Alternator Excitation Problem?

[BigART]

I have a Motorola P type alternator fitted to my Perkins 4108. Recently, the alternator has been slow (2-3 minutes) to come on line after start (orange light staying on, voltage remaining at 12.5 to 12.6v). Having read Mr Calder's tome, I am suspecting an excitation problem. Are there any easy solutions other than sending it to an expensive fixer or a new one?

Angus

 

[damo]

Does the light go out if you rev the engine?

Have you recently changed the bulb to a different wattage?

 

[William_H]

The fact that the bulb glows for some time then eventually goes out indicates that the wiring from power source to the alternator is OK.
Make sure the belt drive is OK and if it has just started acting this way and been previously K then yes it seems like a remove and check the alternator would be in order. olewill

 

[Graham_Wright]

I had a similar problem with a Dynostarter. I flashed a 6 volt torch battery across the field windings and it was fixed.

Of course, if you do the same, it might just blow up??!!

 

[bobgosling]

I had almost the same problem as this ( different motor & alternator ) and it turned out to be corrosion on the bulbholder. Cleaned it up and problem disappeared.

 

[nigelmercier]

[ QUOTE ]
I have a Motorola P type alternator fitted to my Perkins 4108. Recently, the alternator has been slow (2-3 minutes) to come on line after start...

[/ QUOTE ]

What sort of charge controller do you have?

 

[VicS]

[ QUOTE ]
I had a similar problem with a Dynastarter

[/ QUOTE ] So you might have done but a Dynastarter is a different kettle of fish to an alternator. The Dynastarter is like an old fashioned dynamo in that it relies on residual magnetism to start generating. If that is lost then it can be restored by "flashing" in the way you suggest (but if you "flash" the wrong way you'll reverse the polarity and you end up with a generator with -ve on the output terminal instead of +ve, which will have some "interesting" consequences if then put into service)

An alternator does not retain sufficient magnetism to get itself started. The initial excitation is provided by the current that flows through the warning light, regulator, brushes and the field coil, the rotor in the case of an alternator, hence the references earlier in the thread to the warning light.

So sorry a completely inappropriate suggestion for an alternator.

 

[willie4646]

I take it the drive belt is correctly tensioned

 

[ex-Gladys]

My old Landy alternator exhibited the same symptoms. The alt is farked. Either get it rebuilt or buy a new one... The Landy replacement (Indian Lucas) was £39 and 10mins to fit. I hope yours is as easy and cheap!

 

[BigART]

Thanks for everyones contributions, problem solved.

As I said a weird one. Everything seemed OK, tight belt, shiny bulbholder, wiring/connections good, bulb glowing. By a process of elimination, I discovered that the bulb was not letting though enough current, despite being lit, to excite the alternator. Changed bulb for a new one and now works like a champ.

Lesson learnt.

Angus

 

[Heckler]

Maybe fixed maybe not, all the exiteable ones jump in without logical thinking, when the brushes which carry the exitation voltage get worn they just touch the slip rings, classic symptom is that the bulb continues to glow and goes out when you rev it, it gradually gets worse. solution new brushes, cheap and easy to do.
with changing the bulb you might just have changed the parameters a bit enough to get the voltage past the resistance of the poor connection.
Stu