Charger for a DIY battery WITH a bms?

inline_6ix

1 mW
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Feb 12, 2018
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I always hear about how it's super important to buy a $400 charger. If i run a BMS is it okay to use a charger like this? What will happen if I cheap out? What does a fancy charger do?
 

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A decent smart bms is about 100 bucks and a high end charger from mean well is less then 200 depending on the power you want so i dont see where you get 400 bucks for just the charger....
 
You should never use high power chargers anyway. 8h charging time should be a target, not a complaint.

I utterly trash my 16S25P, 72Ah, 60V 4.2kWh battery on the discharge. 200A peaks into a 1.5kW motor aint kidding around. But dispite my desire to see the hub motor go up the majestic flames and plasma i didnt even scratched the surface of the battery after 3 years of punishment of daily driving 75km at 1.2kW discharge rates. The samsungs 29E seem to takr it like a champ. But on the other side i care for them like they are a vintage original copy of the white album. Charging is done at 5A with the inbuilt charger and can take hours. I do have a separate "a frock shit what now" charger that i can connect to 3 phase and can fill that sucker up in 30min. Thing does get mighty toasty when you do this but works fine in those rare emergencys and its really funny going into a factory and pop a fuse becaue my dinky little moped is pulling 8kW from the wall.
Tldr:charge slow and keep under 4,05v for maximum lifespan.
 
flippy said:
A decent smart bms is about 100 bucks and a high end charger from mean well is less then 200 depending on the power you want so i dont see where you get 400 bucks for just the charger....

I was being hyperbolic. Sorry for confusion. If I just run power from a low quality charger into my BMS (slowly) will it shut it off automatically and not wreck my battery?
 
the BMS is a PROTECTION, not a regulator. you need a power supply (aka: charger) that has the proper voltage ceiling, that's it.
 
flippy said:
the BMS is a PROTECTION, not a regulator. you need a power supply (aka: charger) that has the proper voltage ceiling, that's it.

Will a 48v charger charge an 18650 to its nominal voltage or 4.2?
 
That depends on what they mean with 48v on the charger.
 
inline_6ix said:
Will a 48v charger charge an 18650 to its nominal voltage or 4.2?
No; an 18650 would be massively overcharged by a 48v charger, unless it has a BMS on it with protection against that that can handle that much voltage (a single-cell BMS's FET may not rated that high).

But it will charge a series set of them to their full voltage; assuming the 48v charger is for a 13s pack, and you have 13 cells in series, and the charger is set for 54.6v (or higher if it has a pack-level BMS with cell-level overvoltage protection).


Also, the "nominal" voltage of common Li-Ion 18650s is 3.6 to 3.7v. The "full" voltage of those cells is 4.1 to 4.2v.
 
amberwolf said:
inline_6ix said:
Will a 48v charger charge an 18650 to its nominal voltage or 4.2?
No; an 18650 would be massively overcharged by a 48v charger, unless it has a BMS on it with protection against that that can handle that much voltage (a single-cell BMS's FET may not rated that high).

But it will charge a series set of them to their full voltage; assuming the 48v charger is for a 13s pack, and you have 13 cells in series, and the charger is set for 54.6v (or higher if it has a pack-level BMS with cell-level overvoltage protection).


Also, the "nominal" voltage of common Li-Ion 18650s is 3.6 to 3.7v. The "full" voltage of those cells is 4.1 to 4.2v.

Sorry for the misunderstanding. Will a 48v charger charge a 13s pack to 48V or 54.6V?
 
The charger will charge the pack to whatever voltage it's designed to output. You'd have to measure yours with a voltmeter to know what it is.

Most "48v" chargers that are made for 13s packs of Li-ion batteries that have cells with a 4.2v full charge typically output 54.6-54.8v.

How high the BMS allows the pack to charge to depends on the specifics of whatever BMS you have.
 
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