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 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
-Use a BMS for charging only
-large fuse on positive lead
-small fuse on charger port
-RC tweeter to alert high and low voltage.
-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.
-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.
-Having no way to balance your cells
-Using a BMS for discharge, unless you have a separate way to bleed voltage spikes over your max battery voltage from braking hard.
-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.