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Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
If your inductance is correct he impedance at 50 Hz is essentially 480 ohms. The 2 ohms DC means there will be a large unsymeterical inrush. You might trouble shoot it by using a bank of lightbulbs in series and an ammeter. You just keep adding lightbulbs until the unloaded current drops to where the bulbs dim out.
Then use that current and the voltage across the variac to calculate the full voltage inductance.
Registered Member #3883
Joined: Fri May 13 2011, 06:30PM
Location: Norway
Posts: 87
That can't be right. I just swapped probe wires and redid my measurements. Here's the correct numbers: DC resistance: 1.5ohm Inductance @ 120Hz: 2.3H AC resistance @ 120Hz: 5.9k
I also connected it to a 24V transformer and measured 8.4mA @ 26V.
Registered Member #3883
Joined: Fri May 13 2011, 06:30PM
Location: Norway
Posts: 87
You have an excellent point, Steve. I have modern fast breakers, maybe all I need is a inrush limiter.
Update: You were spot on, with a 5ohm resistor in series it works just fine. For low-power experiments I could just run it with the resistor, but I might as well make a more permanent solution. A varistor should fit the bill, need to start searching for a suitable one.
Registered Member #3883
Joined: Fri May 13 2011, 06:30PM
Location: Norway
Posts: 87
radiotech wrote ...
Is the 120 Hz the test bridge frequency?
Correct, I used a 120/100Hz LCR meter.
Everything works now, I've assembled the variac and with the 5ohm resistor it works as it should. Didn't want to test my CW-multiplier directly with mains, a good excuse for fixing the variac (which wasn't broken in the first place).
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Troubleshooting a variac
