Smart relays/ 12S wiring

[Netti_374307085]

Firstly thanks to all those who offered me such good advice before on this.

I need a bit of clarification tho - am just about to hit the caravan shops in search of a smart relay. What else do I need to complete the wiring? Obviously I will also need twin sockets as well but is there anything else?

Is it something like this I need? http://www.towsure.com/product/2973-Self-Switching_Combination_Relay_Wiring_Kit

I honestly haven't a clue if my car has a multiplex or can-bus system like it asks on the website. Going to ask on my owners club just now and see if they know.

 

[rosies]

Hi Netti , yes it is something like this you will need , but also a 20 amp inline fuse connector for the battery end plus most probably further wiring to connect you smart relay to your 12s battery charge and fridge operation pins ( 2 seperate wires ) . Towsure are not overeager on wire lengths , so wise to check , better too much than too little . If you do install the towsure smart relay yourself , you will probably find that when testing it out power to the fridge and battery will either be ON all the time or OFF all the time . This requires the smart relay adjusting . Whilst vehicle engine running , look into the end of the relay and see an adjusting screw , this should be in approx the 3 o'clock position pulling in and out at about 13volts . Please remember the main cable/wire runs from the vehicle battery ( 20 fuse installed ) through the interior along to the smart relay usually fitted in the rear of the rear mudguard well. So wire length being in the region of 6 metres+ then maybe 2 metres+ for the fridge/battery charge , needing a minimum of 10 metres although the 2 metre wires can be lower amperage . Another hint is to ensure you have enough EARTH wire and connectors . I do hope this helps you , same as most things in life , once done then twice as easy . But any problems just ask on here , everyone will help . cheers --- STEVE.

ps. DONT get the 20/17 amp cartridge fuse . ONLY get the 20 amp inline fuse blade type . My cartridge fuse assembly melted on my first outing , fitted a fuseblade type and have had no problems . Blame the poor contact within the cartridge type unable to take the constant high amperage , therefore heat ! . Maybe due to it being a cheapy ( rewrote that last sentence 4 times , did not want to generalise and get the moderators moderating lol .

 

[rosies]

Just a bit of additional information Netti

12N & 12S Sockets To Suit October 1979 to 31 August 1998 Caravans

TERMINAL COLOUR 12N SOCKET 12S SOCKET

1 Yellow L H Indicator Reversing Light(s)

2 Blue Fog Light(s) Caravan Battery Charging

(Ignition Controlled Supply)

3 White Return (Earth) Return (Earth)

4 Green R H Indicator Interior Lights Etc (Permanent Supply)

5 Brown R H Tail Light Sensing Device

6 Red Stop Lights Fridge (Ignition Controlled Supply)

7 Black L H Tail Light

& Number Plate Not Used

Notes

The supplies to 12S pins 2 and 6 must be installed such that they are live only when the vehicle engine is running (see Sections 3.5.13 and 3.5.15 below).

The supply to 12S pin 2 for caravan battery charging has been customary practice in the UK for many years. However, it has never been adopted into a British or other standard for towbar wiring. It is, therefore, frequently ignored by vehicle manufacturers in their wiring kits.

See section 3.5.16 for advice regarding 12S pin 2 if towing a continental-built caravan.

With the exception of the 12S pin 2 connection as mentioned above, sockets wired according to these specifications will comply with British Standard BS AU 149a (12N) and BS AU 177a (12S). These standards are effectively identical to International Standards ISO 1724 (12N) and ISO 3732 (12S).

3.3 1 September 1998 And Newer Caravans

These are built to European standards, one of which defines the 12V wiring, and results in changes to the 1 2S system. (The 1 2N system remains the same.) An extra earth acts to separate the fridge power supply from other circuits, minimising the risk of overloading the return wire when several circuits are used together. Battery charging is now officially included, but via pin 4, not pin 2, as was usual practice in the UK before, but never included in previous standards. Pin 4 also operates interior lights etc, but not at the same time as battery charging. Switching to achieve this is done in the caravan.

12N & 12S Sockets To Suit 1 September 1998 And Newer Caravans

TERMINAL COLOUR 12N SOCKET 12S SOCKET

1 Yellow L H Indicator Reversing Light(s)

2 Blue Fog Light(s) Sensing Device

3 White Return (Earth) Return (Earth) For Pin 4

4 Green R H Indicator Interior Lights etc or Caravan Battery

Charging (Permanent Supply)

5 Brown R H Tail Light Not Used

6 Red Stop Lights Fridge (Ignition Controlled Supply)

7 Black L H Tail Light

& Number Plate Return (Earth) For Pin 6

Notes

The supply to 12S pin 6 should be live only when the vehicle engine is running (see Section 3.5.15 below).

12S pins 3 and 7 should not be joined together at the socket. They should be taken separately to an earth point on the vehicle structure. Failure to do may increase the likelihood of overheating of the 12S plug and socket, especially if damage to pin 7 occurs (see section 3.5.17).

12S pin 4 must be permanently live for both battery charging and interior light etc functions to operate. The fridge circuit must work correctly for switching of the pin 4 supply between these functions to occur.

At the time of writing, the standards for vehicle wiring have not been updated to match the latest caravan wiring standard. The above specification complies with British Standard BS AU 149a (12N) and the effectively identical International Standard ISO 1724. BS AU 177a and ISO 3732 (12S) do not yet include the earth via pin 7, and hence this connection may be omitted by some makers and installers.

4. if all is in order & you still don't have power when the engine is running, then the VSR (volatge Sensitive Relay) that trigger & then supplies power has failed & needs to be replaced

 

[Netti_374307085]

Steve thank you ever so much for taking the time to write such a detailed reply. I will print all that off for my auto sparky. I may actually just ask him to get whatever parts required as I really am lost on this.

Also, I have just had it confirmed that my car doesn't have a multiplex or can-bus system. Does this affect what wiring it will require? Can it be simplified? I'm not liking the idea of having lots of cabling running throughout the car, especially off ignition feeds or alternator feeds, etc.

 

[Netti_374307085]

Steve thank you ever so much for taking the time to write such a detailed reply. I will print all that off for my auto sparky. I may actually just ask him to get whatever parts required as I really am lost on this.

Also, I have just had it confirmed that my car doesn't have a multiplex or can-bus system. Does this affect what wiring it will require? Can it be simplified? I'm not liking the idea of having lots of cabling running throughout the car, especially off ignition feeds or alternator feeds, etc.

Forgot to add - the only relays I could find in the 2 shops I visited were a split charge relay and this kit here http://www.gooutdoors.co.uk/caravanning-equipment/5013008002926

Would the above kit be suitable for my car in conjunction with a pre-wired twin electrics plate?

 

[rosies]

hello again Netti ,as long as your car does not have can-bus or multiplex or bulb failure system then a standard unit can be fitted ( even if you had these or some of these systems then their is still a kit to suit ) . My personel opinion is that the towsure kit ( 12s & 12n sockets, 7 core cables , bracket , smartcom relay and wiring @

 

[rosies]

Netti , if you want a little extra knowledge for yourself they google up STOWFORD MEADOWS FARM , click stowford farm meadows, then click caravan fault finder, click electrics, click exterior lighting then enjoy your read . Many other sites offer good information , just try googling some !!

Have a nice day now ( lol ) --- STEVE .

 

[rosies]

Netti , if you want a little extra knowledge for yourself they google up STOWFORD MEADOWS FARM , click stowford farm meadows, then click caravan fault finder, click electrics, click exterior lighting then enjoy your read . Many other sites offer good information , just try googling some !!

Have a nice day now ( lol ) --- STEVE .

Me again , dont forget that it depends if your caravan is pre or post 1998 how your 12s socket is wired up , the differences are in the information in my 2nd mail . cheers AGAIN ( chuckling) ---- STEVE .

 

[Netti_374307085]

Steve you are wonderful you know! I will buy you a pint if we ever cross pitches! After speaking to my auto sparky today he thinks 2 15ft lengths of 45 core cable will be required, along with a split charge relay. Could I add fuses to this set up to protect the car? Where in the wiring should they go? The auto sparky has done a very neat, thorough job with my single electrics, but it seems I have a duff bulb failure warning buzzer as it doesn't work on the right hand indicator.

AnyWAY, I also seem to remember seeing a relay that would only let the car's battery/alternator charge up the caravan when the voltage rose above a certain level. Is this what a Smart relay does?

Basically what I think I now need is the cabling, some fuses and a relay to both split the charge between battery and fridge and also to ensure the battery isn't drained on the car.

 

[rosies]

Yes Netti , thats what a SMART relay does :-

1) ONE wire ( heavy cable ) form battery to smart relay .

2) the smart relay splits it into three , one permanent power (12v) to 12s socket , one voltage controlled ( 13v+ ) to fridge via the 12s socket , and one again voltage controlled ( 13v+ ) to charge the caravan battery in your caravan via the 12s socket .

3) the permanent power ( 12v) is to work the caravan 12 v system from your car instead of from your caravan , handy if your caravan battery is low , or no caravan battery fitted .

4) that means that when your vehicle engine is running then you get power to the caravan fridge AND charges your caravan battery .

5) As soon as you turn off your engine the power to the operational side of the smart relay ( ie caravan ) decays thereby the smart relay shuts the power off to these items protecting your vehicle battery from any discharge .

6) The best and ideal position for your fuse holder is as close to the vehicle battery as possible protecting anything downline of it .

7) I think your auto electrician is thinking of two seperate split charge relays , one for battery charge and one for fridge . Then both these still going to the 12s socket . therefore 2 wires running through your interior would be required . In fact really 3 wires , one for the permanent 12v .

8) A smart relay is less work and does the job of two split charge relays . Its up to personel choice and reliability in the end . I have a towsure smart relay on my tow vehicle , I fitted it 18 months ago and it works perfect for me always keeps the caravan battery topped up and the fridge cold whilst travelling .

9) So both applications work doing the same job .

In fact I have 3 split charge relays in my toolbox and I am about to use one on my good ladies car for operating a keyless boot entry . But thats me rambling and getting off the point . lol.

Looking forwards to hearing from you when the installation is complete and you are a happy motorist with a caravan on tow .

ps I drink John Smiths ( CHUCKLING ) STEVE .

 

[Netti_374307085]

RIGHT! Now I'm with you! I think.....I am such a girl when it comes to this stuff! I was getting a little confused about the Smart relay, I thought that was related to the more complex wiring system, which my car doesn't have but I understand now....Well, we'll soon see!

So, is this what I'll need - this cabling -http://www.towsure.com/product/565-S-Type_7_Core_Cable_-_Per_Metre Or more http://www.towsure.com/product/13912-21A_Single_Core_Cable_-_Per_Metre Or something else entirely. Can't seem to find the grade of cable my auto sparky was on about tho. No luck on Ebay. Maybe try motor factors?

One of these http://www.towsure.com/product/580-Inline_Blade_Fuse_Holder_-_30A

One of these http://cgi.ebay.co.uk/Smart-12s-Switching-Relay-caravan-electrics_W0QQitemZ380019523606QQihZ025QQcategoryZ33653QQssPageNameZWDVWQQrdZ1QQcmdZViewItem or this http://www.towsure.com/product/1828-Self-Switching_Combination_Relay

And a standard 12S socket for connecting everything to. I see you can buy just the sockets on their own, my auto sparky should be able to wire up the socket with the length of cable shouldn't he? And the fuse needs to be connected up at the battery end, the smart relay at the tow bar end and then to the socket on the towball?

Thank you so much for all your help Steve. I am taking my first trip with a van on the back on Wednesday, just with single electrics for the time being tho. I've put up a separate message about that tho.

 

[WatsonJohnG]

The only comment I would make to the above excellent advice is that I always run 2 seperate wires via 2 20amp fuses at the car battery to the relays at the rear as if one wire is used and the fuse at the car battery blows then the caravan battery can discharge into the fridge on tow

I have had this happen years ago before using 2 wires

I personally don't like the smartcom type of relay because of problems I have had with them not switching off in the past.

I have also seen(helped)other people on rallies where they have packed up or caused flat batteries so I use the 4 pin relays with a trigger from the car ignition circuit

That is just a personal preference and my friend who has an auto electrical business that includes towbar fitting assures me that they fit them and that the latest(now adjustable) version are OK

 

[rosies]

As John says Netti there are several ways to skin a cat , all getting the same results . Naturally its your decision , or maybe your auto/elect, lol . split charge relay have been used for years and are well proven whereas smartcom relays are fairly new , but John has told me something I didn't know about the new adjustable types . So I can't advise you any further its your call . I will just leave you with more info on the smart relay I use .

type :- SMARTCOM (SC200) HEAVY DUTY 30 AMP

THE RELAYS SWITCH ON AT 13.5V AND OFF AT 13.2V

CABLE SPEC for battery to smartcom relay , single 44/o.33mm2 which is rated at 27.5 amps to minimise voltage drop . Inline fuse of 15/20 amp .

I have been trying to scan and copy and paste the instructions but I aint clever enough , it only scans into MY PICTURES as jpeg so can't copy , wish I was reasonable on these dam computers . Think they are for the young whiz kids rather than an aging single finger typer like MOI . BUT IT GIVES ME A LAUGH , Enjoy your time away and relax with hopefully some lovely sunsets , have a drink for me and please let us know how you went on with the break as well as the electrics installation . yours --- STEVE .

 

[Netti_374307085]

John would the leisure battery discharging into the fridge damage the fridge? I know it's not good for the battery for it to go flat but I think those are easier to replace than a fridge.

Can 2 lengths of cabling be run into one single Smart relay? Or is the whole point that you only need one? If 2 cables, what does each connect to? Battery and ignition?

Finally, will a Smart relay normally come with wiring instructions? They're gobbledegook to me but my auto sparky needed the instructions for the bulb failure buzzer as he'd never fitted one before.

 

[WatsonJohnG]

Hi Netti

It would not harm the fridge or any other appliances in any wa

The 2 wires would come from the car battery terminal each via an individual fuse and go either to 2 relays (smartcom or otherwise)or one combination relay which is just like 2 joined together

With the smartcom type as engine revs increase it senses the rise in current/volts and switches on automatically so it needs no feed from the ignition.The 4 pin relay needs a trigger from a car ignition source as well to switch on

The relays come with wiring insructions

Hope that helps

 

[WatsonJohnG]

If using a dual smartcom it would not need 2 wires from the car battery as if the car battery fuse blew them no current would flow at all to the relay so the caravan battery drain would not happen as the relay would not switch on

http://stores.channeladvisor.com/towbar/Items/sc200

 

[colin-yorkshire]

hi netti

I can not add much to the top class information you have had already from steve and john both spot on regarding relays

there are only 2 points I can think of that might help you

first the wire/wires that come from the car battery to the relays can be fitted underneath the car and cable tyed into position before entering the boot (relays in boot for protection) I say this because some cars mine included do not have any accsess into the engine bay from the inside of the car

without drilling a new hole(not recomended)

second the bulb failure buzzer only works on the indicaters not the side or brake lights and should come with its own wiring diaghram but if not basicly it will have 5 wires comming out of it one green,one green/white one yellow one yellow/white and one white

it is spliced into the 12N wire like this:- green to green from lights. yellow to yellow from lights .green/white to green wire to plug. yellow/white to yellow wire to plug. white wire to earth.the buzzer will sound only if all the lights are working.

hope this is not too confusing

colin

 

[WatsonJohnG]

Colin that is so true of my new type Nissan X trail(no problem with the older type XT)

I tried for ages to find a way through for the wiring from the engine compartment and in the end used caravan black waste piping as trunking under the car with lots of nylon ties and avoiding the exhaust

 

[rosies]

Hi Netti , You already have your 12n socket and wiring fitted so dont think about the bulb failure circiut as that should already have been taken care of by your auto electrician . The 12s socket is a completely differnt circiut apart from rear fog lights/ reversing lights . Again all excellent advice from John and Collin on underside cabling , its just that some vehicles have large rubber grommets ( seals between bodywork holes and items passing through the said holes in the bodywork ) which you can make a small hole in to pass a cable/wire through between engine compartment and interior . Such as around the steering column and main wiring harness .

Yes same as most things these days ( apart for ikea ,lol ) you get simple instructions with a smartcom relay , thats what I was trying to copy for you after I scanned it , but I am a dumbo in that department . I Know you said you where going away Wednesday so you will probably read these remarks when you get back . So please tell us how the first outing went , suspect you will have so so many question for everyone ,I am sure other vanners on here will love to help as well as tom , dick and harry , sorry Steve , John and Collin .

IF YOU LAUGH EVERYDAY THEN LIFE MUST BE WORTH LIVING , STEVE .