Killer Amps

TomG2 wrote:
The experiment failed, "Nothing ventured, nothing learned".

How did it fail? The battery fell flat or lacked enough heat output?

Some may be missing the whole point of camper shell camping

I 'camper shell' camped years ago down in Mexico quite often. We had a blast.

Hi,

The "rule of thumb" for heating is 1.25 watts per cubic foot.

So 163 watts would be the minimum. I would stick with the 250 watt heater myself since you wish to take the chill off--quicker is better! There is also a contribution of waste heat from the inverter.

250 watt-hours =~ 21 amp-hours @ 12 volts.

To run the heater for one hour a 100 amp-hour flooded battery would be a good fit.

https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html

TomG2 wrote:
A Camper Shell, for those who do not know about them, is simply a fiberglass shell that fits over the bed of a pickup. Mine creates a box approximately 6.5' X 5' X 4' which can easily be warmed with any kind of small heater.

OK, if it's just a camper shell, we are talking about a drastically smaller space than even most truck campers. 250w might do the trick if it's just a little chilly.

As others have mentioned, a 12v heater probably makes more sense but still need a bigger battery. That or some higher wattage 12v bulbs as most of the energy turns to heat anyway.

The experiment failed, "Nothing ventured, nothing learned". Some may be missing the whole point of camper shell camping and that is Simplicity. I have owned all kinds of RV's including motorhomes and trailers. I still have a thirty foot travel trailer.

The shell is my "Mini Mini Motorhome". Something I use for quick trips in mild weather. I don't want two or three batteries. I don't want a generator. It has a bed, a porta potti, and a cooler. Lots of fun, as long as I keep it simple. 23 mpg isn't bad either.

Tom_M wrote:
I think a better option would be to buy a 12 volt heater. They are typically 150 watt. A search on Amazon found these:
12 volt heaters on Amazon

My old TV heater core started leaking so I bypassed it. Now no heat. I bought one of these at a truck stop to heat my cab while driving to work. I placed it on the floorboard to blow on my feet. I could feel it on my feet but after a 40 minute drive it did not heat up the cab one degree. Granted, it was about 40 degrees outside, moving vehicle, heat leaks, etc..

It may work for your application. Or get a bigger battery and 2 12V heaters. Start with both on and then turn one off after 10 minutes or so.

I think a better option would be to buy a 12 volt heater. They are typically 150 watt. A search on Amazon found these:
12 volt heaters on Amazon

A Camper Shell, for those who do not know about them, is simply a fiberglass shell that fits over the bed of a pickup. Mine creates a box approximately 6.5' X 5' X 4' which can easily be warmed with any kind of small heater. I am not talking freezing temperatures, just a little warmth on a cool Spring morning. Very practical. No furnace, no fireplace. The problem is actually to find a heater that is small enough. Typical 1,500 watt units or a Little Buddy is way overkill for the application. I carry a small AGM battery which proved incapable of operating the 250 watt electric heater. A 20 amp load slammed on a 35 ah battery pulled down the available juice to under 10 volts. Inverter disconnected the load. I would not have even tried the test had I remembered that the heater was 250 watts instead of 100.

its camper shell ? on a pickup truck, no furnace, nothing, not anything on the inside, except what ever portable gear he brings along

unless i mis-understood his OP

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)

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?