Run 3 way fridge on 12v permanently

[wildebus]

as i understand it the 12v only maintains the temp so won’t refreeze if you open doors etc i have just had an episode with a suspected gas leak so ran the fridge on mains through the inverter maximum draw was -23 A couple of that being the inverter overnight about 11hrs it averaged 8A after allowing the aforementioned 2A inverter draw , it certainly cools better on electric than gas so will boost it like that when power is high currently getting 16.8 A going in on the algarve

Do you still have that switching relay setup for automatic switching to AC on good batteries?

 

[nabsim]

I already have the system to run it! So therefore why not?

I was under the impression you didn’t as your post says you can run it for 6 hours, not 24. If sticking to a 3 way then 230V is better than 12V so maybe a smaller inverter with less overhead if you are looking for efficiency

 

[Mark135]

If you've got enough battery power then you'd be better off running it from an inverter on 240v. 12v is on permanently, only intended to run an hour or 2 whilst driving. If you run on 12v it will use close to 3kwh per day.

 

[rugbyken]

Do you still have that switching relay setup for automatic switching to AC on good batteries?

i know lee has one like that david i only have the manual switch over you made up remaining on my system you can set his so that when the battery is 90% or 95 it will click on till battery drops below presets , mine runs on either mains or inverter if selected don’t have any way of presetting it

 

[wildebus]

i know lee has one like that david i only have the manual switch over you made up remaining on my system you can set his so that when the battery is 90% or 95 it will click on till battery drops below presets , mine runs on either mains or inverter if selected don’t have any way of presetting it

ah - mixed your setups up .
Yup, he uses the Victron BMV to control the AC power. I did that with my 3-Way fridge as well, but when I switched to a Compressor one I 'repurposed' it to control the AC power to the Boiler instead.

 

[Trotter]

I bought a compressor fridge to replace my 3way. Sent it back, for free, thank you Amazon.
Couldn't get the 3way out without destroying half the van.

 

[wildebus]

I bought a compressor fridge to replace my 3way. Sent it back, for free, thank you Amazon.
Couldn't get the 3way out without destroying half the van.

You need these guys .....

I expected to have to go through the cab with my 3-Way but it just scraped through the hab door gap once we (me and Rae ) removed the rubber trim around the door. So tight the paper label peeled off the side as pushed it through

 

[trevskoda]

I followed all wildebuses threads on electric 230v fridges and did a bench test myself before installing one, he was correct in all counts.
My small table top fridge uses 250 mA when running which is very low, it takes a few at most hrs to get down to temp 2c and -20 cold box.
It will run 24 hrs easy on 2 full charged 90ah lead acid batteries, so anyone doing a odd day or two wilding should not have much bother as long as you dont have the van lit up like blackpool etc, if you have solar as i do or move there wont be any bother.
Oh and thank you wildebus for the hard work and detaild you went through to post it in the first place.

 

[Pudsey Bear]

If we went down that road it would have to be at least as big internally and externally as the existing 3 way.

 

[wildebus]

If we went down that road it would have to be at least as big internally and externally as the existing 3 way.

A compressor fridge of the same external dimensions will not be any smaller inside and I would think actually bigger if you think of all the space at the back taken up by the heating elements/chimney and the burner. The compressor itself will take up room inside at the bottom, but above that the fridge and freezer will go all the way to the back.

Out of interest, I just looked up the details of my original 3-Way Fridge, the "proper" Motorhome replacement and the Domestic fridge I actually bought to replace it.

Original:
Thetford N175. Nominal 175L Capacity. Real Capacity around 155L. 1245 x 525 x 628 mm
New 12V Replacement:
Thetford T2175. Nominal 174L Capacity. Real Capacity - 158L. 1245 x 525 x 613 mm
Chosen 240V Replacement:
LEC T5039B. Net Capacity 90L (Fridge) + 45L (Freezer) = 140L. 1225 x 500 x 540 mm. So physically notably less in depth but still a fairly close capacity?


The Power consumptions are interesting ....
N175 - Gas is 420g/24h; Electric is 4kWh/24Hr (interesting, the current 3-Way replacement for this - the N3175 is identical energy use)
T2175 - No gas of course; Electric is 600Wh/24Hr. That is 6.67 times less than the 3-Way
LEC T5039B 240V Comp - Electric is 530Wh/24Hr. This is actually 10% more efficient than the 12V Motorhome Fridge/Freezer and 7.5 times more efficient than the 3-Way (my own testing confirms pretty well the same difference between old 3-Way and new domestic fridge).
The inverter overhead when the fridge is running will wipe out the 10% difference, but when the fridge compressor is off the inverter overhead is just 2W (approx 40Wh/Day) - And I could even have the inverter totally off if fridge compressor off to save that if I wanted.


Prices:
A new 3-Way equivalent to the N175 would cost from Jackson Leisure £1,459 (N4175)
The T2175 from Jackson Leisure is £1,450
The LEC T5039B from AO cost me £279

I do like the look of the Thetford T2175 (https://www.jacksonsleisure.com/fri...ressor-fridge-freezer-for-campers-motorhomes/) and had considered buying one, but the price difference between it and something I knew would work just as well could not be ignored. I could buy 5 LEC fridges instead of a single Thetford and still have change.

 

[Pudsey Bear]

Yeah, but where would you put 5 fridges?

 

[nabsim]

Yeah, but where would you put 5 fridges?

Take the bed out silly, mattress on top

 

[Okta]

My 3 way fridge is rubbish on 12V. It just about maintains a coolish fridge temperature if it is starting from cold and there is no door opening. If I am setting out on a journey from storage without a cold fridge I run it on gas (yes I do have rupture protection and a crash regulator). Gas and 240V operation are much better than 12V. The fridge is only 5 years old and from new the 12V operation was poor.

My next van will have a compressor fridge.

 

[wildebus]

There will be a good reason why in the US it is now rare to see Propane (LPG) fridges in anything but entry level RVs. And in all higher end RVs, you only see residential-style AC fridges.

 

[mistericeman]

I took our temperamental 3 way out and replaced it with a nigh on identical external sized (interior actually has more usable room )
240v model and a eco mode Victron 12/800 inverter .....

Runs 24/7 through summer ....always loaded with essentials like wine/butter etc .
No pfaff

 

[Pudsey Bear]

Take the bed out silly, mattress on top

I'm glad we have people like you Niel to iron out the ruffles in a plan

 

[trevskoda]

I'm glad we have people like you Niel to iron out the ruffles in a plan

Mite col your ass down as well.

 

[Pudsey Bear]

Mite col your ass down as well.

I could use some of that still.

 

[funkyronster]

I will answer your actual question if I can - but that is not to say I disagree with some of the opinions on this thread. It is common knowledge that absorption (3-way) fridges need more electrical power than compressor fridges, but you specifically said that you are in Spain and have plenty of solar. I have a similar situation - since a recent upgrade to much bigger batteries, so I can store more, and much bigger solar, so I can generate more, it soon became apparent that I had power to spare in summer, lots of it. My new system is sized for winter full time off grid. so it is inevitable that such a system would have excess capacity in summer. So I started to experiment with how much power I could use to power my 3-way in summer, via my inverter. The results are similar to yours - in sunny weather in summer I can power a 3-way 24/7 on 230v. But it is very hungry - about 10 amps at 12v per hour, but with a potential of 3 to 400a of solar coming in, it is certainly doable, but you have to keep an eye on it - a cloudy day can upset things very easily! Monitoring is essential, and the BMS apps that come with most lithium batteries these days are good for this. But the novelty soon wore off for me, all I was saving was a bit of gas. My fridge is on gas pretty much 24/7 and just works.

With regard to your desire to run it directly on 12v, I can see the sense in this, but as others have said the 12v heating element on a 3-way is usually not as powerful as the 230v one. But putting that aside, how would you actually do it? I don't recognise your actual fridge, but would assume it's a modern one with automatic energy selection. As you say, the 12v part only works when the engine is running, so if you need to override this, then you need to find the 12v supply cable, that will only be live with the engine on, and connect it to a permanent supply from the leisure battery. You can do this either at the fridge end, or the battery end - I don't know your van but presumably you will have an Elektroblock or similar that contains the fuses and relays. I have installed compressor fridges in several vans, and have found it quite easy to do this at the distribution end. You can identify the cables either by referring to the documentation, or poking around with the multimeter. One of the cables from the box will be the fridge 12v supply wire - and it will go +12v when the engine is on. There will also be another 12v supply to the fridge, which will be live all the time - this is for the fridge electronic control board - the fridges controls need 12v all the time no matter what the power source. This wire will be thinner than the other if there is any confusion. Once you find the relevant cable, you can cut it and connect it to one of the permanent 12v supplies, which will also be present - I can't be more specific because I don't know what your equipment actually is. But they all work on the same principle. You would also have to think about additional fusing, and probably also a manual switch.

So you can do it with a bit of messing around. But personally I wouldn't bother. If you have it running from your inverter already, then I would leave it that way. While it is true on paper that inverters have a conversion penalty, in reality it isn't that big, and often overblown. It's about 10%, which isn't that great. Plus the fact that the 12v element is weaker, I just don't think it's worth the hassle - using excess solar to power a 3-way is most likely best achieved doing it the way you do at present, but the only way to prove it is to suck it and see - but you would need accurate measurement - either with a battery monitor app, or a dc clamp meter, so you can actually measure and count the amps used. I very much doubt there would be much difference, and if the fridge then proved to be not as cold as before, then that will kill the idea for sure.

 

[wildebus]

Take the bed out silly, mattress on top

And leave the doors open ... Air Con