Empty Nest, Soon
Southeast Ohio
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I bought an AIMS Part # PWR130012S 300-watt pure sine wave inverter to run Michelle’s CPAP (medical device) in the travel trailer.
I just finished hooking it up. I used AWG 8 cable, with 40-amp in-line circuit breaker on the hot side, and ran it directly to the batteries (2 Trojan T-105’s.) Cable run is about 7 to 8 feet. I used heavy copper battery connectors clamped securely to each cable end.
Batteries were putting out 12.4 VDC no load. (It’s been a couple of weeks since I topped them off.) Output from the inverter read 103 VAC on my digital volt meter.
Plugged in the shore power cord. Batteries were then showing 14.2 volts while charging. Inverter was putting out 107 VAC.
I plugged in a portable radio and turned it on. I hear only a very loud roar (static.)
At this point, I figure I have a bad inverter that I need to return. I don’t even want to risk plugging in Michelle’s $7K CPAP.
Your thoughts? I figure output voltage should be from 110 to 125 and I should hear no noise on the radio from a pure sine inverter. Am I wrong?
Wayne
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smkettner
Southern California
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Since you are on utility power, test the meter by measuring the utility power.
If you come up with 103/107 for utility power then it might be the meter.
I assume you recently tested the radio on the utility power.
I agree it does sound like a bad inverter.
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ozhoo
Anza Borrego Desert
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I while back I used an AIMS PSW inverter in a CarPC install. The inverter acted flaky on small loads, but as soon as the pc was turned on everything would act normal.
So, for the heck of it. Try plugging in something that will put more of a load on the inverter. You may need a smaller less-intelligent MSW inverter depending on how small your load is.
O
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Golden_HVAC
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I agree that more load might need to be on the inverter than a 10 watt radio. You should also not have a lot of "Noise" in the radio if it is working correctly.
Try something with a electric resistance heater, or a light bulb (not florescent). Use a 60 to 100 watt light bulb and the voltage should return to normal. But your meter might not read true RMS that in this inverter is a DC stepped wave inverter.
With a amp meter, you can check the amperage of a 100 watt light bulb on 120 volt shore power, then check the amperage when using inverter power. If the amperage is the same, then the voltage is also the same, and if the amperage is 10% less, then the voltage is also 10% less.
By the way, did you use #8 wire for the 12 volt negative ground lead from the inverter to the battery? Or did you run the inverter wire to the chassis? instead of the battery? I only ask because the way you wrote the question left the question in my mind.
You can call this place and ask about a good brand sine wave inverter, not all are created equal. I have even seen a box marked "Pure Modified Sine Wave Inverter" that is just marketing hype for a really cheap inverter.
www.solarOnSale.com
I have not heard of that brand inverter, but they repair several brands, perhaps they have heard of it? There are several sine wave inverters that are known for their poor quality.
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Empty Nest, Soon
Southeast Ohio
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Well, that was interesting . . .
Fred: I used an AWG 8 lead on both legs directly to the battery. I put an in-line breaker in the red wire. The white runs uninterrupted from battery to inverter.
My digital voltmeter shows 122 VAC on line power, so I’m confident that it is reasonably accurate.
With a 100 watt incandescent lamp for a load on the inverter, it showed 97 VAC output. (I did this before reading Fred’s post.) Notice I was clever enough not to use anything with a motor. 
While I was in the process of reaching behind to check the input voltage right at the lugs (with the incandescent light running on the inverter) it suddenly burst into flames internally (I could see it thru the exhaust port with the fan.) I turned it off quickly but the damage was done. It was powering the light for no more than a minute.
Voltage at the input lugs was 14.07. (TT was plugged into shore power.)
I definitely have a bad inverter. 
Thanks all,
Wayne
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tvman44
Southwest Louisiana
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The radio sounds like the battery charger was connected at that time.
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wa8yxm
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My thought is you did a fairly good job of describing exactly what I'd expect with an MSW inverter (Radio loud roar, on AM no doubt, 107 volts) not a TSW inverter (Radio normal operation, 120 volts+/-5)
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