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Old 06-18-2018, 01:20 AM   #1
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Inverter Shows 1250W When Nothing Was Plugged ==> Electric Blanket Was The Problem

I spent May/June in Montana and the weather was 40F-80F. A very warm season in all respects, but there were a few chilly nights when my new queen size heating blanket with 2 controls came in handy.

After a month of being on AC shore power, with no issues, I packed up camp and was just about ready to hit the road when I noticed my MSW inverter panel was putting out 1250W, which I thought was odd, because nothing was plugged in, and none of my AC circuit breakers were tripped.

So I proceeded to turn off each AC circuit breaker (one at a time) until I found that "Receptical #3" was the problem. (My inverter panel showed 50W which was normal since I have a residential refrigerator running.)

... And sure enough "Receptical #3" was the same outlet I used with my electric heating blanket. However, I was perplexed to see a current draw when nothing was plugged into the wall.

Well it turns out that Winnebago uses these cheap "press fit" type wall receptacles; and by plugging the heating blanket into the cheap wall receptacle (with a unique current draw issue associated with heated blankets) it apparently caused internal damage to the wall receptacle... which appears as a short to ground I guess, since the current has to go somewhere right?

So I did some investigating on IRV2 and after reading other articles on all the major problems a digital heated blanket can cause, decided on doing the following things as the best course of action to take... as opposed to NOT using an electric blanket of course.

Solution: Wire a wall socket so it only works on AC-shore-power or AC-generator-power.

1) Replace the bedroom wall socket with a 15A rated part that has screws on the side to connect the wire ends.

2) Modify the plug by cutting the trace that joins the top plug to the bottom plug. This effectively splits the the wall socket into two...

3) Run a separate Romex 12 gauge line to the Air Conditioner circuit breaker. because this breaker is only hot when you are 120V shore power or when the generator is running. Which is to also say the inverter does not provide AC power to this breaker. Why do this?

So when I plug in the heated blanket it can only operate on shore power or generator power. Why?

Because digital heated blankets are dangerous when used with a Modified Sine Wave (MSW) inverter and that's what I have in my coach.

Note: This also means this bottom wall socket will be "dead" when I am relying on the inverter to provide AC power to the rest of my coach, but that's okay. When I'm in cold weather I will most of the time be on shore power.

* Plus the new wall receptacle has screw ends to tighten down the wires, which will provide for a better connection under load.

4) Then I will still use "Recepticle #3" hot wire will power the top half of the plug I just split in two, and that half of the wall receptacle will be hot all the time... that is when it's on shore power or generator or on inverter AC power; and so will the plug on the other side of the bed.

Remember, the AC circuit breaker only is supplied with 120V when on shore power or on generator power. And this breaker can handle the extra .5 to 1A of AC current load, which is the same a ~60W per side of the heated blanket or 120W if both halves of the blanket are turned on. Anyway, who uses the Air Conditioner when you have a heated blanket on?

Note: I do have a heat pump on my basement AC, but still this extra 1A load max will not be a problem.

=== OTHER QUESTIONS ===

Other people have said this: You can use an old style, analog dial type heated blankets without a problem with modified sine wave inverters. So I'm wondering if this is true or not and why?

Maybe someone can tell us why a digital heated blanket is so much more of fire hazard when using a modified sine wave inverter vs. the old analog type with "turn style controls?"

===

Here's one blanket manufacture that advertises analog controls on amazon:

https://www.amazon.com/Biddeford-Bla...JA41XTA8YDFEG9

My guess is that I will order one of these analog type (full size) blankets or better still get an analog type (queen) mattress cover for future use; and give my new digital blanket to my kids.

https://www.amazon.com/Biddeford-590...r+analog+queen

=== WHAT ABOUT A FLOOR HEATER? ===

I suppose a floor heater can be a problem too with these cheap Winnebago wall sockets. However, only the heated blanket seems to be the problem in my coach so far. Does anyone know why a wall heater at 1500W is not a big a problem as an electric blanket at 60-120W?

And just to be safe, I think I will replace the wall sockets I plug my floor heater into... with the screw type...and use 20A rated sockets for extra insurance.
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Old 06-21-2018, 09:26 PM   #2
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I wonder if the receptacle you had trouble with was inherently flawed and would have gone bad no matter what was plugged into it. So maybe that outlet would have been damaged with any appliance that was used at that moment, and it wasn't something unique to the blanket that caused it.

And electric blankets with digital controllers aren't necessarily dangerous when used with a MSW inverter. It's just that the wonky electricity harms the electronic components in the controller and they stop working--they don't necessarily burn up.

The blanket you linked to is interesting because it does say it has an analog controller, which should work on a MSW inverter (I had an ancient electric blanket that worked fine on my MSW inverter). However, I have run across many modern electric blankets that have dial-looking controllers that look like they would be analog, but they're not. So I can't say I would trust this one just because it says it's analog--maybe they're just trading on the "vintage" craze.

I do know that the Soft Heat low voltage electric blanket has worked fine on my MSW inverter for years of fulltime use: SoftHeat Low Voltage Blanket - Electric Blanket Institute

Now, about using 20-amp receptacles for "insurance," I'm not sure it's going to do what you think it will. I used to think what you're thinking, but now I'm not so sure.

I'm not an electrician, and hope one will chime in, but I think the main thing on the 20-amp receptacles is that they accept a 20-amp plug with one prong that is T-shaped, and the wire leading to that receptacle will be safe for carrying 20 amps. You don't need the T-shaped feature, and your wiring will still be for a 15-amp receptacle, so there won't be any benefit there.

But here's where I've been thinking: I assume that the idea is to have as much of the plug touching as much of the receptacle as possible. When inserting a 15-amp plug into a 15-amp outlet, the prongs get squeezed between the solid pieces of metal in the receptacle.

But in a 20-amp receptacle, one side doesn't have those solid pieces because it has to accommodate the T-shaped plug. So it's not a "custom" fit like in a 15-amp plug, and I wonder if that would make any difference.

Probably not, and even if it does, it wouldn't be a big difference. But I don't see how it could be a benefit.

So I'm thinking "upgrading" to a 20-amp outlet when you'll be using a 15-amp plug won't actually gain anything, but would like to hear what an electrician would have to say.
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Old 06-21-2018, 10:07 PM   #3
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Viva la difference. My bedside outlets were only live when on mains or generator and I wanted to use the electric blankets off the inverter when boondocking so I had been running an extension cord from a bathroom outlet which is a bit of a trip hazard. So I have now run a circuit from the existing inverter supply at the TV to the bedside and installed extra outlets..

My inverter was a mod square wave and I had bought electric blankets widely touted as being good with MSW inverters. Now I have a PSW inverter so it doesn't matter anyway
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Old 06-24-2018, 01:13 AM   #4
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Clarification + Retraction

I need to clarify a few things in my original post that may be confusing and/or incorrect:

1) Any heated blanket should be okay with AC-Shore Power or Generator Power.

2) Many have said the analog heated blankets -- and in particular analog heated mattress pads (the one with turn knobs) -- are safer then their newer designed blankets with digital displays; and I am inclined to believe that when you are using a MSW inverter.

More specifically, I think if you plan on using an inverter (MSW or Pure Sine) to power any heated device you intend to leave on for an extended period of time, then you might consider examining your wall socket after each nightly use... and then look for black marks on the wall socket -- which would signal arching or overheating. And the same goes for your portable floor heater if you use one of those too!

In my case, I replaced two of my Winnebago OEM style wall sockets with a 15W Ground Fault type wall socket and wrapped the sides good with tape for insulation. However, due to space limitations I could not replace other wall sockets.

3) I retract what I said about Winnebago using cheap AC wall sockets. This was a mistake on my part. In fact, Winnebago probably pay more for these specialized receptacles which are better sealed against moisture vs. the ones made for the home.

I'm just not a fan of how strong the inside contacts are made, for carrying heavy load, but that's something Winnebago could have anticipated nor was this socket most likely designed to handle.

Consequently, I think, if you use a heated device of any kind, including a hair dryer, then you should be concerned about this wall socket the device is plugged in to.

This post was meant to point out the safety risks of using a heated blanket or floor heater at night when you are sleeping... WHEN POWERED BY AN INVERTER. (And especially when powered by an older MSW inverter.)

Final note: You may find you will have problems using a conventional wall socket to replace the Winnebago OEM socket. This is because the space inside the wall is so tight. And you will find there is often no circuit box in the wall, which is a problem. This is due to space limitations caused by thin RV wall construction. Hence Winnebago uses their own custom made (sealed) wall sockets. So don't expect to go to Home Depot or Lowe's to find these if you need to replace one.
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Old 06-24-2018, 03:05 AM   #5
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I forgot to mention: If you your inverter output meter is showing AC Watts in the 1200+ range, when you think nothing is turned-on, and most certainly not an AC product like a hair dryer or room heater is plugged-in, then might first check to make sure the "Block Heater" as in the engine block heater switch (brown one) on your control panel was not flipped-on by mistake. This is more common than you think. So check that first!
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Old 06-25-2018, 07:35 PM   #6
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Quote:
Originally Posted by imnprsd View Post
Many have said the analog heated blankets -- and in particular analog heated mattress pads (the one with turn knobs) -- are safer then their newer designed blankets with digital displays; and I am inclined to believe that when you are using a MSW inverter.
I don't think the major concern is safety. The problem with using an electric blanket with digital controls on a MSW inverter is that the MSW inverter will "break" the blanket's controller and the blanket won't work after that, even on shore power.

Of course there's always the chance of something weird happening electrically, whether on shore power or an inverter, but I don't think it's more likely with an electric blanket than with anything else.

The lesson should be: Don't use an electric blanket with digital controls on a MSW inverter because it will break the blanket.


Quote:
Originally Posted by imnprsd View Post
This post was meant to point out the safety risks of using a heated blanket or floor heater at night when you are sleeping... WHEN POWERED BY AN INVERTER. (And especially when powered by an older MSW inverter.)
But I doubt most people will be running an electric heater overnight on the inverter--they don't have the battery capacity for it.

If you're using a compatible electric blanket (e.g. analog if on a MSW inverter), then I don't think there's any reason to think it will be any more dangerous on the inverter than on shore power.


Quote:
Originally Posted by imnprsd View Post
I forgot to mention: If you your inverter output meter is showing AC Watts in the 1200+ range, when you think nothing is turned-on, and most certainly not an AC product like a hair dryer or room heater is plugged-in, then might first check to make sure the "Block Heater" as in the engine block heater switch (brown one) on your control panel was not flipped-on by mistake. This is more common than you think. So check that first!
The block heater on my motorhome doesn't go through the inverter, for obvious reasons. Is it not like that on other motorhomes?
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