Fake UPS Tank Circut

**MP3DUB** · 09-04-2006, 05:22 PM

Here's what im trying to do:
I've got a fake ups circut feeding voltage to pin 8 of the com to work as a ups (old news). I want to hook this up to the remote on lead of my head unit. The only problem is that while the pc survives cranking, the car cuts power to the head unit while the car cranks, so I want a "tank" circut to keep voltage to pin 8 of com1 for ~5 seconds so the pc wont standby when the head unit looses power.

Being a civil engineer and not an electrical, I figured I'd just add a small cap and diode inline with pin 8 of com1, such that the diode would prevent the current from flowing back into the head unit, and the small cap would power the com port breifly. But that's what I thought. I metered out the current draw on the com (2.6 miliamp@ 12v), and hooked up what I thought should work and get nothing. I get a 12v voltage drop (and no current) across the cap, so what am I doing wrong (and yes, the diode is installed in the right direction, I've even pulled the diode for testing). What am I failing to realize with my very limited knowledge of electronics?

**2k1Toaster** · 09-04-2006, 06:16 PM

Electrolytic capacitor?

**MP3DUB** · 09-04-2006, 08:04 PM

Originally Posted by 2k1Toaster

Electrolytic capacitor?

Yup, got a electrolytic and a polyester film cap to try too, both with the same result.

**2k1Toaster** · 09-04-2006, 09:02 PM

Well you said you double checked the polarity of the diode, but you didn't mention the capacitor. Since you have an electrolytic, did you verify the polarity?

Oh, and you say "12v voltage drop". Do you mean that with that circuit in there, you get no voltage (12-12 = 0) on the other side, or that it is sinking no voltage (+12 -0 = +12)?

**MatrixPC** · 09-05-2006, 09:35 AM

Did you change the setting in Window's power property?
Instead of shutdown/hibernate instantly after loosing power, set it shutdown/hibernate after xxx seconds/minutes. I am sure there are option for that if you use the fake COM port UPS thingy with generic UPS.

There are talk about using fake (Generic UPS). This is one of them

**MP3DUB** · 09-05-2006, 05:34 PM

Originally Posted by 2k1Toaster

Well you said you double checked the polarity of the diode, but you didn't mention the capacitor. Since you have an electrolytic, did you verify the polarity?

Oh, and you say "12v voltage drop". Do you mean that with that circuit in there, you get no voltage (12-12 = 0) on the other side, or that it is sinking no voltage (+12 -0 = +12)?

The electrolytic cap is non-polarized (is this a problem?), and even so I tried it in both orientations. And when I said 12v, i get 12v across the cap, so +12-0=+12, which in my understanding means no voltage across the cap.

Originally Posted by MatrixPC

Did you change the setting in Window's power property?
Instead of shutdown/hibernate instantly after loosing power, set it shutdown/hibernate after xxx seconds/minutes. I am sure there are option for that if you use the fake COM port UPS thingy with generic UPS.

There are talk about using fake (Generic UPS). This is one of them

Even with a time set, as soon as the voltage on pin 8 drops out, the pc hibernates, which is why I was hoping for a solution outside of windows.

**Nomader** · 09-05-2006, 06:37 PM

why don't you power your head unit with the "+12volt always " .. hook that up to the "acc on" as well.. your HU will never turn off (only manually)

**MatrixPC** · 09-06-2006, 01:36 AM

This is your other option.
You need 2 diodes and a small fuse 1-3 amp will be fine.
Locate a wire that is on by ACC (your current wire is fine.)
Locate a wire that is on by IGN.
Then combine the 2 with inline diodes and a fuse. The output is to replace your current ACC to your fake circuit.
The whole point is combine ACC and IGN signal so that the output always has power during cranking.
Read this post for more info

**Nomader** · 09-06-2006, 07:23 AM

Originally Posted by MatrixPC

This is your other option.
You need 2 diodes and a small fuse 1-3 amp will be fine.
Locate a wire that is on by ACC (your current wire is fine.)
Locate a wire that is on by IGN.
Then combine the 2 with inline diodes and a fuse. The output is to replace your current ACC to your fake circuit.
The whole point is combine ACC and IGN signal so that the output always has power during cranking.
Read this post for more info

why would he need to combine them? that way it will never cut off so the fake ups can be engaged

**2k1Toaster** · 09-06-2006, 08:47 AM

What about a simple inductor.

Like found in laptop power bricks. You unplug it from the wall, and you have like 5-7 seconds before the power indicator goes off. They'll be dangerous though to just have open...