Re: Recovering 2.5 hp motor for phase convertor (long story with pictures)

Robert Swinney wrote:
"Christopher Tidy" <cdt22NOSPAM@xxxxxxxxxxxxxx> wrote in message news:42F0CABB.2060905@xxxxxxxxxxxxxxxxx

Robert Swinney wrote:

Chris sez:

" It is rewirable for 230 V (see the "Connection: Star/Delta" on the data
plate). There are also six terminals under the cover. I checked before I
hauled it home!"
-- and -- "There's very little corrosion inside the motor and the
windings look clean and undamaged. I haven't measured the insulation
resistance with a multimeter yet, but I thought I'd take a chance on it."

Be careful here. I didn't get the impression it was strappable for 230 - 460 from the pix of the nameplate. "Star/Delta" refers to the way the windings can be configured for approx. a 1.7 x change in operating voltage.

Isn't this the same thing? 230 V * sqrt(3) = 400 V.


Sorry Chris, You are correct! With 6 leads brought out, the motor must be externally configurable for "Star" or "Delta". This would be in agreement with what your name plate says, "star-delta". And your math is correct, also; Converting from one configuration to the other does yield a sq.root of 3 change in voltage and vs. Assume the 6 leads brought out from each internal phase group are thus; (1 and 5), (2 and 6), (3 and 4); therefore the "star" configuration would be; 4, 5, and 6 strapped together and incoming lines connected to 1, 2, and 3. This would be the high voltage connection.

For low voltage operation the "delta" configuration would be: (1,6 and line 1 together), (4,5 and line 2 together) and (2,3 and line 3 together).

Generally, a dual voltage motor (one strappable for 230 - 460) has 9 leads available under the cover.

What are the nine leads for? Most of the three phase motors I've seen in the UK either have three leads (permanent star connection) or six leads (both ends of each winding brought out, so it can be connected star or delta). I also saw a six lead motor which was dual wound (i.e., two completely separate windings, a four pole and a six pole, both with permanent star connections).


The 9 lead arrangement is more common in the U.S. It provides a method of connecting internal coil groups either in series or parallel to achieve dual voltage operation.

Also, better take it to a motor shop for insulation verification with a "meggohmmeter". Not something you can do with an ordinary multimeter.

Do you mean one of those hand cranked insulation testing generators? I'm not too keen to take the motor to a rewind shop to have it tested because of the weight. In the past I've just made sure a motor is dry, measured the insulation resistance with a multimeter to find obvious faults, wired it up through a low value fuse and kept an eye on it. I've not had problems so far.


Precisely. A "megger" test would reveal insulation break down that would not be detectable with an ordinary VOM. Perhaps you could borrow, or rent, a megger and take it to your location. It is more than a little disconcerting to hear a gun-shot like "crack" coming from a RPC you already have a lot of time and money invested in.

Aargh! I saw one of those cheap on eBay last year, but didn't bid as I didn't think I had a use for it. I bet they're expensive pieces of kit normally. What does the hand-cranked megger actually do? I'll keep an eye out for one. Maybe another will turn up on eBay...

Best wishes,

Chris

.

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