Off Grid Cabin - Will this work as intended?

[Daddy Tanuki]

you can cover any sides that are not designed to radiate heat and it will help. how much depends upon a lot of factors. I have seen folks in RV's cover all but the coils and their power usage dropped by 15 or 20% but they usually glued the foam on and the unit was not that efficient to begin with so it makes it appear larger than it is. the problem with the superefficient ones is that they use the entire side, or sides to radiate the heat, so they are more efficient to begin with. hence I wan to find an older one that has back coils and disconnect and move them, which allows me to raise efficiency in several different ways.

 

[Daddy Tanuki]

a small fan might help but if the fans power usage will offset the amount saved will only be known if you test it. you would need a solid reading on what the unit uses over several weeks. you then need to connect the fan (and figure a way to measure its usage as well) and then compare.

 

[Checkthisout]

you mean a cooler? no we are talking about a 8-12 cubic foot refrigerator with external condenser coils. I have two versions of the Engel 12 volt refrigerator and freezers, i use those in my camper. they are quite efficient but my cabin is wired for 120/240 split phase power from my inverters.

I was saying you're going to make your fridge as well insulated as a Yeti cooler.

 

[Daddy Tanuki]

I was saying you're going to make your fridge as well insulated as a Yeti cooler.

Ah Gotcha.... I went nuts looking on line to see if Yeti was selling 12 or 24 VDC coolers like the Engels!

 

[willh]

Going ahead with this project, ordered 16 230ah cells today shipped from China through Amy Zheng! Fingers crossed everything goes well with that. I do have a bit of a design issue that needs to be addressed. I want to use the 125amp Mini Disconnect from Midnite solar, the breaker is rated for 10000AIC at 125vdc. I have poured over the information on this website and others, everyone seems to think Class T/20000aic is a must have/bare minimum. I haven't seen any concrete information that supports or refutes this claim.

I'm left with several options.

1) Add class t fuse before the 125amp mini disconnect purely as a worst case scenario short circuit protection. (Not fond of extra connections and mess)

2) Use 175amp disconnect with 50000AIC and fuse the inverter connection with 125 amp fuse as recommended by Victron.

3) Roll the dice on the original 125amp breaker with 10000aic based on the lack of concrete real world short circuit amperage of lifepo4 and that it's only breaking 48v vs 125vdc that it is rated for.

What would you do?

 

[ericfx1984]

You should seriously consider 24 or even 48 volts especially if you're spending your money on 16 cells

3000 Watts on 12 volts is a PITA... Every connection you make is extremely important.. but it is way more important when you're sitting at nearly 300 amps of current there are many things that are going to work just fine at 48, and even 24 volts but that will be marginal or simply fail to function at 12 volts

 

[Checkthisout]

You should seriously consider 24 or even 48 volts especially if you're spending your money on 16 cells

3000 Watts on 12 volts is a PITA... Every connection you make is extremely important.. but it is way more important when you're sitting at nearly 300 amps of current there are many things that are going to work just fine at 48, and even 24 volts but that will be marginal or simply fail to function at 12 volts

I mostly agree but what are those things?

 

[brownfiasco]

@willh - I too have a cabin that is not used in the winter. I put in solar in 2017. We have had a propane fridge since the cabin was built in 1975, but it is aged and needing replacement, and with the new battery going in this spring (8S 230Ah LFP), we are tentatively planning on replacing the fridge with an electric.

Our system is 24V, like @Steve_S. One of the advantages of going 24V is that there are more appliances that will operate on 24VDC. In our case, our standard operating procedure is to put the inverter in standby, and with a 24VDC fridge we can completely avoid the tare loss from the Inverter and keep the fridge powered.

We're looking at this fridge: https://uniqueappliances.com/product/off-grid-13-cu-ft-solar-powered-dc-refrigerator/ It's 13cf (replacing the little 8cf propane one we have today), and they claim it will only consume 24Ah per 24 hours on 24VDC.

Edit to add: We actually completely shut down our cabin in the winter, and the cabin is unheated in the winter. So our routine is to turn off the refrigerator, prop the doors open, and take the food down to our homes in the valley. There are issues with running a fridge when its surrounding air is below freezing, so you may want to look into that.

I'm in a similar situation, looking at buying a similar fridge. Could you elaborate on your winter shut down routine? Do you remove the battery?

 

[ericfx1984]

I mostly agree but what are those things?

well the current draw for 3000 watts can at full tilt hit nearly 300 amps, and with line loss and lower SOC it may well pull into the 300 amp range

Here is the math 3000w x 1.25 = 3750w on the DC side... so 3750w / 12v = 312.50 amps... likely wont see that, but who knows

those numbers cut in half @ 24v 156.25 amps

and again @ 48v 78.125 amps

The innerconnections at higher voltages are easier to get right(or at least passable) While the connections at 12v are super critical...one example is my own system... 12v @ 3000w, low frequency inverter... blows a single 500 amp fuse on instant peak loads.... BUT does not blow a pair of 200 amp fuses sandwiching the same connection point(likely due to more surface area)

and 24 volts can run wire half as thick as 12v

48v can run wire a quarter the size of 12v...

If you were only wanting to do 1500 watt... maybe then 12v makes sense

But you are building it from scratch, reconsider the expensive 12v invert combo and look at a cheaper, yet better suited 24v or 48v setup... you will be miles ahead and wont be chasing your tail over stupid stuff like this.

 

[ericfx1984]

I'm in a similar situation, looking at buying a similar fridge. Could you elaborate on your winter shut down routine? Do you remove the battery?

what about a RV propane fridge?

 

[willh]

You should seriously consider 24 or even 48 volts especially if you're spending your money on 16 cells

3000 Watts on 12 volts is a PITA... Every connection you make is extremely important.. but it is way more important when you're sitting at nearly 300 amps of current there are many things that are going to work just fine at 48, and even 24 volts but that will be marginal or simply fail to function at 12 volts

Not sure if you are directing that towards my most? Thread has been hijacked haha. My planned system is 48v as described in my first post in the thread.

 

[Horsefly]

I'm in a similar situation, looking at buying a similar fridge. Could you elaborate on your winter shut down routine? Do you remove the battery?

This is a bit complicated to answer. Our current battery at the cabin is an AGM bank. We turn off the inverter for the winter, and leave the solar charge controller running. The battery bank stays in float essentially all winter. I've logged the voltage from the SCC for the past 3 winters, and found that the panels are apparently covered with snow (hence no output from the SCC) for only a few days each winter. That surprised me.

When the snow melts roads clear this spring, I'll be replacing the AGM with my new LFP battery. It will be heated, and so the plan will be the same as it was for the AGM: leave it connected and charged by the SCC all winter. Again, it will probably stay in float.

The whole existing system and my design / build of the new battery is documented in a thread here: https://diysolarforum.com/threads/horseflys-cabin-solar-lifepo4-upgrade.27472/

As for the rest of the fall close-down of the cabin: We drain all the water lines and the water heater, put a small amount of glycol in the traps of the drains, turn off the propane out at the tank, and cart anything that shouldn't be allowed to freeze (e.g. canned goods) down the mountain.

 

[Steve_S]

Horsefly has a really good battery design for this, I'm sure it will work a treat. Do look through his thread.

 

[ericfx1984]

Not sure if you are directing that towards my most? Thread has been hijacked haha. My planned system is 48v as described in my first post in the thread.

Oh, i must have misread... carry on

 

[Snowynorth]

what about a RV propane fridge?

I was in the RV business. My techs worked on a lot of Norcold, and Dometic. The propane fridges are not the most reliable to leave unattended. I'm on my second danby at our hobby farm, and have a norcold in our guest trailer. The first danby was an older model, and actually lasted 12 years, but not without hickups and us going out a few times to a warm fridge. The second danby we just didn't trust at all. We would leave food in the coolers, fire it up, transfer food when it got cold, then empty again when leaving. The 2007 Norcold in the trailer will need it's 3rd board this spring.

That said, I've seen thousands of propane fridges over the years. Most are good, but the failure rate is way higher then electric. Most are not sitting in the city either, where parts and/or techs are right around the corner.

Propane fridge's are pricey too. I think 12v or 120v set up right, is a better long term solution. Just my opinion. I have an old GE 18 cu ft in my garage at home that runs like a charm. I'm going to do a few things to make it more efficient, and it's going to the hobby farm.

 

[12VoltInstalls]

That said, I've seen thousands of propane fridges over the years. Most are good, but the failure rate is way higher then electric.

It’s like the modern propane fridges are thoughtless exercises.
I still half regret selling it but I had a 1977? AEG that came in a Dutch Craft camper. Totally analog/not electric on propane. That’s the desirable part: no boards, no electronic stuff to fail out.

 

[Snowynorth]

It’s like the modern propane fridges are thoughtless exercises.
I still half regret selling it but I had a 1977? AEG that came in a Dutch Craft camper. Totally analog/not electric on propane. That’s the desirable part: no boards, no electronic stuff to fail out.

Exactly! I would never have another propane fridge, unless I could find an old one that's in good shape, and another old one in good shape for back up, when the first starts leaking, which sooner or later it will. Propane is short term last resort, and very finicky.

 

[Checkthisout]

I got my fridge plugged into one of those Sonoff outlets with power measuring. Here is what it came up with:

Why does the wattage read lower than the multiple of the amps/volts shown?

 

[TorC]

Because in an AC circuit VA ≠ W, except in a purely resistive load like an incandescent light or heater. That's useful information anyway, as you should expect it to draw from your inverter in VA, not W. Also, running amperage is different from and lower than full load amperage.

 

[Checkthisout]

Because in an AC circuit VA ≠ W, except in a purely resistive load like an incandescent light or heater. That's useful information anyway, as you should expect it to draw from your inverter in VA, not W. Also, running amperage is different from and lower than full load amperage.

Yes, it peaks at startup (LRA) at 1250 watts (at least within the sampling rate of the device) I understand that.

My curiosity was why it shows 1.2 Amps @ 120 volts and 78 watts.

The load is inductive as you say, so how much power is the refrigerator actually using? The indicated wattage or the higher multiple of the amps/watts shown?

Not a big deal, just curious.