Simple electrical question

gleesonger

I have vw polo 03 and want to run something off the car battery (not the lighter), whats the best way to hook into the electrical system?

I'd prefer not to have to splice some wires, I'd like to do it properly. Is their some board that I can just plug into?

Midnight_EG

gleesonger wrote: »

I have vw polo 03 and want to run something off the car battery (not the lighter), whats the best way to hook into the electrical system?

I'd prefer not to have to splice some wires, I'd like to do it properly. Is their some board that I can just plug into?

Run a wire to the battery through the front of the car...

gleesonger

I was hoping that there would be a socket or something, is this not usually available?
I was poking around and noticed that underneath the driver side beside the fuse box, there was a box which as far as I can tell controls the lights (Plugged them all out and everything bar lights\indicators worked) coming off the input wires was another wire which ends with a unused socket, circled in red below. I was hoping I could just pug into this, do you know if this is possible? I need 5v\1Amp to power the device.
Thanks.

Midnight_EG

I suppose you could wire a cable into the fusebox and run it from a spare fuse from there rather than going directly into the battery!

dougie-lampkin

gleesonger wrote: »

I need 5v\1Amp to power the device.

Your car runs on 12V though. At just 1amp current requirement you could make a simple voltage regulator if you can solder, to bring the 12V down to 5V. But you can't plug the device straight in as is.

At 5V with a small current requirement I assume it's a USB charger for a satnav or phone or something? You can get adaptors like this that let you plug a USB straight in, with the 5V output you want. Or, if I'm wrong and your device isn't USB, the adaptor I linked to is 5V/1A anyway, you could use it and join a USB cable onto your device to plug into it?

Graham_B18C

Midnight_EG wrote: »

I suppose you could wire a cable into the fusebox and run it from a spare fuse from there rather than going directly into the battery!

Well that would be a better option alright, running it straight from the battery would be a very bad idea if there was any sort of fault and it wasn't fused

gleesonger

dougie-lampkin wrote: »

Your car runs on 12V though. At just 1amp current requirement you could make a simple voltage regulator if you can solder, to bring the 12V down to 5V. But you can't plug the device straight in as is.

At 5V with a small current requirement I assume it's a USB charger for a satnav or phone or something?

Yes I'm using the phone as a satnav, so your right either way
I realise I can't plug it straight into the 12v so I'm going to break open a cigarette ligter plug and solder in the connections.

Graham_B18C wrote: »

Well that would be a better option alright, running it straight from the battery would be a very bad idea if there was any sort of fault and it wasn't fused

I pulled up the hopolstory and spliced into the cigarette lighter so it will now be running through the fuse box (which contains a blown fuse!!).

I have a 03 vw polo with a tape stero but I'm putting in the phone so that while charging it can be a satnav and run the phone (hands free)\music through the radio at a minimal cost but still be sightly ie no wires.
My plan is to use a bluetooth to fm transmitor which handles phone and music (a2dp). I will probably place the transmitor behind the dash (powered off the same line that will power the phone) but run its mic out to the top of the door frame. Hopefully in the end all that is visable is 3\4 inches of wire leading up to the phone which will be on the right hand side of the steering wheel, and the small mic.

My only concern at the moment is that I will have two transformors plugged into the battery which is NOT turned off when the engine is.
Do you know what drain this will have on the battery?
If worse comes to worse ill have to build in a little on\off switch as I don't have the ability to have it turn off when the car does.

dougie-lampkin

gleesonger wrote: »

My plan is to use a bluetooth to fm transmitor which handles phone and music (a2dp). I will probably place the transmitor behind the dash (powered off the same line that will power the phone) but run its mic out to the top of the door frame. Hopefully in the end all that is visable is 3\4 inches of wire leading up to the phone which will be on the right hand side of the steering wheel, and the small mic.

Nice tidy idea, you might need to play around with the location of the transmitter though. They can be picky about interference from nearby power wires or even from the alternator. I had a setup like this before, nothing as integrated but the same idea, and found using things like the horn or the rear demister made the transmitter go ape, something to do with surges and back EMF. If you can't get a clean signal off it, you can fit signal cleaneruppers onto the power line going to the transmitter. I used a ferrite bead, it's like a ring you slip over the wire, it's the lump of plastic you find near the end of USB cables and stuff. You can also use two diodes to block reverse voltages and interference.

gleesonger wrote: »

My only concern at the moment is that I will have two transformors plugged into the battery which is NOT turned off when the engine is.
Do you know what drain this will have on the battery?
If worse comes to worse ill have to build in a little on\off switch as I don't have the ability to have it turn off when the car does.

Probably very little drain. I have an inverter running the PS2 in my car, and I worked out it would take about 40 weeks for the inverter to fully run down the battery if nothing was plugged into it, which is one I took from a Golf TDI (the biggest battery I can fit into my car :pac:).

A better solution would be to use a normal automotive relay, triggered off the ACC line to the stereo. On mine I used the remote antenna output on my stereo as a relay trigger, so the inverter only powers on with the stereo. Then your devices will only get power when you turn the key to the first click. Although if you're taking power off the cig lighter, chances are it's probably already switched on the ACC Test with a multimeter or even plug your device in to see if it charges with the key out. If it doesn't, a relay is very easy to add in, and could save you from coming out to a dead battery some morning

gleesonger

I've just spent the morning before work in bed reading up on automotive relays. They do seem pretty simple to implement. I might have a go at it.
Thanks for your advice.

Gary ITR

The safest option for this would be to wire in and extra socket to your existing output socket and hide it behind the dash then have your charger plugged into it there.

It's either that run an ignition live into your charger but you would need to make sure that it's fused and that's not really the safest option so I wouldn't recommend it

langdang

Onkle wrote: »

The safest option for this would be to wire in and extra socket to your existing output socket and hide it behind the dash then have your charger plugged into it there.

It's either that run an ignition live into your charger but you would need to make sure that it's fused and that's not really the safest option so I wouldn't recommend it

This is the sensible way to do it!

How/what are you wiring that you need the car to give you 5V? 5V could be the output of a "car-charger" for phone/satnav etc, but any charger is unlikely to look for 5V input? It will be 12V in, 5V out.

Unless you're cutting off a perfectly good car charger and just trying to use the wire direct into your phone(why?)