My generator seemed to be operating fine until suddenly the light would not go out and the gauge needle not moving. I tried the attach a wire between the studs method and when I attached just one side of my volt meter to either side of the generator it swung wildly and would not settle down. I grounded the other side and no change. I measured 1.9 resistance on the armature and 6.9 on the field. No what do I do?

 

Have the Generator rebuilt at a competent shop or move to a look identical Alternator with PS pump offtake on the rear. Be suspicious of the Regulator. Check all connectors for corrosion. Are there any brushes left in the Generator? What is the state of the commutator?

If you can't sort call in a competent Auto Electrician.

 

these videos are GOLD!

it can also be used when the generator is OUT of the car.

you might want to loosen the belt a bit, although he didn't mention it.

 

The only problem with the video is it can all fall down under load. Not even mentioned!

 

Leave the generator in the car
Disconnect the two wires D and F from the generator.
Jumper a wire between the D and F terminals on the generator.
Connect a voltmeter between this jumper wire and earth.
Start the engine and rev it up but don't rev it over 1500 RPM!
You should see more than 14 volts.
If that is OK then the problem is in the regulator.
If it doesn't make 14 volts or more it is a generator problem.

The two most common problems I have seen in generators are
1. worn out brushes and
2 failed bearings which can lead to poling where the armature ends up rubbing on the fields.

 

I've done that. The problem is when I attempt to connect a volt meter to it the meter goes nuts and will not stop at a certain range. It jumps all over the place.

 

Could be intermittent brush contact. Have you had a look at the brushes?

 

Dynamos are fairly simple and robust. Most often the problem is, as Bill wrote, mechanical wear in the bearings and brushes. In this case, it sounds as if a brush has worn and collapsed.

 

Just to check, is the meter you are using a DC meter and if its both AC and DC are you using the DC voltage scale not the AC one?

 

He miraculously has a running engine & fully charged battery (14.2 volts) to hand. Cranking the engine to start an XK will knock the surface charge off of an SLA, AGM whatever battery pretty quickly thus the generator is placed under load immediately to top up the battery. Listen to Bill et al regarding state of bearings, brushes, comm etc. all not covered in the video.

I'll bet the generator needs a rebuild in the areas mentioned. Thereafter be suspicious of the regulator. It might be out of calibration & not getting the battery up to 14.2 volts or buggered.

 

All modern charging circuits cut at 14.2 volts. All modern Batteries are designed to be charged to 14.2 volts. (with a safety margin)

 

Battery charging circuits
When dealing with these older generator / regulator systems and lead acid batteries the maximum charging voltage parameters which are considered "acceptable" are 13.8 to 14.2 volts.
Anything above 14.2 volts will cause the battery to excessive gassing and possible overheating.
Below 13.8 volts will not allow the battery to not reach full charge.

 

Spot on Bill. Varta as an example that build Mercedes spec batteries that last 12 to 15 years (or more but become unreliable above 15yrs) will tolerate slightly more than 14.2 volts. They have a little clear breather pipe that's built into the car that you simply connect to the battery ~ they do not overheat (unless you stick 20 volts into them). Varta IMHO make the finest batteries available (some are rebranded ~ e.g. Mercedes Benz, Deltec etc.) You can see a Varta a mile away with their fold down carry handles that fold flush with the surface of the top)

I would stick to your rule of thumb ~ safe margin & sensible.

 

I have never seen a Varta battery in Aus. Perhaps I don't move in the right circles e.g. Mercedes etc.
All of the batteries in my 4 Jags and 2 other vehicles have fold down handles. (Korean, Thailand and Japan)
I would like to see a battery that lasts more than 5 years.

I bought a Mk2 3.4 automatic about 20 years ago from a "geriatric sale".
The owner had been committed to a nursing home due to alzymers and the family wanted the car gone.
The owner had apparently "fiddled " with the generator regulator and it was putting out over 16 volts. He only drove it for short periods and was frustrated at the battery going flat.
The underside of the bonnet above the battery area was rusting badly due to excessive gassing of sulphuric acid fumes.
In addition all of the front suspension rubber mounts were completely "stuffed" making it almost undriveable.
Another rescue!
Cheers

 

I replaced the original Jaguar batteries in my X type and XK in the last year making them 15 years old. Both were cases of me being suspicious that they might be tired. The XK had shown fuel levels that seemed too low and the X type slightly reluctant to start. A flat battery is such a pain that I prefer to be cautious and felt that at 15 years, they wouldn't last much longer. The replacements are Yuasa - they have good reviews and are a favoured make at the local spares shop.

I put an AC-Delco battery in the Mk2 in about 1980. The battery was inherited by two other cars and still going well in the second when we sold it in 1994.

A good battery can survive a long time. However, cheaper ones, guaranteed for two years, seem to expire at two years plus one week. I wonder if climate has had played a role in Bill's experience. Queensland may be more demanding than northwest Europe.

 

I'll bet those genuine Jaguar batteries were Vartas. Varta makes many OE batteries. Yuasa makes darn good batteries too ~ Japanese influence. I get fed up with these 3 to 5 year failure batteries like Willard. I always say to my Merc owning colleagues go to the agents for a new battery. Their pricing is competitive with the junk & sometimes cheaper in this country at least. I said to my friend that bought my previous Merc when it got to 15 years, change the battery. It still started the car with a brisk turnover but I said to him that it would likely let him down at an inconvenient time. As you say Peter flat batteries are a pain.

On MBWorld the only time Genuine batteries seem to have a 12 year life is the colder areas of Canada. I think that is climate driven.

 

Look at the Varta website. The have a very distinctive look & lower clamping rail at the base (look at the fine detail). If a battery only lasts 5 years it's cheap junk. Saying that ~ my new Holden Berlina battery failed in under 5 years when I lived in Sydney. I put it down to lack of use with my traveling 230 days a year. Sydney has a Mediterranean climate much like Cape Town. (My car allowance would have permitted a Merc but I thought when in Rome do as the Romans do. Don't draw unnecessary attention to yourself as an expat with the locals ~ drive what they drive ~ My only up-spec was to go for the Berlina version that had a few more niceties fitted vs the vanilla version)

I will show you many zero maintenance SLA (Sealed lead acid & AGM, aggregated glass mat/absorbed glass mat) batteries that last multiples of 5 years.

 

That’s a distinct possibility. The other possibility is that the post insulating the field (F) is loose and worn through and shorting intermittently on the case. I fixed a generator with this a few weeks ago - same symptoms.