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Old 2nd February 2006, 01:47 PM   #1
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Default AC where it shouldn't be.

What does this mean?

I’m testing this power supply: http://www.kk-pcb.com/power-x.html
I’ve connected +PWR and –PWR but not GND. Measuring for AC. There’s a variac between the transformer and my houses power supply.
Between -PWR and GND there’s no AC. But between +PWR and GND there’s AC. But measuring between +PWR and –PWR there’s no AC and between +PWR and the my house ground there’s no AC.
If I have AC between +PWR and GND shouldn’t there be AC between +PWR and –PWR and +PWR and the my house ground?
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Old 2nd February 2006, 01:56 PM   #2
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How much AC do you have really? Don't forget that you have a capacitance between the primary and secondary side of the transformer and this is not completely symmetrical.

If you have rather much AC between + and GND maybe you should load a little, 10-100 mA in order to reduce effects of 10 Mohms from your voltmeter. When you measure you must know the whole circuit including the voltmeter in order to be able to interpret the readings.
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Old 2nd February 2006, 02:07 PM   #3
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For 24V, that's 220V from the variac I have about 50V AC.
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Old 2nd February 2006, 06:46 PM   #4
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I fail to see what you are trying to do?.

For a start WHY are you trying to measure AC voltages on the DC output?, and are you using a blocking capacitor to prevent the meter reading the DC? (although it won't give anywhere near an accurate reading). For that matter, why haven't you connected the ground?, assuming you've connected a load at all?.
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Old 2nd February 2006, 07:05 PM   #5
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As I understands it. If you read AC there’s something wrong with the power supply. For DC I I have 24 V on +PWR and –PWR, as it should be when using 220V before the transformer. Does it matter if I connect GND to the ground? Would that take away the AC?
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Old 2nd February 2006, 08:51 PM   #6
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I think you can stop there. You have approx. 25 volts DC from both halfs. That's good. At the moment you can leave out the "0" to connected to protective ground. Let the power supply be floating right now.
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Old 2nd February 2006, 09:09 PM   #7
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I'm not sure about the AC. I’m afraid I will destroy some Aleph-X mosfet's. At first I did connect the power supply to the PCB. But at 160V using the variac I had about 10V on the mosfet's.
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Old 2nd February 2006, 09:16 PM   #8
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Disconnect the amp from the power supply and measure what you have without any load. Don't forget to discharge the PS )and not with a screwdriver!) before you connected the amp.
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Old 2nd February 2006, 09:23 PM   #9
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I'm not sure what you mean by this. But if you mean the PCB is connected to the power supply. It’s not. I’m just testing the power supply without any PCB.

Using a screwdriver, would it destroy the capacitors?
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Old 5th February 2006, 04:47 PM   #10
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Anyone?
Connecting GND to ground I have 50 VAC on +PW R to ground and 0VAC on -PW R to ground. But measuring between +PW R and –PWR I have 100VAC. And this on transformers which gives 18VAC.
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