How do I know if I need a battery isolator?

jimbo69ny

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Feb 9, 2018
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Hey guys!

I am working on a project to add a battery pack to my 2014 Rav4 EV to extend range. The OEM battery is made by Tesla and uses 2600 mah 18650 cells in a 92s48p configuration.

My plan is to add 3400 mah 18650 cells in a second battery pack. My pack will be 92s31p.

I thought I could simply run them in parallel but someone told me that I would have issues because the amp hour rating is different. He told me I should use an isolator. Is there truth to this? I was worried about the difference in amp hour ratings but I havent read anywhere that it would matter.

I've never used or researched isolators. Do I need one and do they make them that can handle 386 volts and 325 amps?
 
no, you dont need to separate them. as long as you have the same number of cells in series the packs will balance out naturally.
its also a LOT better for the cells as you spread the load.
just make sure they have a EXACTLY the same voltage when connecting them together. with a pack like that you will have some serious current flowing between the packs even with the slightest imbalance.
 
They actually dont have to be the same. This has been tested by Jack Ricard from EVTV. My numbers might not be exact but roughly, he connected 1 Tesla 85kwh pack that was 90% charged to another Tesla 85kwh pack that was 30%. The packs shut down. It was too much current.

So he got them a little closer, one was 90% and the other was around 40% and it worked! The peak current was only 255 amps (nothing for a Tesla pack). They balanced out after about an hour.

So it can be done.

Since posting this I completed my range extending battery pack. I have 2 Tesla Rav4 EV packs running in parallel. Here is my youtube page. https://www.youtube.com/user/jimbo69ny
 
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