reb78 Posted May 31, 2016 Share Posted May 31, 2016 To complement the roof tent and other bits i have added to the 110, I recently bought a second hand Dometic camping fridge - will run on 12v, 240v or butane/propane. For the butane part, it says it needs a 28mbar pressure regulator. A lot of the calor ones and camping gaz ones appear to be 29mbar. Does it matter if it is 28 or 29?? Also, does flow rate matter? the flows seem to differ between regulators, but are these just maximum rates and flow is determined by how the cooler is set? 1 Quote Link to comment Share on other sites More sharing options...
Tim2809 Posted May 31, 2016 Share Posted May 31, 2016 Jet size determines flow. The pressure side should not matter much as most will also run propane and thats a higher pressure again. Watch on the gas side as most need a vent to external of vehicle to clear fumes. Make sure if they do need vent to keep it away from sleeping compartment and dont get fumes in the roof tent Quote Link to comment Share on other sites More sharing options...
reb78 Posted May 31, 2016 Author Share Posted May 31, 2016 Thanks Tim. Good points. When it arrives, i will look at what is possible with the venting issue. What is the reason for 28/29 mbar on butane and 38mbar (?) on propane out of interest? Quote Link to comment Share on other sites More sharing options...
Tim2809 Posted May 31, 2016 Share Posted May 31, 2016 Think its to do with what pressure the gas atomises at to give best energy from it when burnt. Im no nuclear scintist thou so probably wrong Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 1, 2016 Author Share Posted June 1, 2016 I've had a bit more of a read around and also looked again at the label on the cooler. Pic below: Does the 'I3 + (28-30/37)' basically tell me it will run on butane fine at 28-30mbar and 37mbar for propane? It was the 28mbar next to butane that made me think it had to be 28, but i think that is actually telling me the power output and flow at that pressure? Sorry to be so dim! Just trying to understand the thing! Quote Link to comment Share on other sites More sharing options...
AMB Posted June 1, 2016 Share Posted June 1, 2016 I've had a bit more of a read around and also looked again at the label on the cooler. Pic below: 57.JPG Does the 'I3 + (28-30/37)' basically tell me it will run on butane fine at 28-30mbar and 37mbar for propane? It was the 28mbar next to butane that made me think it had to be 28, but i think that is actually telling me the power output and flow at that pressure? Sorry to be so dim! Just trying to understand the thing! That is my interpretation of the information. It gives max operating pressure as 30mbar and separate operating pressures for propane and butane. If I remember correctly butane has a higher energy density and burns cleaner than propane. Because of the difference in energy density, you need more propane to get the same heat, which translates to higher operating pressure for propane in the same equipment. However, propane is preferred to butane in low temperature conditions - butane will only operate down to 0 deg C at best, whereas propane may be able to operate down to -40C. The "at best" and "may be" caveats are because the cylinders cool down as the gas is used and the ambient would then need to be higher in order to maintain minimum operating temperatures inside the cylinder. There were some well publicised camping fire incidents a fair few years ago, when butane cylinders cooled down overnight, the cooled gas then liquified in the feed hose and sprayed out as a flaming liquid under pressure from self lighting camping stoves. Hence move to propane for all weather camping and improved safety advice on use of butane. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 1, 2016 Author Share Posted June 1, 2016 Thanks for this. I wont be camping anywhere too cold (fair weather camper!) but will bear that info in mind for sure. I will buy a regulator directly from Calor Gas then - the question originally came up as all of theirs are rated at 29mbar, as are the camping gaz ones. I have read that it is better to take the camping gaz to the continent as it is freely available there (so i will also buy one of their branded regulators), and Calor is fine within the UK. I have both at the moment. Quote Link to comment Share on other sites More sharing options...
Peaklander Posted June 2, 2016 Share Posted June 2, 2016 The cold weather Butane issue can be frustrating if you camp and there's a frost. Then when it's cold at ground level you will find that the Butane struggles to vaporise and you can't make make your tea! Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 3, 2016 Author Share Posted June 3, 2016 So, left the fridge on overnight on 240 volts and i was distinctly unimpressed this morning - it was tepid inside with a little frost on the tube under the evaporator plate. I got a 28mbar regulator from a local camping store this afternoon and rigged up a butane tank - within 15 minutes there was frost on the evaporator plate itself and 90 mins later, it is 'fridge cool'. Anyone know if this points to a defective 240 volt heater element? It was warm at the back on 240v, but nowhere near the same as with the flame running (i know that sounds obvious, but the manual suggests it should cool really well on mains. (i realise this has got quite off landy topic, but i'm hoping the members on here have some experience of these coolers) Quote Link to comment Share on other sites More sharing options...
Peaklander Posted June 3, 2016 Share Posted June 3, 2016 Hi Reb used these many times in caravans and yours should work just as well on mains as it does on 12v or gas, after all each of the three ways are only doing the same thing- regenerating the charcoal. Quote Link to comment Share on other sites More sharing options...
simonr Posted June 3, 2016 Share Posted June 3, 2016 Hi Reb used these many times in caravans and yours should work just as well on mains as it does on 12v or gas, after all each of the three ways are only doing the same thing- regenerating the charcoal. regenerating the charcoal???? They are known as Absorption Fridges - just need a heat source be it gas or electric (or Solar) to operate. Not much Charcoal! Si Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 3, 2016 Author Share Posted June 3, 2016 Well. Whilst it was precooled on gas, it's now been running on 12v for 3-4 hours now and is still very cool, some ice on the evaporator and it's actually dropped another degree whilst on the battery. The battery started at 12.5v and is down to 12v now. I think there must be something wrong on the 240v side. Thermostat or element perhaps? Will the element partially work? I ask as you could feel the heat at the back, but the cooling was nothing like the gas. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 3, 2016 Author Share Posted June 3, 2016 regenerating the charcoal???? They are known as Absorption Fridges - just need a heat source be it gas or electric (or Solar) to operate. Not much Charcoal! Si I think he meant they all burn something to create the energy to heat somehow Si. Quote Link to comment Share on other sites More sharing options...
simonr Posted June 3, 2016 Share Posted June 3, 2016 I think he meant they all burn something to create the energy to heat somehow Si. Fair enough - sorry if I offended in the process of not getting it! Si Quote Link to comment Share on other sites More sharing options...
Peaklander Posted June 3, 2016 Share Posted June 3, 2016 No I meant what I said. As far as I know these have a charcoal stack that's used to capture the refrigerant after it evaporates and therefore creates the cooling. The charcoal is then heated to release it again to allow the cycle to repeat. The fridge is on the cold side and the heat from the regeneration had to be released outside along with that from the fins. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 3, 2016 Author Share Posted June 3, 2016 I stand corrected! I have to confess, I didn't think charcoal was actually involved. Wouldn't it need replacing occasionally? Quote Link to comment Share on other sites More sharing options...
simonr Posted June 3, 2016 Share Posted June 3, 2016 No I meant what I said. As far as I know these have a charcoal stack that's used to capture the refrigerant after it evaporates and therefore creates the cooling. The charcoal is then heated to release it again to allow the cycle to repeat. The fridge is on the cold side and the heat from the regeneration had to be released outside along with that from the fins. Can you find a reference for this? I've not come across charcoal being used in refrigeration plant other than as a filter for the refrigerant? Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 3, 2016 Author Share Posted June 3, 2016 5 hours on a spare battery (580amp 70ah) and 3volts down to 9.5v. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 3, 2016 Author Share Posted June 3, 2016 Having more of a read about their setup suggests that they have a 12v heater element, a 240v heater element and the gas burner. They all heat the same spot, but still no idea if charcoal is involved! Quote Link to comment Share on other sites More sharing options...
Peaklander Posted June 4, 2016 Share Posted June 4, 2016 Guys I stand corrected then if there are no references. I referred to a question I asked someone years ago ( with good reason to believe the answer) and since then I've always thought that charcoal acted as the adsorber. I'm aware of its properties to adsorbe in other applications such as filters too. Sorry if I've come across as a troll. It was a comment made with the best possible intention and usually I have facts to back up! Now I'm away ( in the 110) on the phone with camp wifi so not much surfing opportunity. Currently using my Waeco cooler which works very well on 12v or mains. Now this uses semiconductor cooling - of that I am sure? Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 4, 2016 Author Share Posted June 4, 2016 No worries! No trolling there, just people figuring out how something works. Well, from being at about 2C on battery at 11pm last night, I switched to 240v overnight and it was at 14C this morning. So, something definitely isn't right there! Thing is, the back is getting warm which suggests the element is working. Any ideas? 1 Quote Link to comment Share on other sites More sharing options...
simonr Posted June 4, 2016 Share Posted June 4, 2016 I would take the heater apart and make sure the 240v element has good thermal contact with the tube. Heat sink compound (I'm assuming that's how it is coupled) eventually turns to powder and falls out if it's not captive. You can buy more compound from Maplin etc. Si Quote Link to comment Share on other sites More sharing options...
AMB Posted June 4, 2016 Share Posted June 4, 2016 I'm with Simonr on this. If working well with gas and 12v the refrigeration part is OK then it's either connections/connector, the element, the thermostat, or thermal coupling. With both 240 and 12v disconnected from the power and no gas, put a meter across live and neutral of the 240v cable. Alter the thermostat. Does the thermostat switch the 240v at any point (note: may not if cool box is near ambient or at minimum temperature). When there is a reading what is it? When running, 75W at 240v equates to 0.3125A or 768 Ohms. However, resistance increase with temperature, so meter reading more likely to be nearer 700 Ohms (wet fingered guess, so don't rely on it). If much higher than 768 Ohms it is probably a connector/connection/cable issue. Start tracking through. If all seems OK then take apart, clean and apply thermal compound. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 4, 2016 Author Share Posted June 4, 2016 Thanks Si and AMB. They're really helpful replies. Camping at a wedding in the roof tent today! but I'll do these checks tomorrow and report back. Without having done any internal checks, on 240, there is heat from the back of the fridge, so hopefully the element is ok and it's just the compound. I will investigate. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 5, 2016 Author Share Posted June 5, 2016 Ok. I removed the back panel. Probes on the terminals to the element and no resistance reading (meter just stayed on 1 as it dies when the probes aren't touching anything). Do the same on the 12v terminals and the reading is 2.1 ohms which I think is right? I disconnected the 240v wiring to be sure and same result. With it across the live and neutral, altering the thermostat produces no reading, but I think this is because of the faulty reading on the element? Quote Link to comment Share on other sites More sharing options...
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