Thread: Creative use of relays - will this work?

Well you'd need to hold down the button on the dash for several seconds for the PSU to fully power up, and you'd need to use diodes to seperate the car mains from the +12V rail on the PSU (on both + and - since the PSU ground is seperate from the car ground)

But yes, I'm no electronics expert but that sounds like it would work for your situation.

Basically you use the power door lock relay to trigger a ATX power switch pulse in the hopes of turning the computer/PSU off.

You use the +12V from your PSU to keep the relay closed for the power to the inverter, and you have a pushbutton in the front that will momentarily give that relay for the inverter +12V from the car to close it until the PSU can power on, at which point the PSU maintains the relay closed.

I think if you use 4 diodes to isolate the car and PSU power from the inverter relay you should be OK. The only problem that I can see is the computer might not always power itself off when the power door locks press the power button, there are many cases in which it might put up a user prompt or something preventing shutdown. In this case you'll drain your second battery, but as long as it is seperate from your main battery then I guess it's not that big a deal.

You could also load a program on your computer to force a shutdown once the power button is pressed, so no matter what prompts come up it will always shutdown. This should limit the cases when it might drain your battery.

Eh...using the PSU for the inverter relay means that no current from the PSU is in contact with the car's power system, it's basically like turning the power on to an electromagnet, as far as I know. Which means that I don't need diodes (and I stay away from anything that's more difficult to pronnounce than "relay"...). And except for during a short test period with Blutetooth control of the media PC (I now use WLAN) I have never seen any user prompts, so that does not worry me. But thanks, it seems I'm not totally off my rocks with these thoughts. Gonna be fun to test it out in real life!

How do you expect to have the PSU isolated from the car mains if the relay can be powered by both the PSU and your pushbutton switch which connects the relay to car power? While the pushbutton is depressed you have essentially connected car ground to PSU output ground and car +12V to PSU +12V output which = BAD. Otherwise you'd have to have your pushbutton disconnect the PSU leads and connect the car leads when you push it, and when you release it return the connection to the PSU leads. I think that you're gonna need to use a few diodes. But not to worry, they are simpler to use than a relay so it's really not that big a deal

I repeat: If you are going to have both car and PSU power to power the relay, then they will be crossed as long as your pushbutton is depressed which will likely cause damage to your computer unless you use relays.

Sorry, Telek, I was thinking something and writing something else. I meant to say that I use two relays that controls two parallell power cables to the inverter, so the PSU runs another relay, only it's the same current that's let through the switch in the relay.

Oh OK, yeah I guess that would work, but it would have been much easier to do just using diodes (and cheaper).

But whatever works!

Perhaps easier, as long as I had you holding my hand through it, but cheaper? Let me give you a hint: A relay costs around two bucks at the local service station. Any other electronic material out here in the sticks will cost me about 12 bucks...in shipping and handling alone! So I think I'll just do a dual relay.

You have no electronics stores at all in your area? These diodes are like $0.10 each

But I guess if the relays are only $2 then it's no problem to just use two

The closest one that I know of is a couple of hours drive. But maybe a radio repair shop has these things? What should I ask for in that case?

And thanks for your help!

Edit: I called my brother who works for a computer company, and it turned out that he had tons of those things laying around, so he'll send me some tomorrow! It's going to be interesting to try to widen my horizont a bit...

My brother didn't get his *** off the ground, so I got the relays and did it that way. It works better than I dared to hope! I only have to press the button on the dash for half a second, and the PC is running! And I have done around 20-30 startups/manual shutdowns so far without a single error. Next step will be hooking it up to the power doors.