Lotus Elan

voltage regulator in a + 2 S

PostPost by: jeff jackson » Sun Oct 18, 2015 11:57 am

Hi all,
I'm a bit confused.
I have a workshop manual that tells me how to check and adjust the voltage regulator with lovely instructions and diagrams.
I want to check this because i have a new alternator, but I am only measuring 13V across the battery when the engine is running at 3000 RPM.
I have a 72/73 Plus 2 S.
Trouble is I can't see where the regulator box is located.
I have had the car 22 years and never had need to seek it out and in that time I cant recall seeing the thing anywhere!
Any help gratefully recieved!

Kind regards
Jeff
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PostPost by: Craven » Sun Oct 18, 2015 12:14 pm

Not totally familiar with the +2 wiring but an alternator usually has an inbuilt regulator, sounds if the workshop manual is referring to a car with a dynamo.
Charing voltage from an alternator is around the 13.8 ? 14.2 volt, I say around because there are lots of differing ideas on this.
Ron.
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PostPost by: rgh0 » Sun Oct 18, 2015 12:19 pm

Hi jeff

The adjustable voltage regulator box is for a car with a dynamo not an alternator like your car. Alternators have the regulator normally built into the rear of them and they are not adjustable. Take the alternator to a good auto electrician and they should be able to diagnose the fault and repair it. Alternatively just buy a new alternator as they are readily available and may be cheaper than rebuilding yours given its age

cheers
Rohan
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PostPost by: david.g.chapman » Sun Oct 18, 2015 6:56 pm

It is possible to raise the charging voltage on a alternator setup, but you should only try to do so if the earthing arrangement on the wiring loom is satisfactory i.e. all earths in place, with tight clean connections.

On some voltage regulators the output voltage is near the bottom end of the range, and may be about 13V.

if the voltage regulator (normally a module forming part of the alternator) has a separate earth wire, then a power diode can be wired in series with this earth line, so the line is cut and the diode wired into it. On negative earth systems the diode cathode goes towards the earth and the anode goes towards the regulator. A 5 amp diode will be plenty to handle the regulator current.

The diode will have the effect of raising the regulated charging voltage by 0.7V to 13.7V. I did this some years ago to my +2 and have not looked back. The only side effect with my Lucas A133 alternator is that the charging current does not kick in when the engine is first started until the revs rise to about 1500rpm. Once engaged though, the regulator stays charging all the time.

I must stress again that the wiring must be in good condition and earths in place or you will make things worse with unstable voltage drops. Also do not go above 14.5V or you will start blowing bulbs and overheating components.

Cheers,

Dave Chapman.
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PostPost by: jeff jackson » Sun Oct 18, 2015 7:46 pm

Hi All,
Thans for the advice and replies.
I'm sure there is something simple going on here (apart from me ) it normally is, it's just a case of tracking it down.
The alternator is quite new, about three years, So i would be disapointed if something has gone inside it.

Kind regards
Jeff
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PostPost by: david.g.chapman » Mon Oct 19, 2015 8:35 am

Jeff,

Its most likely an earthing fault. Under similar conditions with the engine at 2000rpm and nothing switched on have a look at the voltage on the starter solenoid terminals with your multimeter black probe on the engine metalwork. You should see 13.6V or more. The switch the headlights on and check that the voltage stays within 0.1V or so.

If not then have a look at the battery earth to chassis, and the chassis to engine earth strap. Clean everything up and try again.

Dave Chapman.
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