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Old 11-11-2016, 09:10 PM   #1
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Running off House Batteries !!!!

I know I am not the brightest bulb on the string of lights and I felt stupid when I got all upset because the standard plugs on the coach did not work off the house batteries. Then the man camping next to us reminded me that the house batteries are 12 volt and the outlets are 110.

So my question is .... what is needed so I can use the 110 plugs with out cranking up the generator?

Thanks .... hopefully one day I will have all the knowledge needed.
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Old 11-11-2016, 09:26 PM   #2
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You need either "Shore Power" (a term derived from marine use) which is plugging your 120 volt power cord into a fixed power outlet, or Inverter power from your 12 volt batteries.

Inverter info here:

https://youtu.be/jXwr6A37TY8
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Old 11-11-2016, 09:59 PM   #3
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Using "the outlets" is very difficult without powering up your generator because they are wired to your camper's power center breakers.

If you decide to go the inverter route you will need to use the outlets on the inverter and not the camper outlets. I did install dedicated inverter outlets by wiring the inverter outlet with a Romex Cable.
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Old 11-11-2016, 10:12 PM   #4
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Quote:
Originally Posted by Bluepill View Post
You need either "Shore Power" (a term derived from marine use) which is plugging your 120 volt power cord into a fixed power outlet, or Inverter power from your 12 volt batteries.

Inverter info here:

https://youtu.be/jXwr6A37TY8
Thanks for sharing that video .... provided lots of information.
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Old 11-11-2016, 10:14 PM   #5
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Using "the outlets" is very difficult without powering up your generator because they are wired to your camper's power center breakers.

If you decide to go the inverter route you will need to use the outlets on the inverter and not the camper outlets. I did install dedicated inverter outlets by wiring the inverter outlet with a Romex Cable.
That looks nice ..... Boy do I have a lot to learn.
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Old 11-11-2016, 10:20 PM   #6
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Or you could get a higher-end invertor and put it between your generator/line input transfer switch and your main panel. You can even get an option that will auto-start your generator when the batteries reach a certain level of depletion.
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Old 11-12-2016, 07:10 AM   #7
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I added a small 400 watt inverter to run small loads like laptops chargers while we are traveling. i.e. why run the generator to charge the laptop while on the road.

Installing small 400 watt inverter | 2001 Coachmen Mirada 300QB

..
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Old 11-12-2016, 08:08 PM   #8
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If you decide to go the inverter route you will need to use the outlets on the inverter and not the camper outlets.
Not necessarily. You CAN wire the entire camper to run off the inverter.

In fact, many newer units work that way, with automation in switching and protection.

If you retrofit an existing unit to work this way you will need to install switching that does not allow shore/generator power to be on line at the same time the inverter is and then you either need to use equipment that manages switching/loads, or manage them yourself. This requires knowledge of your loads and (oh horror) math.

(I have done this successfully on a variety of campers/boats).

To the OP, you will have to understand that unlike the endless power of the generator (as long as it runs), or the campground pedestal (as long as you are plugged in) running off an inverter is limited by the size of the inverter and the battery bank. If you want to charge a few phones a small inverter and your existing battery bank are OK. If you want to run a space heater, say one that draws 2400 W you would need a large (as in 3000 or more Watt inverter which would be drawing 2400/12 = 200Amps off your battery(s) (yes, the math thing). This is a LOT. In fact if you had a typical RV battery, it would be drained in, oh, 15 minutes or so.......

So, you need to understand how much draw you need and then size the equipment accordingly.
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Old 11-12-2016, 09:04 PM   #9
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Another caveat about using an inverter for 120AC is the requirement to practice power management. A 100W television will draw around 10A/hour from your battery bank. It doesn't take very long to deplete most RV battery banks unless they're designed to run an inverter for extended periods.

I have a remote building that's battery/solar powered. 660A of 12V batteries wasn't enough to support keeping the inverter powered on 24x7 with a base load of less than 50W. All worked well until there was three consecutive days of clouds then the battery voltage dropped too low to keep the inverter and minimal equipment running. That problem has been solved by running all of the equipment in the building directly from the batteries, using buck and boost DC-DC converters.

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Old 11-12-2016, 09:27 PM   #10
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And, to add one more tidbit..... an inverter will draw power when on, even if nothing is plugged in to it. Not much, but it adds up. In fact a large inverter will draw as much as 2-3 Amps...... Yup, that's 24-36 Amps over 12 hours.
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Old 11-12-2016, 09:31 PM   #11
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I have so much to learn!
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Old 11-12-2016, 10:25 PM   #12
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Oscar, what you say is true, but I suggest you wire your converter to its own circuit breaker so you can open it when attempting to run your house AC outlets with an inverter. Otherwise your converter will power up and try to use battery power (through your converter) to try and charge the battery. A vicious cycle that will run your battery down pretty quickly.

IMO, it is much easier to wire a dedicated inverter circuit so you absolutely know what is being powered by your inverter at all times.

Different strokes however...
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Old 11-13-2016, 08:17 AM   #13
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Oscar, what you say is true, but I suggest you wire your converter to its own circuit breaker so you can open it when attempting to run your house AC outlets with an inverter. Otherwise your converter will power up and try to use battery power (through your converter) to try and charge the battery. A vicious cycle that will run your battery down pretty quickly.

Absolutely correct, and I forgot to mention it.

(The tell tale is that the cooling fan of the inverter immediately kicks in.....)

I also did not mention that as part of these off the grid wiring schemes I installed an AC ammeter and/or a condition monitor to accurately monitor loads and/or battery state of charge. The ammeter pegging was also a dead giveaway for the converter still being on line.

That said:

As a professional aviator I have learned to appreciate check lists. (We always say they are written in blood.....) So I have checklists for "departing" (ex. TV antenna-down........Anyone? Those that have and those that will....... ) and for the campers wired as I discussed there was an "inverter" checklist. Not only was "converter-off" on there, there was also "fridge-propane" on there as running the fridge all night on the (smallish) battery bank would deplete it. I also tended to turn off the AC/Micro breakers so no one would accidentally activate either.

Still, I like the convenience of having every outlet, the XM radio,TV and DVD player powered so peeps can plug in phones/iPods/computers where they are sitting without having to run miles of extension cords. It also allowed me to run my exterior outlet to power the led's.
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Old 11-13-2016, 09:48 AM   #14
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Since nearly everything that requires AC when on battery lives at the living room TV, and at 150AH of bank capacity (2 75AH batteries) what can actually BE on battery (I.E. no coffee maker), it made a lot more sense to me to wire one outlet (2 actually as I put one in the basement for the outside TV) on inverter when boondocking with no shore power.

That way I can only be on Propane with the fridge; NEVER have to worry about having the water heater on AC, of the DW forgetting and plugging in her hair dryer and blowing fuses at the inverter.

A 15 amp power strip works great as a distribution system for the inverter provided power. When not boondocking, I just move the plug over to the outlet labeled "GFCI". No other checklist items needed.

Another pilot mantra is "If it's stupid, but it works; it ain't stupid."
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Old 11-13-2016, 10:08 AM   #15
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I know I am not the brightest bulb on the string of lights and I felt stupid when I got all upset because the standard plugs on the coach did not work off the house batteries. Then the man camping next to us reminded me that the house batteries are 12 volt and the outlets are 110.

So my question is .... what is needed so I can use the 110 plugs with out cranking up the generator?

Thanks .... hopefully one day I will have all the knowledge needed.
To parrot what other's said, the simple answer is that you will need and inverter to make 110v (from 12v batteries) without shore or generator power.

But, you might want to tell us more ... like what you plan to plug in.

What are you wanting to run on those 110v plugs, and how long do you want to run things (the instant load and the amp / hours)? Estimating these will lead you to how big an inverter; possibly what kind (pure vs modified sine wave) and how many amp hours of batteries you will need.

Lets say you only want to charge your electronic devices via the 110v plugs, all you need is a very small (400A) inverter wired out to a dedicated 110v plug and nothing more ... no more battery, etc ... but must be wired correctly and with proper wire gauges ... but, if you want to run a microwave, or a curling iron / hair dryer (1000w to 1500w), you have to step up your game; and could drive you to 2000W or more inverter / charger and could double your battery capacity requirement and will make you wish you are an electrical engineer.

Bottom line, all of us will share what we did, but your needs might be entirely different. There is no such thing as a one-size-fits-all solution and I don't have to tell you to take advice with a grain of salt; forums can be dangerous.
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Old 11-15-2016, 09:19 PM   #16
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To parrot what other's said, the simple answer is that you will need and inverter to make 110v (from 12v batteries) without shore or generator power.

But, you might want to tell us more ... like what you plan to plug in.

What are you wanting to run on those 110v plugs, and how long do you want to run things (the instant load and the amp / hours)? Estimating these will lead you to how big an inverter; possibly what kind (pure vs modified sine wave) and how many amp hours of batteries you will need.

Lets say you only want to charge your electronic devices via the 110v plugs, all you need is a very small (400A) inverter wired out to a dedicated 110v plug and nothing more ... no more battery, etc ... but must be wired correctly and with proper wire gauges ... but, if you want to run a microwave, or a curling iron / hair dryer (1000w to 1500w), you have to step up your game; and could drive you to 2000W or more inverter / charger and could double your battery capacity requirement and will make you wish you are an electrical engineer.

Bottom line, all of us will share what we did, but your needs might be entirely different. There is no such thing as a one-size-fits-all solution and I don't have to tell you to take advice with a grain of salt; forums can be dangerous.
WW
I want to be able to run a fan in the bedroom section and living room, I run a dehumidifier in the living room area and other small appliances .... my TV and house lights are already 12 volt.
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Old 11-16-2016, 06:42 AM   #17
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I want to be able to run a fan in the bedroom section and living room, I run a dehumidifier in the living room area and other small appliances .... my TV and house lights are already 12 volt.
I doubt you will be able to do all that at the same time on battery power without significant battery upgrades. Batteries add weight as the weigh approximately 60-75 pounds each depending on individual size.

Remember you can install a 5,000 watt inverter, but you will always be limited to the amount of power in hours your battery (bank) can continuously deliver.

Most OEM camper batteries are in the 75AH (Amp Hour) range (or 900 watt hours total capacity).

At a 5 amp delivery rate (60 watts) your battery will last 15 hours till it is deader than Elvis (5 amps * 15 hours = 75AH).

Doubling your battery in a parallel install will increase your capacity to 150AH so at a 5 amp draw, your bank "should" last 30 hours; BUT because the load is shared, each battery only has to deliver 2.5 Amps (30 watts).

At 2.5 amps the AH capacity actually increases above 75AH because of a battery phenomenon called the Peukert Effect. That same effect "eats" battery capacity the larger the draw you demand (see chart attached).

So at say, 30 amps (30 amps * 12 volts = 360 watts) your brand new 75AH battery will be dead after delivering only 54% of it's rated capacity (40.5AH). 30amps continuously at 12 volts is about an hour and 20 minutes (40.5AH divided by 30 amps = 1.35 hours). See attached graph.

In Layman's terms, it is easier to suck coke through a straw than milkshake.

Adding straws (batteries) allows you to get more coke or milkshake (battery's ability to deliver power) with less work (demand per straw) and your drink (battery bank) can last longer by sharing the drink (amp demand) with more straws.

That same 30 amp continuous demand shared across 2 batteries, results is only 15 amps demanded per battery AND you have more capacity to work with! The doubled capacity (150 AH) is now only reduced by 68% (or 51AH) giving you an available (usable) capacity of 102AH.

That 30 amp (360 watt) load will last 102 divided by 30 or just shy of 3 hours and 25 minutes.

A 1500 watt coffee maker running off of a 3000 watt inverter still needs 1500 watts from your battery bank. 1500 watts divided by 12 volts is 125 Amps. Even with two batteries, you will still need to draw 62.5 amps from each battery.

That is like trying to suck cement through that straw!

Now many will be quick to add that you will most likely never put that kind of demand on your bank continuously using the TV, charging your phones, running your lights for a few hours, water pump momentarily, etc. so the batteries will last much longer than the examples of continuous draw.

If you plan to use your heater (biggest demand besides your inverter), you can toss most of the inverter use out the window with only one battery.

Here is a discussion on battery bank sizing for inverter use that can be useful.
Solar Design Worksheet

A typical RV propane heater draws about 8 amps by itself when running but does not run continuously so the demand on your battery will be temperature dependent. Each incandescent bulb in your fixtures draw 1.2 amps per bulb.

You will see that demand on your batteries adds up quickly before you add the increased demand from the inverter.

Since dehumidifiers are actually little air conditioners, the startup load (called inductive LRA if you want to look it up) on the compressor can actually spike amperage demand on a smaller battery bank well beyond the battery bank's capability to deliver any voltage at all, placing the inverter into alarm and shutting it down due to low voltage.

I hope this helps a little. I know it is a lot to take in all at once.

Baby bites will help you understand what is going on and will save you the money I wasted when I did not know what I was doing and just threw money at the problem of camping without daily generator power.

Herk
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Old 11-16-2016, 07:05 AM   #18
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I looked up some Watt needs for some of your items:

A typical box fan requires an RA (running Amps) of about 1 amp AC (120 watts)
Startup load (LRA) can over 150% of RA so peak demand of around (180 watts)

I had a harder time locating the Wattage on a portable dehumidifier.
Could you post the numbers from your data plate?

Herk
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Old 11-16-2016, 09:15 AM   #19
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I looked up some Watt needs for some of your items:

A typical box fan requires an RA (running Amps) of about 1 amp AC (120 watts)
Startup load (LRA) can over 150% of RA so peak demand of around (180 watts)

I had a harder time locating the Wattage on a portable dehumidifier.
Could you post the numbers from your data plate?

Herk
Lots of good info ... thanks ... as soon as I get my rig back from CW I will post the info off the dehumidifier.
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Old 11-17-2016, 09:59 PM   #20
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......

Most OEM camper batteries are in the 75AH (Amp Hour) range (or 900 watt hours total capacity).
..........

At 2.5 amps the AH capacity actually increases above 75AH because of a battery phenomenon called the Peukert Effect. That same effect "eats" battery capacity the larger the draw you demand (see chart attached).
.........

Herk
There's also a marketing factor at work here that effects battery capacity. Deep cycle batteries used to be rated using a load that's 5% (20 hour) or 10% (10 hour) of the rated capacity. Many I've seen in recent years actually have their capacity determined with a 1A load placed on the battery. This increases the "rated" battery capacity but does nothing to help us for normal RV use. The 75AH battery Herk7769 mentioned will probably be marketed as a 100AH battery.

When comparing batteries, you should always use the "reserve capacity" rating. This number (of minutes) is determined using a published testing standard that is designed to provide accurate battery capacity ratings. For most of the 12V deep cycle batteries used in our rigs, the battery is fully charged, allowed to sit long enough for the surface charge to dissipate, then a 25A load is placed on the battery and the number of minutes it takes for the voltage to drop to 10.8V is measured. I'm not sure what the requirements for rounding off partial minutes at the end of the cycle are but the most difference that could cause is one minute.

Golf cart batteries are tested the same way with one major difference. The load placed on the battery is 75A. Obviously, a 6V golf cart battery will be tested to 5.4V, half of the 12V standard. The Puekhert effect also means that multiplying a golf cart battery's reserve capacity by 3 (25A vs 75A) should understate the battery's reserve capacity when comparing it to a battery rated with the 25A load.

Phil
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