Need some help / advice with EV stuff...
 

Gosh, I never thought I would type that into a subject line. Oh well.

We have this "car" here: https://dempseymotorsports.com/mit-aztec-solar-car/

It currently has six lead-acid Odyssey Red Top batteries in it. They are very old, and I would like to upgrade / replace them with lithium-ion batteries. But I'm slightly confused and Google is not helping too much.

Each Red Top battery is rated at about 50 or amp-hours according to their data sheet page: https://www.optimabatteries.com/products/redtop

Here's a sample "replacement" kit I found while searching the interwebs: https://batteryevo.com/product/72v-falcn-4x-kit/

Aztec has six red top batteries - 12V at 50-amp hours. Putting six together should result in 72V with 50-amp hours? Power is current times voltage, right? So, total power should be 72 * 50 = 3600, I believe the rating is watt-hours then?

So the kit above with the 108 Ah rating would be 72V * 108 = 7200 watt-hours.

Or, more specifically, if I were to replace the batteries with similar capacities, then I would probably only need this? https://batteryevo.com/product/72v-falcon-2x-kit/
This kit is 54 Ah at 72 volts which would be 3,888 watt-hours. Each one is about the same weight as a lead-acid battery, but seems to be three times the capacity.

So, I guess I'm looking for some confirmation - the six red top batteries could fairly easily be replaced with this two-battery set here and would have the same capacity with a lot less hassle and 1/3 the weight? Yes / no?

Thx,

Wayne

Yes. Your series and parallel calculations look good. Power = voltage x Ah.

You also get the ability to discharge the ion battery lower than the FLA without damage.

What’s the peak amperage the motors will draw?
Optima’s CCA is way higher than the 160 from the golf carts.
That’s the only thing I can think of that might meth up the #s.

I would want to know what the motor is and what method or methods are used to recharge the batteries before making any suggestions. Might be an even lighter/better performing and or cheaper option.

The last time I looked at the motor, it was nearly 30 years ago. So, not much info there. This doesn't have to win any races any time soon - just needs to go around the block, pretty much.

As for the charging - the setup appears to come with it's own charger, which is a bonus.

-Wayne

The 2 battery proposal should work fine. Would verify that the red tops are actually all series for 72v in the car.

6000w continuous rating so around 8hp, that should be plenty cant image solar car has more than a couple KW motor.

I think there is a decent chance you could do better by diying with some tesla modules or whatever and riging up BMS and charger from comercially available systems.

But for plug and play ease, if those batteries are known to be decent it should work fine.

May want to pay attention to the nominal battery capacity ratings verses in use. I think Lion you can reliably use about 80% long term but not sure if the 50Ah rating for deep cycle is nominal or in use.

You want Lithium Iron Phosphate. They will tie into any 12V lead-acid battery system

Dakota - https://dakotalithium.com/

PowerSonic - https://www.power-sonic.com/batteries/

Battleborn/Firefly - https://battlebornbatteries.com/