What will this circuit do?

Injector · 11-15-2007, 04:29 PM

a friend of mine made this circuit for me, it's supposed to keep the relay closed for 40 seconds after acc has been shutdown,
and it works great, until i put a current through 87 and 30 on the relay, then it immidiatly shuts down after acc is gone, for
some reason when power flows through 87 and 30 it drains the capacitors as well.
can anyone help me out here?

psyrex · 11-15-2007, 04:37 PM

What's the component on the top left?

Injector · 11-15-2007, 04:43 PM

oo forgot to label that one, it's a transistor

psyrex · 11-15-2007, 05:33 PM

Can you list the terminals on the relay (85, 86, etc) and what you have them connected to?

Injector · 11-15-2007, 07:56 PM

86 and 85 are the coil which get + and -, 87 gets a constant positive from a fused +, 30 goes to + on my power inverter
i'm using an audio system 2 farad capacitor, but this cap is only to the system will survive cracking.

Injector · 11-16-2007, 06:47 PM

well i found the problem, when acc is turned off, the line goes from positive to negative, which causes the caps to immidiatly loose the power in them, any way to combat this?

Curiosity · 11-16-2007, 08:06 PM

Add a small diode in series with that resistor going to ACC.

Injector · 11-17-2007, 10:45 AM

will the resistor keep ground from flowing to the caps?
i have some of this at home will they work?
http://www.radioshack.com/product/in...entPage=search

Curiosity · 11-17-2007, 11:01 AM

That will work fine. Put it before or after the resistor. You're not really getting ground. When you disconnect the source, the other circuits in your car that are on accessory are putting a heavy load on the cap, so it instantly drains. The diode prevents the current from reversing.

Actually, I don't think you need the resistor.

Injector · 11-17-2007, 11:08 AM

sweet, thnx for the help, just before posting here i decided to go check the 12volt for diode info and i found this

so should i place a diode on the constant positive going to the transistor as well? the part that confuses me is that i used a voltage probe which tells me if positive or negative current is flowing through the wire and as soon as i shutoff the key the probe says the current goes from positive to negative