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Determining the size of a 3 phase motor

EliG

Plastic
Joined
Apr 4, 2017
I have purchased a Boye and Emmes lathe that has an old Allis Chalmers 3 phase motor on it. There is no data plate on the motor so I have no idea what size it is. Is there any way to figure out what the horsepower is? I can't get the full load amps on it but could measure the idling current. I only have single phase power at the shop so I need to get/build a rotary phase converter.

Thanks,

Eli
 
Look at the starter and the overload heaters. Their amperage will give you an idea. Also look at the coil voltage. If 110 there should be a transformer if the motor is high voltage. If the coil is high voltage and heaters are low amperage, you know the voltage. Dave
 
Without a nameplate, who would know what voltage it is?

Tom

A little research on the year/model. Ohm the motor wires to determine configuration. Pull motor and pull start on single phase to verify that is runs on single phase, if motor can be wired for 220v.

Next....
 
A motor with two voltages will either be a 6 wire wye-delta or a 9 (12) wire unit wired for a 2:1 ratio, 6 wire can also be Dahlander 2 speed, which can be determined by simply trying it on the lowest voltage you think it could be.

2:1 ratio for a 3 phase will be 230/460 in most cases, since 120 3 phase is pretty rare (I HAVE seen some).

With 3 wires only, you are going to need to guess, perhaps based on typical power for that frame size, vs the resistance of the windings and current for the assumed power.
 
Thanks for the suggestions. The motor is wired for 240 volt but I'm not sure what the control voltage is. I will have to look closer at it. It currently has power to it so I can do some checking before I unhook it to move it to my shop. The controls are home made so all bets are off if it was done correctly. I suspect that the ratings were on the junction box on the motor that is long gone.

Thanks,

Eli
 
Frame size dimensions in Machinery's Handbook might help nail down frame size, which will be related to some power output at some speed
 
Thanks for the idea about the Machinery's Handbook! I had not considered that. I have a copy from the 1950's which is about the time the NEMA frame sizes changed. I think with the running current, shaft speed, and the frame size I should be able to figure it out.

EliG
 
Thanks for the idea about the Machinery's Handbook! I had not considered that. I have a copy from the 1950's which is about the time the NEMA frame sizes changed. I think with the running current, shaft speed, and the frame size I should be able to figure it out.

EliG
 
I think there were a couple of NEMA changes, about 1952 and 1964. I've found machines built a few years after a frame change could still have an old size. Companies stocked up on motors and used them until gone. Dave
 
If you google for a Baldor frame chart it contains pre NEMA, NEMA, and IEC size dimensions.

Once you have a frame type, then use their catalog, to get close on what motor HP comes in that frame.

SAF Ω
 
Here's what I figured out on this motor. Based on the measurements I took the motor is a 324 frame size which would make it a 7.5 or 10 horse depending on rpm. It drew about 11 amps with no load but I didn't get the rpm's. Well as I was cleaning the gunk off the motor off prior to putting it back on the lathe I discovered that the tag was in fact riveted to the the space between the feet of the motor. So it turns out that is a 7.5 horse motor that turns at 1200 rpm.

Thanks for the suggestions in figuring this out.

Eli
 








 
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