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Old 13th Sep 2018, 10:15 pm   #3
Phil G4SPZ
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Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,735
Default Re: Lamp limiter plus Variac tip

I have a similar arrangement in my workshop, with isolating transformer feeding variac followed by lamp limiter. But to be honest I leave an old Avometer in circuit switched to the 1-amp AC range, and find this much more sensitive than the lamp. Whilst winding up the variac, it is easy to watch the AC current drawn as the voltage is increased. It's also possible to measure the VA input quite accurately and compare it with the rating plate data for the device under test.

This can be particularly useful when testing devices like SMPSs which don't have a linear voltage-to-current characteristic.
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