Power Supply/OPUS Kill Switch

**SpaceMonkey** · 08-10-2006, 10:10 AM

After searching for a few days i cant find a solution for this idea. Sorry for the wordy'ness...

I'm creating a switch panel in the dash containing 4 switches: Motherboard Power Switch, Motherboard Reset switch, Ignition/ACC Line switch and an 'emergency' Kill Switch for my OPUS.

The first 3 are easy, but the kill switch is surprisingly tricky.

I want the kill switch to control the +12V line between the battery and the OPUS. I know there's other ways of killing the power, but to me, this is how a true kill switch should work.

Idea One:
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The switch is 12V rated at 15 amps, so at first i thought it'd be ok just to connect it inline on this +12V wire. Then i realised my battery is in my boot, so i'd have to run the +12V wire all the way to the switch in the dash and back into the boot to the OPUS.

I'd rather not do this, mainly cos its just clunky and a potential fire hazard if the carpc goes mental and draws huge current. I know a fuse would save this, but, still, it just seems wrong.

Idea Two:
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Then i thought about just putting a Normally Open relay inline on the +12V wire between the battery & OPUS and having the switch control that. When the switch is on, relay coil charged & closed, OPUS gets its power. Switch off, relay opens, OPUS off.

Problem with this is that under normal conditions i would mostly leave the switch on so that the OPUS gets its power to turn the pc on/off in sync with the cars ignition.This means the relay coil would be charged & closed 24/7. I'm guessing this is bad as I doubt the relay would last too long being on all the time. Also, if the relay momentarily loses power and opens whilst the carpc is on, the OPUS will lose power & the carpc will reboot.

Idea Three:
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Then i thought, why not use a normally closed relay instead. But this means it would have to be charged to open it and turn off the OPUS. This seems like a bad idea for a kill switch. If i wanted to kill the power, the switch would then send power to the relay, causing it to open, and turning off the OPUS. If for some reason the relay loses that power (or even its coil just dies), it will close again and send power to the OPUS again. This seems to be the worst idea of the three.

Idea Four:
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Scrap the idea of having the kill switch mounted in the dash and just put it inline between the battery & OPUS, in the boot. This removes the need to run the power cables up & down the car, but obviously i wont have the conveniance of having the switch in the dash. Only dodgy thing is if the 12v 15Amp switch cant handle the load.

So, what should i do? How do normal, power kill switches work? Any other suggestions?

**evandude** · 08-10-2006, 10:39 AM

How often do you forsee yourself needing an emergency kill switch? If you are safe with your wiring and use trustworthy hardware you should never need one, and I don't think I've heard of anyone on here who's had anything go up in smoke in such a rapid and catastrophic way that they didn't have time to get out and go unplug it...

if you are really so intent on having it be a real, useful, failsafe kill switch, then 1 or 3 are your only feasible options. 4 isn't that great because you'd have to stop the car, open the trunk, get out, run back, and hit the switch. In only a few more seconds you could just unplug the opus instead, making the kill switch not too much of a benefit.

1 is a bad option however because of all the additional loss and potential noise you'd end up with on the +12v lead.

3 is at least somewhat reasonable. You could get creative with some additional circuitry and add a relay in series with the switch that would prevent the kill relay coil from being energized when the car was completely off, so it wouldn't be draining power (or wearing itself out) except when you were using the car. That would also result in the opus being completely disconnected when you weren't in the car, which you may consider good (a little less static current draw on the battery) or bad (well, no +5vsb, so no standby at the very least)

Alternatively, is there any place you could mount it, like above or beside the rear seats, in such a way that you wouldn't have to run very long power cables between the battery, switch, and opus? If you can mount it somewhere that you can reach by turning around and reaching back from the drivers' seat, then at least it would still be a relatively fast way to turn it off, without having to deal with relays or anything, without having to run really long wires, and without having to get out of the car.

**v8 scimitar** · 08-10-2006, 12:16 PM

why not do this option opus 150 stupid??? completely automatic and contained either in your case if you have room or right next to it.

**ming** · 08-10-2006, 01:47 PM

using a switch directly shouldn't be a problem at all for a computer PSU.

**Wiredwrx** · 08-10-2006, 03:10 PM

Is there a reason you can't use NC closed relay, and then have the kill switch energize the relay to OPEN the connection only when you need to kill the unit.

Michael

**SpaceMonkey** · 08-11-2006, 01:31 AM

Thanks for your help lads.

Answers for Evandude:
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I'm planning on using the kill switch when either my pc freezes/goes nuts, or i'm planning on not driving for a week or longer and want to be absolutely 100% sure my battery wont be drained by the carpc.

And yeah, i dont fully trust my wiring skills, so that added layer of protection would be nice. I know its kinda overkill, but... well, it seems kinda cool having a kill switch for it anyway... in a geeky sort of way

I suppose i could mount the switch somewhere else in the car, but i'd much rather stick it on the dash, so its visible and obvious for anyone. Knowing me, i'd need to use it one day and forget where i stuck it

Answer for WiredWRX:
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I'm guessing you mean use a momentary kill switch, to just briefly energise the NC relay, opening it and breaking the bat-to-opus connection. Your right, this would work, but this would only temporarily disconnect the bat-to-opus connection. I'm after a permanent disconnection using some kind of toggle or rocker switch. Using one of these switches with a NC relay is the same of my idea 3.

Ok, after taking a day off work to think about this

, this is what i came up with. Its a combo of the diagram V8Scimitar proposed and my idea 2:

Name: Kill Switch Diagram.jpg
Views: 6320
Size: 21.0 KB

I haven't tried it yet, but could it work? My thinking is:

Normal Operation Scenario:
Ignition & everything is off, kill switch on/closed.
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Turn ignition on,
ACC goes high,
Relay 1 closes,
Relay 2 closes,
OPUS gets +12V from battery and turns on,
OPUS detects ACC is high and turns on PC,
Relay 1 is now being closed by both ACC and +12V from OPUS.

Turn ignition off,
ACC goes low,
OPUS tells PC to shutdown/hibernate,
Relay 1 remains closed by the +12V from OPUS,
PC eventually shuts down,
Relay 1 Opens,
Relay 2 opens,
OPUS turns off.

Kill Switch Off/Open When CarPC On Scenario:
CarPC is running, ACC is high, OPUS is on, Relay 1 is closed, Relay 2 is closed.
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Turn Kill Switch Off,
Relay 2 opens,
OPUS & therefore CarPC turn off immediately,
Turn ignition off,
ACC goes low,
Relay 1 opens

Kill Switch Off When Everything is Off Scenario:
Kill Switch Off/Open, Ignition off, CarPC Off
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Turn ignition on,
ACC goes high,
Relay 1 closes,
...neither OPUS nor carPC turn on...
Turn ignition off
ACC goes low,
Relay 1 opens

**Wiredwrx** · 08-11-2006, 03:13 AM

Originally Posted by SpaceMonkey

Answer for WiredWRX:
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I'm guessing you mean use a momentary kill switch, to just briefly energise the NC relay, opening it and breaking the bat-to-opus connection. Your right, this would work, but this would only temporarily disconnect the bat-to-opus connection. I'm after a permanent disconnection using some kind of toggle or rocker switch. Using one of these switches with a NC relay is the same of my idea 3.

With an NC, there will always be power to the Opus. No momentary is used. The kill switch would then enrgize the relay, killing the connection.

When you go on vacation, you switch it it on, and it stays energized. The relay will use less then 50-100 milli amps. Your battery won't even notice it. Your cars electronics use more then that. It is very easy, uses just a single relay, a single switch, and a single wire.

Sure, if you want to make it complicated, your diagram might work (I with everyone else will take a look and give you some feedback) but seems overly complicated when there is such a simple solution.

Michael

Michael

**SpaceMonkey** · 08-11-2006, 04:33 AM

Originally Posted by Wiredwrx

With an NC, there will always be power to the Opus. No momentary is used. The kill switch would then enrgize the relay, killing the connection.

When you go on vacation, you switch it it on, and it stays energized. The relay will use less then 50-100 milli amps. Your battery won't even notice it. Your cars electronics use more then that. It is very easy, uses just a single relay, a single switch, and a single wire.

Sure, if you want to make it complicated, your diagram might work (I with everyone else will take a look and give you some feedback) but seems overly complicated when there is such a simple solution.

Michael

Michael

Yeah, your right, its 10x easier & would work.... but for how long...

Being of the Pessimistic kind, I tend to think of the worst case scenario. I may be wrong and possibly insane but, I reckon if you leave the kill switch off for a length period of time, (ie. keeping the NC relays coil energised for a lengthy period of time), the coils strength would diminish, causing its switch to eventually close (or worse, half close and start arcing) and send power to the OPUS again. All this without anyone knowing.

The circuit i've posted does not depend on any of the N/O relays remaining energised in order to cut the power. When the kill switch cuts the power, everything becomes inactive. If either of the relays start to lose their coil strength, the worst scenario is that the OPUS wont get any power and the pc simply wont start.

Also, i just realised, as a bonus, it will automatically break the bat-to-opus connection every time the carpc & ignition turns off regardless of the kill switch. So, essentially, this includes the fix for the USB Standby Power problem as well.

Either way, thanks for ya help

**v8 scimitar** · 08-11-2006, 11:58 AM

your diagram will work although its a bit OTT. If your bothered about crashing then just set the BIOS to restart on error and you would never need the manual switch. I guess the advantage of your way would be you have the option of your PC not booting should you choose.