24v through 12v bulbs

[Barrbeast]

One for the electrically minded...

So being a Japan import the 4.2 is a 24v lighting system. It has a 7 pin socket fitted for the towbar and checking with Daemo I knew there was a fair chance that the 7 pin would go through a reducer to turn it into a 12v output.

I had a look and it looked to me like my shorty was probably 24v at the 7 pin as the 7 core looked to be just scotch locked (yuck ) straight to the 24v lighting circuit.

To be sure though I decided to test the 7 pin on a spare lightboard thinking (probably wrongly) that if it was a 24v output it would blow the 12v bulbs in the lightboard. Lightboard test was successful though and all 12v bulbs worked fine. :nenau

Looking at it again today it still looks to me like the 7 core cable is just spliced straight into the 24v system with no obvious reducer so my question is, could the 7 pin socket still be a 24v output even though it worked fine with the 12v lightboard?

 

[rustic]

That's a tricky one... one to look at with a multimeter before taking that further.
Let me think.

First of all, never heard of it... ever...


hmmmm...


Got it...:thumb2:thumb2:thumb2
Now I have thought about it, and I know how it could work, be reliable, and drive 12 volt bulbs on any No. plate board and never blow them.










You connect the so called ground return on the 7 pin socket to the centre tap of both batteries on the vehicle, this will already be at + 12 volts, so any bulb on the lighting board will see +24 but with reference to the 12 volts already there, so... each bulb will get to see only 12 volts.

Now this is my theory, using my electronic knowledge, I cannot assume that it is wired this way, but you check for that +12 volt return and prove me right...

Saturday night.... need a better challenge than this lol....


Uncle Rustic

 

[jims-terrano]

I suspect it is 24v going to your 12n socket. Very short term use the bulbs will glow extra bright. Longer term use I would expect the bulbs to blow.

 

[jims-terrano]

I suspect it is 24v going to your 12n socket. Very short term use the bulbs will glow extra bright. Longer term use I would expect the bulbs to blow.

I can't beat uncles advice :thumbs

 

[terranosaurusdoug]

Get multi meter out matey :thumb2....

 

[rustic]

I can't beat uncles advice :thumbs

Actually Jim just reminded me...

If you have a caravan connected with the 12s socket, and the caravan set to 12 volts, then you might find the 12 volts and not 24 volts appearing in the caravan as hoped... but don't assume..
Especially if the 12s socket is an aftermarket ... aftermarket addition.... and bodged in lol.
Uncle Rustic

 

[rustic]

Get multi meter out matey :thumb2....
View attachment 8538

If all lights activated... pin 3 will be + 12 V compared to car chassis, and the remaining pins will be +24 volts.

Now put the black wire of the multimeter on 3, earth, and now the remaining pins will have +12 volts on them, when activated, compared to pin 3.

Uncle Rustic

 

[Lazy-Ferret]

That's a tricky one... one to look at with a multimeter before taking that further.
Let me think.

First of all, never heard of it... ever...


hmmmm...


Got it...:thumb2:thumb2:thumb2
Now I have thought about it, and I know how it could work, be reliable, and drive 12 volt bulbs on any No. plate board and never blow them.










You connect the so called ground return on the 7 pin socket to the centre tap of both batteries on the vehicle, this will already be at + 12 volts, so any bulb on the lighting board will see +24 but with reference to the 12 volts already there, so... each bulb will get to see only 12 volts.

Now this is my theory, using my electronic knowledge, I cannot assume that it is wired this way, but you check for that +12 volt return and prove me right...

Saturday night.... need a better challenge than this lol....


Uncle Rustic

Interesting idea, as long as the caravan lights don't connect to the caravan body work anywhere, as once hitched up, you could end up with two earths, one via the socket, and one via the hitch, which would create a dead short on one of the batteries...

I think as has been said, you are just running the 12v bulbs at twice the voltage... If you just plugged it in, the only bulbs alight will have been the 5w side lights, did you try the indicators (21w) or the brake lights (21w)? At twice the voltage, a 5w bulb just becomes a 10w, and probably can handle that for a while with out any real issues, but a 21w one becoming a 42w, would not last anywhere near as long and may even melt the bulb holder/lens.

The main thing for a bulb, is how it dissipates the heat, which is why the old 100w bigger pearl house bulbs always lasted so much longer than the little 50w candle bulbs, the heat dissipate easier with the extra surface area, and stops it burning out.

 

[rustic]

Interesting idea, as long as the caravan lights don't connect to the caravan body work anywhere, as once hitched up, you could end up with two earths, one via the socket, and one via the hitch, which would create a dead short on one of the batteries...

I think as has been said, you are just running the 12v bulbs at twice the voltage... If you just plugged it in, the only bulbs alight will have been the 5w side lights, did you try the indicators (21w) or the brake lights (21w)? At twice the voltage, a 5w bulb just becomes a 10w, and probably can handle that for a while with out any real issues, but a 21w one becoming a 42w, would not last anywhere near as long and may even melt the bulb holder/lens.

The main thing for a bulb, is how it dissipates the heat, which is why the old 100w bigger pearl house bulbs always lasted so much longer than the little 50w candle bulbs, the heat dissipate easier with the extra surface area, and stops it burning out.

You got a good point with the earth, some older vans did use the aluminium body as a return, yes if you connected that up... something would burn.

Just a slight correction, I hate doing this but if you double the voltage on the bulb, then the wattage goes up 4 times, the current will be twice.

We all know Watts = Volts times amps you double the current, by doubling the voltage, ( resistance remains same) and from the watts equation, the volts double too, so 2x2 so 4 times... Like I say, don't like saying things like that, but it's just that I know lol...



Dare I sign this.... :hide: Rustic

 

[Lazy-Ferret]

You got a good point with the earth, some older vans did use the aluminium body as a return, yes if you connected that up... something would burn.

Just a slight correction, I hate doing this but if you double the voltage on the bulb, then the wattage goes up 4 times, the current will be twice.

We all know Watts = Volts times amps you double the current, by doubling the voltage, ( resistance remains same) and from the watts equation, the volts double too, so 2x2 so 4 times... Like I say, don't like saying things like that, but it's just that I know lol...



Dare I sign this.... :hide: Rustic

Good point, it's been a long day... This is why it's handy to have other people that know, as they can all look out for what the other missed in their hurry to try and put it into words...

But that does validate my point even more, a 21w bulb becomes an 84w at 24v.

 

[rustic]

...
But that does validate my point even more, a 21w bulb becomes an 84w at 24v.

It would, but it would simulate one of those old magnesium flash cubes that were used in the 60's on 126 instamatic cameras lol...

One brief but very bright flash... lol...
:thumb2

Edited to add...
Saturday night isn't it... had a few beers, got a spare battery or two, a few spare bulbs...

flash.... flash... burn...

Look, just disconnect it all before you go to bed lol...

Lol...

 

[Barrbeast]

Should have said, multimeter check on the pins was the first thing I did and it seemed to indicate 24v at the socket but I wanted to be sure hence the lightboard check.

Only a single socket so 12s isn't a factor.

Lazy-Ferret I tried all lights including indicators and brakes

Rustic, I like the thinking and can follow it but the same downside arises as if you just connected a 12v stereo to the one battery instead of using a reducer in that you'll imbalance the batteries as you'll only be taking power from one instead of two - a 24v system no no as it causes uneven charging which then stuffs both batteries. Drain from a 12n socket won't be much in daylight but at night with the sidelights on you'll be draining more and apparently even a small regular uneven drain buggers the batteries in the Safari 24v system :nenau

 

[Lazy-Ferret]

Should have said, multimeter check on the pins was the first thing I did and it seemed to indicate 24v at the socket but I wanted to be sure hence the lightboard check.

Only a single socket so 12s isn't a factor.

Lazy-Ferret I tried all lights including indicators and brakes

Rustic, I like the thinking and can follow it but the same downside arises as if you just connected a 12v stereo to the one battery instead of using a reducer in that you'll imbalance the batteries as you'll only be taking power from one instead of two - a 24v system no no as it causes uneven charging which then stuffs both batteries. Drain from a 12n socket won't be much in daylight but at night with the sidelights on you'll be draining more and apparently even a small regular uneven drain buggers the batteries in the Safari 24v system :nenau

There is probably so much resistance in those horrible scotch locks, it's current limiting the bulbs...:lol

 

[Barrbeast]

There is probably so much resistance in those horrible scotch locks, it's current limiting the bulbs...:lol

:lol :lol

It's got me proper puzzled though

 

[rustic]

There will be an imbalance, but it depends what you actually have, and I think I've nailed that one.

You need to consider...
How many running hours a week, a month, you are trailing where this imbalance may cause an issue?

So the trailer will be run on the higher battery (12-24 volt) now you could run the radio on the lower battery, 0-12 volt) but as soon as you plug that aerial in.... you are grounding the radio case, which could be 0 volts if using the lower battery. or not

You could have a 24 volt to 12 volt converter, lorries must have these, but it would need a fair few amps if you include the radio too

You would need an interface circuit, that takes the 24 volts from the lights, and takes that to 12 volts from the above converter.
This could be a simple as ... 5 or 6 x 24 volt dc coil relays, with a pair of n/o contacts to send 12 volts to the bulbs.

OR see how it goes, monitor off load voltage for each battery daily, and say give each battery, seperately, it's own charging regime once a week or so...

You might find, "that on average" it balances out, but to be fair probably not, but look on the bright side, at least you know why lol.:doh
I' m going to throw the towel in now, before I say something I don't understand myself lol... :surrender :lol:lol

 

[Lazy-Ferret]

It would, but it would simulate one of those old magnesium flash cubes that were used in the 60's on 126 instamatic cameras lol...

One brief but very bright flash... lol...
:thumb2

Edited to add...
Saturday night isn't it... had a few beers, got a spare battery or two, a few spare bulbs...

flash.... flash... burn...

Look, just disconnect it all before you go to bed lol...

Lol...

:lol

Totally off topic, but when I worked at the university, someone donated a dustbin bag full of assorted Russian 1/8w resistors... they did not use the standard colour code bands, but were dark red, and had a number system, with Russian characters printed on them in black, with such tiny writing, you needed a microscope to read them... Even then, it could be hit or miss as to whether you read them correctly. We left a meter by the bag, in the hope the students would have a go at using them in their projects, but everyone just went to the already labelled draws with the conventional resistors in, and we were sure as hell not going to go through and sort them all out...

In the end, we decided to use them for solder training, and would give the new students a few, and tell them to solder them into cubes... Then to show how good we were, we would make a cube, then solder diagonals across all the faces, and also across the middle to opposite corners.

This raised a question, we wondered how you would draw a cube, with diagonals as a circuit diagram, so we could work out the series/parallel resistances between 2 opposite corners, we never got a solution to that, despite pulling a couple of the professors in on it and even if we assumed all the resistors were of the same value..

After a while, we would keep adding to our sculptures, making them bigger and bigger, until one guy made his into a church, with a steeple... this thing was nearly 18 inches high, and even had a weather vane on the top.

One day, we stood it on an aluminium plate, which we connected to the negative of a 200vDC power supply, and then put the positive to the spire tip, like it had been struck by lightning.... Wow, it was spectacular, as each resistor blew, and that then created another path... and so on....

I took about 2 weeks for the smell to dissipate from the techs room...:doh

 

[Barrbeast]

There will be an imbalance, but it depends what you actually have, and I think I've nailed that one.

You need to consider...
How many running hours a week, a month, you are trailing where this imbalance may cause an issue?

So the trailer will be run on the higher battery (12-24 volt) now you could run the radio on the lower battery, 0-12 volt) but as soon as you plug that aerial in.... you are grounding the radio case, which could be 0 volts if using the lower battery. or not

You could have a 24 volt to 12 volt converter, lorries must have these, but it would need a fair few amps if you include the radio too

You would need an interface circuit, that takes the 24 volts from the lights, and takes that to 12 volts from the above converter.
This could be a simple as ... 5 or 6 x 24 volt dc coil relays, with a pair of n/o contacts to send 12 volts to the bulbs.

OR see how it goes, monitor off load voltage for each battery daily, and say give each battery, seperately, it's own charging regime once a week or so...

You might find, "that on average" it balances out, but to be fair probably not, but look on the bright side, at least you know why lol.:doh
I' m going to throw the towel in now, before I say something I don't understand myself lol... :surrender :lol:lol

Already running a reducer for stereo, cb, 12v socket and two sets of double 12v sockets

Yeh I can buy a dedicated "converter" for a trailer socket which has the relay bank already rigged up and includes a reducer for the trailer output and an audible tell tale for the indicators. Seems to be two types, a cheaper type that needs a dedicated 24v feed for the converter and a more expensive fancier type that takes its 24v feed straight from each individual light circuit as and when... only downside I can see of the cheaper type is there could be a constant (albeit small) parasitic drain on the batteries from the reducer unless they've done something fancy with the relays to disconnect the feed when no lights are working... hmm

 

[rustic]

...unless they've done something fancy with the relays to disconnect the feed when no lights are working... hmm

Most of the trailer lights need only be on when the ignition is actually on.
So the feed to an isolating relay could be fed from.... ohhh


The radio supply, so if the switch is off, or in accessory position, the trailer lights can be on. However.... you might need an over ride, to enable lights if you walk away from the trailer, lock the car and leave side lights on.
Also with using the radio circuit, the trailer lights will drop out all the time the engine was cranking. Call that an easy start feature lol...:thumb2

So that part not too difficult. Your car might sound like a washing machine with all the whirring and clicking of relays lol.

If you can do the wiring yourself, use the correct sized cable and fuses, with a bit of "Support" from your "friends", you needn't spend too much on what has been suggested so far.

Uncle Rustic

 

[Barrbeast]

Most of the trailer lights need only be on when the ignition is actually on.
So the feed to an isolating relay could be fed from.... ohhh


The radio supply, so if the switch is off, or in accessory position, the trailer lights can be on. However.... you might need an over ride, to enable lights if you walk away from the trailer, lock the car and leave side lights on.
Also with using the radio circuit, the trailer lights will drop out all the time the engine was cranking. Call that an easy start feature lol...:thumb2

So that part not too difficult. Your car might sound like a washing machine with all the whirring and clicking of relays lol.

If you can do the wiring yourself, use the correct sized cable and fuses, with a bit of "Support" from your "friends", you needn't spend too much on what has been suggested so far.

Uncle Rustic

One step ahead Uncle (I think) the feed to the 24v to 12v reducer already runs through a relay that only operates when in acc or on (put that relay in last weekend) so I could either split the feed after the relay but before it hits the reducer or just use the feed that operates the relay but the "what do I do if I need trailer lights on but truck locked" did occur to me to.

I like the idea of putting some sort of bypass in (could always come off the sidelights, although I'd need to do similar with the indicators for when I have the hazards on or fit a switched bypass)... have to admit though the fancier converter that takes the feed from each light is looking more and more attractive as it's a neater solution!

 

[rustic]

:lol ...
This raised a question, we wondered how you would draw a cube, with diagonals as a circuit diagram, so we could work out the series/parallel resistances between 2 opposite corners, we never got a solution to that, despite pulling a couple of the professors in on it and even if we assumed all the resistors were of the same value..

You don't need a professor to answer that one, just your plain old Uncle Rustic


You have 12 equal resistors lets say each 100 ohm arranged in a cube as you describe.

The resistance across the furthest corner to furthest corner will be 50 ohms. :thumb2
There you go, did that in my head. :doh

If anyone needs a hint... since all resistors are equal, within the circuit there are 4 resistors that take no part in the circuit at all, they could be open circuit, short circuit it will not affect the resistance from furthest diagonals at the time. :doh how can this be ? :naughty

Look, this was part of my job. If anyone is banging their head against a wall, I can post a sketch as to why 50 ohms.

However, using 12 different resistors is much more difficult, but doable, it would be easy enough ( well for me or other electronic engineer) to write an equation, with 12 unknowns.
You have to look at each arm individually, then combine circuits.

Uncle Rustic :thumb2