My travel companion and myself are going to buy a generator for use on an extended trip this summer. It will definitely be an inverter type, and we are looking at the Champion models. We just need to figure out which one we need.So help me figure out some things here:1) A generator with 3100 watts peak output at 120V can produce 3100/120 = 25.8 amps. Is this correct?2) The Advent 13500 BTU AC info we have says "12.4 amps is the load associated with the AC." So 12.4 amps X 120V = 1488 W. Is this the starting amps or running load?3) The converter is a WFCO 8955. According to the WFCO website, the power input is 950 W. Is this what it will pull off a generator?4) So if we plug into the generator and run both the converter and the AC, power consumption would be 2438 W. Is this correct?5) Assuming a 10% "efficiency" loss, 2438 W/0.90 = 2700 W that would need to be supplied by the generator. Is that a reasonable assumption?6) Is there any way to turn off the converter draw if the AC is running? We are looking at the 3100 watt dual fuel Champion generator at Costco. According to Champion, it has:gas--3100 peak, 2800 runpropane--2800 peak, 2520 runTrying to decide if the propane would be adequate. Looks like it would be IF the 12.4 amps is the starting load from the AC unit. Otherwise, not.If not, we will go with the single fuel 3400 peak version from Tractor Supply (best price we've found.)Any input appreciated!

Hi Coolmom42,Generators are rated in VA.I strongly recommend spending the extra money for the larger Champion. I do not recommend the dual fuel option because it will go through propane extremely fast.The converter may draw a maximum of 950 watts--but if the battery bank is fully charged it may only draw 50 watts.The start up surge from the roof air can be up to 4 times the running amps.

3100 peak, check the specs it is probable close to 2800 continuous. Oops I see that later in post.AC unit is rated for run not for start up. Could hit 15 amps start up.Converter output will vary bases on the condition of the batteries. No, you should not shut off converter. You can by shutting off 120 volt circuit breaker feeding it.You should have somewhere around a 3500 genset.

pianotuna covered things fairly well.The 12.4A rating would be a running rating, though the actual consumption is variable depending on various things such as the outside temperature and the circuit voltage. It's likely a worst-case (or approximately worst-case) running current rating at the nominal rated voltage, presumably 120V.The converter rating is a worst-case rating, i.e. the maximum consumption. The actual power consumption depends on how much power it needs to put out, which in turn depends on the charge current if any going to the battery and the 12V power consumption. I think my converter (a different brand) uses less than 25 watts when the battery is fully charged...indeed, the entire RV uses about that, for the converter loafing along and the microwave clock and other such "phantom" loads.There's no need to assume a 10% efficiency loss; the generator is rated in what it puts out. Typically that would be used for an inverter to figure the power consumed from the batteries.I'd think the 3100 generator should be sufficient (but not offer much leeway), but I'm no expert nor can I speak from personal experience on that. My 4000 watt Onan does start my air conditioner without any hardship, but that's not a very useful data point for your investigation. :)

The converter at 950w has a power factor of 0.7, so it will draw approx 1357VA from the power supply as input at full converter DC output.Kill-A-Watt on a different 55 amp converter powered by a Honda inverter generator showed:124.7v, 11.06a, 980w, 1383VA, PF 0.71 when DC output was 56.8a, battery voltage 13.7 and rising, converter set to 14.8 volts

pianotuna wrote:Hi Coolmom42,Generators are rated in VA.I strongly recommend spending the extra money for the larger Champion. I do not recommend the dual fuel option because it will go through propane extremely fast.The converter may draw a maximum of 950 watts--but if the battery bank is fully charged it may only draw 50 watts.The start up surge from the roof air can be up to 4 times the running amps.OK this make sense.I thought that sounded like a lot of propane. The advantage of propane is how clean it runs... but doesn't seem that this version on propane will have enough power.If we get the 3400 W gas only generator, the price is about the same as the smaller dual fuel. So the decision is really whether to go with dual fuel or not. Probably NOT.Correct me if I'm wrong--but doesn't volts X amps = Watts?

Generator/AC/converter questions | Good Sam Community

14 Replies

BFL13
Explorer II
Mar 31, 2018
The converter at 950w has a power factor of 0.7, so it will draw approx 1357VA from the power supply as input at full converter DC output.

Kill-A-Watt on a different 55 amp converter powered by a Honda inverter generator showed:

124.7v, 11.06a, 980w, 1383VA, PF 0.71 when DC output was 56.8a, battery voltage 13.7 and rising, converter set to 14.8 volts
DrewE
Explorer III
Mar 31, 2018
pianotuna covered things fairly well.

The 12.4A rating would be a running rating, though the actual consumption is variable depending on various things such as the outside temperature and the circuit voltage. It's likely a worst-case (or approximately worst-case) running current rating at the nominal rated voltage, presumably 120V.

The converter rating is a worst-case rating, i.e. the maximum consumption. The actual power consumption depends on how much power it needs to put out, which in turn depends on the charge current if any going to the battery and the 12V power consumption. I think my converter (a different brand) uses less than 25 watts when the battery is fully charged...indeed, the entire RV uses about that, for the converter loafing along and the microwave clock and other such "phantom" loads.

There's no need to assume a 10% efficiency loss; the generator is rated in what it puts out. Typically that would be used for an inverter to figure the power consumed from the batteries.

I'd think the 3100 generator should be sufficient (but not offer much leeway), but I'm no expert nor can I speak from personal experience on that. My 4000 watt Onan does start my air conditioner without any hardship, but that's not a very useful data point for your investigation. :)
enblethen
Nomad
Mar 31, 2018
3100 peak, check the specs it is probable close to 2800 continuous. Oops I see that later in post.
AC unit is rated for run not for start up. Could hit 15 amps start up.
Converter output will vary bases on the condition of the batteries.
No, you should not shut off converter. You can by shutting off 120 volt circuit breaker feeding it.
You should have somewhere around a 3500 genset.
pianotuna
Nomad III
Mar 31, 2018
Hi Coolmom42,

Generators are rated in VA.

I strongly recommend spending the extra money for the larger Champion.

I do not recommend the dual fuel option because it will go through propane extremely fast.

The converter may draw a maximum of 950 watts--but if the battery bank is fully charged it may only draw 50 watts.

The start up surge from the roof air can be up to 4 times the running amps.

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