How do I...

[df909]

I want to run a portable electric heater off of my two deep cycle 6 volt RV batteries. The heater is 1600 watts and I have a 2000 watt inverter.

How do I figure out how long the heater can run before the batteries go to 50% and until they're discharged?

Thanks. By the way, I'm no super genius (I know, it's hard to believe), so please keep it fairly moron proof.

 

[veritas honus]

Re: How do I...

The stats listed on your batteries are assuming brand new and fully charged. You can do the math based on that and maybe come close, depending upon the condition of your batteries and heater. Temperature also makes a difference. The most accurate method is going to be trial and error. If you have a good battery gauge, and you keep an eye on it, you can have your trial without the error. You'll know when you've run them 1/2 way down. You'll know when you've run them 10% down, and so on. A voltometer will tell you the same thing, maybe more accurately. Do your first trial run with the heater set on medium (50%). This will give you a good idea of how much leeway you'll have either way (higher or lower). Good luck, and stay warm.

 

[jlinder]

Re: How do I...

Powering an electric heater is a very heavy draw on a battery. The formula is Watts = Volts x Amps, or W=V*A.

If you assume some inefficiency with the inverter you will be drawing about 1800 watts total power (not quite that but it makes the mathi easier). With your example you have 1800 = 12 *A (assuming you have the batteries connected to produce 12v). Solving for A you will be drawing 150 amps from your batteries.

Now take a look at your batteries. What is the amp hour rating? 225AH? If so you might think you could get 1.5 hours from a full charge (225/150).

But that would be wrong since AH (amp-hour) ratings for batteries are typically measures with a draw that would let the battery last 10 hours, and pretty sure you are doing a lot more than that. As a result you will get significantly less life. So while we can give you formulas that will only get you in the ballpark. Try it and see is the only accurate answer.

However, in the above example if you have 2 6volt batteries with 225AH rating I would say it would be significantly less than 45 min to a 50% charge (1800/12 = 150 amp draw, and 225AH/150 = 1.5 hours, 50% would be half that).

Also don't forget that if you plan on that high you need some really heafty wiring. I would think 00 gauge wire (assuming a short run) or better.

Hope that helps

 

[Don S]

Re: How do I...

so please keep it fairly moron proof.

The inverter will kick out due to low voltage, long before it gets warm in your RV. Inverters were never intended to run heaters, that is what Gen Sets are for.

 

[j_martin]

Re: How do I...

The inverter will kick out due to low voltage, long before it gets warm in your RV. Inverters were never intended to run heaters, that is what Gen Sets are for.

Or better yet a propane heater. A genset/electric heater combo will put about 20% of the fuel's heat into the camper. A propane heater will up that to about 80%.

 

[df909]

Re: How do I...

Hmmm...guess that settles it. Our propane heater in the camper doesn't always feel like working when I want it to, so I figured I'd cheat and bring the electric one. So much for that idea! I'm off to research how much a new camper heater is.

Thanks for all the info and that formula from jlinder will help with other stuff too.

 

[rbh]

Re: How do I...

Hmmm...guess that settles it. Our propane heater in the camper doesn't always feel like working when I want it to, so I figured I'd cheat and bring the electric one. So much for that idea! I'm off to research how much a new camper heater is.

Thanks for all the info and that formula from jlinder will help with other stuff too.

Ok, so this all started with a camper propane heater issue, maybe we can help with that as there are a couple of RV techs here.
Is it a forced air style or the older radiating style?

 

[MTboatguy]

Re: How do I...

Before getting a new one, double check the burner to make sure it is not dirty or possibly partially blocked. How old is the heater? does it have an automatic start feature, is it a forced air furnace with a blower in it? If it is an auto start forced air type, it will have an electronic control board in it, that requires a certain amount of voltage to work properly. So make sure your batteries are up to snuff.

 

[rbh]

Re: How do I...

I think our old style heater had a non electric thermocouple that would shut down the gas flow when the heat got to were we set the regulator?????
Do you have the manual??

 

[df909]

Re: How do I...

Sorry for the delay, I didn't know anyone responded to my post after my last message. It's an electronic start heater with the blower built in on a 2004 trailer. I called a couple of RV places and they recommended that I have it serviced. They made the point that it either works or it doesn't; if it were an intermittent issue like I'm having, then there's probably nothing major wrong with it. We've used it a lot, maybe 60-75 days in the past 2 1/2 years and I've never had it in for servicing. So...I'm learning about RV stuff as well as boating.