Thread: Alternator - Not charging

The starter to alternator cable on the 3.0 is very accessible so shouldn't be much of a hassle fitting an inline fuse.

I'll be asking my SIL this w/e how his employer's alternators accomplish load dump protection. He doesn't have a high opinion of the brand that LR uses but perhaps that's understandable.

Edit: Whilst the cable is accessible the ends are not as the starter probably needs to be unbolted to access the power terminal and the alternator is well hidden.

Originally Posted by LowRanger

There is quite a lot of info here http://www.aulro.com/afvb/d3-d4-rrs/...hing-else.html.

No-one got to the bottom of why the diodes fail short circuit, but now knowing that they are zener diodes and are meant to conduct in the reverse direction once their trigger voltage is reached, it becomes clear that if a power diode fails or if the regulator fails high so that excessive voltage is produced, a short circuit of the battery will occur. However as zener diodes only conduct in the reverse direction whilst their trigger voltage is exceeded yet the current draw becomes permanent, it seems that the zeners themselves must be failing. Using zener power diodes will always expose the alternator to creating a dead short for the battery, whereas using standard power diodes and then zener diodes to shut-down the regulator supply voltage does not expose the battery to the possibility of a dead short.

As suggested in the above thread, a fuse in the alternator B+ cable would prevent the battery from being drained. A better-designed (more expensive?) alternator might not be so prone to failure. If LR had anticipated alternators failing with shorting zener diodes they might have run a seperate, fused cable. However I doubt that LR's alternator specifications to prospective manufacturers include modes of failure.

Had the same charging problem on my 2005 D3 just recently the alternator light even came on for a few seconds then went out. After checking the charging it was around 13.4v quite a bit low. I removed the alternator fuse and re inserted it then started it again. The battery was then charging at 14.4v so I thought everything was OK. A few days later took car up for rego check, left it their, received a phone call about 2 hours later explaining the car had a melt down. Apparently after they moved it to do the brake test smoke came from under the bonnet, you guessed it the alternator packed it in. So a new one was installed. Just reading about the zenner diodes this may have been the problem as at one time away just recently the main battery went dead overnight for no reason. Or maybe the alternator got to the end of its life any way $900 less in my pocket now but car is going great

Early this spring, I ended up replacing my factory alternator with a rebuilt.
I had an independent install a Wilson (WAI) as that was all that was locally available on short notice other than dealer supplied which was about double the money. I could not believe that a LR supplied Denso rebuilt would be twice as good as a Wilson. In reality it may be true as the independent had to install a second a week later due I think to "regulator" failure. Actually they did it a third time as the second unit shipped with a 6 groove pulley and the petrol V8 uses 7 grooves. To date, the independent has not changed his outside sign to add the Land Rover logo advertising vehicles he is comfortable with.

I kept the core with the idea of tearing it down to find out was was wrong with the factory unit. In reality I did not succeed as most of the little screws would not unscrew but instead the Phillips heads tended to be destroyed. I was hence stopped and have not proceeded as what I did realize that if I got it opened up, it was not clear I would be able to get parts as needed. At the same time, perhaps I would then know what was wrong however so the idea still lives. Part of me thinks it is the regulator and that is difficult to test with old style techniques - well impossible.

What I have noted is that while many talk of self rebuilding the alternator, it is not clear to me that anyone really has, (well maybe a half dozen or so), as no once can seem to find parts - certainly not me and if they do, no one seems to provide part numbers or sources.

That is me anyhow and I do not know anyone in the trade that will actually help out so to speak. It just seems that the craft practises of old still prevail when it comes to alternator rebuilds, or almost no one knows.

I cannot believe that Denso has built an alternator that is unique to Land Rover and no other vehicle manufacturer installs a similar design. I can however believe that the PWM "regulator" part is unique to Land Rover. I also expect that the regulator in the D3 is different from the regulator in the D4 alternator, hence one cannot even substitute alternators even if they mechanically fit.

If the regulators were identical or interchangeable, I expect that installation of the slightly larger 180 amp alternator of the D4 would solve a lot of the D3 alternator problems - but not the D4 problems. This presumes that the D4 alternator rating is not badge engineered and that something inside is "bigger" than with the D3. Ideally it would be the diodes, (zener or otherwise), and that they would both mechanically and electrically fit within the D3 alternator frame - but now I am back to the parts problem.

My wife has just come back from Port Macquarie NSW where she took our D3 with a engine fault code that came up on her trip anyway when I spoke to the service guy there he told me that they have had to replace quite a few alternators, so it seems to me that there must be a problem with these alternators. I know they have to pump out quite a bit to keep these guys going but to fail in such a short time keeps me wondering. As far as repairing alternators I repaired one years ago but in this day and age everything is throw away so I sometimes just go with the flow

Originally Posted by Tinman

As far as repairing alternators I repaired one years ago but in this day and age everything is throw away so I sometimes just go with the flow

I suppose at least in the case of the alternators, they do get repaired, but rather than locally, at some distant location.

As best I can determine, parts are not available for our alternators as the test equipment required to determine fault is too specialized to invest in. As such, only some centrally located facility that can accept volume can afford the equipment required.

Then there is the question of parts. I really think the regulator is unique to our vehicles, hence a combination of the cost of stocking a low volume part plus the fact that one needs a special tester even to determine if it is defective means local repair is just not economically practical. Since local repair or testing is not really possible, then it is difficult to even figure out what is failing on our alternators or what is the part that fails most often, (probably the zener diodes).

Still, I would like to know what goes wrong. Maybe the alternator just another of those time use parts where after so long in service, (3 years?), one should just be replacing it - kind of like it was a brake hose.

Very interesting discussion, and information on this thread.

I am getting a bit long in the tooth now, and not up with the latest technology, 3rd brush generators and the odd carbon pile rectifier were still in use when I started off!

However, I spent a big part of my working life in the electrical industry maintaining large, variable speed, DC drives, both with old “Ward Lennard” type systems, magnetic amplifiers / saturable reactors, and more modern SCR systems of various types. I am referring to 1,500—2,000 amp drives, and 800 hp motors.

The only basic difference with an SCR system as compared to an automotive alternator (apart from the voltage), is that with the SCR system the bridge rectifiers are gated and conduction is controlled to give a variable voltage output, rather than continuos conduction, or commutation, for a fixed voltage with an alternator. In both systems the source is a 3 phase AC voltage.

In my experience the two most common faults encountered with failures of the actual diodes were caused by: excessive heat / lack of sufficient cooling; and / or a diode with a low PIV( peak inverse voltage) rating used in a system that was prone to producing unwanted spikes, or “glitches”, as the Americans called them.

The alternator in my old D1 gets that hot I try not to think about when it is going to melt down! But it seems happy enough, and as the car does not have a great amount of electronic systems in it, voltage spikes do not appear to be a problem.

I am not sure where the term “load dump” is coming from? To produce a spike on an automotive system sufficient to damage the power rectifiers of the alternator, I would have thought that it would have to be generated from the switching of an inductive type of load, such as an electric motor somewhere on the system, which maybe what they mean. In the link article they refer to disconnecting the battery as being the cause of “load dump”. I am not aware of anybody likely to be doing this while the alternator is running, and if they do then they only have themselves to blame for any subsequent failure!

The explanation of how the alternator generates a voltage, while basically correct, can lead to some misconception of the actual process. They are again blaming the battery, which is not the cause at all. Automotive alternators use what is termed “machine sensing”(mostly), as compared to battery sensing, to control their output. The internal voltage regulator usually consists of a voltage divider network and a reference Zener diode, which controls the excitation to the DC rotor windings, which in turn determines the output voltage of the alternator, usually around 14.5 volts dc.

Directly after starting the engine the battery voltage will have dropped from cranking the starter and any energy used maintaining whatever systems the vehicle has active while not actually running. The alternator will respond to this lower voltage by charging the battery, as expected. But it does not suddenly get the battery voltage up to the desired level and then abruptly stop charging, thereby causing a “load dump”. The charging rate will taper off in a smooth manner as the voltage of the battery increases and opposes the alternator output voltage, which can be considered a fixed voltage. Once the two voltages are equal no further current goes into the battery, unless there is a big demand on the system, such as a winch, which causes the battery to supply energy beyond what the alternator can provide, and its terminal voltage drops again, so repeating the cycle of charging and maintaining the battery voltage. At no time will this process cause any condition that could be referred to as a “load dump”.

As mentioned above, a “load dump” is more likely to be seen on the system when some, probably inductive, load is switched off causing a voltage “spike” to appear on the system, the magnitude of which may exceed the PIV rating of the diodes in the rectifier bridge, causing failure.

I was surprised to read of the use of Zener diodes in the power rectifier, although there are several different types of Zeners with different characteristics. I can see why they have been used in an attempt to overcome the problem. But their use may be part of the problem, as in using the alternator windings to “absorb” the energy of any “load dump” they appear to have overlooked the complete picture, as it is possible that the alternator stator windings are, by transformer effect, inducing an over voltage into the field windings, which in turn, is destroying the voltage regulator connected across it.

They point out in the link article that the “load dump” voltage can be in the order of 80-100 volts, for a duration of 300-400ms. But again, they are assuming a complete disconnection of the load, which does not happen---even if you disconnect the battery while the engine / alternator is running, there is still a measurable load on the alternator.

Also in the article they correctly state that there are two ways to try and prevent damage to the alternator: either within the alternator, or externally at the point where the problem originates. In my experience it is the latter method that has been the more successful. These “spikes” are transient, and as such are very difficult to both measure and either control or suppress, especially in an automotive system where all the various loads are in effect connected in parallel. If it can be tracked down to just which sub system or accessory is causing the problem, then it is possible to address it directly at the source.

I would also point out that it does not matter one iota where the output wire of the alternator is connected: at the starter solenoid or directly at the battery + terminal, it is just either end of the same cable that connects both the starter and battery.

From some of the postings it appears that when the alternator has failed it has very rapidly flattened the battery, and it is suggested that a mega fuse of around 200 amps may help prevent this. While this modification will not do any harm I have to question just how much current has been involved in those cases where the battery has been run flat. I would suggest that it must have been a lot less than 200 amps, because even that level of amps would have very soon led to a melt down of the wiring at the best, and more than likely a fire. A better method may be to route the alternator output wire via a suitable relay—just like the old “cut out” relays used in days gone by!

Sorry to ramble on so long, I just hope some of it is helpful. I would be interested to learn just what purpose the latest alternators having a connection to the vehicle ECU are trying to achieve. (if that is what I understand from a posting?)

The load dump referred to is that caused by the disconnection of the battery either accidentally, purposefully or by the battery going open circuit due a broken connection between cells whilst the alternator is producing significant charge. I suspect it is a rare occurrance but my understanding is that it is a standard that automotive systems have to achieve for some particular (EU?) certification. One has to assume that the zeners do their job when new but heat dissipation may be inadequate for longevity.

The suggested fuse will only be of use if the short circuit is severe but the fuse needs to handle the maximum alternator output. A dead alternator could be tested to determine what current that particular failure is capable of drawing to see if it is anywhere near the alternator's rated output, at least for the 1st few seconds before the resistance increases due to excessive heat.

I became aware of the certification of electronic equipment to withstand such load dumps when asked if my Llams module has been certified, as it is a requirement for vehicles used in Germany. I suggested that I would replace the module FOC if destroyed by such an event. I suspect vehicle manufacturers have adopted the approach to endeavour to contain the effects of such a load dump within the alternator rather than within every electronic module.

Edit: ECM control of the alternator is for reduced idling emissions and for reduced fuel consumption whilst accelerating (preferably only whilst coasting or decelerating) by preventing high charging unless absolutely necessary.