[corrie]

Hello all ,well today was not a good day. I was 90% through a rouching pass when I noticed that all my axes stoped running and then seconds later my shop filled up with smoke. After quickly turning everything off and pulling out power cables to see what was the matter ,it seems all that smoke came from my power supply. Here are some pics, I,m stumped as to why this happened.

[gary_calfee]

That kind of thing can be complicated to figure out and it is hard to tell the wiring configuration from your pics, but sometimes the most obvious explanation is correct. It looks like there was some arcing to the torroid transformer hold down bolt out near the end. From the picture the wires look very close to the threads; were they in contact with the bolt? The transformer will generally vibrate (hum) as it operates, could it have rubbed through the insulation during operation? The bolt should be at the cabinet or earth ground potential and would provide a very solid ground path. The question is did the arcing cause the problem, or happen after the insulation was compromised due to the short. Of course, all of this is speculation from just looking at the pictures. Hopefully the rest of your electronics were spared....

Do you have a fuse on the primary side of the transformer? Clearly those wires were carrying a lot of current.

Good luck with your repairs!
Gary

[vtxstar]

Identify which lines melted - AC input or DC output of the bridge.

If the AC, suspect the bridge rectifier.

If the DC, suspect anything on that side, but most likely a power driver section.

I think it is time to evaluate your fuse (or lack of). It should have blown before the insulation melted.

[corrie]

Thanks for the reply, unfortunately I,m completely daft when it comes to electronics . The power supply was built for me , I guese it,s time to learn.Yes a fuse would have helped. I,ll be taking it in to get fixed and see what started this mess. I,ll follow up later. thanks.

[Al_The_Man]

It appears to me the secondary conductors to the bridge took the brunt, this might indicate the bridge shorted out, if the primary side was fused right, the short should have reflected back from sec. to pri. and blown the fuse.
Check the bridge for short circuit between connection posts after disconnecting.
Al.

[neilw20]

The steel case would not make a good heatsink for disipating 10-15w
It looks like the rectifier has shorted and may have damaged the transformer.
Bit hard to tell friom the fuzzy pictures.
Wrong sort of fuse wire in this application. (constructive comment).
I bet the builder didn't supply you with a circuit either.
Put a 2 amp fuse in series with the mains supply.
Disconnect the two burnt wires and remove them entirely.
Turn it on.
Leave it on a minute or so.
If the fuse survives and nothing smokes, then replace the rectifier, and give it a better heatsink.
If the fuse blows, it looks like the transformer is fried also.

[corrie]

Thanks to all who have replied , It seems the rectofier had come loose from the casing and over heated .my buddy checked the transformer and it seems ok. It will be rewired with an in line fuse this time and all wires will be better placed.When I get it back I,ll post some pics and a lot clearer this time. Like I said I don,t know much at all about the elctronics end of things but I,m going to learn.Are there any good tutorials of a complete power supply explained in layman turms: ie:where the signal path starts ends,what the seperate components are and do , things like that. Thanks very much to all, Corrie.

[keebler303]

http://www.antonine-education.co.uk/..._3/TOPIC_3.HTM

http://www.antonine-education.co.uk/..._smoothing.htm

Make sure to put that rectifier on a heatsink this time!

Matt

[neilw20]

http://www.antonine-education.co.uk/..._3/TOPIC_3.HTM

http://www.antonine-education.co.uk/..._smoothing.htm

Make sure to put that rectifier on a heatsink this time!

Matt

WITH HEATSINK COMPOUND. AIR GAPS INSULATE HEAT

[Al_The_Man]

I don't see a hot rectifier causing that damage, it has the appearance of excess current, have you checked the bridge for short circuit yet?
Al.

[neilw20]

Spot on Al_TheMan.
Because the input wires to the bridge rectifier melted and the outpuut ones survived, the BRIDGE MUST BE SHORTED!

Save yourself a fuse.

[corrie]

Ok so the bridge rectofier was the problem. Everything else seemed to be fine.Wires replaced and new rectofier instaled also a fuse. Hooked it all back up and joged the machine around and all was fine. Loaded a previous program that I was trying to finish before this all happened and all axes stopped working.Turned the power supply off and found that the fuse had blown. Specs on my transformer are 300 volt amps/ two paralell outputs/ 115 volts on the primary and 20 volts on the secondary. My motors are 4.6 amps .The fuse that blew is a 5 amp. The transformer tested ok for continuity but was not tested under load. i havent yet but if i put in a 10 amp fuse and it runs does that mean all is well and if a 10 amp fuse blows then the transformer is more than likely toast?

[keebler303]

Are your motors 4.6 amps total or each? Is the fuse on the primary winding or the secondary winding? If it blew 5A on the primary, something is wrong, If on the secondary, you need to use a bigger fuse. 300 VA is 15 amps at 20 volts. If you have several motors running at load, you will quickly exceed 5 amps.

Matt

[neilw20]

IMHO you should disconnect the power connections to each axis controller, (if this is possible) then power it up one axis at a time to find out which one is blowing the fuse. If it worked for a long time and all of a sudden failed, just putting in a larger fuse :nono: will enhance the frying (flame2)process.
I think you should measure the current drawn from each axis
(following applies to microstepping controllers in particular)
moving the axis slowly, to see if any controller/stepper is drawing excessive current. The current limit is set by each the controllers (or should be).

Find the fault, but not by smoke and error.:cheers:

[Al_The_Man]

If your fuse blew when using the servo/steppers then it may indicate you are overloading the power supply.
If without a load the power supply and transformer in particular stays cool for an extended period and the fuse hangs in, this will indicate the transformer is OK, you should not require a primary fuse larger than 2amps.
If the transformer gets hot or significantly warm withing a short period when off load then you may have a shorted turn.
If you have two motors that run at max, this is still under the transformer rated VA.
There must be a reason the bridge shorted in the first place, the reason may be some defect occuring in the PS load, drives etc?
Al.

[corrie]

Hey all me agian,each motor is 4.6 amps, during a run today all axes stopped. The 10 amp fuse blew.iforgot about heat sinking the bridge and will do this tommorow asap, can,t hurt. But why after all this the fuse blew, 4.6 amps multiplied by three divide by two, maybe need a twelve amp fuse.Don,t even know if that math is correct and why.

[Al_The_Man]

If you fuse up to the rating of the transformer, you can use a 2.5a on the 120v primary and 15a on the secondary. You may have got a current peak that took the fuse out especially if it is fast blow, or if you had a few repeated peaks, the fuse may have deteriorated over time.
Normally the drives will take care of high continuous current through current limit adjustment.
Al.

[corrie]

Hi Al, replaced the fuse with another 10 amp and the fuse blew agian after an hour or so . I,m wondering if the toroidal has issues, seings some of the covering is missing, it has been checked for continuity and was found to be fine,here are some pics.

[neilw20]

From your previous pictures the transformer damage occurred then.
You may have intermittent shorted turns.
Put a 3A slow blow ON THE PRIMARY SIDE, and continue to use with the secondary fuse replaced by another 10A. If the 3A fuse blows once the transformer gets warm IMHO the transformer must be replaced.
If the 10A fuse blows the problem is on your load side of your transformer.

You MUST have a heatsink on the bridge. A steel case is not good enough.
The rectifier must dissipate about 10 watts. A 4" square of 1/16" aluminum would do.

You taped up your wires to make them neat, now if one fries the fault will be impossible to analyze in this forum. Get rid of the tape. Keep AC and DC wiring separate and use tie wraps. Keep primary side separate from everything else.

Is that damaged heatsink hitting on anything?

[Al_The_Man]

Hi Al, replaced the fuse with another 10 amp and the fuse blew agian after an hour or so . I,m wondering if the toroidal has issues, seings some of the covering is missing, it has been checked for continuity and was found to be fine,here are some pics.

If the secondary fuse is blowing, then it would not necessarily be a problem with the Transformer as the fuse is after the transformer.
I would personally use a 15 amp fuse, and if this blows, monitor the temperature of the transformer, if it is overly warm or hot within a short period, then this would indicate a steady overcurrent, if normal temperature then it would indicate a momentary overcurrent.
Also monitor the temp of the motors, for the same reason.
Continuity will not tell you anything.
Al.