turning off diesel ignition key - bad?

[Burnham Bob]

I know disconnecting the batteries is a no no as the alternator blows, but I have just been on a friend's narrowboat. it has a four cylinder beta and a large ignition panel with the usual lights. the 'instructions' written by the previous owner were clear about starting the engine. but they were also clear that once the engine had started, turning the ignition key off would 'stop the whistle'. as the rev counter didn't work i assumed that someone had done some rewiring along the line, so did as instructed, but realised there were no warniung lights functioning. again i assumed that this was some sort of bizarre rewiring. but my friend now says that revving the engine in neutral stops the whistle. this makes perfect sense as maybe the alternator isn't quite charging on start up but excites itself on revving and the lights and alarms for oil pressure, water temperatire and charging would work as normal - as they do on my boat with a much smaller beta diesel.

so have we done any damage running with the ignition switched off? i have to say that all the batteries seemed to be charged and there was no problem starting.

there appeared to be two alternators and the battery switches were always on in the engine compartment. i seem to recollect the forum advising that switching the ignition off was not a problem but i would welcome advice.

 

[VicS]

I know disconnecting the batteries is a no no as the alternator blows, but I have just been on a friend's narrowboat. it has a four cylinder beta and a large ignition panel with the usual lights. the 'instructions' written by the previous owner were clear about starting the engine. but they were also clear that once the engine had started, turning the ignition key off would 'stop the whistle'. as the rev counter didn't work i assumed that someone had done some rewiring along the line, so did as instructed, but realised there were no warniung lights functioning. again i assumed that this was some sort of bizarre rewiring. but my friend now says that revving the engine in neutral stops the whistle. this makes perfect sense as maybe the alternator isn't quite charging on start up but excites itself on revving and the lights and alarms for oil pressure, water temperatire and charging would work as normal - as they do on my boat with a much smaller beta diesel.

so have we done any damage running with the ignition switched off? i have to say that all the batteries seemed to be charged and there was no problem starting.

there appeared to be two alternators and the battery switches were always on in the engine compartment. i seem to recollect the forum advising that switching the ignition off was not a problem but i would welcome advice.

The alternator(s) are very unlikely to be connected to the battery via the "ignition" switch.
Turning off the ignition switch will normally just kill the power to the engine control panel so warning lights, alarms, gauges and in some cases the engine stop circuit will not function.
The alternator(s) will normally be connected directly, or at least via the isolator switch , to the battery.

Don't turn off the isolators while the engine is running ... doing that can cause a voltage surge which may well damage the alternator(s)

 

[prv]

I routinely turn off my engine electrics before pulling the stop handle in order to avoid the annoying beep after shutdown. Never done me any harm.

Pete

 

[Playtime]

. . . they were also clear that once the engine had started, turning the ignition key off would 'stop the whistle'.

Do you know which alarm was causing the whistle? I would want to know that before I accepted that turning off the power was a sensible response.

If revving stopped the whistle it could be low oil pressure, for instance.

 

[westernman]

The alternator(s) are very unlikely to be connected to the battery via the "ignition" switch.
Turning off the ignition switch will normally just kill the power to the engine control panel so warning lights, alarms, gauges and in some cases the engine stop circuit will not function.
The alternator(s) will normally be connected directly, or at least via the isolator switch , to the battery.

Don't turn off the isolators while the engine is running ... doing that can cause a voltage surge which may well damage the alternator(s)

I thought that usually the alternator exitation connection went through the ignition switch. So if the ignition switch is off, the alterator is not magnetised and won't generate anything. But I can't see any harm in that either.

 

[prv]

I thought that usually the alternator exitation connection went through the ignition switch. So if the ignition switch is off, the alterator is not magnetised and won't generate anything.

The non-official workshop manual I have for my engine says that the alternator will usually self-excite due to residual magnetism, so turning off the key can't be relied upon to stop it generating.

Agree that whether it does or doesn't, turning off the key won't hurt anything unless that somehow (big relay?) disconnects the batteries.

Pete

 

[VicS]

I thought that usually the alternator exitation connection went through the ignition switch. So if the ignition switch is off, the alterator is not magnetised and won't generate anything. But I can't see any harm in that either.

The initial excitation is via the ignition switch ( and usually the warning light circuit)

But once the alternator is "up and running" it supplies its own field current.
It no longer draws any current via the warning light circuit .... so the light goes out.

 

[nigelmercier]

The initial excitation is via the ignition switch ( and usually the warning light circuit)

But once the alternator is "up and running" it supplies its own field current.
It no longer draws any current via the warning light circuit .... so the light goes out.

Good summary.

However, on boats with a smart regulator, they are often wired to power up via the ignition switch, so the ignition needs to be kept on.

 

[westernman]

The initial excitation is via the ignition switch ( and usually the warning light circuit)

But once the alternator is "up and running" it supplies its own field current.
It no longer draws any current via the warning light circuit .... so the light goes out.

But the field current is supplied by a smart regulator to control the output voltage. In my case, certainly no amps are put into the batteries if the ignition switch is off.

I thought the light went out, because the key disconnected all of the control panel lamps and buzzer.

 

[VicS]

I have re-read the original question. There was no mention of a smart regulator.

 

[nigelmercier]

I have re-read the original question. There was no mention of a smart regulator.

No, indeed. I was generalising in case someone read this thread in the future.

 

[TrueBlue]

But the field current is supplied by a smart regulator to control the output voltage. In my case, certainly no amps are put into the batteries if the ignition switch is off.

I thought the light went out, because the key disconnected all of the control panel lamps and buzzer.

Take care - I have an Adverc controller system - it needs the ignition on to control its cycle. However, if you turn the ignition off (which SWMBO manages to do by her magnetic personality .....) it goes into hyperdrive and the alternators deliver maximum output and a bit more. SWMBO allerts by saying "there's smoke and a hot rubber smell".

I'm mystified, but Adverc says it can happen but don't tell me why....

 

[nigelmercier]

SWMBO allerts by saying "there's smoke and a hot rubber smell"....

Try KY

Sorry, childish I know.

 

[Uricanejack]

Well I am probabaly kind of dumb. I had allways heard turning of the ignition key had no effect on a diesel engine once it was running. And smthing about bugering up the solenoid watever that is. So like most people I shut it down by pulling the leaver to shut the fuel off. Untile it stuck. So I opened the compresion lever.

So why are you not suposed to turn the key off

 

[Stu Jackson]

Wouldn't the appropriate answer be: It all depends on how it's wired?

 

[westernman]

Take care - I have an Adverc controller system - it needs the ignition on to control its cycle. However, if you turn the ignition off (which SWMBO manages to do by her magnetic personality .....) it goes into hyperdrive and the alternators deliver maximum output and a bit more. SWMBO allerts by saying "there's smoke and a hot rubber smell".

I'm mystified, but Adverc says it can happen but don't tell me why....

If I turn the ignition off and back on again, there is a pause of 30 seconds or so before the alternator starts delivering any current at all, then it slowly ramps up. If the batteries are a bit run down, it will then go and deliver maximum amps after about a two minutes.

This is with a Balmer smart charger thingy.....