miller big 20

[baney8184]

I bought a miller big 20 on an auction for $600 and I love this thing
its mounted to the miller trailer and it came with 100ft leads.
ive got two questions.
I have to use the idle control to idle it up and down. it wont rev up when I strike an arch what could be the issue?
also it only has a 110v outlet on it can I put a 220v outlet in it?
thanks in advance.

[Aeronca41]

Welcome !

Cruizer will probably have the answer in 2 seconds. The rest of us will need a serial number to look at the diagrams. Please post.

[duaneb55]

Units beginning with SN HJ195999 can be configured for 120V or 240V. Units prior to are 120V only.

We would need the unit SN to determine if the automatic idler was the former reed switch type circuit or later CT (Current Transformer) design in order to offer system specific troubleshooting advice.

[baney8184]

Jg051824

[Aeronca41]

Here is the manual for your Big 20
https://www.millerwelds.com/files/ow.../O449G_MIL.pdf

you can connect it to provide 240 volts AC, just have to install the appropriate outlet. Instructions to change the jumpers to feed it are on page 14.

Paragraph 6-4 describes the auto idle switch. I understand from your post that if you turn the switch off, the engine runs at full speed; it idles down when you turn the switch on, but won't automatically come back to weld speed when you strike an arc?

It uses a control transformer and a circuit board to perform the auto idle function. The board (PC1) is shown as part 153 on Fig. D, page 8 of the parts list. I would first check for a bad connection or loose wires on the board plug-take it on and off a couple of times to clean up the contacts. See if that helps and let us know. Obviously, do this with the engine off.

[baney8184]

thank you very much for the help that is way more detailed info then I expected.
I will can I have both 110 and 220? from what I read on that manual it looks like one or the other.
thanx again,

[Aeronca41]

Glad to help- hope it's something simple like a loose or dirty connection.

Im guessing you have your choice of one voltage-either 120 or 240. I haven't dug into the schematic enough to know so far, but it might be possible to make it switchable by adding the appropriate outlet and figuring out what kind of switch would be needed. Mounting it might be an issue. Could explore if you want.