Introduction to Dynamo Regulators Ltd

At Dynamo Regulators Ltd, our aim is to provide voltage regulators of superior design to improve charging systems of many varieties of dynamo equipped motorcycle. Modern electronics can greatly enhance the performance and reliability compared with original electromechanical regulators. When the commonly weak charging on classic bikes has been greatly improved there are plenty of challenges remain to provide enjoyable fettling!

DRL’s regulators feature surface mounted high temperature rated components, machine soldered onto quality printed circuit boards (PCB) with heavy duty copper layer. The PCB assemblies are produced by UK based subcontract manufacturers to conform to all relevant manufacturing standards.

We mount the PCB assemblies in machined Aluminium cases to ensure excellent heat transfer. The potting used provides complete protection from mechanical and thermal stresses as the regulators will often be situated in extreme engine bay conditions. We never use unreliable components in our designs, such as electrolytic capacitors or even worse potentiometer adjusters which will degrade or lose adjustment over a period of use (due to heat cycling and vibration). The regulation itself results from a low loss switching technique.

The compact nature of the regulators allows them to be fitted inside most sorts of original regulator enclosures. The DVR2 will fit inside an MCR1, MCR2, RB107 or RB108 case for example.

The small size of our regulators helps to make the change to electronic regulation very straightforward, and practical for most enthusiasts with a little electrical ability. But please heed our advice: If in any doubt please employ the services of a qualified auto-electrician, or other competent person.

Although our aim is to help, we are not always able to give detailed advice on a regulator to suit motorcycles of all makes, models and years (we hope that sounds reasonable). Ultimately it has to be down to the purchaser to select the correct earth polarity and voltage to suit their (perhaps rare Vintage or Classic) bike. Most marques will have their experts with all the information to hand, or at least with access to all the handbooks. Such information is often accessible on-line with a little searching. We can’t and won’t do all the leg work; that time is not factored into our pricing! We will of course offer assistance with relevant charging system technical and application information wherever we are able.

Electronic Regulator Questions & Answers

Welcome to our Question & Answer page. You may find the answers to many queries on the individual product pages or in the data-sheets which may be viewed on-line or downloaded. Or you may find the answer to your question here (Click on the question to read answer):

The output voltage from a typical vehicle dynamo is proportional to the rotational speed of the armature, and to the magnetic field strength through which it turns. The strength of the field is primarily determined by the current flowing in the field winding(s). The regulator compares the output voltage with a precise reference voltage, and rapidly switches the field drive on and off such that the average field current maintains the correct charging voltage.

The conventional mechanical regulator achieves output control by means of an electromagnet bobbin coil which opens a set of electrical contacts to cut the supply to the field as the voltage rises above a set level. The output voltage drops a little, then the contacts close again, and voltage is again applied to the field, thus increasing the output in turn. This cycle happens hundreds of times per second so that the dynamo output runs at a steady level, as required to charge the battery and drive the lights and other electrical loads. The contacts in the cut-out bobbin close at a suitable voltage to connect the load side (and open when the dynamo voltage falls below the battery voltage) so as not to discharge the battery at low speeds or when stationary.

DRL’s modern electronic regulators function in an analogous manner. The voltage to the field winding is switched on and off in a rapid cycle setting the average field current as required for the armature to supply the appropriate output voltage, as speed and load vary. But instead of a set of points, the rapid switching is accurately performed by means of a transistor. The cut-out function is performed by a ‘low drop’ diode, which passes current when the dynamo output is greater than the battery voltage, and blocks unwanted current flow when the output is lower than the battery.

There is no easy one line answer to this question. The power consumed in the regulator unit depends on the output current at any time (of course), and also on the speed of the dynamo to some extent (the field drive at lower speed is higher).

For the DVR2 the maximum heat generated at 8 Amp load is about 4 Watts. This heat will increase the case temperature over surrounding still air and with no heat-sink by up to 40°C after an extended period. The maximum continuous safe temperature for the aluminium case is 85°C.
The conventional mechanical regulator achieves output control by means of an electromagnet bobbin coil which opens a set of electrical contacts to cut the supply to the field as the voltage rises above a set level. The output voltage drops a little, then the contacts close again, and voltage is again applied to the field, thus increasing the output in turn. This cycle happens hundreds of times per second so that the dynamo output runs at a steady level, as required to charge the battery and drive the lights and other electrical loads. The contacts in the cut-out bobbin close at a suitable voltage to connect the load side (and open when the dynamo voltage falls below the battery voltage) so as not to discharge the battery at low speeds or when stationary.

DRL’s modern electronic regulators function in an analogous manner. The voltage to the field winding is switched on and off in a rapid cycle setting the average field current as required for the armature to supply the appropriate output voltage, as speed and load vary. But instead of a set of points, the rapid switching is accurately performed by means of a transistor. The cut-out function is performed by a ‘low drop’ diode, which passes current when the dynamo output is greater than the battery voltage, and blocks unwanted current flow when the output is lower than the battery.

Proudly Designed & Manufactured in the UK. The cases are machined locally and the electronic circuit boards are assembled by a specialised sub-contractor in Surrey. That said, component parts are from a variety of countries; there is not much semiconductor manufacture within the UK! For that matter the aluminium alloy for the housing will be imported as well. But the great majority of the added value in the products is to the benefit of UK PLC. Wherever manufacture takes place the key is to maintain good quality control, to which we attach high importance.

Yes. It will still work normally, with one small caveat. If there is no load on the regulator (magneto ignition) and with the battery fully charged the regulator may periodically shut down the dynamo as no output is demanded to keep things topped up. In rare instances this leads to an occasional flicker of the warning light, which is of no real significance. Be aware that the indicator light is at best a crude indicator of charge function. The lamp goes out at a voltage well below that required to give any useful charging current to the battery.

Referring to the ubiquitous Lucas MO1 motorcycle Magdyno the dynamo is driven by a fibre disk friction clutch. Other types are similar in this respect. Like any clutch this one may come to slip as it ages in normal operation. The slipping becomes worse as frictional heat builds up. When stood for a period the friction returns to a maximum and may be enough to again drive the dynamo at charging speed. Increasing slippage shows up as a falling ammeter reading.

Yes, in both cases.

Yes, as long as the field winding is internally wired to earth for live side regulation and the original cut-out is removed or taken out of circuit.

View Miller with DVR2 data-sheet (PDF format)

Maximum output is not really limited by the regulator. It will provide a continuous current of 10 Amps. 75W for 6V system and 100W for 12V system is safe for the regulator.

Nominally 7.2 V in a six volt set-up and 14.2 V for twelve volts. More is definitely not better here. For example 14.5 V as commonly stated as ‘correct’ will mean higher trickle charge leading to more topping up and shorter life for your battery.

Battery capacity when using a DVR2 is not too important. For 6 V use an 8 Amp-hour battery is a good choice, for 12 V setup 4 Ah is a decent size. Larger batteries may give a longer service life, and probably best not to go below half of these capacities as a minimum. Gel type batteries are a good choice, but traditional wet acid types have their advocates.

There is a small current into the regulator’s ‘A’ terminal from the battery. For the DVR2 this will be a little less than 1 mA for 6 V operation (about 1 mA at 12 V), measured at about 20 C (1mA is one thousandth of an Amp). Temperature is significant when making this measurement as the reverse current through the cut-out diode is a strong function of temperature. If the regulator has been working hard and thus running warm the back current might well double or more, temporarily.

A 1 mA current would in theory be sustained by a typical 8 Ah battery for about 5 months before it is half discharged. In practice the self discharge of the battery will likely be higher. It does makes sense to disconnect the battery from all wiring during any long lay up.

To polarise a dynamo for NEGATIVE earth:
Your battery’s NEGATIVE terminal should be connected to the chassis or frame. Disconnect the D & F wires from the dynamo. Take a wire from the unearthed (POSITIVE) terminal on the battery and ‘flash’ it onto the F terminal of the dynamo. That is touch the ‘live’ wire onto the F terminal briefly, for a second will do it. A small blue spark will be seen. Your dynamo is now polarised NEGATIVE earth, simple as that.

To polarise a dynamo for POSITIVE earth:
Your battery’s POSITIVE terminal should be connected to the chassis or frame. Disconnect the D & F wires from the dynamo. Take a wire from the unearthed (NEGATIVE) terminal on the battery and ‘flash’ it onto the F terminal of the dynamo. That is touch the ‘live’ wire onto the F terminal briefly, for a second will do it. A small blue spark will be seen. Your dynamo is now polarised POSITIVE earth.

The above method applies to dynamos with the field wired to earth, regulated on the live side, e.g. Lucas types.

To polarise a Field to Live dynamo for NEGATIVE earth:
(For information only-the DVR2 is not suitable for Field to Live dynamos, e.g. Bosch)
Connect DF to Earth. Lift either brush in the dynamo from the commutator so that a large current cannot flow through the armature. Flash (briefly connect) battery Positive to D+/61 terminal.

Re-polarisation may be used to ‘wake up’ an old dynamo which has not been used for a long period or to confirm polarity in case of any doubt, as well as to deliberately reverse the polarity.

It is not a bad idea to attach a prominent reminder near to the battery when the vehicle’s earth polarity has been swapped, to avoid polarity connection issues in the future.

Field to Earth Dynamo e.g. Lucas: Remove any wires from the Output and Field terminals (Lucas D and F) and connect a wire between them. Connect a 12 V bulb (e.g. 21 W indicator bulb) between the two linked terminals and ‘ground’ or the dynamo case. Spin up the dynamo and at modest revs the lamp should glow brightly, even with a 6V unit. Increase the speed slowly and do not continue this test for long. Even better use a voltmeter to monitor the voltage (the field coil acts as a load). The meter will also allows the polarity of the output to be confirmed. 6V or 12V should be seen on the meter at a speed equivalent to perhaps 30 mph on the road.

For a ‘Field to Live’ dynamo e.g. Bosch or a Dynastarter: Instead of the linking Output (61/D+) and Field (DF), link Field to ground. Connect the bulb or meter between Output and ground.

The output test above is a simple GO/NO-GO check but other factors also come into play. The bulb check does not confirm correct polarity; use a meter for this. Also the speed at which the dynamo gives ‘a good output’ is not monitored. Low output for the rotational speed will delay or even prevent the start-up of an electronic regulator. This can be due to low magnetic efficiency in the dynamo. Some 12 V converted dynamos may give problems as specifications vary and some are poorly done. New dynamo brushes may need to bed in, may be made of poor quality material, or the lead attachment can sometimes be suspect. These are all deviations from standard performance of the dynamo. Manufacturers will normally state a certain power or voltage output with a given load resistance at a specified speed. Or of course there could be a simple problem in the wiring harness, connectors, ammeter or wherever.
For a ‘Field to Live’ dynamo e.g. Bosch or a Dynastarter: Instead of the linking Output (61/D+) and Field (DF), link Field to ground. Connect the bulb or meter between Output and ground.

If your dynamo, with D & F connected, gives a strong unregulated voltage of the correct polarity, and the wiring to the DVR2 is definitely good this PDF describes a test procedure:

Test regulation of DVR2 (PDF format).

It requires the use of a variable power supply and is not a 2 minute job. Unless you are competent & confident working on motorcycle electrics it is not for you. Get it wrong and there is a risk of damage, and we are unable to nurse users through the procedure. Please be warned, but hoping it proves useful to some.

Some 6 Volt motorcycle dynamos work perfectly well at 12 V without modification, with a 12 V regulator fitted. The benefits of running at 12 V might include better lighting and easy parts availability. The downside is that charge balance will take place at typically 30 to 50% higher speed; no problem for cruising but could be around town. More power will be available at 12 V (from a standard 6V dynamo) as a result of lower heating in the armature (half the current for given power out). But at lower speed the standard field winding may produce more heat. The DVR2 makes it easy to experiment with 12 V operation to see if it works for you, and to swap back to 6 V by a very simple wiring change.

6 V dynamos may be rewound for 12 V with more turns of thinner wire to provide higher voltage. The benefit is a lower cut-in speed but this will be offset by lower power output than a 6 V machine run at 12 V (which can provide 50% more power). Reliability may suffer due to the more fragile wire and the less robust construction of some pattern armatures. Maximum safe current depends on the exact number of turns used on the armature. If twice the turns then 4X resistance, and current available is limited to about 5 Amps. The DVR2 gives much more output at lower speeds than some popular regulator units in any event (at least one competitor regulator will actually discharge the battery at low speed). So it is worth trying the lower cost & hassle DVR2 upgrade first.

No, not really helpful. Unless you have say a 12V 60W headlight on and often sit in a lot of slow traffic. A discharged large capacity battery loads the dynamo more and for longer. If a large battery is fitted (as in the case with an retrofitted electric start) a current limited regulator may better protect the dynamo and prevent nuisance fuse blowing, if the battery becomes discharged.

To start with ensure your ammeter works well. It should not flicker wildly all the time if the charge regulation is good. Ammeter current gives a clear indication of the charge at a given time and is a better option in a dynamo system. A voltmeter can sometimes show a misleadingly high reading despite the battery being ‘shot’. An occasional check on the bike with a meter of the battery voltage under charging conditions may be worthwhile to confirm all is well with the charging system.

Yes, the DVR2 will start with a very low battery, down to a few volts in fact. If fully discharged it will wake up with battery disconnected (magneto ignition assumed!), then reconnect the battery. Regulation will not be as good as in normal use, but a useful get you home measure after dark.

Sorry we don’t sell any 24 Volt regulators. We have no plans to despite being asked from time to time. It would mean a complete redesign of our circuitry, frankly for relatively few extra sales.

No. Some original relay types included a bi-metal strip to reduce charging voltage as its temperature increased. The intention was to reduce risk of overcharging the battery when warm. But the voltage change then responds to regulator temperature, not the battery as required to make the scheme work. Varying the electronic regulator’s output voltage with temperature would be quite straightforward but sensing battery temperature would add unreasonable complexity. Our regulators control voltage far more accurately in any case, and the risk of battery boiling is avoided.

A matter of taste and depth of pockets perhaps. But the Lucas dynamo (for example) in reality is a rugged & reliable unit, and requires minimal maintenance. Coupled with a DRL electronic regulator ensures efficient charging at all times for normal electrical loads.

Certain modern motorcycle A.C. generator and replacements have a history of reliability issues, have been noted be noisy, and cruising speed output may be little if any better than with the original d.c. generator.

We certainly do not recommended fitting a lithium chemistry battery. If not correctly maintained there is a serious risk of fire/explosion with some types. The Lithium Phosphate ones are sometimes billed as a direct lead-acid replacement, but these do not offer so much advantage in terms of capacity for size and self discharge rate. The weight reduction is neither here nor there.

There are many variants of lead acid battery, and some offer practical advantages over old tech wet ones. Gel or AGM batteries are all good with our regulators, and some offer such low self discharge rates that you will not get a low battery, even if you don’t use your P & J for an entire winter’s lay-up.

Whatever type your 3 brush dynamo is, ensure that any external charge controlling resistors or switches are removed from the Field circuit after converting it to 2 brush. This refers to Summer/Winter, High/Low, Headlight/Sidelight connections which were a simple method of controlling dynamo charge. If left in circuit these may override the DVR’s control and lead to a damagingly high voltage output.

In addition click Lucas dynamos and charging system (Matchless-clueless) for an excellent practical guide for fettling classic motorcycle electrics. Written with bikes in mind but much is relevant to cars and other dynamo systems as well. (Why reinvent the wheel?)

We have kindly been granted permission to use the attached account of how a DVR2 solved long standing electrical issues on an NSU 250. The full article appears in the Feb23 issue of RealClassic magazine.

A good clear description of fitting a DVR2, in this instance to a Velocette Venom, may be viewed at Newenglandzen: step by step fitting of DVR2.

If your query is not answered above, you may put your question using this form:





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    DVR2N/P data & installation guide
    Test regulation of a DVR2/N/P with a bench PSU
    Using a DVR2N/P with a Miller Dynamo

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