How to use motor from AC power tool for Ebike?

[m_akulov]

I have a DeWalt 120V 10A reciprocal saw with broken slider. I want to use the saw’s motor for electric assist in my MTB. This saw has tiny control (throttle) inverting 120 V from household AC socket into DC applied to brushes of the motor. So questions arise:
1. Can I use the same original throttle to vary power drown from LiPo buttery (48V, 20A) to feed the motor?
2. If I can, should I add kind of buttery management system (BMS) not to blow the precious LiPo pack? Are suitable for my case BMSs on the market for reasonable price?
3. If I cannot use saw’s throttle (pick current can be ~30A), should I buy/make brushed-motor-specific controller or PWM or I can use BLDC motor controller?
In short, how to use motor from wired AC-power tool for heavy-duty electric drive without damaging LiPO buttery?

Anyone has successfully done such a project?

 

[REdiculous]

The simplest solution is to get a 48v inverter so you can run the saw on AC.

My push-trailer is setup that way (battery->inverter->controller->motor) so I could plug in your saw no problem.

Main drawbacks; Multiple conversions will make it somewhat less efficient, inverters are fairly large and weatherizing can be difficult. Also, a cheap modified sine wave inverter may not run some things correctly (though there may be ways to make it work) and pure sine wave inverters can be expensive. later

 

[liveforphysics]

I have a DeWalt 120V 10A reciprocal saw with broken slider. I want to use the saw’s motor for electric assist in my MTB. This saw has tiny control (throttle) inverting 120 V from household AC socket into DC applied to brushes of the motor. So questions arise:
1. Can I use the same original throttle to vary power drown from LiPo buttery (48V, 20A) to feed the motor?
2. If I can, should I add kind of buttery management system (BMS) not to blow the precious LiPo pack? Are suitable for my case BMSs on the market for reasonable price?
3. If I cannot use saw’s throttle (pick current can be ~30A), should I buy/make brushed-motor-specific controller or PWM or I can use BLDC motor controller?
In short, how to use motor from wired AC-power tool for heavy-duty electric drive without damaging LiPO buttery?

Anyone has successfully done such a project?

Most all power tools with variable speed triggers use "universal" motors. They run equally well on DC as AC. Try running it off DC for a second and see if it spins. If it spins, you're perfect.

 

[friedwires]

i once used a skillsaw to power a three wheeler. i drilled the housing and rigged a cable through the backside of the switch.it worked great,but i can tell you,you're gonna need a lot of voltage and some major reduction to get any power out of it.

 

[REdiculous]

1. Can I use the same original throttle to vary power drown from LiPo buttery (48V, 20A) to feed the motor?

The original throttle will probably die if you try that and even if it works, the motor will probably get too hot too fast. Running the motor at half the voltage will cut the power in half - you can't just double the amps to make the same power at the lower rpm since the motor will overheat in a very short amount of time..and if there's an integrated fan it won't be nearly as effective as normal.

Despite the drawbacks, I think running it from an inverter would be best since the saw will run the same as if it were plugged into the wall - simple. Or you could build a 90-ish volt battery and try to find a 90v 10a controller for a brush motor.

That said, if it's not a permanent magnet motor then I'd ditch the idea completely unless you're on a tight budget. :|

 

[liveforphysics]

Inverter is just gonna increase losses (and cost more than a proper motor in the first place)

 

[REdiculous]

A new 1-2kw MSW unit can be had for about $80. The cheapest hub motor I've been able to find is $120 and that's just the motor. :|

I got 4 miles out of my push-trailer with a single 12v 20ah SLA and I was running a 60w light the whole ride...WOT, zero pedaling, windy, riding upright with an open jacket on - definitely a test of the 'worst case'. With the 12v 38ah SLA I have now I can easily get 7-10 miles, depending on wind/terrain of course. According to this thread I should be getting closer to 5 miles - his pack would be 32ah at 12v so it's not much smaller than mine. If the folks that responded in that thread are correct then it looks like my trailer is on-par despite the inverter.

 

[Alan B]

Are these tool motors designed for continuous power? Will they hold up?