Alternator, testing output.

[makemeanoffer22]

Having just got the heater fan going on my Flavia coupe i have noticed that when i press on the brake pedal the fan slows down ( its single speed ) i guess the illumination of brake light bulbs is causing this ?. Surely the output from the alternator would cope with this and i wonder if i turned the fan off whilst pressing on the brake the lights would then glow brighter, any thoughts or is this usual ?. The fan belt seems fairly tight.

[Kevinlincs]

Does it have an alternator, or a dynamo?
Dynamos' are notoriously poor at providing charge at low revs, the kind of scenario you are talking about.
That's why alternators took over, consistent voltage at all revs via the voltage regulator. Dynamos' can't supply enough volts at low revs.

If you do have an alternator then you should see between 13.5v and 14.5v at tickover which will drop with things like lights and heater motor on but still see around 13v all simply measured across the battery terminals.

A dynamo voltage will drop significantly at tickover, normal for what they are I'm afraid.

[Richard Fridd]

I have an ammeter intalled under the Flaminia dashboard. Dynamo charging is positve only at 1000 rpm. Anything under that even with only brake lights on for example, sends the needle to indicate discharge.

  Richard