re hard wiring a 300 watt inverter to my motorhome - Fiberglass RV

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Old 09-12-2013, 07:42 AM   #1
Junior Member
Name: john
Trailer: lunar
isle of wight
Posts: 1
re hard wiring a 300 watt inverter to my motorhome

Hi all. I am a new member and I am looking for help with wiring in my 300 watt inverter to my motorhome.

Can anyone tell me how I need to wire it in to the main engine system and charging system.

I can do some electrics but need help with this.

Look forward for your help.

Thanks John

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Old 09-12-2013, 07:50 AM   #2
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cpaharley2008's Avatar
Name: jim
Trailer: 2019 2ndG Escape21 DeJa View pulled by 2014 Dodge Ram Hemi Sport
Posts: 6,641
Welcome to FGRV John,
We are a forum of molded fiberglass trailers, no motor homes. Although we may share similar modifications, you may be better posting in another forum. Good luck with your search, let's hope you may get some responses here or elsewhere.

Never in doubt, often wrong
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Old 09-12-2013, 09:32 AM   #3
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David Tilston's Avatar
Name: Dave W
Trailer: Trillium 4500 - 1977, 1978 (2), 1300 - 1977, 1973, and a 1972
Posts: 5,853
I will take a stab at it.

I would wire in a separate auxiliary battery. It would be in parallel with your vehicle battery, except, I would wire in a battery solenoid that closes when your engine is running. This way, you have some power after you turn off the engine, without worrying about draining the battery. The inverter, (300 watts?) would then connect to the aux. battery. I would also think about getting a bigger inverter.
Be sure to size the wire to the aux battery, and to the inverter appropriately. The battery wire should be the same size as the wire from your current battery to the alternator. At 300W, your inverter should not be drawing much more then 25A.
I suppose you could skip the second battery, and just use the solenoid.
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Old 09-12-2013, 09:55 AM   #4
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Name: Byron
Trailer: 2006 Scamp 13' towed with a 2005 Dodge Dakota 4.7l Magnum W/full tow package (over kill)
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As with all things electrical and propane I strongly recommend that if have to ask take it to somebody that knows. If a business screws up they're liable, if you screw up you're liable. The loss of a motor home or trailer just isn't worth the risk.
Byron & Anne enjoying the everyday Saturday thing.
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Old 09-12-2013, 10:33 AM   #5
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Name: Brian
Trailer: Boler (B1700RGH) 1979
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What David refers to as an auxiliary battery is also known as the coach battery in motorhomes... and yes, what he describes is standard good practice. The vehicle battery is sized and specified to suit engine starting requirements and other vehicle systems; the coach battery is sized and specified for RV needs. For instance, my Ford gas chassis motorhome has a typical 12V vehicle starting battery like any gas Ford truck, and the coach has a much larger set of two 6V deep-cycle batteries.

The motorhome's coach battery is just like a trailer's battery: it is connected to the vehicle charging system by a suitable isolation device, it normally gets charge by a shore-powered charger as well, it supports all coach loads such as an inverter to run appliances, and it is of a different size and type from the motor vehicle battery.

Motorhomes often have one feature not found on trailers: a switch can be used by the driver to temporarily connect the coach battery to the vehicle battery to assist with starting in an emergency (such the vehicle battery having run down due to problems starting, or leaked down over a long period of not being used). This would generally not be appropriate for a trailer because the wiring between tug and trailer is not heavy enough, but the corresponding connection in motorhomes can be thick cable.
1979 Boler B1700RGH, pulled by 2004 Toyota Sienna LE 2WD
Information is good. Lack of information is not so good, but misinformation is much worse. Check facts, and apply common sense liberally.
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Old 09-12-2013, 11:42 PM   #6
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Name: Brian
Trailer: Escape 13 ft 2010 ('Ladybug') / 2003 Subaru Forester/ 2012 Toyota Highlander
British Columbia
Posts: 387
I installed a 300 watt inverter in our trailer, and installation was quite straight forward. The manual that came with your inverter should provide some guidance. Here is a link to the manual for our inverter: In the UK you will need a 50 cycle 230 volt equivalent.

Is your motorhome similar to this?

Some things to notice:
  1. The inverter should be located close to the battery you use for lights and appliances. It is possible you have only one battery in your motorhome. It is recommended to reduce the risk of explosion that the inverter not be in the same compartment as the battery.
  2. You need to use heavy cables between the inverter and battery. Our inverter came with 4 foot #10 AWG stranded wire (#12 SWG)
  3. Insert an adequate fuse between the battery and the inverter
  4. Make sure to ground the inverter. Our inverter recommended #8 AWG (#10 SWG) stranded wire.
  5. Don't connect the output from the inverter to the alternating current (AC)(mains) distribution system[/B] -- use a separate outlet for the AC power from the inverter or just use the outlet on the inverter itself.
  6. An alternative is to use a transfer switch, but this is more complex -- you had better read up on this if you want to go this route
  7. Good idea to have a remote on/off switch for the inverter as it will consume power even when there is no AC load. Alternatively turn the unit off when you are not using it.
  8. If you have sensitive AC appliances consider a true sine wave inverter

You can find more information on our installation here:
Brian & Maria
2010 Escape 13 "Ladybug"|2003 Subaru Forester|2012 Toyota Highlander
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Old 09-13-2013, 05:29 AM   #7
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Name: Donna D
Trailer: Escape 5.0 TA, 2014
Posts: 25,109
Hi John, I suggest you asked your question at a forum dedicated to your motorhome type: iRV2 Forum | - RV Forum Community and RV News which is owned by the same group that owns FiberglassRV. You'll find equally kind and helpful people there.

Best of luck

Donna D.
Ten Forward - 2014 Escape 5.0 TA
Double Yolk - 1988 16' Scamp Deluxe
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