In message , Chris Bartram
writes
On 09/03/2020 16:45, wrote:
Hi All,
Back in the dark ages (60s,70s, 80s) cars had little bulbs that
would come on to tell you your battery was no longer charging.
There have been a few people on the Peugeot007 self
Help FB group Im on whose alternators have died, but their cars
not charging light hasnt illuminated (despite its passing its POST
before the problem and after its been rectified (see what I did there).
Got me to thinking, how were these bulbs driven in the past (i.e,
what electrics / electronics / circuit lit them when charging stopped)?
And how are they supposed to work in modern Cars?
On the 007, I believe its an LED and I SUSPECT its fed from
the ECU??
Anyone know?
In the old days, the bulb fed the (field?) coil on the alternator from
the battery, and the current through it was required to excite the
alternator and start it charging- when it started to do so, the voltage
both sides of the bulb became the same, so it went out. If the bulb
wasn't connected or burnt out, the alternator wouldn't charge at low
RPM- as RPM increased, it would self-excite.
Ha! Just been there.
Ancient tractor with no ignition warning light at start up. Initial
investigation found ample carbon left on alternator brushes so assumed
the fault was elsewhere.
Not so:-(
The alternator slip rings were worn down to the underlying insulation
leaving a narrow strip of copper either side.
As a temporary fix, refacing the brushes regained contact and the system
is temporarily working.
Seems odd the copper wearing faster than carbon but maybe this was a
recon alternator.
--
Tim Lamb