220v MSW power inverter only giving 117v - Page 1
Forum section: electronics / repair

author: Lowku
author_rank: Newbie
timestamp: July 14, 2015, 03:48:29 am
content: 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

author: mmagin
author_rank: Frequent Contributor
timestamp: July 14, 2015, 04:22:49 am
content: Was that with a load on it?

author: Lowku
author_rank: Newbie
timestamp: July 14, 2015, 10:40:32 am
content: yes, but im using a led light that works even though it is supposed to have 220v it shines on 117v, its quite strange

author: dom0
author_rank: Super Contributor
timestamp: July 14, 2015, 12:26:50 pm
content: Maybe it's just set for 115 V output?

author: Seekonk
author_rank: Super Contributor
timestamp: July 14, 2015, 01:25:16 pm
content: 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?

author: Lowku
author_rank: Newbie
timestamp: July 14, 2015, 01:34:12 pm
content: 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

author: Lowku
author_rank: Newbie
timestamp: July 14, 2015, 01:38:48 pm
content: 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?

author: flynwill
author_rank: Regular Contributor
timestamp: July 14, 2015, 02:30:35 pm
content: 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).

author: Lowku
author_rank: Newbie
timestamp: July 14, 2015, 02:48:38 pm
content: Okay i will try that, but am i testing it correctly?

author: mmagin
author_rank: Frequent Contributor
timestamp: July 14, 2015, 04:02:24 pm
content: I would definitely put a 100W incandescent bulb on it if possible. That would give it a realistic (and mostly resistive) load for testing.

author: oldway
author_rank: Super Contributor
timestamp: July 14, 2015, 06:34:24 pm
content: Measure the ac output voltage with a true rms multimeter.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 14, 2015, 06:36:14 pm
content: Quote from: oldway on July 14, 2015, 06:34:24 pm@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.

author: oldway
author_rank: Super Contributor
timestamp: July 14, 2015, 07:37:07 pm
content: That's right, sorry...

author: Richard Head
author_rank: Frequent Contributor
timestamp: July 17, 2015, 08:56:08 am
content: Don't pull much power without connecting the power devices to a heatsink!

author: oldway
author_rank: Super Contributor
timestamp: July 18, 2015, 09:03:35 am
content: Without measures and without schematics, I think it will be very difficult to make a diagnosis.The only possibility is to do reverse engineering.QuoteAre 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.

author: Seekonk
author_rank: Super Contributor
timestamp: July 18, 2015, 12:35:39 pm
content: 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.

author: oldway
author_rank: Super Contributor
timestamp: July 18, 2015, 01:05:52 pm
content: Schematics of a 1500W 12Vdc/220Vac inverter can be downloaded here...May be, it could help.http://www.eserviceinfo.com/downloadsm/64204/_.html

author: Lowku
author_rank: Newbie
timestamp: July 18, 2015, 05:36:21 pm
content: I am measuring from line to neutral/common