Club 80-90 Forums

bigherb wrote:

itchyfeet wrote: Ok just checked the lucas currently in the van and it does the same as bigherb says, no power until you rev it a bit for say 20 seconds then it starts producing power, let the revs die down and it continues producing power.

It is not actually time, it is RPM dependant, you can rev all day but unless you reach the RPM threshold around 3000 RPM alternator shaft speed 1500-2000 RPM crank speed it won't self excite.

Mmm interesting, i did rev up just past 3k and it took a while to start held at that rpm, is it just a small band of revs?

Hi Itchyfeet,yes I missed the bit about checking the alternator output with the blue wire disconnected!
I replaced the alternator because of a seezed [sp] rear bearing and a broken up front bearing!!
My bit about having to rev to 1200rpm to get the charge light to go out [and the rev counter to work] was just for info [and the blue wire was on tight]

itchyfeet wrote: Mmm interesting, i did rev up just past 3k and it took a while to start held at that rpm, is it just a small band of revs?

No it has to reach a trigger voltage and as a generators voltage is RPM dependant the faster it turns the higher the voltage, left unregulated it can go past 30v. The battery charging voltage is reached around engine idling speed below that the voltage is too low (remember the flickering battery light on a dynamo if the idling speed was to low) above that the voltage has to be regulated. If the alternator is relying on residual magnetism it is less efficient and has to turn faster to reach regulation voltage.

bigherb wrote:remember the flickering battery light on a dynamo if the idling speed was to low

No im not quite old enough all my cars have had alternators

ok so case closed, thanks