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Need help with a 12 V DC circuit.

Need help with a 12 V DC circuit.

Need help with a 12 V DC circuit.

I need a 12 V DC circuit. Here is what I am doing. This is going to be used on a vehicle that we will run
at the Bonneville salt flats in Utah this August.

I am utilizing a automatic shifter to change gears as it goes down the track. When this auto shift as it is called
gets a pre determined RPM reading it sends a momentary 12 V ground to a solenoid on the transmission and it shifts.

My concern is many times when the shift takes place traction can be broken allowing the tire to spin witch allows the RPM
to go up, in turn sending another signal to the auto shift to shift into the next gear. I need to allow my driver a few seconds to
regain traction with the throttle when this happens while staying in the proper gear.

So, what I need to put together is a circuit with a timer or 2? When the momentary 12 volt ground signal is sent I need to
wait lets say 1/2 to 1 second to make sure the shift has taken place. Then I want to open a normally closed relay that will be
wired into the 12 volt ground signal wire. I need that signal wire to be open for lets say up to 15 seconds ( adjustable time ).
After the 15 seconds has passed the relay closes and the circuit resets and is ready for the next signal to shift into the next gear.

I appreciate the help. JC Sparks

RE: Need help with a 12 V DC circuit.

If you've got _that_ much time to screw around, just have the driver watch the tach and press the buttons.

Mike Halloran
Pembroke Pines, FL, USA

RE: Need help with a 12 V DC circuit.

At over 200 MPH he has his hands full.

RE: Need help with a 12 V DC circuit.

You need a 12V relay that activates instantly then after activating waits a settable time and deactivates.
That's a relay called an OFF-DELAY RELAY or timer with separate input signal.

The relay is powered always.
When a signal is received it immediately activates it's output.
The output stays active for the set time then goes off and waits for the next signal.

Normally the signal is an edge signal and in most cases a falling edge (in this case falling from 12V to 0V). The falling part is what activates the output and starts the timing. Most OFF-DELAY relays will extend the timing or re-start the timing if the input signal is repeated before the originally triggered time runs out.

This relay's time would be the output signal that opens your normally closed relay blinding your shift circuit from seeing the high rev.

Alternatively if the OFF-DELAY relay has Normally Closed Normally Open contacts you would just use the OFF-DELAY relay as the normally closed part of your logic. (no extra relay needed)

Here's an example of a Multi mode timer that can run on 12VDC and has a SPDT relay out allowing it to be the normally closed relay in your scheme.

Koyo Timer

Look at the OFF-Delay graph. You will note that it will extend if retriggered. You should also note that the falling edge is where it all starts.


There are a bazillion time delay relays out there, this is just an example.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Need help with a 12 V DC circuit.

Keith Cress, I think this is what you are talking about?

SINGLE SHOT FALLING EDGE Upon application of input voltage, the time delay relay is ready to accept a trigger. When the trigger is applied, the output remains de-energized. Upon removal of the trigger, the output is energized and the time delay (t) begins. At the end of the time delay (t), the output is de-energized unless the trigger is removed and re-applied prior to time out (before time delay (t) elapses).

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