Maximeltman

iTrader: (11)

I have a couple electronic devices in my car that lose all their power while cranking-one is a WB, and I've read that finding a power wire that maintains 12v while cranking the engine is ideal since it's a bit easier on the electronics, thus better for the longevity of the WB...
I've been kinda toying with the subject and it seems that in order to do this, you need your ignition wire to maintain at least some voltage during cranking (around 7v), then use a capacitor to keep it stabilized at 12v until the engine starts. My ignition wire drops to completely zero volts. So now what? there should be a cap to sustain 12v but how big? I am unsure of how many amps are on the wire during cranking, it can't be the 125A used to start the engine can it?

njmaxseltd

iTrader: (19)

A cap will not work. Poke around a bit more, I'm sure there are some circuits that maintain 12 volts while cranking.

Maximeltman

iTrader: (11)

yea a cap wont work which sucks.
http://oreilly.com/pub/h/3649
look like I can use a small batt with a diaode, or just buy a complete separate power supply.

asand1

iTrader: (1)

Get your power from a different circuit, don't go fiddling with a circuit that is already running systems. Your "ignition" circuit already stays hot during cranking, or you engine would never start. Your ACC circuit generally drops out while cranking, not sure about Maximas though.

What I would do is tap into your actual ignition circuit (Coils, ECU, Fuel pump, Etc) to run a relay. Run a tap directly from your battery+ to the relay and have the relay run your aftermarket electronics.

DennisMik

iTrader: (2)

There are 2 relays that power most of what is inside your car. The Accessory relay and the Ignition relay. The accessory relay powers the clock , audio, windshield wipers, cigarette lighter and more. It is energized when the ignition switch is in the ACC or ON positions. Obviously your WB (I'm sorry, I don't know what a WB is) is hooked into the Accessory Relay circuitry.

Now the Ignition relay powers a lot of things regarding the car running as the name implies. A few of the things are the fuel injectors, cruise control, windows, turn signals, heated seats. But the Ignition Relay is energized when the ignition switch is in the ON or START positions. So you could tap into the back of the Ignition Relay and the WB would have power during cranking.

The only catch is that the ignition relay is not energized when the ignition switch is in the ACC position. Would this be a problem?

There is no circuit that is hot in the ACC, ON and Start positions. There are circuits that are hot all the time, even when the car is turned off. Power seats, dome light and lots more. Exactly how do you want this to work?