EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Lowku on July 14, 2015, 03:48:29 am
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Hi guys i really need help here. i have a doxin 12v to 220v 1000w MSW power inverter. It was broken and i replaced a capacitor on the input of the battery side. but now when i measure even with a true RMS multimeter it only registers about 117v. Could it be that one of the 4 transformers that are chained to give 220v might have failed? Is there a way to test it on the board? And finally can i use it when it only give 120v output instead of 220v? . The cap that was replaced was the bottom left 1 from the photos
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Was that with a load on it?
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yes, but im using a led light that works even though it is supposed to have 220v it shines on 117v, its quite strange
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Maybe it's just set for 115 V output?
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These are mostly H bridges. The output floats above ground. Hence when one side is forced permanently to ground for some reason ( short or drive signal), you get 115. Or are you just measuring it wrong?
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Oh is it maybe that i need to measure between earth/ground and say live? ATM i am measuring between live and neutral(COM) and i leave my earth/ground unconnected
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like i said its working with a 220v light, could it be that its working fine and im just not measureing correctly? As im scared to plug something more valuable in. And how would i connect the earth?
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It's not at all surprising that an LED bulb is working.
If you can find one, try testing with an ordinary incandescent bulb. It will not be harmed by a too low voltage (and will probably give a dull red to orange glow at 1/2 voltage).
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Okay i will try that, but am i testing it correctly?
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I would definitely put a 100W incandescent bulb on it if possible. That would give it a realistic (and mostly resistive) load for testing.
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Measure the ac output voltage with a true rms multimeter.
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Measure the ac output voltage with a true rms multimeter.
@Lowku said in the original post that he IS using a TRMS meter.
However, I wonder if even a TRMS meter measures a stepped "sine-wave" properly.
I would use an oscilloscope to measure the voltage.
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That's right, sorry... :palm:
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Don't pull much power without connecting the power devices to a heatsink!
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Without measures and without schematics, I think it will be very difficult to make a diagnosis.
The only possibility is to do reverse engineering.
the 4 transformers that are chained to give 220v
Are they wired in serie ? What is the output voltage of each of those dc/dc converters ?
Be careful, there is high dc voltage in such a converter, don't try to repair it if you are not an electrician or an electronics engineer qualified to work with power electronics.
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Massive overthinking here. I do have an old HF inverter that put the transformers in series, about 35V each. Always thought I could do something with that, but a use hasn't presented itself. This is just another newbie that is measuring line to ground and imagines a problem.
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Schematics of a 1500W 12Vdc/220Vac inverter can be downloaded here...May be, it could help. :popcorn:
http://www.eserviceinfo.com/downloadsm/64204/_.html (http://www.eserviceinfo.com/downloadsm/64204/_.html)
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I am measuring from line to neutral/common