Using 12v from car

[twindaddy]

Hiya all

I had many conversations a year or two back about using the tow elec sockets on the tow vehicle to power the 12v system in the caravan when not on ehu. I used to do this on my old '96 caravan using a lead I made up.

Now I have a 2002 van, will I be able to do the same (not been able to try as new tow vehicle has yet to be fitted with secondary electrics)

Now I remember someone speaking about habitation relay but cannot remember how to check if I have this on my van nor can I remember if it works with it or works only if you have not got it??!

Can someone in-confuddle my mind please? Lol

Cheers all

TD

 

[ProfJohnL]

Hi TD

You might find this web page useful
http://www.caravantalk.co.uk/caravan-advice/new-to-caravanning/electrics-guide/glossary-and-schematics

 

[waffler]

I suspect that the answer is you can't use car battery through van wiring. I think there is a built in switch that only works when the engine is running- this charges the battery and runs the fridge. If your tow car is diesel you might not want to use the car battery anyhow as the car battery will possibly be just enough for the diesel heater and starter motor.

 

[twindaddy]

I used to do this with my pre '98 caravan and it worked a treat when without EHU. I would conserve the battery in the caravan by using the battery from the car via the secondary electrics socket. With the vehicle being a defender, it has a huge battery so never an issue with it draining too much.

So...I take the newer caravan I now have, a 2002, has a habitation relay. Is someone able to explain what this does and why it prevents me doing the same with the battery as I did on my old 'van please, and if any, a method of using the car battery in this way please..

Thanks all
TD

 

[Len_Cuff]

OK so not too sure about this but I agree with previous post that the 'habitation' relay is fitted to prevent you draining your car battery -- no matter how good it might be. Think about it, you might 'get away' with using the Defender monster battery but Mr Average with a standard battery wouldn't! So caravan manufacturers go for the majority and make it a fail safe so you don't end up stranded with a flat battery and no tow car!
I'm sure there is a way to bypass the habitation relay but that's for others to advise.

 

[DrZhivago]

My understanding is that there should be a "Habitation Relay" on any modern caravan. It is turned OFF when the line from the car for the fridge is turned ON. In being turned off, it turns off all the auxiliary electrics in the caravan (interior lights mostly) leaving only the fridge and the legal driving lights powered.

It does this on the assumption that, as the fridge line from the car is (or should be) on only when the engine is running, you are driving along so will not want any caravan interior lights left on. It also reduces the sheer maximum load that the caravan can draw from the car, even with engine running.

So when the car engine is NOT running (or the towbar leads are disconnected anyway), you CAN turn on the caravan interior lights (but not the fridge, unless you are hooked up to a mains supply) which will draw from the caravan battery, and also from the car battery in parallel if the tow leads are plugged in.

So it looks like you have a fault. It may be in the habitation relay, or in the so-called "Splitter Relay" which would be in the car. This latter relay should detect if the engine is running and only powers the fridge line to the towbar socket if it is. If it is faulty then it might power the fridge and the habitation relay coil the whole time and hence turn off the caravan auxiliaries, such as you describe. In this fault state, the fridge would soon flatten both batteries if you park for long with the towbar leads connected.

In some cars the splitter relay operates by measuring the car battery voltage, which will be higher when the engine is running. Such relays have an adjusting screw, so the fault could simply be that it needs adjusting - a job for a screwdriver and voltmeter.

 

[Len_Cuff]

Yes I suppose you could 'fool' the relay in the car to still supply the van at a lower voltage but that depends on the car. On mine it's programmed into the rear ECU and I don't think it's adjustable?

 

[ApuljackEngineering]

Hello People

I think there is some confusion going on here! Below are a few pointers!

There are generally two 12V feeds from a vehicle electrics. One is a permanent live from the battery and the second is generally refered to as D+ and is only active when the engine is running. Traditionally this used to be fed from the ignition light feed from the alternator but in modern vehicles it comes from the ECU.

The habitation relay that is being refered to is designed to cut off all the electrics when the engine is running. A so called European regulation although we have never had anyone who can state a BS/EN/ISO type standard that mandates this!

So, when the D+ signal is active there are generally 4 things that happen:-

[ol][*]The habitation relay is activated (cutting power to the van to everything apart from the fridge)
[*]The split charge system is activated joining the habitation and vehicle batteries together
[*]The step is retracted (if a motor home)
[*]The fridge 12V heater is activated[/ol]

Independantly of that, most vans will still allow you to switch over the habitation electrics to run from the permanent 12V feed thus saving the habitation battery. Incidentally, if you have the charger on then it would also charge the vehicle battery!

HTH

 

[Gafferbill]

Hello People

I think there is some confusion going on here! Below are a few pointers!

.........now that is what I call being diplomatic

 

[colin-yorkshire]

I used to do this with my pre '98 caravan and it worked a treat when without EHU. I would conserve the battery in the caravan by using the battery from the car via the secondary electrics socket. With the vehicle being a defender, it has a huge battery so never an issue with it draining too much.

So...I take the newer caravan I now have, a 2002, has a habitation relay. Is someone able to explain what this does and why it prevents me doing the same with the battery as I did on my old 'van please, and if any, a method of using the car battery in this way please..

Thanks all
TD

hi TD.
when we originally talked about making the lead for your old van you will remember I told you this was possible only because you had a older van with pre 98 wiring, and that such a lead would not work with a newer van like mine (2005) as the habitation relay would prevent power reaching the van from the car once connected via the grey plug. this is an automatic reaction, all the previous posts refer to this.
if you really want to use the car battery (not recommended) you still could by running the patch lead you have from the perminant feed on the grey plug direct to the battery via crocodile clips After disconnecting the van battery (thereby substituting car power for van power, when off grid.

 

[twindaddy]

Thanks all, I thought this would be the case but I was hoping I had missed something.

Appreciate everyone's input.

TD

 

[JTQ]

What I know some people do that might achieve a useful bit of power saving is run specifically the TV from the car's battery.
To do this they make up a lead with a grey [12S] plug at one end and a 12 volt "cig-lighter type" socket at the TV end. With mine the grey 12 S plug's pin 4 is the permanent positive and pin 3 its negative. There are similar pins available in the more modern 13 pin couplings.

Doing this then allows probably for most of us our biggest power user, the TV, to be taken away as a drain from our van's battery and utilise the car's, which typically gets replenished again each day when running about.

 

[WoodlandsCamper]

Ages ago in the millenia BC (Before Caravan) we were tent campers and we used to have a strip light in the tent. The light had a long 2-wire lead with croc clips on the ends which went under the car bonnet in the evenings and clipped to the battery. Could do the same for a TV. But remember to remove the lead BEFORE driving away.

 

[JTQ]

Taking it from the 12 S rather than crocodile clips directly on the battery means the system is fused, is much safer [no sparks by the battery], convenient in that you do nothing but push a plug into the socket and can tolerate driving off without too much risk of shorting things, damaging the car's bodywork etc.

 

[ApuljackEngineering]

The croc clips/12S idea is fine but there is nothing to stop you completely flattening the car battery. If you use the car battery through the normal van system then many systems have a cut off at a certain voltage to prevent you completely flattening the battery. Whether this voltage is high enough to then allow you to start the car is a completley seperate question :S

 

[JTQ]

As an aside:
There used to be a nice little device called a "Uni-charger", welsh if I recall correctly, that only allowed you to run the car's starter battery down to a level where starting was still assured.
Very clever and useful, a friend had one. I used his to power an inverter, which I then connected via the AC, to power a CTEK charger and boost the van's battery. So each night we could sup what was practical to take from the tow vehicles. The advent of cheaper solar cells made doing that redundant in my case, but I always liked his Uni-charger.

 

[Gafferbill]

........I do a lot of caravanning off grid and all the year round.

This is one of the reasons I stick with my 1995 Swift as I can easily utilise 12 volts from the battery of my tow car via the 12S socket and a short extension lead.
A simple switch in the caravan can select power from either battery and the caravan battery condition meter shows what is left in the battery you have selected.
In my outfit making sure this meter is still in the green means I know I can start the tow car engine even on the coldest winters day.
The wiring used is also heavy duty to minimise losses back to the 186 amp hour tow car battery on my 4x4.