Thunderbolt AC/DC won't work

[dumb as a stump]

I have a sneaking feeling that the new switch might be different to the old one. please post a pic of the switch and wireing to it, up close and clear. I cant tell where the wires on the bottom go to.

[johnbro]

Originally Posted by dumb as a stump

As a note on the switch... you understand that the 2 240 volt ac wires must connect to the two wires that feed into the transformer so... the switch is actually 2 switches one for each side of the 240 volt...soo when you use your meter you are looking to see a switch that connects 1 side of the cord to the transformer and the other side of the cord to the other wire to the transformer. both on or off at the same time... that being said, if you look at the the wireing diagram (on millers site) do you understand what the switch is supposed to be doing? is this theory clear? meaning are you with me so far?

Sh**t no.

I'm clueless when it comes to reading wiring diagrams and stuff.

Here's the deal: the original switch was broken in transport. The replacement switch (from Miller) looks different. I switched the wires like this: top right corner on old switch to top right corner on new switch, bottom right to bottom right and so forth. If Gunny is right adn the new switch is wired different than the old one, that would possibly explain why it only buzzes and doesn't arc.

I sure hope Gunny or someone can show me a picture!

[dumb as a stump]

that is fine assuming that the internal connections are the same and I have no idea they are. I have to assume there is a prob though cause the machine should be humming if nothing else. do you have a meter and know how to use it? if not ask around.

[dumb as a stump]

So this is my first guess 1 you broke the switch, 2 fixed the switch 3 smoked the switch when you shut the welder off under load, 4 replaced it and perhaps the switch is different. Is the breaker turned on? cause if the switch is wired wrong you may have tripped the breaker. There are so many variables that perhaps you need to find some one that is more electricallly inclined.

[johnbro]

Yeah, I'm not clueless about electrons, just reading schematics and wiring diagrams.

The switch, if I'm not mistaken, is single throw, double pole. If you look at the pictures in the earlier posts, you'll see the 240V line from the supply coming in the back through the strain relief, unpacked into 3 wires. Ground goes to the case. Each of the two legs goes to the top two terminals on the new switch (left and right side). There is 240V across these two legs when the switch is off. There is 117V measured from each leg to ground.

The other two wires go to the bottom two terminals of the switch (left and right). they go back to the windings on the transformer(s) and have splices to power the fan. When the switch is "on" and plugged in, they also have 240V across them. I will measure the continuity in the switch in on and off positions and post that shortly.

THANKS FOR THE HELP! Really. This is a terrific site.

[papaharley03]

Originally Posted by johnbro

The switch, if I'm not mistaken, is single throw, double pole. If you look at the pictures in the earlier posts, you'll see the 240V line from the supply coming in the back through the strain relief, unpacked into 3 wires. Ground goes to the case. Each of the two legs goes to the top two terminals on the new switch (left and right side). There is 240V across these two legs when the switch is off. There is 117V measured from each leg to ground.

The other two wires go to the bottom two terminals of the switch (left and right). they go back to the windings on the transformer(s) and have splices to power the fan. When the switch is "on" and plugged in, they also have 240V across them. I will measure the continuity in the switch in on and off positions and post that shortly.

That's how it should read. You have it wired correctly and the switch is working, per your second to last sentence above.

No need to measure the continuity since you measured the voltage on the switch terminals with the transformer lead wires attached. That verifies the continuity because the correct voltage is being measured there.

Since you know how to measure continuity, disconnect the transformer primary leads from the switch and measure the continuity of your transformer primary winding. Should be a fairly low ohm reading, but not 0 ohms. If that checks out, disconnect the transformer secondary wires and measure that side of the transformer. Should be a slightly lower ohm value than the primary, but again, not 0 ohms.

Does the fan run?

Papa

[johnbro]

I created a little video showing in more detail how this switch is wired to the welder--it was easier to just point and talk then the try to put diagrams on my photo.

The video is uploading to youtube here: http://youtu.be/hT7J9647r6c


When the switch is off, there is only continuity between the bottom two terminals (right and left). These terminals go to the windings (see video) and also to power the fan with takeoffs.

When the switch is "on", there is continuity across any two connections.


Continuity (using the terminal numbers on the back of the switch):

Switch off:
1 & 3

Switch on:
1&3
2&4
1&2
2&4

[papaharley03]

Originally Posted by johnbro

Switch on:
1&3
2&4
1&2
2&4

You need to disconnect all the wires from the switch to check its continuity.

[dumb as a stump]

ok power unpluged
all wires off the switch
check continuity from 1 to 2 and from 3 to 4 when the switch is on and no contiuity with switch off.
if the1 to 2 is good and the 3 to 4 is good then the switch is prob ok
then carefully meter on ac volts the 2 wires from the cord for 240 volts ac.BUT only if you are comfortable doing this and understand the risks.
I just watched the vid and you are seeing the transformer primary winding and the fan winding as a short (or continuity) seeing up each side of the switch implies the contacts are good too so try metering for 240 or at least check for continuity from the cord wires to the plug (with the plug OUT of the socket). something is not right if there is no transformer humm with the power is turned on. and depending on the cord continuity test and the 240 volt conformation at the switch test the only other thing to test is to take the transformer primary winding leads off the switch and check for continuity. waiting to hear more

[johnbro]

Originally Posted by dumb as a stump

ok power unpluged
all wires off the switch
check continuity from 1 to 2 and from 3 to 4 when the switch is on and no contiuity with switch off.
if the1 to 2 is good and the 3 to 4 is good then the switch is prob ok
then carefully meter on ac volts the 2 wires from the cord for 240 volts ac.BUT only if you are comfortable doing this and understand the risks.
I just watched the vid and you are seeing the transformer primary winding and the fan winding as a short (or continuity) seeing up each side of the switch implies the contacts are good too so try metering for 240 or at least check for continuity from the cord wires to the plug (with the plug OUT of the socket). something is not right if there is no transformer humm with the power is turned on. and depending on the cord continuity test and the 240 volt conformation at the switch test the only other thing to test is to take the transformer primary winding leads off the switch and check for continuity. waiting to hear more

Ok, I disconnected all the wires from the switch and did some checking.

With the switch off, there is no continuity across any two terminals. with the switch on, I have continuity between 1&2 and between 3&4. This makes perfect sense to me.

The measured resistance of my primary transformer windings (measured between the wires at terminals 2 and 4 after disconnecting them) is 0.3 ohms.

I have measured the AC voltage at the switch (both input and output) and it's 240v. I have continuity in the electrical cord from the wall plug back to the leads that hook up to the switch, and the ground lead as well.

When I turn on the welder, all it does is buzz loudly (and the fan runs as well). I measure less than 3V at any of the sockets (AC or DC) for the electrode holder and ground clamp. If I put an electrode in I can get a tiny spark from the AC side but nothing from the DC side when I strike it on a work piece.

I know nothing about how these things work but it seems 240V is going into the tranformer but only a couple of volts (and no current to speak of) is coming out.

[papaharley03]

Originally Posted by johnbro

When I turn on the welder, all it does is buzz loudly (and the fan runs as well). I measure less than 3V at any of the sockets (AC or DC) for the electrode holder and ground clamp. If I put an electrode in I can get a tiny spark from the AC side but nothing from the DC side when I strike it on a work piece.

It is beginning to sound like you have a short in the rectifier stack, or possibly a shorted secondary winding on the transformer.

Papa

[dumb as a stump]

I agree with papa... so now find where the ac feed the recifiers and disconect the diodes. leave the ac ( from the transformer ) connected to the ac terminals and then see if you can weld ( it should). I you can weld with the rectifier diodes disconnected they are bad and need to be replaced. let us know.

[johnbro]

Originally Posted by dumb as a stump

I agree with papa... so now find where the ac feed the recifiers and disconect the diodes. leave the ac ( from the transformer ) connected to the ac terminals and then see if you can weld ( it should). I you can weld with the rectifier diodes disconnected they are bad and need to be replaced. let us know.

Ok, I disconnected what I think is the dilode (flat little thingie)--anyway it's the only thing that isn't a big hairy transformer or just connectors. And it welds!

So I guess I need to get the diode replaced. I'll ask the miller dealer about a new one. thanks for all the help!!!

Out of curiosity, what does the rectifier diode do? What's the improvement I will get when it's replaced over welding without it? I did notice it was really hard to stike and hold an arc with 7018 EP just now when I tested it, but I've never welded 7018 so maybe that's normal.

[papaharley03]

Originally Posted by johnbro

Ok, I disconnected what I think is the dilode (flat little thingie)--anyway it's the only thing that isn't a big hairy transformer or just connectors. And it welds!

So I guess I need to get the diode replaced. I'll ask the miller dealer about a new one. thanks for all the help!!!

Out of curiosity, what does the rectifier diode do? What's the improvement I will get when it's replaced over welding without it? I did notice it was really hard to stike and hold an arc with 7018 EP just now when I tested it, but I've never welded 7018 so maybe that's normal.

The diodes are responsible for converting the AC to DC for the DC output side. You'll have a difficult time running regular 7018 on that welder due to low open circuit voltage. You need the 7018AC version which has some additional arc stabilizers in the flux to help out machines with low voltage. 7018AC is purpose made for welders in the class of your Thunderbolt, the Lincoln 225, Hobart Stickmate, etc.

Glad you have isolated the problem.

Papa

[ccawgc]

if the diodes are pressed in to the plates. you replace the whole assembly.
if the diodes bolt on, you can replace each one by its self.
be careful there are two different polarity diodes, should be a red or blue sleeve.
don't get them mixed up or it will appear to be still shorted.

[gunny]

Originally Posted by johnbro

Gunny, could you take a picture of the back of your switch to show me what you mean by "side to side"? I replaced the switch with a factory unit, but the new switch (in the picture) is different than the original. When I replaced it, I wired it exactly like the original switch. My multi-meter seems to be telling me that the switch is wired correctly, but if it weren't it would explain the thing just not working...

Here are two pictures as requested.
Ignore the small white wires on the transformer side, they are the feedlines for the fan
and a pilotlight installed by me.
One picture shows the inputside (red & black)
The other picture shows the transformer inputs.
Let me know if it makes sense to you or E-Mai me
gunter_getzkow@hotmail.com.

[dumb as a stump]

Originally Posted by johnbro

Ok, I disconnected what I think is the dilode (flat little thingie)--anyway it's the only thing that isn't a big hairy transformer or just connectors. And it welds!

So I guess I need to get the diode replaced. I'll ask the miller dealer about a new one. thanks for all the help!!!

EDITED

I am interested in a pic, if you can get a nice clear image, of the diodes and arc stabilizer (stuff nearby to the diodes) The reason I'm asking is, there seems to be only 2 diodes in your post # 12 pic 1. there should be 4. follow the flat aluminum buss from the dc neg. to the heat sink that the diodes BOLT into. the positive dc should have 2 opposite diodes. You should be replaceing them all. Also Im not shure you are talking about the diodes cause they are not small and flat. Also your cables should fit tight in the plugs and seem to be loose and hanging in the plugs in the same picture. thanks

[fredschrom]

with your diodes out of circiut ohm across the leads, then reverse your leads. There should be approx 10 to 1 difference between the two lead orientations. Not all meters will do these checks ( new digital cheapies ) but most will.

Remember all diodes are different so yours could be 8 to 1 or 15 to 1 but if there under 4-5 to 1 there bad.

[johnbro]

Well, I'm a dope. I didn't disconnect the diodes (I guess) I disconnected this:


According to pictures I found in google, those look like a resistor (on the right) and a capacitor (flat red thingy).

these wires appear to terminate in diodes and bolt to these aluminum plates, which seems to be grounded to me.


I disconnected one of them:


I used my fluke clamp-on meter to measure the resistance both directions. No continuity either way. I tried a couple of others and the same result

Not sure what's going on, but I guess I will have to take it to the miller dealer... And yes, I need to replace the plugs on the ground and electrode leads--they are bent and don't go in the sockets fully.

[papaharley03]

That red thingy is a transient voltage suppressor. It's the device you'll find in surge suppressor power strips, etc. The resistor is in parallel with it. I have a similar set up on the Idealarc. This supressor circuit is in parallel to the + and - outputs from the diodes.

The diodes should read low resistance with the positive meter lead on the threaded stud and the negative lead on the side with the yellow insulation. Isolate and measure each diode individually so you'll know if all are bad or just one.

Papa

[dumb as a stump]

ok if your meter has a diode test it will show a good diode with: low resistance with 1 lead on the bolt and the other on the lead... and when the meter leads are reversed high resistance with the other lead on the bolt and lead . Google how to test a diode.
And despite the fact that you refuse to look at Millers website now you can see that there is very little inside a welder and how it is wired. It is easy to google stuff like "electronic symbols" and look around and find one that looks like what you are looking at, or is in the owners manual. ie diac. this will at least help you know what you are looking for(so as to not sound dumb talking to miller) how to test it and perhaps find stuff on ebay or other sites good luck.
ps that resister is 392 ohms are you shure it's shorted? and not just low?

[fredschrom]

dumb as a stump,

Thats an interesting circiut, not typical bridge rectifier circiut. The caps are there for lack of a better term spring or compression point. basically you can't slam the diodes too hard because the caps charge and absorb surges. BTW I seriously doubt the caps are bad, that type of cap is very visual when they go and break the coating. I can't read the the whole part number on the diode but if there under 15 bucks I would replace all of them because the bridge won't be balanced old diodes to new, I would also use some thermal grease to put them back in.

I would give this 98% odds that this would be welding as good as new sans cables which need attention ( which very possibly was the high current conditin smoked the diodes in the first place )

Connectors, Connectors, Connectors and contacts, almost 40 years as a engineer and technician and when existing stuff doesn't work or smokes besides power its #2 check.

Oh a last thought the caps also stabalize the bridge.

[ccawgc]

The caps that are parallel to the diodes are small disk caps. Almost never go bad. More often get broken during repairs. Their job is the allow electrical noise to go around the diode and protect the diode.
Look at the diode in the pictures, right under the word Italy is diode symbol. It shows which end is the anode or the cathode of the diode. You will need two of each type in the right place on the heat sinks.
You can get diodes from miller or an electronics store.

[johnbro]

Thanks first of all to everyone of you who has been helping me with this.

The Miller dealer (LWS) kind of blew me off. So I went with my diodes to an electronics component store. Here's what I have on my miller (note there are two of each, I only took one of each off):



The guy who apparently owned the electronics store didn't seem to know as much as I did about bridge rectifiers (and I only know what I read in Wikipedia). But finally I was able to pick out these four--two reverse and two positive.


Two are 600v; two are 800v and they're all 70A.

So my questions for you wizards out there is, will these work (assuming I solder the pigtails from the old ones on them)? Or do I need something different?

[Bluewelders]

They are pretty small to use in a welder.