Installing a switch

**bmw_car_pc** · 03-18-2009, 11:10 AM

i am looking to install a switch on the car pc that will not make it turn on when the car turns on if i dont want it to. Would i put the switch on the 12v constant or the ignition. Im just not sure which the power supply uses to turn on

**skeet2331** · 03-18-2009, 12:08 PM

you need to put it on the ignition line.

**strife** · 03-18-2009, 12:12 PM

You want to switch the ignition "ACC" wire to the power supply.
Brian-

**scatebase** · 03-18-2009, 12:23 PM

This may help:
http://www.mp3car.com/vbulletin/powe...ll-switch.html

**RyanB95** · 03-18-2009, 01:15 PM

I just did this in my car. I added one for the main power coming from the battery in case the computer freezes so I can cut power to it and essentially "restart" it. I also added one to the ignition line so that I can have the computer not turn on if I am, for example, just moving my car from one place to another in a driveway or something like that.

I just bought 2 simple "on/off" rocker switches form autozone and they work like a charm.

**2k1Toaster** · 03-18-2009, 03:46 PM

Originally Posted by RyanB95

I just did this in my car. I added one for the main power coming from the battery in case the computer freezes so I can cut power to it and essentially "restart" it. I also added one to the ignition line so that I can have the computer not turn on if I am, for example, just moving my car from one place to another in a driveway or something like that.

I just bought 2 simple "on/off" rocker switches form autozone and they work like a charm.

Make sure if you do this on the constant line that you are using the switch to trip a relay for the power, not just direct.

If you get a 3 way switch with a centre off, then up/down positions, you can make a "normal", "always on", "always off" switch. So if you dont want it to turn on, flip the switch to the centre. Dont want it to turn off, switch to the "always on" postion. Want normal, switch to other pole. Then normal would be wired to switched +12 and always on would go to constant +12.

**RyanB95** · 03-18-2009, 04:00 PM

Originally Posted by 2k1Toaster

Make sure if you do this on the constant line that you are using the switch to trip a relay for the power, not just direct.

If you get a 3 way switch with a centre off, then up/down positions, you can make a "normal", "always on", "always off" switch. So if you dont want it to turn on, flip the switch to the centre. Dont want it to turn off, switch to the "always on" postion. Want normal, switch to other pole. Then normal would be wired to switched +12 and always on would go to constant +12.

So I should have an in-line relay installed after the switch then? As in in-between the switch and the computer?

**2k1Toaster** · 03-18-2009, 04:05 PM

Originally Posted by RyanB95

So I should have an in-line relay installed after the switch then? As in in-between the switch and the computer?

You NEVER want to run the main current through a user switchable source. NEVER EVER EVER.

So basically you need a small (like even speaker wire) guage cable to your mains switch, then from there to a relay coil.

When the switch it flipped, you are toggling the relay on and off. The relay then toggles the main power source for your PC on and off.

If you route it from battery to switch then to power supply directly, you are sending every amp that your system draws through that dinky little switch. Heating up the contact and making a large fire hazard. Also every time the switch moves back and forth you have the possibility of an arc/discharge between the flip part of the switch and the casing.

Relay: $2
Car: $10k-$50k

**RyanB95** · 03-18-2009, 04:20 PM

Originally Posted by 2k1Toaster

You NEVER want to run the main current through a user switchable source. NEVER EVER EVER.

So basically you need a small (like even speaker wire) guage cable to your mains switch, then from there to a relay coil.

When the switch it flipped, you are toggling the relay on and off. The relay then toggles the main power source for your PC on and off.

If you route it from battery to switch then to power supply directly, you are sending every amp that your system draws through that dinky little switch. Heating up the contact and making a large fire hazard. Also every time the switch moves back and forth you have the possibility of an arc/discharge between the flip part of the switch and the casing.

Relay: $2
Car: $10k-$50k

Thanks! Will install ASAP. I don't look forward to my car going up in flames because of a stupid switch!

**rodweb** · 03-18-2009, 09:17 PM

Here is an ON-OFF-ON switch I fitted to my car on the accessory line that goes to my opus power supply. I mounted this in the glove box out of the way. The centre wire goes back to my Opus Power Supply, Input I comes from Accessory power (head unit harness) and Input II comes directly from the battery.

Centre Position (off) means nothing is working, I says turn power on and off with the key, II says powered on all the time.

I don't see a relay is necessary as the power supply is essentially a relay which is turned on via a low current signal of a few milliamps on the accessory wire which tells it to start drawing power from the battery from the constant 12 volt line. As this switch is on the low current side, there is no need to use another relay but switch Position II needs to be fused. It's like putting a switch on a relay for a pair of driving lights, it goes on the low current side.