Welding power Source Voltage

Date 06-08-2003 15:49

Could you please advise the logic behind permitting the welding machines with an Open Circuit Voltage (OCV) of 95 VDC (In certain machines like LINCOLN SAE 400, etc. is about 105 VDC), while there are restrictions for the AC auxiliary power?
- They shall not be more than 55V from the ground.
- In certain areas, they shall be protected with RCCB.

Please help

By RonG

Date 06-09-2003 17:07

You are speaking of Secondary current I hope.

The logic being to weld with. AC & DC aren't the same thing.

Mr. Edison tried to use that point to his advantage when they performed the first execution with AC current, but it back fired on him and Mr. Westinghouse got very rich.

By billvanderhoof (****)

Date 06-10-2003 04:27

I believe he refers to the plug you plug your grinder or whatever into. If so the requirement is unattainable. It asks for 110 volt ac (less than is delivered from the wall almost anywhere in the US, nominal 110 is nearly always 120 v), centralized around ground (doable, wall ac is all to one side of ground in US, nominal 220 is centralized around ground). The trap is that these are RMS voltages (stands for root mean square roughly a kind of average) the actual peak to peak voltages are substantially higher. Thus even centered 110 volt (actual) will at some instants exceed 55 volts from ground.

I know no practical reason for such high open circuit voltages so I assume they are simply stating the characteristics of the electronics in the machine. Even at these voltages if the capacitance of the output side of the machine is low enough it may not be able to store enough power to be harmful. I would want the maker to assure me of that fact.

Bill

By 357max

Date 06-10-2003 22:23

The reason the high open circuit secondary voltage (ocv) is permitted is regulating bodies/organizations specify the amount of dc ripple. If it is high then the OCV would be low like 80 is common. This is very common with single phase AC or AC/DC welding machines. If there is very little ripple, like the inverter welders, ocv may be very common 90 or 95 volts dc. The generators produce a high cycle, three phase ac that is rectified to dc with a mechanical device called the commutator. When rectified it is very smooth very little dc ripple. Therefore the high 95 to 105 ocv dc. Makes for an excellent stick welder.