Alternator / charging problems

[CAPTAIN FANTASTIC]

My boat has a Volvo MD11C engine with a standard alternator (30 Amps??). Last year I suspected that the alternator was not working properly because the amp meter lights was showing that it was not charging the batteries all the time.

So I purchase a new Alternator (70 amp) and I fitted it yesterday but when i started the engine, it does not appear to charge the batteries. I did not have time to carry out any further checks; ie check the output with a multimeter;

However, when i get to the boat next weekend, i would like to have a better understanding of how the system works. Could it be something else apart from the alternator? What other checks do i need to carry out?

 

[VicS]

Check all connections. Check with voltmeter.
Read battery volts ... should be 12.7 ish if battery charged. It'll drop well down while cranking but then should rise again above original volts as soon as running and eventually get up to 14 or so if the alternator is charging

Does warning light come on when switched on but not running. If not the alternator is not getting the initial field current ( via the light) to start it generating. Check warning light and circuit.

What do you mean by "amp meter lights"

Old one the type with no brushes?

 

[CAPTAIN FANTASTIC]

Check all connections. Check with voltmeter.
Read battery volts ... should be 12.7 ish if battery charged. It'll drop well down while cranking but then should rise again above original volts as soon as running and eventually get up to 14 or so if the alternator is charging

Does warning light come on when switched on but not running. If not the alternator is not getting the initial field current ( via the light) to start it generating. Check warning light and circuit.

What do you mean by "amp meter lights"

Old one the type with no brushes?

My mistake it can not be a amp meter, must be a voltmeter. I have installed this little gadget that checks the condition of the batteries and the output of the alternator by means of LCD lights ie when the light is red it means that the alternator is charging well (14 Volts??), when the light is orange is down to approx 13v etc.

 

[VicS]

My mistake it can not be a amp meter, must be a voltmeter. I have installed this little gadget that checks the condition of the batteries and the output of the alternator by means of LCD lights ie when the light is red it means that the alternator is charging well (14 Volts??), when the light is orange is down to approx 13v etc.

Ok I know the sort of thing you mean. got one that plugs into the ciggy lighter socket even.

 

[Playtime]

Do you have any wiring diagram for the batteries/engine covering alternator, charging arrangements (1-Both-2-Off switch, VSR or blocking diodes), engine circuits (keyswitch, starter, panel, glow plugs etc,).

It is almost impossible to give specific advice without some understanding of the circuit and equipment involved.

 

[Billjratt]

Yep, Vic's right.
Give us some information - assume a SEV marchal alternator removed, what was it replaced with? Wiring -did everything transfer like-for-like? Some SEVs had splitters attached, had yours? - any unused terminals on the new alt?
on your next visit,
Ign key on -------------------ign light on?
Engine start (bump the revs)--ign light off?

Measurements : volts on battery before start -
Engine running -

Alternator output -
Is negative via chassis or is engine isolated (and was it always so?)

So many questions...

 

[BabaYaga]

My mistake it can not be a amp meter, must be a voltmeter. I have installed this little gadget that checks the condition of the batteries and the output of the alternator by means of LCD lights ie when the light is red it means that the alternator is charging well (14 Volts??), when the light is orange is down to approx 13v etc.

Not familiar at all with this gadget, but I would think that an orange light (if indicating 13 volts from the alternator) does not necessarily mean bad charging.
The alternator could put out massive amps at that voltage, if charging a depleated battery. Only slowly will the voltage rise as the battery state of charge increases. When voltage reaches 14,2 or 14,4 the output (amps) will fall rapidly.

Agree a multimeter would be useful.

 

[westernman]

Check that the wire which comes from the engine on switch to the alternator excitation connection (the thing which turns on the electro magnets in the alternator) is properly connected. You can check if it is working - when the ignition switch is in the on position you should be able to feel the magnets in the alternator pulling a screw driver towards the pulley at the front.

That was the problem with my alternator when I had the same symptoms - there was an iffy connection which worked some of the time which gradually got worse and worse until it did not work at all. The connection between two bits of wire had corroded and came apart in my hands once I found it hidden round the back of the engine.

 

[Quidi Vidi]

Sorry to hijack this post but i think i may have this problem too, can you tell me which wire this is? Ie. which terminal on the alternator it connects too, i presume the other end connects to the ignition seitch or light

 

[westernman]

It is called the "field" wire. On Balmar alternators it is blue.

On the Balmar web site you can find some documentation about their alternators. If you have a model with external regulator, then this blue wire comes from that regulator. Check that with the ignition on but without running the engine, that you have 12V or so on the wire. If not, fix it ;-)

 

[CAPTAIN FANTASTIC]

It is called the "field" wire. On Balmar alternators it is blue.

On the Balmar web site you can find some documentation about their alternators. If you have a model with external regulator, then this blue wire comes from that regulator. Check that with the ignition on but without running the engine, that you have 12V or so on the wire. If not, fix it ;-)

Thanks for the reply, i will check the wires when I get to the boat soon.

 

[VicS]

i will check the wires when I get to the boat soon

The standard wiring on a Volvo penta panel and an MD11 C is

A Green 1.5 mm wire from terminal 75 of the ignition switch to the warning light

A black 1.5 mm wire from the warning light via the 8 way junction box to terminal 61 of the standard fitted alternator

I cannot see the relevance of the colour code Balmar might use.

See the VP owners manual at http://www.volvopenta.com/volvopent...lication_search/pages/publication_search.aspx

 

[William_H]

Alternator

Just to waffle ona bit. An alternator produces AC in 3 phases which are recified in 6 rectifiers and DC emerges on a fat terminal. (assuming negative is to the body not insulated.) the big terminal connects to the battery. Possibly via battery switch splitters etc.

Now an alternator usualkly has another set of small diodes which provide an DC to feed to the rotor (also known as the field coil). This is fed via brushes and also through the regulator. More current through the field coil gives more output voltage so current through the field is throttled back by the regulator to give exactly 14volts output.
Now problem is an alternator can not generate its own field current on start up because there is no magnetism in the rotor because there is no current.
So we feed some 12v battery supply through the "ignition " switch and via a warning lamp to the point in the alternator where the small diodes would normally supply power to the regulator and field.
So when you switch on the "ignition" switch you get current flowing from the battery via the lamp to the regulator and field coil. this small current is enough so that when engine starts the alternator starts generating and supplies it's own current to the field coil. So no current flows through the lamp from the battery and light goes out.
Light goes out means the alternator should be charging at least to itself for excitation but no guarantee it is charging battery. Light does not light, on turn on means a wiring problem or bad brushes in the alternator so no current is flowing through the field coil.
I hope that explains in some useful manner what the light does olewill

 

[Marsupial]

this may help you.

http://www.kb-kbh.dk/shipslib/el_ombord/alternatorhandbook_ocr.pdf

good luck

 

[nigelmercier]

Now problem is an alternator can not generate its own field current on start up because there is no magnetism in the rotor...

Hold a screwdriver near the rear bearing, there should be no (or very weak) magnetic field. Now turn on the ignition, the field should increase dramatically.