Tuesday, Jun 20, 2006 at 11:38
Peter – you say your alternator puts out over 14V
Craig – you say your alternator puts out 14.2V
I take it that you measured those voltages not long after starting a reasonably cool motor. Have you remeasured the alternator voltage after towing for half an hour?
The modern alternator has temperature compensation. The reason for this is that a battery needs a lower voltage to charge it when it is hot – or the corollary to this if you do not drop the voltage of the alternator as things heat up under the bonnet then you will boil the battery dry. The system voltage in my Disco starts at around 14.5V and 20 minutes down the road it has dropped to 13.8V or less – these voltages vary slightly depending on the temperature of the day.
To
test the performance of your charging system get any old or new cigar lighter plug, wire it to your multi meter, insert the plug in the cigar lighter socket and observe the meter occasionally whilst you drive. There are several ways you can wire this up – if you have (or can get) plugs the same as the ends of your meter leads make a permanent
test lead or just simply attach a couple of wires to the cigar plug you can wind around your meter lead probes.
Some alternators drop to 13.5V when up to running temperature (my first Disco did.) If you have one of these and you do not have any voltage boost then you will be cycling your battery over the range of around 20% - 55% of its maximum capacity. This is inviting sulphation to form – not good for the battery.
I suggest you do these checks before you dispose of your Twin Charge.
My Twin Charge has a 14.5 V output. I have disconnected it as I think it may have contributed to the demise of my low maintenance battery which requires less than that for effective charging. I have not removed from the van as I can simply replace the fuse and give the van battery enough charge for one nights lights without having to run the car's engine.
PeterD
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