How to detect when the ignition on a diesel engine it turned on? - Page 1
Forum section: electronics / projects

author: towlerg
author_rank: Contributor
timestamp: July 14, 2018, 11:43:43 am
content: The engine in question is a very basic small 2 cylinder engine. I guess the only power used is for the heater plugs and relay the drives the starter.I thought perhaps measure the current or put a relay coil in-line (that sounds dangerous or attach to a potential divider and the adc on uC. The las is obviously simplest but is there some drawback?

author: sokoloff
author_rank: Super Contributor
timestamp: July 14, 2018, 11:47:26 am
content: There’s no “ignition” per-se.You might tap into the fuel valve or fuel pump.

author: cs.dk
author_rank: Unknown
timestamp: July 14, 2018, 11:53:59 am
content: Can you be more specific about what your goal is?

author: Ian.M
author_rank: Super Contributor
timestamp: July 14, 2018, 12:07:41 pm
content: A diesel engine can be entirely mechanical with absolutely no electrical system. Unless it uses electrically actuated injectors or an electric fuel pump, there is no guaranteed equivalent to the switched supply to the ignition system of a petrol engine.The easy way to detect if the engine is running is to fit an extra oil pressure switch - if it hasn't got oil pressure, its either stopped or if running will rapidly stop due to bearing failure. You may also be able to tap into an existing oil pressure switch and sense the voltage.If its got an alternator, you can sense the voltage on the warning light terminal as an alternative indication its running, but that can be prone to disturbances due to belt slip or other charging system faults that don't prevent the engine running otherwise normally.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 14, 2018, 12:32:22 pm
content: The ignition on the diesel engine, may turn on the glow plugs.If the engine has glow plugs (heater plugs) make sure they get their voltage and a current flows.On some older engines, the glow plugs are in series and if one is broken, the other one will not get any current.On newer engines they are in parallel, if one is broken, at least the other one will get power to glow.Under warm weather, the glow plugs may not be needed to start the engine.Under cold winter conditions, it is nearly impossible to start without the glow plugs / other help.

author: Tom45
author_rank: Frequent Contributor
timestamp: July 14, 2018, 01:22:30 pm
content: As Ian says, a diesel engine needs no electricity to run. An electric starter cranks it to get it running. A fuel shutoff switch is used to stop it.Older diesel engines have an oil pressure switch that turns on the electrical system to allow gauges to function. The tachometer is done mechanically.

author: Seekonk
author_rank: Super Contributor
timestamp: July 14, 2018, 01:37:00 pm
content: I'd get a knock sensor or magnetic sensor for a keyway in the shaft.

author: tautech
author_rank: Super Contributor
timestamp: July 14, 2018, 01:47:17 pm
content: Tap into the alternator field supply.You'll get full battery voltage with the engine not running and less when it's charging and the charge rate's being regulated but this may suit your needs.Some alternators have a charge light output which goes either high or low when charging (depending on type) and you can use this also. Just invert it or not for whatever you needs are.Old generators with mechanical regulators used the D connection from the dynamo as ground for the charge light when the motor wasn't running and when it was the bulb wouldn't light as it had 12V on either terminal.

author: cs.dk
author_rank: Unknown
timestamp: July 14, 2018, 02:09:00 pm
content: Some alternators would also feature a W-terminal for tacho-output.I recall that some older diesels had a sensor clamped on one of the injector pipes, usually cylinder 1. I don't know the purpose of it, but it may detect a pulse when an injection is happening. Don't remember if it was VW or PSA though.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 14, 2018, 02:12:52 pm
content: Quote from: towlerg on July 14, 2018, 11:43:43 amThe glowplugs are only turned on briefly before cranking and are off when running.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 14, 2018, 02:59:24 pm
content: Quote from: cs.dk on July 14, 2018, 02:09:00 pmThat was a piezo pulse generator, reaction on the tiny expansion of the injector tube.It was used for some service to detect RPM and injection timing.

author: mikerj
author_rank: Super Contributor
timestamp: July 14, 2018, 05:48:13 pm
content: Quote from: GeorgeOfTheJungle on July 14, 2018, 02:12:52 pmTrue for basic diesel engines like the OP's but not true for modern common rail engines, many of then run the glowplugs during normal operation.

author: johnkenyon
author_rank: Regular Contributor
timestamp: July 14, 2018, 06:04:24 pm
content: Quote from: GeorgeOfTheJungle on July 14, 2018, 02:12:52 pmOn PSA (aka Peugeot/Citroen) vehicles fitted with the XUD9T engine (aka mechanical/in-direct injection 1.9D Turbo), the glow plugs remained on for a period after the engine started.Anyone who fitted replacement glow plugs designed for the normally aspirated version would find themselves having to fork out for the correct set after a few weeks, as they weren't tough enough.By the way, on those engines the only way to confirm the ignition was turned on would have been the stop solenoid feed (12v = ignition on).Engine running could be confirmed using the alternator lamp.Good luck with the separate rev counter sensor - it had a knack of getting knackere, leaving you with a randomly flapping meter needle...

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 14, 2018, 08:01:30 pm
content: Quote from: mikerj on July 14, 2018, 05:48:13 pmJeez, I'm getting old.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 15, 2018, 03:35:35 am
content: Quote from: GeorgeOfTheJungle on July 14, 2018, 08:01:30 pmUsername checks out.

author: max_torque
author_rank: Super Contributor
timestamp: July 15, 2018, 10:45:35 am
content: As mentioned above, if the engine in question can be started and stopped from a key, then there must be a "stop solenoid" somewhere on the injection pump (Assuming it's an old mechanically pumped unit and not a modern ecu control common rail unit).As diesel engines don't have spark plugs, the only way to stop them is to interrupt the flow of fuel, so an electromagnetic stop solenoid is fitted, which when powered acts to allow the pump to build fuel pressure, but when unpowered, dumps that pressure, so nothing is injected and the engine stops firing.Look on the injector pump, for a small solenoid with a single wire attached to it. This will be powered from the ignition switch when it is in the "run" position, so you can easily monitor that voltage. (make sure your input circuitry to your micro has sufficient protection to mean the inductive kick of that solenoid doesn't kill your micro btw!)

author: bob225
author_rank: Frequent Contributor
timestamp: July 15, 2018, 10:54:03 am
content: what make and model of engine is it - is it in a bob cat or quadracycle ?

author: Ian.M
author_rank: Super Contributor
timestamp: July 15, 2018, 11:49:10 am
content: Its not uncommon for non-common-rail small industrial and marine diesels to have a manual stop lever or pull-knob, connected by bowden cable to the injection pump where it overrides the governor to move the fuel control rack to a cutoff position. Such an engine may be started by hand cranking even if the 'ignition' switch isn't on. The 'ignition' switch if present, only controls power to the gauges, alternator field supply terminal, via the start button to the starter solemoid coil, and possibly to a relay controlled by a preheat button if the engine has glow-plugs fitted.At its simplest for an engine with electric start and glow-plugs, if a PM alternator is fitted, there may be no switched 'ignition' supply, just a three position momentary keyswitch: Off/Run, Preheat, Start, (spring return to Off/Run) with the (minimal) gauges and/or 'idiot lights' fed from the alternator before the charge controller so they are off with the engine stopped.Therefore unless the O.P. posts the make and model of his engine and either we can find the wiring diagram from the service manual online, or he has a copy, there's not much we can do to suggest where to pick up an 'ignition' on signal or even an engine running signal.

author: towlerg
author_rank: Contributor
timestamp: July 15, 2018, 02:32:32 pm
content: Thanks to all who posted.My purpose is to disconnect PV monitoring when engine (with all its spike and general nastiness on the 12v line) is about to start. Maybe ignition was the wrong word, the engine is controlled by a n way switch from furthest acw, cutout, off, on, heater, crank. The heaters are only on while the switch is held in that position. Both crank and cutoff a springloaded to prevent the switch staying in that position when it is released.There is a solenoid valve in the fuel line which "clicks" when the switch is turned to on and again when turned to cutoff. BTW its a Mitsubishi dumper engine on a small boat.If I go with detected the fuel cutoff solenoid, what sort of protection do I need from the coil in the solenoid?

author: sokoloff
author_rank: Super Contributor
timestamp: July 15, 2018, 02:46:41 pm
content: Does the boat have a load-shedding relay already? Or, said differently, are there accessories that are not powered while the switch is in crank?It's common on cars to cut out some circuits while cranking.

author: towlerg
author_rank: Contributor
timestamp: July 15, 2018, 03:09:31 pm
content: @sokoloff no, there is no automatic system to control exteral loads.

author: tautech
author_rank: Super Contributor
timestamp: July 15, 2018, 08:49:48 pm
content: Quote from: towlerg on July 15, 2018, 02:32:32 pmEasy, reverse bias diode across the fuel solenoid.This WILL be your best and simplest 'engine ON' indicator by far and if you'd said it had an electric fuel solenoid we'd have all jumped on that one from the start.

author: towlerg
author_rank: Contributor
timestamp: July 16, 2018, 11:12:47 am
content: QuoteSorry about that, I thought all diesel engines had cutoffs. How could you stop it without one?I don't see the difference between "looking" at the terminal of the cutoff or "looking" at the start switch.

author: CJay
author_rank: Super Contributor
timestamp: July 16, 2018, 11:20:11 am
content: Quote from: tautech on July 15, 2018, 08:49:48 pmIt'd be more unusual to find an old diesel that doesn't have a fuel cutoff solenoid though, so it'd be the first suggestion I'd have made.They're there to stop runaway engines (even when the diesel from the tank is cut off it's not a guarantee the engine will stop) but aren't as necessary on newer fuel systems.

author: Ian.M
author_rank: Super Contributor
timestamp: July 16, 2018, 01:40:08 pm
content: Quote from: CJay on July 16, 2018, 11:20:11 amShutting off the fuel or opening a 'dump' valve on the injection pump only helps if the runaway is due to a stuck injector rack.2-stroke Detroit Diesels are notorious for running away, and continuing to runaway even with the fuel shut off, though it can happen with just about any poorly maintained turbo diesel, or even with a normally aspirated one with grossly excessive blowby and a high crankcase oil level. Basically if oil can get into the intake and you don't have some means of totally shutting off the air supply, you risk an uncontrolled runaway with the engine consuming its own lube oil as fuel.In the absence of an emergency air shutoff valve, you need something that will seal the air intake effectively. If you are mildly paranoid and have ever been near a runaway diesel, you may choose to keep a pingpong bat clipped to the inside of the engine box lid. Otherwise, grab a closed cell foam cushion or the Nautical Almanac and shove it up against the intake. Don't try to use anything thin and flexible or the palm of your hand as the intake can pull a fairly high vacuum before the engine dies.

author: sokoloff
author_rank: Super Contributor
timestamp: July 16, 2018, 02:33:01 pm
content: Alternately, if you're just looking to protect something from the starting transients, intercept the starting signal (disconnect from the starter solenoid and bring it to your device). Then, shutdown your device and re-create the starter signal out to the solenoid. You can do this with a timer or one-shot RC circuit if you need an orderly and lengthy shutdown, or if you just need a parallel signal, just tap off the starter solenoid (primary) wiring.

author: CJay
author_rank: Super Contributor
timestamp: July 16, 2018, 02:34:43 pm
content: Quote from: Ian.M on July 16, 2018, 01:40:08 pmMhmm, as I said, it's not a guarantee the engine will stop, I've seen a few that have runaway (and actually seen them do it) burning their own engine oil and only stopped when the engine ran out of oil and destroyed itself, as you say, the only sure way to stop it it to prevent it getting oxygen, I have seen CO2 suppression systems but never seen one used..The voltage on the solenoid is a pretty sure sign the engine 'ignition' is at least switched on though which is what the OP wanted

author: sokoloff
author_rank: Super Contributor
timestamp: July 16, 2018, 02:48:33 pm
content: Could be as simple as paralleling a relay off the starter solenoid primary and powering your PV monitoring system from a normally-closed terminal on the relay.Starter engaged: relay triggers, powering down the PV system.Starter released: relay opens, powering up the PV system (because it's on the NC terminals).The relay can take the abuse of the starter solenoid (itself a relay) without other components generally.

author: tautech
author_rank: Super Contributor
timestamp: July 16, 2018, 08:00:25 pm
content: Quote from: towlerg on July 16, 2018, 11:12:47 amMany/most mechanical diesel injector pumps (inline and rotary) had manual fuel shutoffs.Trucks for example had a STOP bowden cable with a knob to pull to kill the engine. Tractors had either a throttle lever that went back past the idle position or a STOP rod linkage that connected to the fuel shutoff shaft on the injector pump. Key switch stops are comparatively recent (last 30-40 yrs) WRT the time diesel engines have been in existence.QuoteCorrect, use the ON position at the switch but check the wiring with the thought of adding a diode if there's no ECU to manage the solenoid back EMF at the switch.