I have a miller big blue 300p, when i use the ac outlets it gives out current but after 1 minute it trips out leaving the outlets with no current. I turn off the machine then start it again and it does the same thing, I get an HL.P code 23 it says one of the scr output rectifiers has failed. I ordered 2 rectifiers from miller i installed them and tested them in all the different spots my removing two old ones and replacing it with the new ones but i still keep having the same problem as i stated before. my question is should i buy the remaining rectifiers and replace all of them. don't know what else to do. will appreciate any ideas .
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Re: MILLER WELDER AC CURRENT TRIPS UNDER LOAD
Rectification is used to change AC to DC.... DC is used for welding (these would be large rectifiers) and to excite the rotor in the alternator (much smaller and probably part of the control circuit). If when you weld in AC the same error occurs, check the voltage regulation control circuit.
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Sounds like an internal problem. You will probably have to take the casing of the welder off and examine all your wire sets. It could be something simple as a connection issue. The transformer may have blown as well.
Look on the specifications plate...there will be an input voltage and/or current/wattage rating. If you need to convert watts to amperage then you would use the following formula:
p=e x i or watts divided by volts will give you the current(amps). I think that unit is 240vac(mine is) and I use a 40A 240vac breaker and have no problems(thats 9600 watts)..you will want to choose a breaker as close to the max rating as possible...don't go too high or the breaker won't trip if something goes wrong
open inspection door,which also the fine tuner knob is ,there's a 2x4 size circut board that snaps out with little force to remove,this is the voltage regulator board,look for 4700 ohm resisitor burnt into,tv tech can fix or order new board at $227.00 what i paid.
You don't say what model welder you have, some Miller welders have 3 slip rings and brushes some have just 2. In either case the next step is to use an ohm meter to check the resistance of the rotor and brush assembly. If this is a 2 slip ring model, take one of the wires off of one of the brushes then measure the resistance between the 2 brush terminals - it should be something between 10 and 100 ohms. If you get an open circuit measure the resistance from one slip ring to the other right at the slip rings - if you now get something other than an open you've got bad brushes (about $10 each to replace),
The 3 slip ring models are similar but have 2 rotor windings - take off the wire from the middle brush and measure from it to each of the ends.
If your rotor and brushes checked out OK you should next check the fuse in the exciter circuit, this will be on the block where the other end of the brush wires go.
If the fuse was good you need to do an excitation test. This is a bit dangerous so be careful. Look at the schematic pasted inside the case and figure out which brush is the positive (+) one. The wires are numbered and so is the schematic so this isn't as hard as it might seem. Disconnect the wires from both brushes (all 4 wires in the 3 slip ring model) and tape them off so you won't get shocked. Get a 9V battery or make up jumpers that will let you connect the welder battery to the brushes. Start the welder and connect your temporary power supply, measure the AC at the outlets (it should be around 60VAC with a 9V battery) and the DC voltage at the weld terminals (should be above 10V), lastly measure the voltage at the wires you disconnected from the brushes (should be around 70V DC). Disconnect the temporary power supply and shut down the welder. If you didn't get AC at the outlets and DC at the weld terminals above, something is wrong with the stator in your welder. If you didn't measure any DC on the wires that go to the brushes (most likely thing to happen), you've got something wrong in the exciter circuit. Check the rectifier, the capacitor, the exciter winding in the stator, and lastly the current control board. Older welders will also have the fine current control rheostat in this circuit (look for burned windings on it).
That's about all of the general advice I can give you without knowing more about which welder you have.