Ah yes wiring practice has changed and I knew this at one point however when trying to remember or find diagrams I'd used originally I'm at a loss.
Line by line critique of your response not to be critical but so we either "sing off the same hymn sheet" or know the points we have to check out. (Mind you readers we could both be wrong)
Anyway, back on topic. The main confusion seems to be around the use of the 12S Pin 2. Pin 2 was always the 12V feed from the car to the trailer going back to the original 12N socket specification before the fog light pinched it
OK don't know about any 12N practice pre dating fog lamps
Anyway, back on topic. The main confusion seems to be around the use of the 12S Pin 2. Pin 2 was always the 12V feed from the car to the trailer going back to the original 12N socket specification before the fog light pinched it.
It appears that use of Pin 2 for battery charging was carried over to the 12S socket but only as custom and practice - not as a defined standard.
Subsequently a standard was defined that mandated 12S Pin 4 as the batty charging feed. This was previously a permanent 12V feed that now needed to be ignition fed.
Not surprisingly the use of Pin 2 for battery charging continued well past the publication of the standard and is still being referenced in technical literature including the diagrams you have included above.
As stated failing to find diagrams I've looked at previously but have used the same source for all these diagrams as he is quite encyclopaedic and I've used him for coupling info. 1983 wiring as per Thomson Caravans. [You must be registered and logged in to see this link.] [You must be registered and logged in to see this image.]
Almost as per up to up to date with a permanent live pin 4 auxiliary caravan, ignition activated pin 6 fridge and alternator or charge light activated pin 2 leisure battery charge. With the only difference being pin 7 left spare resulting in pin 3 earth burn out.
Right so let's go to their 1998 wiring [You must be registered and logged in to see this link.] [You must be registered and logged in to see this image.]
So we can see your removal of the use of pin 2 here and subsequently below even if there is disagreement over 1998 or 1999. [You must be registered and logged in to see this link.]
Sorry no image of the diagram to lift.
So now pin 4 serves as both a connection for battery charging and auxiliary wiring (lights radio etc). Well no wonder this didn't catch on there is no possibility of a good result. A true what genius thought of this moment.
If you connect up to a car as previously wired the first time you stop with a non fully charged leisure battery you don't move again because it's drained the starter battery. So if instead the pin 4 is now on a switched supply be it alternator or ignition key. If for some reason you want to power the caravan (Dandy well it doesn't really apply to us) off the car the engine has to be running or the keys must be in the ignition. That is ignoring the disappointment felt if your battery was wired to pin 2.
If I were to wire up a caravan 12s connection I would not adopt this system ever. Much better to add a missing pin 2 connection.
Ironically I do now believe that the requirement on modern wiring systems is that only the fridge and battery may be powered (Of course road lights as well but that is the 12N) whilst on the move any auxiliary power supply as per pin 4 must disconnect upon either the ignition key being turned or upon the engine running. This is to prevent interference with car borne electronic systems.
To add confusion manufacturers of split charge relays, such as the TEC3M you have shown, encourage the use of Pin 2 as a parallel connection to help overcome the overheating / voltage drop problems associated with the fact that the wires in the multicore cables are smaller than they should be.
As long as the fridge was wired to pin 6 there shouldn't be that much extra current through pin 4 compared to the previous current through pin 2. The major burnout was always through pin 3 if pin 7 had not been wired to earth. Could the encouragement to wire through pin 2 not just have been because only wiring through pins 6 and 4 sucked and everone could see this?
Later saw this
What about pin 4?
Modern caravans have their own relay switch. When the vehicle’s engine is running the power is switched from the interior lights to allow the caravan’s own battery to charge.
from [You must be registered and logged in to see this link.]
Still treat pin 4 and 6 only wiring as dubious.
In the picture you have shown, the two 12v connections are common (just allowing the use of two parallel supply cables). Terminal 6 and Terminal 4 are switched through separate relays to control the fridge and battery charging respectively. Terminal 2 is connected internally to Terminal 4. This provides for the use of a parallel connection using both pins, or caters for a trailer that is wired to accept the battery charging supply on Pin 2 only.
I assume this is also the case in the two schematic diagrams you have shown i.e., once the relays detect 'engine running' the 12V supply is provided to Pins 2, 4, & 6 covering all bases.
Ah Um, Ah Um Ah. This is where I start to get stuck. I think the 1st diagram is poor as it shows nothing of how the three 12v +ve supplies are wired within the self sensing device. [You must be registered and logged in to see this image.]
As you're going into the detail of telling me that terminal 2 is wired to terminal 4 I presume you are referring to the 3rd diagram or 2nd wiring diagram. [You must be registered and logged in to see this image.]
To reiterate. I don't understand the nature of how the relay in the 2nd wiring diagram energises the supply pins. what I originally wrote:
I've seen wiring diagrams with the No4 Supply being an unswitched supply straight from the vehicle battery. Though this will not apply to Dandys are not live feeds other than the battery charging and fridge actually switched off when the engine is running on newer vehicles as other feeds could interfere with car electronic systems?
Though on a 12s system is that what this is doing. I'm not understanding what points are energised when with this relay system.
For all I know the pin 4 could be energised upon ignition or it could be of a modern standard and deactivated upon ignition.
I can understand a relay when given an illustration of the internal switching but not just from a representation of the pins as above. Sorry for my numptyism.
To be fully compliant with the standard, caravan manufacturers should ground the 12S Pin 2 at the caravan end. The tow car can then detect this when the caravan is attached and adjust any electronic vehicle systems accordingly. It is perhaps fortunate that manufacturers have chosen to ignore this part of the standard as, for most tow car wiring, it would provide a direct short circuit on the high-current 12V feed.
1) This is beyond me and I'd never heard of it at all. Can you provide a link to this standard?
2) I can see why earting pin 2 on a caravan might result in misery if it's wired to a supply on a split charge relay.
3 I've seen pin 5 described as a spare or the loose term of sensing be it reversing or other. But we are talking of pin 2 wired to "ground" to allow the car to sense this. The issues I can see even if everything was wired to this standard:
a) You are speaking specifically of "Grounding On The Caravan" from pin 2 not a caravan side connection to pin 3 (or 7)How does the car sense being grounded to the caravan there is no return except a variable one of indeterminate resistance across the tow hitch itself? This looks strange to me. It is to pin 3 and was often taken from pin 5 See Bugger Bugger Bugger at the end.
b)With reference to [You must be registered and logged in to see this link.]
OK I know it's 16th edition and we're on 17th but it's the only prescriptive piece I could find. The mains earth is grounded but all 12v (ELV) cabling is isolated. From the above
Where 240 V and extra-low voltage circuits (usually 12 V) are both used, the cables of the two systems must be run separately and must both be insulated for 240 V.
. Now a grounded wire from pin 2 would become disconnected when the 12s plug was removed from the car (other than in the bizzare Dandy set ups where the 12s plug is inserted into a second 12S socket in the dandys body to energise the 12v sockets from a transformer or the leisure battery)but this has got to be contrary to the spirit of the 16th edition and with a non specified sensor would possibly (probably) breach the regulations if one connected mains while still attached to the car with the 12S plug?
Allied question relating to mains charging springing from point 3b) So the 12v (ELV) system must be isolated from the 240v supply?
If so how are the transformers of battery chargers wired, are they isolating transformers or are they wired with a common earth potential? If the latter then the 12v (ELV) system is not isolated. Do we have to take care of the type of charger we use? I'm not pretending even 5% of caravanner's would get this but it's a dotting our i's and crossing t's type point.
I'll go with you on the mains charging or to be truthful I know nothing better. Didn't realise the sort of lead thickness a mover would require from a third party source. 252
mm is a bit thick.
See you have not ventured to wind or solar charging yet. Perhaps as well.
Decided to have a look at 13 pin wiring and saw that while you now have 3 earths that pin 9 has now become similar to pin 4 as in it is permanently live. It's switching between auxiliary functions and fridge being reliant on the battery charging circuit. I still have a belief about the auxiliary functions not being available whist driving I wonder if I'm mixing these up? With this set up if you did not have a battery would you then need to wire the fridge to pin 10? See Bugger Bugger Bugger.
You kill yourself trying to find a well written guide then after you have written all of the above you find one.[You must be registered and logged in to see this link.]
Third parties if you can help please do so this is not meant to be a 2 person conversation. If you don't understand a bit do say, this needs to be easily readable eventually.
The only thing I would be cross at is an opinion without any supporting evidence (and probably only then if it were silly or meant to troll) I don't want the sort of rubbish that you see if you go to UK Campsite and search "Reverse Polarity" [You must be registered and logged in to see this link.]
where correspondants are either trolling or so thick their death would be no loss to the gene pool.
I know it has limited interest but all this does take a while to write.