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Electrics 240 v


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Lunar Roadstar 2001 on Ducato Maxi


Hi electricians,


We normally use sites that have electrical hookup and therefore never select 'CAR' or 'VAN' on the plug-in panel. Power to internal lights etc presumably coming from 240 v mains supply..


Last week when arriving on site and hooking up to mains as usual I was tuning in the Camos Sat dish when it suddenly ceased to work. I checked the interior lights and these too did not work (all 240 volt sockets and appliances were working ok.)


I discovered a 15 amp fuse located next to the battery had blown. This was replaced but still no joy with interior lights. By switching the'Plugin' panel switch to 'Van' or 'Car' we were able to use the lights ok for the rest of the week.


Question: Why won't lights work off mains hookup only. Has something else 'blown'?


Any ideas would be appreciated bearing in mind that I am almost completely electrically dyslexic!

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Nothing blown with the type of panel you have with the switch in the Van position the 12 volt electrics will run of the habitation battery, in the Car position the will run off the engine battery (not a good idea). It is the type of panel that used to be fitted to caravans & Lunar are predominantly a caravan manufacturer.


With the switch in the centre position the 12 volt electrics are turned off, I suspect in the past it has been in the Van position without you realising it. Also it would be wise to check the habitation battery is charging in the off position you may need to leave it in Van postition to charge, I don't know if your charger is capable of charging the engine battery as well.


To check charging use a cheap multimeter and check the voltage on the battery if the battery is charged should be around 12.7 - 12.9v, when charging 13.6-14.5v. you can check both batteries with the switch in different positions and you will then learn what is happening.

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Plug-In Systems produced a range of equipment for leisure-vehicle applications




I don’t know which control-panel your 2001 Lunar motorhome will have, but details of the PMS3 system are here




It would be logical for a 3-position battery selector switch that can select the “Car” battery (ie. the starter-battery in a motorhome) or “Van” battery (ie. a motorhome’s leisure-battery) as the 12V power-source to have its 3rd position used to isolate both batteries.


In principle then (with a PMS3 system) interior 12V lights should not operate when the battery selector-switch is in its central position and (as lennyhb suggests) it seems more likely that, in the past, your switch has been in the “Van” position. (If you are certain that’s not been the case, so be it...)


Do as Lenny advises and check what’s happening with a digital multimeter. (I use a “VC97” multimeter that is obtainable for around £16.)

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Thanks for your replies.


It's a 3-way rocker switch, up for van, down for car. Each position has an indicator light to show which has been selected. The centre position selects neither and I have always kept it in this position exept when driving, when it is recommended to switch it to 'car' in order for the engine to maintain a supply to the 'fridge.


I am still curious as to why the 15 amp fuse blew.

However, I have a multi-meter and will do as you suggest.


Thanks again.

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If you were getting a 12v supply in the centre position when on mains it could have been supplying direct from the charger, maybe your charger has blown, this is not the normal way of doing things.

Also a 15 amp fuse in line with the battery is very low I would expect at least a 30 amp fuse, 50 is more normal.

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