Inverters and Power Draw - Fiberglass RV


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Old 10-14-2011, 10:28 AM   #1
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Inverters and Power Draw

Rainy day in NH.

Thought I'd make some measurements of Inverter current drawer. As most know an Inverter takes 12 volts, typically from your battery, and converts it into 110 Volts AC. 110 Volts AC is what you find at most home outlets.

My goal is to measure how much the Inverters devices draw from the battery under no load conditions, with nothing plugged into their AC outlets.

We have five Inverters; 2 of them are 100 watt Inverters

Interestingly the 400 watt Inverter, the biggest of the three I tested, drew the least when attached to the battery and nothing plugged into it's AC outlets. (It is not presently easy to test the 1200 watt Inverter but I will when I get my watt meter.

100 watt Inverter draws 0.3 amps
200 watt Inverter draws 0.35 amps
400 watt Inverter draws 0.1 amps
1200 watt Inverter draws ???

After looking at their current draw with nothing plugged into their AC outlets I loaded each Inverter with our LCD TV, electric blanket and Dish satellite receiver to see what the Inverter draws from the battery to run these devices.

Our Sylvania TV drew about 3 amps from the battery, indicating it uses 36 watts.

Our Sylvania twin electric blanket drew about 5 amps when fully on, indicating it draws 60 watts when fully on.

Our Dish Satellite Receiver draws about 1.2 amps when fully on, indicating it draws 15 watts.

15 inch Sylvania TV draws 2.9 amps from the battery.
Twin Electric Blanket draws 5.5 amps from the battery.
Satellite Receiver draws 1.2 amps from the battery.

For comparison an individual LED lamp draws about 0.2 amps from the battery.

All 7 LEDS 1.4 amps from the battery.
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Old 10-14-2011, 11:53 AM   #2
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So it appears you can turn on the satellite and the tv as well as all the lights for the same amount as keeping your buns warm, tough choice!!
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Old 10-14-2011, 12:18 PM   #3
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Was the 400W consistent in being the best when loaded? Compared to the other 2.
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Old 10-14-2011, 01:08 PM   #4
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My main goal was to see what the TV, Receiver and electric blanket drew from the battery.

I actually didn't make comparative measurements when the Inverters were loaded. I did run the each of the three loads on all of them and the numbers were similar. When I get my precision watt meter I'll more accurately compare them.

What I concluded is that running the TV and Electric blanket will have little negative effect on the battery.
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Old 10-14-2011, 01:27 PM   #5
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Quote:
Originally Posted by honda03842 View Post
My main goal was to see what the TV, Receiver and electric blanket drew from the battery.

I actually didn't make comparative measurements when the Inverters were loaded. I did run the each of the three loads on all of them and the numbers were similar. When I get my precision watt meter I'll more accurately compare them.

What I concluded is that running the TV and Electric blanket will have little negative effect on the battery.
Isn't 5.5 a/h a lot of draw for the electric blanket off your battery? Certainly more than your furnace, who do you consider that negligible draw? That would kill a 100 a/h battery over night.
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Old 10-14-2011, 03:30 PM   #6
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Power Usage

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Originally Posted by cpaharley2008 View Post
Isn't 5.5 a/h a lot of draw for the electric blanket off your battery? Certainly more than your furnace, who do you consider that negligible draw? That would kill a 100 a/h battery over night.

The high current for the electric blanket is it's maximum draw, when it's fully on. We typically only turn it to Preheat (fully on) before we get in bed for maybe 10 minutes and turn it down to a much lower setting when sleeping.

Though I haven't done the test I would be surprised if the duty cycle is more than 25% after completing the preheat cycle. I expect it will average no more than 1.5 amps per hour, a guess for sure but it definitely would be less than 5 amps. When I get my watt meter I'll run it for 8 hours and get a 'watts used number'.

As well it is not uncommon for us to shut it off totally during the night, I guess I like getting into a warm bed.

We never run the Propane furnace when sleeping we find it too loud. If we feel we're going to really need heat during the night we camp with services and sometimes turn on the electric heat, but rarely. Our secondary rule is not to be places that are truly cold, below freezing.

Another interesting point is a typical human body produces a 100 watts of heat output just lying there, like 3 electric blankets. I suspect body heat is why those penguins stand in those big circlular groupings.

Part of the reason we RV is to avoid NH like winters though we've been to Labrador in the Spring where snow could be found taller than my 6'1" height.

More data to come but it's a reasonable starting point...
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Old 10-16-2011, 12:31 AM   #7
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Quote:
Originally Posted by honda03842 View Post
Rainy day in NH.

Thought I'd make some measurements of Inverter current drawer. As most know an Inverter takes 12 volts, typically from your battery, and converts it into 110 Volts AC. 110 Volts AC is what you find at most home outlets.

My goal is to measure how much the Inverters devices draw from the battery under no load conditions, with nothing plugged into their AC outlets.

We have five Inverters; 2 of them are 100 watt Inverters

Interestingly the 400 watt Inverter, the biggest of the three I tested, drew the least when attached to the battery and nothing plugged into it's AC outlets. (It is not presently easy to test the 1200 watt Inverter but I will when I get my watt meter.

100 watt Inverter draws 0.3 amps
200 watt Inverter draws 0.35 amps
400 watt Inverter draws 0.1 amps
1200 watt Inverter draws ???

After looking at their current draw with nothing plugged into their AC outlets I loaded each Inverter with our LCD TV, electric blanket and Dish satellite receiver to see what the Inverter draws from the battery to run these devices.

Our Sylvania TV drew about 3 amps from the battery, indicating it uses 36 watts.

Our Sylvania twin electric blanket drew about 5 amps when fully on, indicating it draws 60 watts when fully on.

Our Dish Satellite Receiver draws about 1.2 amps when fully on, indicating it draws 15 watts.

15 inch Sylvania TV draws 2.9 amps from the battery.
Twin Electric Blanket draws 5.5 amps from the battery.
Satellite Receiver draws 1.2 amps from the battery.

For comparison an individual LED lamp draws about 0.2 amps from the battery.

All 7 LEDS 1.4 amps from the battery.
I hope you don't mind this question. But how do you measure the energy draw from your inverter and the individual appliances. If you use a voltage meter, where do you get one, and how do you use it?

I have a radio, which will be in use for a couple of hours each morning; and from the time I get back to the trailer in the late afternoon till lights out. I also may have to recharge some of my dog training equipment all night long.

Thanks for another helpful thread.

JMP
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Old 10-16-2011, 07:46 AM   #8
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Energy Requirements

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Originally Posted by Jane P. View Post
I hope you don't mind this question. But how do you measure the energy draw from your inverter and the individual appliances. If you use a voltage meter, where do you get one, and how do you use it?

I have a radio, which will be in use for a couple of hours each morning; and from the time I get back to the trailer in the late afternoon till lights out. I also may have to recharge some of my dog training equipment all night long.

Thanks for another helpful thread.

JMP
Jane,

Virtually all devices have a wattage rating on them. If you send me a list of items and their wattage I can give you a pretty good idea of what you'll need and your batteries ability to recharge them. Just PM me with the items.
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Old 10-16-2011, 10:46 AM   #9
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True, max wattage must not exceed the inverter capacity, but keep in mind that once it is connected, the inverter is drawing power even idle !!! it can drain your battery doing just nothing. If you can eliminate AC accessories and use only DC versions (such as power transformers and AAA / AA battery chargers, etc) you will greatly extend the power of your 12V RV battery.

The other problem is that a powerfull AC draw (electric blanket) will result into a very amp draw: You will likely have to increase the 12V wiring gauge and fuses that feed our 12V inverter, preferably on a dedicated circuit.
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Old 10-16-2011, 01:39 PM   #10
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Nice work Norm and much appreciated. I'll be looking forward to some more measurements when you get the watt meter.
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Old 10-16-2011, 01:56 PM   #11
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Interesting thread. I wondered about energy usage of an inverter.

I also have wondered how much amperage is wasted by the inverter during actual use of 12v appliances.... whether the amp usage of the inverter itself increases as it works harder (although if it gives off waste heat, that heat is not truly wasted during a cold night). I suppose one would have to be able to measure the appliance's draw directly from, say, the car's cigarette lighter plug, and then compare that to the draw of the inverter-appliance combo?
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Old 10-16-2011, 08:16 PM   #12
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Interesting thread. I wondered about energy usage of an inverter. (...)
At least on my inverter, there is a ON/Off switch
I've experienced very quick battery drain simply with 110V AA/AAA battery charger. Based on the fact the inverter casing gets warm even idle, I think it may depend on the internal circuitry. Any 110V appliances connected to it also use power when idle: it is called Standby power...Standby power - Wikipedia, the free encyclopedia. It can vampirize your RV battery faster than you may imagine.
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Old 10-16-2011, 08:22 PM   #13
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Martin

We have a large Inverter for the big items and it is located as close as possible to the battery. It is under the front couch. The Inverter Power cords to the battery are thick and as short as possible and go directly to the battery. (The Converter is located beside the Inverter and has it's own wires that run to the battery as well.)

The Large Inverter is right next to an AC outlet. We unplug the Converter from that outlet and plug the AC output of the Inverter into that outlet so the AC from the Inverter feeds back thru the Breaker Box to all other outlets in the trailer. The biggest thing we ever run off the Inverter is our four cup 600 watt coffee pot. It only runs for probably 5-10 minutes for morning coffee.

The small inverters we use are for running the TV and/or Sat dish in the evening and together they draw about 50 watts and that's maybe 4 hours a night. That load represents only about 4 amps from the battery, a rather light current draw for any wire in our trailer. The small cigarette lighter Inverters (100 watt) plug into cigarette lighter outputs. We own two, one for the car and one for the trailer ($20 at Walmart by Black and Decker.)

As to Inverter efficiency, the small ones seem to be relatively efficient. In the small Inverters it seems to be the order of 4 watts or less to run the Inverter. I'm not sure what it is for the large one but I'll know and post it.

Thank you for your thoughts, power usage is important to think about.
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Old 10-16-2011, 08:33 PM   #14
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I'm amazed at all the effort one takes to make a pot of coffee using a battery. Why not use the stove and a coffee maker. I envisioned with dual batteries,LEDs and a solar setup that everything in the trailer would operate off 12v or propane, with no 120v needs. You can just about buy any appliance now that operates off 12v albeit some are inefficient, but that is why you have propane, for your refer, heat, and for cooking. Why not eliminate any 120v use unless you have hookups?
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