Engine electrics - what was going on here?

[MoodySabre]

I was working on the boat (in the water) and needed to run the engine (VP 2003) at tickover. Having already run the engine for a bit so it was warmish and would start immediately, I got SWMBO to start the engine,with no throttle, whilst I was down below. The engine started but the charging warning alarm was wailing. "Give it some revs" I said as that normally excites the alternator and stops the alarm. She does but no change. I go up top and notice that the rev counter is on zero. Gave it full throttle, the rev counter leapt into action and the alarm stopped.

What would give that effect? Do I just need to clean all the contacts on the back of the rev counter and the alternator?

 

[leomagill]

Have you got a bad connection in the charging light? alternaters need power down the warning light wire to kick them into life.

 

[andy01842]

Do you have a alternator light, dose it work? This light often supplies the power to get the alternator started. If the light dose not work the alternator sometime dose not have enough residue magnetism to get started. Chicken and egg.

 

[alanabnala]

An interesting one.

Alternators are three phase and the W terminal is from one of the three phases, so it could just be a problem with that one phase. The W terminal gives a modified output solely to run a tachometer.

I think the first thing I would do would be to check the voltage supply to the alternator, followed by the negative return, as an alternator requires power in order for it to operate, unlike a dynamo. The best way to do this is by using a volt drop method rather than measuring resistance. PM me if you want me to talk you through how to do this.

As you say, the most likely problem will be a bad connection somewhere, due to being laid up over winter.

 

[bobgosling]

[ QUOTE ]
Have you got a bad connection in the charging light? alternaters need power down the warning light wire to kick them into life.

[/ QUOTE ]

I had a very similar problem. I originally thought I had burnt out the alternator but it turned out to be just corrosion on the light contacts. Disassemble the engine control panel and clean it and see if that fixes the problem.

 

[Hoolie]

Had similar symptoms while motoring which caused some anxiety. Turned out to be a vibration fractured negative lead on the alternator. I'm not sure how but the alternator suffered no ill effects and worked fine after re-making the connection.

 

[halcyon]

Could also be worn or sticking brushes in the alternator.

Brian

 

[MoodySabre]

I have a light - can't recall if it was working as the sun was out /forums/images/graemlins/smile.gif Will check it next time.

 

[MoodySabre]

[ QUOTE ]
due to being laid up

[/ QUOTE ]
I haven't been laid up - out three times in the last three weeks with no problem.
Thanks all - will clean all the contacts and keep fingers crossed.

 

[dje67]

Been here with my old MD11. The underlying fault is due to the "ignition switch" not making contact once the key had been returned to "run" position after starting. Once the engine is running, there is no need for the electrics to be switched on and it will run happily, but not show charge and not show any revs. Solution:- gentle wiggle of the key immetdiately resores supplies and the rev counter bursts into life. Soring this probably means cleaning contacts etc at the back of the key switch. It is on the "get round to someday" list of jobs...!

 

[VicS]

[ QUOTE ]
Been here with my old MD11

[/ QUOTE ] Could be but the wiring of the MD11 and the 2001/2/3 series is very different. The panels are vastly different.

I dont think the alarm will sound if the keyswitch, or panel switch, whichever it has, is not making contact.

 

[Phoenix of Hamble]

Agree... almost certainly the switch.... I have the same problem.... quick wiggle of the switch, and all is well...... will get sorted one day! /forums/images/graemlins/grin.gif

 

[RAI]

Had SWMBO turned the key switch to off after starting the engine?

(duck and run)

 

[Juggler7823]

This is common with Volvo and 2003 engines in particular. They need some revs to excite the alternator before it starts charging. It should start up if revved. Occassionally it can be due to a faulty electronic alarm unit in the instrument panel, cost £200 approx

 

[MoodySabre]

[ QUOTE ]
Had SWMBO turned the key switch to off after starting the engine?

(duck and run)

[/ QUOTE ]

/forums/images/graemlins/shocked.gifI'm not going to ask her /forums/images/graemlins/grin.gif