Charge light not going out

[Leighb]

I have just taken over a Halmatic 30, with a Volvo MD7A engine,
it starts and runs OK, but the charge light stays on when engine running, it does go quite dim compared to when you first switch on, but does not go out. Other lights not on (Oil/water temp) no audible warning once engine has started.
Does this mean no charge from alternator?
If not what other causes.
How should I investigate with multimeter?

 

[orizaba]

check the batteries before you start the engine then a few minutes after you have started it if the voltage has gone is /going up then your alternater is charging,
sometimes you can get a slight glow from the ignition light,but check to see if its charging first.

 

[GeorgeTina]

Hi
Sounds like the alternator is not providing any charge. Check across the battery with the engine running (fast tickover should be enough). The voltage should be greater than 13.5V. Normal charging voltage is up to 14.4V. Battery voltage without charging will be less than 12.8 V. If one of the diodes in the alternator has failed you will get the symptoms you describe. The alternator voltage with blown diode(s) will be about 13.2V.
It is usually possible to get the diode pack changed by an auto electrical repair shop.

 

[captainslarty]

Dim light after stert usually indicates diode failure. check all connection first though to make sure they are clean, and check voltage etc as above

 

[Thistle]

Are the alternator belts OK? Much easier to check than diodes, wiring, connections etc and not infrequently overlooked.

 

[Leighb]

Thanks for replies,
I will check battery voltage with engine running tomorrow.
I am pretty sure the belt is OK, quite tight with no signs of wear or slipping.

 

[Billjratt]

You don't say if it momentarily goes out ( were you watching) it could be over-voltage and damaging your battery. Measure for the conditions already supplied above. Your alternator could be one of those french brushless things and may even have a splitter diode fitted. It won't be a terrible shame if it as to be replaced by a standard car alternator from your local scrappy, which will give about twice the charging power.

 

[CPD]

I would check voltage first, then drive belt and if that doesnt show where the prob is then spanners out, off with the alternator and get it to a garage. Good luck.

 

[VicS]

[ QUOTE ]
off with the alternator and get it to a garage

[/ QUOTE ] No way

Take it to proper automobile electrician. The sort of place that can test it, diagnose the fault and repair it. Garages, at the very best, can make a poor job of fitting a new alternator to a car.

 

[CPD]

Sorry VicS, thats what I meant, somewhere that can test, analyse and hopefully repair.

 

[William_H]

High Billjrat I am intrigued by your comment about those dreadful French brushless alternators.
Now the laternators could be bad for various reasons but the concept of brushless is really good. All large jets use brushless alternators for extremely low maintenance.

The idea is that a DC field is applied to thye outside of a small alternator at the back of the main alternator. This small alternator rotating coils have rectifier diodes which are connected along the shaft to the main alternator field (rotating) coil. Which then produces AC or presumably in the car alternator goes to rectifiers. So the only wear point is the bearings. It is controlled by varying the current to the outside field of the first tiny alternator.
So is this how the French one works and why is it so bad? olewill

 

[Guest]

a) Check battery voltage before engine start.
b) Start engine and bring to fast tickover ... over 1000rpm should be good
c) While engine running check battery voltage now.

Voltage should have risen dramatically as you are now really seeing alternator voltage supplied to batterys ... and should be over 14V ... ideally about 14.4V

I have a cheapo Draper battery / alternator tester - cost me 9.99 in halfords .. you can get them cheaper than that about 4.99 now .. They have a row of LED's on them and simple instructions on the item. Engine not running it puts load on battery and shows battery voltage. Engine running it shows alternator charging or not.

Generally light not going out means exciter current is not being stopped by reversed current from alternator field ... ie Diodes are shot on back of alternator. If you check all connections and find OK ... then simple way is to take of alternator and bring to Auto Electric servce guy - he will run the alternator up - tell you if efficient or not ... also diagnose any problems - he can re-wind / change diodes etc. etc.

My alternator did same - my cheapo tester indicated only very small charge from alternator ... so of to local guy ... 20 quid / 2 hrs later alternator better than ever been ... charges like a good'un ...

In fact to most - I would advise having alternator checked by similar service ... can mean a new lease of life even to a working alt.

 

[Niander]

Hi can i ask 2 questions alternator related?

can the bearings be changed or lubricated?

can someone draw a simple wiring circuit from alternator to battery as after a rebuild I'm going to run my gm10 in the shed to test ...before putting back into boat
cheers .

 

[pampas]

The brushless alternator was developed to overcome the problem with high wear at low altitudes caused by the Oxegen entrapped within the Carbon mix escaping,making the brush split and distort. low maintainance was a by-product of advancement.

 

[ralf2]

click the throttle into neutral,push the revs up until the light goes out(maybe 2000 or so),alternator knows engine is working hey presto!try it worked for me.

 

[Guest]

The trick of increasing revs till light goes out - is actually what I have to do if I only have tick-over after starting .. it's to get enough energy into producing the counter voltage to reverse the exciter lead and put out the light - actually its the field coils sustaining their field ...

But if you open throttle even in gear enough to get up to about 1/2 revs - that should do it as well ..

It is generally down to a "tired" alternator coils / field that causes this ... so I'm told ! But once I "kick" mine into action - charge is good as ever !

But honest - get a Tester - cheap enough .. fiver at Maplins etc. - it is useful for all sorts ... (one job they don't tell you ... if you have a socket that doesn't power a light etc. - you stick this across it ... as it puts a load on - it will show if the voltage coming to socket is weak or has enough umph to do the job !! Laymans terms of course !!)

 

[Leighb]

Thanks everyone,

I have done some checking today.
Battery voltage, engine OFF 12.97V
Battery voltage, engine ON 14.38V
Charge light remains ON all the time, but does dim once engine starts.
The voltage is the same with engine ON, on both batteries even though only one battery is selected on the Main battery switch.

So from what has been said I do have an alternator producing a charging voltage, BUT the light does not go out so something is wrong.
Also why is it giving a charge to both batteries when only one is selected?
There does not seem to be any clever battry management system fitted, is it likely on a 1982 boat?

 

[Mudplugger]

Are you sure you havn't got a Voltage sensitive relay fitted? VSR's relatively inexpensive and easy to fit, and quite small as well. Possible post build addition?

 

[Leighb]

Hi Tony,

No not sure, what would it look like, and where would I find it?

Thanks
Leigh

 

[halcyon]

We were making clever battry management units in 1982, but you would know if one was fitted.
Could be a failed field diode check the voltage either side of the warning light.
The warning light has a back feed from the field diode circuit to turn it off, ie both sides of the bulb have the same voltage. In the age of alternator you probably have there will be 3 field diodes in the alternator, it is possible that one of these is blown. This will produce a missing phase, thus a lower field diode voltage than the alternator output, thus a dim warning light.

Brian