Power hungry inverters

[Motrukdriver]

I know a lot of inverters will draw power even if nothing plugged into it is being used.  I wonder if a resourceful person could add a solenoid that switches the inverter on and off and trigger it with a temperature sensor in a dorm fridge.  Fridge, well insulated, gets to 36 degrees and triggers the solenoid, turns on the inverter, cools the fridge down to it's set temp around 34 degrees and the solenoid turns the inverter off again.  Just a thought I had while sitting on the porch today....  yes? no? maybe?  Numbers are just guesses and the actual on and off would need to be adjusted as needed.

[Wayne49]

Yes, it can be done. Solenoids are not a good answer. An 80 amp DC solenoid sucks a non-trivial amount of current to keep the contacts closed.

A remote port on an inverter can be utilized to toggle the inverter on and off with a small current.

Problem. The remote toggle switch is just that, a momentary pulse that toggles the inverter state. Cannot hook it straight to the thermocouple.

Solution is to use a RaspberryPi or Arduino to sense the thermocouple contacts closing. Then supply the momentary pulse to the remote switch. The components outside of the Arduino/RPi are not expensive.

Energizer 2000 and Samlex PST-1000 are two units I have worked with. The Energizer was interesting as it has two USB ports which can power the process controller, the Arduino or Raspberry Pi. And the Energizer uses 5VDC as its signal voltage available from either RPi or Arduino. The Samlex was a bit more complicated.

Using jumper wires it is possible to quickly switch the unit back to shore power without the process controller in the loop.

That being said, those AC fridge units can be hell on batteries. You need a big bank to run through non-solar time. And during the day less solar will be available to charge those batteries.

[BradKW]

I'm wondering what your inverter draws with no load?

My 3000 watt only draws 0.5 amps in power save mode, or 1 amp with power save turned off. I never run power save because my bank is very large and I have wall-warts using parasitic amounts, but in your scenario it would work well with only 1 appliance. I don't know if this is a normal feature across brands, but I've been very happy with Go Power...here's a demonstration of the feature:

Another thing to consider is that your remote temp sense idea might not actually save power, as it sure seems to me that my fridge works much harder to drop temps by a degree than it does to maintain it. And when I say "seems", it's just that...dunno if it's true or not.

[sternwake]

There are latching solenoids which only require a momentary switch, and use no juice once latched.

https://www.amazon.com/Cole-Hersee-24200...B001FQMZQU

That link was the first google hit, not a personal recommendation.

I've been encouraged to learn arduino and rasperry Pi but have not yet made the effort.

I think if one chooses the residential fridge on the inverter route, they should make sure the condenser is not in the walls of the fridge, but has exposed fins or coils on the backside which can be properly ventilated.

So much efficinecy gain to be had when one can ventilate the condenser properly, and add insulation to the walls/ floor and hopefully door.

i think the idea that the fridge would cycle normally, but the inverter would only turn on when the compressor would seek to run anyway eliminating all that wasteed battery when theinverter is just waiting for the compressor to fire back up..

The Idle current of Various inverters varies wildly, and the start up surge of a residential fridge likely requires an inverter that can handle 10 to 15x the running wattage, but I have no experinece actually doing it and actual excperience always beats theory, or what i read on the internet.

[justjim]

There was a huge thread about how to do this on the other site. Then again you can get a load sensing inverter that will turn on and off only when power is called for.

You are right though. Some inverters use ridiculous amounts of power in stand by or powering small loads. I use to use two inverters, a power hungry PowerJack that was only on for the coffee maker and microwave and a tiny 150w that used less power actually powering the small loads than the big inverter did in stand by.

[Motrukdriver]

I had a 1500 watt Cobra inverter in the big truck. What I liked about it was the remote on/off switch so you could locate it as close to the battery bank as possible and it still be usable without going thru contortions trying to turn it on or off. Dunno how much power it used in standby mode. A load sensing inverter makes more sense than trying to reinvent the wheel. And of course insulation... lots and lots of insulation. If I ever get to do this that would probably be the route I'd take but now with the planned move to Australia... I dunno. 230V 50Hz and that is a big jump from 12 volts. A whole nuther world where everything spins in the opposite direction.. hahaha

[Motrukdriver]

Those crazy Aussies.

[speedhighway46]

The simple solution, for me, would be a nice heavy duty Blue Sea manual battery switch.

[BradKW]

The simple solution, for me, would be a nice heavy duty Blue Sea manual battery switch.

You must have much better memory than me...this would only result in warm beer and spoiled eggs in my fridge 

[bLEEp]

The problem i see here is the dorm fridge. We had one for a few months in Bertha, and the amount of energy those things use is outstanding. Our Dometic just sips the power, I would say one of the best investments we have made aside from the good solar setup we installed. I know the price is prohibitive, but so worth it.