Intermittent voltage regulator cut-out

XJ
1

Hello all,

so far I had no reason whatsoever to complain about the electrics of my XJ: left unmolested and kept in shape most everything has worked so far.

The one thing that has not worked as it should over my years of ownership is the rear heated window. After I got annoyed somed days ago I made up an electric flow diagram and found out that the RHW has a second control light in the speedo. Last night I checked, found out that the control light didn’t come on and tried to “exercise” the switch. In the course of this repeated switching a mysterious thing occurred.

All of a sudden my windscreen wipers became faster and the instrument lighting much brighter. The dashboard voltmeter maxed out. I reacted by reducing engine speed, switching off the wipers, turning down the rheostat and - finally - switching off the rear heated window.

Some moments later things got better and system voltage returned to a normal state.

It all looks as if the voltage regulator cut out for a certain period of time. Is this a typical failure mode? Do you see any connection with the heated rear window thing - the heated rear window is supplied through the ignition protection relay? Why on earth does the voltage rise to +18 V at engine speeds around 1500 RPM? I would have expected this to happen more at like 4000 RPM. Questions over questions for the holiday seasons …

Thank you all in advance

Best wishes

Jochen

75 XJ6L 4.2 auto (UK spec)

2

Jochen,

Your charging voltage should never reach 18 volts. Ever.

If it does then it is definitely a problem with the voltage regulator.

I can’t remember the details of your model, but i think it’s an internal regulator with a sense wire. Check the wires at the alternator, it could be as simple as a poor connection on the sense wire.

Don’t run the car until you’ve tracked the cause down, that will just ruin your battery.

3

Jochen,

a few things:
-The light in the speedo is 24 Volts afaik.
-Could it be that the regulator gets too hot under that high of a load and then stops regulating?
-What do you mean by second light - is the first light in the switch (not the case), did you refer to the backlight (heh heh), or is there another lamp?
-It would be weird if all the current went through the protection relay. You should find that the switch is supplied by that one, but the heating current is certainly switched by a RHW relay. In SIII RH cars it’s above the drivers side fuse block.

My guess would be that the wiring is fine, but the regulator is toast. The sensing wire might be a good guess, but that would probably be more intermittent - I think? What happens if you switch on all lights, full AC, wipers and the cigarette lighters? Provided the load is similar you might be able to rule out something… good luck!
Don’t ruin your battery, but it should be able to take higher voltage for a few seconds.

David

Second guess, a bit wild though: what if the battery is bad, stops charging and the missing load and voltage tricks the regulator ot alternator into supplying all it can?

4

I had the same issue with my newly acquired Series III. it cooked the OE radio. to answer the question why? The mosphet(s) are cooked; which essentially lets any amount of current pass through the regulator until a capacitor pops. then it’s lights out. :frowning_face:

In a perfect world, voltage should hover around 14.5 volts. Like I said, I had the same issue and I replaced the alternator. I don’t know if your Series II has a separate voltage regulator, my '74 SWB Series II doesn’t (it’s in the alternator). Replacing the alternator. Problem solved.

Well one of them. Now I’m having to flush the fuel system. The car was $400.00 I can’t complain too much. Right? I keep telling myself that…

Cheers!
Mark

5

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In principle, David; a properly working regulator cannot increase voltage - it can only prevent excessive voltage…

There are of course dire warnings about shorting the alternator to ground or running the alt disconnected - but like a battery; increased load lowers voltage. A voltage regulator fault, for whatever reason, is the most likely problem for Jochen…?

Frank
xj6 85 Sov Europe (UK/NZ)
**

6

The ‘ignition protection’ is sort of a misnomer, Jochen - the relay activates by ignition key, but diverts high power unit currents past the ign key. It actually protects the ign key against overloads…

The warning lamp is in parallel with the heating strips and should come on whether the strip is broken or not - unless the bulb itself is blown. One safe test is to disconnect a battery clamp and connect a test lamp between the post and the clamp. If the heating coils draws power, the test lamp will brighten…

Frank
xj6 85 Sov Europe (UK/NZ)
**

7

Thank you all!

As for the high voltage situation: without any real world check my car should be equipped with a Lucas alt with integrated regulator. And yes, (>)18 V is a killer. On Friday night the system was exposed to that kind of voltage for maybe one minute. The next start (in 2018) will show whether the battery survived the abuse …

With regard to the reasons for the short-term overload: I’ll check the sense wire. In the course of some research in the books I found an interesting passage in the ROM (86.10.00). It says:

"Surge Protection Device

The surge protection device is a special avalanche-diode, fitted to the outer-face of the slip-ring end bracket (not to be confused with a suppression capacitor, similarly fitted in the end bracket). The avalanche-diode is connected between terminal “IND” and frame and its purpose is to protect the regulator from damage by absorbing high transient voltages wich occur in the charging system […] when certain switching devices are operated." (emphases added)

To my limited understanding this might mean that most every switching operation leads to very short voltage spikes and the surge protection device might be little more than a capacitor buffering these spikes. On the other hand, this language might also explain why repeated switches of the high power relay for the HRW (ignition protection relay) might have disturbed the system. Does that sound reasonable? Of course, I’ll keep an eye on the voltmeter on the next rides, anyhow, and, if necessary replace the alt, Mark, or have it serviced.

As for the HRW and to clarify, David: indeed, I referred to the amber control light in the speedo as “second light”, as the switch itself indicates with the red light in its lower part that the HRW is turned on.

Frank is right, of course, in that this amber control light is in parallel with the heating strips (and in my case gave a clear hint that the HRW didn’t work). As I’m happy to have another HRW switch available, I’ll change the switches first to see whether anything changes and then check power at the HRW connectors. Thanks, Frank, for the testing instructions. Unfortunately, it won’t be before the new year that I’ll get at it.

For the moment, thank you all again! I wish you a wonderful Christmas Eve, if you celebrate, and otherwise some peaceful holidays!

Best wishes

Jochen

75 XJ6L 4.2 auto (UK spec)

8

Okay! That light is always on when the light is switched on - the switch either blocks it, or not.

I thought that the alternator would be able to give higher voltage than needed? And the regulator would regulate that to be at 14.4V give or take.
Alternator delivers say 18V at x RPM, regulator regulates that down to 14.4, and when load increases output is still 14.4 when otherwise it’d drop - take out the regulator because it gave up and what happens?
It’s never increasing voltage, rather always decreasing voltage - at least that’s what I think. And if failing it allows higher voltage to pass through…

Frohe Weihnachten,
David

9

I think the system is too simple for that. It is just a diode to eliminate voltage spikes, common in most appliances with electric motors as a protection device. - oh! You think the diode broke due to repeated spikes, then those went on to damage the now unprotected regulator? Now that’d make sense to me!
That would all fit together. Again, a few seconds of high voltage won’t damage anything, a few minutes might do damage (but can’t lead acid batteries be rejuvenated by high voltage high amps when been drained for too long?)

10

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The alternator, unloaded delivers higher than necessary voltages, David - the regulator drops that voltage to a more suitable voltage for the battery and electrics…

However, as the load increases, alt voltage inevitably drops - much like what happens to a battery. Also, the alt output varies with rpms; in idle, the voltage will inevitably drop - and there is nothing the regulator can do about it…

On dynamos ‘regulator’ was used to break the battery connection when output dropped - to prevent the battery from backfeeding to the dynamo. A different concept, of course…

Frank
xj6 85 Sov Europe (UK/NZ)
**

11

Yes, Frank, that’s what I meant to say. So, do we agree that the regulator is at fault in any case?
David

12

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Well…er… possible, David…

In the original post you implied that ‘the voltage returned to normal’ - which indicates a hiccup. However, if the high voltage reading persists, whatever the rpms; the voltage regulator is indeed the prime suspect. The dash voltmeter is to slow reacting be a reliable warning sign - a ‘proper’ voltmeter must be used…!

There is a very vague possibility that this relates to the alt rectifier diodes, so a battery current leakdown test should be done - a high current reading will indicate a diode problem. But whatever the problem with the rear screen heating; it should not interfere with alternator state…

Point again being that the alt ‘raw’ output voltage is likely some 18V - and a voltage regulator is required to keep it at safe voltage levels…

Frank
xj6 85 Sov Europe (UK/NZ)
**

13

Hi everybody,

after my recent “high intensitiy use” of the Jag I decided to go after that voltage regulator even though the last couple of hundred kms there was no more voltage surge - it’s just because it is quite obvious that the voltage surge cannot be caused by ground issues and I don’t want to run into it in worse form when I don’t need it … Whenever the voltage surge occurred it was obvious not only from the guage reading, but also from brightness of lights and performance of other electrical consumers. It would alway last like 20 to 50 secs. So, yes, I think it is the voltage regulator.

It looks like I have installed a Lucas 18ACR alternator. It should have a Lucas 19TR (UCB 100) regulator with two wires (orig. part # RTC1071). To address my issues there seem to be three options:

  • Replace the alt.: While there are quite low-priced 18ACR replacement units on the market I tend to keep my original piece of engineering as it seems the repro units are of questionable quality.

  • Recondition the original alt.: Parts sets are available, but again with doubtful contents (esp. voltage regulator, rectifier)

  • pull the original alt and replace only VR with NOS.

My personal preference is quite clear the third option, but I’m wondering first: is it practicable? - My car is RHD and without A/C, so I think pulling the alt shouldn’t be like giving birth. Or am I missing something? Secondly: At around 120000 km do you think it is worth replacing the VR without doing a full overhaul of the alt? Finally, whtat do you think of NOS parts in this area?

Any and all ideas welcome!

Best regards

Jochen

75 XJ6L 4.2 auto (UK spec)

14

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Intermittent faults are awkward, Jochen - always some uncertainty as to the problem…

The 18 RCA has a ‘control unit’, and I do not know if it is accessible for changing without removing and/or stripping the alt. And in any case, you need to source the replacement unit before starting the process - given that it is the cause of the problem, which is not unlikely…

The alternator is a very robust item; wear is usually confined to brushes and bearings - and 120 000 km is no great shakes for the OEM. I would restrict repairs to remedy obvious faults; rebuild/rebuilt, and repro units’ reputation is not all that hot…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
**

15

Thanks Frank,

indeed, the ROM only refers to the “control unit” and suggests that the alternator has to be removed to get access (86.10.26). As I didn’t have the time to check out at the car I have to rely on my memory - I always thought that removing the alternator wasn’t a big thing as the l/h engine side is fairly relaxed space wise as there is neither a steering column nor an AC compressor in the way.

The parts catalogue refers to the control unit as part # RTC1071 and the same part # shows up at a parts supplier’s list as Lucas 19TR regulator. It seems this regulator came as UCB 100 with two wires and as UCB 110 with three wires.

It seems though that to get access to the brush gear and the regulator it is necessary to unsolder the stator winding connections (different from 20ACR and 25ACR). I’m quite a bit nervous to fry the rectifier diodes … The ROM suggests to shunt the heat.

I think I’ll go the way to leave the bearings and the slip ring alone for the moment and only replace the brushes and the regulator.

Thanks again and best regards

Jochen

75 XJ6L 4.2 auto (UK spec)

16

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Still requires an alternator ‘out’ operation, Jochen…

…which allows for proper identification of parts required. I think you should check the brushes - to see if replacement is warranted. Soldering is required due to the high current flow and reliable connection. With the proper tools and some soldering experience it is not much of a problem.

Frank
xj6 85 Sov Europe (UK/NZ)
**

17

Hi Frank,

some investigation further down the road has given some relief:

Thanks to the lack of an AC the alternator is presented on a silver plate - it looks like I could even leave the alternator mounted.

The alt carries a Jaguar label with the part # “DAC3480E”. The original part number being “DAC1188E” and the Jaguar label make me suppose that it is a replacement part and - as I cannot find it in my documentation from the last two owners - probably exchanged before 1990 at a mileage below 45000. Fortunately, it seems to be the correct part as per some parts suppliers’ “superseded by” indications. Even these orginal parts are sold new at around 400 EUR by now. Certainly, I won’t hand it in for a core refund on the purchase of a Chinese repro part … Then there is the original Lucas metal tag “24065”.

P9010255a
P9010255a.JPG1024×768 145 KB

For the moment I have ordered a NOS Lucas 19TR (UCB100; 37647) regulator and some generic brushes. As soon as they arrive I’ll get into it. Bosch has a nice website with all of their classic production and part numbers. Do you know of anything similar for Lucas parts?

Thanks again and best regards

Jochen

75 XJ6L 4.2 auto (UK spec)

18

Hi all,

with another distance run lying ahead I thought I didn’t want to take a chance, bought a cheap alternator ( +Line LRA 103+) and installed it today.

It wasn’t a big thing, but not a drop in either. The pulley that came with the new alt is smaller, so I had to use the tensioner which was pretty much solid. In the end I had to undo the entire tensioner from the block, put it into the bench vise and after some time of penetrating oil doing its job got the tensioner free again.

Unfortunately, the third eye of the alternator housing was not a bolt through, but threaded - and wrongly. I had to drill it open to make use of the pre-existing bolt. Otherwise the fit was perfect.

At the end of the day the new alt puts out 13.9 V @ idle in gear (600 RPM) and 14.1 V from 1000 RPM on (measured at the cigar lighter). The voltage guage pegs shortly befor the “l” of normal at this point, so it seems it charges quite a bit more than the old one did.

I’m going to open the Jaguar labeled Lucas unit to recondition it as soon as I find the time.

Best

Jochen

75 XJ6L 4.2 auto (UK spec)

19

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With a smaller pulley, the alt will turn faster, giving a higher rate of charge per engine rpms…

Providing the voltage regulator works as it should it is no big deal. However, the smaller pulley may cause the alt to exceed its rev limits at high engine revs - causing instant dismantling…

Frank
xj6 85 Sov Europe (UK/NZ)
**

20

Thanks Frank,

point well taken! I’m quite optimistic though that the changes brought about by the smaller pulley will not affect the functionality of the system: the difference in diameter is probably approx. 5 mm - I had to move the tensioner bolt out by approx. 3 mm.

Will report back after next week ends drive!

Best regards

Jochen

75 XJ6L 4.2 auto (UK spec)