.2v x 10a = 42w, times 12 is 500w. You’re better off with the big bulk chargers, and balance charging once a month.

1 Like

i have a bunch of those resistor boards already. the last plan. maybe will revisit it and read your post a couple more times later.
thanks guys …night!

I have a built in resistor board on my 10s4p pack just as @TowerCrisis is suggesting

1 Like

aha i gotcha, why not just a cheap ebay bms for charge only? :joy:


He wants 10A charging, and most cheap bms’s won’t allow for that. You’d probably need a programmable BMS or one you can special order with specific settings.

Lol, you’ve been told no in the past


So pass the blunt and lets see what gives


Why don’t alot of people do it this way instead of picking up a pricey bms?

Interested to see the 12s model too

Screenshot_20180811-155808_eBay this is 45a charge and discharge?

Do you plan on putting this on the board or use as an external balancer?

BMS vs Balance Board

There’s a few inherent disadvantages of using a bare board instead of a BMS or charging BMS.

Whatever charging port you add will be connected directly to the battery pack with no buffer in-between. Most BMS’s have protection on their charging ports and don’t allow significant current to flow in reverse, incase something has shorted out the charging port. So you’ll likely need to put a small fuse on your charging port for protection.

You don’t have any over voltage protection So if your charger goes haywire and for whatever reason gives too much voltage, or god forbid, you use the wrong charger :grimacing: then you have no protection and you could damage or end up venting your battery.

You also don’t have cell level protection, although I guess this only applies to BMS’s used for discharge. If I accidentally leave my board on and it bleeds power for a week, the BMS will cut power once any of the cells reaches 3V. That’s useful if you want to save some cells and labor incase of accidental mistakes.

Over current protection is also a benefit from a BMS. If for whatever reason your motor or main battery leads short out, and it pulls significantly more than 60A in my case, then the BMS will cut power. I think that’s a safety feature that all builders should consider, it’s good fire protection.

But with BMS you also risk not being able to brake on a full battery, because it will prevent cells from getting overcharged. This also only applies to a BMS that also discharges.

Overall there are many pros and cons to both scenarios that one should consider.

Setups I recommend

In my opinion these are some necessary precautions to take. Here’s one setup: -RC tweeter that will alert you upoun lowor high voltage (left on too long or overcharging batteries on braking) -Large fuse immediately after the base of the battery positive terminal, isolate all bare unprotected positive contacts -Small fuse inline with charging port -Balance board to keep cells in sync

Another option: -Use a BMS for charging only -large fuse on positive lead -small fuse on charger port -RC tweeter to alert high and low voltage.

One more: -Use a BMS for charge and discharge -Dont charge to full capacity but reach balance voltage of the BMS.

What I DONT recommend is this:

-Using a bare battery with no fusing or BMS. Or -Having balance leads exposed outside of the case for easy balance charging. (Unless you have every wire fused.) You really don’t want your balance wires to become the fuse when the port gets shorted somehow. Or -Having no way to balance your cells :skull_and_crossbones: Or -Using a BMS for discharge, unless you have a separate way to bleed voltage spikes over your max battery voltage from braking hard. Or -Not properly recognizing the inherent and minimizeable risks we take by using high capacity, voltage, and density batteries.

In response to this threads initial proposal

There are some methods that are safe and some that aren’t. Using a balance charger intended to charge a pack is safe. Using a balance board is safe. Using a BMS is safe.

What is not safe is strapping 12 chargers together and expecting them to function properly while their outputs are all connected in series. There’s too many risks in my opinion. One of the chargers could stop working and that would likely end very badly. You could of course really engineer these things and ensure they all work right.

But then again, if this thing’s really redesigned from the ground up you’ve effectively created a very expensive unproven balance charger for significantly more time and money.

The much better method is to have an external BMS connected to a 12S 10A charger, or to buy an actual 10A balance charger. I haven’t even gotten into the risks of charging at 10A, I wouldn’t use that on anything under 10Ah less you risk degraded battery lifetime.

This whole debacle is only to squeeze out a little less charge time. Sure, you can now charge your pack in an hour. But to me that isn’t any more useful than charging it in 2 or 3, because at that point after waiting an hour there’s no need or immediate urgency to use your board that could have waited that long.


Use stuff the way it’s intended and add adequate protection the way actual companies do to protect their users. Spend more (or in this case actually less) to be as safe as you can be.


Thanks! I appreciate the detailed response. Book Marking this for reference :smile:

I do like the benefits of a BMS but having it on board adds another possible point of failure like losing brakes like you mentioned, something shorting inside and not being able to see if the BMS is balancing the cells as intended so relying on it on that point.

Which is why I would preferr a simpler method of not having a BMS on the board and have the charging done separately I think those points are why @Hummie is into the non BMS route.

This is for discharge BMS? Would there by any way to do this besides a BMS?

Yes, it’s for a discharge BMS. The only other way I really know of is to add a fuse.

Some builders have integrated a fuse into their antispark loop key, but that doesn’t have the same amount of protection against internal shorts like a fuse that’s close to the battery terminal.

A fuse isn’t easily replaceable or necessarily available whereas a BMS will automatically reset, which is why I have a preference towards it.

1 Like

I’ve read that discharge BMS have to be able to also take the amount of draw which usually causes them to be large and expensive otherwise they cut off early under heavy riding

Do you have any BMS that you recommend for 12s? Also how do you get to the balance voltage with a charge/discharge bms? Do you just get the average total voltage by reading it straight from the pack as the BMS doesn’t usually display the volts per cell

Supower battery has some good ones. Rated at 60A continuous for $40. The balance voltage is a spec of the BMS. In the case of supower battery, most of theirs are 3.9V. So as you charge it will only begin balancing a cell with the others once it’s voltage reaches 3.9V. It will fully charge to 4.2V.