stopping a diesel

I wrote: A friend just bought a yacht with twin Hino diesels. They are started by a key switch but when they you want to shut them off you have to press a stop button until the engines quit, then turn the keys off. I don't have much experience with diesels but years ago when I had a job repairing forklifts I ran into a similar situation. This seems to me to be unnecessarily complicated. After all, most diesel powered cars turn on and off with a key switch. I have asked many people this question but have gotten answers that didn't seem plausible. So now I'm asking the experts. Thoughts?

Some of the replys I got:

< Modern diesel automobiles that I have encountered (and, indeed, modern tractors and whatnot) have fuel solenoids that shut off the flow of diesel to stop the vehicle when you shut the key off. A mechanical diesel (as opposed to an electronic-injection diesel) will run as long as it has fuel, unless something makes it stop. Every diesel will have a kill-switch under the hood in case you lose electrical power - without power you can't move the solenoid to shut off the fuel. If the solenoid is sprung then you might have a situation where without power the spring returns the solenoid and the fuel shuts off. That, to me, is not a good thing. I've made it home in my old diesel truck with a frozen battery and without enough power to run the turning indicators or anything else, but the engine ran fine to get me home. If it had have stopped dead somewhere I would have not been amused. A diesel of an older design may not have a solenoid but rather a spring-return lever that acts both as the emergency kill switch and the usual method of stopping the engine via a cable-pull from the operator's position. In the case of these Hinos, if they're similar to the Hinos that I have dealt with, they will be mechanically injected and definitely of the 'run until they're out of fuel' variety, so they have to be stopped manually. I haven't yet seen a Hino with a compression release, so I would strongly suspect that the button you're pushing is attached to a solenoid that pushes against a spring-return lever on the injector pump to kill the engine. The old Mercedes 240's & 300's start and stop with the ignition key but "off" is not electric. The key off position closes a vacuum valve that is part of the switch assembly, connected by hose to a diaphram-actuated fuel shutoff on the injection pump. So it is not dependent on the electrical system but if there is a major vacuum leak, in addition to the door and gas cap locks and I forget what else stops working, there is a red shutoff lever under the hood. Wait until that diesel runs away by consuming it's own lube oil. You have never been really frightened until you share a bilge with this event. The diesel I have shuts down by cutting off the fuel flow to the injectors. There is a solenoid that, when energized, retracts and lets the fuel cutoff level move to the run position. When de-energized the same solenoid moves the fuel level to the stop position and holds it there. Works nice. For emergency shutdown use a board over the air intake. >>>

I appreciated the explanations and stories and I'm not criticizing anyone but I still don't have a definite answer. I liked the jacket story best. A solenoid controlled shutoff makes the engine independant of the electrical system.(for shutoff at least) but some engines die hard. Since there doesn't seem to be any hard and fast reason for a separate shutoff button, I am thinking of converting my friend's boat to keyswitch start and stop for safety reasons,. He's technologically impaired (he had a VCR for 2 years before I pointed out to him that it was one of those that can't be programmed-he was surprised when he found out that he could push the scan button on his car radio to find stations automatically and he has a cellphone but carries phone no's on a piece of paper. I'm thinking of bypassing the stop button with a normally closed relay which when the keyswitch is turned on will open and release the solenoid which is stopping the fuel supply. When the key is turned off the solenoid will be energised and cut off the fuel. Since we don't want to run the batteries dead over a long period we'd have a time delay relay to cut off the power to the solenoid and itself after say, 5 minutes. This I hope is a simple method of accomplishing this purpose with easily obtained materials and not having to make major changes to the system, or is there a loophole in ny logic? Engineman1

Reply to
Engineman1
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Sounds to me like you're just adding complications, ie more things that can go wrong.

Gary

Reply to
Gary Coffman

Not to be flippant, but since he carries phone numbers on a piece of paper maybe the best solution would be to print the start and shutoff instructions on a card, laminate it, and post it above the ignition switch. Even better, engrave it on a piece of brass or that laminated plastic used for name plates. It seems that he would understand this better and anybody who is competent to service the boat won't find anything unusual when it needs to be serviced away from home. ERS

Reply to
Eric R Snow

This may burn out the solenoid, and you won't be able to shut it off except by the manual override. Why on earth do you need 5 minutes for a Diesel to stop turning? It should stop in 5 seconds, easily! Maybe set the time delay for 10 seconds or so.

Well, yes. If the solenoid needs to be activated AFTER the key is off, then the timer needs to be powered all the time. So, the TIMER will run the battery down. That will take longer that the solenoid would, but in a couple of days the battery will be dead. Hmm, I suppose there could be some relay arrangement that would keep the timer powered on until it was done, then turn it off, also.

Jon

Reply to
Jon Elson

I agree! What ever happened to KISS - Keep It Simple Stupid! Greg

Reply to
Greg O

On 25 Sep 2003 06:01:35 GMT, snipped-for-privacy@aol.com (Engineman1) wrote something ......and in reply I say!:

AFAICS In the event of an electrical failure, you have a fail to unsafe mode setup. The fuel can still flow.

It's interesting that people have described both types of solenoid. I reckon I would rather one that failed to dead engine than one where I could not stop the engine. Once an engine has stopped, then I can work out hos to get fuel back. I suppose in a boat, heading through a reef passage, this may be different. But there are the odd few other thikngs that could stop the engine as well,,,,

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Reply to
Old Nick

Do you know if the fuel solenoid is engergized to run or to stop?

Rick

Reply to
Rick

The solenoid has to be energized to stop the engine.

I may not do anything to my friend's boat but just as an exercise in elementary circuit logic I'm using Turbocad and trying to design the simplest circuit to allow an engine to be controlled entirely by the key switch. My parameters are: no modifications to the fuel injector or engine, no solid state components, IE no 555 chips, nand gates, and gates ETC. I'd like my device to be just an add on, keeping the kill button active and using the existing key switch. My circuit would consist of dpdt relays and time delay relays. Since the boat may not be used for a month or more at a time, the system cannot have any devices which would drain the battery during nonuse without any extra switches to turn off. So far this last requirement has been my biggest hurdle.

A friend just bought a yacht with twin Hino diesels. They are started by a key switch but when they you want to shut them off you have to press a stop button until the engines quit, then turn the keys off. I don't have much experience with diesels but years ago when I had a job repairing forklifts I ran into a similar situation. This seems to me to be unnecessarily complicated. After all, most diesel powered cars turn on and off with a key switch. I have asked many people this question but have gotten answers that didn't seem plausible. So now I'm asking the experts. Thoughts?<

over a long period we'd have a time delay relay to cut off the power to the

Reply to
Engineman1

Hmm ... I would opt for a solenoid which had to be energized to allow fuel to reach the engine. I'm presuming that when the engine is running, there is a generator to keep the batteries charged. Under those circumstances, the relay and solenoid power consumption is less of a problem.

Turning on the key should pull in the solenoid valve (with or without the help of a relay, depending on how much current the solenoid valve happens to draw.

Anything with a time delay relay to turn off the fuel with a apply-power-to-shut-off solenoid valve would either need a continuous power drain for at least one relay, or a mechanically latching relay to

*hold* it off once the time delay is past. (There are old time delay relays which operate with a heater and a bi-metalic strip in a vacuum envelope if you *absolutely* want to avoid solid-state devices. But they draw *lots8 more current than a well-designed solid-state timer. If you want a minimum current way to operate the solenoid, I would go for a power-to-fuel-flow solenoid, and a logic circuit (including counter-timer) build around CMOS logic, which can draw *extremely* low power at slow clock speeds -- except for the driver to a solid-state relay, which is why the apply-power-to-flow option is preferred.

Of course -- there is the problem of making it survive the electrical glitches which are often present in motor systems.

Good Luck, DoN.

Reply to
DoN. Nichols

The solenoid has to be energized to stop the engine.

I may not do anything to my friend's boat but just as an exercise in elementary circuit logic I'm using Turbocad and trying to design the simplest circuit to allow an engine to be controlled entirely by the key switch. My parameters are: no modifications to the fuel injector or engine, no solid state components, IE no 555 chips, nand gates, and gates ETC. I'd like my device to be just an add on, keeping the kill button active and using the existing key switch. My circuit would consist of dpdt relays and time delay relays. Since the boat may not be used for a month or more at a time, the system cannot have any devices which would drain the battery during nonuse without any extra switches to turn off. So far this last requirement has been my biggest hurdle.

A friend just bought a yacht with twin Hino diesels. They are started by a key switch but when they you want to shut them off you have to press a stop button until the engines quit, then turn the keys off. I don't have much experience with diesels but years ago when I had a job repairing forklifts I ran into a similar situation. This seems to me to be unnecessarily complicated. After all, most diesel powered cars turn on and off with a key switch. I have asked many people this question but have gotten answers that didn't seem plausible. So now I'm asking the experts. Thoughts?<

over a long period we'd have a time delay relay to cut off the power to the

Reply to
Engineman1

Ah, oops. Most of the present time delay relays (the square white ones, with the black knob on top) are solid state inside. They have semiconductors inside. You have to go back to the older, all-glass tube type time delay relays to achieve your goal then.

I think there's at least one member of the ng here who would be first (second?) to point out that relays and mechanical switches have a poorer fail rate in the field than properly designed solid state circuitry. Even more so for consumer grade, unsealed relays that are pressed into service in marine applications.

If you want reliable, you need to be able to figure out a way to do this without electricity. No solenoid.

Jim

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Reply to
jim rozen

This is how aircraft magneto ignitions work. The coil wire gets grounded to kill the spark. If anything along the way goes open, the motor keeps on running.

Jim

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Reply to
jim rozen

The photocell controllers I use for my porch lights are all solid state. I think at some point (above 5 or 10 amps) the triac to control this current becomes more expensive than a cheap relay to do the same thing.

My suspicion is that if you take apart a failed consumer grade motion sensor light, that had a mechanical relay in it, it's the relay that ultimatly failed. Because consumer grade stuff cuts right to the profit margin, they skimp on components. The difference in cost between a one year MTBF relay, and a 20 year MTBF relay is a lot.

For a marine application where lives might be at stake, it makes sense to look at all the failure modes and figure out a motor control setup that does the utmost to keep the engine running when it's needed. If that means using a manual shutdown by the engine then that's still best.

Jim

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Reply to
jim rozen

Yes, it is, and properly applied relays usually fail "off" whereas silicon normally fails "on" unless subjected to massive overload.

Best regards, Spehro Pefhany

Reply to
Spehro Pefhany

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