Wirering

Hi,
I have noticed that most RV solar systems wire the a/c in a way that it won't run off the inverter on solar and only run when it transfer over to shore power because even if the system is powerful enough to start it and run it, the batteries would not last long. I've noticed that my a/c fan only gives the TT good ventilation. Couldn't I leave the a/c wired in to the breaker panel as is, I will have a 3K inverter, wire in the solar system and when I am on solar power boondocking, just remember to use the fan only from the a/c, how much power could it use? And only use the a/c when I have shore power? Thanks.

joegambler0 said:

just remember to use the fan only from the a/c, how much power could it use?

Click to expand...

That is the correct question to ask. Anything with a motor should be considered high power till proven otherwise. On boats, people often get surprised how much power a little fan on their diesel space heater uses. In your case, you have to add the inverter loss on top of it. You should clamp an ammeter on the battery and turn the fan on to see how much the current jumps

Yes, you could do this but as @FilterGuy says it would be useful to know your fan's power rating in order to calculate how long your batteries/inverter could power it. You could find the fan's power rating either by reviewing the specs of your a/c unit or (preferred) measuring it.

Once you have the power rating you can do some simple maths to work out how long your batteries will power it:

Let's say your fan draws 300W and you have a 400AH / 12V lead-acid battery bank coupled to your 3,000kW / 110Vac / 12Vdc inverter that is 85% efficient:

• Your 300W fan requires 345W from the DC side of your inverter (at 85% efficiency)
• 345W being supplied at 12V requires 29A (P=VI)
• It is common practice to avoid discharging a lead-acid battery below 50% DoD (battery longevity)
• So a 400AH battery bank can really only supply 200A for 1 hour (ignoring Puekert effect), or put another way, 29A for 7 hours (200AH / 29A = 7 hours)

So you could happily run such a fan for 7 hours, ignoring all other loads.

If your fan is half the wattage in the example, double the the run time.

If you have solar, whilst you can just subtract the PV wattage from the fan wattage as a simple calculation, it is usually best to calculate consumption and generation over a 24 hour period - there are plenty of posts on here about how to do that.

Thank FilterGuy and tictag, Now I know how to measure the draw and then I can figure how much of the batteries it will use, then I can determine if it's worth running the a/c fan or just stick to my vent fans. Thanks.