P38A Mobiletron VR-VW010 alternator regulator.

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Datatek

Datatek

Well-Known Member
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Near Poitiers SW France
I have 2 P38 alternators fitted with this regulator and now have voltmeters in both cars so I can monitor the voltage. The Mobiletron VR-VW010 appears to be a smart regulator, the web site claims a 14.7 volt set point, but it also states operating voltage is 14 volts. Immediately after starting, I see 14.6 volts dropping in a few kilometres to 14.2 volts and on a long run in the car to13.2volts which is a float charge level for a fully charged battery. Both batteries are almost new and are kept charged with solar panels, so the alternator does not have a lot of work to do to replace the energy used for starting.
I have fitted a few smart regulators in boats, but they were always external to the alternator, I have never before seen a built in smart regulator for an old alternator. So either I have learnt something, or both the regulators are faulty, not very likely. Mobiletron so far have not responded to enquiries.
 
Interesting stuff there i have one fitted and have posted the link to them quite a few times on here, i must get round to fitting a usb come voltage like you did to keep track of mine, hopefully they are smart regulators.
 
Different Mobiletron VR on mine (VR 153A)- for the MM GEMS alternators, but the parameters are the same as Data's 14.7V set point, and 14 V operating voltage. My batteries are not in such good condition as Data's and will usually be 12- 12.4V at start-up. The charging voltage is usually c 14.2/14.3V on the 4.0 and 14/ 14.1V on the 4.6. Neither spend much time, if any, below 14V, while charging. I have put this behaviour (ie not achieving the 14.7v set point) down to the alternators themselves, which are 20 y.o. - reasoning that an old alternator may not be putting out a sufficiently high unregulated voltage in the first place to satisfy the higher set point (and maybe was never designed to).
I think this is one of those areas where it's easy to lay out loads of cash with little/ no effect. My batteries will start the car from 11.6V up, so while I could replace them, there's really no point. Likewise replacing the alternator - no point if the old design does not generate a high enough voltage. There may be a more up-to-date alternator design using the same body (A127M for the GEMS) that you don't necessarily find by inputting the LR part code and looking for alternates.

Of course the diesel ones are different - so some of the above may not be relevant to some readers
 
BMW alternator/starter units etc for diesels. They tend to be half the price for same actual thing.

When I took my regulator out was easy to see it needed doing though. Had to be done anyway as new battery type
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59FE020A-5AA0-4EAC-A137-3870E170C405.jpeg
I used to have a lot of trouble with voltages. still working fine now
 
wammers said:
As far as i am aware all alternator voltage regulators work like that.
Click to expand...

I dimmly recall an alternator needs a small current to get it started and after that it varies the power depending on load but I thought the voltage was constant and the current was what varied?

Might be wrong though. I'm trying to remember the difference between an alternator, dynamo and magneto.
 
Grrrrrr said:
I dimmly recall an alternator needs a small current to get it started and after that it varies the power depending on load but I thought the voltage was constant and the current was what varied?

Might be wrong though. I'm trying to remember the difference between an alternator, dynamo and magneto.
Click to expand...

Yes unless they are self exiting. The set point on a voltage regulator is the maximum it can provide. It is not it's constant output. It will do this on a flat battery but the output will reduce as the battery gains charge. It does not throw 14.7 volts at the battery all the time. The output varies subject to battery state and load being applied to it. Take a look at your home battery charger. Say it is 10 Amps. Connected to a flat battery the needle will be at or near 10 Amps and the output voltage will be well above 12. Maybe 14 - 16 or more. When the battery is nearing full and the needle is on maybe 2 Amps or so, the output voltage from the charger will be more or less the same within a couple of volts as the battery voltage. Obviously if the battery is under load then the output voltage increases to support the load and maintain full charge in the battery. It's all variable and as i say as far as i am aware has always worked like that.
 
wammers said:
Yes unless they are self exiting. The set point on a voltage regulator is the maximum it can provide. It is not it's constant output. It will do this on a flat battery but the output will reduce as the battery gains charge. It does not throw 14.7 volts at the battery all the time. The output varies subject to battery state and load being applied to it. Take a look at your home battery charger. Say it is 10 Amps. Connected to a flat battery the needle will be at or near 10 Amps and the output voltage will be well above 12. Maybe 14 - 16 or more. When the battery is nearing full and the needle is on maybe 2 Amps or so, the output voltage from the charger will be more or less the same within a couple of volts as the battery voltage. Obviously if the battery is under load then the output voltage increases to support the load and maintain full charge in the battery. It's all variable and as i say as far as i am aware has always worked like that.
Click to expand...
The set point is the fixed maximum voltage, it will go lower if the load is excessive but in normal circumstances the out put will always stay at the set point, it is the current that varies not the voltage unless the revs drop below the threshold required to meet the current requirements. My Transit puts out a constant 14.7 volts, my MR2 a constant 14.2 volts, wife's R11 a constant 14.2 volts. The regulator I removed from the P38 put out a constant 13.8 volts. I used to make money fitting smart regulators on boats, they would put out up to 15.8 volts dependant on battery and alternator temperature for a short period and then scale back as occurs with the Mobiletron.
 
Grrrrrr said:
I dimmly recall an alternator needs a small current to get it started and after that it varies the power depending on load but I thought the voltage was constant and the current was what varied?

Might be wrong though. I'm trying to remember the difference between an alternator, dynamo and magneto.
Click to expand...
The start current is provided by the charge lamp on the dash via the D+ terminal, lamp goes out as the alternator starts to produce power.
 
Datatek said:
The set point is the fixed maximum voltage, it will go lower if the load is excessive but in normal circumstances the out put will always stay at the set point, it is the current that varies not the voltage unless the revs drop below the threshold required to meet the current requirements. My Transit puts out a constant 14.7 volts, my MR2 a constant 14.2 volts, wife's R11 a constant 14.2 volts. The regulator I removed from the P38 put out a constant 13.8 volts. I used to make money fitting smart regulators on boats, they would put out up to 15.8 volts dependant on battery and alternator temperature for a short period and then scale back as occurs with the Mobiletron.
Click to expand...

As said the charge voltage varies subject to load and battery state. Always has done. What i suggest you do is put a meter across the battery and start the car. The initial voltage from the alternator will be high but will fall away as the battery regains charge lost on starter application.
 
wammers said:
As said the charge voltage varies subject to load and battery state. Always has done. What i suggest you do is put a meter across the battery and start the car. The initial voltage from the alternator will be high but will fall away as the battery regains charge lost on starter application.
Click to expand...
You clearly have never seen the circuit diagram of an alternator voltage regulator, in simple terms it comprises a fixed voltage reference and a 2N3055 power transistor or equivalent, there is no means of varying the voltage, only the current changes as the potential difference between te set point and the battery voltage diminishes so the current reduces. Until more recent times, domestic battery chargers were the same, fixed voltage, variable current based on PD. I have voltage indicators indicators on all vehicles.
 
Datatek said:
The start current is provided by the charge lamp on the dash via the D+ terminal, lamp goes out as the alternator starts to produce power.
Click to expand...
Datatek said:
You clearly have never seen the circuit diagram of an alternator voltage regulator, in simple terms it comprises a fixed voltage reference and a 2N3055 power transistor or equivalent, there is no means of varying the voltage, only the current changes as the potential difference between te set point and the battery voltage diminishes so the current reduces. Until more recent times, domestic battery chargers were the same, fixed voltage, variable current based on PD. I have voltage indicators indicators on all vehicles.
Click to expand...

Ok carry on. The lamp goes out as the voltage equalises in effect reversing the polarity. I have no need to see inside a alternator voltage regulator i know what it does, i have no need to study the theory. When i select a higher amperage charge rate on my 200 Amp garage charger and boost starter the output voltage increases on the meter. That is all i need to know.
 
wammers said:
Ok carry on. The lamp goes out as the voltage equalises in effect reversing the polarity. I have no need to see inside a alternator voltage regulator i know what it does, i have no need to study the theory. When i select a higher amperage charge rate on my 200 Amp garage charger and boost starter the output voltage increases on the meter. That is all i need to know.
Click to expand...
There is no reversal of polarity, the bulb ends up with 12 volts on both ends.
When you select a higher amperage on your garage charger, of course it increases the voltage, a potential difference is required to create a current flow, the greater the PD the greater the current flow, it's basic Ohms law, V/R= I.
You clearly do not know what an alternator regulator does other than the fact that it works.
 
romanrob said:
Different Mobiletron VR on mine (VR 153A)- for the MM GEMS alternators, but the parameters are the same as Data's 14.7V set point, and 14 V operating voltage. My batteries are not in such good condition as Data's and will usually be 12- 12.4V at start-up. The charging voltage is usually c 14.2/14.3V on the 4.0 and 14/ 14.1V on the 4.6. Neither spend much time, if any, below 14V, while charging. I have put this behaviour (ie not achieving the 14.7v set point) down to the alternators themselves, which are 20 y.o. - reasoning that an old alternator may not be putting out a sufficiently high unregulated voltage in the first place to satisfy the higher set point (and maybe was never designed to).
I think this is one of those areas where it's easy to lay out loads of cash with little/ no effect. My batteries will start the car from 11.6V up, so while I could replace them, there's really no point. Likewise replacing the alternator - no point if the old design does not generate a high enough voltage. There may be a more up-to-date alternator design using the same body (A127M for the GEMS) that you don't necessarily find by inputting the LR part code and looking for alternates.

Of course the diesel ones are different - so some of the above may not be relevant to some readers
Click to expand...
I matters not how old the alternator is, if the windings and slip rings are in good order it will work just the same as if it was new. A standard 12 volt alternator can be upped to 24 volts simply by changing the regulator, so 14 volts is well within the capacity of the alternator.
 
Datatek said:
There is no reversal of polarity, the bulb ends up with 12 volts on both ends.
When you select a higher amperage on your garage charger, of course it increases the voltage, a potential difference is required to create a current flow, the greater the PD the greater the current flow, it's basic Ohms law, V/R= I.
You clearly do not know what an alternator regulator does other than the fact that it works.
Click to expand...
Not really interested to be honest. It just controls the maximum charge volts.
 
Datatek said:
There is no reversal of polarity, the bulb ends up with 12 volts on both ends.
When you select a higher amperage on your garage charger, of course it increases the voltage, a potential difference is required to create a current flow, the greater the PD the greater the current flow, it's basic Ohms law, V/R= I.
You clearly do not know what an alternator regulator does other than the fact that it works.
Click to expand...
There is according to Land rover.
 
Datatek said:
I matters not how old the alternator is, if the windings and slip rings are in good order it will work just the same as if it was new. A standard 12 volt alternator can be upped to 24 volts simply by changing the regulator, so 14 volts is well within the capacity of the alternator.
Click to expand...
OK, so what you are saying, is that it doesn't matter how old the alternator body is as long as it's all in good condition ? : o) Mine are 22 years old, including rectifiers, so I'm realistic as to condition
 
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