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Help with time delay relay circuit

duke37

Jan 9, 2011
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Kris,
That looks good.
The only thing that I have reservations about is the high current of the fuel solenoid. Does it have a very high current coil to energise and then a low current coil to hold?
Duke
 

steamngn

Aug 27, 2012
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How do you feel about the project now?
ummmm.. WOW! :D
That's super, and like you said tidier. I think I see one small issue, though...:eek:
If I'm correct, the bouncing up and down of the lower float will cause the beeper to go on and off, as there is no time-delay to compensate for that, right? So then the beeper would need to be on some sort of delay less than the fuel relay? Damn this gets tricky! I did do some mechanical work on the tractor yesterday, and it required draining the fuel tank. I was able to calculate the time between the lower float hitting the fully(stays) closed position and the critical must-shutdown fuel level. We actually have several minutes (5.93) before we MUST shut down, so there is plenty of wiggle room to make adjustments if needed.
Kris, this is a lot of work on your part and I greatly appreciate it! The mechanical world is where I live, and with your patience and guidance I am learning the world of electronics as well!
Andy
 

KrisBlueNZ

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The only thing that I have reservations about is the high current of the fuel solenoid. Does it have a very high current coil to energise and then a low current coil to hold?
From what Andy said, I think it has separate coils, and the hold coil is the one that draws nearly 9A. I assume the energise coil is operated by a separate pushbutton. It's not part of this circuit. Andy, can you clarify this?
If I'm correct, the bouncing up and down of the lower float will cause the beeper to go on and off, as there is no time-delay to compensate for that, right?
Yes, I thought that would be a GOOD thing... People are more likely to notice it if it's going on and off as the tractor moves around. Then it stays on for longer and longer each time, then eventually it stays on for the full 20 seconds, then it stops, and so does the engine. I thought that would be good behaviour...?
I was able to calculate the time between the lower float hitting the fully(stays) closed position and the critical must-shutdown fuel level. We actually have several minutes (5.93) before we MUST shut down, so there is plenty of wiggle room to make adjustments if needed.
OK. The delay is proportional to C1, so you can increase it if you want to. You can increase RT and Q3's base resistor, but I would increase C1 first. If you want to delay longer than a minute or so, it would be worth looking at a different type of delay. There are ICs for that purpose.

What do you want to do about the beeper?
Kris, this is a lot of work on your part and I greatly appreciate it! The mechanical world is where I live, and with your patience and guidance I am learning the world of electronics as well!
Thanks for saying so :) It's no problem for me; I have a lot of spare time and I like to help people, and I like to learn about their projects too.
 

steamngn

Aug 27, 2012
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Duke,
The only thing that I have reservations about is the high current of the fuel solenoid. Does it have a very high current coil to energise and then a low current coil to hold?
That is correct, but be aware that the coil is higher current than seems to be normal. The Pull winding draws 15.3 amps, and the hold winding nearly 9!
And I did some research on that, too. The design spec says pull coil is 14.5, and hold is 8.5!!
This is all ignition-switch operated, similar to an automobile; When the key is in the run position, the holding coil is energized. When the key is turned to the start position, the pull coil is momentarily energized to pull in the solenoid. Switch the key to off, and the hold coil de-energizes, shutting off the engine by allowing the governor spring to pull the fuel valve closed. Usually on a diesel injection pump the fuel shutdown valve is NOT part of the governor, and a tiny amount of force will open and close it but on this engine the governor and fuel valve are integrated, and the fuel solenoid needs to react against this. The mechanical force is pretty high, and explains the current draw...
I think on Kris' schematic connector CN3 pins 2 and 3 should actually be to two wires going out to relay K1, which would be mounted externally to the circuit. K1 is not the fuel relay, it is just an interrupter to cut the holding coil circuit and kill the engine.
Yes, I thought that would be a GOOD thing... People are more likely to notice it if it's going on and off as the tractor moves around. Then it stays on for longer and longer each time, then eventually it stays on for the full 20 seconds, then it stops, and so does the engine. I thought that would be good behaviour...?
Ok, didn't think of it like that; Since it gets longer and longer, that makes sense!
Thanks for saying so :) It's no problem for me; I have a lot of spare time and I like to help people, and I like to learn about their projects too.
You're welcome, and this goes for everyone who has input! Perhaps some time you will need some mechanical design help, and I can return the favor.
Ok, so last part of this:
Looks like this circuit is pretty complete, and I can get building. How do you guys feel about sealing the circuit against vibration and moisture? Should I coat the entire thing in some sort of resin or rubber, or just put it in a project box? Remember that this is a high vibration/moisture environment!
Andy
 

KrisBlueNZ

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I think on Kris' schematic connector CN3 pins 2 and 3 should actually be to two wires going out to relay K1, which would be mounted externally to the circuit. K1 is not the fuel relay, it is just an interrupter to cut the holding coil circuit and kill the engine.
OK, it's up to you how you do it. The drive from Q4 is no more than 500 mA, and I assumed it would be driving a relay coil that draws 160 mA as you said earlier. The drive is normally not present, and becomes active when it's time to kill the engine. So I guess you would use the normally closed contact of the relay, in series with the 12V to the hold coil. It's probably a good idea to put put K1 external to the circuit because it needs some heavy wiring to its contact terminals! Does that match what you were thinking Andy?
Looks like this circuit is pretty complete, and I can get building. How do you guys feel about sealing the circuit against vibration and moisture? Should I coat the entire thing in some sort of resin or rubber, or just put it in a project box? Remember that this is a high vibration/moisture environment!
Good question! I think I would put it in a waterproof box. You may need to get into it later, so I wouldn't seal it permanently in anything. Something like a diecast aluminium box with a rubber seal around the mating surfaces, maybe.

You would have to bring the cables in through a rubber gland of some kind, and maybe seal them with silicone or something. It might work out better to use a single sealed plug and socket with all the connections on it. No doubt Digikey have something suitable.

Does anyone else here have experience with weatherproofing electronic circuitry?
 

steamngn

Aug 27, 2012
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It's probably a good idea to put put K1 external to the circuit because it needs some heavy wiring to its contact terminals! Does that match what you were thinking Andy?
Exactly. Since the N/C wiring is heavy, that is what I will do.
I will go online and order my parts today! As for the sealing up, lets see what others have to say before we finalize the design. I will keep everyone posted as to my progress and outcome!
Andy
 

steamngn

Aug 27, 2012
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Hey Kris,
what is the value for R7 in your schematic? is that supposed to be 100K ohms or 100 Ohms?
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Does anyone else here have experience with weatherproofing electronic circuitry?

Potting is a favorite in the marine industry but it makes the module totally un-serviceable. Perhaps sandwiching the board between two layers of foam rubber in a tight box? Foam rubber deteriorates over time so it would have to be replaced yearly.

Chris
 

duke37

Jan 9, 2011
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I have mended electric fence energisers and they seem to last better if they are in a box with a small ventilation hole in the bottom. I have coated boards with Waxoyl which is intended for car undersealing. It gives a wax coating which can be removed with paraffin or white spirit, the problem is that thrips get stuck in it. I have to clean out the cowshed clock every thirty years or so, I might not do it next time.

I would keep away from foam since this could hold water.
 
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KrisBlueNZ

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I have mended electric fence energisers and they seem to last better if they are in a box with a small ventilation hole in the bottom. I have coated boards with Waxoyl which is intended for car undersealing.
Right... There are lots of spray-on and brush-on coatings available. Mouser have a range of them - look in the "Tools and Supplies -> Chemicals" category and choose "Coating products" and "Sealants". The coating will seal everything completely, so you'll need to choose your trimpot setting before you seal it!

At my previous job, when we sold our products for use in Rotorua, we had to coat the boards with a spray-on "conformal coating" to stop corrosion. Rotorua is a town with a lot of geothermal activity and sulphur fumes in the air. The place smells like rotten eggs.

I think coating the board would be a good idea, as well as protecting it with a box.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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I would keep away from foam since this could hold water.

The first generation of double hulled foam filled boats suffered badly from this. Owners reported their boats gaining many hundreds of pounds as the years passed. The newer generation of foam fill is closed cell and does not retain water. It still may not be the best choice though.

There is a spray that's sold specifically for PC boards. It goes on the component side of the board and looks sort of like thick brown spider webbing. It has a rubbery texture

Chris
 

steamngn

Aug 27, 2012
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Ah Kris,
Ok, got it! Just wasn't sure if that was a typo or not...
@CDRIVE & dike37; Thank you for the input!
I do remember reading about potting, and yes the drawback certainly is that the unit is no longer serviceable.
I've use closed-cell foam on other parts of this machine; not so good it the winter time! Even the limited amount of moisture that the outer edge of the foam retained would freeze and expand the foam, with ugly and unpredictable results!
I've ordered a heavy duty aluminum project box with a breadboard, and I think it is a good idea to coat the circuit as well. By moving the relay out of the project box I can now mount this circuit up into the dash cowling quite a bit higher, and so will provide it good protection from the weather I think...
All the parts should be here this week, will keep everyone posted!
Andy
 

KrisBlueNZ

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I've ordered a heavy duty aluminum project box with a breadboard,
I hope you mean stripboard... A breadboard is used for prototyping, and doesn't hold the components very strongly. If you put a breadboard on a tractor, all the components would probably fall out of it because of the vibration!
By moving the relay out of the project box I can now mount this circuit up into the dash cowling quite a bit higher, and so will provide it good protection from the weather I think...
Good! Please keep us posted :)
 

KrisBlueNZ

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Cool! That looks good. Have you worked out how you're going to get the signals in and out of the box? Maybe a single connector mounted on a wall of the box?
 

steamngn

Aug 27, 2012
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Yep,
I ordered an 8 screw terminal strip to handle the floats and led wires; I will pass the wires in to the case through 3 grommets; one for each float and one for the led wires. On the 12v side, I will use a piece of 16 gauge 4 conductor trailer wire that I will solder right to the stripboard and pass out through a grommet to a 4 wire automotive weatherpak connector. This way I have +12v, -12v and both of the relay coil wires in one cable...
The fuel tank is a custom built piece that I fabricated to also hold the battery on top; this assembly is 3/32 inch steel, and is quite heavy duty (Diesel batteries are BIG). With this design I can mount the circuit box on the top rear of the battery box, and all of the float/led wiring is up and inside the cowl. The only connector exposed then is the 12v weatherpak, and I can make that cable sufficiently long to provide a drip loop so water cannot migrate to the grommet. Where I live the snowfall can get pretty wild, and it isn't uncommon to have this tractor in snow all the way up to the cowl line (the tan top)! Drip loops are important! :D
 

steamngn

Aug 27, 2012
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Drum roll........ badabadabadabadabadabada....
Here it is, my first attempt at electronics for the tractor! I made two little changes:
  1. In the schematic, connector CN1 ("floats") pins 1 and 3 combined onto pin 1. This allows
  2. Moving the buzzer external to the box using the freed up CN1 pin and the blank pin on CN2 ("leds")
I didn't do so well laying the pieces out on the board, and things got a bit cramped toward the end, but it all fit. For the positive and negative 12v lines (PL3 pins 1 and 4) I ran the red and black wires right through the pc board and created a buss for each leg to attach to. I don't know if this is stronger/weaker/overkill but it seemed better than using a bunch of little jumpers...
So all that is left is to double check my work, drill the holes for the led and float wires and then test it out!
How's it look? Comments? Criticism? Accolades? :p
Andy
 

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CDRIVE

Hauling 10' pipe on a Trek Shift3
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At a glance the soldering looks skillful. In fact better than my old coworker and buddy Ron. His motto is "The bigger the glob the better the job"! :eek:

Ron, if you see this post I couldn't help myself. :p

Chris
 
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