Help determining charger size

Bikebuilder

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I am currently converting a gas moped to electric. I am building a 20S9P battery using a Samsung 50E 21700 5000 mAh 9.8A battery. I will be using a 100 A BMS. The controller will draw 60A.

I am looking for a charger for it and need a recommendation. I see many chargers are 3-5 amp, but also see some at 20A. I am assuming the higher the A, the faster the charge. My question how large a charger (Amp) can I go and how large should I go. Looking for recommendations on power, speed and even specific charger.

 
A 20S9P pack can safely take a LOT. A 72v pack thats 84v at a 100% charge, with 9 parallel banks, will soak up one hell of a lot of current.

With that said, heat is the enemy of your cells, and heat is generated by fast charging. So yeah sure you can take a 10a+ charge no problem (assuming the right connector and wire gauge), but why pour all that money into a pack just to degrade its lifespan? 3 amps is a good number for a pack that size as a routine slow-charge.

With 14S9P 21700 packs, I sometimes go up to 5 or 8 amps using a Mean Well charger I keep onboard my adventure bikes. But those are special for charging fast in a remote area. I want to gas up before the tide comes in on a remote beach ride. When I'm in the garage, for a daily driver, I do 0.50 amps and let it go long.

Its too bad your voltage is too high to use a Mean Well. MTBFs are 150,000 or more hours depending on how big you go. If I were doing a 72v pack I'd use a Cycle Satiator. Same internals as an LED driver and they have a model that goes up to 96v. If portability is not an issue, then find a lab power supply. If it has CC+CV mode that effectively makes it a smart charger.

 
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