.

I would say you are in the wrong hobby.

Nick

One no-cost option would be to put the Clarke motor on the Meddings until something better come along.

The ultimate option would be to use the 3 phase motor with a VFD. I have bought several secondhand between £15 and £40 and only ever bought one new (the very common Chinese one about £75) because I needed it quickly for a 1.5HP motor.

Be patient…

Ian P

Sounds good Richard. There was a very good website many years ago that had all the details but it sadly disappeared. I knew the information would be very useful to me so I wrote up my own "idiot guide" and filled it away.

Richard

I ran a Pollard Corona 100A on single phase for may years using the capacitor trick with no problems. 1/3rd Hp motor on it, memory says 20 µF run capacitor, 100 µF start. Having done the capacitor trick a fair few times I tend to go high on the start capacitor to ensure things work. Ended up devising my own start / run box assembly with automatic start capacitor cut out as being the easiest way to deal with folk asking me to convert their motors! VFD is more cost effective now.

Worst problem with the Pollard was digging into the motor to find the star point to convert the windings from hardwired 440 V wye to delta to run off 240 V. For motor control I usually made a little box with two start push buttons controlling two contactor units. One contactor wired normally via keep alive contacts and a stop button to handle normal running and one with the coil wired directly to the pushbutton so the start cap was only in circuit whilst the button was held down. Usually a couple of seconds was plenty of start time (count "one monkey and two monkeys"). Have used big octal base relays instead of contactors when stocks were low, last well enough for home shop but obviously pukka thing is better.

Mr Pollard used monster "home made" pushbuttons on the A100 which were well up to handling the start cap current so I onkly had to hold the one button down and didn't need to find another contactor.

I do have a circuit to run 440 V motors off 240 single phase using the capacitor trick but it needs more capacitors and, usually, tuning to get the right capacitors for the specific motor.

Ian

Done correctly the UK version of the capacitor trick with a properly specified run capacitor permanently in circuit and separate start capacitor gives close to full power at rated rpm.  At one time this was an official way of exploiting 3 phase motors where only single phase was supplied.  Older books give the technique its proper name and claim up to 95% power with suitable motors.  Major power related drawback is that torque falls off rapidly with motor speed changes so its much easier to stall under load.  On full fat 3 phase torque actually rises if the motor slows a little.  Our American cousins frequently simply add a start capacitor to run-up three phase moters on single phase.  In this case considerable power is lost as only one winding sees full voltage, the other two see half voltage and the phase balance is seriously disrupted.

Clive

Edited By Clive Foster on 30/03/2015 12:14:38

The '£12 VFD' might exist but I've not got any laying around.

What I was indicating is that running the motor off capacitors is a compromise that allows the machine to work, maybe at close to its original spec. A VFD on the other hand brings a lot of side benefits and enhances the machine significantly. If you have a tapping machine or tapping head or have a fully equipped machine shop than you might not have need of an upgraded pillar drill but I find my Fobco Star indispensable now.

I have the Jim Cox book in which he shows various schemes for running three phase motors. I if you use a start and a run capacitor and fit the appropriate switching and relay, then by the time you have enclosed and mounted it all safely you will have spent quite a bit of time and money, and the result is a machine that will still be less than it was designed to be.

If you have scrapboxes of suitable parts and can put something together that works for you, then go for it. (I'm biased, I just love the flexibility that VFDs bring)

Ian P

My 3 phase 10" Elliott shaper has been running for many years using the capacitor mod. I had to locate the star point to separate and bring out the 3 wires for 240v connection. I already had a suitable capacitor so it cost only my time. The shaper performs well but sometimes needs a very light nudge on the pulley to start easily; this is easy to do so I'm not bothered by that as it's only once to get running then I just use the clutch. I could add a capacitor to help starting. Poor starting torque is always likely to be a disadvantage with this conversion so a machine that has a clutch is the best type to convert. Colin

If a motor self starts with only a run capacitor odds are that capacitor is a little oversize. I always used to trim the run capacitors to get the phase voltages as close together as I could. The closer they are the smoother the motor runs and one has to assume that if the voltages (and currents) are nearly equal any stresses will be minimised. As far as I recall once the run capacitor was set as close as I could reasonably get to optimum the motor would not self start on run capacitor alone without a pretty serious spin of the pulley with no belt fitted.

Capacitor optimisation was much more of an issue with larger motors say 1 hp and up than smaller ones.

Clive

Edited By Clive Foster on 31/03/2015 20:14:00