Looking for small relay part

Actually not arduino related but i bet this is a good place to ask …

I’m looking for a small 12V DC powered relay that takes a small voltage ±1 volt to trigger on and make one simple wire connection with adjustable return delay.

I want to try if i can make an rpm limiter by using the red led (max rpm warning) on a digital tachometer to kill the spark (ground the spark coil) in order to make over-revving the engine impossible.

Possible with a adjustable delay so it takes some time for one to rev the engine back up again.

Project is a gokart with a briggs engine.

Use a BJT to switch the relay perhaps? You'll only be able to get a few mA from an LED circuit due to the series
current limiting resistor - perhaps there's a better place in the tacho circuit to connect to?

You'll need to protect the relay from inductive arcing or it might weld shut, defeating the protection.

Good think i asked. its been 18 years since my last class in electronics.

I want to try if i can make an rpm limiter by using the red led (max rpm warning) on a digital tachometer to kill the spark (ground the spark coil) in order to make over-revving the engine impossible.

My gurss is you want to use the voltage drop across the red LED to make things happen. The red LED likely has a series resistor and if you place another load like a small relay coil in parallel with it things may not work. If you can see the red LED series resistor you may want to note its value. Then maybe think about using an opto coupler circuit with a transistor to drive a relay with a 12 volt coil. Just something to think about.

Ron

Will sleep about it tonight, and quite possibly have a nightmare.

Simplest explanation about what needs to happen.

Red LED on = connect spark coil to ground.

This may be stupid but what if i use a "12v light sensitive relay module" and tape the sensor on the led.

I honestly don't care how it looks i'll put it all in a tiny project box.

"This may be stupid but what if i use a "12v light sensitive relay module" and tape the sensor on the led.

I honestly don't care how it looks i'll put it all in a tiny project box".

Crude but works. I have done similar but in this case you are just duplicating what an opto-coupler would do. Hardly nightmare material. :slight_smile:

Ron

Be aware that if you just cut the ignition , but the fuel still runs , it’s likely to back fire a lot .

I was going to mention that! Quite a lot when you thoroughly fill the muffler with mixture and the ignition cuts back in.

Can you limit the travel of the gas pedal?

i know it can go pop-pop ban bang...and no throttle pedal yet i have to build it :smiley: i'll check back in a few weeks when i have all the parts.

I played around with the killswitch on my old lawnmower at full throttle and it never backfired or anything special. sometimes a little puff of smoke.