Killer Amps

MrWizard wrote:

this NOT how i would heat a camper shell

Tell me how you would do it then.

TomG2 wrote:

pianotuna wrote:
Better off using a small fan and ten candles.

I can fire up the propane stove for a few minutes, but prefer no open flames.

Quite right--RVs are plastered with warning stickers about doing that.

I say that it doesn't matter if the battery will last. A 100W heater or a 100W light bulb will not heat a camper shell. It will probably not even keep up with the heat loss through the skin.

exactly how you would not

i would light the stove, fix my coffee

that would warm up the camper shell and me

that is NOT the same as using an open burner all night for heat

but then again that was not question of the OP
or the idea

The scenario is unclear, but the OP says it works for him on shore power, so that is clear enough. So it is all down to whether he can do it on inverter on that little battery.

It seems possible from a steady amps point of view, but the inverter will be doing its "amps creep" upwards to maintain the watts against falling voltage, so that skews the steady amps results.

We also don't have the voltage seen at the inverter from the start for however long it stays above low voltage shut off, whether that will happen right away or last the whole hour.

The OP will find out in the morning. Hope he reports how it went! :)

MrWizard wrote:
exactly how you would not

i would light the stove, fix my coffee

...snip.....

Seen to many examples of "Murphy's law" to light a fire inside the camper shell. Curtains, propane, sheets, paper, all burn quite well.

Test report:

I was wrong on the wattage. I was wrong on the wattage. It is a 250 watt electric heater, which explains why it performs okay on shore power. The result was that the 400 watt inverter immediately went into low voltage shutdown with the application of the 250 watt load. Won't work with the 35 ah battery. Might work with a Group 27 battery, which I will try someday. Little battery is still handy for light loads and I will put up with cool mornings if I have to. No, I am not going to buy a 100 watt heater to see if that works.

TomG2 wrote:
Test report:

I was wrong on the wattage. I was wrong on the wattage. It is a 250 watt electric heater, which explains why it performs okay on shore power. The result was that the 400 watt inverter immediately went into low voltage shutdown with the application of the 250 watt load. Won't work with the 35 ah battery. Might work with a Group 27 battery, which I will try someday. Little battery is still handy for light loads and I will put up with cool mornings if I have to. No, I am not going to buy a 100 watt heater to see if that works.

The 400w inverter can handle a 250w load no sweat. EG mine ran a 20 amp charger that was showing 320w doing the 20 amps charging. The continuous rating of the 400w inverter is 320w so it was maxed, but it did it ok.

All you need is good enough wiring inverter-battery, and enough battery.

I was thinking yor camper must be very well insulated if 100 watts of heater for an hour was effective, judging by my 200 watt heater's efficacy.

Just out of curiosity, how thick and how long are the inverter's cables to the battery?

TomG2 wrote:
Test report:

I was wrong on the wattage. I was wrong on the wattage. It is a 250 watt electric heater, which explains why it performs okay on shore power. The result was that the 400 watt inverter immediately went into low voltage shutdown with the application of the 250 watt load. Won't work with the 35 ah battery. Might work with a Group 27 battery, which I will try someday. Little battery is still handy for light loads and I will put up with cool mornings if I have to. No, I am not going to buy a 100 watt heater to see if that works.

Still marginal for much more than taking a little of the chill off (ie: bringing the temp up by just a few degrees) in a very small space but a little more logical.

If all you need is to take the chill off, running the furnace for 5-10 minutes should do the job much better...and even if you only have a small BBQ tank, that should be good for several weeks (maybe even a few months) of daily taking the chill off. (this assumes you have a furnace)