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?
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?
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.
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.
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?.
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?.
Measuring it with a voltmeter. Setting it for VAC. Using a variac before the transformer. Having 220VAC to the transformer which gives 18VAC before the bridges. For measuring I’m just having one wire connected to the voltmeter which should correspond to +PWR and the other to the ground (I get 50VAC). The same goes for –PWR and ground (0 VAC).
I’m measuring this because I think it’s no good having AC especially 50V AC connected to the mosfet's on the PCB. As I understands it you only wants DS.
I’m measuring this because I think it’s no good having AC especially 50V AC connected to the mosfet's on the PCB. As I understands it you only wants DS.
anders.a said:
As I also asked above, do you have a blocking capacitor in series with the meter lead?, a multi-meter set to AC doesn't normally have such a capacitor internally and will read the DC volts off the supply (but won't give anywhere near an accurate reading).
What does it read if you measure on a DC range? - I've NEVER tried reading across a DC supply with a meter on AC, nor ever heard of anyone doing so (as it's a completely pointless exercise!).
Unless you have some sort of load on the supply, it's almost inevitable that you will read some AC across the output. If you're using a typical modern meter, t has an impedence upwards of several hundreds of kilohms. As has been pointed out, there will be some capacitative coupling across the transformer at least, which will show up under these circumstances.
You can easily read a considerable voltage across your body at this impedence, and that's relatively isolated (think of induced hum when you touch an input terminal).
Load the supply down a bit, and watch the AC fall to virtually zero!
Remember that you are measuring a difference in potential, not a flowing current, which *would* indicate a fault.
You can easily read a considerable voltage across your body at this impedence, and that's relatively isolated (think of induced hum when you touch an input terminal).
Load the supply down a bit, and watch the AC fall to virtually zero!
Remember that you are measuring a difference in potential, not a flowing current, which *would* indicate a fault.
Ok, I didn’t know you need a blocking capacitor.
As for DC I have 24V as it should be. Would you say I shouldn’t worry about the measured AC.
Initially I did the measurements because I had too much voltage over the mosfet's, about 10V when connecting 12 V, it shouldn’t be more than 4V.
So I measured for AC over the supply and there it was 50V.
As for DC I have 24V as it should be. Would you say I shouldn’t worry about the measured AC.
Initially I did the measurements because I had too much voltage over the mosfet's, about 10V when connecting 12 V, it shouldn’t be more than 4V.
So I measured for AC over the supply and there it was 50V.
anders.a said:
Without it you're measuring the DC on the capacitors, and NOT any AC that might be present.
You are measuring the voltage across a 47,000uF capacitor, it can't have AC across it because it will be a serious short circuit at 50Hz - under load there will be a small amount of ripple on it, but no AC - it's not possible is everything is connected correctly.
I wouldn't worry about the AC, because there isn't any, and you've never actually tried to measure any!. If you have 24V DC then it's working fine!.
Again, you haven't ever measured for AC, you've measured DC on the AC range of your meter, which will read completely wrong!.
Hi Anders,
you are likely to damage your caps.
What is a certainty is you'll vaporise the end of your screwdriver in the explosion and some of the metallic particles ejected in the explosion could damage you as well.
Use a kohm resistor (10k to 15K) to discharge your caps. Check for dissipation when selecting your resistor. It can easily get hot enough to burn you if you are holding it to do the discharging. To speed up the discharge you can select a lower value resistor as the voltage falls.
you are likely to damage your caps.
What is a certainty is you'll vaporise the end of your screwdriver in the explosion and some of the metallic particles ejected in the explosion could damage you as well.
Use a kohm resistor (10k to 15K) to discharge your caps. Check for dissipation when selecting your resistor. It can easily get hot enough to burn you if you are holding it to do the discharging. To speed up the discharge you can select a lower value resistor as the voltage falls.
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