Parts For Conversion Motor/Battery

koolkev said:

If I wouldn't mind short range, like 45 miles, what is the smallest battery pack to drive a leaf motor?
Assume 3 miles per kw so 15kw

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remy_martian said:

45kWh, not kW.

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As remy_martian said, what gets you 3 miles is 3 kWh (kilowatt-hours) of energy, not 3 kW (kilowatts) of power, so for 45 miles you need 45 kWh. If you understand the difference between power and energy, then use the correct units to communicate effectively; if you don't, then it's time to do some reading.

koolkev said:

Tesla's are nominally 24v, no?

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Not quite. The modules of the Model S and Model X batteries (before the Plaid version) have six groups of cells in series (6S), so their nominal voltage is about 22 volts... and 16 of them in series run at about the voltage expected by the Nissan Leaf components. Model 3 and Model S Plaid modules are very different.

kennybobby said:

At 75mph in a leaf the motor will be spinning at around 8400 rpm.

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... assuming the same gearing and tire size as the Leaf. The gearing is the same since the transaxle is being used, but if the tires are a significantly different height then the motor speed for a given road speed will be different.

kennybobby said:

i don't know the motor constant but suspect that the back emf generated in the windings at this speed will be quite high and a substantial fraction of the pack voltage.

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At 8400 RPM the stock Leaf configuration is still well within the speed range (about 2700 to 9800 RPM) in which power is limited by the controller (to 80 kW, 110 kW, or 160 kW, depending on battery) to protect the battery, not yet limited by available battery voltage.

remy_martian said:

In your case, 15kWh pack size. The problem at thos point is getting enough current out of a pack that small since you'll need several hundred volts to run the Leaf motor.

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The obvious solution is to use the entire pack from a plug-in hybrid, which has about the same overall voltage as a Leaf, but only about 15 kWh energy capacity. These batteries can handle the power demand of a Leaf motor, at least in the 80 kW and likely 110 kW versions, at least for the duration of an acceleration burst. The classic example is a Chevrolet Volt.

remy_martian said:

A Tesla module has the wrong granularity for such a small energy need.

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True, any pack configured to deliver much more than 15 kWh (which means any modern EV pack) will have only a fraction of the desired voltage when you use only a fraction of the pack. If you take modules from a pack which is six times as large (in energy capacity) as you need, you will be using only one-sixth of the modules and thus get only one-sixth of the voltage.