72v on Front Geared Hub Motor?

I have a geared hub motor running 52v 20a , and tops out at about 28mph on a 700 x 38c tire.

I'd like to get a little more speed out of it, but can't go too big on the torque. So, it seems that running 72v and 12~15a would be a way to do it, after replacing the controller and battery. It won't push the motor that much harder, while allowing it to turn at a faster speed.

Does this sound reasonable? Anything crazy going to happen from a geared motor going over 30, but not quite 40? I'll be happy with a quick blast to 35mph or so.

Or just get a DD motor and enjoy more speed. Once you hit 1000 watts and up with the proper windings geared motors become useless. Geared motors are best on assist only settings like if you wanted a road bike with a motor to assist with hills that still felt like a bike. Other then that DD hub motor and Mid drive kits are the way to go when you up the wattage.

If you increase the voltage but drop the amps a little, it should work fine. Others have done it. You will reach a point where the wind resistance equals the power input and it won't go faster. Too much current and expect the gears to die an early death.

I'll be building a separate one for DD. Just curious how and if I can modify this existing one, as it is.

Wind resistance wise, it seems that 1000w should be able to push it to 35 or 37. I think the legal ebikes that do 28mph run only 750w. So, 1000w would be good for 7-8 mph more. Add some pedal assistance, and it'll get there quick.

hypertoric_amplituhedron said:

I'll be building a separate one for DD. Just curious how and if I can modify this existing one, as it is.

Wind resistance wise, it seems that 1000w should be able to push it to 35 or 37. I think the legal ebikes that do 28mph run only 750w. So, 1000w would be good for 7-8 mph more. Add some pedal assistance, and it'll get there quick.

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72 volts is going to put you over 1000 watts.You are already running 1000 watts with 52v and 20 amps. You are almost at 1500 watts at 72v

Weird though your geared hub motor is giving speeds of my DD motor only a few miles off. My DD gives 30 and 33 with hard pedaling at the same wattage always thought geared was slower then DD. I run knobby tires currently though due to winter.

The idea is to keep it at 1000w, by upping the voltage to 72v, and lowering the amps to 15 or so.

hypertoric_amplituhedron said:

The idea is to keep it at 1000w, by upping the voltage to 72v, and lowering the amps to 15 or so.

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I missed that part sorry.

It's okay. I know about the nylon gears wearing out, so I don't want more power, but a little more speed, while trying to be nice to the gears. I probably shouldn't do anything to it. The DD bike is for speed and power, after all!

hypertoric_amplituhedron said:

Wind resistance wise, it seems that 1000w should be able to push it to 35 or 37. I think the legal ebikes that do 28mph run only 750w. So, 1000w would be good for 7-8 mph more...

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Unlikely. Power vs. Speed is not linear.

http://kreuzotter.de/english/eindex.htm

In theory it all seems doable but in practice you may discover limitations of over volting geared hubs. Remember, majority of geared hub motors were originally designed for 24-36V and as the industry moved to 48V the designs didn’t change much. At least with the smaller geared hubs.

My experience over volting geared hub motors ultimately met with failure. For one thing unless you get a very customizable controller or use CAV3 with throttle ramp capability the majority of sawtooth stuff will simply hammer clutch/gears much harder on 72V than lower voltages.

Even limiting the power on my Infineon to 8A on 72V found the controller applying too power much too quickly. I played around with a throttle tamer to help reduce the sudden forces that occur from higher voltages but those have their own set of issues.

Throttle tamer and eventually CAV3 helped reduce start-up shock loads but then all it took was a nice long extended run at the higher voltage motor RPM to soften the white nylon gears used in smaller geared hub motors.

4-5 miles not much of a problem but 10-15 miles sustained at close to max RPM seemed to heat the gears enough to fail pulling from a stop.

Nice, that's some good information. I would only ride at max speed for no more than 30 seconds. Most of the time would be 15 to 20 mph sustained. My only intent with overvolting would be the extra top end speed, for just a short burst. And, the whole time would be spent worrying about the nylon gears.

I found that it is an Amped Bikes geared front hub motor, of the largest diameter I could find from the FB page photo section. It looks an awful lot like this one, but silver:



They're out of business, so anyone have experience with this one, or know of its strengths and weaknesses?

Thanks for this subject. I was about to build a 72v battery for a mxusxf15r i will receive soon. I wanted to be sure i will reach 50kmh. After reading this post i will probably be reasonnable and build a 52v battery. Sadly i already bought a 72v battery charger and a 72v bms. If someone is interested i sell both. Is 52v still reasonnable ? I think so.

If i put some ATF oil in my xf15r maybe i can keep m'y overvolting project? It will have a better cooling and provide melting nylon gears??