Most likely a gremlin in the alternator, IMO.
Kind of dangerous, running around with the alternator stuck on "full on".
The electrolyte in the battery "boils", which isn't water changing to steam
but instead water being separated into oxygen and hydrogen. Normally, the
explosive gas mixture escapes out the vents and dissipates with no harm done
(until the battery runs low on electrolyte). But any kind of spark nearby
can set it off, resulting in a battery explosion.
I suggest carrying a voltmeter/DMM in the car. Next time it happens (if
there is a next time), pull over and check battery voltage with engine at a
fast idle. If you see more than about 14.4 volts, shut the engine off and
disconnect the alternator for the drive home. Should be no problem driving
for 4 or 5 hours without the alternator and no headlights, 2 or 3 hours with
headlights.
You'll also know for sure that it's the alternator gone wonky, and not a
shorted cell in the battery. I suppose it's possible for a shorted cell to
un-short; but I've never seen it happen.
-- Randall
56 TR3 TS13571L once and future daily driver
71 Stag LE1473 - awaiting engine rebuild
71-2-3 Stag - awaiting gearbox rebuild
> -----Original Message-----
> From: Triumphs [mailto:triumphs-bounces@autox.team.net] On
> Behalf Of Peter Arakelian
> Sent: Saturday, October 12, 2019 11:58 AM
> To: triumphs@autox.team.net
> Subject: [TR] battery, alternator, or gremlin?
>
> 1971 TR6. Driving home last night I noticed my ammeter was
> at the + sign, half-way between neutral and full. It is a 40
> mile drive, stayed there the entire way. I stopped to pick
> up a pizza. the car cranked and started as usual after a 20
> min stop. Ammeter was now halfway between the neutral
> position and the + sign. today I checked volage of battery
> from pole to pole: 12.60 volts. Start the car today, cranked
> and started as usual, ammeter shows normal - slight charge at
> first then to neutral position.
> Battery, alternator, or Gremlin?
>
> Peter Arakelian
>
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