Charging Issue (again!)

[YellaBelly]

Having recently replaced the alternator on the Locost, all was well. But the car has been sat for a few weeks doing nowt and after I sorted the clutch pedal mod, I gave the car a start to get things moving again, but unfortunately the charging light is being silly!

When I first start the car, the light stays on (always has done - revving the engine used to extinguish it), but when I rev the engine, the light almost goes out but stays on as a faint glow. When I take the revs up to 2500rpm or so, it gets brighter!! I have checked the voltage at standstill and it is around 12.6V, when the car is started it rises to about 13.2V or so. If I take the revs up past 1500rpm it goes up to around 14.6-14.8V and steady. If I hold the throttle at around 3000rpm, the light stays bright for a couple of seconds, then goes dim and back to bright again. It keeps doing this as long as I am holding higher revs??

I'm guessing the regulator is OK as the voltage seems to be around the normal. Switching the main lights on drops the voltage by around 0.2V so no problems that I can see there.

Has anyone got any ideas please?

JB

[stevel]

Hi John

I had a problem with my alternator not charging and initially thought it was the regulator so bought one off ebay (couple of quid).  When i took the cover off my problem was apparent.  One of the spade connectors was broken but would make contact occasionally.  For example the light would come on going over bumps, etc.  May be a complete red herring for you but worth a check.

[Camber Dave]

I'me no car sparky but the alternator charges alternating current (no s**t Sherlock). 3 phases of Alternating current pass through a grid of Diodes (one way gates).
The diodes only pass +  direct current to the the M8 terminal to charge the battery and feed the car electrics.
One of your diodes has failed so allowing a - flow of current. This also goes to the smaller terminal and so disrupt the opposing balance of currents that normally distinguish the light .
The earlier small glow in the warning lamp is an early warning of diode/alternator failure.

Dave

['The Gaffer']

First thing I would check is all of the light circuit and regulator connections for corrosion, I would then check all ground and battery connections for the same.

[paintman]

Just get another alternator......it's less stressful!!!

[YellaBelly]

Thanks for the input guys. Dave, I am a techy by trade and know exactly what you mean with the diodes but I must admit, I never thought about a single one going and giving an output on the negative cycle! I think it would be worth me taking the didode pack out and whacking a DVM across them to check

I don't really want to get another alternator as this one has only done a handfull of miles from new.

[Grin-a-lot]

A full wave rectifier will most likely be a graetz bridge type or centre tap - either way a failed diode will allow some current leak which might explain the light being on; we use a similar light principle on the 4160v systems I work with to detect a diode ring failure (which stresses the others meaning the system will fail completely within hours).

It should be easy enough to find the defective diode and swap it out.

[YellaBelly]

Yep, that's my next step Darren. I'm going to remove the unsolder the diode pack and check them out. If need be, I've still got my old alternator to use for spares if they're OK. If not I think a new Diode pack is only around £10. I might even upgrade the diode pack to a 70Amp one as they fit the same plate.