Jackal Posted May 7, 2011 Share Posted May 7, 2011 Just got myself a Dometic 1600 PLUS Air Con Unit and am planning to get an inverter to allow us to briefly run the air con for a few minutes with the engine running. Thanks to Tomo3090 I know that this works but was wondering whether the inverter has to be connected to the vehicle battery or could be connected to the leisure battery? Surely as long as the alternator is taking care of business, either of the batteries will cope? But would it be better to use the leisure one, in view of the fact that, if other items were run off the inverter without the engine running and they flattened the battery, it wouldn't be so catastrophic? I'm probably missing something here, as usual but any help would be greatly appreciated. Thanks in advance. Link to comment Share on other sites More sharing options...
BGD Posted May 7, 2011 Share Posted May 7, 2011 Wiser heads will be along in due course, but......... I thought that because the Dometic air-con unit runs on " mains" electricity not 12 volt DC, then any inverter to run it would be connected directly between the engine alternator supply and the unit; ie it wouldn't have anything to do with the wiring to/from either your engine battery or leisure batteries. We've got a Dometic 1600plus roof mounted air-con unit....brilliant piece of kit, but I do remember the fitter saying that there was no way that the alternator on our older MH would give anything like the output that a big capacity inverter (which is what you'd need to power it) would need in order to run the unit when on the move.......and neither would lots of the existing vehicle wiring and other bits of vehicle electrickery. So we've just stuck to running the air-con unit when on mains hook-up.......and it's still excellent . I'm not sure why you feel you'll want to run it for just a few minutes when the engine is running......I don't think you'll feel much effect in such a short time. We've found that really they need quite a bit of time to "extract" the hot air from your MH, as they also need to extract the heat from all the fittings and furnishings too........an hour or more with all shutters down and window blinds in place is the sort of timescale to get decent inside-MH cooling, at least in the height of Spanish summers....... Link to comment Share on other sites More sharing options...
Jackal Posted May 7, 2011 Author Share Posted May 7, 2011 BGD, If you remember, we discussed this back in January and what I really wanted, was the ability to cool the van a bit when wild-camping in Greece this summer. Tomo3090 said that he had used such a set-up to cool the van a little bit when stopped and just before they went to bed. I do realise the limitations but will be using it in conjunction with Cab Air Con and would still like to know the ins and outs of which battery it is best to connect. By the way, I bought the 1600Plus on your recommendation! Link to comment Share on other sites More sharing options...
Brambles Posted May 7, 2011 Share Posted May 7, 2011 It is not really feasible to use the engine battery for the power required which wil be around 83 Amps. Draining your engine battery by the amount required is a bad idea as sometime it struggles enough to start a diesel engine. From memory I think dometic recommend around 220 Ah capacity to supply the invertor. Part of requiring a high capacity is to maintain the volts under such a heavy load and I also believe the invertor is wired into the liesure battery to get the power it needs when the alternator is running slow such as when you are idling the engine when you stop at junctions etc. Confirmation of how it is wired is needed and you should get this from the dometic installation guidelines or instructions and recommended battery capacity. I also wonder about the effectivemess of just running for 5 to 10 mins say befiore going to bed. It may drop the temperature of the air a bit to then quickly be warmed up agian by heat retained in furniture and fittings etc., which will not have had time to cool down. You may find more effective just to have an extractor fan pulling fresh cool night air into the motorhome which wil only draw about 5 amps and could be left running for a lot longer. Link to comment Share on other sites More sharing options...
dwaviation Posted May 8, 2011 Share Posted May 8, 2011 Shouldn't that aircon unit be used in conjunction with the Dometic inverter? I believe that unit to be 'smart' and it connects to both the vehicle battery and the leisure battery and monitors the charge rates of both. It really only needs the battery power when idling in traffic etc when the alternator is not charging - Running it for five minutes purely of of the batteries is definately not a good idea. Link to comment Share on other sites More sharing options...
dwaviation Posted May 8, 2011 Share Posted May 8, 2011 Shouldn't that aircon unit be used in conjunction with the Dometic inverter? I believe that unit to be 'smart' and it connects to both the vehicle battery and the leisure battery and monitors the charge rates of both. It really only needs the battery power when idling in traffic etc when the alternator is not charging - Running it for five minutes purely of of the batteries is definately not a good idea. Link to comment Share on other sites More sharing options...
dwaviation Posted May 8, 2011 Share Posted May 8, 2011 Shouldn't that aircon unit be used in conjunction with the Dometic inverter? I believe that unit to be 'smart' and it connects to both the vehicle battery and the leisure battery and monitors the charge rates of both. It really only needs the battery power when idling in traffic etc when the alternator is not charging - Running it for five minutes purely of of the batteries is definately not a good idea. Link to comment Share on other sites More sharing options...
Jackal Posted May 8, 2011 Author Share Posted May 8, 2011 Just to clarify, the Air Con will be used in conjunction with a Fan-Tastic fan when the vehicle is stationary to cool the van as opposed to when on the move. I'm well aware of the standard Dometic DC kit but have no desire to run the Air Con off the batteries on the move. It's merely just to make the van a bit more pleasant once we have stopped and before bed which as long as the engine is running shouldn't have too much of a draining affect on the battery. The question is though, to which battery should we connect the inverter? Or doesn't it matter? Link to comment Share on other sites More sharing options...
Tomo3090 Posted May 8, 2011 Share Posted May 8, 2011 Just to clarify our set up. The inverter, a 2000W/4000W model, is connected to the vehicle battery. We also have a Batterymaster. From the inverter we have a, extention to an ordinary three pin plug socket fitted into the side of the off side lounge settee. If we are off hook up and need 240V for smaller items such as laptop charging, electric toothbrush charging or even Anns 1600W hairdryer, we just plug them into the plug and we don't need the engine running because the vehicle battery/leisure battery/Batterymaster combination works just great and there isn't a problem. If the temperature is hot enough to need the aircon, and we're off hook up, we shut all the blinds down on the sun side of the van during daylight hours. Then after the sun has gone down we close the doors and windows and start the engine. Blip the accelerator to 1500 revs to get the alternator to kick-in. Then switch on the inverter with it's remote switch and turn on the air con unit. We run this for 10 -15 minutes and the van cools down. Then before we go to bed we run it again for the same length of time, again just with the engine ticking over. We've had this set up in two vans now for a total of four years and it's worked perfctly fine. I've been assured that the alternator has sufficient output, 90 Amps to power the inverter and keep the vehicle battery topped up, and it has. Even if it did reduce the level of the vehicle battery the Batterymaster will bring power from the leisure batteries to top it up, they in turn are topped up by the 2X85 Watt solar panels on the roof. It was explained to me that the vehicle engine and alternator are doing what they should, i.e providing power within its' capabilities and isn't causing damage to the engine because diesels are ok ticking over for this length of time. True the interior isn't as cold as if the aircon was on hook up for an hour or so, which it can be by utilising the normal three pin socket fitted in the van, but it does cool it down to a comfortable temperature both for the evening and certainly later at bed time. I can't explain the technical stuff because I trusted the guy who fitted it when he told me it would work. He had a motorhome and had done it to his and had no problems. Leisurepower in warrington were intrigued when they fitted the aircon unit and I asked them for a three pin plug on the end of the lead, but when I explained why they were happy to do so because in their opinion there would be no problem powerwise or to the running of the unit itself that might affect any warranty. Link to comment Share on other sites More sharing options...
Jackal Posted June 6, 2011 Author Share Posted June 6, 2011 All, Had the Air Con and Inverter fitted two weeks ago. Had a normal plug fitted to the Air Con unit, a socket placed inside a cupboard, next to the inverter which was connected directly to the leisure battery. Tried it out during last Thursday's heatwave for 15 minutes. Started the engine, plugged the Air Con into the inverter, switched the inverter and the Air Con on and left it running for 15 minutes. The problem was that when we switched the Air Con off, followed by the inverter and then unplugged the Air Con from the inverter, we found that the 12V system in the whole van wouldn't work. On closer inspection the 40Amp fuse in the leisure battery had blown! Can anyone help to explain why the Air Con ran OK but the fuse blew after we had turned it off? I was advised to put a higher rated fuse in it, which I did, just so that we could restore the 12V but am wondering how high a fuse we should use and whether, in fact that is a sound idea! Any help in just getting our head around why it may have blown, would be helpful. ??? Link to comment Share on other sites More sharing options...
terry1956 Posted June 6, 2011 Share Posted June 6, 2011 Gi we have a dometic air con unit and an inverter. But there is no way that the air con will run from that inverter from just the engine. the alternator does not give out the amps needed to run the air con., on my old hymer the alternator gives out 85 amps. the air con needs you will need mains power or a gen to make this work. alternator pumps out around 450 watts, air con needs 450, more to start up.plus what the inverter needs to work. it will just not work. michael Link to comment Share on other sites More sharing options...
Brian Kirby Posted June 6, 2011 Share Posted June 6, 2011 The problem is, you have substituted a "home made" system for one specifically manufactured by Dometic to do what you want. As Bruce (BGD) said, that bridges both batteries, and there is also a recommendation for minimum installed battery capacity to make sure it can all cope properly under a range of circumstances. Tomo's system sounds as though it more or less replicates what the Dometic system provides, using the Battery master to do some of what the Dometic package does. You have to remember a fuse is present to protect the wiring, and is rated so that if the safe load for the circuit is exceeded, the fuse will blow. If that 40A fuse is trying to feed the inverter, neither it nor the wiring downstream from it, are adequate for the load. If you simply put in what I suspect you need, which is about double that capacity, there is a high probability wiring somewhere will seriously overheat, to the point at which something catches fire. What you say suggests that whoever did the fitting didn't do all that is required, which is a risk factor with "home made" remedies. We can all guess but, because even 12V can cause fires, if you don't understand the installation sufficiently yourself to sort it out, it will far safer to get the installer to sort out the problem he has created (which in any case is what you have paid him to do), than to try to DIY based on advice from any of us, because none of us knows exactly how your van is wired. Even if someone has an identical van, and has the full wiring diagram, they still won't know what has been connected to which with your new installation, or what gauge of wire has been used, or what other possible modifications may have been made previously. Sorry, but you are where you are. Link to comment Share on other sites More sharing options...
Jackal Posted June 6, 2011 Author Share Posted June 6, 2011 Thanks for your inputs. I'm still at a loss to understand how the Air Con worked perfectly well and yet the fuse blew after the event? The reason why I'd like to understand why, is because the initial response by the people who installed it was simply to put a higher rated fuse in place of the 40 Amp one which I am loathed to do for the obvious reasons. In fact the supplier of the inverter also said the same, stating that the only way the 40 Amps would be exceeded was when the Air Con was being used, so that in fact, there would be no risk from other appliances. All the manufacturers instructions were followed, including the "double" wiring from the inverter to the leisure battery and at no point were eyebrows raised in any way as to what I had asked them to do. I wasn't trying to replicate Dometic's DC kit, merely trying to have the opportunity to power the Air Con whilst stationary from the alternator, in addition to using the Air Con whilst on hook-up. Link to comment Share on other sites More sharing options...
Brambles Posted June 6, 2011 Share Posted June 6, 2011 Can you clarify a few points please. Does the feed to the invertor have its own fuse. Is the fuse that blew in the alernator feed to the leisure batteries( via slave relays), or is it the fuse feeding from the leisure battries to the 12 volt habitation circuits. Are you sure the Invertor is not being supplied via the fuse if habitation side of battery? Are you certain the fuse blew when switching off the invertor etc and not during the 15 min trial run. Link to comment Share on other sites More sharing options...
Jackal Posted June 6, 2011 Author Share Posted June 6, 2011 Brambles, The feed from the inverter to the leisure battery does not have a fuse.The fuse that blew is the standard 40 Amp fuse which is connected in between the leisure battery and the 12 volt habitation circuit.I'm sure that the only connection that the installers made was the double lead connection that went directly from the two sets of connectors on the rear of the inverter via the two lots of heavy duty cable to the the two connectors on the leisure battery. No other connection was made and this was all in accordance with the instructions on the inverter. I am absolutely positive that the Air Con worked and noticeably cooled the van for the full 15 minutes it was on. It didn't trip on start up as I've been told it would and it certainly did work throughout, again unlike what others have said. It wasn't until my wife went to use the tap a couple of minutes later, that we realised that the 12v circuit had been broken. The only other thing that I'd like to add, is that having now asked my wife again about what happened, she reckons that instead of turning the Air Con Unit off at the unit, I actually turned the ignition off first! In which case, could it be the case that in the absence of the alternator assisting the draw of current, the fuse blew??? Link to comment Share on other sites More sharing options...
Guest peter Posted June 6, 2011 Share Posted June 6, 2011 It could be that because you turned off the engine first that the battery took the full load and that caused the battery voltage to drop. The result of this is that the amperage draw went too high and resulted in the fuse blowing. Just a supposition, but it's feasable. If the voltage is too low the amps go up and without the fuse it would eventually melt your wiring. Why hasn't the inverter got it's own inbuilt fuse or trip?. Link to comment Share on other sites More sharing options...
Jackal Posted June 6, 2011 Author Share Posted June 6, 2011 Yes. That is what I'm beginning to think happened. The inverter has it's own protection in the form of "heavy duty fuse protection", an audible warning if the battery drops below 10.5 volts and a cut out if it drops below 10 volts. Link to comment Share on other sites More sharing options...
Brambles Posted June 6, 2011 Share Posted June 6, 2011 It cannot be the voltage dropping and hence a higher current because the current to the invertor is not going through the 40 Amp fuse. It would be very unusual for a voltage drop to cause a surge of current through to the habitation circuit to blow the fuse. Rather intriquing indeed. You only have one batterry connected and no others hidden away anywhere by chance? I guess not, but if you did and was wired after the habitation fuse then it could be the reason. So all rather baffling if wired as you say. Link to comment Share on other sites More sharing options...
Jackal Posted June 7, 2011 Author Share Posted June 7, 2011 Nope. No extra batteries or anything else connected that may have overloaded it. My understanding is that the connections were made directly to the leisure battery terminals and not to any other part of the leisure battery/Hymer 12 volt circuit and yet it was the fuse on the 12 volt circuit that blew. The van is relatively new (57 plate) I've not modified any of the electrical connections in any way, shape or form, as has been suggested. The Air Con and inverter are the first non-factory fitted items that I have ever connected. I simply don't do DIY. I'm not after a home based substitute to Dometic's DC Kits and finally, I'm not trying to save money. All I am just trying to understand is why a bog standard 2500W inverter wired according to the instructions cannot power a relatively soft start Air Con Unit via a healthy alternator, when I know it can and it has done, without the fuse to the 12 volt circuit somehow being affected! Link to comment Share on other sites More sharing options...
Brambles Posted June 7, 2011 Share Posted June 7, 2011 I think the next step is to replace the fuse. I most certainly would not put a larger on in. The check all the 12 volt appliances work .If one does not then it needs to be investigated further as to why not. Another suggestion - With the fuse open or unplugged, can you test if you get 12 volts in the habitation area when the engine is running. I am wondering of the charge from the alternator is connected to the 12 volt circuit after the fuse and not on the battery side. This would mean all the power from the alternator would be going through the fuse when charging the battery as well as the air-con. Link to comment Share on other sites More sharing options...
Dave Newell Posted June 7, 2011 Share Posted June 7, 2011 The major difference between Tomo's installation and Jackal's is that Tomo's inverter is connected to the vehicle battery and Jackal's is connected to the leisure battery only. When the AC was switched on the load would initially be taken by the leisure battery, once the engine was running the split charge circuit would connect (Schaudt Elektroblock) and the inverter load would be shared between leisure battery and alternator/engine battery via the split charge circuit which is fused at each end with a 40 amp fuse. The leiusre battery fuse would hasve blown almost immediately but the leisure 12 volt circuits would continue to operate because they were taking power from the engine battery via the split charge circuit. Once the engine was switched off the split charge circuit would disconnect and therefore the power to the leisure circuits be cut. DO NOT UNDER ANY CIRCUMSTANCES FIT A HIGHER RATED FUSE! The Dometic 12V kit includes a heavy duty 150 Amp split charge supply to prevent the original wiring trying to carry loads well in excess of its capabilities. The inverter should also be fused! D. Link to comment Share on other sites More sharing options...
Jackal Posted June 7, 2011 Author Share Posted June 7, 2011 Thanks for your input Dave. What I understand from you then is that by having it connected to both the vehicle and leisure batteries the BatteryMaster provides the split charge circuit which protects the wiring. If so, can a BatteryMaster be used along side the Hymer Electroblock to perform the same function? To be honest, I was under the impression that the BatteryMaster unit was there merely to balance the draw between the two batteries so that neither got flattened. My original post asked for advice on this but Towtal in Stoke on Trent when I enquired, said that it would be preferable to attach it to the Leisure Battery. Link to comment Share on other sites More sharing options...
Jackal Posted June 7, 2011 Author Share Posted June 7, 2011 Brambles, Everything seems to work as it should and we get 12 volts when the engine is running as well as when it isn't. Tomo has told me that his van does not get 12 volts when the engine is running. Could this make a difference? Link to comment Share on other sites More sharing options...
Jackal Posted June 7, 2011 Author Share Posted June 7, 2011 Brambles, Everything seems to work as it should and we get 12 volts when the engine is running as well as when it isn't. Tomo has told me that his van does not get 12 volts when the engine is running. Could this make a difference? Link to comment Share on other sites More sharing options...
Dave Newell Posted June 7, 2011 Share Posted June 7, 2011 Battery Master is a device that will trickle charge to the engine battery from the leisure when the leisure is the higher state of charge. I seem to recall quoting to fit your AC, what happened there then? D. Link to comment Share on other sites More sharing options...
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