Stay alive while cranking

**MerlinDaHapyPig** · 03-22-2004, 06:06 AM

There is a lot of discussion over "tank" circuits and other ways to keep your car-pc alive while cranking

When testing my computer system i hooked the invertor directly to the battery, without using a relay or anything, i noticed the computer stayed alive whilst cranking

The current setup has a relay, controlled by the ACC+ line to trigger it. As the car cuts out the ACC while cranking, the invertor shuts off, killing the computer power.

As the invertor survived the "crank" when i tested it, the cutout isn't because of the voltage draw of the starter.

Logically couldn't i put a smallish capacitor on the ACC+ line (used as the relay trigger) to keep voltage supplied to the relay whilst cranking? Would this work? would there be any possible harm to anything if it tested this?

**P4_2.66GHz** · 03-22-2004, 10:56 AM

You'll need to isolate capacitor used and the relay by a diode. Otherwise, the capacitor will get discharged by the rest of the electrical system.
Capacitor, however, will need to have big capacity to hold the relay for long. I'd say try 4,700 uf.

You're not likely to hurt anything, if wired correctly.

**sfay93** · 03-22-2004, 11:11 AM

Or, you could just hook it directly to one of the ignition wires. They maintain 12V through the crank.

**MatrixPC** · 03-22-2004, 11:12 AM

Check these topics
How to keep your invertor alive while cranking.
and
Need to find acc wire that stays alive during crank.

**MerlinDaHapyPig** · 03-22-2004, 08:14 PM

yeah, i've already looked at that thread, but it's alot less hassel if i can use a cap, as i won't have to run another wire to the back of the car, and wont have to unscrew half the dash to get to the wire.