Clutch Switch Bypass For Big Blue

[viven44]

I'll check that the engine will crank if I arm the system in Start. It should. But I'm out and about and may not get to check it today.

I think I'm almost convinced the Bosch relay is just fine.

I have also been wondering why in your schematic, every time the clutch was pressed the starter relay wasn't energized and running the starter motor.

- If that LED wasn't there, there would nothing in between the starter relay and the VCC power (12.5V with truck off and 14.5V with truck running at VCC).. which is similar to an ignition circuit. All that is between the starter relay and VCC is the LED. How does the LED prevent the starter relay from getting energized with the VCC voltage ? I saw an explanation earlier that the LED's max draw is much less than what the starter relay needs. Sounded like the LED was limiting the current (although I had assumed the total current which is Voltage/total resistance in series would flow through whatever was in the circuit)… As long as the starter relay didn't run I was satisfied. Moved on.. but now I'm wondering still.

I am interested to see what you find from the Start + 'Arm'. I am thinking while cranking the battery the usual voltage drop would somehow interfere with VCC, and that's you need a capacitor anyway...

I always recall how switched power devices like dash cams and head units turn off while cranking... those are acceptable because the duration of crank is small.. but here you are trying to move a while by cranking. Very interesting problem.

 

[viven44]

I think I'm almost convinced the Bosch relay is just fine.

I have also been wondering why in your schematic, every time the clutch was pressed the starter relay wasn't energized and running the starter motor.

- If that LED wasn't there, there would nothing in between the starter relay and the VCC power (12.5V with truck off and 14.5V with truck running at VCC).. which is similar to an ignition circuit. All that is between the starter relay and VCC is the LED. How does the LED prevent the starter relay from getting energized with the VCC voltage ? I saw an explanation earlier that the LED's max draw is much less than what the starter relay needs. Sounded like the LED was limiting the current (although I had assumed the total current which is Voltage/total resistance in series would flow through whatever was in the circuit)… As long as the starter relay didn't run I was satisfied. Moved on.. but now I'm wondering still.

I am interested to see what you find from the Start + 'Arm'. I am thinking while cranking the battery the usual voltage drop would somehow interfere with VCC, and that's you need a capacitor anyway...

I always recall how switched power devices like dash cams and head units turn off while cranking... those are acceptable because the duration of crank is small.. but here you are trying to move a while by cranking. Very interesting problem.

Another thought.

If you do find that VCC voltage drops too much while cranking and affects module functioning and even 12V Bosch relay switching perhaps a 5V module might work better.

Of course you will need something to step down battery voltage to around 5V. Something like a Buck or LDO step down DC-DC converter but it will be stable with any input voltage fluctuation.

Some examples I quickly came across

https://a.co/d/8b3NjxU

https://a.co/d/5SVmjmK

 

[Gary Lewis]

Another thought.

If you do find that VCC voltage drops too much while cranking and affects module functioning and even 12V Bosch relay switching perhaps a 5V module might work better.

Of course you will need something to step down battery voltage to around 5V. Something like a Buck or LDO step down DC-DC converter but it will be stable with any input voltage fluctuation.

Some examples I quickly came across

https://a.co/d/8b3NjxU

https://a.co/d/5SVmjmK

Yes, that would work - assuming the voltage is the problem. But I should know that when I arm the system in Start as that is the worst-case test. Will try that later this morn.

Thanks.

[viven44]

Yes, that would work - assuming the voltage is the problem. But I should know that when I arm the system in Start as that is the worst-case test. Will try that later this morn.

Thanks.

Along the same lines here is another contraption that says it will take anything from 5-11V and produce stable 12V (looks an awful lot like DS-II)

https://a.co/d/6iuTZuu

Did the timer manual call for input voltage stabilization of any kind, if not then I’m still hoping the 3300uf capacitor will do the job as it’s the simplest solution in front of you. The criteria should be crank&move for up to ? seconds.

[Gary Lewis]

Along the same lines here is another contraption that says it will take anything from 5-11V and produce stable 12V (looks an awful lot like DS-II)

https://a.co/d/6iuTZuu

Did the timer manual call for input voltage stabilization of any kind, if not then I’m still hoping the 3300uf capacitor will do the job as it’s the simplest solution in front of you. The criteria should be crank&move for up to ? seconds.

Well....

I turned the key to Start and then armed the module: w/o capacitance nothing happened. But with 3000 mfd if you armed it within a few seconds the engine started. So I put a meter on and the voltage was slowly falling off after the caps charged and it you armed while the voltage was north of 10v it started.

As it turns out I'm not tied to a circuit with power in both Run & Start. I cannot explain why it even starts at all.

But, having now run a jumper from the ignition coil to the circuit it starts every time, with or without capacitance. With or without a diode.

So the nut behind the wheel is, and maybe always has been, loose.

Looking at the EVTM & Big Blue's documentation the circuit I needed to have tapped is #640, the R/Y wire off Fuse 18 that feeds the seatbelt buzzer, warning indicators, tach, and fuel pump control. There's really only two fused circuits, that one and #973, that are hot in both Run & Start.

[viven44]

Well....

I turned the key to Start and then armed the module: w/o capacitance nothing happened. But with 3000 mfd if you armed it within a few seconds the engine started. So I put a meter on and the voltage was slowly falling off after the caps charged and it you armed while the voltage was north of 10v it started.

As it turns out I'm not tied to a circuit with power in both Run & Start. I cannot explain why it even starts at all.

But, having now run a jumper from the ignition coil to the circuit it starts every time, with or without capacitance. With or without a diode.

So the nut behind the wheel is, and maybe always has been, loose.

Looking at the EVTM & Big Blue's documentation the circuit I needed to have tapped is #640, the R/Y wire off Fuse 18 that feeds the seatbelt buzzer, warning indicators, tach, and fuel pump control. There's really only two fused circuits, that one and #973, that are hot in both Run & Start.

I went and watched the video again. Sounds like you just need the truck to start after its armed, correct ? Is that the mission profile of this module ?

After being tied to the correct circuit, any difference in behavior when clutch is pressed ? Does the starter relay do anything ?

So the nut behind the wheel is, and maybe always has been, loose.

And lastly, is that literal or figurative ? Was the nut actually loose ? Sorry i struggle with metaphors

[Gary Lewis]

I went and watched the video again. Sounds like you just need the truck to start after its armed, correct ? Is that the mission profile of this module ?

After being tied to the correct circuit, any difference in behavior when clutch is pressed ? Does the starter relay do anything ?

So the nut behind the wheel is, and maybe always has been, loose.

And lastly, is that literal or figurative ? Was the nut actually loose ? Sorry i struggle with metaphors

First, I'm the nut behind the wheel.

But there won't be any change to starting when the module is connected to the right circuit. Without arming the module you'll still have to depress the clutch pedal to get it to crank. But once the module is armed you'll have 10 seconds to start it with the clutch fully engaged.

And yes, that's the intent for this module - start with the clutch engaged, but only for a brief period of time. That way it pretty much has to be a conscious decision to start it in gear, meaning it is unlikely that someone will arm it and then hit the starter w/in 10 seconds accidentally. And when you do arm it you'll be staring at a very bright red LED that warns you that you've done something dangerous.

Speaking of the LED, with just the change to a circuit that is hot in both Run & Start the LED will still light any time that the clutch is fully depressed if the key is in either of those positions. But with Bob's suggestion of adding a diode I'll fix that so that the LED only comes on when the bypass is armed.

[viven44]

Speaking of the LED, with just the change to a circuit that is hot in both Run & Start the LED will still light any time that the clutch is fully depressed if the key is in either of those positions.

In this condition (without the diode) does the starter relay have enough power to be energized ? I still don't understand why the VCC voltage doesn't cause the starter relay to be energized with just the LED in the midst. I know with the diode this is a non-concern (very clever fix by the way).

Speaking of that diode, it will cause a forward-bias voltage drop. Might be 1 volt right there?

[Gary Lewis]

Speaking of the LED, with just the change to a circuit that is hot in both Run & Start the LED will still light any time that the clutch is fully depressed if the key is in either of those positions.

In this condition (without the diode) does the starter relay have enough power to be energized ? I still don't understand why the VCC voltage doesn't cause the starter relay to be energized with just the LED in the midst. I know with the diode this is a non-concern (very clever fix by the way).

Speaking of that diode, it will cause a forward-bias voltage drop. Might be 1 volt right there?

First, you may have missed that the starter relay I'm talking about is one of those large fender-mounted units that Ford used. Not a little Bosch relay.

And it depends on what you mean by "energized". The LED lights at .02A and the starter relay takes 3.5A to pull it in. So all the LED is doing is use the starter relay's pull-in coil as its ground. But the starter relay is not pulled in so the contacts don't close.

Yes, the diode is a clever solution. And there will be about a .7v drop across the diode, but that's not a problem because the starter relay would easily be pulled in with a lot less than 12v.

I've had a look and I've not found easy access to the R/Y wire for circuit 640. It looks like the best place to get to it is under the dash cover, so I'm going to pull that and do the wiring. But while the dash cover is off I'm about half way to getting to the module, so I'll go ahead and add the diode while things are apart.

(We need an emoticon where a guy is wrenching or turning a screwdriver so we can imply to people that "I'm off to solve this problem and I'll be back.")

[viven44]

Speaking of the LED, with just the change to a circuit that is hot in both Run & Start the LED will still light any time that the clutch is fully depressed if the key is in either of those positions.

In this condition (without the diode) does the starter relay have enough power to be energized ? I still don't understand why the VCC voltage doesn't cause the starter relay to be energized with just the LED in the midst. I know with the diode this is a non-concern (very clever fix by the way).

Speaking of that diode, it will cause a forward-bias voltage drop. Might be 1 volt right there?

I assume you are not a fan of using add-a-fuse and just draw power from fuse 18 output.

When you are back, maybe I need to understand more about why the relay won't pull in when simply exposed to voltage. (It will draw the current it needs, right?)... See you soon!