Miller DialArc 250 AC/DC - Tripping 50 Amp Breaker on Start Up

Something is broken I would guess. I don't see any reason for such a machine to create a startup surge and I can't believe Miller would design a machine that would blow a fuse unless you turned down the amp setting.

Looking at the manual, I would suggest double checking the wiring of the jumpers that set the input voltage. Make sure the jumpers, and the wires running to the transform didn't get switched. That would be my first guess of what to try.

I'd also put an ammeter on it and measure all the currents in the various transformer leads to try and figure out what was drawing the current. And look to see what is getting hot from the extra current.

It could be there's a short in the transformer in which case there's not much you can do.

Or maybe some of the output diodes are shorted putting a constant high load on the machine even when you are not welding? In which case they need to be replaced. But I thought the standard failure was for them to fail open an not fail shorted.

That's all I can think to suggest.

Rick Barter (rvb) wrote: > If I turn the machine on with the amperage set to wherever I left off > welding, it trips a 50 amp breaker on start up. If I turn the dial > down to zero, it will start up fine.

Maybe I am missing something here, The manual calls for 100 to 150 amp fuse @ 230 volts depending on which model you have. I would think that until you size your input fuse, appropriately, it is just plain and simple luck? that it would start up at anything other than the lowest setting on a 50 amp fuse. I have a similar sized machine of a different color and it sometimes pops a 100amp 230v breaker on startup.

That's what I was thinking too. I'll check it today.

-- As Iron Sharpens Iron, So One Man Sharpens Another. Proverbs 27:17

Ah, OK. I take back everything I said. I assumed the guy was running the machine on a breaker of the correct size for the machine. If the machine is designed to work on a 100 amp+ breaker then it doesn't surprise me (too much) that it might create a surge on startup that would trip a 50 amp breaker.

As per that other post, if you are running the machine on a 50 amp breaker and it's designed for a 100+ amp breaker, it might just be a characteristic of this machine that it creates a startup serge that would blow a 50 amp breaker if you have the amp setting turned up. In my thinking, I didn't check the manual and I assumed the breaker you were using was the correct size for the machine.

So it might just be something you will have to live with if you want to continue running it on a 50 amp circuit.

I have two machines that say input power of more than 50 amps, but they don't blow the 50 amp breaker I have. It shouldn't trip unless I'm pulling more than 50 amps while using the machine I would think.

-- As Iron Sharpens Iron, So One Man Sharpens Another. Proverbs 27:17

In general, that's true and it's what I would expect. But startup could be a different issue.

That machines uses a "magnetic amplifier" second transformer to regulate amperage and I can't help but wonder what type of odd load it puts on the primary transformer at start up as the magnetic fields first build up.

I don't understand the technology well enough to know if it should or should not have such a surge, but it doesn't surprise me that it might. If you have the non-power factor corrected model, the manual says you need a

150 amp fuse on it. If such a unit pulled 100 amps for 1/10th a second at start up it wouldn't surprise me and that could well be enough to trip your 50 amp breaker.

And that's the other issue. If it's got a bad power factor, it can be pulling a lot of current even though it's not using much power because of a phase shift between the voltage and current. It's "fake power" in a sense. But it can cause your breaker to trip. Note that the manual says you need a 150 amp breaker for the non-power factor corrected model and only a 100 amp breaker to for the power factor corrected model. This means there's about 50 amps of extra current not applied to the load which could be part of what happens at start up.

I don't know enough about those machines to give you a good answer but my hunch is about 50% that the behavior is just normal for that machine, and

50% something is wearing out and causing extra power to be drawn which causes an extra large serge at startup.

I have a DialArc HF which is the same welder except with some extra stuff. I run mine off a 60A breaker, works fine. I'm guessing that the 50A breaker might be a little light.

It probably doesn't have PF capacitors. If the owner wants to keep using his

50A breaker he could add some power factor correction which would definitely lower the surge current. The manual should show exactly where the PF caps get wired in.

Grant

Yeah, it's wired in series with an extra winding on the transformer which only comes with the P model. So he would not only need the cap, but a whole new transformer to wire it the way they did. Maybe copying the design of some other unit he could find a way to do it by just adding caps???

If you increase the breaker size, you will probably need a larger conductor as well. What about switching from a breaker to a time delay fuse?

Or he might look into options of a different breaker with slower trip time curves to have the same effect but which is still a 50 amp breaker and a simple swap with his current breaker.

Put a clamp on Amp meter and have it measure peak hold current.

It will show the peak current drawn and hold it (not showing steady or zero.) That will show what happened.

Martin

Mart> Rick Barter (rvb) wrote:

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If his dialarc has PFC, his current draw should be more than 50 amps.

i

You are mixing up inrush current and peak load current, Igor. Not many guys at home will actually weld with 300 amps. Most of us won't go much over 140. At that output amperage, the welder shouldn't draw anything like 50 amps from a 230VAC source - except perhaps for the startup transient.

Grant

Ignoramus19762 wrote:

I believe that PFC reduces current at full power, but substantially increases current at low power and idle. I was not talking about inrush current.

i

I will try and get ahold of an amp meter to see what the draw is at startup.

And then I may just go to a 60 amp breaker like Grant said. I found that 3 out of 5 times, I can turn the machine on with the dial set at

100 amps or so and it won't flip the breaker.

Thanks for the help guys. I'll keep you posted.

rvb

-- As Iron Sharpens Iron, So One Man Sharpens Another. Proverbs 27:17

Did you read the manual? The recommended breaker size for a Dialars is

125 amps with PFC, 150 without PFC.

Here's the manual.

See page 10.

i

From his first post in this thread:

Yup. I read it. But, I don't really accept it much. I have two different welders that say the input amperage at rated output of blah blah blah say 50 amps, 90 amps, whatever. They all run off a 50 amp breaker just fine.

Someone else said that it may be a characteristic or a problem with this machine. My next step is to find out which it is. I borrowed an amp meter from work and am heading out to the barn to figure this out.

I'll keep every>Ignoramus15569 wrote:

-- As Iron Sharpens Iron, So One Man Sharpens Another. Proverbs 27:17