Occasionally charging through the discharge port of a separate port bms

[Drewlrox]

I was wondering if there is any reason it would be unsafe to charge via the discharge port of a separate port bms occasionally (maybe 1 out of 20-40 charge cycles).

I have an electric scooter with a 20s 40ah battery pack using lg 21700 cells rated for a max charge rate of .7c, or 28 amps on this pack, the scooter does have regen braking. I want to do some long range rides utilizing ev charge stations j1772 220v supply, so I purchased a compact charger which can deliver 28 amps with the intention of occasionally using it to its full potential at ev charge stations. However the bms on this battery caps charge rate at 14.9 amps when using the charge ports, at 15 amps or anything higher, the bms disconnects the charge port temporarily.

Is there any risk of damaging the bms by occasionally charging thru the discharge port to 90-95% capacity to bypass this charging current limit? The scooter has regen which can be quite aggressive on the highest setting, which makes me think this should be okay. But these are momentary bursts. I understand there may not be balancing taking place when doing this, which should be okay for 1 cycle occasionally.

 

[fechter]

The only real risk is the BMS is essentially bypassed and won't turn off if a cell group gets too high. If you only charge this way to 90%, there is less chance of overcharging a bad cell group. The BMS will handle this fine, just watch the cell voltages.

 

[docw009]

I own a couple of bluetooth BMS that allow monitoring of individual cell voltages with a phone App, but I never have installed them, so I can't say that they will work., If they do work reliably, and if you watched the voltage, then I think you could charge thru the discharge port with reasonable safety,

 

[E-HP]

I understand there may not be balancing taking place when doing this, which should be okay for 1 cycle occasionally.

Does your pack regularly balance or does it fully charge without needing balancing? If your pack stays relatively in balance, bulk charging won't have a big affect how quickly it goes out of balance, so I'd monitor the pack to see how often it really needs balancing, then use that as a count an approximation for how many times you can bulk charge before balancing. I fully charge my batteries about twice a year to 4.2V/cell and bulk charge the rest of the time to 4.15V/cell before going out to ride.

Can you post information on your EV charging once you get it all working? I'm interested in that since there are a lot of charging stations popping up all over around here, some free, most paid.

 

[Drewlrox]

Does your pack regularly balance or does it fully charge without needing balancing? If your pack stays relatively in balance, bulk charging won't have a big affect how quickly it goes out of balance, so I'd monitor the pack to see how often it really needs balancing, then use that as a count an approximation for how many times you can bulk charge before balancing. I fully charge my batteries about twice a year to 4.2V/cell and bulk charge the rest of the time to 4.15V/cell before going out to ride.

Can you post information on your EV charging once you get it all working? I'm interested in that since there are a lot of charging stations popping up all over around here, some free, most paid.

Unfortunately this bms does not have any smart features to monitor cell voltages, and the entire battery pack and bms are potted in silicone inside of an aluminum enclosure. But I never plan to charge this way for more than 1 or 2 cycles at the most, and will likely only charge to 90% ish when I do. When charging thru the charge ports, it always balances.

Im using a roger charger sc(the new smallest version) from roger euc, he custom ordered me a lower voltage version of it (60-86v) as most of his customers are euc with battery packs in the 100-160v range, will do 20.5a on 110v and should do around 26-28 amps on 220v (2100w limit), I believe he ordered more than just one in my voltage range. The charger has both bluetooth control and can set voltage/amps on the unit itself, over bluetooth can setup 2 stage charging and some additional things. J1772 to nema 5-15 adapter is the somewhat common one you will see pop up if you search for it, can be had for $35 on aliexpress or $70 from usa sellers, Also have the parts from Kenzi Mudge on the way which makes it a lot more compact and swaps the nema 5-15 for a 5-20.

The only real risk is the BMS is essentially bypassed and won't turn off if a cell group gets too high. If you only charge this way to 90%, there is less chance of overcharging a bad cell group. The BMS will handle this fine, just watch the cell voltages.

Thanks for the feedback, just did a test charge and it seems to be working.

 

[E-HP]

The charger has both bluetooth control and can set voltage/amps on the unit itself, over bluetooth can setup 2 stage charging and some additional things. J1772 to nema 5-15 adapter is the somewhat common one you will see pop up if you search for it, can be had for $35 on aliexpress or $70 from usa sellers, Also have the parts from Kenzi Mudge on the way which makes it a lot more compact and swaps the nema 5-15 for a 5-20.

So is the idea that you just get one of these adapters and that allows you to plug your charger into? Does the charger need to be 240V? This looks simpler than I had envisioned.

 

[Drewlrox]

So is the idea that you just get one of these adapters and that allows you to plug your charger into? Does the charger need to be 240V? This looks simpler than I had envisioned.

Yes, you will get 220v (240) out of j1772 using one of these adapters, because this is going to a nema 5-20 plug, you do have to be mindful of what you plug into it. If you plug a 110v device it, it will likely fry it. Nema 5-15/20 is not intended to be used with 220v, but if the device you plug in accepts 220V, it will of course work fine. Because the current on 220 is half of what it would be on 110, you can plug multiple chargers into 1 adapter.

 

[E-HP]

Yes, you will get 220v (240) out of j1772 using one of these adapters, because this is going to a nema 5-20 plug, you do have to be mindful of what you plug into it. If you plug a 110v device it, it will likely fry it. Nema 5-15/20 is not intended to be used with 220v, but if the device you plug in accepts 220V, it will of course work fine. Because the current on 220 is half of what it would be on 110, you can plug multiple chargers into 1 adapter.

Thanks for the info. A couple of my cheap chargers can toggle between 110V and 220V. I've been looking for a more compact charger, so now having a 220V option will be part of my criteria.