A battery drain experiment

[Mike Lewis]

I ran an experiment on how fast my batteries discharge when being charged only by solar panels. My initial conditions were: 400 Ah of lithium batteries at 100% state of charge, 355W of solar panels, and about -4.15 amps of constant drain on the batteries. Weather during the test has been variable, with sunny days, partly cloudy, overcast, and rain. Also, we are nearing the winter solstice.

I stopped the test after five days when my batteries reached 26% state of charge. Given this result, I am doubtful that I could support a compressor fridge in my method of travel, which is boondocking for weeks on end. Those who go out for a week or two might be okay with my setup.

Caveats:
- I don't have any real-world data on how much current a compressor fridge actually draws.
- I have a portable solar panel but I did not use it for this experiment.

Comments?

[Mike Lewis]

Addendum: The -4.15A drain was to mimic the load from a compressor fridge. Again, I don't actually know how much current one of things draws in real life.

[rubicon327]

Originally Posted by Mike Lewis

I don't have any real-world data on how much current a compressor fridge actually draws.

Comments?

Mike: The two door Nova Kool fridges that a few have installed draw 5.2A when running. I would figure on it running 30-50% of the time depending on ambient conditions. So worst case 63Ah per day? So I think you’ll do a bit better than your test which was about 100Ah use per day with your 4.15A constant draw.

[John in Santa Cruz]

i find compressor fridges run maybe 20% of the time if you don't open them often and everything in them is already cold or frozen and the ambient temps aren't 100F. so if the fridge is 5 amps running, thats an average of 1 amp*hour per hour.

[alanmalk]

Originally Posted by rubicon327

Mike: The two door Nova Kool fridges that a few have installed draw 5.2A when running. I would figure on it running 30-50% of the time depending on ambient conditions. So worst case 63Ah per day? So I think you’ll do a bit better than your test which was about 100Ah use per day with your 4.15A constant draw.

Some back-of-the-napkin calculations...

Mikes wattage use was 4.15A * 12.8V * 24 * Hr = 1274.9 W.
20% came from the batteries, 80% from solar. The solar
contribution was .8 * 1274.9 = 1020 W.

Now, rubicon's drain: (worst case) 5.2A * 12.8V * 50% * 24 Hr = 800 W.

There is a surplus of 220 W per day. Not great - but - add in the portable (which at winter solstice will be 200+% more efficient than flat panels), and a bit less rain; you ought to be just fine. Also, as I write this, John is giving you even more reasons to be optimistic.

[Hawkeye Ed]

Let's be careful not to confuse watts and watt-hours, two related but different physical quantities: energy and power. (Similarly, don't confuse amps and amp-hours.)

A watt is the basic unit of power. We're all familiar with a 60-watt bulb that draws a constant 60 watts of power no matter how long it is turned on. But if we're running that 60-watt bulb from a battery, we need to know how long we can run that bulb before the battery runs down. That's why we need to talk about energy too, not just power.

When we’re talking about electrical energy, the most common unit is the watt-hour. One watt of electrical power, maintained for one hour, equals one watt-hour of energy. A thousand of these is a kilowatt-hour (kWh). One thousand watts for one hour, or one watt for a thousand hours, both equal one kWh. They’re the same amount of energy. While energy measures the total quantity of work done, it doesn’t say how fast you can get the work done.

Bottom line: “Power and energy are not the same thing! Power is energy per unit of time.”

"BUT," you say, "What about volts and amps and amp-hours? That's what I really need to know when I'm working on my RV's electrical system. I have a 100 amp hour battery and I need to know how long I can run my 12-volt, 2.5 amp fan."

Well, our standard unit of electrical power, the watt, is defined as a current of one ampere, pushed by a voltage of one volt. In other words, volts x amps = watts. For simplicity sake and ease of calculation (since our RV battery power is rated at 12 volts) you can convert watts and watt-hours to amps and amp-hours by dividing by 12. So, 120 watts at 12 volts equals 10 amps; 1200 watt-hours at 12 volts equals 100 amp-hours.

So the thing to remember when you're talking about batteries is that there are two performance parameters of interest. How much total energy can the battery store? Think watt-hours or amp-hours. How much power can it deliver at 12 volts at any moment? Think watts or amps.

The usefulness of a battery depends on both of these quantities. A battery that stored an enormous amount of energy wouldn’t be very useful if it could only return that energy a few watts (or amps) at a time. And a battery powerful enough to light up a whole campground wouldn’t be good for much if died after a few minutes. Batteries have to be able to store enough energy to last until recharged, and they have to be able to deliver that energy fast enough to meet the electrical load.

[Centex]

Originally Posted by Mike Lewis

- I don't have any real-world data on how much current a compressor fridge actually draws.

Forum member gklott (signs his posts "gus") collected instrumented power consumption data for his Cruise Inox 195 (dual) compressor fridge/freezer for at least some period of time after he did that installation in his E19. You might contact him for that interesting real-world data.

In direct correspondence with Gus he noted ~1650 W/day power consumption for that dual compressor unit over a period of testing during 95F+ daytime highs with nighttime lows in the upper 70'sF at his location in Texas. That while maintaining 36-38F in the fridge and 10-12F in the freezer. Per his correspondence "Measurements include initial cool down, occasional door opening, nothing in either compartment to establish a cold mass ....". Gus shared plots of power consumption over time which revealed the 'cycling' of the compressors.

[Mike Lewis]

Thanks, Alan. I re-read that thread. As Gary said in his posting, having a larger battery bank just postpones the day of reckoning. That was my suspicion when I started my experiment.

[alanerickson]

Originally Posted by Mike Lewis

Thanks, Alan. I re-read that thread. As Gary said in his posting, having a larger battery bank just postpones the day of reckoning. That was my suspicion when I started my experiment.

Your experiment wasn't correct. The fridge doesn't run all the time (or you are not pulling 4.15 amps continuously). As John mentioned it could be around 20% (this varies some based on the ambient temperature, how much food is in the fridge, ect.). From the little bit I've used my new 19, it's around 25% of the time.

Based on the numbers in your first post you pulled in around 200AH of solar from your panels (batteries had 100AH left and you used 500 AH during your test, so 400 AH start + 200AH solar - 500AH load = 100AH left). If you assume load was only on 25% of the time then you would have used 125AH over five days and you pulled in 200AH, so it does work.

[Mike Lewis]

I was trying to come up with a worst-case scenario. Perhaps my "worst case" was a little too bad to be realistic. As I find more real-world power use numbers from owners of compressor refrigerators I'll adjust and try again.

[TTMartin]

Originally Posted by Mike Lewis

I was trying to come up with a worst-case scenario. Perhaps my "worst case" was a little too bad to be realistic. As I find more real-world power use numbers from owners of compressor refrigerators I'll adjust and try again.

Doesn't sound like your loads were too high.

Reading the thread and the one linked too.

Originally Posted by Upfisk

As reported by others, once cooled, we expect to consume ≤ 1 kW-Hr/day, or about one Battleborn GC2 battery.

Originally Posted by Centex

In direct correspondence with Gus he noted ~1650 W/day power consumption for that dual compressor unit over a period of testing during 95F+ daytime highs with nighttime lows in the upper 70'sF at his location in Texas. That while maintaining 36-38F in the fridge and 10-12F in the freezer. Per his correspondence "Measurements include initial cool down, occasional door opening, nothing in either compartment to establish a cold mass ....". Gus shared plots of power consumption over time which revealed the 'cycling' of the compressors.

Originally Posted by alanmalk

Some back-of-the-napkin calculations...

Mikes wattage use was 4.15A * 12.8V * 24 * Hr = 1274.9 W.
20% came from the batteries, 80% from solar. The solar
contribution was .8 * 1274.9 = 1020 W.

I agree with your conclusion unless you are going to add additional solar panels like JonnyH. (10 total, 8 on the trailer and two on the tow vehicle)





A compressor refrigerator is not practical for extended boondocking.

[alanerickson]

Originally Posted by Mike Lewis

I was trying to come up with a worst-case scenario. Perhaps my "worst case" was a little too bad to be realistic. As I find more real-world power use numbers from owners of compressor refrigerators I'll adjust and try again.

I was curious if you were looking for a fridge the size of that Isotherm or if you couldn't get by with something smaller?

Our 2021 E19 came with this fridge and we're only using around 30AH ~ 400 watts per day.

https://norcold.com/product/norcold-...-refrigerator/

[John in Santa Cruz]

Originally Posted by alanerickson

I was curious if you were looking for a fridge the size of that Isotherm or if you couldn't get by with something smaller?

Our 2021 E19 came with this fridge and we're only using around 30AH ~ 400 watts per day.

https://norcold.com/product/norcold-...-refrigerator/

I will be installing this one, and plan on monitoring its power usage for awhile before deciding how much battery I need.
https://norcold.com/product/n2175/

I've got a 360W solar panel on order to replace my 160W, and worse case, I'll get a 2nd one, I'm buying a big enough MPPT controller to run two.

[Mike Lewis]

Originally Posted by alanerickson

I was curious if you were looking for a fridge the size of that Isotherm or if you couldn't get by with something smaller?

I had in mind something to fill the space now occupied by my Dometic fridge, such as the Norcold N2175 that John is getting.

But it's early in the decision-making process and I don't know enough yet. Also, I haven't quite given up on my Dometic. After all, with all the battery storage I have now I can run the Dometic on 12V power while towing, all day if necessary. It works fine on 12V. If I keep an ear out for the fridge's burner when parked my problems may be over. Right now I think I'll make one more long trip with the Dometic before deciding to replace it.

[John in Santa Cruz]

FWIW, I'm replacing my RMD8555 strictly because its controller is blownup, and my RV service guy, who is authorized Dometic Repair, can't get them to return his calls about parts availability, he's had another customer with a broken Dometic for a YEAR now with no ETA. AND, he says Norcold is easy to work with and on. You can't even get a service manual or wiring diagram for a RMD8555

[rubicon327]

Originally Posted by John in Santa Cruz

FWIW, I'm replacing my RMD8555 strictly because its controller is blownup, and my RV service guy, who is authorized Dometic Repair, can't get them to return his calls about parts availability, he's had another customer with a broken Dometic for a YEAR now with no ETA. AND, he says Norcold is easy to work with and on. You can't even get a service manual or wiring diagram for a RMD8555

It's really sad that a company so pathetic can exist operating the way that they do with such poor product support. Customers should be demanding more and OEM's should be finding alternative products. They may be waking up - my buddy has a newer Jayco that has a lot of items from Furrion. I see they even have a couple 12V compressor fridges. Personally I go out of my way to avoid any products from Dometic.

[oldwave]

On our last 21, the 3 way Dometic worked very well. Unfortunately our on order trailer is 2 way only as the 8 foot version is only available in 2 way. Given I’ve already stretched the budget and absorbtion frig has worked for us I’m going with it. We did use the 12 volt side of the 3 way a few times on a short tow an on a ferry or 2. I am getting 350 watts of solar and a lithium system with 200 amp hours. So with the standard frig boondocking will be practical.

[Centex]

Originally Posted by TTMartin

.... I agree with your conclusion unless you are going to add additional solar panels like JonnyH. (10 total, 8 on the trailer and two on the tow vehicle) a compressor refrigerator is not practical for extended boondocking.

Your certainly entitled to the opinion, but methinks that might be a bit of an over-broad conclusion as stated.

I suspect there are other combinations of PV array, storage, and compressor fridge choices which are much less extravagant than Mr Hung's setup and may be very compatible with 'extended boondocking' for many folks.

There's certainly many factors to consider, among them other electrical demands one places on the PV and storage system. In Mr Hung's case, he's forthright in describing that his typical boondocking electrical demands include much more than just his dual-compressor fridge/freezer.

I'd suggest that other folk's use habits may well be amenable to 'extended boondocking' with a compressor fridge in the manner they choose to practice that type of camping, and with much less extravagant equipment choices than those exercised by Mr Hung to meet his overall needs.

Just suggesting that it could be a mistake for folks who enjoy 'extended boondocking' to run with your conclusion as stated and discount a compressor fridge out-of-hand without actually studying the feasibility in consideration of their particular situation.

[TTMartin]

Originally Posted by Centex

Your certainly entitled to the opinion, but methinks that might be a bit of an over-broad conclusion as stated.

I suspect there are other combinations of PV array, storage, and compressor fridge choices which are much less extravagant than Mr Hung's setup and may be very compatible with 'extended boondocking' for many folks.

There's certainly many factors to consider, among them other electrical demands one places on the PV and storage system. In Mr Hung's case, he's forthright in describing that his typical boondocking electrical demands include much more than just his dual-compressor fridge/freezer.

I'd suggest that other folk's use habits may well be amenable to 'extended boondocking' with a compressor fridge in the manner they choose to practice that type of camping, and with less extravagant equipment choices than those exercised by Mr Hung.

Just suggesting that it could be a mistake for folks who enjoy 'extended boondocking' to discount a compressor fridge out-of-hand without actually studying the feasibility in consideration of their particular situation.

No you don't have to add 8 additional solar panels.

But, I do agree with Mike Lewis's conclusion that it is not practical with the two stock solar panels.

You are going to need to add more solar or other power sources to run a compressor refrigerator for extended boondocking.

I have a 100 quart dual zone chest style compressor refrigerator/ freezer in my Sprinter van, and a 3 way refrigerator / freezer in both my previous trailer and my Escape. Having had 2 year experience with the compressor refrigerator in my Sprinter, and many more years experience with a 3 way in my previous trailer, I didn't give a second thought to getting a 3 way refrigerator in my 2020 Escape 19.

For what it's worth I find JohnnyH's posts often misleading. Rather than being forthright, his reply about the other things her runs off of solar are often used to dodge comments that he is running his compressor refrigerator, or air conditioning, etc.. off solar that he has way more than the stock 2 solar panels. While he has posted that he has the additional solar panels, he often neglects to mention it in posts proclaiming you can run air conditioning with solar, and the like. A more appropriate proclamation would be with my 10 solar panels and a 10.2kwh lithium iron phosphate battery bank, I accomplish this.

[Jwinfrey]

In our Northstar truck camper, I have the big brother refrigerator (Norcold DE-0061) to the model Escape installs. It’s almost double the amp draw and runs about 50% of time. I would kill to have it run only 20% of the time. We have 340 watts of solar and 2-12v AGM batteries. If we stay out in the sun, it would almost run indefinitely. The advantage of the camper is, it’s very easy to move and get to a spot where the is sun. We chose the 3 way in our new 5.0 because I knew we would be in areas of heavy shade, low sun, etc. I have been very impressed by the performance of the 3 way in our Escape. Quick to cool in 4-6 hours, much better freezer than the Norcold, and no power anxiety listening to the compressor run 😂.