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Tool Talk Discussion Forum

More power for port. welder

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txblu

09-05-2004 06:40:07




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Have a 6kw portable power unit. Will only allow me to stick weld with 1/8" rod. Can obtain second 6kw power unit very inexpensively. $350 lot cheaper than $2200 for a 12kw unit.

Have a Miller 220v 200A AC-DC Stick welder. Thought about taking the 2 power units and tieing one 115v output leg (correct phasing observed) of each together and using the 230 v output (other 2 wires) to drive the welder.

Governors on the 2 separate units may not be synchronized, but I don't care (I don't think).

I doubt the welder cares as it is just a variable inductance chunk of copper wire and soft iron.

I guess the only problem would be if the generators didn't develop opposite voltages simultaneously, like one is in the voltage swing trough of the other, I couldn't maintain 230v across the outputs. They would just follow oneanother and I'd wind up with 115.

Since this site is full of farmers and tinkerer's and people making do with what they have, maybe someone has already been through this.

Safety is not a problem, as I understand what has to be protected, proper grounding, and how the wiring needs to be connected.

Thanks,

Mark

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buickanddeere

09-06-2004 08:46:15




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 Re: More power for port. welder in reply to txblu, 09-05-2004 06:40:07  
The guys have listed pretty much what will happen. The two small one won�t make a whole lot of sparks/melted metal as engine power is limited. Seen a turbine shaft sheared off when someone tried to parallel a standby generator to the grid for the monthly run up/load testing. Closed the tie breaker without synchronizing����.wham,groan,shudder��bang,RRRRR RRRrrrrr rrr, thumpa thumpa,thumpa. Before any Frankenstein paralleling experiments get a hulking big capacitor rated for at least 370 volts. This will instead supply the reactive power now circulating between your welder and generator. The welder probably circulates 5-15 amps back and forth to the generator even when there isn't an arc being struck. Discount electronic tinker/salvage shops should have some power factor correction capacitors cheap that are in the 5 to 15amp range.

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buickanddeere.......PS

09-06-2004 08:50:36




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 PS...Re: More power for port. welder in reply to buickanddeere, 09-06-2004 08:46:15  
Forgot to mention, don�t try connecting the generators 120 + 120 in series to attempt 240V. They have to be paralleled 240V to 240V.
Odds are the governors will fight like two cats in a sack.



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txblu

09-07-2004 06:02:33




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 Re: PS...Re: More power for port. welder in reply to buickanddeere.......PS, 09-06-2004 08:50:36  
I disagree. I think parallel is the wrong approach for reasons given. No offense to anyone, but it doesn't take a rocket scientist to see that if you have 2 ac gens in parallel, and they are 180 out of phase, it's just like putting 2 batteries in parallel with the + hooked to the -.....infinite amps, BOOM!.

I'm talking about 2 power supplies in series across a common load. If they are synchronous in phase, they only put 115 across the load but have the potential for double the amps. If synchronous 180 out of phase, I have a +115 p/s sitting on top of a - 115 supply which is a 230 ckt....just like the power transformer hanging on the utility pole feeding your house.....only difference is the phasing. Mine may be a little erratic.

Just thought I'd bounce the question off y'all figurin someone had done it before.

Thanks,

Mark

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buickanddeere

09-07-2004 07:09:12




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 Re: PS...Re: More power for port. welder in reply to txblu, 09-07-2004 06:02:33  
If you phase the two generators in series and mechanicaly lock the shafts to turn together. Then you will get 240 but there still is the issue of the govenors fighting each other. If the generators run at slightly differnet speeds while in series. The output voltage will vary from zero to 240V every few seconds. Another factor is the winding design/impedance of the two generator windings. If different the machines will be busy just ciculating current between them instead of out to the load. In short the capacitor carrying all the reactive power will allow the generator spend it's time making an arc. Instead of circulating lagging current. Could be enough to get by? A single bigger generator is the next and sure step. Sorry you can't cheat the laws of physics.

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txblu

09-07-2004 09:19:29




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 Re: PS...Re: More power for port. welder in reply to buickanddeere, 09-07-2004 07:09:12  
Yeah, but you don't have to bend over either. Besides, products let you move the elements around as long as the product remains constant and you don't drive one into the limit as f(x) approaches the limit.

Another large generator is so much out of the question that I'd pay someone to do the job for me. I'd pull up a lawn chair with a beverage of choice and watch.


Seriously, I realize the average value of an ac voltage is zero and that the two gens could be tracking each other which would be another zero, but I felt that the law of averages would get you at least a 20% or so improvement cause they wouldn't track 100% of the time and I'm that close.

Mark

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buickanddeere

09-07-2004 12:50:46




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 Re: PS...Re: More power for port. welder in reply to txblu, 09-07-2004 09:19:29  
We are adding AC voltage vectors here not DC vectors. Unless both generators are timed and mechanically locked and turned together. You will be adding any thing from +120 plus +120 right down to +120 plus -120. when in series using the 120V connections. Try it with a 240V light bulb first. Every few seconds the bulb will vary from full brightness to no light at all. In short try correcting the power into the welder to unity power factor first with a cheap surplus capacitor. My math is a little rusty but an 80mf capacitor should do and correct with 7.0 amps. Sorry I give you the news you want. The generators have to be connected in parallel 240V after being synchronized first. Some careful governor tweaking and the hunting could be reduced. Are the two 6KW generators identical? May have better luck setting one generator to hog the load running in Droop mode rather than equal sharing between them in Isochronous mode. I've tried saving money with short cuts and it's always cost me more than doing the job right in the 1st place.

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txblu

09-08-2004 05:52:05




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 Re: PS...Re: More power for port. welder in reply to buickanddeere, 09-07-2004 12:50:46  
Well I just had a brain fart and thought I'd pass the gas and see if anyone was within sniffin range.

Seriously, thanks,

I agree it's an iffy thing and by the time I mess with it trying to perfect the process, I'd been better off to not do anything, have it done, or buy a suitable power source.

Now let's see, if I could just get a center terminal on the welder, I could feed half the transformer therein with one gen and feed the other half with the other gen..... ..... ..... ..... ..... Grin.

Mark

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NC Wayne

09-05-2004 17:28:22




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 Re: More power for port. welder in reply to txblu, 09-05-2004 06:40:07  
Please don't try hooking two generators together unless they are syncronized for your own sake. I saw firsthand what happens when this is done while aboard the USS America. The two turbine driven generators, that were supposed to be syncronized before they were paralleled, were much bigger than yours but the results will be the same. In this case it blew a LARGE hole in the top of a load center and sent melted parts from the explosion flying throughout the load centers enclosure. The explosion from a smaller unit may not be as large, but the end results will be the same...a burned up generator....and hopefully no personal injuries. Just my .02

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txblu

09-07-2004 05:54:36




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 Re: More power for port. welder in reply to NC Wayne, 09-05-2004 17:28:22  
Thanks, but I want to series them.

Mark



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Coloken

09-05-2004 13:38:11




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 Re: More power for port. welder in reply to txblu, 09-05-2004 06:40:07  
Are you going to catch heck on this one. Output must be synced. do not try with each half. Parallel the two output together and if the speed is close, they will load down and follow each other. You can not just pull the switch to connect the two togther. If they are out of phase there will be a direct short. Tie one side together,then hook a light bulb between the other side. Light will go from bright to out, as the phase slowly varies. when light is out, switch the second generator in. If 220 volt the bulb must be 440. You get the idea? This is the way you have to use to add AC generators to a running system. If you all ready have two generators...maybe, but there has to be better ways.

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arthur h

09-05-2004 16:11:24




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 Re: More power for port. welder in reply to Coloken, 09-05-2004 13:38:11  
when you connect 2 generators togeather one will hog the load. must turn the same RPM exactly cant be done easly do your small gen. put out 240v at a good wattage if not you will smoke them . cheaper to rent a engine powered unit for work away from electric power



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Brain Fart #2

09-08-2004 10:51:27




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 Re: More power for port. welder in reply to arthur h, 09-05-2004 16:11:24  
Its $60 to rent a 10kw generator for the day. That might be an option.



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txblu

09-09-2004 05:50:46




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 Re: More power for port. welder in reply to Brain Fart #2, 09-08-2004 10:51:27  
Great idea, too far to the rental place.

Thanks,

Mark



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