How to hook up battery to breaker Box

[Carmella & Kevin Byers]

 

Hello, I have been trying research this on the web but have been having a hard time finding direct answers to my questions.

We have a 12ft trailer that has had all the wiring pulled for a remodel however we left the breaker box. I would like to add 2 6v batteries to the trailer to run the few lights, outlets and an electric burner for cooking.

So my question is, how do you wire the battery up to the breaker box and still leave a plug in for when there is shore power?

What I do know is that we will need and inverter from the battery to make it A/C but the invertors that I see on-line all have a cigarette lighter hook up. Is there one that can be connected to the battery cables? Then how do I wire the inverter to the breaker box? Or is there a special inverter for just this need?

Lastly, how will the batteries re-charge, if I am hooked up to shore power will they re-charge?

Thank you

Carmella

[Matthew Tritt]

Carmella,

You need two distinct wiring systems, each distributed and protected by their own distinct breaker panels. The breaker box you have is an AC version? You can distinguish this by looking at the breaker(s), which will be plainly marked as AC. DC distribution panels are readily available through alternative energy sales outlets, or I can sell you one. :-)

 

The system goes like this:  Batteries make the central core of the system. Energy inputs to the battery can consist of A. Vehicle alternator connected via a coupling at the hitch. B. DC source such as photovoltaic panel(s) mounted to trailer or arrayed at camp site on the ground. C. AC generator, which can also supply AC to your AC panel, supplying power to a battery charger, or D. Shore power cord connected to external AC hookup powering a battery charger or E. On-board AC/DC power converter-charger that is powered by any AC source listed above.

 

DC energy supplied by the battery (single or multiple batteries count as a "battery") feeds both the DC distribution panel and DC/AC inverter. Breakers or fuses are required between the battery and the inverter and between battery and DC loads, a main high amperage fuse and smaller individual fuses/breakers for each individual circuit.

 

If you understand and are comfortable working with electricity there's no reason you can't do the work yourself. If you aren't, you'd be better off to hire someone who is, preferably with a license.

 

Ask any questions you want!

 

Matt

[Matthew Tritt]

Carmella - again - I forgot to address your inverter questions, so let me try.

The type and capacity of your inverter is dictated by the expected total AC demand for the RV. If you can do without AC, then the size and type of inverter can be kept at a minimum, let's say around 1 kW. In this range there are a number of very good units available, none of which connect to DC via a cigar lighter, and all require external protection in the form of a breaker or fuse. The best one I can think of right off would be the Magnum MMS1012, which has a pure sinewave output (good for sensitive electronics. These are high quality industrial devices that you won't find in a truck stop or auto parts store that I have used for small off-grid residential applications.

 

Matt

[Bruce]

I am wondering about the capacity of the batteries when it comes to running an electric burner/stove element.  I think a burner would drain the battery very fast.

Bruce

[Jimco_W001]

A big battery bank can do it but you need some way to recharge them.I use my alternator when driving or the charger in the inverter/charger when plugged into 120 volts A/C.Right now I'm using a Heart Interface model.It can surge to 3000 watts AC from 12 volts DC and has an auto transfer switch so when you are plugged into 120 volt AC power it feeds the AC power right through to the AC breaker box and uses some of that power to charge the batteries.The 12 volt house fuses are just hooked up to the same battery bank.With this system I no longer need a 120 AC CONVERTER to 12 volts DC to run my 12 volt DC loads.

[Matthew Tritt]

Good way to go, but this guy has a 12' trailer. A 3 kW inverter isn't going to cut it in his case, and the battery bank would need to be way big for the space and load capacity of the springs.

Cook with gas!

[Jimco_W001]

The 3000 watts of AC power from the battery bank by way of the inverter/charger in my Class A 17' motorhome works great for me.The 4 G24 sealed gel cell batteries are 60 pounds a battery.

[Matthew Tritt]

Actually, Watts is a measure of volts X amps and equals power, not capacity. Ampere hours is the true measure of storage capacity, which is why batteries are rated in amp hours - not Watts. A 60 lb battery is usually something in the order of 75 to 100 amp hours, depending on the discharge rate and fixed time (ie: "20 Hr rate").

My little MH has 2X 220 amp hr 6 volt VRLA batteries for 220 amp hours capacity @ a 100% discharge rate @ 12 VDC - but remember that you can only draw the batteries down to a maximum of 50% state of charge without damaging the batteries. This means that I have an effective amp hr capacity of only 110 amp hours - and that's with 200 lbs of batteries.

[Matthew Tritt]

Forget electric burners and use propane. Resistive loads (like hotplate coils) will nail even large capacity batteries quickly and propane is a much faster heat source.

[Jimco_W001]

In the 20 years of operating my 1970 Winnebago model F-17 with 12 volt battery power and a big 12 volt DC to 120 volt AC inverter its been nice to have an all electric motorhome.I changed it way back then.Haven't spend  money on propane gas for this unit ever!

[Matthew Tritt]

It's great that you're happy with all electric, but for those of us who enjoy dry camping and can't tolerate a generator running much of the time, propane is virtually indispensible. I have to add that I've been in the business of designing and building off-grid power systems for >30 years and am a big fan of big deep-cycle batteries and all things DC, so admitting that I like propane is, well, kind of a cop-out. But the BTU conversion from natural gas, LNG and propane is far superior to that of jamming electrons through a resistive load to extract heat in amounts great enough to heat a living space. If you compare an all-electric residential energy bill to that of the exact same home with virtually identical useage, but run with gas heat, the electricly heated home will run about 50 to 100% higher costs in a temperate climate. It's the same thing in an RV or boat.

 

I know that the downside to propane is the risk of blowing yourself to the moon, but a well maintained system operated with informed caution is, I think, just about as "perfect" and energy source for heating, refrigeration and cooking (all heating!) as is currently available.

[John "T" Nordhoff]

  I agree Matthew, I do a bunch of dry camping and use Propane for my fridge, hot water heater and furncace ID HATE TO CARRY ENOUGH BATTERY CAPACITY AND SOLAR TO TRY TO DO ALL THAT ELECTRICALLY YIKES. Actually 30 Lb of propane is relatively cheap (My last was $1.69/) and you can get an awful lot of run time especially from the fridge and hot water out of $20 worth of LP. Of course, if its real cold now that furnace can suck some LP butttttttttttt imagine trying to carry enough batteries to heat with electrical energy !!!!!!!!!

 I have 375 Amp Hours of battery energy storage capacity and that coupled with a roof top solar panel, an Onan 4 KW Genset, 110 gallons of fresh water storage and 30 # LP allows me to dry camp a longgggggggggg time and have all the hot water and cold LP Fridge and occassional furnace I need. No way I could justify enough battery storage and charging capacity (and all that cost) to give me hot water and heat and a cold fridge for extended periods if I wanted to go all electric. Give me the combination of electric and LP RV anytime.  

 

 But to each their own and Im happy with my set up and wish others the best with their RV set up be it all electric or LP/Electric combination (like mine) or Coal  lol

 

 John T

 

[Matthew Tritt]

No kidding. My rig, a 73 Hall GTC, has a propane Suburban "Trail" forced-air furnce, a 3-way fridge that mainly stays on propane* and a water heater that is heated via a heat exchanger by engine coolant and by 120 AC when on shore power or generator. All this stuff is original equipment and works well, with the exception of an annoying "ting - ting - ting" that the blower fan makes in the furnace before it's heated all the way up. It especially annoys my wife..........

 

I bet that what some people don't know about their RV reefers is that, with few exceptions, they do their cooling with heat - not a compressor as found on residential refrigerators. The heat required to do the cooling works best and most efficiently when the source is the flame provided by propane. When electricity is used without propane to do the cooling it is converted to heat (resistance), which is hugely inefficient compared to gas. My 3-way even will work on 12 volt DC to do the cooling, but one would have to be pretty much out of their mind to use this mode any other way than when on the road with the engine alternator doing the work. Even with my 220 AH battery bank, the SOC would be down to 50% in no time running on batteries alone. Baaaaaaad!

 

My propane tank holds 13 gallons. Since you can only fill a tank to 85% by volume, it effectively holds 10 gallons. @ 4.2 lbs/gallon, that comes to 42 lbs of useful capacity. I know because I filled it this morning @ $3.85 per gallon! Do you own a propane station? ;-)