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IDAHO Jim · 10-23-2011, 12:27 AM

I recently had an LED night-light catch fire in our 2007 Diplomat that was plugged into a GFI receptacle. The night light had been functioning normally while under shore power but, caught fire after having turned the inverter on for less than 20 minutes. I didn't see the fire but smelled smoke and discovered the problem a short time later. Lucky that it didn't cause any damage other than soot and a melted night-light. I verified that I had 120 volts true RMS at the receptacle and chalked it up to a faulty night-light.

However, I just read a similar occurrence of an LED night-light catching fire while also using an inverter in the November (2011) issue of MotorHome magazine (Coach & Powertrain). The writer who has a 2010 Phaeton also verified proper voltage thru the inverter but, did not specify the type of receptacle (GFI ?). He also chalked it up to a faulty night-light but expressed the concern in writing to Motorhome Magazine.

I emailed MotorHome magazine about a week ago and didn't get a reply back so I just thought it might be something to think about....at least I'll feel better for having said something.

frankdamp · 10-23-2011, 08:47 AM

Did you look at the wave-form of your electrical power on an oscilloscope? The LED itself is a low voltage device and so a 115Vac lamp will contain a transformer and control board. The transformer could get upset if the voltage isn't close to a pure sine-wave.

If the "inverter" is a plug-in low cost individual one, rather than a whole-house true sine-wave inverter, it could be simply a diode that cuts off half the sine wave. You'd still get a voltmeter reading of 115 - 120 Vrms, but without the negative half of the sine wave, a transformer in the lamp will overheat.

Been there, done that with a voltage converter for use of 240V power with US implements when I first started travelling for Boeing. It was fortunate that I didn't set the hotel room afire! I did burn up a company "luggable" computer (long before lap-tops).

RCLImperial · 10-23-2011, 09:56 AM

Your inverter is a modified sine wave output, meaning that it has a stepped waveform rather than a smooth one. While the voltage will register as 120VAC, there is a significant high frequency component to it. If the component is sensitive to this high frequency, it can overload. Most appliances have adequate filters to eliminate these high frequencies. Toasters and heaters don't care.

In my case, just a few minutes on the inverter can smoke my Black and Decker pest repellers. They work just fine on line AC, but start to overheat as soon as I switch to the inverter.

Dick Lucas, '04 HR Imperial

sc3283 · 10-23-2011, 09:37 PM

Quote:

Originally Posted by frankdamp

Did you look at the wave-form of your electrical power on an oscilloscope? .

I'm sure that is a tool most all of us carry in our tool boxes...right?

ottffss · 10-23-2011, 10:00 PM

While few folks probably carry an oscilloscope, it is good practice to know if you have a MSW (modified sine wave) or a TSW (true sine wave) inverter. Household electricity (i.e. shore power) is TSW.

Certain electronic devices (and the definition of "certain" is nebulous) do not operate well on MSW and will quickly overheat. Knowing that you have a MSW inverter means you should be cautious when initially plugging in very small electronic devices - while under inverter power - to make sure they are not reacting to the MSW. RV manufacturers use MSW inverters as they are far less expensive than TSW inverters. The only difference is in the internal circuity of the inverter itself, a TSW being more complex and sophisticated. Externally they connect exactly the same to the RV.

Often the types of devices that react poorly to MSW are very small devices that are very low power items (like some appliance battery chargers, and what I'll very loosely call cheap gizmos plugged into an outlet - LED nightlights, pest repellers, air fresheners, etc) things that tend to have a small low power circuit board feeding the actual device. It is that circuit board that seems to dislike MSW.

It is also prudent to point out that some big electrical items can also react badly to MSW. Residential refers have historically had significant issues running on MSW inverters causing compressor failure in many installations. Many RV manufacturers have gone to TSW inverters on all electric rigs because of this. Some microwave oven controls also do not like MSW and folks report clocks on those ovens rapidly gaining/losing time, flashing LED displays, or other strange anomalies.

Resistance heat devices - stoves, space heaters, etc. don't mind MSW at all, however, if they have electronic thermostats and controls, those could be a problem under MSW.

StuckySB · 10-24-2011, 06:24 AM

We also had a night lite smoke when plugged into on the GFCI. I don't believe the GFCI had anything to do with the failure. If anything it probably would have tripped if I hadn't caught the problem when it happened.

We had just changed over from shore power to inverter. Started up and going through checklist before driving when DW starting yelling about smoke. It was one of those lights with what looked like water and little fish floating around.

We no longer leave night lites plugged in when in storage.

smlranger · 10-24-2011, 06:57 AM

This explains why two new LED night lights we put in our coach last year started to melt. I smelled something burning in the coach one evening and found both LED lights very hot and starting to melt. We do have a MSW inverter.

97windsor · 10-24-2011, 07:05 AM

[QUOTE=ottffss;991027]While few folks probably carry an oscilloscope, it is good practice to know if you have a MSW (modified sine wave) or a TSW (true sine wave) inverter. Household electricity (i.e. shore power) is TSW.]

How can you tell without an oscilloscope if your inverter is a TWS or a MWS??

sc3283 · 10-24-2011, 09:18 AM

Ott, very good info!! TY for passing it along. I'm like probably most....I had no idea of this....and my literature with my inverter makes no mention of this...Thanx again

HeapBigEngin · 10-24-2011, 09:38 AM

Ottffss....that is OUTSTANDING info to have. Like some others, I have never given a thought to device/inverter compatability. I copied your post and will keep it in my files for reference. I now suspect that is why my somewhat inexpensive shop vac recently...and suddenly...gave up the ghost after using it up at the motorhome (in storage at the time). Good Stuff....Thanks again!!

ottffss · 10-24-2011, 10:21 AM

Is your inverter a MSW or TSW?
Look in the inverter manual or go the inverter manufacturer web site and look for you inverter model. Also call the inverter tech support number/email. Generally, unless your rig is a pretty high-end rig, you are likely to have an MSW inverter. I'll also mention that RV "converters" are NOT "inverters" and in no way are "converters" part of this phenomenon.

I want to emphasize, that this issue has absolutely nothing to do with GFCI (nor is GFCI designed to detect/protect this type of occurrence). It is the MSW inverter.

frankdamp · 10-24-2011, 11:00 AM

A much more detailed explanation than I was able to give - thanks, ottffss. I certainly didn't expect anyone wouold have an oscilloscope in their toolbox, but they're fairly common capabilities in the multi-funtion gear most auto repair shops have.

The cheapo "converters" I referred to are the kind you can get for "converting" from 240V European power to run 115V equipment. They just block half of the sine-wave and are even more damaging than MSW inverters to anything but pure resistance things like curling irons.

I did have an interesting experience when I was a research engineer for a machine tools manufacturer in England. We were testing a newly-built planer and part of the equipment I was going to use was a strip-chart recorder. I plugged the equipment trolley into an un-marked wall outlet, turned the recorder on and got a big blue flash. I got a meter out to verify the voltage on the outlet and discovered it was 240V as I expected, but it was DC. They drove the planer with a DC supply and had the factory wired to test the motor controllers before they were installed.

wa8yxm · 10-24-2011, 01:40 PM

Question: Is that a True Sine inverter or an MSW?

Some small electronics, to save weight and space, use a capacitive divider to drop the voltage, These devices assume a true sine wave and if you feed it a stile wave (MSW) they may malfunction.

What is a Stile Wave... Well, the word has at least 3 meanings I know of

A character (The Blue Adept, or Citizen Blue) Is named Stile... He got that name because he looked at a pile of horse dung and diagnosed (Correctly) a medical problem with the horse that dropped it.... Thus saving his "Master" many dollars in vet bills.

It is also (And this is why I call it a Stile wave) A set of stairs that go up and over a fence, Dogs and People can cross the fence easily, Pigs can not

The wave form is the same as the steps.

With some capacitive divider devices, this will cause over voltage, which can result in a fire.. Since it appears to be like a 180 or 360 HZ and the reactance of the capacitor goes DOWN with frequency.

IDAHO Jim · 10-24-2011, 01:58 PM

Thanks for the info regarding the cause of the night-light turning to toast. It is certainly reassuring to know the reason for the problem and the preventive measure. I knew that my Inverter/charger (Magnum-Energy ME2012) did provide a modified sine wave but I wasn't aware of the potential problems that this could cause with LED night-lights,etc,.

Thanks again and especially "ottffss" for the clear explaination