Help with my 72 volt bike

[Beavinator]

Hello I am totally new to this e-bike thing and LOVE it! My buddy built a 100 volt bike and once I rode it I was hooked. I am building a 72 volt bike for a steep hill I live on. I have a X-5 motor with an infineon controller I got from e-bikes. They advised me that they dont have a battery for 72V and referred me to EV Assemble in China. They didnt have a 72V either but the guy at e-bikes told me to get 2 36 volt 20ah and run them in series. I ordered them and a 72 volt charger. My question is will running the batteries in series be OK with the BMC? I really dont want to damage the batteries considering they are 500 bucks each! Thanks for your help!

 

[FMB42]

Welcome to ES Beav.

You could also charge each 36v batt separately (using either 1 or, 2 chrgrs) just to be on the safe side.

 

[number1cruncher]

Beave,

You should be able to run those batteries at 2C, twice the 20AH capacity = 40Amps, which is not shabby. Make sure you have the correct gauge wire, at least 10 gauge for consistent 40 Amp use. At that amperage things can get hot with undersized wire. I stick to 30Amps and 12 gauge wire, because I'm cheap, lol.

 

[Grizzlybear]

If those batteries are LIFEPO4 then you need a diode between them, otherwise the BMSs will be toast, tread carefully!

Griz

 

[Beavinator]

I need VERY specific instructions on what diodes I need and exactly how to install them. Do I have to solder them to the BMS? Im totally lost. Thanks for help!

 

[beast775]

use the search function on the top of the page,you can read and find out exactly what you need.put in series diodes,plus volts you want to use.if that dont work someone who knows will tell you.i dont want to guess. i would agree with two chargers although,good luck take pictures of your build.

 

[John in CR]

You need a diode between the 2 batteries in series that is rated for the current and voltage you are running. This protects the battery packs from voltage spikes when one BMS is tripped so the other doesn't "see" the spike. The best answer is Tiberius's ideal diode which doesn't have the normal voltage drop of a diode (voltage drop means loss in the form of heat).

No it doesn't have to be soldered into the BMS, just somewhere in the connection between the 2 packs.

John

 

[J Barrie Wilkinson]

I am a little confused (not unsual), you start off talking about an X5 and end reffering to a BMC.

 

[Beavinator]

Thanks for all your help guys but I think I found a better solution. I managed to contact EV Assemble before the order left and they said they can just put the 2 36 volt packs into 1 big 72 Volt pack with 1 BMS and 1 72 volt charger. I never knew they would do this but apparently they will. Thanks for your advice!

 

[Demosthenes]

Thanks for all your help guys but I think I found a better solution. I managed to contact EV Assemble before the order left and they said they can just put the 2 36 volt packs into 1 big 72 Volt pack with 1 BMS and 1 72 volt charger. I never knew they would do this but apparently they will. Thanks for your advice!

I totally didn't know they would do that either! Good for future reference.