What's the difference between 250w 24v vs 36v DC motor and 350w 36v DC for EV?

[SeamlessPurse]

Hi

I'm converting a gocart. I have a few choices for DC brushed motors. 250w in 24v or 36v and 350w 36v. They all have the same spindle speed under load 2650rpm.

My understanding is they should all have same top speed but the 350w should accelerate quicker and have better load capacity?

What's the effect of voltage on the 250w motor? Is it just the current requirements of the battery are lower for 36v or what other pros / cons exist?
Thank you

[Siwastaja]

One could assume the 36V version has longer windings (larger number of turns) of thinner wire, than the 24V version.

Net effect is, you get the same torque with less current, but need more voltage to do so. So between the two motors, you can choose whether to have larger U smaller I, or smaller U larger I. Basic Ohm's law apply. Just like you can buy 230V or 115V products and both perform roughly the same.

Assuming the power rating is the same, torque rating likely is too, and the two motors likely have similar amount of copper and iron in them. If this is so (i.e., they are truly different voltage versions of otherwise same design), neither is better or worse, choose based on your available battery voltage.

Remember you can have larger battery voltage than the motor nominal voltage, it does no harm (within moderation). The maximum voltage is defined by the components used in the motor controller circuit. Motor nominal voltage is useful so you know the minimum battery voltage you want to have to get the rated performance.

350W motor obviously produces more power than the 250W motor. If they are both rated to produce the same RPM under this nominal power, it must then mean the 350W motor produces more torque.

Just like power = voltage times current, power is also rotational speed times torque. Motor voltage is in proportion to RPM, motor current in proportion to generated torque.

[Benta]

Pretty low power for a gocart. 250 W is around 1/5 HP. Is it for a kid?

[SeamlessPurse]

Thanks. This was my understanding to however having watched a number of reviews and modifications of the American ride on Razor vehicles for kids in 24v and 36v I noticed the 36v variants seemed to have a greater top speed. Considering the same spindle speed I assume the lower voltage cars are limited by available current or not enough torque for the combined weight.

@benta
Correct, it's for a 3yo kid. They're to big for the plastic ride on cars but not coordinated enough for anything faster. The plan is to limit it to ~5kmh then bump it up as their skill progresses.
The 24v Razor ride on quads seem fast enough. I just need to make sure I'm in the same net weight as my vehicles pretty rugged.

[Siwastaja]

If you have a given fixed battery voltage, then the 24V version will deliver higher top speed. But if you scale the battery voltage in same proportion, then there is no difference. And you can always supply more than rated voltage, to get more top speed, but then to prevent overheating the motor, you should derate torque (current) so that you don't exceed the power rating. This operation region is called "field weakening".

This is of course assuming the two versions truly are the same and only differ in design voltage. It's entirely possible though that random Chinese products with limited specifications are completely different designs even if sold as different "versions" of same motor.