The Rovering Member
Well-Known Member
stina said:O.k Ron .
Thanks
I second that emotion.
Glowing Ignition Light
- Thread starter The Rovering Member
- Start date
I second that emotion.
Is it silly comment season ?
If your alternator doesn't charge at tickover , it means that when you stop at junctions ,traffic lights etc, the battery is discharging . Not good if you've got your lights , HRW etc in use. If I was using mine daily I'd upgrade to a modern high output alternator
If your alternator doesn't charge at tickover , it means that when you stop at junctions ,traffic lights etc, the battery is discharging . Not good if you've got your lights , HRW etc in use. If I was using mine daily I'd upgrade to a modern high output alternator
darth sidious
New Member
DaveHerns said:
Certainly not desirable to have the alternator giving little charge out when in tickover. That said, our old Vauxhall Astra had a similar characteristic; at tickover (engine hot, about 800rpm, no extra electrical load) the voltage across the battery was ~13.5V. However when the throttle was just slightly opened to increase the revs ever so slightly, the voltage increased instantly to ~14.2V, where it stayed no matter how fast the engine was revved up (i.e the regulator was working)
I think the 'problem' was because the diameter of the bottom pulley wasn't that much larger than the alternator pulley, so at tickover the alternator rotor speed was maybe below a threshold, but crossed that threshold with a slight increase in engine revs above tickover speed.
The Astra only had a 4 speed box and a low ratio final drive; I'm sure the engine was revving ~3500rpm @ 70mph. My theory for the bottom pulley being not that much larger than the alternator pulley was because the engine wasn't that big/strong and also would likely spend more time at higher revs; in other words if the bottom pulley was larger, the alternator would spend most of its life being subjected to higher rotor speeds than it would if it were fitted to a larger engined car.
Now given that stina's V8 idle is quite low, I think that's the main factor to her alternator not charging as much as would be hoped for at idle i.e. even if she were to fit a high output alternator, I'm not sure that would solve the issue as the idle speed (and therefore the alternator rotor speed) could possibly be still too low.
suffolkpete
Member
When the warning light is on, the alternator is being excited via the light. As the revs increase, then the output rises until the alternator is able to self excite and the light goes out. Once this threshold is passed, then the excitation current is often sufficient to maintain the output even if the revs drop again. All modern alternators have this characteristic, it's just that in a lot of cases the revs are always high enough for you not to witness it. Alternators are capable of withstanding rotor speeds of 12-15,000 rpm so you could probably drive it at 2.5 times engine speed on a P6.
darth sidious
New Member
suffolkpete said:
Ah, that's not quite what I meant: I was meaning when the car was idling (even after being revved for whatever reason - being driven, been on choke, etc), the voltage level dipped somewhat without the ign light coming back on. I've no doubt the thing was 'charging' (i.e. the alternator was still self-sustaining and not pulling current through the lamp), just not quite able to hit the regulated voltage without the engine being slightly above tickover
The wonders of modern components! The Astra wasn't what I deem modern though (1990ish, it had bloody points and condensor would you believe?!). Still miss it though, had many journeys and adventures in it.