Anti_Climax
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Re: Adding Extra Battery Power to FFE

A supplementary pack would operate connected in parallel. You want to get them close to the same voltage but they don't need to be exact. They will equalize as they are being used which may make your range indicator go up if the new pack is higher and starts to "charge" the original or lower if it draws the original down. But that's just indicating the state of charge for the pack the car can directly monitor rather than the combined capacity of the two.
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Re: Adding Extra Battery Power to FFE

i would like to know your opinion on an aux battery consisting of LiFePo4 cells but with a bms and same end voltage so the onboard charger would be able to charge it but the aux battery could also be charged separately with a second j1772 or dcfc connector as well
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Re: Adding Extra Battery Power to FFE

Any specific opinion you're seeking?
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Re: Adding Extra Battery Power to FFE

i know that the different chemistries have different discharge/charge rates etc so im simply looking for what others thoughts are on mixing chemistries
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Re: Adding Extra Battery Power to FFE

By discharge rate, you mean voltage versus state of charge, yeah? That shouldn't be a problem during actual use so long as neither pack operates outside their nominal cell max/min, but that could be a nightmare to manage. Could also preclude using the on board charger to fill the supplementary pack (or even regen outside a certain state of charge range).

I'd personally try to match chemistry, anything else just creates compounding problems to manage.
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Re: Adding Extra Battery Power to FFE

i dont like the orig chemistry as much as LiFePo4 but i was thinking it wouldnt be a problem to mix the chemistries esp since im going to have a separate bms for the aux bat
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Re: Adding Extra Battery Power to FFE

If they don't have the same state of charge voltage curve, you would need to restrict your use to the least extreme limit for charge and discharge.

Say that one has a full charge cell voltage of 4.2V and the other is 4.1V, you would not want to charge the first past 4.1V or you'll immediately be overvolting the second when they are put on the same bus.

It's not anything insurmountable, but you basically end up needing to build an entire battery system that also has to coordinate with what's already there.

Document what you do, chances are there isn't much help others can offer.
2012 Candy Blue FFE
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Re: Adding Extra Battery Power to FFE

Im building a pack that is the same pack voltage but the per cell voltage is different hence the need for a bms

im hoping to make a separate battery can bus and send the car only one pack at a time or both if desired
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Re: Adding Extra Battery Power to FFE

What are the actual nominal full charge and full discharge cell voltages on the other chemistry?
2012 Candy Blue FFE
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Re: Adding Extra Battery Power to FFE

LiFePo4 cells are nominal 3.2v fully discharged at 2.5v and fully charged at 3.65v

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