Absorption Fridge, Solar and Batteries

Anjay74 · Newbie

Absorption Fridge, Solar and Batteries

Anjay74 · Newbie

*plus draw for other things

daffyfrancis · Senior Member

Our Dometic 2350 3 way fridge thermostat only works on gas & 240v & the thermostat is bypassed when on 12v - I imagine yours will be the same & you will need to run on gas when camped without 240v power & only use 12v when your engine is running -

David

Leshill · Veteran Member

I have that type of 3 way fridge and find it is not much good on 12 volts.The elements are 120 watts..both 12 & 240 volts. I only use 12 volts while traveling..240 v at home or in a caravan park.All other use is on gass.
I do have 120 watt portable sola but use that to keep my onboard battery topped up for 12 volt led lights / sink water pump & the phone etc charging. I do have a Honda generator to run an 800 w panasonic micro wave .
Running 12 volt on fridge all the time may not be best overall
Good luck.

Mamil · Senior Member

It's not that compressor fridges are "more modern", rather that a different process is used for cooling, in effect adsorption fridges heat to cool. The only advantage to this is it allows you to use gas to operate them, but the downside is that they are a lot less efficient and use about three times the amount of electricity. And yes, as David said, the when running on 12V DC the thermostat doesn't operate so they draw the rated current constantly, and to cap it all they don't even cool particularly well on DC, it's only really meant as a temporary measure during driving, and in fact most vans with 3-way fridges are wired so you can't run them off your van battery even if you wanted to.

For these reasons I would not advise trying to run an absorption fridge off solar, and if you tried, it certainly wouldn't be 'small and simple" as you want. Honestly, you'd be better off running on gas if you keep the fridge, or replacing the fridge with a compressor type (or a domestic unit and an inverter) if you want to run off solar.

-- Edited by Mamil on Wednesday 6th of February 2019 10:28:51 PM

Whenarewethere · Guru

There has to be something wrong with 192AH per 24 hours. My fridge even though it is small uses 23AH per 24 hours at 35°C set at 2°C (extensive testing). Typically over 24 Hours about 13 to 15AH. It does have quite a few modifications to make it more efficient but that is about 25% improvement.

Mamil · Senior Member

Whenarewethere wrote:
There has to be something wrong with 192AH per 24 hours. My fridge even though it is small uses 23AH per 24 hours at 35°C set at 2°C (extensive testing). Typically over 24 Hours about 13 to 15AH. It does have quite a few modifications to make it more efficient but that is about 25% improvement.

Judging from your previous posts, your fridge is a compressor type - but correct me if I'm wrong? Absorption type fridges use about three times the electricity as compressor types while they are running, and on DC they don't cycle on an off, it's a constant draw, so 192Ah is actually quite good, my absorption fridge would use 326 Ah over a 24hr period if I tried to run it on DC for that long! It's why you can't run absorption fridges on solar.

-- Edited by Mamil on Thursday 7th of February 2019 09:33:32 AM

Bobdown · Guru

When at Coober Pedy, my mate left the 3 way fridge running on 12 v while in the carpark for approx 1 hour, flattened the Ford Ranger enough so it wouldn't start.
3 way should always be on gas when stopped for any length of time.....my experience anyway.
Cheers Bob

Whenarewethere · Guru

I have a compressor fridge.

It's ridiculous that they use that much power. It would be worth looking at a fridge compressor kit & installing both in the same space. Gas one side & 12 volt the other.

Mamil · Senior Member

Whenarewethere wrote:
It's ridiculous that they use that much power.

It's the price you pay for being able to run a fridge on gas. The absorption process is inherently inefficient, like any heating system, most of the energy goes up the flue instead of doing useful work! However, before solar, it was really the only way to run a fridge "off-grid" for any period of time unless you ran a generator of some kind for a few hours a day. As solar and battery technology continues to improve, the days of absorption fridges are probably numbered.

Jaahn · Guru

Mamil wrote:
It's not that compressor fridges are "more modern", rather that a different process is used for cooling, in effect adsorption fridges heat to cool. The only advantage to this is it allows you to use gas to operate them, but the downside is that they are a lot less efficient and use about three times the amount of electricity. And yes, as David said, the when running on 12V DC the thermostat doesn't operate so they draw the rated current constantly, and to cap it all they don't even cool particularly well on DC, it's only really meant as a temporary measure during driving, and in fact most vans with 3-way fridges are wired so you can't run them off your van battery even if you wanted to.
For these reasons I would not advise trying to run an absorption fridge off solar, and if you tried, it certainly wouldn't be 'small and simple" as you want. Honestly, you'd be better off running on gas if you keep the fridge, or replacing the fridge with a compressor type (or a domestic unit and an inverter) if you want to run off solar.
-- Edited by Mamil on Wednesday 6th of February 2019 10:28:51 PM

Hi Anjay74 smile

I think the reply above and others have correctly said it all. That is my experience too. Do not bother with the trouble and expense to run the fridge off solar. They work well on gas and do not use much to do so. In very hot weather they are marginal and need to be in a shady spot to keep a bit cool but putting bottles of water(beer !) in them helps to get them over the hottest part of the day. biggrin You can improve the fridge with one or more 12v fans on the condensor at the back. The solar will help with that. I also replaced the 12V wiring with much heavier gauge wires which improved it a lot.

I used the car 12v power to run the fridge while driving in my MH. Then switch to gas when stopped. Worked ok for years. If I stopped for a short break the solar on top would keep the battery from getting too flat but you had to be careful as it does use excessive power and WILL flatten the battery if you forget. furious

My suggestion is to just use the solar to power your other items and a battery that will carry them overnight, considering poor weather as well. The vehicle can also charge the battery too. Search for ideas on here or ask. It depends on your tow vehicle alternator what you will need for this. hmm

Jaahn

-- Edited by Jaahn on Thursday 7th of February 2019 10:10:06 AM

-- Edited by Jaahn on Thursday 7th of February 2019 10:13:43 AM

Aus-Kiwi · Guru

Trust me . Fit extra solar and fit compressor fridge . But if your only going away
Camping two or three times a year for a weekend or so ? An absorbsion fridge is fine. Dont rely on DC . Its mainly as temp
Measure . Best to fit a voltage sensitive relay to prevent total battery discharge ? Doing it manually is fine if you remember! Better having it set up auto or youll rather have flat batteries or hot fridge !! Btw what made my mind up over 3way was the price for gas in the outback !! $60 9 kg bottle . No thanks !!

Leshill · Veteran Member

The original post also refered to a poptop van.Mine is a poptop also and if I added solar panels to the top I would never get it to go up. May be air lifter would help ..but more expense..No I will use gas when camped
Hope all of the info posted by everyone has helped .

Warren-Pat_01 · Guru

Hi Anjay74,
On 12v, an absorption fridge draws something like a constant 17A so if you're running on 12v whilst driving, consider adding a Fridge Switch to prevent the battery from discharging while you are stationary. The fridge will not defrost until some considerable time if it is kept shut.

I agree with Jaahn's statements - fitting 12v computer fans at the rear of the fridge (if possible) and shading the fridge side of the van during the warm/hot afternoons. I used sail tracks attached to the van, shade cloth & rope on our Jayco Eagle & that worked fine.
My fans were powered by a 10w solar panel ensuring that they operated only when the sun was on that side of the van.

Gas is the only way of ensuring these fridges work well when you're out camping without 240v access.

Regarding solar for your ancillaries, there is a lot written in this Techies' Tab - also have a look at www.campertrailers.org & you'll find spreadsheets that show how much solar/battery(ies) you need.

T1 Terry · Guru

I've fitted up a few systems where the 3 way fridge was retained, mostly because it was a new rig and they planned to wait until the thing died and then install a household inverter 240vac fridge with its own dedicated inverter. this is the best option if you plan to upgrade from the 3 way at some stage. The total cost including the dedicated inverter is about 1/3rd the cost of a 12v compressor fridge but will work just like the one at home ... or better if the home one is more than a few yrs old.
Back to running the 3 way on solar and battery. You need at least 200w of solar and only run the fridge on 12v when the sun is shining on the panel, that is different to sunrise and sunset. If you use portable panels with a decent size cable back to the solar regulator mounted near the battery, you can keep shifting the panels to face the sun and get a longer run on 12v before you need to switch back to gas.
To run the fridge 24/7 on 12v you would need a lot of battery capacity and a lot of solar. Forget about trying to do it with lead acid batteries, the weight would be prohibitive and they are just too slow getting the last 15% to 30% back in each day. But seriously, just not worth the expense and effort.
If you are looking at long term free camping and don't want the bottle refill hassle and expense, then convert to the household 240vac inverter fridge, enough solar to recharge the battery even on poor solar days and enough battery capacity to last 2.5 days without some form of recharging being available. If it rains that hard for 2 days that there is no solar input, you probably wouldn't want to stay there anyway.
If you want an idea on cost to do such an upgrade, best idea is to send me a PM so world war 3 doesn't start about me trying to use the forum as a sales platform

T1 Terry

oldtrack123 · Guru

Whenarewethere wrote:
There has to be something wrong with 192AH per 24 hours. My fridge even though it is small uses 23AH per 24 hours at 35°C set at 2°C (extensive testing). Typically over 24 Hours about 13 to 15AH. It does have quite a few modifications to make it more efficient but that is about 25% improvement.

That is amazing

You are saying that a 12V absorption fridge with at the very least a 125 W 12V element shouldis only be using power for around 2hrs per 24hrs

Are you in Iceland?

Best tell us about all those modifications

I did think I knew them all but must have missed some

T1 Terry · Guru

oldtrack123 wrote:
Whenarewethere wrote:
There has to be something wrong with 192AH per 24 hours. My fridge even though it is small uses 23AH per 24 hours at 35°C set at 2°C (extensive testing). Typically over 24 Hours about 13 to 15AH. It does have quite a few modifications to make it more efficient but that is about 25% improvement.
That is amazing
You are saying that a 12V absorption fridge with at the very least a 125 W 12V element shouldis only be using power for around 2hrs per 24hrs
Are you in Iceland?
Best tell us about all those modifications
I did think I knew them all but must have missed some

I think you need to read a few more posts before you jump in on the attack Peter. It has already been established the fridge with the low consumption was a small 12v compressor fridge, not an absorption type fridge. I think the consumption also referred to the over night battery draw, not 24hrs.

T1 Terry

oldtrack123 · Guru

T1 Terry wrote:
oldtrack123 wrote:
Whenarewethere wrote:
There has to be something wrong with 192AH per 24 hours. My fridge even though it is small uses 23AH per 24 hours at 35°C set at 2°C (extensive testing). Typically over 24 Hours about 13 to 15AH. It does have quite a few modifications to make it more efficient but that is about 25% improvement.
That is amazing
You are saying that a 12V absorption fridge with at the very least a 125 W 12V element shouldis only be using power for around 2hrs per 24hrs
Are you in Iceland?
Best tell us about all those modifications
I did think I knew them all but must have missed some
I think you need to read a few more posts before you jump in on the attack Peter. It has already been established the fridge with the low consumption was a small 12v compressor fridge, not an absorption type fridge. I think the consumption also referred to the over night battery draw, not 24hrs.

T1 Terry

No ,I did not miss it biggrin

Why was it posted in answer to an absorption fridge question

It was a go @ a bloke who made a totally irrelevant post as far as absorption fridges are concerned

A reply that in no way applied to an absorption fridge smile

Jaahn · Guru

oldtrack123 wrote:

No ,I did not miss it

Why was it posted in answer to an absorption fridge question
It was a go @ a bloke who made a totally irrelevant post as far as absorption fridges are concerned
A reply that in no way applied to an absorption fridge

Hi Peter smile

Another example of how you jump in aggressively to argue instead of just saying nothing and letting the discussion go. IMHO cry

I believe it was relevant to point out how much better off you would be with a compressor fridge. Spending the money on the fridge replacement instead of a big solar/battery system. Just my non aggresive thoughts on the discussion and no more from me disbelief

Jaahn!

T1 Terry · Guru

oldtrack123 wrote:
T1 Terry wrote:
oldtrack123 wrote:
Whenarewethere wrote:
There has to be something wrong with 192AH per 24 hours. My fridge even though it is small uses 23AH per 24 hours at 35°C set at 2°C (extensive testing). Typically over 24 Hours about 13 to 15AH. It does have quite a few modifications to make it more efficient but that is about 25% improvement.
That is amazing
You are saying that a 12V absorption fridge with at the very least a 125 W 12V element shouldis only be using power for around 2hrs per 24hrs
Are you in Iceland?
Best tell us about all those modifications
I did think I knew them all but must have missed some
I think you need to read a few more posts before you jump in on the attack Peter. It has already been established the fridge with the low consumption was a small 12v compressor fridge, not an absorption type fridge. I think the consumption also referred to the over night battery draw, not 24hrs.

T1 Terry

No ,I did not miss it
Why was it posted in answer to an absorption fridge question
It was a go @ a bloke who made a totally irrelevant post as far as absorption fridges are concerned
A reply that in no way applied to an absorption fridge

As Jaahn has already posted, this says a lot about your posting style, especially the smiley emoticon after the acknowledgement, that shows you get pleasure from picking something you find you can use to launch an attack.

Sad, but that is just the way it is and thankyou is sort of in order, so others can better understand your motive behind the attacks, it is not to clear up wrong information but rather your perverse choice of pleasurable entertainment, you do it for sheer pleasure.

Is that the ultimate description for an internet troll?

T1 Terry

Leshill · Veteran Member

Back to the subject....I posted that my 3 way fridge 12 volt & 240 volt elements were 120watts they are actually each one is 150 watts. Thats why they draw so much power on 12v.I could only get 30 to45 minuets before my engine would not start.

T1 Terry · Guru

Leshill wrote:
Back to the subject....I posted that my 3 way fridge 12 volt & 240 volt elements were 120watts they are actually each one is 150 watts. Thats why they draw so much power on 12v.I could only get 30 to45 minuets before my engine would not start.

150w @ 12v = 12.5 amps =0.2Ah per min. x 30 mins is only 6.25Ah. Either a very small start battery or one getting close to the grave. Start batteries are rated in RC (reserve current) and that is supposed to represent how long in mins it can supply a 25 amp load, 12.5 amps is only half that load so it should have lasted a lot longer than 30 mins before the battery was that flat it wouldn't start the engine.

Might be a good idea to get the whole charging system checked to make sure the battery actually getting properly recharged and not half charged the way most late model vehicles seem to be doing.

T1 Terry