Inverter question

[okmunky]

I'm trying to understand 12 volt power. Does a 400 watt plug-in inverter use 400 watts the entire time it's plugged in or does it only use the wattage of what is plugged into it plus a little extra?

I have a solar system to charge my house batteries and I am trying to figure out what I can run while boondocking?

[Dave78Chief]

An inverter only provides the power the load requires plus some overhead. Typical efficiency is 85-90%.
If a load requires 100 Watts, then 100 x 1.1 (90% Efficiency) = 110 Watts.

Dave

[okmunky]

Thanks Dave! That's good news.

[wa8yxm]

Does a 400 watt inverter use 400 watts all the time: NO, in fact almost none of the time.

If it is running "Flat Out" powering exactly 400 watts of load it might draw as much as 450 watts.

If it's running a 100 watt TV perhaps 140 watts (There is some loss)


If it's not really doing anything just now (Running but no load) perhaps 10-20 watts.

NOTE: all usage numbers are guesses, not really estimates but most of the inverters I've checked out use like 110-125 percent of their output it gets a bit easier if you seperate out the "overhead" or standby power. but the fact is the power used depends on the power out.

[Dunner]

And don't believe the advertised DC idle current draw. It's usually higher.

[HotMech]

Inverter ratings are for output power.
Input current is 10x more, at 10x less voltage.
A 400w inverter will deliver about 3.33a at 120v at full capacity,
so the battery current draw will be about 25-30A at 12 volts nominal, so the math would say 12Vx30A=360W, again, at full output.
At no load, the draw will be minimal, but enough to still make you want to turn it off, when not using it. Smaller inverters are not as frugal with your power, as the larger, inverter/chargers at no load.
K.

[okmunky]

Thanks guys!

[Dunner]

I was just reading up on my 500W(1000 Peak) Power On Board inverter. It say No Load Current .3A, but my amp meter says .6A. It also says for 500W, the source must be 50A. That would drain the house batteries pretty quick.

I only use it for my laptop and a 200W foot warmer heater. I don't remember what the current draw was with the heater on, but will check the next time I use it.

I mounted it close to the batteries and wired it to the disconnect solenoid with 10 gauge wire and ran the AC through the basement to a point where I could route it to a duplex outlet below my dinette cushion and extended the on/off switch there also.

[beemerphile1]

Quote:

Originally Posted by Dunner I was just reading up on my 500W(1000 Peak) Power On Board inverter. It say No Load Current .3A, but my amp meter says .6A. It also says for 500W, the source must be 50A. That would drain the house batteries pretty quick. I only use it for my laptop and a 200W foot warmer heater. I don't remember what the current draw was with the heater on, but will check the next time I use it. I mounted it close to the batteries and wired it to the disconnect solenoid with 10 gauge wire and ran the AC through the basement to a point where I could route it to a duplex outlet below my dinette cushion and extended the on/off switch there also.

Ten gauge wire is no where near heavy enough for a 500w inverter.

500w/120v = 4.17 amp
500w/12v = 41.67 amp plus maybe 10% - 15% inefficiency
1000w/12v = 83.33+ amp surge

Ten gauge wire is only good for 30 amp. If you try to run that inverter at capacity you will heat the wires and will have a huge voltage drop on the 10 gauge. I have my 400w inverter wired with 4 gauge and fused at 75 amp.

[Dunner]

I was just guessing at what wire size I used. I know it was hard to work with, so it is probably heavier than 10. I only use it for my laptop and a 200W foot warming heater.