100A DC welder - help needed

[Aussiebushman]

G'Day all. Hope there are some experts on this forum who can tell me what I'm doing wrong and how to fix my newly built DC welder. I followed the "Chrysler 120A" details found on the Internet and only added a shunt and 100mA meter to measure amps because I could't find a serious enough analog amp meter.

The motor is 5.5 Hp 4 stroke and a car battery is used to excite the alternator. The leads are industrial quality. The switch between the alternator field and the battery is double throw with a 1 Ohm resistor on one side and no resistor on the other. The latter switch position does produce a spark at the electrode but it is pathetically weak and the voltmeter reads on around 6V. I have obviously screwed up somewhere. Please refer to the schematic attached.

Any help appreciated

Alan

 

[KennyV]

It looks like you did not modify the alternator by removing the voltage regulator... got to do that.
Check this link... On-Board Welder
KennyV.
BTW you do not need to use the switching relay shown at this link if you are using a switch with enough amp cap...

 

[Aussiebushman]

Yes Kenny

I fear you are right. The Bosch alternator was modified by an elderly mate who used to be a very capable marine electrician, but has sadly gone a bit ga-ga. I'll take it apart and try to see what he did wrong. It surely should be putting out something close to its 100 Amp rating

Cheers

Alan