PDA

View Full Version : Static phase converter shorted



radkins
05-01-2013, 04:36 PM
I tried to start my lathe but no power, one of the output wires from the phase converter to the lathe switch had shorted to the converter housing and was burned completely in two although the incident had also burned out one of the two line fuses (yep it's an old shop and still uses screw-in fuses). I repaired the wire and replaced the fuse but no go, it's still dead although I can see nothing burned or out of the ordinary inside the box, it was an output wire that shorted to the converter case so I am going to assume at least one component of the converter is damaged. As of now my old Craftsman multimeter has crapped out on me but I just checked and Lowes home supply has a nice Fluke which I am going to pick up right now. Any suggestions on what to check for when I get back? I have a basic understanding of this thing and I can identify the individual components but I would surely appreciate any advice anyone might have before I tear into this thing.


:EDIT This is a Phase-A-Matic 3-5 HP heavy duty model.

Alistair Hosie
05-01-2013, 04:57 PM
Fuses obviously didn't you have a trip switch on the wall first thing to do is fit a trip switch for future it might also be a small micro timer usually in these things check for burning or with meter in that region my transwave one blew,and I replaced it. Most things components are easily replaceable on the transwave and from what I understand the phase a matic is a good unit so should be cheaply and easily fixable.Alistair

MaxHeadRoom
05-01-2013, 05:11 PM
It must have been a short on the manufactured phase, as the 1ph pair is passed right through on a Phase-A-Matic as it is on a RPC.
It is most likely going to be a power MOSFET or IGBT, whatever they use for power switching.
Max.

radkins
05-01-2013, 05:14 PM
Both in lines from the power panel are fused with fast acting fuses instead of trip breakers, I know it's old tech but fuses do work ok. The fact the line fuse didn't burn out makes me think the wire must have burned in two almost instantly but the wire that burned was on the output side of the converter circuit and had shorted to the converter housing, I opened the converter box and nothing inside looks to be burned nor even appears to have gotten hot (with the exception of the burned wire which was outside the box), however visibly burned or not I strongly suspect one or more of the components has been trashed.

MrSleepy
05-01-2013, 07:16 PM
From the Phase-A-Matic website...

#5.. The Phase-A-Matic™ Static Phase Converter has a built-in weak link which is designed to fail rapidly if hooked to a higher horsepower motor.

Cryptic... but may indicate you have blown an internal link or fuse etc..

Rob

radkins
05-01-2013, 09:23 PM
It must have been a short on the manufactured phase, as the 1ph pair is passed right through on a Phase-A-Matic as it is on a RPC.
It is most likely going to be a power MOSFET or IGBT, whatever they use for power switching.
Max.


As soon as I read your post I went and checked to see if it was the manufactured phase but as it turns out the wire is connected under one of the single phase line connections along with one of the input wires. Now after you point that out I am puzzled as to why shorting either of those two wires to the case would hurt anything? The center connection is the Manufactured phase with only the one output wire connected there and that wire was intact and unaffected. I just got home with the new meter so I will see what I can find tomorrow morning.

J Tiers
05-01-2013, 10:24 PM
Did it or did it not blow a fuse? One place you seem to have said it didn't, in another you seem to say it did.

"The fact the line fuse didn't burn out makes me think the wire must have burned in two almost instantly "

"although the incident had also burned out one of the two line fuses "

Which is it?

A static converter has no real "manufactured" phase, it has a 'start output", and the rest of it is basically a pass-through of the incoming wires. It starts with a capacitor phase shift like a single phase motor, and then most run as purely single phase.

SOME have a 'run capacitor", and many such capacitors have an internal 'fuse" that protects them against overcurrents. That internal fuse is a one-time fuse, after which it is open and non-replaceable. I don't *think* Phase-A-matic has a run cap.

It IS possible that the start capacitor somehow got "across" the line due to the way it shorted.... that cap goes from one line to the 3rd phase wire on the motor, so it will conduct a lot of current on start-up,. But that is normal, should not cause damage, and without a good look at the circuit it's hard to see what happened.

if it got across the line somehow, that would pull a lot of current and their "safety link" might have blown.

HOWEVER.... if a fuse did NOT blow, but a wire was burned in two, that's an indication it was NOT over-current, but a possible bad connection that got hot. They do that, and the short to the case might have been a result and not a cause.

Also an arc can do that with current that won't blow the fuse. That's the reason for arc-detecting circuit breakers.

Was it burned near a connection? Or out in the middle of the wire?

Any indication it might have been trapped under a piece of metal when the case was closed up years ago? it can take a long time to start arcing.

Any pictures of the culprit? That might help.


It must have been a short on the manufactured phase, as the 1ph pair is passed right through on a Phase-A-Matic as it is on a RPC.
It is most likely going to be a power MOSFET or IGBT, whatever they use for power switching.
Max.

T'aint got none.... it's a "static" converter.

radkins
05-01-2013, 11:01 PM
Did it or did it not blow a fuse? One place you seem to have said it didn't, in another you seem to say it did.

"The fact the line fuse didn't burn out makes me think the wire must have burned in two almost instantly "

"although the incident had also burned out one of the two line fuses "




I had to go back and read my posts to see what happened there and I found that I had left out something in the second post, I said "The fact the line fuse didn't burn out makes me think the wire must have burned in two almost instantly" but I left out "other", what I meant to say was the fact the "OTHER" line fuse didn't burn out. But now that I think about it why would it have? Both lines from the box are fused independently so if one burns out it leaves the other line "hot". Still there would have been no reason for the remaining line/fuse to burn out also because the load would not have increased.


I was ready to leave to go pick up the meter and I was in a hurry, I should have waited until I got back before posting my hasty and confusing reply.

MaxHeadRoom
05-01-2013, 11:26 PM
If it is anything like the Phase Perfect, then it has a DSP controlled electronic switching unit, a DC power supply followed by a electronically switched DC-AC convertor on the artificial phase.
The single ph lines are passed directly through.
Max.

J Tiers
05-02-2013, 01:22 AM
Ah.... the first fuse DID blow, the other side did not.

OK, no problem, we've got it now.

Still wondering if the wire burned off of a connector, or if it burned in half elsewhere. If it was on a connector, it could easily have arced and melted due to poor connection, only blowing the fuse later when it hit the case.

Since the PAM only connects two wires, one to each 220 wire, I'm not entirely sure which are meant speaking of the "output" wires. The wires come to the converter from teh source, and then one wire (start wire) goes to the third phase. In use, that wire has essentially no current after starting.

Assuming one of them was the one burned in half, it's possible the first problem was actually an issue with either the "potential relay" or the start capacitors. If the relay doesn't open, the light either stays on or doesn't go off, I forget which, and the start caps are never removed from the circuit. This stresses them, and they may fail. When tehy fail they may short and cause a problem. Unfortunately they also usually pop open, which you didn't have happen.


If it is anything like the Phase Perfect, then it has a DSP controlled electronic switching unit, a DC power supply followed by a electronically switched DC-AC convertor on the artificial phase.
The single ph lines are passed directly through.
Max.

It isn't anything like that.

http://www.phase-a-matic.com/StaticDescription.htm

http://www.phase-a-matic.com/PDF/SIS.pdf

The phase perfect is a "system drive" in one box, with the bidirectional head end and motor drive portions (B phase only) both in it. A good solution to some problems, but you need to want that pretty badly to spend the money.

radkins
05-02-2013, 06:02 PM
I was puzzled as to why this wire had shorted in the first place but now I know, I pulled the cover off the box on the lathe with intentions of making a "health" check of the entire circuit before doing anything and right off I found the cause of the problem and it was my error. When I wired the lathe several years ago and tightened the connections I didn't notice, due to working in cramped quarters, one of the wire connectors had twisted and was pressed against the box. Over time and I suppose vibration the insulation had failed and the wire had shorted there first and then due to the load had burned in two at it's weakest point, where it entered the phase converter connector box, when the wire burned off the stub which still had power then shorted against the converter housing. Now where were the fuses while all this was going on? Happily carrying more current than that wire could support obviously so a down size to 10 AMP fuses is on the to-do list also. Still not sure what's malfunctioning in the converter but I just decided to order a new one and repair the old one later (try anyway), basically from the looks of the problem the converter simply suffered a severe overload which the manufacturer warns will cause damage.

J Tiers
05-02-2013, 10:42 PM
Probably a wise choice to replace converter.

But the fuses may not be to blame. the wire may have burned off from arcing. The melting current for even a small copper wire that is one strand of a larger (but still smallish) wire can be over 30 amps. When you get to 14 ga wire, the melting current is in the hundreds of amps.

Arcing creates heat out of proportion to the current flow. After all, the current that flows through a smallish copper wire can be sufficient to melt steel when welding, because of the arc. But if you get the electrode stuck to the steel, the same current is no longer able to melt anything much.

So there is no need to drastically undersize the fuses to avoid the "problem".

If the fuse is sized to the wire per the electrical code tables, which are widely available for reference, you will be perfectly safe from melting due to over-current. Arcing might still be an issue, of course, but it is very hard to avoid that.

Just imagine.... with an arc, the 120V (half the 230V line) is across the arc, and even if only 8 amperes is flowing, that is almost 1000W concentrated in a small area. Obviously it can melt the wire, and burn up things.

Just reducing the fuse size cannot help you avoid arc damage. That 8A would not blow your 10A proposed fuses.

radkins
05-03-2013, 08:37 AM
I see your point and the fact the connection in the lathe box did not short out for several years indicates that arcing might have been going on for some time and as the wire eroded it got hotter until it burned the insulation on the crimped terminal end allowing it to then fully short against the connection box housing, that's a theory anyway. Well a lesson was learned and while I may not yet have the converter repaired at least I know what caused the problem and I most assuredly will double check everything the next time before turning the power on!