Converting to Lithium

[Rwalsh77]

Originally Posted by Riso

I got 30 miles on a charge yesterday. 2 Chevy Volt 47AH batteries in parallel (94AH).

Sweet, good to know what to expect. What motor are you running?


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[Riso]

stock motor

[NCPW]

Riso, what's you charged (max) voltage and what did you run you batteries down to for the 30 mile run? What kind of speeds were you doing?

[Riso]

I was at 50.1 volts and ran it down to 42.5 volts.

[NCPW]

So, 4.175V per cell to 3.54V per cell.

So you're charging to roughly 95% SOC?

[Rwalsh77]

Originally Posted by Riso

I was at 50.1 volts and ran it down to 42.5 volts.

Are you running a BMS?


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[Riso]

Originally Posted by Rwalsh77

Are you running a BMS?


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Yes. One on each battery. Chinese boards for balancing cells only. The charger is not connected through them.

[Rwalsh77]

Originally Posted by Riso

Yes. One on each battery. Chinese boards for balancing cells only. The charger is not connected through them.

At 42.5v, are you roughly 20%?




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[JohnnieB]

Originally Posted by cgtech

Also, lead acid batteries are rated deceptively. They are rated at a "20 hour rate". If rated at a "1 hour rate" like lithiums are, the lead acid batteries would only have about 55% of the rating we commonly use to select lead batteries. In my testing, 100ah lithiums deliver the same energy as a set of (higher AH rated) T-875 batteries. Factor in the weight loss for the cart, and you will easily have more range than a set of 8v lead batteries.

I might be wrong, but I think there are a couple more favorable factors for Li batteries.

Depth of discharge. 50% is typically the max recommended discharge for lead-acid batteries while about 80% of the energy stored in Li batteries can be used. That means if the LI and L-A battery packs had identical storage capacities, the Li would have about 30% more range before the reduction in weight was factored in.

Consistency of performance. (This is theoretical, so correct me if I'm wrong.) The internal resistance of a lead-acid battery increases as it is discharged, so the amount of voltage drop per 100A of current draw increases and performance suffers towards the end of the max usable discharge. The internal resistance of Li batteries is less than that of lead-acid batteries and doesn't increase much during discharge (more or less linear), so performance stays pretty much the same throughout the discharge.

[Rwalsh77]

Originally Posted by JohnnieB

I might be wrong, but I think there are a couple more favorable factors for Li batteries.

Depth of discharge. 50% is typically the max recommended discharge for lead-acid batteries while about 80% of the energy stored in Li batteries can be used. That means if the LI and L-A battery packs had identical storage capacities, the Li would have about 30% more range before the reduction in weight was factored in.

Consistency of performance. (This is theoretical, so correct me if I'm wrong.) The internal resistance f a lead-acid battery increases as it is discharged, so the amount of voltage drop per 100A of current draw increases and performance suffers towards the end of the max usable discharge. The internal resistance of Li batteries is less than that of lead-acid batteries and doesn't increase much during discharge (more or less linear), so performance stays pretty much the same throughout the discharge.

[emoji1303]

All correct if you ask me!!






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