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Electric Motor Question

D

Duane WI

Member
I have an old repulsion start induction run electric motor. This motor is 3/4 hp and is a beast. They don't make them like this anymore. It uses brushes on the rotor to create high starting torque then switches over to induction operation. So it has both a wound rotor and field coils. Very similar to a DC motor or universal motor. I am working on a project and have a need for a motor that I can change the speed via a dial. Harbor Freight sells a speed controller for routers or any other brush type universal motor. It is a triac speed controller. Is there any reason I can't rewire a repulsion start induction run motor to work like a universal motor? It looks like all I have to do is change how the brushes and field coils connect to each other. Right now I am using a 1/2 inch electric drill and that works pretty well but could use a little more power. Using my drill as the motor also means I need to buy another drill so I have something to drill holes with. I have this old motor sitting in the corner for free. Any electric motor experts out there who can help me? Thanks
 

Once the repulsion start motor is up past "pull down torque rpm". The springs let the shorting rings convert the motor into a high resistance rotor induction motor.
Dorking around with a variable voltage , 60hz supply or a variable voltage DC supply will just make really smelly smoke.
A VFD is required for variable rpms on any induction motor. Your repulsion start induction run motor is not a universal series motor.
As for starting torque. A compressor rated capacitor start , capacitor run induction motor will start anything the RTIR motor will.
 
I 100% understand it won't work the way it is currently wired. My question is if I wire the brushes in series with the field coils like a universal motor will it work? Can I convert it to a universal motor? This motor has brushes, armature windings and field coils just like a universal motor. They are just connected to each other differently. I would have to remove the centrifugal switch that puts the motor into induction mode. The brushes and coils have wire leads on them so all I would need to do is change how the leads are connected together. It is a nice running motor I just don't have a use for it right now but I also don't want to ruin it. I know I can go buy exactly what I need but why spend a few hundred dollars when this old motor is sitting in the corner.
 
repulsion induction motors slow down with increased load but have more torque at the lower speed, using a speed control on that motor I dont think is a good plan
 
I had a 1 1/2 hp repulsion-induction motor on a Delta Unisaw. You could reverse it by shifting the position of the brushes. When it got unreliable and could not economically be repaired,I replaced it with a capacitor start 240 single phase 2 hp and had much better performance.
 
(quoted from post at 13:19:02 01/13/16) I 100% understand it won't work the way it is currently wired. My question is if I wire the brushes in series with the field coils like a universal motor will it work? Can I convert it to a universal motor? This motor has brushes, armature windings and field coils just like a universal motor. They are just connected to each other differently. I would have to remove the centrifugal switch that puts the motor into induction mode. The brushes and coils have wire leads on them so all I would need to do is change how the leads are connected together. It is a nice running motor I just don't have a use for it right now but I also don't want to ruin it. I know I can go buy exactly what I need but why spend a few hundred dollars when this old motor is sitting in the corner.
Click to expand...

No
 
If you want something variable speed find a 3/4 or 1hp 3 phase motor and put a VFD [variable frequency drive] on it. You can buy 3 phase motors cheap and the VFR will be about $100 for that size. Works great have it on my Bridgeport mill and 7hp lathe motor both now variable speed. They are on single phase power. email is open
 
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