Thanks for all the quick replies!! Rather than respond to each reply I'll
try and answer an abbreviated version of everyone's questions here.
What killed the original?
I don't know at this point. In my limited experience it's been fairly
common to find a failed transformer with no apparent cause in older
equipment. I've replaced 3 or 4 in furnaces and other similar circuits in
the past and successfully fixed the problem so I haven't looked further on
this problem yet. I mostly wanted to know if 2 phases of 3 phase power
might introduce a problem I wasn't aware of. It seems to me that having 2
separate windings connected in series might be different from having one
winding but I still can't get that part clear in my head.
As for running it at 208v instead of 240v, the original transformer had a
terminal strip mounted on top of it with 2 wires going in labeled 0v and
240v and another 2 wires labeled 0v and 24v. I used that original terminal
strip and left all connections from the saw as original. On the transformer
I then connected a red wire and a black wire together and capped them off
and then connected the other black wire to the 0v in and the other red wire
to the 240v in as shown on the example diagram on the mpja.com page for 240v
operation. I then connected the 2 blue wires to the 0v and 24v output
terminals and capped off the unused yellow center tap wire. Sound right?
The saw is available in a 240v single phase version and the schematic of the
controls is identical using all the same part numbers. The difference is
that only the 2 legs of the 240v are tied to the 3-pole contactor so the
208v vs. 240v difference isn't what concerns me.
If anyone is interested in seeing the schematic it's on page 39 of the
manual he
http://cdn0.grizzly.com/manuals/g0682_m.pdf
And the 240v version is shown on page 30 he
http://cdn0.grizzly.com/manuals/g0665_m.pdf
It also has nothing to do with a neutral because the neutral isn't even
connected to this saw. It's not used on the 240v single phase version
either.
In answer to someone's question about smoke, I definitely do see smoke,
progressively getting worse the longer I leave the power to the saw on. At
this point I'm sure the new transformer is fried, I'm just trying to
determine how I fried it. :-( And more importantly how to keep from doing
it again!! :-)
I'm starting to think that the problem may lie in a short on the output
which is just the coil of a contactor, but the contactor does work so I
still have to wonder. If it is causing too much load then it may be that
the first time I pulled the trigger to test the saw the insulating coating
on the new transformer windings began to break down and now it's to the
point where it doesnt need a load on the output for it to continue to
worsen. Since I have no way of knowing what the resistance of the
contactor coil should be I may have no choice but to purchase another
transformer, probably one with a single primary winding this time just to be
sure, and connect it but not actually pull the trigger until I know it's not
going to smoke. But then I still won't know for sure until I pull the
trigger and then if it DOES smoke I'll know it's the contactor. That's a
really dirty way to do it but I don't know what else to do so I'm certainly
open to suggestions...
"Keith Marshall" wrote in message ...
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:
http://www.mpja.com/24V-4A-Center-Ta...tinfo/7845+TR/