I have an accusump on my car that I would like to wire in such a way that it only opens when engine revs are over about 3000 rpm (BEC). This will stop it dumping all that extra oil in the sump when the car is at tick over with low oil pressure and also prevent me ever forgetting to turn it on!

So.... to do that I need some form of switching circuit (preferably adjustable) that will pick up the signal to the rev counter and open the (electric!) accusump at the right time.

Does anyone have any ideas on how that might be done, or know the name of that type of switch or circuit so that I can do some searches?

Thanks.

I am no electric whiz but it sounds like a shift light circuit switching a relay?

Yes, I did think about using a shift light - presumably I would have to just take a feed from the relevent LED output to a relay.

I did wonder whether the tiny current required to light an LED would be enough for a relay?

You could use a transitor to trigger the relay, or if you want it to latch a thyristor both could take the signal from a shift light.

Thyristor sounds best to me as it resets when you shut down the engine so intial start up acumsump does not trigger, first time you hit the required revs' it cuts in and stays in, when you power down the car it closes the valve.

Here's a numpty link.

thyristor

[Edited on 9/2/08 by mark chandler]

Mark,

thanks for the numpty link - certainly appropriate - however, I want a switch that will come in when revs exceed Xrpm and cut out again every time they drop below that number, that way when the revs drop to tick over (or below X) they accusump remains off and holds its oil.

My understanding from your link is that the thyristor will hold the switch on until I cut power to the ignition? If so it's not what I want - but would a regular relay do what I want?

Thanks for your input.

A bright shift light will be driving the led at at least 20mA.

Simplest solution is perhaps to use that to drive a high sensitivity relay (perhaps a reed relay - try farnell.com etc), use that to power the coil of an automotive relay. Make sure you have a reverse biased diode in parallel with the reed relay to prevent it damaging the shift light. One across the automotive relay would also be wise to minimise the risk of welding/burning the contacts on the reed relay.

Think what will happen if a realy burns out or the fuse blows... will it fail safe?

Or better still, buy one with a rev-limiter and use the rev limiter switch to drive your relay/solenoid directly?

jk

[Edited on 9/2/08 by jkarran]

[Edited on 9/2/08 by jkarran]

I suppose if I have a dashlight run from the automotive relay, I'll know when I've got power to the accusump.

I will have to wire in an override switch anyway to be able to dump the oil with the engine off for preoiling or oil changes.

http://www.autospeed.com/cms/A_2810/article.html

seems just the job....

36 Aussy dollars for the kit....

I'm not sure who they get to make up the kits but bloody hell!!! It's over 100 Aus $ for a built and tested kit!!!

Can you get your ECU to do it? Very locost if it is possible.

I have been out of the electronic design world for a bit and time has dulled my memory, but what would be wrong with using an opto isolator to switch the relay?

Thanks for the replies folks - but - having never been in the electronics design world - what is an opto isolator and how can it help me?

Jaycar do the frequency operated switch kit for £11.75, hardly worth designing your own for that money.


[Edited on 10/2/08 by MikeRJ]