Hi all,
Last night I had chance to investigate my 2.5 hp motor in more depth. There's good news and bad news, so I'll tell the story the way it happened.
First I removed the bearing covers and fan cowling. The ball races appear sound and are still packed with grease. Peering into the stator the windings look clean and shiny. There's a little rust on the rotor, but this could easily be brushed off and painted over. The inside of the motor is coated with this orange-red paint or resin, which looks a bit like red oxide paint but isn't. I've seen it in motors before but I don't know what it's called. Anyone know?
Next I opened the terminal box and removed all the links. I measured the winding resistances with a multimeter. All are 6.5 ohms. There was no measurable leakage between any winding and the motor casing. So far so good. I now planned to connect a run capacitor and power up the motor with no load, just to check everything worked. So I worked out the correct link positions for a delta connection.
Aargh. Problem! The motor had originally been wired in a delta connection. Of course 240 V is the line-to-neutral voltage of the UK's three phase system, so I wondered (hopefully) if this motor had been wired for 240 V three phase. But then I realised that there was no neutral wire entering the terminal box, so it must have been wired for
415 V. Apologies Bob, you were right. Damn!I've never seen a motor of this size which uses a delta connection for
415 V before. In fact, I don't think I've seen a motor below 10 hp which uses a delta connection for 415 V. But I've never seen a motor of this size with a fan cowling which weighs 20 lbs, or a rotor which is fabricated from individual pieces of stock before, so I guess I shouldn't be surprised. I guess in 1931 there may have been less export, and it seems LSE specialised in large motors, so maybe a delta connection was their standard?On the plus side, this motor is a really cool piece of work. Had I known it was 415 V only I would most likely have rescued it anyway rather than letting it go to the landfill. I've got rather keen on the phase converter idea, so it looks like I've now got the challenge of finding a
240 V -> 415 V transformer with a rating of around 3 kVA. Anyone know of likely sources? Jim Cox's books "Electric Motors" and "Electric Motors in the Home Workshop" (which are a goldmine of practical information about motors - Igor might like them if he hasn't got them already) suggest modified old-fashioned welding transformers. I'm usually pretty good at scrounging industrial junk, so if anyone can think of equipment containing likely transformers please let me know!A 415 V output is actually more useful than a 240 V output in the UK, as I could then just wire a plug onto any equipment I buy and plug it into the convertor. Almost all three phase equipment in the UK is wired for a
415 V line-to-line voltage. Jim Cox's books also note that smaller capacitors are adequate for 415 V operation, so this setup has its attractions. I doubt I'd want to run loads over 1.5 hp, so a carefully designed convertor using a 2.5 hp idler should be okay. Food for thought, anyway.Sorry for the long post. I'd be interested to hear people's thoughts.
Best wishes,
Chris