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Running a 12v (cigar) socket straight off battery?
jps - 21/1/19 at 01:47 PM

Always looking to save a couple of quid where I can...

Can I make one of these: https://www.carbuildersolutions.com/uk/trailing-lead-remote-12v-lighter-style-power-socket-with-crocodile-clips

Simply by buying one of these - and attaching the crocodile clips I have lying about? https://www.carbuildersolutions.com/uk/black-lighter-power-socket-rubber-plug-iva-ok

The saving is that I will refit the 'IVA OK' one into my car once I get to that point.

My electrical knowledge is pretty much zero - but I'm somewhat surprised I don't need to put a fuse in-line or something?

I'll be running a tyre compressor off it...


Oh - and an additional point: I assume all batteries provide DC (how could they alternate?!) - but cars have alternators, so I assume car electrics run off AC? Why don't I need something turning DC into AC to drive my cigar lighter/air compressor?

[Edited on 21/1/19 by jps]

loggyboy - 21/1/19 at 01:52 PM

Is this a joke post?

jps - 21/1/19 at 02:00 PM

quote:
Originally posted by loggyboy
Is this a joke post?


Err - no? Why?

I wasn't kidding when I said "My electrical knowledge is pretty much zero - but I'm somewhat surprised I don't need to put a fuse in-line or something? "

nick205 - 21/1/19 at 02:03 PM

https://en.wikipedia.org/wiki/Alternator_(automotive)

peter030371 - 21/1/19 at 02:05 PM

quote:
Originally posted by jps
Always looking to save a couple of quid where I can...

Can I make one of these: https://www.carbuildersolutions.com/uk/trailing-lead-remote-12v-lighter-style-power-socket-with-crocodile-clips

Simply by buying one of these - and attaching the crocodile clips I have lying about? https://www.carbuildersolutions.com/uk/black-lighter-power-socket-rubber-plug-iva-ok

The saving is that I will refit the 'IVA OK' one into my car once I get to that point.

My electrical knowledge is pretty much zero - but I'm somewhat surprised I don't need to put a fuse in-line or something?

I'll be running a tyre compressor off it...


Oh - and an additional point: I assume all batteries provide DC (how could they alternate?!) - but cars have alternators, so I assume car electrics run off AC? Why don't I need something turning DC into AC to drive my cigar lighter/air compressor?

[Edited on 21/1/19 by jps]


https://www.carbuildersolutions.com/uk/trailing-lead-remote-12v-lighter-style-power-socket-with-crocodile-clips
These should have a fuse if they wanted to be safe, I have seen some that do but that is a cheap one.

https://www.carbuildersolutions.com/uk/black-lighter-power-socket-rubber-plug-iva-ok
You can add wires and crocodile clips as you say but even better is to also add an inline fuse like this https://www.carbuildersolutions.com/uk/in-line-waterproof-blade-fuse-holder

All car electrics are DC, yes an alternator does produce AC but this is rectified by diodes to DC (these are built into the alternator normally).

The voltage in your car is nominally 12V DC but can go as high as 14.5V and under extreme load (cold day, lights on, trying to start) it can drop well below 12V.

jps - 21/1/19 at 02:07 PM

Thanks Peter

HowardB - 21/1/19 at 02:09 PM

car battery terminals and wiring should be done in such a way as to be safe.
In line sockets that are fixed in the car like a 12v cigarette socket should be fused, often with a 20A inline fuse.
A temporary attachment of an ancillary device direct to the battery with crocodile clips can be done for the duration of requirement. As you can imagine they are not a fixed or permanent installation.

battery - 12v+ red - inline fuse - SOCKET
battery - 12v- black - inline fuse - SOCKET

hth

H

James - 21/1/19 at 02:36 PM

JPS,

As a cautionary tale- both Jasper and Hicost had car fires that totally destroyed their beautiful cars.

Please don't skimp on this for the sake of 4 quid!

Look at the benefits of the proper cigarette lighter you've shown- you get a decent mount to screw it to the back of your dash and also a dust/rain cover.

Cheers!
James

jps - 21/1/19 at 02:55 PM

quote:
Originally posted by James
JPS,

As a cautionary tale- both Jasper and Hicost had car fires that totally destroyed their beautiful cars.

Please don't skimp on this for the sake of 4 quid!

Look at the benefits of the proper cigarette lighter you've shown- you get a decent mount to screw it to the back of your dash and also a dust/rain cover.

Cheers!
James


Thanks James - yes, i'm intending to buy the 'proper' one - and for now just wire it straight to the car battery. With stuff I already have lying about I'll probably make a little tray to hold the battery and to mount the socket on. This post was really because I'm just a bit surprised it's a simple as attaching that socket (with an inline fuse) straight to a car battery.

snippy - 21/1/19 at 06:07 PM

I use the rubber plug type 12v sockets as they keep the rain out in our open to all weather cars. Make sure you fit an in line fuse.

coyoteboy - 21/1/19 at 10:25 PM

Fwiw 12v in a car is generally accepted to spike to 80v in worst cases. Most cheap stuff is rated to 30v, automotive grade stuff to 60iirc

computid - 21/1/19 at 11:34 PM

Really this should be switch on ignition live, unless you plan to be able to run it when the car is switched off.

So it should go:

Battery + -> Fuse -> SPST Relay Terminal 1

SPST Relay Terminal 2 -> 12v Socket Live

12v Socket Neutral -> Battery/chassis ground

SPST Coil Terminal 1 -> Ignition live

SPST Coil Terminal 2 -> Battery/chassis ground

That'll ensure that if you accidentally leave something plugged in it doesn't drain the battery, and if you have an electrical fire from something plugged into it switching the ignition off will kill it.

peter030371 - 22/1/19 at 08:22 AM

quote:
Originally posted by coyoteboy
Fwiw 12v in a car is generally accepted to spike to 80v in worst cases. Most cheap stuff is rated to 30v, automotive grade stuff to 60iirc


It can be far worse than that but we are only talking milliseconds or even microseconds, anything you buy that plugs into a car power socket should be designed to cope with automotive transients As far as the OP is concerned 'normal' car voltage is 12VDC plus or minus a couple of V

nick205 - 22/1/19 at 10:07 AM

quote:
Originally posted by computid
Really this should be switch on ignition live, unless you plan to be able to run it when the car is switched off.

So it should go:

Battery + -> Fuse -> SPST Relay Terminal 1

SPST Relay Terminal 2 -> 12v Socket Live

12v Socket Neutral -> Battery/chassis ground

SPST Coil Terminal 1 -> Ignition live

SPST Coil Terminal 2 -> Battery/chassis ground

That'll ensure that if you accidentally leave something plugged in it doesn't drain the battery, and if you have an electrical fire from something plugged into it switching the ignition off will kill it.



VAG cars (Alhambra, Passat, Touran etc.) are all done this way. The 12V accessory socket (as they call it) is switched live and therefore doesn't power anything without the ignition turned on. Mildly annoying sometimes, but it does prevent you draining the vehicle battery and then not being able to start the vehicle. Particularly useful to prevent the vhicle battery being drained by my kids on camping trips!

Mr Whippy - 22/1/19 at 12:23 PM

buy a foot pump

nick205 - 22/1/19 at 12:40 PM

quote:
Originally posted by Mr Whippy
buy a foot pump



Fair comment!

jps - 22/1/19 at 01:33 PM

quote:
Originally posted by nick205
quote:
Originally posted by Mr Whippy
buy a foot pump



Fair comment!


What happened to 'work smart not hard'?!

I have build wheels on my chassis - all of which have slow punctures. I'm getting a bit bored of pumping them up everytime I go to work on the car...

nick205 - 22/1/19 at 01:57 PM

quote:
Originally posted by jps
quote:
Originally posted by nick205
quote:
Originally posted by Mr Whippy
buy a foot pump



Fair comment!


What happened to 'work smart not hard'?!

I have build wheels on my chassis - all of which have slow punctures. I'm getting a bit bored of pumping them up everytime I go to work on the car...



Get a mains powered air compressor (and some air tools) then

cliftyhanger - 22/1/19 at 03:40 PM

Or cut the fag lighter plug off the end of the 12V compressor, ad a fuse to the live, then croc clips direct onto the battery?
I have done that, only downside is popping the bonnet, but if you are doing all the checks it doesn't matter.

jps - 22/1/19 at 03:59 PM

quote:
Originally posted by cliftyhanger
Or cut the fag lighter plug off the end of the 12V compressor, ad a fuse to the live, then croc clips direct onto the battery?
I have done that, only downside is popping the bonnet, but if you are doing all the checks it doesn't matter.


Battery is not in the car yet - so popping the bonnet is not a problem - but I do use the compressor on my tin-top, so don't want to hack it about.

gremlin1234 - 22/1/19 at 08:26 PM

quote:
Originally posted by jps
quote:
Originally posted by cliftyhanger
Or cut the fag lighter plug off the end of the 12V compressor, ad a fuse to the live, then croc clips direct onto the battery?
I have done that, only downside is popping the bonnet, but if you are doing all the checks it doesn't matter.


Battery is not in the car yet - so popping the bonnet is not a problem - but I do use the compressor on my tin-top, so don't want to hack it about.
move the tintop closer to the work.

note, most cigar-lighter type plugs on accessories have a fuse in them which is good, especially when you shut the door on the wire...

snapper - 23/1/19 at 09:22 AM

As stated above, if you do use crocodile clips, only use for to duration of the need to attach the tyre pump.

DO NOT DRIVE THE CAR WITH THEM ATTACHED

Crocodile clips will present a bare metal surface for something to touch as you bounce along and if it is the earth clip that makes contact or worse come adrift and hits a metal part of the car the full power of the battery will short through the cable which will probably melt and or spark a lot.

jps - 23/1/19 at 09:43 AM

quote:
Originally posted by snapper
DO NOT DRIVE THE CAR WITH THEM ATTACHED


Chance would be a fine thing - it's just a rolling chassis with no wiring loom, no fuel system and no brake system. But it does have the engine and gearbox in, which is why pushing it out of the garage with flat tyres is a bit of a bind....

quote:
Originally posted by gremlin1234
move the tintop closer to the work.


It's too tight down the side of my house to get my tintop through - otherwise I would do exactly that... It is however wide enough to get my Haynes out (that was checked before I bought the house!)...

[Edited on 23/1/19 by jps]

Mr Whippy - 23/1/19 at 12:13 PM

quote:
Originally posted by jps
quote:
Originally posted by nick205
quote:
Originally posted by Mr Whippy
buy a foot pump



Fair comment!


What happened to 'work smart not hard'?!

I have build wheels on my chassis - all of which have slow punctures. I'm getting a bit bored of pumping them up everytime I go to work on the car...


Get the tyres fixed?