100 amp low voltage power source

[Tmoose]

I'm looking for a low dollar method to provide 100 plus amps, either AC or DC, probably for an extended period, to test some bolted connections' resistances. With the connection likely having a small fraction of an ohm resistance I think I don't need more than a volt or 2.
I've been thinking of tranformers or one of those 6 volt car battery with the external series connector links cut and run in parallel.

I bet many of you have much more clever ways to accomplish this.

Thanks,
Dan T

 

[roydm]

ScottyUK,
Then why are you still reading it? I fail to see how using a low burden CT can be any more accurate, surely you would be doing a Drop Test . I agree if you kept the leads real short and voltage very low a CT would work but surely the core will saturate fairly quickly. I have used the method I proposed to test switchgear trips up to and over 1KA.
Yes I did read the previous old posts, lots of people do, to get ideas, otherwise they would be taken off after a few days.

Regards
Roy

 

[ScottyUK]

Roy,

Who mentioned a low burden CT?

A typical Class X CT is capable of producing some fairly large voltages at currents considerably in excess of the nominal secondary current rating. It isn't uncommon to find them with a kneepoint voltage of 800V or so, which means they will connect directly to a voltage source up to (say) 415V in the UK or 480V in the US. I have one which needs either a fork lift or four men to lift, to give some idea of scale. In the mode of use Bill and I suggested the CT is behaving just like a voltage transformer, but is physically more amenable to having a few turns of heavy cable or bar looped through the aperture.

There really isn't any difference in what we are proposing other than the hassle of chopping the secondary windings out of a power transformer varies between time consuming to outright difficult. We have successfully got over 5kA out of the protection CT mentioned earlier which was rescued from a transformer bushing. We were driving it from a large 415V variac and could have gotten a fair bit more than 5kA if we had wanted to. You are right about keeping the connections short and thick, but this applies to any transformer based solution unless it involves a very high power source capable of delivering a lot of voltage at high current. If you look back in the old threads this type of high energy test has been done a couple of times to carry out primary injection on a large transformer's protection scheme - the last one I was involved with used a 1250kVA generator with the load directly strung across two phases.


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If we learn from our mistakes I'm getting a great education!

 

[roydm]

ScottyUK
The original request was for a low dollar solution. Your CT sounds awesome, unlike anything I have seen lying around spare. I was picturing something 500:5 or there-about. Either way I think we agree a transformer is more practical than a DC solution for a long term test. My experience was testing low voltage switchgear where the client insisted on testing the protection by injecting through the busbars to verify CT wiring. The usual low current test set was useless for that. An old 1KVA trany, hacksaw, welding cable and a couple of hours later we had a workable low cost (Kiwi) solution.
Cheers
Roy

 

[ScottyUK]

Low dollar is so open to interpretation - we saved ours from the skip so it was pretty close to a zero dollar solution!


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If we learn from our mistakes I'm getting a great education!