Powering compressor fridges

[Philip M]

While I am awaiting parts which I hope are going to fix a particularly elusive fault on my existing three way fridge, my mind has been increasingly turning to the idea of replacing it altogether with a 12 volt compressor fridge. 

I've been looking at Just Kampers JKF50 which would fit easily into the existing cabinetry and only uses 0.7Ah at 25 degrees ambient temperature once cold and set to eco mode. That would use approx. 17Ah in a 24 hour period.

I was wondering if anyone here has any experience of running a compressor fridge and what power I might need to comfortably power it off-grid for a week.

I have an Eriba 320 poptop van with a 115Ah battery which gives me a usable 57Ah, and I would need to upgrade my portable solar panels. I have insufficient space to fit them on the van, plus I'm very tight for weight. 

From my experience of the 40W panels that I already have, I know I can expect around 15 to 75% of their rated value depending on the weather plus electrical losses. 

I use very little battery power as there is no TV or shower and all lights are LED. 

Anyone have any thoughts as to the minimum size panel I could get by with?

[hja]

I dont know about the model you are looking at but i can tell you about our compressor fridge. Ours is a Dometic undercounter fridge with freezer box. We had a 95ah battery and 120w solar on the roof. Other battery pull is pump, lights, ipad & phone charge. Arrived at site with full battery. Two nights on the site, no hook up. Didnt take van off site. Rained most of the day so no solar. By morning after second night battery was down to 12v. Regained its power as soon as we drove, but obviously not what we wanted. We swapped to lithium and a new solar controller. We have now done four nights without moving van, but we did have solar. We are unlikely to stop any where longer than that without moving.

[Philip M]

Thanks for your reply, it's very helpful to hear real experience about these devices. Your set up sounds about the same as mine. In theory a 95Ah battery ought to provide a useful 47Ah which, if the fridge drew 1Ah on average, two days sounds about right. I'm encouraged that your new set up works well though. What's the size of your lithium battery?

[hja]

230ah. We could have had a 100ah lithium which would have given us more power than the original battery because of being able to run it down more.  However, we had our system installed for us and there wasnt much difference in the overall cost of installing the bigger battery. So more power, within reason, cant be a bad thing, so went for the bigger battery. Still fits under the front passenger seat, and still lighter than original battery.

[Philip M]

That is considerably more useable power than the lead acid. The charger in my van is a Sargent PX-300 smart charger which charges at a maximum of 20 amps at 14.4 volts. Looking at the specification it is for flooded and AGM batteries, but I wonder if it work and be safe with a lithium battery. Anyone tried this combination?

[Puddlejumper]

We had a compressor fridge in our old motorhome and will be changing our current three way this winter with another compressor fridge. Our experience was really positive, they keep stuff consistently cool irrespective of ambient temperature, they don’t get all moody if you’re not level and they don’t use any gas when off grid. In comparison this year with our new van we’ve already gone through x5 6kg gas bottles as we’re almost always off grid. With the old van we would maybe use x2 a year. Electricity consumption was pretty low, with our solar set up (200W roof mounted) it would keep the fridge going during the day with no real draw on the leisure batteries. Current draw was around 2-3A when compressor was running which was around 40% of the time so realistically it would draw around 1.5Ah per hour, we would see something like 10Ah being taken overnight but the solar would have us topped back up by 10am on a bright day. 
The only downside was it was noisier than the 3 way but not particularly noticeable, I slept with my head next to the cabinet where the fridge was and it never disturbed me. I also had to wire it so it ran directly from the battery via a fused and switchable spur so it would run while we were driving but the plus was I got rid of the relay.

Hope this helps

[Philip M]

Thanks that's very encouraging and I may well change over to a compressor fridge. Like you, I spend most of my time off grid when I'm away.

Since I changed my motorhome for a little Eriba 320 I was reckoning on upgrading my solar to a foldable 100W set up as I'll need to carry it separately in the car and want to keep the physical size to a minimum. That should provide about 6Ah at best and probably no more than 2Ah in overcast conditions.

I currently have a 100Ah battery but since I have a spare new 115Ah doing nothing I could easily add that to the van which would give me a usable 107 Ah assuming 50% usage, and the installed Sargent PX300 charger will cope with that. So with a small 50 litre fridge using a 45W compressor I'm hoping that would give me at least seven days usage with a little help from the solar panel and run indefinitely in mid-summer sun. Does that sound reasonable?

[Puddlejumper]

That sounds eminently sensible to me but if you could up your solar to 150-200W then you would have loads of reserve. The only issue with the batteries is a personal one, I would use batteries of the same capacity rather than mix up capacities. Also you have to make sure you take the positive feed from one battery and use the negative feed of the other one. This will ensure you draw power evenly from both batteries to give an even discharge.

Edited September 23 by Puddlejumper

[Philip M]

Thanks. I know you're quite right about the battery size and connections. I was hoping I might get away with the additional battery which has had similar usage and is only slightly different in Ah, but on reflection I'll not do that.

The balancing act for me is to provide sufficient power to run a small compression fridge  (plus a couple of LED lights and a phone charger) for probably a maximum of five days off grid, and keep the solar as physically small as possible.

Let's say I stick with the one 115Ah battery which should provide a usable 57Ah. The fridge I'm looking at is advertised as using an average of 0.7Ah once down to 5 degrees with an ambient temperature of 25. That's about 17Ah/day. Say 20Ah to cover everything.

In the summer on fine days a 100W panel ought to produce at least 27Ah/day which with my frugal usage would be more than enough. If on equinoctial grey days a 100W panel worked at 25% efficiency for five hours, it should provide 10Ah/day. That's a battery plus panel deficit of 10Ah/day, which should give me a maximum of five days off grid.

As I said, it's a very small van and a bit of a juggling act. Do you thing my figures stack up?

[Trialsriderz]

I've had 3 dometic crx50s in my last 3 vans. They are excellent. To preserve battery I use the freezer compartment to freeze 6 icepacks during the day when there is sunlight and plentiful solar energy . Then put the icepacks in the fridge section at night and turn off the fridge until the morning. Main reason is because the fridge cycling wakes me up and I'm a light sleeper. I had a 100amp battery, 150w solar combo. Lots of devices running in the day too. Never had an issue during the summer. 

[Philip M]

Thanks. It's very helpful to know how others get on with these fridges. To be honest, it's only because I've got a particularly elusive fault with the gas on my 3 way fridge that I started looking at the compressor type. I had previously rather written them off, prematurely it would seem.

[Puddlejumper]

On 23/09/2024 at 09:27, Philip M said:

Thanks. I know you're quite right about the battery size and connections. I was hoping I might get away with the additional battery which has had similar usage and is only slightly different in Ah, but on reflection I'll not do that.

The balancing act for me is to provide sufficient power to run a small compression fridge  (plus a couple of LED lights and a phone charger) for probably a maximum of five days off grid, and keep the solar as physically small as possible.

Let's say I stick with the one 115Ah battery which should provide a usable 57Ah. The fridge I'm looking at is advertised as using an average of 0.7Ah once down to 5 degrees with an ambient temperature of 25. That's about 17Ah/day. Say 20Ah to cover everything.

In the summer on fine days a 100W panel ought to produce at least 27Ah/day which with my frugal usage would be more than enough. If on equinoctial grey days a 100W panel worked at 25% efficiency for five hours, it should provide 10Ah/day. That's a battery plus panel deficit of 10Ah/day, which should give me a maximum of five days off grid.

As I said, it's a very small van and a bit of a juggling act. Do you thing my figures stack up?

I don’t think you’re far off with your estimates. We originally ran 160W of solar (roof mounted so not the most efficient) and a 115ah lead acid battery with the compressor fridge and never had a problem during reasonably sunny weather but if you could uplift your battery capacity it would give you a bit more confidence 

[Philip M]

Thanks for your thoughts. If I have any further troubles with my 3 way fridge, I'll definitely make the change over to compressor. I feel confident I can make work for my use.