Agree with Peter,, you will need massive battery capacity for oil filled,,, consider a small electric say 1200 or 1400W.

As a practicle example I draw down our batteries with a good load every now and then and we have a top quality pure sine wave 1000w inverter and when connected to 1000w  flood lights (ie the load) it draws between 70-80 amps at 12V from the batteries.

I don't use this inverter for heating etc it is for high loads when out bush for short periods only and the loads I put on the inverter result in about 15A at12V being drawn from the batteries.

Hope this also helps and this confirms Pete's advice on the formula. I know it's hard to believe but it's true.

Baz421 wrote:

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..........,,, consider a small electric say 1200 or 1400W.

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??????????

 A 1200W electric heater will draw 50% more power than an 800W electric heater.

If he can't run the 800W one he certainly can't run a 1200W one.

Cheers,

Peter

Baz421 wrote:

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you missed the point again Peter,,,,, an oil heater runs for hours to heat,,, a small electric heater runs for say 30 min and warms a small van,, therefore draw the current from 12V quickly and then turn inverted off.

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 The bit "..,,, consider a small electric say 1200 or 1400W" had me puzzled a bit as well.

Firstly, you did not suggest using it for a quick heat only. At any rate 1/2 an hour with a heater would not do much for heating in a van or motorhome. That time would raise the temperature a bit but then it would would decay back the norm in a short time. The cook turns our larger heater off to get me to bed (and put the light off) when she goes to bed. The heat does not last long after the heater is switched off.

Secondly, I demonstrated above that his battery would not last much over 1/2 an hour on his set up. Peukerts Constant results in a non-linear available total discharge availability as you increase the current draw. Your 1400 W heater would contribute a fair bit towards the destruction of the OPs battery if left on for 1/2 an hour. You would probably only get a bit over 1/4 of an hour before it was flat, more than that would be deleterious to the battery.

Thirdly heat is heat, is heat . . . . It does not matter which way you produce it, when you produce heat by running electricity through an element the device is 100% efficient. The difference between a column heater and a blow heater is the area over which you distribute the heat. The discharge area of a fan heater is a very much smaller area than the column heater. That is why the discharge air is much hotter than the surface area of an oil filled column. People have an illusion that the heat produced by a column heater is different from other forms but it is not. Some even think a column heater is cheaper to run, poor disillusioned fools they are.

Baz421 wrote:

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 you missed the point again Peter,,,,, an oil heater runs for hours to heat,,, a small electric heater runs for say 30 min and warms a small van,, therefore draw the current from 12V quickly and then turn inverted off.

As I said I don't use inverter for heating,, but if he has the batteries he can.

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 Sorry Baz421, but I did not miss the point at all.

As others have explained, heat is heat. If you require 2kWh of heat energy to warm the van, it will use the same energy from your battery irrespective of what type of electrical resistance heater you use.

Cheers,

Peter

Scotty01 wrote:

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Didnt expect this to get so involved, I dont really understand a lot of whats been said but thanks anyway. To explain a bit more I run a 1000w inverter and 2X100ah batteries. I decided to give the column heater a run last night and Only had it on for about 15mins and it turned itself off on the thermostat, it had taken the chill off the air in the van but even when it was idle it was still giving of a fair amount of heat. Cut back in after approx 10-15 mins and within an hour the interior of the van was quite warm. Volt meter was showing 12.6 when turned on and after the hour I turned it off meter was reading 12.1 and everything was still working fine. Dont think I would like to run it longer than an hour.

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 Hi Scotty01

12.1 volts, you are close to your usable power, 50%, without shortening the life of the batteries. You have used almost 100 amps. You have to put more back into the batteries than you remove, to fully recharge them. (Maybe somebody can quote a figure). This means you would need a big recharging system. As you are using battery & inverter, means 240 volt isn't available, so lots of solar.

I stand to be corrected on my assumptions. 

I have a 100ah battery with 130 watt solar panel. I only run lights (LED), radio, TV (2-3hrs / day), bug zapper (10 watt through inverter, when needed), 30 lt waeco in summer. My battery rarely gets below 12.5 volts.

Cheers Pete

Peter_n_Margaret wrote:

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Baz421 wrote:

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 you missed the point again Peter,,,,, an oil heater runs for hours to heat,,, a small electric heater runs for say 30 min and warms a small van,, therefore draw the current from 12V quickly and then turn inverted off.

As I said I don't use inverter for heating,, but if he has the batteries he can.

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 Sorry Baz421, but I did not miss the point at all.

As others have explained, heat is heat. If you require 2kWh of heat energy to warm the van, it will use the same energy from your battery irrespective of what type of electrical resistance heater you use.

 

Cheers,

Peter

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 you've still missed the point,,, I was talking about the time the heater was ON,,, not the wattage,, amps use etc etc