Guest david lloyd Posted February 23, 2006 Share Posted February 23, 2006 Hi everyone I thought I had just missed out on the 300 watt inverter from Maplins being sold at £19.99 - just been to the shop and there is a new offer of a 600 watt but it was either £39.99 or £49.99 - I was so disappointed that I didn't take much notice. Then I asked the sales guy if the 300 watt offer had finished and he said he thought a new batch had just arrived - sure enough they had AND - they are only £14.98 now!!!!!! Having never had an inverter before there are just a couple of the instructions I'd like to confirm with anyone who has used them. I wanted to have the inverter permanently connected to the leisure batteries and leave it fixed beneath one of the seat bases - actually next to the rest of the vehicle electrics and just above the battery box which would keep it out of harms way and minimise the DC run of wire. BUT.... 1. It advises that the inverter should not be connected when the vehicle is started OR when the charger is being used as leaving it connected could result in an input spike that could seriously damage the unit - does that mean it cannot be permanently wired to the leisure battery? 2. Having said that it also says that the unit has a grounding connection (wing nut) on the side casing which should be connected to the chassis if fitted to a vehicle - alternatively a short piece of wire can be connected to the wing nut and then to the earth terminal on the back of the unit - If it is connected to the vehicle chassis does this contradict the above? What is the best way? 3. It says the inverter should be unplugged (I think they refer here to using the cigar lighter socket/plug) when not in use and also when the vehicle is being started. Again, does this mean it cannot be permanently connected to the leisure batteries as it would be a bit of a pain to keep connecting and disconnecting? Help please anyone. Regards, david ps - please bear in mind that I am quite good at DIY but not a genius with vehicle wiring - if necessary I will have whatever needs doing done professionally although I would like to do it myself if I can. Link to comment Share on other sites More sharing options...
Guest martin Posted February 23, 2006 Share Posted February 23, 2006 We have one of the Maplin 600 watt inverters mounted behind the driver's seat, with a couple of self-tappers) and linked to the two leisure batteries under the cab seats. For the past two years we've run all sorts of stuff - computers and screens and the like and recharged other batteries on the move with no problems ... but check: we have a slightly modified, sophisticated and separate charging/maintenance system. I would never plug 600 watts, and have my doubts about 300, into the cigarette lighter drawing from the vehicle battery ... Better connect it the separate leisure battery. We have a serious key turn isolator switch on the positive incomer (remember inverters draw current event when off and you need heavy duty cable - which ours came with: bell wire is verboten! Remember to use grommets, or other insulation, if coming through the metal of the seat and also to shield the tags on the positive input at the inverter as well. The advice you've read is correct, but geared to folk who only have the fag lighter to plug into ... we have broadcast standard 4 pin locking XLR sockets around the van too for light 12 volt loads as this guarantees polarity at all times. Hope this helps. Link to comment Share on other sites More sharing options...
Guest david lloyd Posted February 24, 2006 Share Posted February 24, 2006 Hi Martin - thanks for the info. I don't want to do anything too complicated with the inverter - mainly use it for the laptop or charge other batteries when not on a hookup - and would prefer to have it permanently connected to the batteries to save connecting/disconnecting and have it available whenever we need it. A couple of things I'm not clear on though: 1. If wired permanently direct to the battery do I still have to wire the ground pin on the casing direct to the chassis? 2. Is the on/off switch on the front of the unit sufficient to isolate the inverter when not in use or should a separate isolator switch be fitted on the live input? If yes - is there a particular type I should use? 3. The instructions reinforce the point that the inverter should not be used and disconnected before charging the battery - this is a simple matter if using the cigar lighter but with it permanently connected can I still start the engine or use the leisure battery charger. I know the last point sounds odd since why would you want to use the inverter if you are on an electric hookup anyway but I often plug the van in at homw when not in use. regards, david Link to comment Share on other sites More sharing options...
Guest Mel B Posted February 24, 2006 Share Posted February 24, 2006 Hi David I got one of the inverters from Maplins, last year I think. I've wired it permanently under the permanent bed base, next to the the leisure battery housing which means I can keep the cable run short. I have put in a separate switch between the inverter and the battery as well as an in-line fuse between the battery and the switch. This means that when starting the engine if there's a problem the fuse would blow and the inverter is further protected by the separate switch being turned off unless we are using it. As the in-line fuse is above the battery box in an area used for storage, to protect it I used an old plastic glasses case, drilled holes at each end, threaded the wires through and put the fuse inside connecting it to both wires. It's easily accessible if you want to check the fuse and keeps it safe from damage. The thing to remember though is to turn the inverter off when you're not using it to avoid it drawing power from the battery unnecessarily. When we do want to use it we simply plus a 2 metre 4 way extension into it which flops out from under the bed and we just plug bits and pieces in as required (usually our laptop computer). Link to comment Share on other sites More sharing options...
Guest david lloyd Posted February 24, 2006 Share Posted February 24, 2006 Hi MelB - many thanks for that. The inverter already has an inline fuse on the red input wire so I could just put a switch between that and the battery connection then - is there any particular isolating switch to use? Also, did you connect the grounding pin on the side of the casing to the chassis, or to the negative (black) terminal on the inverter, or not at all? I had some good advice on the Motorhome Today forum including one which said they had taken the 3 pin outlet off the front of the inverter, cut a hole in the side of the locker base and mounted the 3 pin socket on the outside using the long bolts to fasten it to the inverter which was mounted on the inside of the locker - saved lifting the seat to get at the inverter. He had also soldered two wires to the front mounted switch and fed them through to a slave switch alongside the 3 pin socket on the outside of the locker - so I suppose I could do that with the isolator switch between the battery and the inverter? regards, david Link to comment Share on other sites More sharing options...
Guest Mel E Posted February 25, 2006 Share Posted February 25, 2006 The switch should either be a battery isolator switch (available at Maplins) or you need to wire an illuminated-when-on rocker switch via a relay to the + wire between leisure batteries and Inverter. These two solutions will switch the high-amperage wire you need to use to connect from the inverter to the batteries. Caqlculate the amperage as watts / volts and add at least 50% to allow for power-on surges. Thus: 300 watt inverter needs 35 amp wire 600 watt inverter needs 50 amp wire. You will not find a conventional switch that can handle that kind of amperage load. Also, make sure that the inverter is well ventilated - it generates a lot of heat. Link to comment Share on other sites More sharing options...
Guest martin Posted February 25, 2006 Share Posted February 25, 2006 Every van is different which is why I wasn't too specific ... just get it as close to the battery as you can! There is a standard rotary switch available at most accessory shops - a lot of the classic and vintage car owners hide them in the bodywork as a secondary security device. By bolting the unit to the seat base containing one of my leisure batteries I only used 9 - 12 inches of 50 amp pos and neg cable from the inverter directly to the battery terminals with a 50 amp isolator switch on the positive side. I didn't bother with a fuse, as you rightly say there's an external and internal fuse on the unit. The point is that inverters are transformers, and the switch on the unit does not totally isolate the unit, as power is connected to one side of the transformer even when switched off. Link to comment Share on other sites More sharing options...
Guest MelB Posted February 25, 2006 Share Posted February 25, 2006 Hi David I earthed the inverter by attaching it through the bottom of the battery box to the chassis to be safe. As for the switch, I just used a good quality fused socket that I picked up cheap at a car boot sale, the type that has the fuse holder on the front that you can pull out of easily if needed. Thus, if I want to make sure that the inverter is isolated and don't want to rummage around for the in-line fuse, I can switch it off at the fused socket and also pop out the fuse in case I accidentally knock the switch on. Belt, braces and safety pins, that's me! I wouldn't go cutting holes in the cabinet work of your van though, just think how messy it would look if you then removed the inverter and sold the van. You'd be better mounting a normal domestic wall socket somewhere and then wiring into it through the back of the switched socket with a lead going to the inverter's socket. At least that way it wouldn't look out of keeping and if you subsequently removed the inverter you could just leave the domestic socket in place so that a new owner could connect an inverter to it if they so wished. Make sure that the wire from the domestic socket to the inverter is out of harms way though as you don't want to catch it with anything and pull it apart/damage anything. If you're not sure how to wire it up make sure you get someone to do it who does know. Link to comment Share on other sites More sharing options...
Guest david lloyd Posted February 26, 2006 Share Posted February 26, 2006 Martin - MelE - MelB Many, many thanks for all your information and ideas. Lots of options there and when I get the Knaus I'll probably get a nice looking socket to mount externally that matches with the rest as suggested and then determine the best placement of socket/inverter/isolator switch. Once again, many thanks, david Link to comment Share on other sites More sharing options...
Guest Mel E Posted February 27, 2006 Share Posted February 27, 2006 If it's in a new 'van, Clive will provide you with an excellent wiring diagram so that all your 13 amp sockets automatically switch: - to the mains source when hooked up - to the inverter when on internal batteries, automatically switching the inverter on as well. He did this design for my new motorhome and the fitted it to his own, he was so impressed with the diagram. It was in a recent MMM in the Tech section. Link to comment Share on other sites More sharing options...
Guest david lloyd Posted February 27, 2006 Share Posted February 27, 2006 Mel E That sounds like a good idea - how do I get in touch with Clive - or will he be monitoring this thread? david Link to comment Share on other sites More sharing options...
Guest clive Posted February 28, 2006 Share Posted February 28, 2006 Probably! Look at www.motts.dsl.pipex.com/INVERTER.htm Link to comment Share on other sites More sharing options...
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