Failing alternator on K-series?

[Markharrison2]

Hi there, 
 
New owner here with a charging issue on my K-series. I've taken the car on two long runs (>50miles) but on the way home from the last drive, the battery started to go flat and after I got back to the garage the car would not start. Both times I've had the headlights on the whole time but been concious not to leave them on whilst the car is not running.
 
Whilst driving home down the motorway, it was getting dark and I noticed the headlights were intermittently/randomly getting brighter and then dimmer, but in general everything was slowly dying.
 
I enlisted the help of the previous owner (a mate) to help diagnose the fault. At first we thought it was an easy win as we noticed that the plug on the back of the alternator had a parted wire (brown with yellow stripe). So after repairing that and plugging this in now we had a red light on the dash when the ignition on...
 
So some testing
 
Engine off - ign on - red light on the tacho is on
Engine running - 13.5v (going on the multimeter reading) but the red light is still on
Engine off - ign on - unplug the brown/yellow wire from the alternator and the red light goes off
Engine off - ign on - short the brown/yellow wire to earth and the light comes on
Engine off - ign on - short the brown/yellow to 12v terminal on battery and the light is off

Charge at idle speed (1000rpm) - 12.8v
Charge at 2000 or above - 13.5v
 
Resistance to earth is 0.01Ohm between the engine block/alternator body/bracket and the negative terminal on battery.
 
FIA kill switch was replaced 700miles ago as this was faulty.
 
Its a 2006 car, but has been converted to EU2 spec as its got a VVChead/285's/jenveys/emerald etc and coils mounted under the intake.
 
Alternator is a bosch unit. Also noticed that the plug on the back of the alternator only has one wire (brown/yellow). The other wire is cut off flush with the plug. Only other conneciton on the alternator is the main chunky charge wire.
 
We tried checking the charge on Wednesday night and had trouble getting any charge from the alternator.... voltage between engine running (over 2000rpm) and stopped did not really change from ~12.2v. On Thursday we got the 13.6v readings mentioned above.
 
We are 99% sure its an intermittant fault with the alternator but want to double check before I buy a new one as Caterham are asking £270-odd for a new one. Is there a cheaper option off a Rover? I read the pulley might be different on a caterham.
 
Just to add another interesting twist, the low oil pressure light (yellow light on dash, triggered from a pressure switch in the oil feed to the mechanical oil pressure gauge) stopped working after we jumped the car... if you earth the lead to the switch the light on the dash works fine... and the body of the switch appears to be earthed fine as well based on multimeter readings. Coincidence or bad earth somewhere??
 
Any advice welcome
 
Thanks
Mark

[Albert Donaldson]

After changing the regulator on my bosch alternator 3 times due to it giving up on a 1600K with rev limit at 7600rpm, finally found that rpm was killing them with standard crank pulley regulator pack was turned to bottom to avoid heat which at first I thought it was.  Changed to R500 pulley and problems dissappeared, now run a rimmer bros aftermarket one without issues.

Alternator Assembly - 65 Amp - New - Aftermarket

Part No.: YLE101520P
- See more at: http://www.rimmerbros.co.uk/Item--i-YLE101520P#sthash.r8zGGOpd.dpuf

 

125 UKP.

Hope this helps...

Albert

[Markharrison2]

Thanks, what is the diameter of the r500 pulley you use? Is it as you received from rimmer? In which case around 50mm. My current alternator pulley is 52mm. Cheers

[Albert Donaldson]

The r500 pulley is at the crank, I couldn't measure the difference between the r500 alternator pulley and standard so didn't change:

its this one:

Crankshaft Pulley - R500

[Crankshaft Pulley - R500]

SKU: 73405

Crankshaft Pulley - R500
Price:
£57.60 inc. VAT
£48.00 ex. VAT
Availability:
Currently out of stock
0 in stock
Notify me when available

Unfortunately as you see out of stock. I was told that alternator rpm should not exceed 17000rpm, higher revving K's with standard pulley are exceeding this.

Rgds

Albert.

[Paul Deslandes]

Sounds as though the secondary diodes are failing in the alternator. Take it to a local auto electric specialist and they should be able to repair it for a lot less than the price of a new replacement.