First Build Direction; Test Motor Voltage, Safety Logic

[tinkering]

I have been given parts from 2 friends. The electric front hub has no markings. The DC Motor Controller says it's good for 12V, 36V, or 48V.
How do I test the motor to see what voltage rating it is so I can buy the correct battery for my build?
Nothing is coming to me.

 

[gromike]

Generally, up to a point, motors aren't voltage sensitive. The motor was probably run at 36v, but should do 48v fine. Higher voltages give you a higher unloaded top speed.

 

[tinkering]

Generally, up to a point, motors aren't voltage sensitive. The motor was probably run at 36v, but should do 48v fine. Higher voltages give you a higher unloaded top speed.

If this motor likely ran at 36v, would 52v battery be OK? Would a 52V battery be too much for a controller rated 24v, 36, 48v?
Thanks

 

[gromike]

I'd say it's no for the controller, but maybe. 60v is the common rating for components in a 48v controller. So it might work. 52v nominal should be OK for the motor. Hopefully you have a motor temp sensor.

 

[harryS]

Most 48V controllers will run on 52V, but the low voltage safety will be set for 40V, about 3 V too low for the 52V battery, This is not a big thing, as the battery has its own low voltage alarm set around 43V.

Since it's a front hub, you have to be knowledgeable when you want to go for higher voltage and higher power. There will be traction problems. There will be reliability/safety problems as front hubs want to spin out of the fork. When they do, the rider usually faceplants. Take care!

I figure the motor came with a wheel/spokes laced up?

 

[gromike]

Front hub motors do have some inherent issues, as harryS noted, but of late I have become a big fan of a lighter weight front motor in a light bike.
This is my latest build:

A 350w rated motor, 48v battery, and a 22a KT controller in a mid-2000's Cannondale Badboy. It's crazy quick. I pass cars on this thing, though you be pedaling.

 

[tinkering]

I'd say it's no for the controller, but maybe. 60v is the common rating for components in a 48v controller. So it might work. 52v nominal should be OK for the motor. Hopefully you have a motor temp sensor.

I haven't seen a temperature sensor but I guess it would be in the internals of the hub with a feed wire to the controller? If it exists it would indicate on the readout?

Most 48V controllers will run on 52V, but the low voltage safety will be set for 40V, about 3 V too low for the 52V battery, This is not a big thing, as the battery has its own low voltage alarm set around 43V.

Since it's a front hub, you have to be knowledgeable when you want to go for higher voltage and higher power. There will be traction problems. There will be reliability/safety problems as front hubs want to spin out of the fork. When they do, the rider usually faceplants. Take care!

I figure the motor came with a wheel/spokes laced up?

I'm not sure what a low voltage safety is. So you are saying maybe I should go with a 48v battery just to sidestep low voltage possibilities?

The hub axle flatted surface locked nice into the fork ends but I had to slip one side back out a little to center the wheel. I thought about safety at that point. Is there a good way to make a safety setup that will capture the axle to the fork ends? I do not want to plant my face.

Yes the hub came laced to the rim. The full diameter from lip to lip is somewhere around 22.5 inches. The forks are kind of narrow and the rim is kinda wide so I was going to try to find a modest profiled tire that won't rub.

The chain that came on that frame at first glance looks like it drove a single speed rear hub; not long enough to run through a changer. I thought I would keep it that way.

 

[tinkering]

Front hub motors do have some inherent issues, as harryS noted, but of late I have become a big fan of a lighter weight front motor in a light bike.
This is my latest build:
View attachment 198736
A 350w rated motor, 48v battery, and a 22a KT controller in a mid-2000's Cannondale Badboy. It's crazy quick. I pass cars on this thing, though you be pedaling.

This is a light/slight frame. I have a feeling though that it might be a 500w hub. I am not sure though. Is there an easy way to measure it?

We often want to choose more power but I don't want to die on it. Racing means constant maintenance and repair, and shorter lifespan. I'm usually pretty conservative on the throttle but it's good to have some reserve.

It would be nice to have a bigger capacity battery so I can go across town in the winter, say.

 

[indianajo]

I've run front geared hubs for 13000 miles. Although my Yuba had a steel front fork, I made a torque arm of 6" of bed frame rail, just one flat of it. I captured the end of the arm with a U-clamp of box fan shell around the fork in the pull direction. I ran motors of up to 1300 w off 48 v without spinning out.
I find 1000 and 1300 motors have resistance of 0.6 ohms and 300-500 w motors have resistance of 0.8 ohms. You will need a fixed resistor to calibrate the ohms scale of a DVM. They are inaccurate at that range.
10-15 amp controllers will fault out on a 1000 watt up motor. 30-40 amp controllers will burn up a 350 watt motor if run up more than 2 dozen hills of 100' each. Most front hubs these days are designed for 36 v battery, but 2018-2020 they were designed for 48 v. The amps of the controller is more important to be matched to the motor than the voltage.
A 17.5 AH 48 v battery got me 24-30 miles to my summer camp with up to 60 lb groceries or supplies. There were 77 hills on some routes. The battery is still good at 7 years and 13000 miles, but I have worn out the gears in the 1300 w motor (~4500 miles) and worn out the one way clutch in the 1000 w motor (~4000 miles). You can't tell if either one is bad in a used motor until you waste money on a battery and try to drive it under load.
Riding electrically powered is non-starter in winter IMHO. It is unsafe to charge indoors, and LiIon batteries will be damaged if charged at or below freezing outdoors. Temperatures below 45 F make the discharge rate higher by 40%, cutting range to uselessness. I put the battery in storage in my garage under a heating pad in freezing weather, and rode the bike unpowered for 6 months. I don't ride the bike to summer camp in the winter, so the trips were 7 miles one way or less.

 

[harryS]

Gromike has steel forks on his front drive bike, as I do on mine. Alloy forks are brittle and likely to snap at the slots where steel bends. Some forks, even if steel, are too delicate for a motor. People use torque arms. which you can buy.

The dropout slots are 10mm wide and sized for a 10 mm round axle. Most ebike motors use a 12nn x10 mm axle, so when you drop it into the slot, it will ride higher in the slot by 1 mm. You're supposed to file the round section down 1mm so the axle remains at the right depth in the dropout. It also allows the washers to remain centered.

If you have to cock the axle to get the tire centered, something must be off. Does the wheel spin true? If it is offset so one side of the tire hits the fork, you can move the rim over by adjusting the spokes. The process is called dishing, .

 

[tinkering]

Gromike has steel forks on his front drive bike, as I do on mine. Alloy forks are brittle and likely to snap at the slots where steel bends. Some forks, even if steel, are too delicate for a motor. People use torque arms. which you can buy.

The dropout slots are 10mm wide and sized for a 10 mm round axle. Most ebike motors use a 12nn x10 mm axle, so when you drop it into the slot, it will ride higher in the slot by 1 mm. You're supposed to file the round section down 1mm so the axle remains at the right depth in the dropout. It also allows the washers to remain centered.

If you have to cock the axle to get the tire centered, something must be off. Does the wheel spin true? If it is offset so one side of the tire hits the fork, you can move the rim over by adjusting the spokes. The process is called dishing, .



View attachment 198739

Thanks for all of that. I will reference this when I get to it again after some pre snow priorities.
I will reply to this hopefully tonight.