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Re: Welders

Quoting DELCOKEVIN-at-aol-dot-com ( Kevin M. Conkey ) :

> I picked up my variable inductor (welder) this weekend.I was
> originally going to pick up a Century 225 amp lever action 
> welder. When I got there, I found out that they now carry the 
> Century 'PowerDisk'. This is the one I believe Scott has. It 
> allows you to vary the current while it is powered up! 

Good buy.

> I have a couple questions for the group. How far can you push the
> current through one of these? (the welder draws 50 amps I believe) 
> I am planning on using lots of forced air cooling around it. 

I am serious here. I have run 100 amps through a core rated 60 amps
intermittent, and have only warmed the core slightly in Tesla coil/
Jacob's Ladder applications. My arc welder ( MEDCO - BIG RED, 60 amp 
primary ) has a load reactive blower mounted in the cabinet. The 
greater the load the faster the blower runs. At 100 amps throughput 
the cobwebs on the vents are waving about, but that is about the 
extent of the distress I am detecting in this welder/inductive 
ballast. I have never had the slightest problem with overheats on 
a welder core. I know I am coiling hard when I warm one up!

Correct me if I am wrong here (with a bit of practical experience to
back up the claim) but how long do you guys expect to run at 50-100
amps??? With five minute run times on commerical equipment of this 
type you are beginning to warm (from a cold start), not beginning to 
overheat. Your gaps are going to melt/vaporize/burn to slag before 
your current limiter is going to get dangerously hot.

At least that is what happens to me when I push very long run times
through this equipment. I would focus on cooling the gaps to prevent
damage before I would worry about dropping 60+ pounds of current
limiting in oil to sink heat. Some airflow on the core of the welder 
will not hurt, but in this application it is not required. A chilled 
oil cooling loop to the stationary electrodes on the rotary gap would
be more practical from a bottom line RF throughput point-of-view. With 
input powers of 40 - 100 amps -at- 240 volts feeding commercial capacitors 
your gaps are switching several megawatts every few microseconds. Tell
me where the blast furnance going to be?

> My second question is, Where should I direct the air flow? at the 
> coil section, at the core, or attach heatsinks to it and cool the 
> heatsinks? And finally my 3rd question, I am using a centrifical 
> (large squirrel cage type) blower (1 for the welder core, and one 
> for my variac), does it matter if blow air past it (outlet pointing 
> to inductor) or sucking air from it (inlet twords inductor). The fan 
> and inductor will be in its own chamber within my cabinet. 

I have no complaints about the basic cooling of the cabinet, just that
if you decide to go overboard, do it on the spark gaps. 

Richard Quick


... If all else fails... Throw another megavolt across it!
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