Quote:
Originally Posted by Laird Scooby
Hmmmm, 2.4kW through 1mm^2 cable - on 240V yes, definitely but on 12V?   
Don't forget though, that's the AC rating of the cable, DC is usually different.
Also the numbers on the cables in the diagram refer to AWG so the 14 next to the wire refers to 14 AWG which is just over 2mm^2
https://www.powerstream.com/Wire_Size.htm
A few points that might help when working it all out, the full beam uses the 55W filament in the H4 lamps and the the H3 (usually) lamps in the auxiliary lights are 55W each.
That's rated at 12V though, remember when the engine is running and the alternator is charging, the voltage will be 14V so the output will be around 66W on each.
That said, if you look on pg3 of the pdf wiring diagram i linked to previously, (also pg30) you will see the driving lamps are simply connected in parallel with the outer main beam filaments. I'd suggest 2.5mm stranded or 28/0.30, although on a short run you'd probably get away with 14/0.30 :
https://www.autoelectricsupplies.co....66/category/11
To save confusion on the front fog lamp wiring, here's what i would do.
Run a +ve feed from the sidelight circuit to the front fog lamp switch. Use a relay with a flywheel diode and also use a series diode (1N4000 series is fine) in the switched feed from the switch output.
A relay like this is what i mean with a flywheel diode.
https://www.ebay.co.uk/itm/High-Qual...f/131348827790
From the switch, go through the diode (the series diode, not the one in the relay) to terminal 86 on the relay. Take a cable from terminal 85 on the relay to the main beam feed.
Run a 15A fused feed from battery +ve to terminal 30 on the relay and then from termial 87, run two feeds, one to each front fog lamp. This should go to the flying lead on the lamp, there is a tab on the holder for the erth terminal. Run an earth wire from the light to a convenient earth point, usually the mounting bolt of the light is a good point if it's on the bumper.
In diagram form :
Hope that makes sense and is useful!  |
Many thanks Dave,
You are right about the I^2R being a bit too high in a 12V system - well spotted. Regard mine as a bit of a gross error check.
I see what you mean about pp3 and pp30 of the quite excellent wiring diagrams you sent me, the additional driving lamps on each side are just wired to the full beam of the adjacent headlamp. I'm guessing they are all 60W bulbs, so we entirely agree on that being a very sensible plan for the driving lights. I might get round to fixing the driving lamps tomorrow before getting the tyres fitted as it won't take long.
Thank you for your work on the fog lamps - yes, I had envisaged something similar although I hadn't drawn it out yet. What I need to do, perhaps on Thursday if time allows, is to take apart what is there already. I'm hoping I'll be able to use some of the wires from the dashboard switch (the scruffy one that is going in the bin) to a relay in order to save me having to pull through more cable. I have not looked yet, but there must be a relay somewhere to control the existing installation, which I might just be able to re-purpose (being an environmentally friendly sort of chap. I'll take some photos as I take the old installation apart if there are any real howlers - I suspect there might be :-)
I'd quite like to get these two jobs done this week as next is half term (my son and I will have a road trip to Devon and Hampshire (not is the Volvo - if the weather isn't too bad we'll take the Porsche, if it is poor we'll use the sensible car (diesel estate car)).
The Royal Barge is coming along quite nicely - at this rate I should have all the jobs on my current to-do list finished by about the end of February (but of course I'll find some more as I go...).
Thank you so much for your help.
Alan