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ummmm.. WOW!How do you feel about the project now?
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?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?
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...?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?
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.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.
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.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!
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!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?
Ok, didn't think of it like that; Since it gets longer and longer, that makes sense!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...?
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.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.
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?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.
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.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!
Exactly. Since the N/C wiring is heavy, that is what I will do.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?
Does anyone else here have experience with weatherproofing electronic circuitry?
"100R" = 100 ohms.what is the value for R7 in your schematic? is that supposed to be 100K ohms or 100 Ohms?
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!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.
I would keep away from foam since this could hold water.
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!I've ordered a heavy duty aluminum project box with a breadboard,
Good! Please keep us postedBy 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...