20 replies to this topic

[mullet]

Hi all.  I installed a 'cigarette' plug a couple of years ago.  I followed the advice to install it so that it was only live when the ignition was on and I remember distinctly following advice well when I did this (just lost the link to the thread!).  However, when a satnav was attached it made the idle erratic, with the satnav charging/discharging (never constantly charging).  A mechanic neighbour advised to wire it direct to live.  This solved erratic behaviour and behaved just like a charger in any other car.

 

However, whilst it solved erratic behaviour I see most people on here keep advising to have it only live when the ignition is on.  Can someone please advise on these questions?

 

1) what inline fuse is advised?  I think I used a 10amp, which since blew and I have forgotten what I used (d'oh!)

 

2) what diameter of wire?  I used one as advised by a shop, but it does feel rather hot when I use an electric tyre pump making me think I should use a thicker diameter to reduce the resistance.

 

3) is there concern with the cigarette/charger socket being connected to live all the time?  It does work best this way, but if a worry then would others here agree/disagree I could add an on/off switch next to the cigarette/charger socket?  I mean, of course it's always 'off' if nothing is plugged into it.  But just extra security this way.

Edited by mullet, 04 June 2025 - 01:15 PM.

[stuart bowes]

fuse and diameter of wire will be dictated by whatever you connect to it, everything will be 12v but the amps required will vary (sometimes even just milliamps)

 

when you know what the largest amp draw is going to be, you wire and fuse accordingly (the lighter itself probably has a rating which should be your minimum, but I'm assuming this is for accessories)

 

if you have it perm. live then you have to remember to unplug things when you leave it parked, unless you like having a flat battery

 

the switched live circuit has a few things on it already, if you want you could use that to switch a relay (i.e. no actual 'draw' added to that circuit) and run the fused power supply cable direct from perm live, through the relay.  possibly a tad overcomplicated but safe and does what you need (if you want the accessory to turn on when you turn the car off)

 

side note I would consider a dash mount USB socket instead, wiring issues will be the same but most things are USB now aren't they anyway, get rid of those horrible wobbly plastic ciggy lighter adaptor things eugh

Edited by stuart bowes, 05 June 2025 - 08:46 AM.

[mullet]

Thanks Stuart.  The device that is will be drawing most power will probably only ever be this product: https://m.media-amaz...A1SIV3OYgKS.pdf

Says 7.5amps as a maximum.  It has a built-in fuse of 15amps.  So I think I should use an inline fuse also of 15amps.

 

Only question I have is what diameter of cable to use, considering this 7.5amp device seems to cause a lot of resistance (thus heat) in the current cable of unknown diameter.  Any suggestion?

 

As for USB, this pump is the old bulky socket type.  But I have a USB adapter that I can run a satnav from.

[Spider]

I have mine and a USB charging outlet live all the time. As far as the cigarette socket goes, there's no down side, however a very small down side of the USB is this particular one has an LED in it, while dull, it does put a small drain on the battery, even so, I find after 3 - 4 months, there's well enough charge to start the car.

As for fusing, it really only needs a fuse about 1/3 to 1/2 more than the rated load, so if your Satnav draws say 2 amps, a 3 amp fuse will be fine.

[stuart bowes]

in terms of cable probably the easiest way is to check here and compare your requirements for amp rating to their desriptions

 

https://www.12voltpl...pper-cable.html

 

you'll need a length of red and a length of black, possibly a 12v normally open (NO) relay with a decent rating, this one's 30a

 

https://www.12voltpl...h-resistor.html

 

and then some sort of fuseholder, various choices available, this is a nice simple one but you'd have to make sure the connectors are well insulated

 

https://www.12voltpl...use-holder.html

 

(I don't work for 12v planet or anything, other sites are equally useful, etc)

 

let us know if you need a wiring diagram sketched out for that

Edited by stuart bowes, 05 June 2025 - 10:05 AM.

[mullet]

in terms of cable probably the easiest way is to check here and compare your requirements for amp rating to their desriptions

 

https://www.12voltpl...pper-cable.html

 

you'll need a length of red and a length of black, possibly a 12v normally open (NO) relay with a decent rating, this one's 30a

 

https://www.12voltpl...h-resistor.html

 

and then some sort of fuseholder, various choices available, this is a nice simple one but you'd have to make sure the connectors are well insulated

 

https://www.12voltpl...use-holder.html

 

(I don't work for 12v planet or anything, other sites are equally useful, etc)

 

let us know if you need a wiring diagram sketched out for that

Thanks for the advice.  I got a 15amp inline fuse and 2mm wire.  My guess is the wire that was getting hot was due to being too small, creating too much resistance within the cable itself.  I'll wire it up and pump the tyres to see.