How to determine polarity of a transformer welder?

[123rover50]

I have a little welder with 10gg and 12gg outputs with voltage at 24.
Now I want to use it to jump start my 24v skidsteer but the welder does not show polarity on its terminals.
How do I determine +ve and -ve terminals?

Keith

[p38arover]

Put a multimeter across the terminals.

[123rover50]

I was going to but wasnt game.
It wont blow the multimeter up?

[tact]

Do you have a DC voltmeter handy? Does it give polarity indication somehow?
(If it's digital does it indicate negative volts if you connect it back to front? Some other indicator if you got wrong polarity?)

Assuming so. Connect voltmeter to your 24v battery with correct polarity (assumes red lead to positive). Connect with incorrect polarity to be sure the indication you get differs somehow (negative, or some polarity warning)

Now do the same checks on the welder 24VDC .... Deduction Sherlock will tell you which is the "positive" side.

Cautions: your 24VDC welder may not be a nice neat DC supply. May not make batteries or other 24VDC equipment very happy (smoke comes out - you own the smoke AND what's left of the equipment)

[bee utey]

It may of course be an AC welder if it's old enough. In any case a good multi meter will suss it out starting from a high enough setting until you get a good reading. If its AC you'll need a nice big diode pack to rectify it to DC.

[LandyAndy]

You can jumpstart a 24V from a 12V as long as the only real issue is a lightly discharged battery.
DO NOT CONNECT 12V TO THE MAIN +VE and NEG on the skidsteer,THEY ARE 24V AND WILL FRY YOUR 12V ALTERNATOR on your donor vehicle.(2x 12V in Series)
However,if you connect to one of the 2 batteries you will normally be able to start the 24V engine.This works as 2x12V in series as installed,but boosting 1 12V battery in parralel so the voltage remains 24V in the 24V system and 12V in the 12V system
Trust me it works,we have to do it at work from time to time due to a mixed 12V 24V fleet.

WARNING TAKE ALL NORMAL JUMP START PRECAUTIONS!!!!
Andrew

[123rover50]

It may of course be an AC welder if it's old enough. In any case a good multi meter will suss it out starting from a high enough setting until you get a good reading. If its AC you'll need a nice big diode pack to rectify it to DC.

Good point. I did not think of that.
I have done it before with my CIG petrol welder but its terminals are clearly marked and I can weld either -ve or +ve earth.
Its not here ATM so I thought use the little one.
Perhaps play safe and boost one battery as LandyAndy suggests.
Or go and get the petrol one

[JDNSW]

If it does not have the polarity marked, it is probably an AC welder, and hence useless for boosting a 24v system. A multimeter would confirm this - put on the 200 range, set DC - if no reading , change to AC, should show you the answer.

John

[123rover50]

Risked my multimeter, and yes its an AC output.
Had to go down the back shed and get the petrol welder. Its output is 27 volts DC. That boosted the battery enough to get the engine firing anyway.
I have just replaced the head on the Toyota skid steer now the waterpump is leaking.
More issues

Keith