Battery time of use wth inverter - RV-Dreams Community Forum

burdy · RV-Dreams Community Member

Battery time of use wth inverter

azrving · RV-Dreams Family Member

http://www.donrowe.com/inverters/inverter_faq.html#how_long

RetiredGuy · RV-Dreams Community Member

It is very easy to compute the answer to your question. You need to know the amp-hour rating of your battery bank. For my example I'll assume 100 amp-hours.

First compute the amps you are drawing:

amps = watts / volts

amps = 500 / 12

amps = 41.7

Then compute how long your battteries will support this load. Most recommend you use no more than 50% of your battery capavity. So if your battery bank is rated at 100 amp-hours, you have 50 amp-hours available.

hours = amp-hours available / amps

hours = 50 / 41.7

hours = 1.2

So for a 100 amp-hour battery bank, you can expect 1.2 hours drawing 500 watts. You can draw for a longer time but your battery life will be shortened by doing this.

LandYachty · RV-Dreams Family Member

Thanks a lot of watts. a 40" flat screen with direct tv uses about 19 amp hours of DC. What are you trying to run?

burdy · RV-Dreams Community Member

27 inch flat screen,lap top, dvd play. these are must have.

Byrdy · RV-Dreams Family Member

flat screen aprox 130watt,dvd aprox 60, puter maybe 30. They are must have. also a small space heater I will use from time to time by itself, at max this will take 1250 watts, so I will run this at half power or less just to take the chill off.

Jack Mayer · RV-Dreams Family Member

Under no circumstances -EVER - do you want to run a space heater off of batteries. That is what your propane furnace is for.

Byrdy · RV-Dreams Family Member

ok didnt know that , why and thanks

Byrdy · RV-Dreams Family Member

Under no circumstances -EVER - do you want to run a space heater off of batteries. That is what your propane furnace is for.

why is that please explain

Terry and Jo · RV-Dreams Family Member

Tom,

While I am not an electrician, I have done some electrical work in my day. I've also dealt with heating systems, although I'm not a heating repairman. That said, I think Jack's reasoning is that electric heaters have a tendency to use quite a bit of electricity, thus draining batteries too far and perhaps even too fast.

Oh, by the way, I'm also not a battery expert. But, I have heard that one doesn't want to run them down too far. I have wondered if there could be a problem with some equipment should the power source be diminished too much. For instance, while a lot of things aren't affected by low voltage, I know that some motors can be damaged by running at low voltage.

We even had a motor ruined on the farm when the power line running to that motor wasn't heavy enough to carry enough voltage to power it. We had tried running it with an extension cord, and it wouldn't even start. We talked with an electrician about using wire of "x" size gauge, and he told us we needed a lot heavier.

Hope this is some help, and if I'm mistaken about some of this, I hope the better electricians on the forums correct me.

Terry

bjoyce · RV-Dreams Family Member

Most RV batteries are roughly 100 amp-hour batteries. Since you shorten their life if you run them down below 50% then each battery gives you about 50 amp-hours of usable electricity. At 12 volts this is 50 times 12 or 600 watt-hours of power, which is 0.6 kilowatt-hours. A space heater normally runs at 1500 watts, so it can use a kilowatt-hour in 1000/1500 hours or about 40 minutes. If you do the math each battery will give you 24 minutes of space heater usage. This does not account for inverter inefficiency, so each battery will give you somewhere between 15 and 20 minutes of 1500 watt usage.
Plus each battery is limited in how much power it can supply and the voltage coming out will drop below the inverter's limit and it will cut off. Most inverters alarm/cutoff around 10.5 to 11 volts. To run 1500 watts you would need about 3 batteries minimum and my experience says the low voltage cutoff would kick in before 30 minutes of usage.

Jack Mayer · RV-Dreams Family Member

I think Bill explained it well. It is the same reason you don't run an air conditioner with an inverter. It is too heavy of a load for most battery banksand the bank can not store enough power. And in the case of a space heater there are far more efficient ways to heat while boondocking.

Byrdy · RV-Dreams Family Member

Thank you guys for all your in put, as usual i can alway depend on help on anything in this forum. This is always the first place I start for RV related questions. thanks again for all your willingness to help a fellow RVer!