Battery pack from a prius cell

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Nov 27, 2021
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Hi folks, i have a couple of prius cells that i was given from a lexsus hybrid. Anyone have any pointers on the correct method of charging and balancing them? From my research i have found.

-Dont charge them in parallel because they're nimh.

-Charge them until you detect a increase in delta T.

-you dont need to balance them because of there charging process?

-safest/ easiest way to charge them is to only charge it to 90% capacity (does this then require balancing as the batterys wont be able to self balance)?

I would appreciate some insight as it seems these batterys are quite common. Is there a solution allready avalible? I dont really want to design a pcb for it, especially withe the current state of shipping.

I plan on a 36v 5s1p configuration if its of any help.
 
nootnootmachine said:
I plan on a 36v 5s1p configuration if its of any help.

How exactly do five 1.2v nimh cells = 36v? Or you meant 5 whole modules?

They are 7.2V @ 6.5aH @ 1kg.

So a 13aH @ 36v battery would weigh 22 pounds at the minimum. So like 3 times heavier than a typical li-on bike battery?

I own a hybrid that uses those batteries, and they are used exclusively between 40-80% charge.
 
Each battery "cell" (which i think is what prius defines them as) contains 6 1.2v cells so in reality it will be 30s1p however you cant access the individual cells.

I was just planning on 6.5Ah as my city is flat and i only need some light pedal assist. My main idea for using them was because theyre free and dont want to see them go to land fill.
 
nootnootmachine said:
Each battery "cell" (which i think is what prius defines them as) contains 6 1.2v cells so in reality it will be 30s1p however you cant access the individual cells.

If they are used, you might be getting 30-40% less than their original 6.5aH rating. At this point you might be better off buying three new 12v lead acid batteries. It's probably going to be lighter. :mrgreen:
 
Ha ha ha , most likely. Either way ill see what performance i can get from them. Worst case scenario i have to throw out somthing i got for free anyway. I allready got a 10s li-ion bms so ill just switch to that. Is there anything i should be consirned about when charging these cells?
I did a bit more research on some old posts (was quite a bit of diging). Looks like these cells keep in balance quite well so i was just going to charge them to 41.5V (8.3v per cell) all in series. Anything i might be doing wrong or not considering? Id rather not set my bike on fire.
 
Like I mentioned earlier, these cells are designed to operate between 40% and 80% charge, ONLY. The hybrid system will not let them get outside that range. Ever. More realistically they live most of their life between 45%-65%. This is a narrow range, which might be the reason why balancing at cell level is not implemented. It just wasn't needed when they ran within those narrow parameters. You are in uncharted territory if you start charging them to 100%. They would probably need to be trickle charged very slowly to bring all cells to 100% since you will be doing this blindly.
 
There are some good threads about Prius cell sticks, if you haven't seen them. Some of them have some useful info:

This just lists all of the ones I know of; it doesn't filter them by usefulness. ;)
https://endless-sphere.com/forums/search.php?keywords=prius+nimh&terms=all&author=&sc=1&sf=firstpost&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

IIRC, the Vectrix also used a NiMH pack, so threads about those may also have useful info for you.


FWIW, there are RC chargers that can do NiMH, that should have a balance mode you can use to individually ensure each cell is not overcharged. None of them will do all your cells at once, but you could easily do one stick at a time.

To do the whole pack at once, you'd need 5 of the same 6s charger, as long as the chargers used are "isolated", meaning there is no connection between the input voltage side and output voltage side (reads OL on a meter set to ohms, between any output lead and any input lead). If they're powered by external DC sources, then just using isolated DC sources would do this, if the chargers themselves are not isolated. If you don't use isolated units, you're essentially shorting across the entire pack "below" the top charger unit thru the "grounds" of the chargers. :(
 
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