One possibility is that, on some modern alternators (certainly on the Bosch
Compact range) the regulator will cause deliberately a higher regulated
voltage at lower ambient temperatures. This is because, chemically,
lead-acid batteries require a higher charging voltage at lower
temperatures. The variation in regulated voltage with temperature is about
-10mV/deg. C.
At the recent ambient temperatures in the UK (5 to 10 C), a regulator
putting out up to 15v would be just about within spec. If you have a
flooded cell battery then overcharging will cause it to consume water;
However, the alternator assumes that the battery is kept under the 'hood'
in close proximity to the alternator regulator. If your battery is in the
'boot', then this set-up will tend diminish the possibility of
overcharging.
Did you have your top cowl off when you made the measurements?
Duncan McF
On Saturday, November 16, 2002 9:36 AM, Kevin Taylor
[SMTP:kevin@eastyorkshire.co.uk] wrote:
> Folks,
>
> Anyone got any ideas on the following observation.
>
>
> I have noticed a recent chance in my on board voltage.
>
>
> The voltmeter used to read 12.7 (approx as its an analogue meter) volts
all
> the time and never really moved that much that I ever noticed. Now it is
> reading much higher 14-15 volts on the gauge.
>
>
> I put a digital AVO on to get an accurate reading and I'm finding the
> battery is reading 12.9 volts when off load and engine off. With the
engine
> running its reading 14.2. My interpretation of this is that the
alternator
> is permanently charging the battery and therefore overcharging.
>
>
> The previous owner did say that the regulator had blown before and if I
saw
> more than 14v then pop out the Alternator field fuse to stop the battery
> overcharging then fit a new regulator.
>
> I have fitted a new one and its no different so I'm wondering what might
be
> going on.
>
> This does coincide with me fitting a new intercom and GPS tot he panel
and
> while carrying out a few jobs on the plane I did inadvertently
momentarily
> short out the battery. Hence the reason I thought I may have damaged the
> regulator/rectifier.
>
> Any ideas please? Subaru not Rotax.
>
> For any Subaru owners make a note of the following part number for the
> rectifiers as it will save loads of searching when you need one!
>
> Alt is off a Suzuki Swift car 1.0L & 1.3L. Nippon Denso 100211-2200 or
> Suzuki part no 31400-82110 cost ?35 inc post and vat. or you can pay ?231
at
> the Suzuki garage if you prefer!!!!
>
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