Technical > Wiring & Sensors
Fuel pump relay staying on when VEMS powered OFF through P259 output
Mads Lund:
I've made this P259 amplifier http://www.vemssupport.com/forum/index.php?topic=2863.0
And it's working fine on a 3.8B board.
A small note is that I had to insert a 18V zener in front og the FET protection diodes, to ensure the power from the relays didn't run backward and powered the 12V ECU mains. But except from that little "bug" did it solve all my P259 issues.
I have plenty of raw boards, FOC for who ever need one.
Mads
Wolf_Tm:
--- Quote from: Mads Lund on December 25, 2016, 08:39:56 pm ---I've made this P259 amplifier http://www.vemssupport.com/forum/index.php?topic=2863.0
And it's working fine on a 3.8B board.
A small note is that I had to insert a 18V zener in front og the FET protection diodes, to ensure the power from the relays didn't run backward and powered the 12V ECU mains. But except from that little "bug" did it solve all my P259 issues.
I have plenty of raw boards, FOC for who ever need one.
Mads
--- End quote ---
Thanks, very interesting...
Anyway, any other way to fix it?
Would it be ok to connect the Injector Flyback on a switched 12v?
Mads Lund:
I think your magic trick will be to insert a 18V zener diode. They work in a way, that current will flow in one direction, and no current the other way (like a normal diode works) but when the reverse voltage exceed the zener level (eg. 18V) can current flow in both directions.
In your case, where a protection diode potentially make current flow from a relay power back toward the FET, throu a protection diode, and back to a mains somewhere, can a zener allow the spike protection, but stop the reverse current a normal voltages (12-14v).
It's a common issue when the design controls the electornics on both the positive and negative side. Even I thougt that I was carefull when I designed the complete loom for my TVR, did I end up with the nice feature that turning on the long beam, with the key out... made the ECU power up..... a couple of hours and a few diodes later, did it work as expected :-)
Injector flyback, that is powered from the injector +12V should normally not have power without the ECU is on power, Either by using the same relay for both injector + ignition + ecu power, or by powering the injector and ignition with the fuel pump relay
Br Mads
fphil:
What about connecting a resistance to drop this 4V Under the threshold voltage of the relay? Or else you could upper the thereshold with a diode.
Kamuto:
--- Quote from: fphil on December 28, 2016, 04:59:56 pm ---What about connecting a resistance to drop this 4V Under the threshold voltage of the relay? Or else you could upper the thereshold with a diode.
--- End quote ---
why just not make relay supply die when ignition is off? :)
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