Charge light not going out

[VicS]

[ QUOTE ]
The voltage is the same with engine ON, on both batteries even though only one battery is selected on the Main battery switch

[/ QUOTE ] Both batteries are being charged together either via VSR or a diode splitter system. The selector switch is only selecting which battery is in service.

A vsr or diode splitter will be located near the batteries i would expect or at least the selector switch. The output from the alternator will be connected to one terminal while the two batteries will be connected to two others. A vsr will also have a negative connection.

If you do have a vsr then it will charge one battery preferentially to the other. That one should normally be used as the starter battery.

Still thinking about the warning light. Probably a poor connection somewhere in the circuit that supplies the +ve feed to it via the ignition switch. Might even be the ignition switch.

 

[VicS]

[ QUOTE ]
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.


[/ QUOTE ] And that will also mean that the maximum field strength will be lower and therefore the maximum output of the alternator will be reduced ... will it?

 

[Guest]

As KDD says - one diode may be out .. mine was charging albeit at lower voltage than you show ... mine was approx 13.8 ... and light barely changed ... Auto Electrics guy fixed it in couple of hours and all was fine.

Now I show 14.4 ... 14.6 on my Plotter which monitors the battery in use .. OK - not the best way to do it ... but agrees with DMM and Draper tester ..

 

[Leighb]

Many thanks all,

I have more checking to do !!

 

[halcyon]

It can be lower, but it depends on diode failure, if it fails short circuit, it reverse conducts, the warning is earthed via the rotor windings on one phase, thus maintaining the magnetic field ( possibly at a lower level ) and lighting the warning light every third phase.
Thus the dim warning light.

Brian

 

[webcraft]

Our MD6A ran like this for nearly 3 years, with a dim warning light, and the batteries always charged - though at a bit under 14V rather than the 14.2+ they charge at now with the new engine and alternator.

Never had any battery problems though.

 

[Mudplugger]

small ally box with heat sink, somewhere on the alternator output line to batteries....1 inlet..2 outlet...?