Camping Fridge

[AMB]

If measured directly on the element and on clean metal then likely to be the element itself. Not that expensive if you shop around (£30-£40). Leisure Shop Direct has some exploded diagrams with part numbers here

Still worthwhile checking the thermostat before you spend money.

[reb78]

I didnt dismantle the shroud around the element at this stage, but did disconnect the 240v element wires and test the resistance at the end of them wires. That gave the reading above so i think that means the element is knackered? The 12v one had a reading at the end of its wires.

There is a change in the resistance measured at the terminals from the thermostat as i turn it on and off, but no alteration as i turn it from 1-5. I presume this is because the box is warm though and so even on setting 1 (just turned on), it will be on as the stat is at ambient air temp?

[FridgeFreezer]

Stat is just an on-off switch, usually you can hear the contacts click when they switch. If the back gets hot when on mains I'd think the heater is working, likely the stat isn't very accurate. The mains heater element is about 100W so should be ~600 Ohms ish.

I've just been round the whole absorption fridge thing for the Campbulance, long story short unless you're running it on gas 99% of the time it will eat your battery, and as you managed to get yours down to 9.5v I guess it doesn't have a safety cutoff to prevent battery damage. The way the majority are wired the thermostat only affects mains operation, the gas knob varies the gas mode, and in 12v mode it just runs flat out all the time. Left unattended it will kill (as in permanently damage) your battery in a day.

We bit the bullet and bought a Waeco compressor fridge, uses about 1/10th of the power and has better usable space.

Anyone want to buy a 60L Electrolux 3-way fridge in good nick?

[reb78]

To test it, could i bypass the thermostat and wire the mains element straight up, so that when plugged in, it is on?

If only your fridge had been for sale a week or two earlier. Cant afford a Waeco compressor fridge at the moment, but point taken.

[FridgeFreezer]

With all the caveats about mains safety etc. if yours works the same as our then yes, you can bypass the stat.

I actually temporarily re-wired ours to make the stat switch a 12v relay to try and reduce battery use, made it ~30% better but 70% of terrible is still pretty bad!

The compressor fridges aren't such a great deal if you can run gas, but if you can't they quickly stack up against the cost of more batteries & solar panels / generator etc. etc.

The big test is 2 weeks away so I'll write up how well our setup fares

[reb78]

I think the wiring is exactly the same as in your pic above from memory of what was on the back of mine when i looked at the weekend.

I will give it a go.

What compressor fridge (model) did you go for in the end? I think i recall that you were going for a front opening unit, whereas i would specifically want a top opening unit for the back of the 110.

[AMB]

I didnt dismantle the shroud around the element at this stage, but did disconnect the 240v element wires and test the resistance at the end of them wires. That gave the reading above so i think that means the element is knackered? The 12v one had a reading at the end of its wires.

There is a change in the resistance measured at the terminals from the thermostat as i turn it on and off, but no alteration as i turn it from 1-5. I presume this is because the box is warm though and so even on setting 1 (just turned on), it will be on as the stat is at ambient air temp?

If you measured directly at the element wires and got open circuit, the element is knackered.

The thermostat should only click once during it's total travel - it should switch on/off (ie click) at the setting equivalent to the temperature inside the coolbox. Setting 1 is presumably the warmest.

I'm puzzled as to why you should get a change in resistance when measured at the thermostat terminals when you have open circuit at the 240v element. The element should be the only thing connected. You should be able to just bridge the stat - ideally with a meter on ac current. Check the stat by measuring impedance between the terminals (with no other connections to the fridge!). Should be near enough zero over most of the setting and open circuit at the warmest setting.

Have been half looking at an absorption box. What are you asking for yours Fridge?

[Jon W]

I haven't read the whole thread but I had one of these and it worked great on gas, 240v, drank batteries on 12v so I only used it while the engine was running. The other thing I did was to run it on an inverter whilst the engine was running as this seemed to get it cooler quicker than the 12v.

I did have a few occasions when I thought it wasn't working on 240v in the house, but the solution was to give the whole fridge a good shake as it appeared to get a bit of an airlock in the system if it had been moved around or turned on when not quite level.

Hope that helps

Jon

[Bowie69]

As I understand most caravan fridges, 12V is really only for when hooked up to the running car, once on pitch, you use 240 or gas.

[reb78]

If you measured directly at the element wires and got open circuit, the element is knackered.

The thermostat should only click once during it's total travel - it should switch on/off (ie click) at the setting equivalent to the temperature inside the coolbox. Setting 1 is presumably the warmest.

I'm puzzled as to why you should get a change in resistance when measured at the thermostat terminals when you have open circuit at the 240v element. The element should be the only thing connected. You should be able to just bridge the stat - ideally with a meter on ac current. Check the stat by measuring impedance between the terminals (with no other connections to the fridge!). Should be near enough zero over most of the setting and open circuit at the warmest setting.

Have been half looking at an absorption box. What are you asking for yours Fridge?

The fridge is confusing me (not difficult). Those terminals on the element definitely showed an open circuit on the multimeter. I turned it on from being off for two days this evening to check the element didnt get hot at all. Now, there is definately warmth at the back and a tiny bit of cooling in the internal pipes. But, an element either works or it doesnt doesnt it? So the open circuit makes no sense given that there is now some heat in the back and some colling (not a lot in the pipes inside)?! I'm puzzled.

[AMB]

Richard, yes heating elements usually fail open circuit. I have known of occasional insulation failures which would decrease the impedance and thereby increase the power into the element. However, that is patently not happening here.

There is one other possibility which comes to mind. It can be difficult to make electrical connection to the resistance wires used in heating elements, ceramic resistors etc. Manufacturers use acid fluxes, welding and mechanical/crimp techniques. It's vaguely possible that the connection between copper flex and heating wire has gone either high impedance or intermittent. That was a common failure mechanism on ceramic coated wire wound resistors.

Whatever the reason, if you are not getting of the order of 780 Ohms or less with a cold element as measured directly on the connecting flex of the element, it needs replacing. Disconnect and measure, if in doubt wiggle the wires whilst measuring.

[hangover]

With all the caveats about mains safety etc. if yours works the same as our then yes, you can bypass the stat.

I actually temporarily re-wired ours to make the stat switch a 12v relay to try and reduce battery use, made it ~30% better but 70% of terrible is still pretty bad!

The compressor fridges aren't such a great deal if you can run gas, but if you can't they quickly stack up against the cost of more batteries & solar panels / generator etc. etc.

The big test is 2 weeks away so I'll write up how well our setup fares

You will love the Waeco, its nice being able to pull old a cold beer or even icecream (when in freezer mode ) . The only time a 3 way fridge is better is when you are stationary for a few days and can run the fridge on lpg which only uses a pilot light sized flame for the thermal element , for on the go travelling you cant beat a 12V compressor fridge.

On my last trip away i would turn the fridge off at night and then back on in the morning at which time it had only got up to 4C, didnt really need to turn it off with the 105AH auxiliary battery i have in the disco.

[hangover]

As I understand most caravan fridges, 12V is really only for when hooked up to the running car, once on pitch, you use 240 or gas.

Exactly , they suck the juice on 12V but work ok on 240V and more efficient on gas.

[FridgeFreezer]

Reb - we went for a CRX50, the latest greatest. Despite "losing" 10L of space to the electrolux it's actually easier to fit stuff in as it's much deeper. Also the new CRX ones use ~25% less juice; Waeco's figures are 1.1Ah average, compare that with the ~10Ah average of the 3-way on 12v. Plus it gets down to temp waaay faster.

I'll be doing a full write-up on our site as I spent far too long staring at fridges, batteries, generators, solar panels to forget!

The short version is we've got the CRX50, a 100W solar panel and 100Ah battery which in theory should keep us in cold beer almost indefinitely.

[Peaklander]

Do you mind if I ask a quick question in the middle of this thread?

FF how are you mounting the solar panel? Is it rigid or flexi is it fixed or will you get it out and prop it up somewhere?

[FridgeFreezer]

It's rigid, fixed flat on the roof picking up the original roof rack mounts on the ambulance body:

[simonr]

I can run my Waeco CFX40 Compressor cool box pretty much continuously from an 80W Solar Panel with an MPPT charge controller. Over night, it doesn't require much cooling and hardly uses any battery. During an average day, the panel generates more than the fridge uses in 24h.

I'm very impressed with the efficiency.

I'm going to buy a CRX50 Fridge for my forthcoming camper project. Bought a Van Today!

Si

[reb78]

Would it be possible to rig the 12v element to the thermostat on my absorption fridge to make it less power hungry on 12v, or is the point that it needs to run at full power on 12v just to keep up?

[hangover]

Would it be possible to rig the 12v element to the thermostat on my absorption fridge to make it less power hungry on 12v, or is the point that it needs to run at full power on 12v just to keep up?

They are so inefficient on 12V that they need all the power they can get.

[AMB]

Would it be possible to rig the 12v element to the thermostat on my absorption fridge to make it less power hungry on 12v, or is the point that it needs to run at full power on 12v just to keep up?

It would be possible, but the gain may not be worth the effort. The amount of power required to cool to a given level below ambient should be virtually identical for 230v and 12v. However, operation at lower voltage incurs more losses in the feed cabling, hence manufacturers advice for heavy duty cabling etc. Ignoring feed issues, the big difference between 230v and 12v operation is, as you imply, lack of temperature control when running from 12v - it is always flat out.

Controlling via the thermostat would only take less power from the battery if you set the thermostat to a temperature above minimum. If you want to control via the thermostat, you will need to do so via a 12v relay or power FET capable of running continuously at the rated maximum current, the thermostat is unlikely to be rated at 6A.

[reb78]

Thanks.

I see FridgeFreezer actually said he did this to his earlier now. It's just my slow comprehension that took time to understand his post!

[garrycol]

Our experience in Aust with 3 ways is that on 12v it will just maintain temperature and there is not enough power to do much else extra heavy duty eiring must be used to reduce power losses. Also as 12v will not lower temps it is important that the contents are cooled elsewhere first or the fridge run on gas or 240v with the contents in for a day or so before hand.

They are really inefficient but in a colder climate like the UK they might be OK but in warmer climates they just do not work - we are moving away from them. They work best on gas, then on 240v and a bad last on 12v.

I have one in my camper and just use it to cool the salad and use my compressor fridge for the real stuff, like the beverages. The solar panels keep the battery topped up OK.

Garry

[FridgeFreezer]

Would it be possible to rig the 12v element to the thermostat on my absorption fridge to make it less power hungry on 12v, or is the point that it needs to run at full power on 12v just to keep up?

Possible, done it, for a steady 3-5deg internal temperature it shaves ~30% off the power budget. With a bit of tinkering you could wire relays so the one stat controls mains & 12v. Biggest improvement IMHO would be a low-voltage cutoff to save damaging the battery.

Worth noting the mains element is exactly the same wattage as the 12v one (92W) so efficiency is identical, it's purely that they don't really expect anyone to run on 12v for long periods and hence won't spend the money on adding more controls.

[reb78]

Possible, done it, for a steady 3-5deg internal temperature it shaves ~30% off the power budget. With a bit of tinkering you could wire relays so the one stat controls mains & 12v. Biggest improvement IMHO would be a low-voltage cutoff to save damaging the battery.

Worth noting the mains element is exactly the same wattage as the 12v one (92W) so efficiency is identical, it's purely that they don't really expect anyone to run on 12v for long periods and hence won't spend the money on adding more controls.

Thanks. I realised after i asked that you had mentioned it earlier - just seems to take me a while to digest the info.

From what everyone has said, the compressor fridges are much better but, i cant afford one at the moment, so will make do with what i have.

I guess the trouble with gas is that you dont want to run it on gas inside the vehicle and, given that i have a roof tent, there is nowhere secure to put it to store it outside of the vehicle (not that a ground tent is massivley secure, but it does offer more options for indoors placement. I was wondering about building a box that i could bolt to the front of the roof rack to house it securely when i am parked up (not whilst on the move), but the more i think about it the sillier the idea seems!

240v would be fine if at campsites that have it, but others have made the point in some camping threads that i have read elsewhere that if you want to get off the beaten track a little, then 240v wont be available!

[reb78]

Ok. This fridge has me well and truly stumped.

I bought a new element. Whilst fiddling with the old one, I checked it's resistance again and it was reading 672 ohms, so not quite what it should be, but nearly the same as the new one at 674 ohms.

I tried the old element directly to 240v (bypassing the stat) and got the same tepid result, but the back of the unit was getting hot - the pipes by the boiler would burn my hand to touch it.

I fitted the new element back via the thermostat and again a bit of frost on the evaporator tube, but only about an inch of it and very little real cooling even after being on for 6 hours!

Just put it back on gas and within ten minutes, the entire evaporator tube was frosty (stuck my hand to it as it was a bit damp!) within an hour it'd dropped it 10C.

So what are your thoughts? The cooler works on gas but not on 240v. It gets hot on 240v, but won't do any cooling!!!