Electrical Queries

[Ben Stratford]

I would be very grateful for assistance so I get this right.
I would like to install a 10 point fuse box to run 12V things in the front of the cruiser.
The stereo, aerial, rear view camera and a couple of small LED lights are planned.
Thanks to @Richard Turner I have a 10 amp dropper to provide the power. I would like to draw from a switched 24V supply so nothing can get left on by mistake. An easy solution would be to tee off from the cigar lighter as it is in the right area so I could fix everything behind the glovebox where it is dry.
Queries:
Is this ok for say 5 to 10 amps max?
Would i need a relay before the dropper?
Where should any fuses be inserted?
What wire gauge should I use?
Or if it is a bad idea, what should I do please?

 

[Chris]

Oh Richard .... one for you perhaps.

 

[Ben Stratford]

Another job is to attach the rear view camera activation wire to the reverse light circuit.
I envisage finding the circuit by locating the switch on the gearbox. Then using a small 5Amp dropper to privide the 12V feed to the stereo.
Could I strip some insulation and solder the switched wire to the dropper then heatshrink?
Do I need a fuse?
Any other feedback most welcome.

 

[Ben Stratford]

Once I have removed the 12V connections to my second battery (24V) system, I would like to connect a pair of volt meters - one to each battery. But only want them to come on when the ignition is on rather than all the time.
I could install a switch and combine their earth wires to manually switch them on and off but there must be a better way?

 

[Richard Turner]

Is the cigar lighter permanent live or switched by the key? What is the standard fuse rating for it?

If the cigar lighter is useless 24v, and is switched so it works on acc and ignition, you could disconnect it and run the power through the dropper, then your fusebox, then you could reconnect it to the cigar lighter at 12v, and use the other spurs in the fuse box for the radio etc.

I think 24v draws half the current that 12v uses, so your 12v wires need to be twice as thick as 24v 10A.

 

[StarCruiser]

Your best bet is to run a fuse from 24v+ somewhere, a 10A circuit, like the lighter socket is probably a good one and replace it with a 12v lighter/power socket or USBs maybe. If you want it switched and the lighter circuit isn't then a relay is a good idea.

What Rich says is partly correct, for the same power, the wattage, a 24v circuit will have thinner cables as the current will be half. But 10A cable is 10A cable whatever the voltage (it's the insulation thickness that increases with voltage, the copper increases for the Amps.

 

[Richard Turner]

Can 12v and 24v earth be combined? Or will Ben have to ensure the radio and other things are insulated from the body of the truck and the earth must go back through the dropper?

 

[Ben Stratford]

Is the cigar lighter permanent live or switched by the key? What is the standard fuse rating for it?

If the cigar lighter is useless 24v, and is switched so it works on acc and ignition, you could disconnect it and run the power through the dropper, then your fusebox, then you could reconnect it to the cigar lighter at 12v, and use the other spurs in the fuse box for the radio etc.

I think 24v draws half the current that 12v uses, so your 12v wires need to be twice as thick as 24v 10A.

It is switched and works in ACC and On. The fuse for it is 15Amps. Would like to keep it functional as a cigar lighter but may install a 12V socket at a later date for charging something

 

[Towpack]

Can 12v and 24v earth be combined? Or will Ben have to ensure the radio and other things are insulated from the body of the truck and the earth must go back through the dropper?

You could use a common earth for both 12 & 24v, just make sure both pos supplies are kept isolated at all times.

Edit
The picture of the 24 to 12v dropper Ben has looks like it uses a common earth....https://www.landcruiserclub.net/community/threads/over-charging.149199/page-3

 

[Ben Stratford]

Your best bet is to run a fuse from 24v+ somewhere, a 10A circuit, like the lighter socket is probably a good one and replace it with a 12v lighter/power socket or USBs maybe. If you want it switched and the lighter circuit isn't then a relay is a good idea.

What Rich says is partly correct, for the same power, the wattage, a 24v circuit will have thinner cables as the current will be half. But 10A cable is 10A cable whatever the voltage (it's the insulation thickness that increases with voltage, the copper increases for the Amps.

I have some 35A wire, is that too big?

 

[StarCruiser]

From an electrical point of view you can never go too big, it's the mechanical consideration, having the right size terminals, enough room to fit them, the space and above all the flexibility to use said larger cable which often limits anything too big. What AWG or Sq mm is it?

It may be on the big side given where you are taking a connection. The correct size is cheap enough and easy to get hold of so you may well be better off getting some 20A wire or thereabouts.

It's worth getting a decent fusebox.
These are quite nice, they need crimped ring terminals but are pretty good.
http://www.polevolt.co.uk/acatalog/Power_Distribution_Fuse_Boxes.html
Or they do some modular ones which are probably too much for what you need but nicer IMO.

 

[Ben Stratford]

From an electrical point of view you can never go too big, it's the mechanical consideration, having the right size terminals, enough room to fit them, the space and above all the flexibility to use said larger cable which often limits anything too big. What AWG or Sq mm is it?

It may be on the big side given where you are taking a connection. The correct size is cheap enough and easy to get hold of so you may well be better off getting some 20A wire or thereabouts.

It's worth getting a decent fusebox.
These are quite nice, they need crimped ring terminals but are pretty good.
http://www.polevolt.co.uk/acatalog/Power_Distribution_Fuse_Boxes.html
Or they do some modular ones which are probably too much for what you need but nicer IMO.

Nice looking fuse box Rich.
The wire spec is:
Conductor Specification (mm): 65/0.30
Nominal Current Rating (AMP): 35.0
Conductor Cross Section (mm²): 4.5
Maximum Overall Diameter (mm): 5.1
Maximum Loading (Watts)
12 Volts - 420
24 Volts - 840
Resistance per Metre at 20ºC (Ohms): 0.0041

 

[StarCruiser]

I think your dropper is rated at 10A or so isn't it? TBH this will be a bit tricky to bend around under the dash just because of its bulk. If there's not far to go then it may be fine but once you've got lots of them running about it tends to look like you really didn't know what you were doing and just used the biggest wire that would fit. Which is ok electrically speaking, it can just look untidy.

 

[Ben Stratford]

Thanks Rich, 20A will be acquired, which mm or awg would suffice please?

 

[StarCruiser]

2.5mm will cope with more than 20A, though vehicle wiring differs in sizes from mains wiring. It's generally sold by the current rating of the fuse it is expected to be protected by in Halfords or the like. 1.5mm should be good for 16A depending on the construction. If you intend to fuse at 10A or 15A then 1.5 would be ample. If it's 20A you want then go for 2.5mm or whatever gives the correct current rating.