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Old 06-24-2014, 01:28 AM   #1
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Question regarding inverters at a very low load...

I have a question regarding inverters, and the power they consume with no load or very little load. Does an 80 watt inverter with little to no load on it use less battery power than say a 400 watt inverter?

Just wondering if I added an additional inverter to my motorhome, (and with the size based on my actual needs), if a small inverter does the job, does a larger inverter serve no real purpose other than maybe using more power? Or in low or no load situations, does it take the same power requirements? I'd like to install a larger one for the additional output receptacle, but not if it's more parasite drain on the batteries.

Thank you. -RT
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Old 06-24-2014, 01:57 AM   #2
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Yes, small capacity inverters have a lower idle power consumption rate than that of larger units...I think of it like a "tax" for having a large capacity.
Experienced boondockers use many smaller "point of use" inverters for this reason.

The reason to have a larger unit is for the largest load expected (often the microwave).

Because of these dynamics, when designing an inverter system, it is smart to use a mixture of small inverters at the point of use - that do most of the routine work. Then have a large one that will fit your needs, but where it does not need to run idle or under low load.

Best luck
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Old 06-24-2014, 03:29 AM   #3
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Yes smaller inverters are more effecient for smaller loads. I have multiple small point of use inverters, plus a large inverter wired for whole coach powering. large inverter is used to operate large loads such as microwave and powered off when not needed. Smaller inverters run the TV, sewing machine, most everything. My favorites are the Tripplite 150 and 375.

Also realize most inverters consume power at idle with no load, so select your inverters accordingly.
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Old 06-24-2014, 10:32 AM   #4
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Thank you Scarab0088 and vsheetz for the replies. My motorhome only has one 12v power outlet on the dash and with a portable GPS, iPod, cell phones and iPad that need to be powered when on the road. Even worse is that the outlet is mounted so high that when I use a dual outlet splitter, the weight of the cords pull the splitter out and I lose all power, with things going dead before I realize it. I'm trying to decide if I want to install a couple of dual 12v outlets, mounted low along the dash, or maybe an inverter floor-mounted near the passenger seat.

I guess another question is that as the inverter size increases and uses more power at 'idle', is it really that much of a difference and does it really need to be a concern? A 400 watt or so inverter would be the maximum I would install.

Any suggestions from owners that have done something similar? -RT
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Old 06-24-2014, 12:29 PM   #5
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Most RV's just don't have enough 12VDC outlets. I have added several at the dash and by the dinette for the exact reasons stated above.

Adding inverter power will be for other things that do not have 12VDC options (TV, DVD, Laptop charger, etc).

Just like Vince (Vsheets), I have a mixed system with a point of use inverter at the front passenger seat, and a 3000W whole house mounted near the batteries.

It is all in what the individual needs. If 400W is all you need - that's easy to add most anywhere. There is little need to break-up a load lower than 400W

Reminder for any inverter install, keep the 12VDC leads short (12VDC has higher voltage-drop over distance) and use a 110VAC extension cord as needed.

Best luck
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Old 06-24-2014, 01:31 PM   #6
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Most RV's just don't have enough 12VDC outlets. I have added several at the dash and by the dinette for the exact reasons stated above.
Hello Scarab0088;

I might go that route, which 12v power is mainly what I need, though the electronics could be run on 110v. Did you run separate wiring to each 12v power outlet? I'm thinking of one dual outlet near the bottom of the dash on both sides of the doghouse.
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Old 06-24-2014, 01:42 PM   #7
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Question regarding inverters at a very low load...

Even a small inverter draws quite a bit of power, so separate runs and separate inline fuses will be more efficient. Do you have a 12volt bus bar to connect to? How big, amp wise, is your alternator? You don't want to overload it.
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Old 06-24-2014, 02:44 PM   #8
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You won't get 400 watts from a 400 watt inverter plugged into a cigarette lighter plug. You'll only get 80 to 100. To get the full rated 400 watts you'll have to hard wire the inverter to a good 12 volt source > 30 amps with 8 AWG wire. Just a heads-up for you.
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Old 06-24-2014, 03:18 PM   #9
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Quote:
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Hello Scarab0088;

I might go that route, which 12v power is mainly what I need, though the electronics could be run on 110v. Did you run separate wiring to each 12v power outlet? I'm thinking of one dual outlet near the bottom of the dash on both sides of the doghouse.
I took power off the existing (20amp) cigar lighter for 2 add'l sockets for the GPS and cell phone charger - because I knew I would not exceed the original load rating.

I added a new direct feed (unswitched) to the chassis battery that doubles as a plug-in for a dashboard solar panel used when parked.

The added dual socket (12VDC and USB) at the dinette is connected to the power in the adjacent cabinet (powers several lights). If a high draw was needed there, I would have run a wire to the fuse panel, but we only plug in the GPS for route planning and cell phone chargers. The socket set was only $5 at Wal*Mart automotive section.

Best luck
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Old 06-24-2014, 07:19 PM   #10
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Originally Posted by Scarab0088 View Post
I took power off the existing (20amp) cigar lighter for 2 add'l sockets for the GPS and cell phone charger - because I knew I would not exceed the original load rating.

I added a new direct feed (unswitched) to the chassis battery that doubles as a plug-in for a dashboard solar panel used when parked.

The added dual socket (12VDC and USB) at the dinette is connected to the power in the adjacent cabinet (powers several lights). If a high draw was needed there, I would have run a wire to the fuse panel, but we only plug in the GPS for route planning and cell phone chargers. The socket set was only $5 at Wal*Mart automotive section.

Best luck
Okay, so I'll admit that I'm electrical-engineering challenged but like you, will probably go with the dual 12v power receptacles as the easiest solution, or the one 12v output and the dual USB receptacle. (A second project might be an inverter installation next to the passenger seat for a MacBook Pro, which I believe uses 85 watts.) I would likely hardwire back to the fuse block to either the cigarette lighter fuse or an unused 20A fuse. If the maximum for either of these is 20A, I would then make sure to stay within that maximum, probably allowing for some sort of safety margin. Not sure about the GPS, but the two cell phones are 1.0A each and the iPad is 2.1A, so I'm probably at no higher than 6A. It seems to me that I'm fine with all four electronics plugged in to two dual outlets, as long as I use the appropriate gauge wire. Typically when we stop, I unplug all those items so as to not negatively impact the battery.

Do I sound like I'm on the right page so far?

Thank you. -RT
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Old 06-24-2014, 07:26 PM   #11
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Okay, so I'll admit that I'm electrical-engineering challenged but like you, will probably go with the dual 12v power receptacles as the easiest solution, or the one 12v output and the dual USB receptacle. (A second project might be an inverter installation next to the passenger seat for a MacBook Pro, which I believe uses 85 watts.) I would likely hardwire back to the fuse block to either the cigarette lighter fuse or an unused 20A fuse. If the maximum for either of these is 20A, I would then make sure to stay within that maximum, probably allowing for some sort of safety margin. Not sure about the GPS, but the two cell phones are 1.0A each and the iPad is 2.1A, so I'm probably at no higher than 6A. It seems to me that I'm fine with all four electronics plugged in to two dual outlets, as long as I use the appropriate gauge wire. Typically when we stop, I unplug all those items so as to not negatively impact the battery.

Do I sound like I'm on the right page so far?

Thank you. -RT
Yep...sounds like a good plan

And a 100-150W Inverter is a nice option to have too. They are getting very affordable and you won't realize how useful they are until you have one.

Best luck
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Old 06-24-2014, 10:50 PM   #12
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Yep...sounds like a good plan

And a 100-150W Inverter is a nice option to have too. They are getting very affordable and you won't realize how useful they are until you have one.

Best luck
Thank you very much for all your help in this thread. Next step will be to determine what kind of access I have to that big dash. I know most of it is fairly flush to the carpeted base that the dash is attached to. Hoping to be able to do it from there, as I really don't want to disassemble the top of the dash. (One of the reasons I was thinking of an inverter just mounted to the floor.) -RT
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Old 06-24-2014, 11:42 PM   #13
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I have 12v power ports in the bedroom, dining, and front passenger seat area. Inverters at these points are Tripplite 150w and 375w units. These are well made with metal cases, draw no power when turned off, and the 150w unit has no fan (so no fan noise). The 150w units are most often used - DW's sewing machine, TV/DVD, etc.

For whole house I have a 2300w unit. Used for running the microwave, coffee pot, large food mixer, etc. Also on when traveling to power the refrigerator.

Here is a write up of my system, to include the solar charging.
Attached Files
File Type: pdf VSheetz - Solar Setup for my RV v1.1.pdf (473.7 KB, 24 views)
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Old 07-10-2014, 08:09 AM   #14
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bought inverter at walmart along with deep cycle battery.boondock a lot, so we can have power any where we want it. in or out of the mohome.
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