Mysterious alternator issue

[CycleSi]

My Brise alternator failed recently on my R300K and Brise didn't have one in stock so I bought an equivalent AC Delco version (it looks identical). Fitted it and all seemed fine.

However, I have now noticed that around 5000 rpm and above, the red ignition light comes on. I am using exactly the same pulley sizes & drive belt as before. I was at Track n' Road with the two Steves on Thursday and they tested and it shows that the alternator seems to be working fine throughout the rev range even when the red light comes on above 5000 rpm as the battery is still showing around 14.0/14.1 volts so the battery is obviously charging. If the revs drop below 5000 then there is no red light and again the battery is showing around 14.0/14.1. 

So it all seems to be working except for the red light coming on at higher revs. I'm a bit confused why this might be happening and having the red light on indicates something is wrong.

Any ideas please?
 

[Jonathan Kay]

Those voltages are current rather than the original test?

What’s the terminal pattern and what wires are connected?

Is the lamp an LED or incandescent?

Jonathan

[CycleSi]

Hi Jonathan - those voltages are what we took on Thursday using firstly Steve's laptop for the MBE ECU and then secondly directly from the battery using a meter.

I have wired it up exactly the same as the old Brise alternator as they are identical. I just unplugged the two wires from the old one and plugged them into the same terminals on the new one.

I don't know what the lamp is - I don't really know what you mean other than it is the standard Caterham rev counter.

[anthonym]

Belt slipping? Nah. Loose connector in the light circuit.. vibrates loose ove4 5000?

[Golf Juliet Tango]

I'd say it is a dashboatd light/circuit problem not an alternator issue

[CycleSi]

Hopefully you are right. Is there any way of testing/checking this?

BTW, the belt is the correct tension and definitely not loose.

[EEK]

My understanding, +ve supply to one side of light, that then goes to earth via the alternator, so the light comes on, once engine running and voltage from alternator increases then affectively the earthing is switched off by the produced voltage.

So if the issue is a vibration or something causing an effective earth of the light and reason it comes on,  then if the wire from the light to the alternator is disconnected at the alternator then light won't work but once engine is at 5,000 light should come on. If it doesn't then suggests something in the alternator regulator pack is not quite right.

[CycleSi]

That sounds like a good idea to test that theory. I'll have a word with my mechanic mate and see what we find.

Thanks.

[CycleSi]

UPDATE - everything was pointing towards the new alternator being at fault so I ripped everything out/off today (including the exhaust) and refitted the original (now repaired) Brise alternator and everything is working perfectly again.

Just goes to show that identical alternators on the outside can be very different internally in terms of stators and other electrical gubbins.

[anthonym]

thanks for the update; been following your story (had my own a while back). Do we know what it was that was faulty and fixed inside the unit?  - anthony

[CycleSi]

Sorry Anthony - I don't know exactly what was fixed/replaced, but it was done by Lee @ Wood Auto who I stumbled across on the internet and he was brilliant. Real old school kind of chap. Charged me £80 inc. VAT & shipping.

Wood Auto Supplies Ltd
Cromwell Works · Colne Road
Huddersfield · HD1 3ES
United Kingdom
tel. +44 (0)1484 439000

[anthonym]

Np. Good recommendation too, thanks.