Alternator or battery issue?

[Bill Jennings]

Hi All,

Hope you all had a Very Merry Christmas!

The car is a 1977 Carrera 3.0 with external regulator.

A few days ago I noticed the alternator light was starting to stay on first at low revs then gradually higher revs. I have also noticed occasional erratic tach either no reading or wrong reading the past month or two.

The alternator belt is tight and the Bosch battery is of unknown age though it held it's charge for three months last april when I shipped the car from the UK to OZ.

I use the car at on average once a week and it has always started and turned over easily.

I realised the car was running on battery only after a 50 km drive on Christmas day when I only just had enough juice to get home.

I also had a very erratic tach the last 20 minutes of the drive.

It took over 24 hours to fully recharge the battery with my smart charger and I then did the following tests. This is the only time I have had to charge the battery since owning the car.

Battery voltage
13.21v car switched off
12.29v at 1000 rpm no load
12.29v at 2000 rpm no load
11.91v at 2000 rpm with load (fan, rear defrost + lights on)
12.65v after tests with car switched off.

So is my issue battery, alternator or regulator or a combination of more than one.

Many thanks in advance and a Happy New Year to all.

Cheers

Bill

[twistoffat]

Its the Alternator. With the Car running the Battery Charge should jump to 14.5

[James Brown]

yep, sounds like a alt./regulator

[Bill Jennings]

So are these alternators fixable/rebuildable or do I need to buy a new one plus a new regulator?

I note from the regulator part number with our host that this alternator should be a Marchal 55 amp which is not available.

I see that design911 in the UK has a replacement alternator but it is not a Genuine Porsche part.

Anyone have a working alternator they are willing to ship to OZ?

Cheers

Bill

[mreid]

You can't say alternator just because the voltage doesn't come up when the engine is running. It's not the battery, but if it is older than five years I would replace it for peace of mind and avoidance of future trouble. That won't fix this problem.

There is a test where you jumper the regulator sensor wire to turn on the regulator to see if it works properly, but given your battery isn't charging at all and it hasn't overcharged, it probably is the alternator. However, the regulator is easier to change and cheaper and given the age of your car wouldn't be bad to have a spare on hand, I might change it first before the alternator.

[Bill Jennings]

mreid,

Any pointers on the regulator test? Anyone?

I was planning on ordering a regulator from our host as a starting point but didn't realise their was a test you could do on it first.

Cheers

Bill

[K Sykes]

An alternator shop can test and potentially rebuild yours. Given shipping costs to your area, I'd suggest that as a first step. You can have the battery load tested as well, to avoid the trap of just buying new stuff and hoping it works.

[K Sykes]

One other thing, if you buy a new or rebuilt, you can get a newer one with an internal regulator. Lot's of threads on the conversion.

[CCM911]

Find a good auto electric rebuilder. I had mine rebuilt for about $100USD. I think you really should be seeing about 14V when you rev the engine.

[scomiro]

Wouldn't even waste time messin with it , just replace both , i spent the better part of the day screwing around with mine ,replaced the voltage regulator , then the alternator went out four days later , had mine rebuilt, kept the new regulator i just bought ....no problems since.

[timmy2]

If you are budget concious, you can take out the regulator, drill out the 2 rivets holding the metal top on, and look to see if the resistors or other components inside have failed.
Easier than pulling the alternator.....

That is what happened to mine last spring.
I put a new electronic regulator from our host in, and it has worked fine since then.
(I have a new alternator sitting on the shelf as well)

[sp_cs]

K3 alternators are Australian
PRTechnology » Porsche Service & Porsche Racing » K3 replacement alternators

[wwest]

Originally Posted by Bill Jennings

Hi All,

Hope you all had a Very Merry Christmas!

The car is a 1977 Carrera 3.0 with external regulator.

A few days ago I noticed the alternator light was starting to stay on first at low revs then gradually higher revs. I have also noticed occasional erratic tach either no reading or wrong reading the past month or two.

The alternator belt is tight and the Bosch battery is of unknown age though it held it's charge for three months last april when I shipped the car from the UK to OZ.

I use the car at on average once a week and it has always started and turned over easily.

I realised the car was running on battery only after a 50 km drive on Christmas day when I only just had enough juice to get home.

I also had a very erratic tach the last 20 minutes of the drive.

It took over 24 hours to fully recharge the battery with my smart charger and I then did the following tests. This is the only time I have had to charge the battery since owning the car.

Battery voltage
13.21v car switched off
12.29v at 1000 rpm no load
12.29v at 2000 rpm no load
11.91v at 2000 rpm with load (fan, rear defrost + lights on)
12.65v after tests with car switched off.

So is my issue battery, alternator or regulator or a combination of more than one.

Many thanks in advance and a Happy New Year to all.

Cheers

Bill

"Slow" degradation of charging capability would indicate worn out, wearing out, slip ring brushes.

[Bill Jennings]

sp_cs,

Many thanks for the local supplier of new alternators they are $825 though!

I might try and see if I can find a local rebuilder first!

Cheers

Bill

[wwest]

Originally Posted by Bill Jennings

sp_cs,

Many thanks for the local supplier of new alternators they are $825 though!

I might try and see if I can find a local rebuilder first!

Cheers

Bill

You can buy a slip ring "kit" for less than....$25?

Buy even if it's only the slip rings you should closely look over the stator wiring insulation and the wiring mounting insulators.

[Bill Jennings]

Finally got around to pulling the alternator out and I believe it was removed recently.
I bought the car last april but I don't know it's recent history before then.

The fan just pulled from the shaft by hand no resistance at all and the alternator looks clean compared to the fan and shroud.

I also noticed that one of the female spade connectors (3 brown wires) was much wider than the male spade terminal it plugs onto and it was a little loose. Is this an original connector if so I can just squeeze it to tighten it or should I solder the 3 wires together and connect to a smaller connector with a single wire?

Another observation is that my external regulator's part number gives my alternator as a 55A Marchant but this alt is a Bosch 0120400 cant read the rest of the number. I guess it may be a remanufactured replacement?

Can anyone identify this alternator?

Cheers

Bill

[Targalid]

Hey Bill,
I had the same problem and it was the voltage regulator. On your car, I believe the voltage regulator is right next to the CDI box on the driver side of the engine bay unless your car has been changed to a more modern VR/alternator system with the voltage regulator mounted on the base of the alternator. You can check VR function while driving with a voltage tester plugged into the cigarette lighter to check for errant pulses from the VR. Mine would jump to 17 volts and then drop to 11 or so, indicating intermittent charging. A voltage regulator is pretty cheap, less than $50, while the alternator is more as you have learned. Change the voltage regulator first and see if it fixes the problem. It only takes a couple of minutes to swap it out.
Al

[Porboynz]

With the alternator on the bench its easy to inspect the slip rings and brushes, simply undo the 2 slot head machine screws and take a look. The brushes should have plenty of length and spring tension to hold them against the slip rings which should be reasonably smooth and ungrooved. My next bet would be poor contact with those spade connectors, clean them up then use pliars to carefully crush them just a little so they have renewed stiction when you slide them on.

[Porboynz]

By the way, where is the earth strap from an engine case bolt to the fan housing? I can not see it in the photo.

[Bill Jennings]

Porboynz,

Your right there isn't a earth strap to the housing from the engine and there hasn't been once since I bought the car.
There is a brown wire to the housing that exits from the coil loom though!
That bolts on the same place on the housing as the ground straps for my spark plug wires.

Does a Carrera 3.0 need/have another earth strap?

Cheers

Bill