Using a home fridge...The internet is not always correct (an understatement)

[JD GUMBEE]

This video is very well done...and the guy seems to know what he is talking about.

But he is, quite simply, dead-wrong.

I wonder how many people gave up on using a home fridge because of his seemingly thorough video?

1. Most RV's I have seen where the Dometic was replaced with a home fridge used 10 cu ft max, not "18."

2. I have not seen 100 watt panels used on a setup for use with a fridge...ever.

3. His figures depend on the compressor running half the time. (When is the last time your compressor fridge ran its motor HALF the time??)

You can use a residential fridge without a problem if you size the setup correctly and refrain from leaving the door open for extended periods.

 

[lenny flank]

I can't speak to the fridge thingie, since I don't use one, but I learned long ago that the Internet is the collective brain of humanity. Sadly, though, most of humanity has **** for brains.

 

[Trebor English]

After the last hurricane I helped people with generators to power their fridges.  Mostly it was gummed up carburetors.  I remember one fridge particularly.  It was about 18 or 20 cubic feet, pretty common residential fridge.  When it was defrosting it took 460 to 480 watts.  Running it took 166.  All the arithmetic in that linked You-Tube video was based on 720 watts.  With all that hog washing there must be a lot of really clean pigs.  

I remember that fridge because it was a Montgomery Wards Admiral fridge.  They went out of business in 2000.  It was an old fridge but still working great.  When I first got the generator running the fridge was in a defrost cycle.  It seemed like it took forever to finish.

A modern 10 to 12 cubic foot not automatic defrost residential fridge freezer combo powered by an efficient MSW inverter will not require 14 100 watt solar panels and 11 batteries.

 

[tx2sturgis]

Yeah his use of the term 'amps per hour' makes me cringe....although I think his basic calculations are in the ballpark, for the unit he is using. We really need him to toss in a Kill-a Watt unit to verify the power consumed. 

But, AH is NOT 'amps per hour',  it means amps (used) TIMES an hour.

You can say that you have used 20 AH per hour...that's acceptable. Or 20 AH per day...again...acceptable. 

And yeah many of the bigger residential fridges are power hogs....that's why so many RVers and van dwellers who boondock find another solution.

 

[Trebor English]

Yeah his use of the term 'amps per hour' makes me cringe....

If a cruise ship leaves port at 10 knots it will go 10 nautical miles in an hour.  If you say it is going ten knots per hour I'm not sure what you mean.  I think you are saying it will be going 240 knots a day later.  

If the fridge uses energy at the rate of 720 watts per hour is it using 17,280 watts 24 hours later?  At what point does it burst into flames?  

Cringe....

 

[Canine]

txsturgis, I'm not sure what you mean. The rating of 20 ah means if the device were running 100% of the time, it would use 20 amps in an hour. Another way to put that is 20 amps times 1 hour. Still the same result.

My understanding is an average residential fridge is rated at around 700 watts. Then a rule of thumb is that it runs about 1/3 the time, so the actual use is about 230 watts or 21 amps an hour with the inverter loss figured in. Over the course of a day, it will use 504 amps. This comes to 8 or 9 solar panels to run just the fridge. Now if the fridge is in really hot weather, like what one would see in a poorly insulated RV, then the number of solar panels is going to be higher. I can see 11 solar panels, assuming no losses other than the inverter, being needed to power that one fridge.

If the fridge was rated at 500 watts, it would need 6 to 7 panels to power it. Still a lot of panels. We may disagree with how big of a fridge he used in his example, but all we need to do is scale it down to the size of fridge we would be using. The math still works out; we get a good idea of what would be needed should we decide to use a residential fridge in an RV.

Yes, I can see a fridge running half the time in hot weather. Nothing would have to be drastically wrong to create a scenario where a fridge would need to run that hard to maintain temp. Would most conditions with a decent fridge make it run half the time? No, but it isn't unreasonable.

Another consideration is the durability of the fridge. How well can it withstand not being level? How well can it handle bumps and vibrations? Factoring in the Peukert Effect, how well will the battery bank be able to start the compressor? Not at all at 50% battery capacity. The Peukert Effect is much less of a factor with DC fridges. A DC fridge probably would start at 50% battery capacity with a 400 ah bank. One reason why the small DC fridges are so expensive is because they are built to a much higher durability standard. They also have soft starts, which isn't cheap. Economy of scales plays a large factor in the price as well.

If the opportunity presents itself, I will be switching to the 36 cell (generally referred to as 100 watt panels) to power my needs. I've seen many setups that use 100 watt panels that have fridges; I'm don't understand when the OP said, "2. I have not seen 100 watt panels used on a setup for use with a fridge...ever." Can that be clarified?

 

[tx2sturgis]

txsturgis, I'm not sure what you mean. The rating of 20 ah means if the device were running 100% of the time, it would use 20 amps in an hour. Another way to put that is 20 amps times 1 hour. Still the same result.

Not exactly. Again, the term 20 amps per hour as the man in the video says, means 20 amps divided into an hour....it should be 20 ah in that hour, or 20 ah in a day, or whatever. 

Amps, (amperage, current) is an electrical current flow (usually electrons) with time already factored in. So many coulombs (it's a big number) passing a certain point in a second. 

AH is that amount of flow, equal to a certain number of amps, flowing for the duration of an hour. And that is what he means...

It's a similar situation to a residential electric bill...you are billed for the kwh's (killowatt-hours) that you used...they don't bill you for killowatts per hour.

He does finally use the term amp-hour correctly towards the end of the video.

 

[SchortBus]

[quote pid='372660' dateline='1519587198']

You can use a residential fridge without a problem if you size the setup correctly and refrain from leaving the door open for extended periods.
[/quote]

If you wanna run a 110v frig on solar, the first thing you need to do is buy a chest freezer, then swap out the thermostat. There is plenty of info on this jerb online...

The chest freezer saves a ton of juice because everytime you open the door, all the cold air doesn't fall onto the floor, and get yer toes cold. Sure, it's a hassle to get stuff out of the bottom, but living on batteries requires some give and take.

I'm running a peltier coleman cooler at the moment, and while it beats buying ice, she loves her some wattage....pretty much 60w, 24/7 if the ambient temp is above 70f. Right now, being "winter" (I'm on the beach in Cali), I can shut it off all night and save watts. Oh, and if you never have used a thermoelectric cooler, they are kinda cool, and will literally freeze everything if the ambient temp is low enough.

 

[Trebor English]

Where does this 700 watt figure come from?  I just looked up a random Samsung 26 cubic foot side by side monster.  It is 502 kwh per year.  Figuring 365 days, 24 hours, it is 57.3 watts average.  If it runs 1/3 of the time thats 171.9 watts.  Josh Garage says 720.  Canine says 700.  I measured 166 on a unit at least 17 years old.  I don't understand the 700 watts figure.

 

[tx2sturgis]

I like the freezer idea...some off-grid home owners have been doing this for decades. Simply bypass the built-in thermostat with a mechanical or digital unit that cycles the compressor at a higher box temperature.

The advantages are many: Top opening as was mentioned, better insulation, plus, no fan, and no energy robbing defrost cycle on most of them. The one issue with many of them is the 'skin mounted condenser'....I assume you can still buy units with external (back mounted) condensers but I havent been looking lately.

 

[tx2sturgis]

Where does this 700 watt figure come from?  I just looked up a random Samsung 26 cubic foot side by side monster.  It is 502 kwh per year.  

This is why we need a kill-a-watt reading for a week or so to get an average.

The energy ratings on the ad and the sticker on the front of the fridge is a 'best case' scenario, done under a specific set of lab conditions...sorta like MPG ratings on cars....and actual home use or RV use would make the numbers much higher....

How much higher?....well that is the question.

 

[wayne49]

Chest format is not always possible, if ever, in an RV when replacing an upright unit.

If chest format is possible then just buy a ready to go Whynter or whichever your fancy tells you.

Available floor space is scarce in RVs. May require removing some built in furniture to make space and then running wires to that spot.

 

[JD GUMBEE]

My electric fridge is only 10 Cu ft, not 18, but we have 400AH of batteries and have had zero problems. (Ours is 296KWH yearly on the yellow sticker)
(Two TV's/microwave/laptops/dish network box/lots of ham radio gear...and we do not need to watch it. We don't even think about it.) We run both TV's till around 12AM at least and all the rest is 24/7 plugged in.

Strange that they sell the big fridges in RV's and along with all the stuff most people use, they recommend 1,000 to 1,200 watts if you want to be able to use the A/C some also...all on solar power.



The 100 watt comment meant that everyone I have seen with more than 400 watts on the roof have gone with 250 watt panels or the 330's like we have, which were more efficient space-wise than 100's. (At least when we got ours 3+ years ago it was...) Had we gone with 10 100 watt panels, we would not have been able to fit them on our roof. Then again, that was what I had to choose from when I bought them. YMMV. Just our experience.

Again, our fridge is 10 cuft, but our batteries are going on 4 years old now and are just deep cycle lead acid cheapies. Still going strong.

At night, the compressor in ours can go for two hours or more without running. Then when it does run, it works for 15-20 minutes and turns off again.
Also, it is running the hardest is when the sun is brightest.
Turn the microwave on anytime after 9-9:30AM and it will peak up to 60amps. It does not lose the 60 ampere ability till 3:30 or later in Quartzsite in December. Flat mounted panels, no tilting.

"The Wynns" also run their huge electric-pig triple-door fridge on solar. They have about the same wattage on the roof, but much more battery than I have.

Not sure how long the fridge will live, but it has already paid for itself over a tiny DC unit for 500 dollars with no freezer and half the space in the fridge itself.
If it dies tonight, I would go buy another one in the morning.
We strongly prefer it over the "dollar per day" propane Dometic that always made me nervous...and is a big reason the old RV's go up in smoke.

The point I was trying to make is, there are people on the Internet (and in person) who claim that using a residential fridge in your RV unit on solar power is near impossible.
This is simply not true. (Just like the guy in the video with the white-board examples...huge over-done compressor run time assumptions.)
Rainy days can mean the Honda comes out for a few hours. For us, it is still a whole lot less costly than propane...not to mention safer.

 

[John61CT]

> I have not seen 100 watt panels used on a setup for use with a fridge

Huh? That's the most common size, 2 or 3 is enough for the more efficient ones plus a fan

> His figures depend on the compressor running half the time. (When is the last time your compressor fridge ran its motor HALF the time??)

You mean that's a lot right? An efficient unit in mild conditions can get down to 6-7 minutes per hour, but in freezer mode or hot weather over 50% is common.

> You can use a residential fridge without a problem if you size the setup correctly and refrain from leaving the door open for extended periods

If you already have excess solar fine, but people in smaller vans or planning from scratch are much better off with as efficient a fridge as possible.

 

[Canine]

Where does this 700 watt figure come from?  I just looked up a random Samsung 26 cubic foot side by side monster.  It is 502 kwh per year.  Figuring 365 days, 24 hours, it is 57.3 watts average.  If it runs 1/3 of the time thats 171.9 watts.  Josh Garage says 720.  Canine says 700.  I measured 166 on a unit at least 17 years old.  I don't understand the 700 watts figure.

The 700 watt rating is just that- a rating. When the fridge runs 100% of the time, it will use 700 watts. When I say "watts", I am actually saying "watts in an hour". The "an hour" part is understood.

Let me elaborate on the watts/hour thing with an analogy. Let's say my friend Jeff is visiting me from Canada, but you don't know he is from Canada. You hear him telling a story that he was going 40 in a school zone, but he got a ticket anyway and this was wrong because he was going the speed limit. You think, "What?! What is wrong with him? 40 in a 25? That's crazy." But what you don't realize is he is using KPH not MPH. Same with watts. When someone says watts, is it watts an hour? A day? A second? It's an hour unless stated otherwise. Understanding this would be easier if we said Watts per hour every time in the same way we say miles per hour every time. When people ask use how fast we were going, we usually answer, "50 miles per hour" or "25 miles per hour", etc. Even when we truncate it and answer with just a number like 50 or 25, we understand it is 50 miles per hour. Unless we are in Canada, then we understand it to be kilometers per hour. In either case we don't say, "Um, do you mean you were traveling 50 miles in a second? That's kind of fast, don't you think?" or "Um, do you mean 50 miles in a week? Were you walking there?" You intuitively know it is per hour. When discussing watts, it usually isn't intuitive for the layman, so don't feel bad. It is a little awkward at first, but you get used to it.

Now that you understand that, we use the fridge rating of 700 watts an hour to know how much electricity it uses compared to other fridges. We know apples are being compared to apples because the 700 watt rating uses the same context and factors that all the other fridges use to get their individual ratings. There are other factors that are kept the same as well like ambient temperature, etc., to keep the apples to apples comparison accurate. The 700 watt rating doesn't mean that is how much electricity you will be using in your specific situation. If one fridge is rated at 700 and another fridge is rated 500, you know the latter fridge will use less electricity. How much specifically will be used in your specific situation depends on many factors, but you will know that the latter fridge will use less electricity than the former.

A fridge doesn't run 100% of the time after it reaches the temperature set by the thermostat. It will run non stop, maybe for a few hours, until everything is frozen to temp, but than it will cycle on and off to maintain the temp. If a freezer is rated at 700 watts, and you fill it with elk meat at room temperature, it is going to use 700 watts until it hits the setting on the dial. How much it will be using will depend on your needs. How full do you keep your fridge? How cold do you have your settings? How well insulated is your RV? How clean do you keep the cooling fins? If you have a normal environment and everything is working as well as it should, you can expect your fridge to run about 20 minutes out of every hour. Therefore, 1/3 of the rated 700 watts is actually 233 watts used. The same way to say that is 1/3 of the rated 700 watts an hour is actually 233 watts an hour used.

Then how many hours in a day? 24. Then you multiply 24 times 233 which equals 5592 watts a day. Then to get amps you divide 5592 by 12 and get 466 amps used over an entire day. Then you continue with the math from there.

I don't understand what tx2sturgis is saying. All I can say is how many amps are used in an hour or a day or whatever span of time is needed to clarify how much electricity is being used. Maybe what he is saying is something like when people ask, "What is the VIN number for your vehicle?" In this sentence what the person is asking is literally, "What is the Vehicle Identification Number number for your vehicle?" For me to point that out would be annoying as all get out. That would be a petty thing for me to do unless this was in the context discussing the nuances of grammar. In any other context, I'm going to easily and intuitively know what that person is talking about even though they are absolutely wrong. I'm not saying that is what tx2sturgis is doing. All I am saying is I don't understand his point. He may be talking over my head; just because I don't understand him, doesn't mean he is wrong or at fault somehow.

 

[tx2sturgis]

The point I was trying to make is, there are people on the Internet (and in person) who claim that using a residential fridge in your RV unit  on solar power is near impossible.

You got it figured out....sounds impressive.

There have been some threads about this topic before....and in a bigger RV with plenty of roof real estate it can certainly be setup to work well. Many here have done this exact thing. 

Of course, in a normal van, the roof space for panels is not as much, and it's probably best to use a smaller 12v compressor fridge, or maybe even a portable propane fridge, since power production using solar on the roof, not to mention the space for lots of batteries, tends to be limited.

I would have enjoyed seeing the system you have set up....maybe next time I'm out west, you can give me a tour.

 

[Canine]

Even with an RV with tons of roof space, using a residential fridge isn't quite as cost effective as most would think. Yes, the fridges are less expensive to purchase and replace, but that cost is offset in needing more solar panels, and more charge controllers, or a more expensive charge controller, and a larger inverter or two inverters. Then a larger battery bank with more batteries needing to be replaced and batteries ain't cheap. Then a need for more sunny days. Or if the days aren't sunny enough, a generator or camping with hookups, which both cost more money. Then the need to stay on nicer roads so you don't beat up a fridge that can't handle rough roads or being parked on an incline. Most people would have a hard meeting all those needs. Using a residential fridge is possible and it isn't inherently wrong, but seldom does it make economic sense.

 

[JD GUMBEE]

I did not realize that I had not disclosed my RV in this thread. Sorry folks.
It is a 32 foot class A. Not a van. Now I see why people are reacting like they are about the big panels...LOL

The thing Mrs G and I are considering is...to throw in a few more variables...if we got two chest freezers, one 10 cu ft and one 5 cu ft. (We have room to do this if we re-purposed a bench.)

Use the 10 cu ft freezer as a fridge only.
The 5 cu ft would be used as a regular freezer.
The 10 cu ft, used as a fridge would be on all the time.
The 5 cu ft, that we would use as a freezer, would run wide-open but on a timer.
The idea would be to get the inside of the 5 cu ft unit used as a freezer down as cold as we could while the solar was producing a lot.
Around 4PM, the timer shuts the 5 cu ft freezer off. If we got it to (??? -5 maybe???) by 9AM the next morning, when the solar was putting out the amperage again, have the timer switch it back on.
If the stuff inside would have only gained 15-25 degrees overnight...it would still be frozen and safe.
Since they are insulated really well and you do not usually open a freezer at night anyway most of the time, I wonder if we could have 15 cu ft of space between the two, but still use only the four batteries.

Any ideas on this scenario?

tx2sturgis, do you check the email your account is registered to? I sent you a msg.

 

[tx2sturgis]

tx2sturgis, do you check the email your account is registered to? I sent you a msg.

Yes, received and understood.

 

[bonvanroulez]

Let me elaborate on the watts/hour thing with an analogy....

Now that you understand that...

A fridge doesn't run 100% of the time...

Then how many hours in a day? 24. Then you multiply 24 times 233 which equals 5592 watts a day...

It seems you need to do some reading on basic electricity.  Everything in your lengthy post (that I trimmed per forum rules) is basically gibberish.

I don't understand what tx2sturgis is saying.

What you don't understand that tx2sturgis is saying is that in the context of this discussion, there is no such thing as "watts an hour, or watts per hour, or amps in an hour, or watts a day, or amps used over an entire day".
Watts per hour is a thing but not what you think it is. Trebor was trying to point that out above, "If the fridge uses energy at the rate of 720 watts per hour is it using 17,280 watts 24 hours later?" That is an actual example of watts per hour, expressed as W/h.

From Wikipedia: "Misuse of watts per hour...
Watts per hour (W/h) is a unit of a change of power per hour. It might be used to characterize the ramp-up behavior of power plants. For example, a power plant that reaches a power output of 1 MW from 0 MW in 15 minutes has a ramp-up rate of 4 MW/h.
The proper use of terms such as watts per hour is uncommon, whereas misuse may be widespread."
(bolded by me)

In lieu of a course in Basic Electricity 101, read this excellent little summary, quoted from Northern Arizona Wind and Sun's website:

[font=Verdana, Arial, sans-serif]WATTS
[/font]
[font=Verdana, Arial, sans-serif][font=Roboto, Verdana, Arial, sans-serif]The poor watt is often misunderstood. Watts are basically just a measure of how much power a device uses, or can supply, when turned on. A watt is a watt - there is no such thing as "watts per hour", or "watts per day". If something uses 100 watts, that is simply the voltage times the amps. If it draws 10 amps at 12 volts, or 1 amp at 120 volts, it is still 120 watts. A watt is defined as one Joule per second, so saying watts per hour is like saying "miles per hour per day".[/font][/font]
[font=Verdana, Arial, sans-serif]WATT-HOURS[/font]
[font=Verdana, Arial, sans-serif][font=Roboto, Verdana, Arial, sans-serif]A watt-hour (or kilowatt hour, kWh) is simply how many watts times how many hours that is used for. This is what most people mean when they say "watts per day". If a light uses 100 watts, and it is on for 9 hours, that is 900 watt-hours. If a microwave uses 1500 watts, and runs for 10 minutes, that is 1/6th of an hour x 1500, or 250 WH. When you buy power from your friendly utility (look at your last bill), they sell it to you at so much per kWh. A kWh is a "kilowatt-hour", or 1000 watts for one hour (or 1 watt for 1000 hours).[/font][/font]
[font=Verdana, Arial, sans-serif]AMPS[/font]
[font=Verdana, Arial, sans-serif][font=Roboto, Verdana, Arial, sans-serif]An amp is a measure of electrical current at the moment. (Amps do not come in "amps per hour" or "amps per day" either). Amps are important because it determines what wire size you need, especially on the DC (low voltage) side of an inverter. All wire has resistance, and amps flowing through a wire makes heat. If your wire is too small for the amps, you get hot wires. You can also get voltage drops in the wire if it is too small. This is not usually a good thing. An amp is defined as 1 Coulomb per second.

A Coulomb is the charge of 6.24 x 1018 electrons. Therefore, 1 Amp is equal to the charge of 6.24 x 1018 electrons passing a point in a circuit in 1 second.[/font][/font]
[font=Verdana, Arial, sans-serif]AMP-HOURS[/font]
[font=Verdana, Arial, sans-serif][font=Roboto, Verdana, Arial, sans-serif]Amp-hours (usually abbreviated as AH) are what most people mean when they say "amps per hour" etc. Amps x time = AH. AH are very important, as it is the main measure of battery capacity. Since most inverters run from batteries, the AH capacity determines how long you can run.[/font][/font]

I wish there was a sticky thread to point to when these discussions so frequently go haywire over the misuse of electrical terminology.