Introduction to the Lucas voltage regulator unit
This article is a follow up to my earlier post describing ‘How the Lucas charging system works.‘ This previous article described how the system as a whole (i.e. the dynamo, battery, ammeter and voltage regulator) function to keep the battery topped up and the lights glowing.
But now I’d like to look a little bit more in depth into exactly how the regulator unit (also known as the AVR (Automatic Voltage Regulator) or CVC (Compensated Voltage Control) box actually works. I gave a brief description previously, but in order to be able to attempt to fix or adjust the regulator, a more in-depth technical understand is required.
I’m going to use the Lucas ‘MCR2’ device, as fitted to my 1951 Matchless G3LS motorcycle as a basis, but the same principles should apply to other car and bike units of the same era (although note that alternator charging systems are completely different).
Table of contents for this article:
Terminology: Shunt versus series windings
Firstly just to clarify the meaning of the terms ‘shunt’ and ‘series’ which are often used when describing DC dynamos and regulator units. These each refer to a particular way of connecting the windings (coils) with the dynamo or regulator units.
Lucas dynamo units are referred to as ‘shunt-wound’ DC dynamos as the armature and field windings are wired in parallel to one another, each with their own independent connection to earth. They are therefore also sometimes referred to as parallel windings.
Other manufacturers, most notably Bosch, used ‘series-wound’ DC dynamos in their charging circuits in which the armature and field coils are wired in series, one after the other in the same circuit.
There are also coils inside the Lucas regulator unit, four in total. Two of these coils are series-wired in circuit with the main current path to the ammeter and so are also referred to as the ‘current windings’. The other two are shunt-wired in parallel to the main current flow to the ammeter. These have a higher resistance than the series windings and so a smaller current flows, hence they are also referred to as the ‘voltage windings’.
Overview of regulator operation
The voltage regulator is a digital device in that its two primary internal circuits may each be either ON or OFF. There is no sort of variable output from the device, although as we shall see, it does have a couple of simple but clever features that allow it to adapt its output within certain limits to the operating conditions.
For this overview, I’m going to start by repeating the description I originally gave in the ‘how the Lucas charging system works’ page, thus:
The voltage regulator, as it names suggests, regulates the fluctuating voltages supplied by the dynamo into something more usable by the motorbikes electrical system. In the most basic terms it consists of two electrical contacts (switches) which are opened and closed (turned off and on) by two sets of solenoid coils. These electro-mechanical switches work in the same way as a relay; current passes through the coils creates a magnetic field which, when it is strong enough, pulls the lever of the switch towards it, thus completing (or breaking) the circuit and turning it on (or off). The automatic bit comes in to play because the regulator knows (by means of how the contacts and springs have been adjusted) at which voltages to open and close the contacts, thus automatically maintaining the desired output voltage range.
The first of these two switches is the cut-out. When the dynamo is giving less volts than the battery, the regulator disconnects it from the system so that it cannot draw any current. A DC dynamo is basically a simple electric motor working in reverse, therefore if you connect it to a suitable power supply it will try to spin just like a motor (see my article ‘Testing a Lucas dynamo‘ for more info on this). The large current drawn would quickly sap battery power if the dynamo was left connected when it was not generating, so the cut-out isolates it from the rest of the electrical system.
When the engine attains sufficient speed that the dynamo output voltage exceeds the preset charging voltage, the cut-out switch closes to connect the dynamo into the charging circuit in order to recharge the battery and power any lights that are on. However, when the voltage coming from the dynamo gets too high, the regulating switch opens connecting a resistance into the field winding circuit. This reduces the magnetic field strength in the dynamo which reduces its output voltage, thus regulating the charging voltage supplied to the battery.
So now let’s look at each of these two circuits in a bit more detail.
The cut-out circuit
The ‘cut-out’ circuit should perhaps be more accurately called the ‘cut-in’ circuit since its default position is open with the contacts being held apart by a spring. Therefore with the engine stopped, the dynamo is electrically disconnected from the battery.
Primary operation of the cut-out contacts is via a shunt coil which is connected directly between the dynamo armature input (D) terminal and the earth (E) terminal of the regulator unit. This coil is formed of thin wire with a relatively high resistance so that little current flows, however the large number of turns on the coil means that it produces a reasonably strong magnetic field. When the output voltage from the dynamo armature coil exceeds a certain preset voltage (6.3 to 6.7 volts), this magnetic field is strong enough to overcome the spring which normally holds apart the contacts, completing the circuit and connecting the dynamo to the ammeter.
This setup would be fine by itself if no battery was to be included in the circuit. However once the battery and dynamo have been connected by the regulator, current is free to flow in either direction. This means that when the engine speed and dynamo output voltage falls, current could flow backwards through the regulator from the battery into the dynamo. This reverse current would flow through the shunt coil in the same direction as a charge current, and hence would keep the contacts closed even though the battery is being discharged.
To overcome this, a second coil is also included in the cut-out circuit. This time it is a series coil located just after the cut-out contacts, in-line between the dynamo armature (D) input and ammeter (A) output terminals of the regulator. It is made from thicker gauge windings since it must carry the full charging current from the dynamo. When the dynamo output exceeds the charging voltage, current flows through the coil in such a way that the magnetic field produced assists the main shunt cut-out coil with keeping the cut-out contacts firmly closed.
However when the dynamo output voltage falls below the preset value (4.5 to 5.0 volts), the current flows back through the series coil in the other direction (from battery to dynamo) which sets up a magnetic field in opposition to the shunt coil. With the help of the spring, this opposing magnetic field separates the cut-out contacts and disconnects the dynamo from the battery, preventing its discharge.
The voltage regulation circuit
The above section described how the cut-out circuit connects the dynamo output to the battery once the charging voltage has been exceeded, and disconnects it once the dynamo voltage falls to prevent the battery discharging. However there is no regulation of the charging voltage above this minimum threshold and so the full maximum output of the dynamo (which could be up to 20 volts) would be applied to the battery. The maximum charging voltage for a 6v battery is normally limited to less than 7.2 volts (see the ‘Motorcycle battery voltages’ page for more details) as anything higher will lead to gassing and damage the cells. Some form of limitation (regulation) of the charging voltage is also required.
Regulation of the voltage output to the battery is achieved by rapidly opening and closing a set of contacts within the regulator unit, maybe up to 50 or 60 times per second. These contacts are operated by a shunt coil which is connected between the dynamo armature (D) and earth (T) terminals. Since the contacts have only two states (open or closed) there is no analogue control over the output. However by varying the proportion of the time that the contacts are closed, the average voltage over a period of time can be determined.
When the contacts are closed (the default state) then the full voltage output from the dynamo armature is applied across the field coil giving a maximum magnetic field strength within the dynamo and hence full output. When the contacts are open then the dynamo field current must take an alternative path through the regulator and the only one available is via an in-built resistor. This resistor uses up some of the supplied voltage so that a lower voltage is applied to the field winding, resulting in a lesser magnetic field and hence a reduced dynamo voltage output.
As an example, lets assume that the dynamo is producing 10 volts. Then if the contacts are constantly closed the full 10v output will be fed to the battery. However if the contacts are open constantly then the field winding current and dynamo output will be reduced, and so a reduced dynamo output voltage (for the sake or argument, let’s say it’s 6v) will be fed to the battery. In reality the contacts will be constantly opening and closing at high speed. When the contacts are open and closed for even durations, then half the time the battery will get the full 10v output and half the time it will get the reduced 6v output. Because the switching between the two states happens very fast, what the battery actually sees is an average 8v charge (50% of 10v + 50% of 6v = 8v).
If the contacts are closed for a quarter of the time then the battery sees an average of 7 volts (25% of 10v + 75% of 6v = 7v). If the contacts are closed for three-quarters of the time then the battery receives an average of 9v (75% of 10v + 25% of 6v = 9v). By varying the proportion of the time that the contacts are open and closed it is therefore possible to produce an average voltage output to charge the battery that is anywhere between the upper and lower limits. (Note that the voltages I used in this example were completely arbitrary so that the numbers work out easily; the actual voltages will differ).
In reality it is the voltage output from the dynamo that is continuously varying with engine speed (up to 20 volts) and we wish to main an approximately constant output to charge the battery (around 6.5 to 7.2 volts for a 6v battery). Therefore the regulator is continually adjusting the proportion of the time that the contacts are open and closed for in order that the average regulated voltage output remains within the desired range.
The current regulation circuit
Neither the cut-out or voltage regulation circuits discussed so far place any limitation on the maximum current that can be drawn from the dynamo by the charging battery. This is not normally an issue with a charged battery in good condition since it will self-regulate the charge that it will accept depending upon the voltage of its cells. However a flat or damaged battery (or maybe a wiring fault) could potentially draw a very high current from the dynamo that may cause it to overheat and melt the internal windings and connections. The current flowing out of the dynamo therefore also requires regulation, and this is the ‘compensation’ aspect of the regulation referred to in its official Lucas ‘CVC’ (Compensated Voltage Controller) title.
Just like in the cut-out circuit, there is a secondary series (current) coil alongside the main shunt coil in the regulation part of the circuit. The series coils for the cut-out and current regulation circuits are actually part of the same connection between the dynamo armature (D) input and ammeter (A) output terminals of the regulator. The current from the dynamo flows first through the cut-out series coil then through the current regulation series coil before going off the the battery via the ammeter connections.
However unlike in the cut-out circuit, the series and shunt regulation coils both operate in the same direction against the spring such that the required current flowing through either coil will open the contacts and hence bring the regulating resistor into play.
Under normal charging conditions the voltage regulation shunt coil controls opening and closing of the regulator contacts in order to maintain the output voltage in the required range. However when the current output is increased beyond a certain level, the series (current) coil assists the shunt (voltage) coil in opening the contacts such that the limiting resistor is connected much sooner and for a greater proportion of time. The current drawn from the dynamo is therefore also limited alongside the primary voltage regulation.
Temperature compensation
The voltage characteristics of a lead-acid battery vary depending upon the ambient temperature, fluctuating by around 0.2 volts per 10°C rise or fall. Similarly the resistances of the copper windings in the regulator unit will also vary with temperature. The dynamo regulation circuits described so far will operate the same under all climatic conditions which means that the voltages supplied to charge the battery will be too high in summer and too low in winter.
The Lucas regulator units overcome this problem by using a temperature compensation device which makes its output conform more closely to the voltage characteristics of the battery. The device takes the form of a bi-metallic spring that is located behind the tensioning spring of the regulator contact armature. Being made from two different metals (each with different thermal expansion characteristics), the tension of the bi-metallic spring varies with temperature causing the charging voltages to be increased in the cold and reduced when it is hot.
Temperature compensation of the regulator output voltage is therefore automatically achieved to match the battery charging characteristics, without any input or adjustment by the rider.
Adjustment of the voltage regulator
The voltages at which the cut-out and regulation contacts described in the preceding sections open and close are set by adjustment of the respective spring tensions and contact gaps. The correct procedure is described in the original ‘Lucas MCR2 regulator service manual‘ which can be downloaded from the Resources section of this website.
Having changed to using a modern electronic voltage regulator unit on my own bikes, I have never needed to make these adjustments myself although I’m sure that the service manual should tell you everything you need to know.
Conclusions and your comments
So hopefully this article has explained in simple terms how the sometimes rather confusing Lucas electro-mechanical voltage regulator unit works. It is based upon the Lucas MCR2 unit fitted to my bike, but is the same for the earlier Lucas MCR1 units and also for the Later RB107 Control Box bar a few re-ordered connections.
If you found this ‘how it works’ guide useful then please show your support by leaving me a message below. Similarly if you have spotted any glaring errors or omissions, or think that something is not as clear as it could be, then please also do get in touch.
[sc:disclaimer]
Never found so much useful stuff, be it carbs or even better, living with Lucas;-)
many many thanks for this wealth of information – much appreciated while restoring an 1961 AJS model 31
John
Thanks John 🙂
Well done for keeping the knowledge alive.
I would like to add a couple of details of my understanding of the device based on much tinkering with the things. Perhaps these are the very details coming anyway in the later sections.
Firstly, the cut-out has a coil that is connected across the dynamo terminals, the voltage coil, but also has a much heavier winding in series with the dynamo, which carries the current. The purpose is this: if the cut-out were operated by just the voltage coil, when the cut-out has pulled in on rising dynamo voltage, the battery and dynamo are connected and so the cut-out could not open again until the battery voltage had dropped to a low value. The current coil however produces a magnetic field which augments the field from the voltage coil when charging, but which is in opposition when the battery is discharging though the dynamo. It is this reverse current that opens the cutout when the dynamo voltage drops below the battery voltage.
Secondly, I believe that the function of the regulator is not to divert some of the dynamo output by closing a contact, but to reduce the output by opening a contact in series with the field winding, which is what reduces the magnetic field and the output. Sometimes there is a resistor across the regulator contact to reduce sparking, which is usually seen because in operation the regulator contacts will be opening and closing many times per second.
Thirdly, except for the function of the cut-out current coil the device does not compare dynamo and battery voltage. Both the cut-out and the regulator will pull in at voltages which are set by the adjusting screws on the back plate, independent of battery voltage. This is where the fun lies in trying to set up an MCR2 or any similar device that has lost its settings due to wear and tear or due to mis-adjustment.
I hope that these comments are useful.
Mike
Cheers Mike,
Thanks for some really useful comments, and also for reminding me to get around to finishing off this article at some point!
Regards, James 🙂
can u tell where i get the mcr2 regulator 6v or can be repaired in india mumbai city.
Hi Vijay. No idea where you might go in Mumbai, sorry. Ask around at some of the bike shops, there must be someone who specialises in classic bikes somewhere. Enfield shop might be a good starting point. I suspect you won’t be able to buy a new one but you should find someone to repair yours hopefully. Failing that, maybe a good auto-electrician might be able to help?
very helpful indeed, I am trying to get a fordson major charging and this will be a valuable lesson, many thanks Stan
I have a question. As I’ve learned; when the bike is off and the cut-out is in it’s default position, NO current flows through the dynamo, as the live wire is disconnected. My question is: Where does the field coil in the dynamo attain it’s initial exciter-voltage in the first place, in order to complete the cut-out contacts?
-Ragnar
Exciter Voltage is derived from the F terminal. I may be wrong but on small units like this there is sufficient output from the dynamo to activate the cut in and then of course the field coils get the full supply.
I am at a loss. I am rewiring my 58 jaguar and the diagrams I have show connections to an earlier RB.106.1 regulator. My car was a later model that was updated with a RB310 regulator.
The diagrams call for connecting the accessory lights wire to A, the ammeter wire to A1, and ground to E. Where do I connect these wires if not to the newer regulator?
Mike Kurtzweil
New London, WI
Hi Mike. Thanks for your message but sorry I can’t help much as I’m only familiar with the Lucas charging systems on classic bikes. Good luck and hope you get your problem solved soon! James
James, just a quick point before I try to adjust my Regulator and Cutout in accordance with the Lucas document you have provided in your Resources area for download. I think there’s a small mistake in the final sentence of the last paragraph of “Shunt versus series…” I think that “shunt” should read “series” so the the first part of the sentence reads: “These have a higher resistance than the series windings and so a smaller current flows…”
This is just to show that I’m paying attention!
I’ve already resolved 2 issues with the charging problem on my 1953 BSA C10 (no, NOT a C10L) using your excellent descriptions. Now I just need to fettle the Regulator and Cutout. It already looks as though I will be able to heartily recommend many of your tips and tricks so far and have even found a new fault! All being well I will send you the details in the near future (before I forget what I did).
Thanks Bob. Glad to know you’ve found the articles useful, and bonus points for spotting my deliberate (cough!) mistake! I’ve corrected this now. Looking forward to hearing how you get on with your bike. Regards, James
First of all, thank you very much James for this article and the one about Lucas Dynamo, they were of great help for me.
I’ve just one more doubt, perhaps you could help me or the rest of readers.
As you mentioned in the article of testing lucas dynamo, when you join both dynamo conectors D + F , you get 1 oe 2 volts as a result.
Is this very little voltage enough to get the cut-out coil exited? this would happen when you first start your motorcycle for example..
Perhaps i’m missing something…
Once again, thank you very much, this article is incredibly detailed and i’m a DIY Fan!
Best wishes from Argentina
An excellent explaination of the workings of the Lucas regulator which I have often puzzled over!
Cheers Ray and Rodrigo 🙂
Hi James,
Having a Norton 16H with Lucas electrics, I loved reading your pages, and learned a lot.
Thanks a million, and keep up the good work!
btw: the picture “The inside of a Lucas MCR2 regulator” (https://matchlessclueless.com/electrical/how-it-works/lucas-voltage-regulator/) doesn’t load (or didn’t, anyway).
Cheers Tangopeter 🙂
The ‘inside of a Lucas MCR2 regulator’ image should now be fixed – thanks for letting me know.
I’ve read that one can adjust the cut-out and regulator upward so that the dynamo delivers current to the battery when it is between 12.5V and 15V and thus can be used in a 12V system. Of course it means the battery is only charged at higher engine rpm, but with more efficient LED lights that should be enough.
Has anyone tried adjusting a Lucas regulator for a 12V system?
Great article, however, I have a problem with my control box, it will not come into operation unless I push down the cut out armature contact then it charges normally. When I stop the engine it has to be disconected manually or by cutting the supply from the battery, by the way, its positive earth, or it shows discharge on the ampmeter.
Funny thing is it was working fine till I got caught in a rain shower, the box being situated under the saddle was completely dry. Also, I have a spare and this reacts in exactly the same way.
Any ideas would be useful. tHE MACHINE IS A 1954 G3LS, Safe riding, John.
Hi John. No ideas off the top of my head I’m afraid, especially since the same problem seems to exist if you swap the control box to a spare (unless they both have the same fault?). I wonder whether the rain storm is a bit of a red herring though and not actually anything to do with the fault? I’d start by checking all of the connections at the dynamo, control box, ammeter and battery. In particular, make sure that all of the earth connections are good. And of course, the battery is properly connected and the dynamo appropriately polarised, right? Good luck and let us know how you get on and what you find. Regards, James 🙂
Cheers James for your feedback, I shall check the whole system again, wish me luck, safe riding, John.
Hi James
Your explanation about Lucas electrics in total is very excellent and is helpful to every vintage motorcycle owner.
I have a Royal Enfield bullet 350 singles with magdyno mag is m01L and dyno is e3lm , recently I have restored my bike by myself. Now everything is in order the except that a modern electronic regulator that mentioned by u is not available in the place I live. So can u help me to build one on my own by guiding me with circuitry schematics and etc , I would be thankful if you can do it.
Regards
Mallikarjun
Bidar district, Karnataka state
India
Hello James I am currently rebuilding a TriBSA that I originally built in the late 60s and found your articles when looking up details regarding electrics in general.I found them very informative thank uou very much. I did not have much luck looking for data to bench test my Lucas RB107 Regulator and put a post on the A10 forum, as a result I have been in communication with a very helpful chap on the forum and he has given me some info on bench testing my regulator. I’m sure he would not object to me sharing it with you so I have copied below.
“Measure between “D” & “F”. You should have something close to 0. Press down the regulator armature and you should get over 35 ohms.
Measure between “D” & “A”. Should be open circuit. Press down cut-out armature and should be close to 0.
Just one more thing to test before you get into it, momentarily apply a 12V supply between “D” & “E” and ensure that both armatures operate. Don’t take too long about it! The DE test is testing the two shunt coils which are connected at one end to the bobbin which is at the same potential as the frame and the other to the earth terminal. Normally you should get around 30 ohms resistance if both coils are OK, much higher if one is OK and infinity if both are open circuit.”
I have used the above to check my RB107 regulator and it complies with all the figures except the 30 Ohm between D&E, mine is only 14ohms. I put this to him and he replied as follows:-
“I measured some resistances D-E on a few regs. The MCR2 are all around 24 ohms.One RB107 type was 28 Ohms and two others were around 14 Ohms”.
Can you throw any light on this please.
Regards
Pete
Hi James and peter Michell
I am Mallikarjun from India Karnataka state.
I have a 1957 Royal Enfield Lucas E3lm and m01.
I rebuild both the mag & dyno armature, dyno for 12 voltage with more turns of winding’s. Dyno is giving good output at just above idling rpm that I amp meter is flicking more to right at higher rpm meter shows more to right and the battery gets charged very well. Now the regulator I am using is made in India product for some commercial vehicle and not a branded one the good part of it is works so well the it cuts of the charging current as soon as the battery fully charges. To check this charging and cut-off what I simply do is I switch on the head light to high beam then soon after few seconds the amp meter shows just little and the battery discharges more amp shows more. By now I have done nearly 10000 kms and the system is working fine, I hope I will continue further…
I have read many articles on internet including your gained knowledge about the dyno.
What trick I have used is I accidentally came to know about a regulator already existing in the market and soon I took it to the armature rewinding person and explained few things and asked the do more turns then the previous.
This way the whole system is working very fine .
James if at some time you need a regulator then contact me and I can help you.
Good bye for now
Regards
Mallikarjun
India
hi can anybody help I have a 1959 bsa that starts and runs fine but have noticed that when I switch on the ignition the ammeter is registering a maximum discharge and no this is not right does any body have any idea what is causing this many thanks
Check for wiring connection if same then try another amp meter.
Sounds like there’s a short or a light on. Does the ammeter go to zero or + after the engine starts? Is there wire that gets hot when you switch it on?
Hi James,
A very informative piece, helping me to build my knowledge immensely. You mentioned that you have changed to a modern regulator on your bike and I wondered if you could give me some advice on how to do this, and where to source the part please? My bike is a 1960 AJS 31, 650 twin.
Kind regards, Andy
Hi Andy. Thanks for your kind words and glad you found this page useful. Checkout the following page for a guide to installing a modern solid-state regulator: https://matchlessclueless.com/electrical/lucas/12v-conversion/
The page is titled “Converting to 12 volts”, but you could just as easily leave your bike at 6 volts should you wish. The choice between 6 or 12 volts is just a matter of how a single wire from the reg is connected.
I would very much recommend the DVR2 regulator from here as it is the best currently available.
Regards, James
Thanks James. Very useful.
Andy
Good stuff James.
I’ve found that as soon as I connect the dynamo terminals it tries to motor – so presumably this is a problem with the regulator? As the dynamo is attached to a Fergie 35 it objects and gets hot! The dynamo itself does work and it will charge. Do you think the regulator is fixable or willmit be “toast”?
Brilliant! After years of reading manuals and guides, yours is the only full and layman-friendly explanation of the Lucas regulator. I can now finish re-wiring my 1953 MG. Thanks very much.
Excellent. It was difficult to find an article that explained the function of the regulator in a logical, unequivocal, straightforward way. Your article is perfect. Thank you. I needed to know in order to set the regulator on a friend’s old 12 volt Morris. I’m assuming the voltages that apply are doubled.
Hi John. Glad you found it useful. Yes, the voltages would all be doubled for a 12v system, so long as it is a 12v regulator you have and not a 6v one. The currents / loads are very different between 6 and 12v charging systems, so you shouldn’t adjust a 6v reg up to 12v (it will work, but the load limiting circuits won;t be right).
For an even better description of how the regulators work, as well as loads more electrical matters, you might like to check out my new book!
http://amzn.to/2cxT8Fr
I am restoring a 1955 Matchless 3GL and while the Voltage Regulator on my bike is the same as the one illustrated above, I cannot find where to locate it on the bike. At the moment I have it lying loosely under the seat, but cannot really ride the bike with it there. Any help would be appreciated!
I have a 1948 Sunbeam S7 with the MCR1 regulator. Will the MCR2 fit and work in my bike? What are the differences please.
Paul.
Hi Paul. A MCR2 should fit and work in theory, so long as you get the right one. They are not all the same as there are different models depending upon the dynamo they were paired with. A bit too complicated to explain the differences and what to look for here, but there is a very good book available (wink wink!) called the “Classic Motorcycle Electrical Manual” which has a whole big chapter on dynamo control boxes. I think you’ll find that a useful read! See here: http://amzn.eu/bMtxj6C Regards, James
I used to have a BSA C11 and often wondered how the voltage regulator worked. Now I know.
I suspected that it used variable on/off ratios to get an effectively analogue result from a digital system, and I connected my simple cathode ray oscilloscope to it to check, but I don’t recall seeing anything.
Very helpful, thankyou.
A question if I may. Is it possible to convert a two bobbin regulator to a three bobbin. I have an RF95/2 and wonder whether an RB310 can be substituted by connecting together the A1 and A to go to the B terminal. The others are straightforward. The generator is a C45PV4.
Thanks
Richard
Hi Richard. I’m not sure to be honest as I don’t have any experience with the three bobbin regulators. What type of vehicle is this fitted to? My gut feeling is that a conversion could probably be made to work, but that the various resistances, cut in/out voltages, current limits, etc. would not be quite right. The coils vary in ways that might not be immediately obvious (wire diameter and resistance and number of coils, for example), so might not perform the same even if they look similar. My advice would be to find a modern electronic regulator to do the job instead which will give much better performance. Take a look here: http://dynamoregulators.com/
I have a question regarding voltage regulator operations outside normal operating conditions.
What is likely to happen to a 6V system if a 12V battery is inadvertently installed?
I thought that perhaps the dynamo would remain disconnected as it could never match the battery voltage – however this could only be true if there was some sort of balance coil system – it seems from your excellent explanation this is not the case.
I initially surmised that the regulator could have been damaged but the dynamo could have been spared.
Wow, what a calm and clear description. I really feel as though I can take on the god of darkness now. I have looked at several old charging systems using the prescribed voltages for indications of function, but I now I feel I know what I am doing. Many Thanks
Dave 31 Aug 2017
Hi,
i am renovating a 1953 “Monet & Goyon” – Koehler Escoffier. it has a Villiers 197 cc engine. it has resided in a garage in the uk for 30 years and before that a hay loft in France for 30. i am at rewire stage. i have tried to maintain the loom but it is a bit fragile. i have looked for similar wiring diags but there are so many to choose from. not sure if its + or – earth? or how to determine. i have a regulator with three terminals and absolutely no markings of any sort. diags i have seen described 4 terminals D F E & A. how do i map these 4 to my 3 ? any help would be much appreciated
Hi Bob. To be honest, I have no idea! I’ve don’t have any experience with Villiers engines and their associated wiring diagrams. But hopefully a few tips to get you started in the right direction: Firstly, are the electrics powered by a DC dynamo or an AC alternator? Hence is it a regulator (device to limit the voltage output) or rectifier (device to turn AC from alternator to DC for battery) that you are trying to wire up?
I’d start by working out the make and model of the dynamo / alternator. Then work out whether this is designed for positive or negative earth (some can be made to work either way by ‘flashing’ the polarity. Then hopefully you can find a wiring diagram to suit.
Also, have you seen my book “The Classic Motorcycle Electrical Manual”? it doesn’t explicitly cover Villiers electrical systems, but will give you all the help and info you need to complete your rewiring. Take a look at it on Amazon perhaps. Here’s the link:
http://amzn.eu/hCm97cf
Regards, James
Excellent write up, all my bikes have been post 1960 alternator machines but I have always wondered how the little Lucas electrons work inside that black box and how they get fed. I’ve just had to help a friend with a problem with a BSA A7 and it revived my interest in the regulator, especially as the it has relays and having been, in the 60’s, a GPO telephones strowger telephone exchange engineer where we had millions of relays I thought this is just my bag. Anyhow I now do understand how it works and realise that adjustment of these things is not for the bodger even if he thinks that he was an expert in the 1960’s. Just shows how a little knowledge is a dangerous thing. I’ll offer a well done to the much maligned Mr Lucas for such a well thought out device.
AND well done and thankyou MR Matchless clueless.
A great article and a great read. My grandad would have known everything about these clever devices but now he’s no longer here to guide me this information has been very valuable! After learning about the regulator I got the meter out and tested across all the points for continuity as the battery was not charging on my 1954 BSA B31. I’ve used 1200 grit to clean them and a new battery should arrive tomorrow. All being well the lights and horn will be working and the battery will charge while she’s running. I’m very grateful that the author (and readers in the comments) have taken the time to share their knowledge to help my generation of enthusiasts to keep our loved machines working as they should.
Hi
i have a 1952 Sarolea, a belgian made bike.The mass is here on the negative.The bike had a Lucas regulator but it is broke. can i replace it by an MCR2 ? Does the fact that the mass is negative or positive play a role here?
Thks for your reply
Sorry Ludo, think something got lost in transnational here! Not sure what you mean by “Mass”. Do you mean “earth” perhaps? The MCR2 regualtors can be used with either positive or negative earth electrical systems, if that answers you question. Regards, James
Hi, great read thanks.
I’ve replaced the Lucas regulator on my Fordson Dexta but found that Ford made a running change and the replacement regulator (it appears not to be a Lucas), no longer has the A1 terminal. The manual notes this change along with the comment that a new wiring loom is required for the upgraded regulator. Now, given that the wiring diagram, in all its glorious detail, occupies less than a single page, it would not appear too difficult…
My question, is it simply a matter of connecting the “A” and “A1” wires to the “A” terminal?
Many thanks
Hi Dave. Yes, it probably is a relatively simple tweak to the wiring diagram, but I am not exactly sure what or how of the top of my head. You will need to compare the wiring diagrams for the two different regulators and see how they differ. These electrical systems were / are very versatile which means that there were lots of variations as different manufacturers tweaked the setup for different models of vehicle. The same switch or regulator could be wired in many different ways! So you’ll need to do some detective work, good luck! James 🙂
Thanks James – I just connected the 2 wires together, and it worked like a charm. My tractor doesn’t have a set of lights, so the A1 terminal, which was supposed to provide voltage to the light (an on/off) switch was redundant once I put a key ignition switch in anyway. It is now simply supplying voltage to the manifold heater.
The old Lucas gave up after 60 years of service, which isn’t too bad. the cut-off relay looks fused, but I’ve got it on the bench to see if I can resuscitate it.
Thanks for your prompt response.
Hi James,
Thanks for this very clear and informative article. It is the best I have seen and I now understand the principles of how the RF91 regulator/Control box on my 1939 Wolseley 25 Drophead Coupé work.
The problem I have is that the dynamo is not charging the battery.
I can get the Dynamo to charge the battery if I short the D and F terminals at the control box. As soon as I remove the short from the D and F terminals there is no charging at the battery.
Any ideas would be appreciated.
Thanks for putting this article together.
Regards,
Gordon
Very helpful article, thank you.
My Sunbeam S7 Deluxe blows the light which should go out when the bike is charging (it goes out first and then, as you rev the engine, it goes brighter and then blows). I’ve replaced the entire wiring loom and get the same problem so I think it is the regulator…
Based on what you have helpfully written, the cut out (cut in) circuit is working and is allowing the charge from the dynamo to feed into the system but then either the voltage or the current regulation isn’t kicking in to limit the voltage from the dynamo (I think). I’m going to set to with a voltmeter to test the regulator switch and maybe try giving it a clean with some fine sandpaper and contact cleaner… Wish me luck!
Hi James!
Very useful knowledge you’re sharing, thanks!
I’m strugling to get my after-market regulator to work correctly.
I have B+ to chassis, is the regulators polarity sensitive?
BR / Erik in Norway
Hi James!
Very useful knowledge you’re sharing, thanks!
I’m strugling to get my after-market regulator to work correctly.
I have B+ to chassis, is these DC-regulators polarity sensitive?
BR / Erik in Norway
I started by bemoaning your waffle at the beginning and now I’m commenting regarding the lack of detail !
My guess as to the purpose of the cut out was correct. You say vaguely that it disconnects the battery from the dynamo so as to not flatten the battery when the dynamo’s not charging. So now please explain what the cut out disconnects:
Field winding
Rotor winding
Both ?
I’m suspecting just rotor winding.