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Alternator on my Crossflow


Golf Juliet Tango

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Ignition light does not extinguish.

Voltage = 12.8V when not running
Voltage = 12.5V at 3,000rpm

Are 90% of all alternator faults the voltage regulator?
What else should I check?  I want to be able to check exhaustively before swopping it out.

History:
Light came on as I queued to get out of Silverstone Classic on Saturday.  Got home (30miles) but bailed out of going on Sunday (shame but discretion...)
Driven a few times since (10 mile trips), always starting with a well charged battery.  No issues.

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Did the light used to go and off sensibly? Any recent work or changes?

Voltage = 12.5V at 3,000rpm

That's definitely too low.

Are 90% of all alternator faults the voltage regulator?
What else should I check?

Could still be a wiring fault. How many wires of what colour and thickness are connected to the alternator on how many terminals?

Check belt.

Check all connections including at the battery and the relevant earths: inspect, wiggle, disconnect, clean, reconnect.

Then measure those voltages again, and if they're still the same, measure at the alternator terminal.

Jonathan

 

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+1 failing to do that cost me an un-necessary new alternator. Ideally disconnect the B+  to be sure you are testing the alternator and not the connector. Mine looked fine, but wasn’t, it was held together by the pvc cover on the wire. A local garage assured me it was goosed: it wasn’t. 

Anthony

 

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To add to Anthony’s point, if you haven’t yet checked the alternator push, it is best to do so with the earth direct to the battery at this stage. That should help isolate earthing issue with the unit or the engine

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@Jonathan: 

NB: That test should be done with all of the wires still connected.

Why? Is there a risk to the alternator?

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could do with a better pic, can't zoom this as it loses resolution.

B+ usually brown (never seen other on Caterham, but only seen K)

D+ usually black  (never seen other on Caterham, but only seen K)

If that thin one is the D+ (warning light) then disconnecting it will extinguish the dash warning light and identify it (switch off first to remove) 

You mention a sense wire, that (from painful experience) goes either direct to the battery (to sense the voltage and this feed back (inform) to the regulator) or nearby distribution post if there is one (cutout switch decides this) -

If the two thick ones are a combined (I've never seen thus so new to me) B+ (main feed to the battery, can you see them arriving at the battery positive?), then the thin one is the D+(warning light) not a "battery sense" wire.

As far as I know we always have B+ and D+ and sometimes a sense wire, based on alternators I have here (for K). The (battery) sense wire is optional if present, say the instructions (and Time Brise) on my Brise (and anyone reading this in the future watch out for a parasitic drain via sense wire, make sure it is cut by the cutout if you have one). 

Wiggle the wires, make sure they are not overly stiff (heat fried=bad, or fried covering=misleading).

of course a flat battery will be an indication! Carry a booster, park on hills :-)

Wonder if your 21 alty works in a Crossflow (no idea).

... must be someone here with a crossflow? 

edit: following others' suggestions on here after my alternator trials (both tintop and 7 this last year) I use something like one of these now: https://www.arc-components.com/0-534-10-durite-12v-24v-red-lcd-battery-voltage-monitor.html  (there may be better device suggestions, but that's the concept). I have found it a great comfort knowing my voltage is always good and it's also interesting to see the ups and downs as circumstances change, not least start up).

anthony

 

p.s. are those labels on the wires? 

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My understanding is that in"modern" alternators the ignition light gets +ve feed which is earthed via the alternator, this is the sense wire that "feeds" the alternator regulator. The sensed voltage determines how much current to feed to the rotor, controlled by the regulator,  and thus the magnetic field strength of the rotor. The strength of this magnetic field determines how much current the stator produces and sends to the rectifier assembly and thus the output current at B+

I say "modern" because being as it is a cross flow not sure how old alternator is and if the technology has changed. I currently have a couple of alternators off my 1994 Defender in pieces so fairly well versed on issue around that vintage. My sense wire is brown/yellow stripe but that is NOT on the Caterham, that being said on the Caterham there is a brown /yellow so some consistency

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There's quite a large range of terminal patterns, but age and country of origin does narrow it down. 

I'm being deliberately cautious in ascertaining what Stephen has because it's an old Caterham!

The last factory wiring diagram for Ford engines (before the modern era) is 1996 and has:

Screenshot2019-08-03at10_20_30.png.166e9eea09ca6faea93b611ba6061ac6.png

Jonathan

PS: British "standard" wiring colours: often helpful in finding what's what. 

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All connectors at rear connected, wiggled, cleaned.

I'd check the other connections before swapping anything, as in post #2 above: the connections at the battery, and however the alternator is earthed.

And the voltage at the alternator output terminal at idle and 3,000 rpm.

Which is the case - ignition light extinguishes if removed

The wire coloured NY should be "Alternator to "no charge" warning light". Sounds as if that's fine.

Do you also have NB: "Alternator battery sensing lead"? (Usually thin.)

Jonathan

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