Transformer help with 3-phase

something smells funny here. If You disconnected the load on the secondary side and you are still getting heat on the secondary side? Something is not correct.

Going by memory, you stated you had 2 primaries that allows you to wire for 120 or 240 on the input, that being the case you should have an order of H1 H2 H3 H4 in your case, L1 = H1, H2+H3, L2/L3 = H4; in other words, you use both primary windings but in series. If that was a 120 volt source it would be L1 = H1+H3, L2/L3= H2+H4

Also, it may sound stupid however, make sure you do have the ground as the ground on the plug coming in and no legs are grounded in the shop.

If you knew how many times this kind of stupid error happen with extension cords and equipment cords being missed wired like this, hot attached to ground etc., you'd be shocked.

Jamie

No, I don't actually know which side the heat is on. I see smoke coming from the transformer but it takes it 20 seconds or more to start and I can't tell which winding it's coming from. The way it's setup, there is nothing actually loading the transformer until you pull the trigger to start the saw. When I first turned power on with the new transformer I measured input and output voltages on the transformer and all looked good so I pulled the trigger and the saw came on. I ran it 5 seconds or so and released the trigger. A few seconds later I noticed a smell so I shut it down and looked for obvious problems. I turned power back on and didn't pull the trigger but the smoke came back after 20 to 30 seconds.

Correct, it's wired in series and the output is correct so I'm fairly certain I have it wired correctly.

I'll check it but the saw has been working in the shop for over a year without any problems until this incident.

Oh no I wouldn't. :-D I've seen plenty of it myself. In fact, my home had some outlets with the neutral on the wrong prong and a few other very strange quirks when I moved in. The previous owner worked for a large, national home improvement company and thought he knew how to wire, among other things! You wouldn't believe some of the simple things he screwed up!! He even ran 2 wires overhead to feed power from the house to the garage and swapped neutral and ground on the feed lines so that everything in the garage was backwards. And didn't even run a ground because most of the outlets in the house are old 2-wire.

"Keith Marshall"

** FFS do a finger test !!!

The secondary is not covered so check that - if it is cool then the primary must be the culprit.

.... Phil

Thanks, I'll give it a try. Unfortunately it'll probably be next week before I get a chance to look at it again.

have you measured the actual voltage going to the primary yet?

Yes, it's 212-213v. Sorry to take so long to reply but I have back problems and have been out of commission for a few days so I haven't thought much about the transformer.

Anyway, mpja.com is send>>>** FFS do a finger test !!!

have you measured the actual voltage going to the primary yet?

I received the new transformer and installed it yesterday and it worked great with no smoke so the first transformer was faulty. Of course I checked quite a few things before powering the new one up and left the output completely disconnected for the initial power-on but it turned out to be unnecessary.

Thanks for all the input and help!!

I need help and this seems the best place to ask for it. If not I'd greatly appreciate it if someone would point me in the right direction.

I'm repairing a metal-cutting cold saw that is powered by 3-phase with each leg being 120 volts. It has a transformer that has gone bad and the input to the transformer is labeled as 240v but it's actually 2 phases giving

208v. The output is labeled as 24v and is dead so I went looking for a suitable replacement.

I found a transformer from mpja.com for $12.95 that can handle 4amps which is way overkill because the only thing this transformer powers is a 3 pole contactor to switch on power to the motor when you pull the trigger. It's a bit oversized but the price was right and there's plenty of extra room for it. So it arrived today, I wired it in and powered the saw up and it worked great... until I started smelling smoke!! :-(

The output isn't even connected to anything unless you're pulling the trigger but the smoke kept getting worse even without the saw running so I'm trying to figure out if they sent me a bad transformer or if I've screwed up when it comes to 3-phase vs split phase and that's where I need the help.

The transformer actually has 2 input windings and if you wire them in parallel you can connect it to 120v or you can connect them in series for

240v but will that actually work for 2 phases of 3 phase? I mean I'm getting 24v at the output so it SEEMS ok but it's kind of hard to ignore the smoke which I expect will not stop until the transformer windings short together and melt into an ugly mass. :-(

There's also a center tap on the output which I'm not using but I can't imagine that being a concern.

Is there a problem wiring a transformer this way because of the 2 phases being 120 deg. out instead of 180 deg?

I've just never worked on anything where this might matter before so I'd appreciate any help!! Is it a bad transformer or will I have to find one with a single winding on the input? Or is there some other detail I'm missing entirely????

Here's a link to the transformer which has schematic on the page if it helps:

I can't follow the mishmash here, but clearing the air isn't hard.

a) 240V is 240V. This is a single-phase transformer. If you correctly strap it for 240 in, that's what matters.

If you have 208wye 3phase, you'll get 208. BFD for this case. You'll get ~21V out, not 24.

b) If it's smoking, I'll bet you screwed up. I don't know how.

But pull it out, put it on the bench, and CAREFULLY feed it 240 with the secondaries floating. The best way to do is is to put a 20W or so

120v lamp [The kind Edison made; NOT a CF/LED or whatever....] in each leg of the power.

If you draw too much current, the lamps illuminate.

For CAREFULLY, I recommend a safety man ready to kill power while you measure the secondary voltage with ONE hand.