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#### fbw4

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This is a Medium Size 110 Quad that I converted to Electric Power. I'm using a Mars 0708 Motor, AllTrax 4844 Controller, and ThunderPower 36Volt 40AmpHour Batteries. With a 40 tooth rear sprocket and a 12 tooth in front I have a 3.3-1 gear ratio with 16" tires. I have the Controller limited to 300amps or around 14HP with a top speed of around 30mph. This Gearing gives good acceleration and 30mph is fast enough for taking the kids for rides.​
We usually use this for very light duty rides with the kids, but this past week I let my teenage son ride it harder than usual and after about 5 minutes it over heated. I had read some ware that upping the voltage to 48 is actually better on the motor? Does this make any sense? If I run the quad at 100amps on 36v or 48v wouldn't the 48v make more heat? Or dose the motor have to try harder on 36v hence making more heat? I am very happy with the performance but would like to know it's going to last on the days my son pushes it. I am also considering raising the gear ratio because top speed is a little high and more torque in the low end would tax the motor less.

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#### Ziggythewiz

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Bike looks good! Font, not so much.

#### fbw4

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Sorry I copied and pasted some of the text and didn't change the font.

#### Ziggythewiz

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Much better.

Heat losses are linear with respect to voltage, but exponential to current. So though "100amps on 36v or 48v" would give the same heat/hp, to get the same power you need less amps and less heat with the higher voltage.

100A @ 36V = 3.6kW = 75A @ 48V
Heat = 100^2 x R vs 75^2 x R

#### OUTLAW---666

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Sir, i need to tell you this.
Congratulations, you have made my life a living hell right about now.
I will not be able to sleep again, before i have a similar project.
MAN I LOVE IT, it right about solves all the issues i have with Quads, and i love it.
Especially the price, i might actually afford it
I cant come to this forum anymore, i will be selling body parts soon to afford so many awesome projects

#### Ziggythewiz

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I cant come to this forum anymore, i will be selling body parts soon to afford so many awesome projects
If you sell your legs you'll have more space for lithium, but you might have to drive to another country before the car will stop.

#### RIPPERTON

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Motor could have been mounted further back on the swingarm for more battery room.
But yeah Im long past my air cooled days. Its amazing how fast those things overheat.
higher voltage will give you higher top speed, not sure you want that on quads which
tip over with a slight side wind = dangerous for the kids.
It really kW that make a motor overheat not just amps or volts.
so 36v 300a =10.8kW
72v 150a = 10.8kW
both these configs will result in the same motor temp just the 72v will have twice the top speed
but a little less wheel spin of the mark.
If I was you, keep it where it is may turn the amps down for your revhead son

#### major

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.....son ride it harder than usual and after about 5 minutes it over heated. I had read some ware that upping the voltage to 48 is actually better on the motor? Does this make any sense? If I run the quad at 100amps on 36v or 48v wouldn't the 48v make more heat? Or dose the motor have to try harder on 36v hence making more heat?
Hi fb,

Yes, it will run hotter at 100A, 48V than at 100A, 36V. But it would also be running at 4800W instead of 3600W. So 33% more power to the wheels. If you are satisfied with the present power then run it at 3600W on 48V using 75A. You'd need to change the chain ratio by a similar percentage to change the load on the motor and also to maintain (or reduce) the top speed.

If you take that approach you may be able to lessen the motor load. If possible you could turn down the current limit in the controller. You'd have more gear so could afford less amps on acceleration. Going from 36 to 48 volts on the motor means a 4/3 factor in RPM (33%) faster at equal loads. Even though motor efficiency (and heat) will be roughly the same at equal power (36V vs 48V), the higher RPM will likely help ventilation and cooling. Some type of fan forced air on or thru the motor will help.

These brushed PM motors are fragile when it comes to EVs and the overload type duty cycle seen on accelerations. This is why I cringe when I see guys wanting to use them on their EV conversions. They are particularly vulnerable in the brush/comm area where most of the heat (damage) comes from high current. So increasing the voltage lowers the current for equal power profiles and favors the comm.

Regards,

major

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