Alternator biffed

[Anchorite]

Motor running at 1500 rpm: alternator (110A with internal reg) charging a single 110Ah battery.
Incident: the positive cable 'fell' off the battery (don't ask how) /forums/images/graemlins/blush.gif.
Motor stopped, cable replaced (tight), motor restarted with bated breath.
Alternator is still giving >13.5V, up as much as 14.3, but voltage is not steady (should it be?).
Can the regulator be damaged yet give a charge (warning light goes out and stays out)...(or is it waiting for the worst possible moment to expire /forums/images/graemlins/confused.gif)?

 

[savageseadog]

I don't know what you mean by steady. The output is a rectified three phase AC and won't necessarily be easily read by a digital voltmeter.

 

[ex-Gladys]

I would expect the alternator feed to the batteries to fluctuate slightly, particulaarly at low revs. It should be steady within .1/.2 V at steady RPM, but may vary from 13.x up to 14.x between 1200 and WFO rpm

 

[VicS]

[ QUOTE ]
I don't know what you mean by steady. The output is a rectified three phase AC and won't necessarily be easily read by a digital voltmeter

[/ QUOTE ] I don't know about that but once a battery is connected you'd expect to see a reasonably steady reading. It may vary a bit in the long term but should not show short term fluctuations. Those would suggest poor connections or brush wear to me.

Anchorite,

You ask, "Can the regulator be damaged " I don't know if the regulator can be damaged if the battery is disconnected. It is usual to suspect that the rectifier could be damaged, although you may have got away with it if the alternator is protected against surges or if it was only lightly loaded at the time of the incident.

As SSdog says it is a full-wave three phase rectifier consisting of 6 diodes (and in most cases 3 field diodes) and it is possible for only some of the diodes to have been "blown". If that is the case you will not be able to get the full rated output. Therefore it would be sensible to verify that you can get the full current output.

For peace of mind, if you have any doubts I suggest you get it checked by a good automobile electrician.

 

[William_H]

As suggested a Digital Voltmeter can be unsteady in the readings with fluctuaions of AC or sometimes for no real reason.
A light turned on (in darkness) may indicate if the voltage is really unsteady.
Fluctuating output from an alternator usually means bad rushes or slip rings. These are easily inspected by removing the integral regulator which will have brushes attached to the regulator. The slip rings can be seen down the hole. The rings should be smooth and shiny. Any burnt or black patches indicates brushes are not making good contact. On some alternators you replace the brushes by replacing the regulator. Yours may be completely different of course.

I suspect you have only found the unsteady voltage because you checked after the wire failed. So it may be a completely different fault.

Get a really heavy load connected on the system ie a lot of lights or inverter at least 25 amps and check that the battery volts hold at 14 volts for say half an hour. If a diode is gone the volts will slowly fall as the alternator can not give the 110 amps it is rated at. (or even 25A) good luck olewill
As always an amp meter would be far more useful to check the alternator output.