This is for a project that utilizes a v-twin 25hp motor, but I feel the nature of the question is more electronics oriented, thus I have posted here.

We have constructed a device that drives itself with a small 25hp gas engine. The transmission is hydraulically actuated and we use a series of remotely-controlled valves to spin one side of the drivetrain (left front and back, or right front and back,) so effectively a skid loader in a sense. Anyhow, the remote control for this unit has e-stop functionality, which is provided in the form of a 12VDC normally-closed line available off the hydraulic transceiver's harness. The hydraulic transceiver is powered by the 12V battery, which is the primary cold cranking source for the engine. Simply put, everything is sourced from the battery.

I want to integrate this function to the engine to shut down the fuel pump. On the engine it's simple: ground a wire and it does just that. My original thought was to run the 12V (NC) from the hydraulic harness into the control line/coil of a normally-closed relay so that if the e-stop is engaged, it open circuits the e-stop line and the relay is closed, grounding the ignition shutoff circuit and disabling the fuel pump. This circuit should work fine, but I need something that won't be disrupted when the engine cranks. While cranking, the 12V is temporarily unavailable, thus the primary relay channel will close and ground the engine shutoff circuit, presumably not allowing it to start.

Is a timer or a capacitor the best fundamental approach to this issue? My thought is to either create a timed latch or create a temporary capacitance, though admittedly the capacitance might not be the safest approach if an emergency stop situation is desired.

Thoughts? References to example circuits?

Thank you,
Mel

 

This is for a project that utilizes a v-twin 25hp motor, but I feel the nature of the question is more electronics oriented, thus I have posted here.

We have constructed a device that drives itself with a small 25hp gas engine. The transmission is hydraulically actuated and we use a series of remotely-controlled valves to spin one side of the drivetrain (left front and back, or right front and back,) so effectively a skid loader in a sense. Anyhow, the remote control for this unit has e-stop functionality, which is provided in the form of a 12VDC normally-closed line available off the hydraulic transceiver's harness. The hydraulic transceiver is powered by the 12V battery, which is the primary cold cranking source for the engine. Simply put, everything is sourced from the battery.

I want to integrate this function to the engine to shut down the fuel pump. On the engine it's simple: ground a wire and it does just that. My original thought was to run the 12V (NC) from the hydraulic harness into the control line/coil of a normally-closed relay so that if the e-stop is engaged, it open circuits the e-stop line and the relay is closed, grounding the ignition shutoff circuit and disabling the fuel pump. This circuit should work fine, but I need something that won't be disrupted when the engine cranks. While cranking, the 12V is temporarily unavailable, thus the primary relay channel will close and ground the engine shutoff circuit, presumably not allowing it to start.

Is a timer or a capacitor the best fundamental approach to this issue? My thought is to either create a timed latch or create a temporary capacitance, though admittedly the capacitance might not be the safest approach if an emergency stop situation is desired.

Thoughts? References to example circuits?

Thank you,
Mel

Hi,
For precise timing I would use a small Microcontroller (Try PIC micro). You can then control a relay, or a MOSET directly, to control your voltage.

This would mean you have to program the Micro. The tool to do that are freely available.

Regards

Francesco C

 

Can you run the estop stuff from a DC-DC converter? e.g. http://www.orbitmicro.com/global/dcdc-usb-p-13297.html

This would allow operation down to 6 volts?

Something is still missing from my understanding.

 

Nothing complex is necessary-- All you need is a 12VDC source, and an RC circuit that will keep a transistor holding the 12V feed open for 5 seconds.

 

That too, if the currents are not excessive. A diode isolated capacitor can keep deal with droop too.

 

That too, if the currents are not excessive. A diode isolated capacitor can keep deal with droop too.

If the current is high - you can get one farad supercapacitors from places that sell high power car audio systems.

But they're not cheap - there are cheaper supercapacitors, but they may have to be stacked in series to handle 12V.

 

What about addressing it at the battery? Would a "higher rated," presumably referring only to cold cranking amps capability, significantly prevent voltage drop, or is this usually inevitable during starting?

 

Theoretically, it could lower the voltage drop.

With a "traditional" automotive ignition switch, the accessories turn completely off during starting. Note the radio doesn't play. A higher CCA means a lower effective battery series resistance.

 

What about addressing it at the battery? Would a "higher rated," presumably referring only to cold cranking amps capability, significantly prevent voltage drop, or is this usually inevitable during starting?

Inevitable. When starter not turning, it's a short circuit. You avoid this to everything else by creating your own 'mini-battery' with an RC circuit that will meter out the cap's charge at 12V until the starter circuit is no longer in a shorting condition.

 

As everyone has said, an RC circuit.

However I want to point out that you have to use the RC circuit to engage the starter after the caps charge up. You'd also want your shutoff driven on a p channel so it's only blocked while the 12v is saturated.

And as far as your question on the battery, only if the starter is limited. Otherwise current follows least resistance. So even though caps act as a short-circuit on the current, you'll need a diode to keep the starter from pulling from the caps... so you have more resistance going to the caps than the starter and hence the caps won't charge.