12v ignition source plx devices

[Robzki]

Hi

 

I've got a question regarding aftermarket gauges, hu's modules etc, basically anything that requires a 12v ignition source to supply power.

 

I'm in the middle of fitting 5 Oled screens that get their power from 5x separate display modules. then there are 8 sensor modules(poss 2 more) that each require a supply, then there is a bc and a turbotimer, these 2 are already fitted.

 

So I need a 12v ignition supply for 15 additional things, I can find out the power consumption of these if there is anyone clever enough to work out what cable I need and fuse in the inline holder.

 

Can I just pick up a supply from under the steering column? Is the cable under there overengineered enough to cope with more drain.

 

I was planning on putting 2 fused links as close to the source as possible and having the display modules on 1 and the sensor modules on the other, is this ok?

 

Do I just earth the units as close as possible or do I try and earth as near to the ecu as I can? the only reason I ask is that the sensor modules have 0-5v analogue out for later use. Hopefully someone clever will know whether this is relevant.

 

Thanks for your help

 

Rob

[Scott]

Hi

 

I've got a question regarding aftermarket gauges, hu's modules etc, basically anything that requires a 12v ignition source to supply power.

 

I'm in the middle of fitting 5 Oled screens that get their power from 5x separate display modules. then there are 8 sensor modules(poss 2 more) that each require a supply, then there is a bc and a turbotimer, these 2 are already fitted.

 

So I need a 12v ignition supply for 15 additional things, I can find out the power consumption of these if there is anyone clever enough to work out what cable I need and fuse in the inline holder.

 

Can I just pick up a supply from under the steering column? Is the cable under there overengineered enough to cope with more drain.

 

I was planning on putting 2 fused links as close to the source as possible and having the display modules on 1 and the sensor modules on the other, is this ok?

 

Do I just earth the units as close as possible or do I try and earth as near to the ecu as I can? the only reason I ask is that the sensor modules have 0-5v analogue out for later use. Hopefully someone clever will know whether this is relevant.

 

Thanks for your help

 

Rob

 

Very easy to do, so easy in fact that you can work it out yourself.

 

All you need to do is total up the amount of power, maximum, you will be using per line.

 

Say you wanted all the monitors on the one line and they used up 20w each, that would be 160w total on the fused line. You know that the voltage is 12v so you do the simple calculation as follows..

 

P = VI (P=Power, V=Voltage, I=Current)

 

I = P/V

 

I = 160/12

 

I = 13.3333

 

In that instance I would simply use a 15A inline fuse. 20A cable would be plenty for that setup.

 

If you need anything else just ask

[Robzki]

Scott you're a star, I will dig around and find out the power usage later and post back my workings.

 

Any opinion on whether the ignition cable under the column is up to it?

 

Appreciate the comprehensive answer

 

Rob

[Robzki]

Also, in theory if it needed a 20a fuse then use a 30a cable? or a 5a fuse = 10a cable?

Edited May 4, 2011 by Robzki (see edit history)

[Scott]

Also, in theory if it needed a 20a fuse then use a 30a cable. or a 5a fuse = 10a cable?

 

I personally wouldn't go off of the ignition, it would be asking a LOT.

 

I would work out the total consumption and buy the appropriate cable for that total, plus a little headroom. I would then get a relay capable of handling the current required and a distribution box. I would fuse the main cable for the total current required, and seperate the items into 4 groups (monitors, modules etc). I would then work out the total for all the monitors, get the appropriate cable and fuse for that total. Do this for each of the 4 groups.

 

The main cable would be fused and connected to the relay. The relay would be activated by the ignition. This connection would then feed into the distribution block. From there you would have 4 seperate cables all suitable for the current you require and all seperately fused appropriately. You would then hardwire all the positive cables together for the appropriate group and connect them to the cable using either a terminal or by soldering/heatshrinking (I would go with option 2) and do this for each group of cables.

 

That would sort out the positive side of everything.

 

You would still need to group all of the ignition cables together as well as all the earths together. Finding one good solid earth and just connecting them individually, if within range, would be the easiest solition. If not then you would need something along the lines of what you did with the positive.

 

 

As for the cable I would just work out what you need, and add a little headroom.

[Robzki]

Wow, Now that is the answer I needed, I knew I had to do it properly, it would have all been soldered and shrinkwrapped etc but the supply was causing me concern. In the back of my mind I had thoughts of a relay but was trying to ignore them mainly because I don't know how they work.

 

I guess you have a main in +12 from battery then an out +12v to the device you want to power. these wont power up until a trigger wire gives the relay +12v?

 

If I understand you correctly. And just working with what I have available would this be the sort of thing you would do:

 

I have some nice shiny colourcoded 'big' cable from an amp kit with an inline mahoosive fuse. I would route this from the battery to behind the dash with the fuse as close to the battery as possible, this would supply power to a relay.

Then I would use a 30a cable from the ignition under the steering column to the 'trigger' of the relay.

Then run the 'triggered' +12v supplied from the relay to an aftermarket fusebox. I would then use these separate fuses to supply the groups of devices.

If I got a 6 fused holder then I could add other bits later without interfering with the existing stuff or just rewire the bc and turbo timer to these if I wanted

 

Is this a good start?

 

Would a relay kit (ring) for spotlights give me the required parts, would the relay be up to the job?

 

I know thats a lot of questions but you have helped me out so much. I just needed a grown up to point me in the right direction

 

Thanks and sorry for being a pain

 

Rob

Edited May 4, 2011 by Robzki (see edit history)

[Swampy442]

BOOM! Good answer

 

Very easy to do, so easy in fact that you can work it out yourself.

 

All you need to do is total up the amount of power, maximum, you will be using per line.

 

Say you wanted all the monitors on the one line and they used up 20w each, that would be 160w total on the fused line. You know that the voltage is 12v so you do the simple calculation as follows..

 

P = VI (P=Power, V=Voltage, I=Current)

 

I = P/V

 

I = 160/12

 

I = 13.3333

 

In that instance I would simply use a 15A inline fuse. 20A cable would be plenty for that setup.

 

If you need anything else just ask

[Robzki]

Lol, yep, best answer to any question I've asked on here

[Scott]

I'm just finishing off in work so I'll get back to you when I get home.

 

Your thinking is correct but you don't need 30A to switch the relay, it uses very little current to switch so a thin gauge remote type wire is plenty. Don't want too many fat wires behind there

[Robzki]

Aaah cool thanks, no rush, your advice is very much appreciated. I'll pick out some bits and pieces to buy and post pics here b4 I commit to buy them

 

Rob

[Scott]

Right...

 

I've done a wee picture of what you are looking to do. Obviously you can choose whichever colours you wish. For the thin wire (the relay trigger wire) 18 gauge will be fine. The main fused cable will be down to yourself. I would hazzard a guess that if you have some thick stuff from an amp install it would be overkill, depending on the quality, but definitely fine to use so that end should be sorted. The wire you use after that, and the fuses you use for the entire thing, will depend on how much power it all uses.

 

If memory serves you will be connecting the ignition plus to 85 on the relay and then earthing 86 (this is the coil that makes the contact). You would then have the input from the battery connected to 87 and the output to the distribution block connected to 30.

 

The rest should be easy as pie

 

[Robzki]

Now I have your pic in my head it all seems simples Today I have learnt 'how to do it properly' and saved myself loads of worry in the future as to whether I can smell burning or not

 

I have also learnt how relays work, before I could put them in(spots etc) but never really made sense. Earlier I was looking at relays(30a fused) and couldn't work out why they had 4 pins and also how the ignition triggered it because all that was going in were 2 x 12v supplies, Now you say there is an earth there it has answered both of them.

 

Been on a hunt since and now understand 5 pin 6 pin and latching relays

 

Off to find a decent auto electrical supplier and hopefully get the braid I'm after too, then its on a mission to see how I can fit 15 of these modules behind the dash :/

 

Thanks again, you have been a wealth of information, and appreciate your time taken to educate a numpty, I will be back asking opinions I'm sure but for now you have me on the right track.

 

Rob

[scotty71]

sounds like you need the flux capacitor