Sooty Posted January 25, 2012 Share Posted January 25, 2012 When I fitted the water tank last year to my self built camper van I also fitted a thermostatic tank heater too as we often go away in winter and this van has it's tanks under the floor. I also have a Sargent electrical panel to power the whole van,(EC325 I think) it's the one were nothing can be connected to the battery due to the potential high voltage so everything is connected directly to the panel.. I wired the tank heater up to an auxiliary point that was capable of supplying 10 amps but has to be manually switched on at the panel to allow power if needed to the heater (or so I thought). When I turn this on even if the temperature is well above freezing the panel indicates a draw of 2.5 amps which is the same amount as the heater uses when on. When i checked the heater before it was fitted I had to put it in the freezer to get it to come on so I'm quite surprised it shows that it's drawing it's full power even when I feel it's not cold enough. I have left it on for about an hour and drained the water tank to feel if the water has had a very slight change in temperature but it hasn't. I also crawled underneath to the water tank and felt around the heater were it screws into the tank body and this was also stone cold which I was a little surprised by as I would of thought there would of been a little bit of warmth. I have even tried today with no water in it and it still shows that it's drawing power when the auxiliary switch is switched on. So I would like to know if anyone else has one fitted and is this normal or is it possible for the wire going to the heater to draw 2.5 amps even though the thermostat on the heater isn't actually switching it on. Personally I feel that this must be wrong but then me and electrics don't exactly get on! Hopefully someone with more knowledge than me can help me answer this question. Thanks Link to comment Share on other sites More sharing options...
Guest peter Posted January 25, 2012 Share Posted January 25, 2012 I would check that you have wired it correctly, first. With the positive wire from the switch going to the thermostat and from the same to the heater and the negative from the heater going to the battery negative. Wen you've done that put a meter across the element terminals and check if you get a reading when you operate the thermostat. You won't be able to test the thermostat unless you put water in the tank that is hotter than the temperature set on the thermostat. At which point it will switch off when water is at set point and come on when it goes someway below set point. There will be a difference owing to the hytseresis of the 'stat. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted January 26, 2012 Share Posted January 26, 2012 Sooty I'm guessing from your 2.5A power-consumption reference that your tank-heater came from CAK, and (being thermostatically-controlled) will have an integrated thermostat. If that's the case, there will be no user control of the thermostat's operation - you switch on 12V power to the heater and the thermostat automatically turns the heater on or off according to the temperature of the water in the tank. CAK's catalogue says that the thermostat should turn the heater On at 5°C and Off at 10°C Logically, the tank-heater should not be drawing 2.5A unless it is actually heating. The thermostat is just a simple switch and, if it is 'open', then no current should be drawn. If the thermostat were 'closed', but the heater had developed a fault preventing it actually heating, I'd also expect no current to be drawn. It would be nice if you could withdraw the heater from the tank to test it, but I recognise that this may prove difficult as such heaters are often retained by a nut inside the tank. However, as your experiments have confirmed that there's a 2.5A drain when you switch on the tank-heater (and, presumably, that the drain ceases immediately when you switch off the heater), I really can't think of any obvious alternative. For the technically-minded... http://www.zen22142.zen.co.uk/Circuits/Switching/therm_sw.htm Link to comment Share on other sites More sharing options...
Sooty Posted January 26, 2012 Author Share Posted January 26, 2012 Hi Peter and Derek, thanks for the reply's. Yes the tank heater is the type that CAK sells although we didn't purchase it from there we got it from a caravan parts supplier near Sheffield, I forgot their name, I think it was autocraft or something like that. Anyway, yes it is buried in the depths of the tank and would be a nightmare to get out as it would involve dropping the tank and taking off all the different sensors etc and insulation, but if this is the only option available then it will have to be done. You are also correct Derek in saying that as soon as I turn it off the power draw stops. I have even tried it today when the outside temp is around 10 degC with no water in and as soon as it's turned on at the panel it shows the 2.5amp draw. The frustrating thing is that I tested to see if it worked and how hot it got before fitting it into the tank, (very,as it happens!) although I never thought about testing for it's power draw when not on but connected to a battery. I think I will have a think for a while as to what to do next as I may just leave it for the moment and keep it turned off and look at it when the weather is a little bit warmer and dryer as lying outside on the ground in the cold and damp doesn't really appeal at the minute. 8-) I may live to regret that idea if when we are away it suddenly gets very cold!! Once again thanks Link to comment Share on other sites More sharing options...
Brambles Posted January 26, 2012 Share Posted January 26, 2012 I think the concluson has to be the thermostat as failed closed or indeed does not actually have a thermostat and is the non thermostat version. At 30 Watts (2.5 Amps) its not a lot of heat and would take a long time to warm up the body of the tank or any water. I suggest you diconnect at the heater end and check again if curremt flows, if it does not then you must assume the heater is working, but themostat possily not. Link to comment Share on other sites More sharing options...
Robinhood Posted January 26, 2012 Share Posted January 26, 2012 Sooty - 2012-01-26 1:10 PM Hi Peter and Derek, thanks for the reply's. Yes the tank heater is the type that CAK sells although we didn't purchase it from there we got it from a caravan parts supplier near Sheffield, I forgot their name, I think it was autocraft or something like that. Anyway, yes it is buried in the depths of the tank and would be a nightmare to get out as it would involve dropping the tank and taking off all the different sensors etc and insulation, but if this is the only option available then it will have to be done. You are also correct Derek in saying that as soon as I turn it off the power draw stops. I have even tried it today when the outside temp is around 10 degC with no water in and as soon as it's turned on at the panel it shows the 2.5amp draw. The frustrating thing is that I tested to see if it worked and how hot it got before fitting it into the tank, (very,as it happens!) although I never thought about testing for it's power draw when not on but connected to a battery. I think I will have a think for a while as to what to do next as I may just leave it for the moment and keep it turned off and look at it when the weather is a little bit warmer and dryer as lying outside on the ground in the cold and damp doesn't really appeal at the minute. 8-) I may live to regret that idea if when we are away it suddenly gets very cold!! Once again thanks Autocraft (based in Staveley, nr Chesterfield) do a 30W version both with and without the thermostat - are you sure you got one with? Link to comment Share on other sites More sharing options...
dikyenfo Posted January 26, 2012 Share Posted January 26, 2012 I think you already know the answer - the unit is tatered. The switches are v. cheapo and unreliable. Industry uses Otter switches but it does not help your case. From what you say it will be easier to drill a hole in an accessible position and fit a new one knowing you can replace it easily. It is a simple enough job reallyyou can extend the existing wiring so save some time. Good luck. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted January 26, 2012 Share Posted January 26, 2012 The snag with the idea that the heater may have no thermostat is Sooty's statement "When i checked the heater before it was fitted I had to put it in the freezer to get it to come on". It is possible to do as dikyenfo suggests and install a tank-heater from outside the tank (via an external mounting plate) so that it's much simpler to replace if there's a problem. It also needs saying that these heaters aren't particularly cheap! GOOGLE-searching on "motorhome water tank de-frost heater" (omitting the quotes) retrieves some material - including a 2008 Out&AboutLive thread - but nothing that's obviously helpful. There is some suggestion (including Sooty's freezer experiment) that the cut-in temperature may be below 5°C, but that still wouldn't explain why there's a 2.5A current drain but the heater shows no indication of getting hot. I find it difficult to imagine how, if the heater were actually working and the part of it that's inside the tank were heating up, the part of the heater that's outside the tank would stay stone cold (which is what I understand is the case). Might be worth contacting the heater's vendor: Autocraft Motor Caravans, Fan Road, Staveley, Chesterfield, S43 3PT Phone: 01246 471199 Fax: 01246 477086 Email: sales@autocraftmotorcaravans.com Link to comment Share on other sites More sharing options...
ips Posted January 27, 2012 Share Posted January 27, 2012 It is impossible to record a draw of 2.5A and the heater not be on, if your meter is "true" and it says its drawing 2.5A then the heater is definately working. One has to remember that 2.5A is bugger all and will take ages to notice a difference in temp, if indeed it is ever noticeable. Link to comment Share on other sites More sharing options...
tonyishuk Posted January 27, 2012 Share Posted January 27, 2012 Is it actually drawing 2.5 amps, or is the panel just saying it is ? Maybe an independant check on the current drawn, might show a different result (Maybe ?) Rgds Link to comment Share on other sites More sharing options...
ips Posted January 27, 2012 Share Posted January 27, 2012 Good point my reply assumed that it had been checked with a clamp metre or similar. Link to comment Share on other sites More sharing options...
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