Fridge power consumption and operation

[Limoges_Camper]

Hi there,

I am in the process of installing an inverter and making some automatic circuitry to make the transition between shore power and battery power fully automatic. In this process, I am going to turn off certain circuits that have a high drain on power.

What puzzles me a bit, is the fridge: there is a switch that has 3 positions: auto, off, and gas. So far, I figure the way to go is if you are on shore power, stick it to "auto". If you aren't, then stick it to gas. What I don't is what happens if the shore power goes out while it's in the "auto" position. I'm concerned that it will draw too much current from the 12 VDC side of things, and will quickly drain the battery.

Does anyone have any figures on what the fridge should be drawing from the 12VDC side? I understand that in the gas position, the fridge still required 12 VDC to operate the ignition and possibly gas valve. I assume that when it is in the "auto" position, that it uses an electric element to replace the heat from the propane flame.

Here is a wiring diagram of what I am proposing. As you can see, it will automatically switch to inverter power if the power drops off on the shore power side (and if the inverter's on/off switch is in the "on" position).

[pianotuna]

Hi Limoges,

Four of my batteries are 10, the others are 5 years old. It is about having enough battery capacity, and recharging to 100% when ever humanly possible.

Limoges_Camper wrote:
Using it in electric mode, be it in 120VAC or 12 VDC uses up more of the battery's power than the propane does of the total available capacity, thus the effect of using it would be quite noticeable in battery drain.
another reason to not use the battery/inverter is wear and tear on the battery: the more you use it, the less sooner it dies.

[MrWizard]

Several times I ran a 700w MW using a 1000w "freedom 10" heart interface inverter
It's all about having enough battery power

[Limoges_Camper]

shooted wrote:
Hi Limoges_Camper,

For the operation you describe, it seems R3-R6 should be connected to the normally open contacts.

Limoges_Camper wrote:

Does the team here have thoughts on operating even the smallest microwave on a 1kw inverter? Maybe an inverter type microwave at some % of full power and using the agm battery will work?

Thanks! Fixed it. 🙂

[Limoges_Camper]

pianotuna wrote:
Hi Westend,

For the difference in price I'd go with the 2000 watt Pro-Watt if I were going "stand alone".

Unlike Mr. Wizard, I run my fridge as much as I possibly can on 120 volt. Mine is a 3 way, and initially worked well on 12 volt, but doesn't even maintain on 12 volt any more. Draw on the battery bank is pretty much identical between 120 volt and 12 volt at 34 amps. I imagine there is some inverter overhead of perhaps at a maximum 2 amps.

I just finished a trip that extended from Oct 11 to Oct 26 and covered 2500 kilometers (1600 miles). Only on the last night did I not have access to shore power, so I ran the fridge each day on 120 volt powered by the inverter. I also burned no propane for heating.

Having looked at both setups, I think that operating the fridge on propane is the way to go, as it uses very little fuel, and thus the effect of using it in that mode is unperceivable. Using it in electric mode, be it in 120VAC or 12 VDC uses up more of the battery's power than the propane does of the total available capacity, thus the effect of using it would be quite noticeable in battery drain.
another reason to not use the battery/inverter is wear and tear on the battery: the more you use it, the less sooner it dies.

As I plan to get a flame sensor to have as a spare, I will only use the electrical operation as a back-up.

[Limoges_Camper]

westend wrote:
if you decide to replace your existing 1KW inverter and want a quieter one, the Xantrex Prowatt 1000 pure sine inverter is virtually noiseless. I use mine to power a residential fridge and misc. entertainment devices. The fan, AFAIK, has never spun. Or, it is so quiet I can't hear it in it's location, in the middle of the cabin in a ventilated cabinet.

I'd go with the 2000 watt version for the difference in price. as far as the location: I plan to install mine in the real outer storage compartment. I just need to figure out how to ventilate it properly.

[shooted]

Hi Limoges_Camper,

For the operation you describe, it seems R3-R6 should be connected to the normally open contacts.

Limoges_Camper wrote:

Does the team here have thoughts on operating even the smallest microwave on a 1kw inverter? Maybe an inverter type microwave at some % of full power and using the agm battery will work?

[pianotuna]

Hi Westend,

For the difference in price I'd go with the 2000 watt Pro-Watt if I were going "stand alone".

Unlike Mr. Wizard, I run my fridge as much as I possibly can on 120 volt. Mine is a 3 way, and initially worked well on 12 volt, but doesn't even maintain on 12 volt any more. Draw on the battery bank is pretty much identical between 120 volt and 12 volt at 34 amps. I imagine there is some inverter overhead of perhaps at a maximum 2 amps.

I just finished a trip that extended from Oct 11 to Oct 26 and covered 2500 kilometers (1600 miles). Only on the last night did I not have access to shore power, so I ran the fridge each day on 120 volt powered by the inverter. I also burned no propane for heating.

[westend]

if you decide to replace your existing 1KW inverter and want a quieter one, the Xantrex Prowatt 1000 pure sine inverter is virtually noiseless. I use mine to power a residential fridge and misc. entertainment devices. The fan, AFAIK, has never spun. Or, it is so quiet I can't hear it in it's location, in the middle of the cabin in a ventilated cabinet.

[Limoges_Camper]

MrWizard wrote:
fridge electric heating element 345w, 3amps at 120v
but thats 30amps at 12v input into the inverter..
your 1kw inverter is No problem, but your batteries will only last a few hours

the fridge uses 12v control circuit, but that very small only 1 amp , unless there are fans on the cooling unit

switching from electric to gas on power failure it will last a long time on batteries and propane

but propane fulltime is best, then if shore power fails, the only drain on batteries is the 12v control circuit and the fans..
like i said a long time.. days..unless there are 12v fans involved
even then it will be many hours

Yup: propane all the way for this guy now. 🙂
It just makes sense: the performance of the fridge doesn't diminish, the reliability of the setup is there. The only thing is that flame sensors wear down: they get "burned" out. I will have to find a replacement flame sensor and have it on hand to replace if necessary. 🙂

[Limoges_Camper]

AnEv942 wrote:

Limoges_Camper wrote:
So there is a 120VAC as well as a 12 VDC heating element in yours?

Yes- however I reread your original post and my response doesnt apply-yours is a 2way (Ac & gas) ours is 3 way (AC/GAS & DC). I had 1st read as concern for how much 12v was being drawn due to 12v 'heater'
-which you dont have.

What Im gathering the fridge is one of the items to be disabled when power falls off, and your concern is the 12v it will use because it will switch to Gas when in auto mode and still use 12v for the controls? Though small draw (Ive never measured control 12v required)if fridge will default back to AC/auto when power cut/restored, yet another relay on the 12v feed?

Not quite: my concern is that when in inverter mode, the fridge will "see" the 120 VAC, and thus use it instead of the gas.

I can disable it, but I think I will just run it on propane since it is such a small draw on that fuel compared to how much it draws when in AC mode.

[MrWizard]

fridge electric heating element 345w, 3amps at 120v
but thats 30amps at 12v input into the inverter..
your 1kw inverter is No problem, but your batteries will only last a few hours

the fridge uses 12v control circuit, but that very small only 1 amp , unless there are fans on the cooling unit

switching from electric to gas on power failure it will last a long time on batteries and propane

but propane fulltime is best, then if shore power fails, the only drain on batteries is the 12v control circuit and the fans..
like i said a long time.. days..unless there are 12v fans involved
even then it will be many hours

[AnEv942]

Limoges_Camper wrote:
So there is a 120VAC as well as a 12 VDC heating element in yours?

Yes- however I reread your original post and my response doesnt apply-yours is a 2way (Ac & gas) ours is 3 way (AC/GAS & DC). I had 1st read as concern for how much 12v was being drawn due to 12v 'heater'
-which you dont have.

What Im gathering the fridge is one of the items to be disabled when power falls off, and your concern is the 12v it will use because it will switch to Gas when in auto mode and still use 12v for the controls? Though small draw (Ive never measured control 12v required)if fridge will default back to AC/auto when power cut/restored, yet another relay on the 12v feed?

[Limoges_Camper]

MrWizard wrote:
when i had an RV fridge
it was NEVER in AUTO mode..never on elec...unless i ran out of LP and Temporarily switched to elec

leaving it on LP all the time is .. IMO the best way to operate an RV fridge
save the 120v mode for emg use, it use so little propane in can run months on some RV LP tanks

running on 120v all the time is the best way to have it NOT work on LP when you need it to

This makes it simple then: leave it on propane and my have to worry about it being an AC load when in inverter mode.

[Limoges_Camper]

sch911 wrote:
Jeez that's allot of work. Why not just get an inverter that has a ATS integrated into it. There are many....

For starters, I already own one and it doesn't have an ATS.
Second, I want to do more than just transfer the power, I want to disable certain circuits at the same time.
Lastly, I have access to these parts for free.

As a bonus, this is also fun to do.