Graziano SAG-17 smoke leak?
My lovely SAG-17 has been working well and I've resigned myself to just using it and having fun.
Today I switched over to the mill for a while and when I went back to do some more turning the lathe wouldn't fire up.
I have a phase converter ( VFD ) that I have wired in before the lathe and it has been working fine this way for a few months.
I leave it set on 60hz all the time and just use the machine as the pope intended.
Poking around in the control cabinet :
I discovered one of the fuses to the primary of the control transformer was popped.
Installing another one, it popped too. At this time I noticed that the transformer was dead cold as I hadn't been using the machine for a while. Installing the third fuse, defeating the door interlock, and powering up I was able to observe that the transformer makes more than the usual amount of noise, almost a ringing noise, and, small quantities of magic smoke were wafting out of the bottom of it. It was warm after that. It does have a secondary side fuse and that was not popped. In and out fuses are 3A.
I don't have a manual for this machine, I do have a copy of the -14 manual. I'm not an electronics expert.
It looks to me like the transformer is only there to allow the start button to energize and lock the contactors for the main motor and the coolant pump motor. The stop buttons then interrupt that current to allow those contactors to drop out. Since neither contactor was pulled in during my tests I have to imagine that there was no load on the xformer and thus it's failure was internal.
I have removed the transformer:
Can anyone help me test it? I have a voltmeter and a basic understanding of ohms law etc. I also manually pushed the contactors in and the motors run, but of course they don't stay on because there is no voltage to latch the coil in.
Any suggestions for testing the circuit the xformer was connected to?
Here's a thought as well, the xformer name plate indicates 208/220/480, and it has two sets of input connections. No labeling to indicate which set is for what voltage of course. Is it possible that its wired up to the 480 primary and that by feeding it with 220 I am overtaxing it? Is there a way to figure out which input is which by measurement?
Finally, anyone know where I can get a suitable replacement for this? I presume OEM is out of the question. Can I have it rebuilt?
Thanks in advance!
The transformer primary will typically have two windings in parallel for 220; in series for 480. it might have a tap for 208 on each. I don't know what your secondary is but 24 or 120 would be common. Disconnect the the secondary fuse- does the primary fuse still blow? if so, it's likely that the transformer has an internal short (may or may not show up on a voltmeter ohms test). Magic smoke normally indicates it's fried.
To test can just connect it to 240, and measure the output from the secondary. Unless you have an obsure secondary voltage (or multiple outputs), control transformers are common and easy to find. Match the VA - without data the easy way is if it weighs about the same it will be about right!
BUT...even though it appears to have been working, you should not be feeding the machine and controls system from a "traditional" VFD. You can do with with an RPC (make sure the control transformer is not connected to the generated leg), but a VFD is normally directly connected to the motor. Never mind that the VFD may not be happy, but the output waveform is far from utility and may well have taken out your transformer directly, or caused failure of other devices downstream.
Last edited by Lakeside53; 07-12-2012 at 10:16 AM.