Ideas about charging batteries

avoleoo

10 W
Joined
Feb 12, 2014
Messages
87
Location
West Palm Beach, FL
I run 2 x 7S6P Tesla 18650 packs on my ebike in series for total 14s6p. Since I ride a lot, Im getting tired taking them off the bike, bringing them inside, charging them and putting them back on the bike, so maybe you guys can share with experience about alternative and more convenient ways to charge them.

Two options so far:

1. Taking them off the bike every time to charge with the RC charger. Charging in parallel, using in series. Good option, gives full control and peace of mind. But it's not convenient.

2. Attaching a BMS and charging with 14s charger, but..... ( this is a no go for me )
2.1. I dont trust BMS where I dont see individual cell voltages.
2.2. I dont have an option to choose state of charge, I mostly do 4.05 per cell and 4.15 when going for 40 mile rides.

What other options are there?

Thanks.
 
I don't know what situation I could be in where I'd trust an RC charger more than a full time, hard wired BMS. Maybe if I knew the battery was faulty?
 
Allright, I think I came up with the solution.

Buy a charger that would still bulk charge to 4.05 x 14 = 56.7v and charge them off the bike only when going for longer rides. Sounds like a good compromise.
 
Meanwell's are what you need to bulk charger
HRP models

You can connect them in series to desired voltage, there is a voltage pot to adjust range is like 10V on my 24V model, but there are no current pot's.
There are some Meanwells that you can adjust both voltage and current.
 
Since you've paid attention to detail cell voltages, how much out of balance is typical? If it's small, then you can generally just bulk charge and occasionally take them off to check the details. Since the only risk of out of balance conditions is over-charging or over-discharging your pack, your very conservative 4.05V/cell typical charge reduces risk tremendously.

While I've never used Tesla cells, I use automotive cells for my packs for several years, and before that I used RC lipo for years. I've never used a BMS, and very rarely balance charge. Instead I am the BMS for my battery packs. I'm very familiar with their behavior at the individual parallel group level, and I combine that knowledge with conservative full charge voltage (not as conservative as yours) to ensure that I never come close to over-charging or over-discharging my packs as long as I don't have a bulk charger failure in cutoff. That did happen to me once, and for extra security I added an electric cutoff timer to stop power to my chargers before the pack reaches expected full charge. Then in the morning I turn the chargers back on, so the pack is ready for me to head off for the day.

I've never had an ebike that required pack removal for charging. I can't imagine that level of inconvenience. Just park, connect the charge plug and push a button, is all the inconvenience I'm willing to accept, and once you have that level of convenience then you'll understand.
 
John in CR said:
Since you've paid attention to detail cell voltages, how much out of balance is typical? If it's small, then you can generally just bulk charge and occasionally take them off to check the details. Since the only risk of out of balance conditions is over-charging or over-discharging your pack, your very conservative 4.05V/cell typical charge reduces risk tremendously.

While I've never used Tesla cells, I use automotive cells for my packs for several years, and before that I used RC lipo for years. I've never used a BMS, and very rarely balance charge. Instead I am the BMS for my battery packs. I'm very familiar with their behavior at the individual parallel group level, and I combine that knowledge with conservative full charge voltage (not as conservative as yours) to ensure that I never come close to over-charging or over-discharging my packs as long as I don't have a bulk charger failure in cutoff. That did happen to me once, and for extra security I added an electric cutoff timer to stop power to my chargers before the pack reaches expected full charge. Then in the morning I turn the chargers back on, so the pack is ready for me to head off for the day.

I've never had an ebike that required pack removal for charging. I can't imagine that level of inconvenience. Just park, connect the charge plug and push a button, is all the inconvenience I'm willing to accept, and once you have that level of convenience then you'll understand.

Do you ever park your bikes away from home?
 
Tesla use ncr cells these are not immune to thermal runaway but they are not as vulnerable as a high discharge cell.
As for using a bms over a hobby charger like chalo said, the issue I have with this is most cheap bms have no way of checking what it's actually doing and the amount of posts I've seen on here about faulty bms means I would either go the Bluetooth route with a decent bms I can monitor or just balance charge and discharge naked.
Running a bms is like a Condom if your not familiar with what your doing and committed then wrap up but don't pic any cheap rubber or you may inabvertibly created the accident.
 
Buk___ said:
John in CR said:
Since you've paid attention to detail cell voltages, how much out of balance is typical? If it's small, then you can generally just bulk charge and occasionally take them off to check the details. Since the only risk of out of balance conditions is over-charging or over-discharging your pack, your very conservative 4.05V/cell typical charge reduces risk tremendously.

While I've never used Tesla cells, I use automotive cells for my packs for several years, and before that I used RC lipo for years. I've never used a BMS, and very rarely balance charge. Instead I am the BMS for my battery packs. I'm very familiar with their behavior at the individual parallel group level, and I combine that knowledge with conservative full charge voltage (not as conservative as yours) to ensure that I never come close to over-charging or over-discharging my packs as long as I don't have a bulk charger failure in cutoff. That did happen to me once, and for extra security I added an electric cutoff timer to stop power to my chargers before the pack reaches expected full charge. Then in the morning I turn the chargers back on, so the pack is ready for me to head off for the day.

I've never had an ebike that required pack removal for charging. I can't imagine that level of inconvenience. Just park, connect the charge plug and push a button, is all the inconvenience I'm willing to accept, and once you have that level of convenience then you'll understand.

Do you ever park your bikes away from home?

Of course, daily. My batteries are mounted in a manner that thieves would have to steal the entire bike and get to the batteries with proper tools. If I'll be away from my bike for an extended period, then I use pay by the hour parking lots.
 
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