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Old 05-22-2012, 11:44 PM   #1
Toothman
2006 OM647 5 cylinder eng
 
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Default Will I overload the inverter?

I have a 400 watt Superex power inverter that my tv is plugged into. If I wanted to unplug the tv at night and plug in a 360 watt electric blanket would the initial surge turning it on, put me over 400 watts and blow the fuse? Would I draw less from the house battery by using the electric blanket compared to running the furnace? Haven't been able to figure out how many watts the furnace blower uses. thanks
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Old 05-23-2012, 01:00 AM   #2
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Default Re: Will I overload the inverter?

I use a electrowarmth.com 12 volt 36" x 60" heating pad under the sleeping bag. Its maximum amps is 6.2 or only 75 watts. Having the heat under you instead of on top of you is better. I have found that the combination of the refrigerator running and heating pad uses less power than the combination of the refrigerator and the Espar water heater I used before. Let van get cold inside so refrigerator runs less and stay warm with the heating pad. The heating pad has 7 settings and I use the lowest # 1 setting. If it is 12 volts you do not need to run the inverter so it is also quieter.
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Old 05-23-2012, 01:49 AM   #3
Charlie
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Default Re: Will I overload the inverter?

According to the Superex website, your inverter has 1200 watt surge protection. They don't say exactly what that means, (e.g. how long can it handle 1200 watts?) but at least they have tried to do something.

Even without any surge protection, you should be ok because an electric blanket is a purely resistive load and will not require the high inrush power of a highly reactive load such as an electric motor.

I think the bigger question has to do with overall energy consumption. Best case, a small inverter will be 90% efficient, so you will be drawing 360/0.9 or 400 watts from the battery bank. At 12.5 volts, that is 32 amps. If it stayed on full time for an 8 hr sleep, that is 256 amp-hours. I assume the blanket has a thermostat and is not on full time, but I suspect the energy use will still be high. How big is your battery bank?

Dave has looked into and posted on this problem in detail. Check his previous posts. If you are careful like Dave, you can make it work, but it is easy to go wrong using 12v batteries for heating.

As far as your furnace fan goes, you should be able to look it up. The standard Atwood small furnaces draw about 2.9 amps. I purchased the model 8012 with a low power fan that draws only 1.8 amps. (And is somewhat quieter) Once you find the power draw, estimate the duty cycle and compute the nights energy use. We tend not to use our furnace at night as it wakes us up. We preheat the van with the furnace, use two down comforters during the night, then in the morning we heat the van again with the furnace.

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Old 05-23-2012, 03:57 AM   #4
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Default Re: Will I overload the inverter?

Most inverters, even the cheap ones, have a double power surge handling; thus a 400 watt inverter will handle 800 watts for a short amount of time. My 400 watt inverter is about 10 years old, and is getting tired. It screams when I plug in my laptop if the motor is off now. I'm going to get an 800-1000 watt cheapo to use for the next 10 years. They seem to always be on sale at Harbor Freight for $60-70.
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Old 05-23-2012, 04:25 PM   #5
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Default Re: Will I overload the inverter?

Just to add a bit more information on the heating pad. I emailed the mfg. and asked what the amperage draw is at the # 1 setting that I use. The web site says 6.2 amps maximum. The reply I got from the mfg. stated that when it is on it draws 6.2 amps. They cycle it on/off for the lower settings. I know I do not use 6.2 amp x 8 hrs (run time) = 50 amp hrs. each night. That would discharge my 255 amp-hr battery down to 80% SOC. The most I have seen it discharge with the heating pad is 8%. The 8% discharge includes the heating pad and the 80 liter refrigerator. If I assume the refrigerator and heating pad use equal amounts of power, then the heating pad alone uses about 10 amp-hrs for the night.
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Old 05-23-2012, 05:00 PM   #6
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Default Re: Will I overload the inverter?

Thank you for all the information and suggestions folks.
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