Plantoil/diesel conversion basics
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Posts: 934
Reply with quote  #1 

The following circuit is a simple timer circuit for operating a 12V relay. With the parts specified it will have an on time duration of 0 to about 60 seconds. Using a different capacitor for C1 will change the maximum on time. The timer can be triggered by a simple switch across the trigger points ...such as the switch used to change back to diesel from VO fuel. The SPDT relay can activate a light, a buzzer, or both.  The design is highly adaptable and so can be used for other purposes as well...such as automating your purge cycle or allowing your vehicle to run for several minutes while it purges at idle...and then shut itself off.
Here are the parts needed.

Part NameQuantity
100K Variable Resistor1
1K Resistor (1/4W)2
1N914 Diode2
220 Resistor (1/4W)1
3 pin Terminal Block1
470µF Electrolytic Capacitor1
LED (Green)1
NE555 Bipolar Timer1
SPDT Relay (12V)1



Posts: 934
Reply with quote  #2 
A mostly pre-assembled option...

And a list of places in the US to purchase it.

• 12 to 24 Volt DC Operation
• Adjustable Time Delay
• SPDT (Form "C") Relay
• Low Current Input Trigger (<1mA)
• Selectable Positive or Negative trigger
• Selectable Initial Relay State: ON / OFF
• Operating Modes: One-Shot or Repeat
• LED Indication of Relay State
• Lifetime Limited Warranty

• Operating Voltage:
• Current Draw:
• Time Settings:
• Relay Contacts:
• Size:
• Trigger Voltage
12 to 24 Volts DC.
40 mA DC with relay on.
1 to 60 Seconds or 1 to 60 Minutes.
Form "C", 7A @ 30VDC, 10 A @ 125VAC.
3" x 2.2" x 1" (Fits Standard. Snap Track).
4.5 - 24VDC.


Posts: 10
Reply with quote  #3 
I would like to buy two of these 12v delay timers, but I have no idea how to wire them. I want to automate my purge cycle and have my vehicle automatically shut down.

Will I need two of these ELK-960 delay timers to do this?
How do I wire them up?

I use Pollak valves and they are activated with an OEM GMC tank switch. The switch has a spring so it only activates when it's fully depressed and then it springs back to the open position. The switch lets me switch beween my VO system and diesel system. It's the only switch for my whole system. It controls 3 Pollack valves. The 3rd valve is for purging and directs the return fuel to the proper tank. This is the valve that needs to be time delayed. 

Here's what I want to achieve:
  • I want to press the switch (from VO to Diesel) and have the Pollak valve activate 5 minutes later. This will let the VO and VO/diesel mixture return to the VO tank and when the 5 minutes is up the valve will activate letting the pure diesel return to the diesel tank. The purge is complete when the 5 minutes is up.
  • IF the purge is in progress the engine will continue running even after I turn off the ignition. This means no more sitting in my vehicle for 5 minutes while it purges. Perhaps the engine can be on it's own timer or connected logically to the first timer, so that it only shuts off after the valve activates.
  • IF the purge is not in progress then the engine will shut off immediately when I turn off the ignition. (This means I was driving on diesel and would simply want to shut off the engine with no delay, since no purge is required.)
  • IF the purge is in progress and I turn off the ignition, then I change my mind, re-insert the key and continue driving, the engine must not automatically shut off. This would be dangerous.
  • When I switch from diesel to VO the delay should be zero, so that the return fuel immediately goes to the VO tank. 
  • If I need to abort a purge I should be able to do this by pressing the button from diesel to VO. Doing this should stop the timer and keep the valve in the same position (returning fuel to the VO tank).
Hopefully I have covered every senario that I might run into.

Any help would be appreciated. Electronics confuse the heck out of me... 


Posts: 934
Reply with quote  #4 
Any help would be appreciated. Electronics confuse the heck out of me... 

There are some general "rules" on the wring configuration you would nee to accomplish what you want with these timer modules. The problem is that you have to first figure out which wire must be powered (after you turn off the key) to allow the engine to be kept running by the timer module. 

Can you identify that wire?

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