Operation of three phase motor on single phase supply

[AlanBeckett]

I've had a look at my other Suds Pump although in all honesty I can't remember much about how I did it. That usually means it was so straightforward I didn't bother remembering. Of course, it could be old age and decrepitude

   

All I can really say is that there's a 10uF Motor Run Capacitor to feed the 'other' Winding. I suppose I must have rewired it to Delta.
It works fine - give it a go.

Alan

[Refugee]

Why wouldn't it be primed?
The Impeller normally sits in the Suds.

Alan

There should be enough air space above the impeller in the pipe for the motor to start before it starts lifting the suds up to the tool.
A short bit of wide pipe could also be added if needed as long as the tank has the capacity to provide it before the pump starts lifting the suds.

[AlanBeckett]

Sorry, still don't understand what you're getting at.
They're usually like this:-

http://www.ebay.co.uk/itm/3-PHASE-415v-S..._Equipment&hash=item27c822c324

The Flange sits on top of the Tank with the Housing extending into the Suds, say half way up.
The Impeller and the Outlet Pipe will be full of Suds. The Motor actually has to start against the rsistance of the Suds around the Impeller.
So where does Priming and extra bits of Pipe come in?
However, you could be thinking of a different sort.

Alan

[Refugee]

I was thinking of the space in the riser above the level in the tank and below the connector where the narrow pipe joins on.
When the pump is switched off the suds will either dribble out at the tool end or siphon back to the tank leaving an air space that is just big enough before the air is all pushed into the narrow pipe with more resistance.
If the tank was too full it might have trouble starting with just a run capacitor.
Full load is when the pump is lifting the suds three feet or more up the narrow pipe with all the corners.

[pwdrive]

I've never done much with electric motors, is a delta connected three phase motor designed to run on single phase using a run capacitor or is it a frig/compromise?

Is there a formula for calculating the value of the capacitor or is it a case of try it and see? I'm thinking impedance arms etc.

Lawrence.

[AlanBeckett]

I've never done much with electric motors, is a delta connected three phase motor designed to run on single phase using a run capacitor or is it a frig/compromise?

It's a frig. It works but you never get the full Torque, particularly when starting. On my Chipmaster I swich in an extra 500uF to get it going then switch it out again, like this:-

   

So there's 600uF to get it rolling and 100uF to keep it going. Even so, it's reluctant to start if the Variator is wound up too far.
VFDs are getting cheaper all the time so I might invest one of these days, although 3hp ones are still pretty expensive.
The other problem is that they - Motors - take horrendous Currents when Starting. I run it off a Type C Breaker otherwise it would trip all the time.

Is there a formula for calculating the value of the capacitor or is it a case of try it and see? I'm thinking impedance arms etc.

Lawrence.

Not exactly, although there are rough figures available. You can always measure the Voltages and/or Phases, although they will vary with Load.

Alan

[ex 2 Base]

I suggest you follow Ed instructions. I have fitted capacitors to my friends sud pumps motors in the past using capacitors from fluorescent light fitting. As Ed has said, keep increasing the cap value until the three voltages are about the same. I fitted them in an earthed metal box at the back of the lathe, done a few, it works and never had any problem starting on load. I have made up similar boxes with two lots of capacitors, one lot start ( large value) , the other run ( much smaller value). I wired them such that both lots were in circuit on start up and then the large value was disconnected. I used two small contactors to do the switching and all was controlled by two push buttons. When the green push was depressed both contactors pulled in, when you released the pressure on the green button one contactor dropped out leaving the small value cap in circuit. If there was a mains failure the whole thing provided no volt release. This worked for years on a Colchester Bantam lathe. On the first one I made I found that it took a bit of trial and error to get the voltage near the same, so after that I fitted a big rotary selection switch for the start capacitor arrangement. The idea is certainly not new. Oh one thing, fit discharge resistors to each cap and ensure that they have a high working voltage.Ted

[pwdrive]

Thanks fellas, I thought that was the case, as said, I have not had much to do with motors, I switch them on and the shaft goes round and round, that's about my limit.

I did run a three phase motor off single phase years ago when we had the sawmill but that was using a Transwave converter which has long since gone.

Does the capacitor method cause vibration levels above what they would be if ran from three phase?

Lawrence.

[AlanBeckett]

Dave,

Did you get it?
I seem to remember I paid more than that for just the Pump assembly.

Alan

[Framer Dave]

Not me Alan. I did bid, but was a bit nervous about it in the end, on the basis that it might turn out to be a right mither to fix up and use. However I do very much appreciate the contributions from all you gents, which have certainly increased my knowledge base. At the end of the day I may buy a new s/phase one from Axminster, if nothing else crops up in the next few weeks.

Thanks again to all and kind regards,