Current-limiting impedance to turn variac into current source

[electricpete]

I am looking to do some quick easy testing of some connectors.

I have access to a 120vac variac 15A max.

I'd like to be able to vary the current at least form 0 -10 A.

I'd like to be able to adjust the current using the variac voltage control and not have it drift. If I relied on the source impedance of the variac set to very low voltage along with series resistance of the circuit, I think the resistance of the conductors/connections might become significant and cause the current to drift with temperature.

So I'd like to put an impedance in series much larger than the impedance of the connection to stabilize the current.

A quick check shows order of magnitude 10 ohm impedance is required. That would dissipate 1000W if a resistor so I think it probably needs to be a reactance. Inductive makes more sense because capacitive might create a resonance with the inductive source impedance.

Any ideas of a quick easy cheap way to do it?

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[itsmoked]

Get a 1000W light bulb and screw it into a porcelain base. Then if you decide you need 750 watts just screw one of those in.

1000W might require a mogul base but you can use a mogul to std adapter. Alternatively put in three or four standard bases in parallel then you can do all sorts of mixtures for fine tuning.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

A very neat and adjustable constant current circuit is the transductor in constant current mode. The so-called Krämer (Kraemer) transductor is used to measure DC and can be employed to generate a constant AC current.

It produces a somewhat "chopped" current (switches when the cores saturate) so it contains a lot of odd harmonics. But it is constant and easily adjusted.

Google transductor and kraemer.

Gunnar Englund

http://www.gke.org

 

[ScottyUK]

ePete, do I recall you work in a power plant?

If your plant has 'junk' lying around waiting for the day when it becomes useful, can you find a current transformer core which you can sacrifice or borrow? If you estimate the core CSA and assume a maximum flux density of 1.5T or so, you could design your own inductor using some high school physics. Wind it with PVC insulated panel wire.


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I don't suffer from insanity. I enjoy it...