Electric motor specs - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: August 01, 2017, 05:02:33 pm
content: Hi all,I picked up a 230V/50Hz motor recently whose specifications plate is all scratched off. How do I determine the nominal power ?Here's what I mean:It pulls a bit over 4 Amps no load. On startup, it might go up as high as 11 Amps, and then stabilizes at around 4A.Is it a 1Kw motor? Is the power of the motor calculated with no Load? Or under load?The shaft also spins at around 2900 - 3000 Hz, I assume it is 2 pole?Thanks,

author: Zero999
author_rank: Super Contributor
timestamp: August 01, 2017, 06:25:55 pm
content: Post a picture.How heavy is it?Have you looked inside it?Are you sure it's an induction motor and not a universal motor?

author: Vtile
author_rank: Super Contributor
timestamp: August 02, 2017, 09:33:30 am
content: 3-phase or 1-phase?

author: Benta
author_rank: Super Contributor
timestamp: August 02, 2017, 10:26:17 am
content: 230 V, 50 Hz would be 1-phase.

author: Vtile
author_rank: Super Contributor
timestamp: August 02, 2017, 11:58:42 am
content: Quote from: Benta on August 02, 2017, 10:26:17 amIt can mean anything. Better to ask and not spill 3 pages of instructions and then find out that it meant that the motor were driven in a country with 230/50 system.

author: Benta
author_rank: Super Contributor
timestamp: August 02, 2017, 12:35:13 pm
content: True, especially as the OP is very secretive about his location...

author: made2hack
author_rank: Frequent Contributor
timestamp: August 12, 2017, 11:30:45 am
content: Hi,Sorry for the late reply, it is a 1 Phase (by the looks of it) 230V AC.I posted a picture.It weighs maybe 8 kg?

author: made2hack
author_rank: Frequent Contributor
timestamp: August 12, 2017, 11:39:46 am
content: Maybe it was 3 phase, but adapted via caps for 1 phase?I mean, the caps don't have a place to connect them, they just kinda float.

author: EPTech
author_rank: Regular Contributor
timestamp: August 12, 2017, 11:51:27 am
content: Yes,Looks like a 1 phase induction motor with running capacitors, maybe 750W.The running capacitor looks a bit bulky for such a small motor IMO. That is why the current may be higher. The previous owner may have done this in an attempt to increase the starting torque, but you may end up burning the auxiliary winding. What are the values on the capacitors? If the motor starts up and keeps running with a smaller running capacitor in your application, leave it at that.Happy, commutating.

author: made2hack
author_rank: Frequent Contributor
timestamp: August 12, 2017, 05:20:43 pm
content: HiQuote from: EPTech on August 12, 2017, 11:51:27 amThey are 4 x 4.7uF 380V in parallel, so I guess just under 20uF total. The previous owner stated they used the caps to start the engine under load. I might omit them entirely as the motor will be used for a disc sander which shouldn't be started under load.Thanks,

author: Zero999
author_rank: Super Contributor
timestamp: August 12, 2017, 10:13:10 pm
content: Quote from: made2hack on August 12, 2017, 05:20:43 pmThe capacitors are required for the motor to start reliably. Without them, it might hum or start in an unpredictable direction, if you're lucky. You might be able to get away with less capacitance, in an application requiring less starting torque, but some is still needed.

author: EPTech
author_rank: Regular Contributor
timestamp: August 13, 2017, 11:24:01 am
content: Hero999 is right.You should not get rid of them. If they are only used for starting, there may be a centrifugal switch somewhere. If so, that switch should detach the start capacitors at about 2/3 of the synchronous speed (about 3000 rpm for a 2-pole motor), so 2000 rpm.But looking at your terminal box, I think the capacitors are permanently attached.Happy sanding.

author: SeanB
author_rank: Super Contributor
timestamp: August 13, 2017, 12:46:59 pm
content: Needed to start and run the motor, and inside the terminal cover there is a wiring diagram, which might still have a legible value for that capacitor. Typical value for these on that size motor is from 8-12uF 400VAC rating.