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  #21  
Old 04-11-2007, 08:37 AM
VW cat VW cat is offline
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GWIZ, apologies for the spelling. The connections inside the blue circle are okay and original, after pulling the side cover off for a look. Bolted together 2 leads, both #28, one goes to the high/ med/low switch and the other goes to a center position on the AC/DC switch. The only other lead going to these switches is #25, the bottom lead in the rectifier portion of the schematic.
Only other wires I can find are 2 leads coming up from the terminal block possibly for the fan. Another separate wire may have bolted to the rectifier as one end is correct for it. All the nuts on the terminal block are tight, the jumpers on both sides are correct for 230V, but I don't believe one of the 2 leads is in the right spot for fan power. Phil
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  #22  
Old 04-11-2007, 12:38 PM
ventureline ventureline is offline
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Best to rent, or borrow a megger to test for a ground fault in the windings BEFORE you continue on. Check both power and weld windings. There has to be a reason for the rectifier removal. Pretty simple to replace a diode or 2 withough removing the whole rectifier, soooo, I'd imagine there's a fault elsewhere in the unit.

As for the fan, since you don't have the shroud that the fan motor bolts onto, best look at a 230volt tubular unit. Works way better anyways and simple to mount. A good 12" unit will come in around the $100 mark.
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  #23  
Old 04-11-2007, 05:20 PM
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GWIZ GWIZ is offline
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Quote:
Originally Posted by ventureline
Best to rent, or borrow a megger to test for a ground fault in the windings BEFORE you continue on. Check both power and weld windings. There has to be a reason for the rectifier removal. Pretty simple to replace a diode or 2 withough removing the whole rectifier, soooo, I'd imagine there's a fault elsewhere in the unit.
Just looking at the space required to mount the fan.
you would need to remove everything as an assembly. If you don't have the parts, take it to the shop and replace them in the shop.
With the outrages prices that miller wants for parts. estimate repair cost over $500 why would a school want it repaired.
Just the parts, Control and 4 diodes about $400.00.
VW cat, appears to have found the parts that came out of his machine and who removed them, post #17.
___________

It would be rare for a machine this size to have a ground fault without frying.
A megger is a ohm meter that can measure Hi resistances in the 100 meg ohms ranges with a higher output test voltage.
_______________

We can do a basic check to ground with the meter you have.

**This is done WITHOUT any power connected to the machine.**

Set your meter to the higher resistance range about 1 meg ohm.
Don't worry about the polarity of your meter probes.
Place the welders power switch in the ON position.

Measure the resistance from the ground (metal case) on the machine to each of the 230 volt line wires on the terminal block.
I don't expect your going to get any reading. Let me know what you get.
__
While your at it, measure the resistance between the two 230 volt terminals.
meter on low ohms range.
I would expect a reading less then 5 ohms between the two.

____________
Now we can check for ground leakage at the welding output Lugs.
Hi meter range about 1 meg ohm.
one test lead to ground metal case on the machine.
other lead on one of the lugs.
You will need to go thru all the selector combinations with the two switches.
That would be the AC/DC selector switch and the Amp selector range switch.

Amp selector on HI, switch the AC/DC selector thru all its positions.
Amp selector on Med, switch the AC/DC selector thru all its positions.
Amp selector on Low, switch the AC/DC selector thru all its positions.


Then do that with the other Lug.

I don't expect your going to get any reading. Let me know what you get.
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  #24  
Old 04-11-2007, 05:31 PM
ventureline ventureline is offline
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Well, thats good, if you can retreive that parts to put it back together!

I meg every unit that comes in my door on the primary side. I find that using an ohm meter doesn't tell the whole story, even power at 230 jumps real quick to a potential ground. Saved alot of fuses so far....

Last edited by ventureline; 04-11-2007 at 05:40 PM.
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  #25  
Old 04-11-2007, 10:40 PM
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Tape up the two fan wires. we don't want any accidents.
If the machine works we will get back to them.

_________________
Rheostat.

See both pictures.

Your Rheostat has a resistance of 3 ohms.
by adding more resistance in series we bring it up to 3 + 20 = 23 ohms. close enough to the 15 ohms for a Test.

Anything below the 15 ohms would place more of a load on the DC supply feeding the rheostat.
so going a little higher in this case will be fine with less of a load on the supply.

Trace your wires and match the A, B ,C terminals in my drawing.
All your doing is using the Resistor + rheostat in place of the missing one.

The wiper (B) terminal is the important one.

___________


Bear in mind, I don't know Canadian power systems.
Its up to you.
It would be best to use a double pole 25 amp circuit breaker to feed power to the machine.
Double pole circuit breaker will remove power from both hot lines when tripped.

If you feed this welder from two single breakers, Its possible to trip one breaker and still have power feeding into the machine from the other breaker.


If there's a 100 amp short in the machine it can make a Hell of a noise and you will jump thru the roof.
That's why I'm saying use a smaller breaker.

__
Setup.

Set the welders power switch to the off position.
Set all the other switches to off, especially the Hi-freq..
Set the amp switch to Low.
Set the AC/DC switch to AC.

Rotate the Rheostat to the middle.

Wire up the welder to the power.
***You MUST also connect the GROUND !***
The miller manual shows the location for your ground wire.

______

***Wear some safety glasses !***
I had a fuse blowup behind my back once, good thing I wasn't looking at it.
The parts of the fuse traveled about 20 feet.

***NOTE!***
You don't want to use the circuit breakers feeding your machine as the ON/OFF switch for This TEST.
If they need to trip the instant you flip them ON, your finger on the breaker will prevent the breaker from tripping, You can/will/may blow whatever is feeding the power to this breaker.


Turn on the power that feeds the welder.
Go to the front of the welder and flip the switch ON and OFF Quickly.
If it didn't make any unusual loud noise Turn it back ON
Leave it on for 10 minutes.

If you don't see or smell any smoke your good.
BTW Higher wattage resistors will get HOT like the Rheostat and will burn you.

_______
If your using that 25 amp breaker, it will trip at some point if you start welding in the upper current range.
In that case you will need to replace it with a larger one.


Turn it back off.
Connect up your welding cables and run some welds.
Try welding at all the three ranges HI/Med/Low.

If there's a problem try pushing the white circuit breaker buttons on the front panel.

________

Now we need to see if the current control transformer is working.

I think the best way is to.

Turn OFF the power to the machine.
Switch the wires on the resistor/Rheostat ends.
That would be reversing A and C only.

That would have the effect as if we turned the Rheostat in the opposite direction.

Try welding again, go thru the ranges HI/Med/Low.

The current should have dropped quit a bit on all three ranges.
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  #26  
Old 04-12-2007, 02:38 PM
VW cat VW cat is offline
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GWIZ, I did the resistance checks today, all readings are infinite except between the two 230V supply lugs, which read .5 ohm. Yes, I have what I believe is the correct fan and shroud.
Powered the unit also, we used the infra-red gun to check for warm spots. The machine will not weld, there is no voltage across the lugs(not sure if I used my analog meter safely there). Input voltage okay. Between the lugs and ground reads 15volts, same as the center point of the high/low switch and the 2 center leads of the polarity switch. Reading of .5 volts across any connections on the rheostat or resistor. Also we switched A & C, no difference. Should we throw in the towel? Thank you again for all your help.Phil

Last edited by VW cat; 04-12-2007 at 05:38 PM.
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  #27  
Old 04-13-2007, 12:09 PM
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GWIZ GWIZ is offline
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Looking at the schematic.
There's a large relay somewhere in the machine. I didn't see it an any of your pictures.
The relay is controlled by the remote switch, If the switch is in the remote position you will not get any welding power.

If the remote switch is in the ON position when you turn ON the welder you will hear it click loudly when you turn on the power switch to the welder.
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  #28  
Old 04-13-2007, 01:13 PM
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GWIZ GWIZ is offline
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"GWIZ, I did the resistance checks today, all readings are infinite except between the two 230V supply lugs, which read .5 ohm. Yes, I have what I believe is the correct fan and shroud."

Sounds about Right.
_________________

"Powered the unit also, we used the infra-red gun to check for warm spots."

Excellent.
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"The machine will not weld, there is no voltage across the lugs
(not sure if I used my analog meter safely there)"

Be careful.
Don't shoot your self in the foot.

See MY post #27 about the remote switch.
Does the BIG relay make any noise when you switch the switch ON and OFF ??
( Or did someone remove it ? and you did not see the loose wires going to it?)

Did you push in (reset) any of the white circuit breaker buttons on the front panel ?
If not push them if their out.

_________________
"across any connections on the rheostat or resistor. Also we switched A & C, no difference."

You can measure the voltage between A and C it should be about 30 volts DC.
What do you get ?
_________________
"Between the lugs and ground reads 15volts,"
Too be clear, is that the welding output lugs ?

Not the 230 volt lugs right ?.
_________________
"Should we throw in the towel?"

NO !, not yet.
The fact you did not trip a breaker is a good sign.
_________

**Next time make a new post, I did not know your edit had new information.
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  #29  
Old 04-13-2007, 03:13 PM
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GWIZ GWIZ is offline
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There's two remote switches.

You don't have any remote cables.
place both switches in the their non-remote positions.
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  #30  
Old 04-13-2007, 03:36 PM
VW cat VW cat is offline
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GWIZ, turning the power switch on results in a transformer hum, the unit at the bottom of the top view picture. There is no relay sound anywhere. The only relays I can see are the 3 shown side by side in the top view. There are 2 remote switches, remote amperage and remote contactor. Not sure which you are referring too.Switching the first on, makes no difference; switching remote contactor on, turns off the 'hum'. Still no DC voltage across A & C with this test( didn't switch wires back yet), and no voltage between the welding lugs.
Both of us scanned the front of the welder unable to find any removed wires or relays. Checking voltage at the power( on/off) switch found all 4 wires okay. Attaching pictures to see if you can spot the 'remote relay'. My efforts to find it on the schematic failed. Circuit breaker button is in, do you want me to unplug the wires to it and check with the ohmeter? Phil
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