What size inverter and how did you decide?

[John in Santa Cruz]

for sure. I only use my small inverter to charge a few things that I have no 12V charger for, and I normally do it during sunshine hours so my solar is running it

[CarlD]

John,


Your efficiency numbers sound a bit high. I would think 90% at full load would be high for a consumer item. Please do your efficiency test and let us know the results.



Carl

[gordon2]

Originally Posted by John in Santa Cruz

..... in particular we don't seem to have any 100W incandescent lamps left around here, they make a good 'standard load'..

But how standard?

I always heard the watt rating was an approximation, and just by chance I had my box'o bulbs out for another reason, so I tested a few incandescents...

Bulb, measured load
40 Watt, 45 watts
60 Watt, 61 watts
60 Watt, 60 watts
100 Watt, 109 watts

[CarefreeLad]

Originally Posted by John in Santa Cruz

for sure. I only use my small inverter to charge a few things that I have no 12V charger for, and I normally do it during sunshine hours so my solar is running it

Great plan - I'll add solar at some point - mostly weekend camping at this point and I can't kill a battery that fast. Heck...barely use power anyway - it's about the ice in the cooler for the beer more than devices. I own a software company and when I go to the woods I go to the woods

[John in Santa Cruz]

Originally Posted by gordon2

But how standard?

I always heard the watt rating was an approximation, and just by chance I had my box'o bulbs out for another reason, so I tested a few incandescents...

Bulb, measured load
40 Watt, 45 watts
60 Watt, 61 watts
60 Watt, 60 watts
100 Watt, 109 watts

was that measured with an inline(series) ammeter, or a clamp-on ampguesser? the latter are at best 10% accurate in my experience.

[gordon2]

Originally Posted by John in Santa Cruz

was that measured with an inline(series) ammeter, or a clamp-on ampguesser? the latter are at best 10% accurate in my experience.

Good point.. My Fluke is out of order.. so I used a Kill-A-Watt. Still, I am sure there is at least as much tolerance in the bulbs as the meter. Neither are precision devices.

[CarlD]

Incandescent bulbs are a good resistive load with low inductance. The resistance varies with voltage. The cold resistance is approximately 10% of the hot resistance. This makes them a convenient constant current source. It really does not matter what the bulb wattage is because you can just turn on more bulbs to get the load you want! To properly determine the efficiency you have to measure the input voltage and current and the output RMS voltage and RMS current. Cheap AC meters use a rectified average value calibrated to RMS which is probably fine for a true sinewave inverter. A quality meter, like a Fluke true RMS meter is the best.

[GaryM]

Originally Posted by bobblangley

I am contemplating adding an inverter to my 1994 Bigfoot trailer. I do not have an AC unit or a microwave but might want to run a 100-w lamp, charge a laptop computer, charge a cordless drill battery, etc.

I would be interested to know what sizes others have installed and how they decided on the right size for their needs.

I boiught a 400 watt inverter for cheap money. It plugs into a 12 volt power socket in the truck or in the camper. It handles charging a laptop, cordless drill, etc. As for the lamp, switch to an LED. It's much more efficient.


Gary