strange charging light behaviour!

[cortinaman]

I like your logic - thanks for the info.

[cortinaman]

Quick update - I roped in my mate Martin, who knows about old car electrics. We found that the conversion to an alternator seems to have been done by someone with even less knowledge of car electrics than me (if that is possible). So having replaced the wiring to the generator light, which was wired up wrong,(but didn't cure the problem) and then followed fr€$h&m1nt¥ 's advice and ran a cable directly from the alternator to the battery we have 13.5v - 14v across the battery! Hooray!

The wiring has been bodged, and where it hasn't been it is 50 years old - so I think its time to bite the bullet and re-wire it. Any suggestions for universal wiring looms? I can get a standard replacement loom, but ideally I would like to add a few more fuses (only two as standard!) and relays, plus relocate the battery in the boot.

cheers folks

cortinaman

[fr€$h&m1nt¥]

Good news cortinaman glad I helped in some way.

[joostvdw]

For future reference, if it's an internally regulated alternator (and not a dynamo, or externally regulated alternator like on some older cars) it will have at least 1 fat connection for the charging current and 1 connection for the battery light on the dash. Besides being a charging indicator the battery light is an essential part of the alternator; when the engine isn't running but the ignition is on, the light is illuminated meaning there is a current going through it, this very same current is also going through the rotor of the alternator via the indicator connection. This current is what is needed to "kickstart" the alternator into working. Once the engine is running and the alternator is generating it's own power, the indicator light connection on the alternator goes to +12v turning off the indicator light (it will have +12v on both sides, so will be off!).

This all means that to get an alternator to properly charge, you will need a proper low-resistance connection between the battery + and alternator and a small light bulb (test light if you want to check if the alternator is properly "kickstarted")connected to +12v on one side and indicator light connection on the alternator.

[cortinaman]

Hi Folks - I can't believe its 2 years since I started this thread! The jag has been in the garage for most of that time being welded! Back on the road now, and the charging problem is largely sorted...........but!

Generally, when driving around the charge light is out, but when it's first started and is sitting idling (warming up) if the idle speed drops the charge light comes on (it tends to go off when idling with the choke on, and when you turn the choke off the revs drop a little and the charge light comes on) a blip of the throttle puts the light out again. All fine - I can live with that.

However, now when the engine is hot after a run, the charge light sometimes flashes on when running at fairly slow speed (20mph) and comes on when idling and needs quite a big "rev" to put it out.

Is there anything other than a duff alternator it could be? I do wonder whether the alternator/regulator was damaged by the previous dodgy wiring.

any thoughts?

cheers

Cortinaman

[colnerov]

Hi, Sounds like it's as simple as raising the tickover a little. Or if you don't want to do that because it thumps into gear if automatic, see if you can find a smaller alternator pulley

Colin

[jifflemon]

Quick and simple charging checks:
1) Make sure the dash light illuminates before cranking - It provides a 12V to the alternator to start the charging process.
2) Standing Voltage at battery should be 12.6 or above
3) At idle, you should be seeing 13.6 or above at the battery.
4) Check the voltage at the alternator (sound like you've a euro plug - 2 big spades, one small), check between one big spade and alternator body - Should be above 13.6 at idle.
5) Check voltage between alternator positive (big spade) and Battery positive terminal - Anything more than .5v is bad and investigating (new wiring/terminals)
6) Check voltage between alternator body and battery negative. Again anything more than .5v and you need to be checking earthing (engine to body, or sometimes, alternator to body)

[cortinaman]

Oct 24, 2016 18:21:23 GMT jifflemon said:

Quick and simple charging checks:
1) Make sure the dash light illuminates before cranking - It provides a 12V to the alternator to start the charging process.
2) Standing Voltage at battery should be 12.6 or above
3) At idle, you should be seeing 13.6 or above at the battery.
4) Check the voltage at the alternator (sound like you've a euro plug - 2 big spades, one small), check between one big spade and alternator body - Should be above 13.6 at idle.
5) Check voltage between alternator positive (big spade) and Battery positive terminal - Anything more than .5v is bad and investigating (new wiring/terminals)
6) Check voltage between alternator body and battery negative. Again anything more than .5v and you need to be checking earthing (engine to body, or sometimes, alternator to body)

Thanks for that Jifflemon - really helpful. I'll get the multimeter out at the weekend and see what we have!

Cortinaman

[cortinaman]

Well, I've finally found some time to look at the jag. Checked the voltages as per Jifflemon's advice and got:

Across battery (engine off) 12.6v
Across battery at idle 12.6v
Across battery at about 2000rpm 14.1v
Same results from the large spade connector on the alternator, both when earthed to the casing and to the battery earth.
Voltages from alternator spade to battery positive and casing to earth both 0v.
Now the odd bit. The charge light going on and off does not seem to relate to the charging voltage. It sometimes comes on when the voltage is 14v and sometimes is off when the charging voltage is 12.6v. It tends to go off when I rev the engine, but the other day came on about half brightness when driving along.
Seems to make no sense, any thoughts?

Thanks in advance
Cortinaman

[slater]

Your underspeeding the alternator by the sound of it. Probably just need a smaller pulley on it.. If you need to do anything at all that is. If it ain't broke don't fix it!

[cortinaman]

Cheers Slater. Doesn't the fact that the charging light doesn't seem to relate to the charging voltage suggest something is wrong - maybe I'm still not understanding how this works?

Hmmmmm....where am I going to find a smaller pulley?

[cortinaman]

A little update for anyone who is interested.

I found I had a spare Lucas alternator in the shed which I had forgotten about, and thought I might as well try it to see if it made any difference - well it only fixed the problem! Charge light goes out when it should and all working normally (fingers crossed). Looking at the alternator which I took off the car, its a Chinese Lucas copy which I guess says a lot about its quality.

I'm still going to get the wiring done but at least the charging problem is sorted.

thanks for all the help.

Cortinaman