Jump to content

Why disable the Habitation 12v electrics when the Engine starts?


Recommended Posts

We are working on a Elddis Encore Motorhome where the Motorhome owner wants to be able to Start the engine so the Alternator can provide upto 60amps to the habitation batteries when he operates the Invertor.

By 'powering up to half' his Inverter from the 'Alternator'. His batteries, although still getting a hammering, will last longer. That's the theory.

But the minute he starts the engine, 12v shuts down.


This shutdown is allegedly due to EMC regulations. While any Electrical device can be used in a vehicle while it is static, only those devices tested to conform to certain 'electrical interference' tests may be 'powered' while the vehicle is in motion.


Owners of Continental built motorhomes can, and do, use their engine as a part time generator to boost the battery so they don't miss the last 4 laps of Formula One on the TV, or the last five minutes of the Footie.


A Bailey owner may find that when his battery is getting low and the Tele starts complaining, that starting the engine switches off the TV and lights anyway.


The biggest issue as far as I am concerned with this operation, is that once the engine starts, I can't check that the Alternator is putting 14.4v into the habitation battery. On most UK built Motorhomes, the minute I start the engine the very voltmeter I want to check, shuts down.



Motorhomes, do not require their habitation electrical systems to be disabled when the engine is started as is commonly believed. It is the path taken by UK Motorhome builders to save them conformance testing each installed product.


There is no law I can find saying Motorhomes 'Must have the lights, etc, 12v deactivated once the engine starts'.


Continental Motorhome builders install electrical equipment which is already ratified, so they have no need to disable the Motorhome 12v systems, as British built vehicles do.


I understand that it saves money to take the easy way out by shutting down the Motorhomes 12v, rather than get it properly tested under UNECE Regulation 10, but the regulations relate to a MOVING vehicle.

Not one where the engine is started.


So why not adopt a mechanism that actually senses movement, not a mechanism that senses the starting of the engine?



We are going to try and find a way to allow the Elddis Encore mentioned above to fit within the 'law' so that when the engine is started the 12v electrics stay on. Only when it actually moves will the 12v shutdown. This work is already quite advanced.



We are also looking for an Elddis Autoquest (circa 2006 BCA pwered vehicle) owner who would like to work with us on changing their electrics so they stay within the law, but where the owner is able to start the engine whenever they wish without losing the TV, Water pump, lights, etc. Obviously at no cost to themselves.


If you are interested, please use the website to contact us via email, not this thread.




Regulation history and some more info :


To ensure the electrical/electronic devices we use in vehicles don't create interference to both other users and the electronic devices in our own vehicle, like Brake/stability electronics, every device has to pass a test. This used to be known as the 'EMC' but is now UNECE Regulation 10.


These tests verify that a device emits only minimal interference and additionally is immune from interference itself when used in a moving vehicle. This is done as part of the vehicle conformace certification.


More details here on the laws/regulations :







Link to comment
Share on other sites


I cannot help with the van, but I would like to come to the defence of British build motorhomes (even though I have a German one myself).


Given the huge costs and time involved in full EMC compliance testing of large vehicles (anything from over £100K to $M's), I cannot believe that continetal manufacturers would actually test each and every model they build given the relatively small volumes they make (compared to high volume motorcars, or the cost of jet fighters, tanks etc. where these tests are essential). The test involves putting the vehicle on a dynamometer inside an RF chamber so is quite complex.


I think this is more to do with how the manufacturers interpret the regulations and the general feeling is that UK manufactures tend to obey the letter of the law while many others comply with the spirt of the law.

Just because a manufacturer has used all CE compliant apparatus in the motorhome, it doesn't mean that the whole motorhome is compliant (https://www.emcstandards.co.uk/ce-ce-does-not-equal-ce). You either need to prove the design through testing or you put together a technical file to justify your reasons for CE marking.

I think this point is probably more understood by UK manufacturers hence they play safe and disable the "non-vehicle" equipment when the engine is running. The consequences of ABS failure, unintentional airbag deployment, cruse control activation etc. could be catastrophic. For a small manufacturer, this is quite a big risk to take.






Link to comment
Share on other sites

My little old 1998 Autosleeper Montana is very basic in the electronics department, no ABS, airbags, engine management system or electric windows so I think I'll go with the handbrake switch as suggested. Mind you it is the 16 valve model but 8 of those are in the radio :D
Link to comment
Share on other sites

aandncaravan - 2017-03-24 8:54 PM


...This shutdown is allegedly due to EMC regulations...


The policy for UK motorhome manufacturers to disable certain habitation 12V services (eg. lights, water-pump, hob/oven/fridge gas-igniters) goes right back to the 1990s when electronic safety-systems (ABS and the like) began to be fitted to vehicles.


I remember asking Mr Dave Thomas (now MD of Auto-Trail) about this some 18 years ago, as my Herald motorhome (that he had designed) included this ‘feature’. I said that Continental motorhome converters clearly did not disable habitation-area 12V services, so it seemed strange that UK converters apparently considered doing this to be essential.


Mr Thomas’s reply was that the ‘ploy’ originally permitted any 12V equipment that was fitted to UK-built caravans to also be used in UK-built motorhomes without being concerned about whether the equipment might have an EMC-related impact on the vehicle. Having introduced this ‘fix’, it had become standard practice and all UK motorhome converters now did this irrespective of whether the practice was necessary or rational.


I asked if there were any UK regulations forcing UK motorhome converters to disable the 12V system as a matter of course. Mr Thomas replied that he was not aware of any, adding that if I was able to establish the legal position he would be interested to learn what I had found out.


12V-disabling is a habit UK motorhome converters developed in the ‘fear of EMC problems’ days and, although there’s nothing forcing them to do it, the habit is deeply ingrained and they will not be prepared to break it.

Link to comment
Share on other sites

Plwsm2000, I understand the reasons for them taking the easy way out and disabling the electrics.

My issue is with the method of using the 'engine starting' as the trigger, rather than producing a proper mechanism where the van electrics are only disabled when the vehicle actually moves.


It is only when the vehicle moves that the alleged 'safety' issues and Radiated interference become an issue, so make movement the trigger.


Audis have had a motion sensor mechanism that prevents the Alarm/immobiliser triggering accidently on the move since around 2001, so we are not talking about any thing radical or expensive.

Link to comment
Share on other sites

Never done it and know nothing about it.


But from the grapevine............... you remove one fuse and the habitation is no longer deactivated when the engine starts? heard this mentioned loads of times, as I say, I have no experience of it but assume it to be the case?

Link to comment
Share on other sites

How easy it would be to disable a motorhome’s EMC ‘isolation-relay’ will depend on the vehicle’s electrical system.


The sample wiring-diagram in my “Motorcaravan Manual” indicates that merely removing a fuse would not work, but it would still be a simple matter to twiddle the wiring to stop the relay from opening.


Sargent PSUs apparently incorporate an isolation-relay


"The PSU also includes an EMC isolation relay to turn the outputs off whilst the engine is running. It is a legal requirement to ensure that equipment that is not approved for use whilst a vehicle is in motion is isolated during motion. This ensures such items as an oven igniter cannot interrupt or affect vehicle systems. To enable this please ensure an ‘engine running’ (D+) signal is connected to the EMC input terminal.”


but presumably not providing a D+ signal to the EMC input terminal would do the job.


This 2006 (partial) thread




shows that circumventing the isolation relay is nothing new.

Link to comment
Share on other sites

  • 1 month later...

Well we finally have an Elddis Encore that does not shutdown the Habitation area electrics when the engine starts.


The BCA controller board (PCB 269-MD) fitted to the Encore, Approach, etc from around 2012 onwards is quite different to earlier units in that it has a single feed in that switches on the Fridge 12v first.

From there it operates EMC shutdown, etc. All this is done within the PCB, not separate wires, so has been quite time consuming to work out.


Some of the boards use the same EMC relay as the trigger for shutdown, so if you disable EMC you can't then switch everything off when putting the van into storage.


But we finally cracked it, and we now have a happy customer who can run his engine to supply 12v to the Inverter to save the habitation batteries being hammered quite so hard, without being plunged into darkness.


The PCB has something like 10 relays, so saving them continually switching on/off should improve reliability?

I only found out the other day that not all UK Motorhome builders follow the 'guidelines', one for the very reason of reliability.



So if anyone wants their British Built Motorhome to behave more logically, and the way the whole of the rest of World do, you can specify it as an option with your Dealer.



I have to say I find the UK approach odd. In my 7 seat car I can drive around and have WiFi (EE 4GEE ) working flat out, with my children watching a mixture of TV or playing gaming handhelds, make phone calls, using iPads, etc. I can have 3 reversing/rear view cameras transmitting the picture via Bluetooth, WiFi, etc to the display screen. Remote control toys, etc


In short a car is legal when radiating all manner of Electromagnetic 'interference' but some UK built Motorhomes can't even have one light bulb illuminated!!



Link to comment
Share on other sites

It can be done, so a Dealer with their resources should be able to do the same.


If they can't, they have the option to get the vehicle to someone who can, prior to delivery.

They probably won't want to, but depends on how much they want the sale?


We have received an email this morning from someone who wants their vehicle modified. He has two young grandchildren who travel belted up in the habitation area with no power for Internet, DVD, toys, lights etc.


His wife sits with them but has a problem keeping them occupied after about an hours traveling.

That is when it becomes dangerous as the bored children want to move around the vehicle.


He was about to wire all the 12v power points directly from the battery but then found out the Sargent EC328 can put up to 18volts charge into the battery.


The more we go into it, the more unexplainable the British Motorhome builders approach is.


Surely it puts British built Motorhomes at a disadvantage when it comes to exports? At the very least, couldn't they have an 'export' version that behaves as all other countries motorhome electrics do??


Good to see that at least some British Motorhome builders apply their own judgement with their builds not shutting down the Habitation power.








Link to comment
Share on other sites

aandncaravan - 2017-05-18 10:23 AM


...Surely it puts British built Motorhomes at a disadvantage when it comes to exports? At the very least, couldn't they have an 'export' version that behaves as all other countries motorhome electrics do??...



Perhaps they do.


You might want to ask Moto-Trek whether the motorhome models they sell in the UK have the EMC isolation feature and, if so, whether or not that limitation is removed for the LHD equivalents the company has been marketing in France since mid-2016.

Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Create New...