trouble with magnetic switch

Thread Starter

speedrazor

Joined Jan 22, 2020
12
Hi , I am wanting to know what I need to make a magnetic sensor turn a relay on when a shaft is rotating and off when its not. I cant seem to find the right parts to do that. It goes need to be reliable.
 

Alec_t

Joined Sep 17, 2013
10,708
Does it have to be a magnetic sensor, or would an optical one be ok too?
How big is the shaft and what is it made of?
 

MaxHeadRoom

Joined Jul 18, 2013
19,685
What device is the shaft rotating ?
What is rotating the shaft? If a motor, what type/model etc, there are several ways of doing it depending on the present device and conditions.
Max.
 

Reloadron

Joined Jan 15, 2015
4,883
You can build or buy a turn key solution but you will need to provide much more information if you expect good answers with possible solutions. Describe the project in fine detail along with any parameters which must be met.

Ron
 

Thread Starter

speedrazor

Joined Jan 22, 2020
12
Does it have to be a magnetic sensor, or would an optical one be ok too?
How big is the shaft and what is it made of?
The shaft is a car engine crankshaft , when I turn the ignition switch off I want to turn an electric fuel pump off and close a fuel shut off solenoid but when I turn the ignition switch on I don't want the fuel to come back on until the engine starts turning
 

Thread Starter

speedrazor

Joined Jan 22, 2020
12
You can build or buy a turn key solution but you will need to provide much more information if you expect good answers with possible solutions. Describe the project in fine detail along with any parameters which must be met.

Ron
The shaft is a car engine crankshaft , when I turn the ignition switch off I want to turn an electric fuel pump off and close a fuel shut off solenoid but when I turn the ignition switch on I don't want the fuel to come back on until the engine starts turning
 

Reloadron

Joined Jan 15, 2015
4,883
Then you have a few options. Using discrete components a retriggerable one shot multi vibrator is an option. As long as pulses from a sensor are triggering it the output will remain in a stable state. A Google of "Watchdog (Retriggerable One Shot) module" should find you some already to go turn key modules requiring very little to no assembly or building on your part. Another option is the use of a micro-controller which involves a little programming and building the circuit. Unless you are comfortable with the latter I suggest looking for a retriggerable one shot setup for 12 volt operation.

Ron
 

Thread Starter

speedrazor

Joined Jan 22, 2020
12
Then you have a few options. Using discrete components a retriggerable one shot multi vibrator is an option. As long as pulses from a sensor are triggering it the output will remain in a stable state. A Google of "Watchdog (Retriggerable One Shot) module" should find you some already to go turn key modules requiring very little to no assembly or building on your part. Another option is the use of a micro-controller which involves a little programming and building the circuit. Unless you are comfortable with the latter I suggest looking for a retriggerable one shot setup for 12 volt operation.

Ron
Would this have to have a magnetis sensor conncted to it and would this unit work for what you are talking about ? : https://www.zoro.com/macromatic-time-delay-rlay-12-to-240vacdc-15a-dpdt-te-8812u/i/G6135385/
 

dendad

Joined Feb 20, 2016
3,253
A coil and magnet running on a gear can sense the rotation.
There will be AC generated as the shaft rotates, so rectify that and feed it to a comparator to trigger a relay.
 

Reloadron

Joined Jan 15, 2015
4,883
Would this have to have a magnetis sensor conncted to it and would this unit work for what you are talking about ? : https://www.zoro.com/macromatic-time-delay-rlay-12-to-240vacdc-15a-dpdt-te-8812u/i/G6135385/
Using Macromatic since you linked to one here is how things get defined:
WATCHDOG
Retriggerable Single Shot
Upon application of input voltage, the time delay relay is ready to accept a trigger. When the trigger is applied, 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). Continuous cycling of the trigger at a rate faster than the time delay (t) will cause the output to remain energized indefinitely.

The module you linked to is a multi-function version and it does mention the watchdog function. Before popping the bucks I would call Macromatic and ask to speak with an applications engineer.

Do you already have a signal available like an ECM tachometer signal?

Ron
 

shortbus

Joined Sep 30, 2009
7,337
The shaft is a car engine crankshaft , when I turn the ignition switch off I want to turn an electric fuel pump off and close a fuel shut off solenoid but when I turn the ignition switch on I don't want the fuel to come back on until the engine starts turning
I don't think this will work like you think it will. Is this a vehicle your building yourself or retrofitting an engine into? Can I ask what kind of engine is being run a 9000 RPM? That is two cycle chain saw type RPM not a normal vehicle RPM.

The way many car engines work when it comes to electric fuel pumps is they use the oil pressure switch to control the pump and cut off. When first starting the pump must run before the engine even turns over, so that eliminates the crankshaft sensor. If you don't have fuel up to pressure when the engine turns over it will have to crank over longer before starting. This is the common way of an engine first being started; the key is turned on to the run position and the fuel pump runs until a pressure sensor in the fuel system gets to a preset value, then the starter motor turns the engine over, when oil pressure is up to a preset value the fuel pump continues to run, until the engine is shut off and oil pressure drops shutting down the fuel pump.

If you use a crank sensor to manage the fuel pump the vehicle will be hard to start.
 

dendad

Joined Feb 20, 2016
3,253
Use the starter signal to bypass the engine stop fuel cutoff so the pump is powered while the starter motor is running.
And I do like the idea from @Alec_t about using the alternator.
 

Thread Starter

speedrazor

Joined Jan 22, 2020
12
Using Macromatic since you linked to one here is how things get defined:
WATCHDOG
Retriggerable Single Shot
Upon application of input voltage, the time delay relay is ready to accept a trigger. When the trigger is applied, 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). Continuous cycling of the trigger at a rate faster than the time delay (t) will cause the output to remain energized indefinitely.

The module you linked to is a multi-function version and it does mention the watchdog function. Before popping the bucks I would call Macromatic and ask to speak with an applications engineer.

Do you already have a signal available like an ECM tachometer signal?

Ron
Yes , I have a tach signal and I already called macromatic and they said it would work . Will the tach signal work to trigger it ?
 

Thread Starter

speedrazor

Joined Jan 22, 2020
12
I don't think this will work like you think it will. Is this a vehicle your building yourself or retrofitting an engine into? Can I ask what kind of engine is being run a 9000 RPM? That is two cycle chain saw type RPM not a normal vehicle RPM.

The way many car engines work when it comes to electric fuel pumps is they use the oil pressure switch to control the pump and cut off. When first starting the pump must run before the engine even turns over, so that eliminates the crankshaft sensor. If you don't have fuel up to pressure when the engine turns over it will have to crank over longer before starting. This is the common way of an engine first being started; the key is turned on to the run position and the fuel pump runs until a pressure sensor in the fuel system gets to a preset value, then the starter motor turns the engine over, when oil pressure is up to a preset value the fuel pump continues to run, until the engine is shut off and oil pressure drops shutting down the fuel pump.

If you use a crank sensor to manage the fuel pump the vehicle will be hard to start.
Yes , in a normal street vehicle that is the way it works but that's electronic injection. I respectively submit that this system is different and that nascar engines turn over 9000 rpm all the time and so do mine. This car is a prototype
 

Reloadron

Joined Jan 15, 2015
4,883
Yes , I have a tach signal and I already called macromatic and they said it would work . Will the tach signal work to trigger it ?
I don't know what your tach signal actually is? I have seen all sorts of sine, square and other wave shapes used and sent to the ECM in a few amplitudes. If you get the one you linked to then you want a small short piece of DIN Rail as that is how it mounts.

This is the actual data sheet for the timer.

Ron
 
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