homebuilt welding rectifier: single diode instead of bridge rectifier?

Question

G'day,Recently I've been given a defect welding inverter for parts.While stripping it, I noticed the low-voltage rectifier (an inverter isbasically a switchmode PSU, a grizzly-computer PSU) that rectifies thelow-voltage AC to DC before exiting the machine. It consists of 3diodes of 100A/600V each (RURU10060, for anyone interested).The question: could I use this for rectifying the output of anAC-welder (transformer type) to DC? Or should I use full-bridgerectification for that (the 3 diodes in the inverter were wired as onebigger diode; as normal in switchmode PSU's). Commercial rectifiers forwelders that I've seen all use full-wave rectification, which makes medoubt if my 'grizzly-diode' would work satisfactorily.Hope anyone with an electronics+welding background can help here...Grtz,Peter Dingemans,The Netherlands.

RoyJ · Accepted Answer

You could try it but your welder will run at half power and you will probably lose a lot of the advantage of using DC. With the full wave bridge, the voltage (and current) goes to zero for only a small portion of the cycle and allows the plasma in the arc to continue.  With your half wave setup you will have 8ms of 'dead' time.peter     wrote:

Ignoramus20247 · Answer

Are you interested in selling parts of your inverter? Can you say whatinverter it is?i

Ignoramus20247 · Answer

By the way, regarding your question, rectifier bridges cost verylittle on ebay. You can buy a fully working one for  afew dozenbucks, rated for 375A. Try searching for "semikron bridge". i

dcaster · Answer

AC welders need to be used with AC rods. The reason is that the current reverses and the arc may tend to extinguish while the current is zero.

If you only use one diode to rectify AC, there will be a much longer time that the current does not flow and the welder will not work as well as it does as an AC welder.

Dan

Mark Rand · Answer

Using a single diode will cause DC to pass through the welding transformersecondary winding. This will cause the core to saturate. This will cause thefuse to blow.Mark RandRTFM

axolotl · Answer

How d'ya figure?Kevin Gallimore

homebuilt welding rectifier: single diode instead of bridge rectifier?

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