Wiring 3phase motor for single phase usage

Thread Starter

jmcgr

Joined Feb 23, 2021
2
Hello,

Not sure if this is the correct place to ask this but can't seem to find the answer online. I'm rewiring a 0.75kw Electric Motor from three phase 380v to single phae 240 volt. I changed the configuration from star to delta (the one with the bars going across not laterally) and wired in a start capacitor (150uf). The motor started and ran and then the capacitor overheated and smoked. Looking back at the tutorials online it seems like the mistake I made was that in connecting the capacitor to the third phase i joined it with the live wire and not the neutral. Would that cause it to smoke. All the tutorials online have the capacitor joining the phase the neutral wire is connected to to the third phase. Just want to check and make sure that i've correctly identified my mistake before i attempt to attach a new capacitor. Thanks for any help you can give.

Ps. the motor runs fine when i give it a push to start.
 

MaxHeadRoom

Joined Jul 18, 2013
23,123
The capacitor has to be matched to the winding in order that the phase angle in the start winding is correct. Otherwise it will not start as you have found out.
Over 0.5HP the start winding is usually higher impedance than the run winding, so it may be touch and go to make that into a PSC motor where the windings are equal.
Are you automatically disconnecting the cap, as in a RPC? (Rotary Phase Convertor).
In the large RPC motor, you use a quite large value start capacitor for 2 -3 seconds and then rely on the non-electrolytic bank left in while running.
Max.
 

Thread Starter

jmcgr

Joined Feb 23, 2021
2
thanks for the reply. I'm very new to this so please excuse if i'm missing the obvious. It seems from further reading that a start capacitor is needs to only run momentarily and then be cut off, none of the youtube tutorials seem to mention this though. I've decided that it's since iI have the choice of ordering a new capacitor or figuring another solution I am just going to order a vfd to control the motor as i'm sure that will work.

Thanks for your input!
 

MaxHeadRoom

Joined Jul 18, 2013
23,123
Probabally the best plan, The RPC idea is to use the 3ph motor as a generator, for 3ph output, you feed it with the 240v 1ph and the 3rd phase with a large capacitor to start it turning, as soon as it reaches speed, the large capacitor is switch to a lower value bank and it then runs as a 3ph generator, but I agree, the VFD is the better option, IMO.
Max.,
 
Top