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Working on our first DIY EV conversion, a 1990 Miata.

From another project we have an Alltrax 7245 and 2xME1003 motors which we plan on running in parallel, driving the transmission input shaft using a belt drive. The belt drive is 1:1 from motors to transmission input shaft. Alltrax max voltage is 90 volts and max current 450 amps.

Question is what batteries to use. Our goal is to keep this conversion simple. Target range is 40-50 miles (so, about 10 kwh usable). We can add range and power in another version.

Currrent plan is 3x Tesla modules which would give about 15kwh rated (so I figure about 10 kwh usable) and 60-72 volts of operating voltage... That operating voltage, for our motors and transmission, produces 45-55 mph top speed in 5th (kV is 46 rpm/v -> unloaded RPM for those voltages are 2,760-3312 RPM -> reduce by 15% under load -> 2,350-2,815 rpm -> 46 to 55 mph top speed according to this wonderful calculator https://www.flyinmiata.com/tech/gearing.php ).

If we wanted a higher top speed, we need more voltage. A 4th Tesla module brings me to 80-96 volts which too high as it is just beyond the highest allowable voltage for the controller (max 90 volts)

Question for the group is what other battery modules could or should we consider if we wanted to build an 80-90 volt pack?

Thanks in advance for any suggestions.
 

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That's a little less than one-quarter of the voltage of a typical production EV pack, which has a 96S cell configuration. That means a roughly 60 kWh or larger pack would have modules of the desired amp-hour capacity, so you can use just under a quarter of them (or 24 cells in series) for the desired energy... if they reasonably split up the way. Just two of the larger modules of a Bolt would be 20% of pack voltage and capacity, with 20S for 75V nominal and perhaps 82 V max. The only common EV packs which are larger are in Teslas; with 16 modules in a newer Model S pack that's the three modules that you have already considered.

Modules from any lower-capacity pack would require connection in parallel to get enough capacity. If you are willing to do that, it would presumably be possible to reconfigure most of the modules of a Chevrolet Volt pack into a workable combination, although you would need to look at the specific module sizes to confirm that it would work without splitting modules.
 

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From another project we have an Alltrax 7245 and 2xME1003 motors...

Current plan is 3x Tesla modules which would give about 15kwh rated (so I figure about 10 kwh usable) and 60-72 volts of operating voltage... That operating voltage, for our motors and transmission, produces 45-55 mph top speed in 5th (kV is 46 rpm/v -> unloaded RPM for those voltages are 2,760-3312 RPM -> reduce by 15% under load -> 2,350-2,815 rpm...
At only 15% under no-load speed the motor will be able to produce very little power. Motenergy's published data is horribly lacking, with the only performance chart that I've found being the same nearly unusable format as NetGain's test data and only for 48 volts. Do you have any useful performance data which would show how much power you would have available in that voltage range at that speed?
 
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