Large inverter mean more power draw?

[khigh]

I'd never EVER planned on a huge inverter. What I've been doing and planned to continue was using a 750 when the generator's not running - just for lights and a fan, maybe a laptop and other odds and ends.

But I just had a 3000/6000 fall in my lap. So I could wire it up and do things I'd never dreamed of before - run the microwave, AC, space heater, etc. Not A LOT because I still have to think of the batteries, but heat the occasional snack or get a space heater going for 5 minutes before getting out of the covers on a chilly morning - that kind of thing. If the batteries are up to it, maybe set up a digital timer to get the window unit to come on 2,3 times during the night. Heck I've got dual hybrid AGMS in my truck so I could even hook it into the system and be at like 500 a/h (but never using more than 50%, of course).

But say that inverter was spending almost all of its time doing what the old one did - running a fan overnight, a few lights etc, would it create more drain on the battery because it takes more to "get it going" as it were? Or is it apples to apples about the consumption no matter how big the inverter?

Thanks for looking.

[bdosborn]

Inverter efficiency is proportional to load. You typically get best efficiency in the 90% of rated capacity range. Here's the only graph I've ever found showing an inverter efficiency curve. BUT, It's for a 300W Morningstar Suresine inverter, which BTW is specifically designed to be efficient at lower loading by sacrificing efficiency at higher loads.



Here's a UPS efficiency graph, it's probably closer to the characteristics of your inverter:



Your inverter is going to be very lightly loaded, probably in the 50% efficiency region. That means half of all your battery usage goes to spooling up the inverter. That might not be a big deal if you're not using much battery power in a night, but it might be a good idea to cough up the dough for an inverter that is closer in output to your load. A lot of motor homes will use 2 inverters; one for big loads like microwaves and a little one for small loads that are run often.

Bruce

[felixx]

sell the bigger one and buy a smaller one with the proceeds?

[khigh]

I'm thinking now it sounds like my best bet might be to keep both inverters wired up, but on different circuits - The 750 for all the basic stuff, and then the 3000 for the big stuff, so as long as there's no big stuff running, the draw is closer to the capacity for better efficiency.

[OverTheTopCargoTrailer]

WOW

Even crazy OTTCT- only uses his 300 watt morning star 98% of the time
and he has almost 2,000 ah lithium to store the power.

[khigh]

Well the two approaches aren't mutually exclusive.

High draw with moderate storage for someone who's charging up every day and is considering the ability to heat up a late night snack or do some intermittent climate control vs. someone doing low draw with large storage for someone who wants to run lights and fans for a week or two.

[MtnDon]

One of these days, whenever Midnite Solar finally comes out with a line of inverters we may have the ideal inverter option. An inverter that has built in dual ability; a lower power range coupled with a higher power range. Near instant switching from low to high depending on the demand. Coupled with a user tunable sleep/search mode. However, it may take a while to get to the point where the products are released.