Low alternator charge

[andyhay]

Hi All

I would really appreciate some advice on an alternator charging issue I have with my plus 2.

The car has a Lucas 17acr alternator. Some time ago the battery went flat and the alternator would not supply enough power for lights etc.

I replaced the battery and all was well but at 2000rpm the charge to the battery was only around 13v - I believe it should be 14v. I suspected a tired alternator and so replaced it. Charge to the battery is still only 13 volts. There is obviously a loss of voltage from the alternator to the battery in the back.

This is fine on a freeway trip during the day without the cooling fan, but if the lights are on and the fan is going the battery voltage drops and I could get caught out. The car was fully restored around 10 years ago including a new wiring loom.

The alternator is earthed with a thick cable to the chassis and everything else electrical on the car works well.

Any suggestions on what I should check next?

Any help is much appreciated

Regards

Andy Hayes

[john.p.clegg]

Check the size of the alternator pulley,lotus ones were a larger diameter to slow the alternator down as the engine is high revving,if you're not racing around at 6500 all the time,decrease the pulley size..

John

[oldchieft]

if it's gone from working right to a problem then it won't be pulley size.

(unless the new alternator had the wrong pulley already fitted)

I would be looking for a bad connection in the feed to the battery

Jon the Chief

[nmauduit]

I assume you are sure your battery is not bad - if it's on the low side of 13V I would suspect a rectifying diode getting bad, then the charge intensity would be weak as well : you can check them with when taking out the plastic back, and you can easily replace them (in the UK a kit with the diode unit plus regulator can be found for less than 15 pounds).

[bob_rich]

HI Andy

How did you check the battery voltage? was it with the battery condition meter on the dashboard-these are not that accurate. A Multimeter, preferably a digital one, would confirm the battery voltage.

Hope this helps best of luck

Bob

[andyhay]

Thanks for the responses

A few clarifications:

The battery is brand new and performing well

Voltage taken at the battery with a digital multimeter.

The new altenator is behaving exactly the same as the one I replaced- 13v at the battery so the altenator isn't the problem.

I suspect the car has had this issue ever since it was restored but the previous owner didn't detect it because he always trickle charged the battery.

It could be the pulley size but then it would reach 14 v somewhere in the rev range - which it doesn't.

Thanks again

Andy

[Grizzly]

Andy,

I have a similar issue with my 17acr, if i leave it idling for more than 10-15 minutes with anything electrical on i would find things like the window motor and Wipers would start going slower. To fix this i tried all sorts (fitted the smallest pulley i could find, new Bushes in the alt things like that) with no joy.

Thing is though if i drive the car rather than it sitting idling i get the same 14v at the battery and every thing works as it should which started to make me wounder if the Crank pulley was not big enough for that Alternator?

Strangely if i start my car without revving it and it idles below 900rpm the Ignition light doesn't go off..... The battery stays at 12v until i blip the throttle to say 1000rpm, the light goes out and the Alt comes to life. That also makes me think it's not turning fast enough.

[Craven]

I posted this some time back, you may find something useful here.
Check the alternator output voltage at the alternator itself and work back toward the battery using different earth points as well.
Ron.
http://www.gomog.com/allmorgan/LucasFault.pdf

[nmauduit]

Thanks for the responses

A few clarifications:

The battery is brand new and performing well

Voltage taken at the battery with a digital multimeter.

The new altenator is behaving exactly the same as the one I replaced- 13v at the battery so the altenator isn't the problem.

I suspect the car has had this issue ever since it was restored but the previous owner didn't detect it because he always trickle charged the battery.

It could be the pulley size but then it would reach 14 v somewhere in the rev range - which it doesn't.

Thanks again

Andy

ok, then an other lead would be to look into the alternator wiring : in case of a conversion reusing the old dynamo regulator, you may want to double check that this dynamo regulator is not working against the internal ACR 17 regulator. There may be different ways to do it, what I did was to unplug (and isolate) all the "hot" (not earth - if you have negative earth that is) wires from the old external regulator. The wiring of the ACR unit is very simple : the 2 wide spades go directly to the battery positive (2 thick brown wires in the standard loom - I routed one to the starter solenoid input, the other to the fuse box), then the thin spade goes to the dash charging light circuit.

When you rev a bit (say 3000rpm) you should go over 13.0V with a circuit behaving normally, and if your battery has gone a bit low for some reason you should see the voltage increase slightly over a minute or two with a digital multimeter. If this restores your charging circuit, you may then look further into the old dynamo circuit to see which wire was triggering the old unit against the new one and isolate only what needs to be.

good luck !

[bob_rich]

HI again Andy

as an earlier post says the voltage at the alternator output with the negative on the alternator body would confirm if the alternator can give around 13.8V to 14.4V

A re-check on the voltage at the battery terminals would be worth while then switch on the a significant load current say full side and main beam headlights. How does the battery voltage look now? How it changes will give a clue.
If it dips noticeably then there could be a wiring volts drop. but if it doesn't change then the charging circuit seems to be basically working.

It is not unusual to loose around 0.5V in wiring and also in the earths. It is unusual but not unknown for corroded terminals to pass current oneway ( so car starts OK) but then when current reverses alternator pushing current into the battery a small voltage drop is developed A corroded terminal can sometimes behave a bit like diode.

Hope this helps

best of luck

Bob

[rcraven]

Could it be something simple like a faulty or dirty alternator plug or poor connection to the plug? The plug and wiring can get quite hot from the exhaust.

[andyhay]

Thanks everyone

Plenty for me to investigate this weekend. Very helpful.

What voltage do others with this alternator get at the battery? Maybe it's not far off normal with the voltage loss to the back of the car?

One other thing I've noticed, the alternator gets very hot very quickly. After a 10 minute drive it's too hot too touch. If I wet my finger it won't sizzle so it's under 100 degrees c. But still very hot
Is this normal?

Thanks

Andy

[Grizzly]

One other thing I've noticed, the alternator gets very hot very quickly. After a 10 minute drive it's too hot too touch. If I wet my finger it won't sizzle so it's under 100 degrees c. But still very hot
Is this normal?

I found when i had a Stainless exhaust manifold on the Alt would get so hot the black plastic cover on the back melted, i replaced the Stainless with a Ceramic coated manifold and the Alt still gets warm but is comfortable to touch. On my other Elan i have an original Mild steel manifold and that is firmly in between the two (Alt gets hot but on the verge of comfortable/uncomfortable heat).

As for battery voltage, at idle i get about 13.8v and at 3000rpm i get 14.2v from my ACR17 (when the ignition light is out)

[nmauduit]

Thanks everyone

Plenty for me to investigate this weekend. Very helpful.

What voltage do others with this alternator get at the battery? Maybe it's not far off normal with the voltage loss to the back of the car?

One other thing I've noticed, the alternator gets very hot very quickly. After a 10 minute drive it's too hot too touch. If I wet my finger it won't sizzle so it's under 100 degrees c. But still very hot
Is this normal?

Thanks

Andy

if it gets hots just by itself (i.e. electrically) what I would do is take out the alternator and check the circuit : it could be as simple as a small short (wire bent, isolator cut...) in one of the 3 charging loops, or a plain short. 2 out of 3 charging loops would give a behavior as you described, 13V at most a low current. This is assuming you have by now unplugged any potential conflicting wires from the old regulator.

[andyhay]

I think it does get hot by itself. It was hotter than the engine after running for 10 minutes. I will try and investigate the regulator and charging loops. I think I'm getting out of my depth doing this. Should I just take it to an auto electrician?

Thanks again for all help everyone.

Regards

Andy