Questions & Answers

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

How do your regulators work?

The output voltage from a typical vehicle dynamo depends on the rotational speed of the armature, and the magnetic field strength through which it turns. The strength of the field is determined by the current flowing in the field winding(s). The regulator compares the output voltage with a precise reference voltage, and controls the average field current to maintain 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 similar 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 controlled with a transistor. The cut-out function is performed by a diode or transistor switch, 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.

How much heat do your regulators generate?

Not an easy one line answer to this, I am afraid. The power consumed in the unit depends of course on the output current at any time, and also on the speed of the dynamo to some extent (the field drive at lower speed needs to be higher). For the DVR2 the maximum heat generated at 8 Amp load is about 5 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. For the DVR3 and 4 units the maximum heat generated at the maximum 22 A load current is about 6 Watts. temperature increase for the larger case in still air is about 35 C maximum. For the 11 Amp unit the heat emitted is a maximum of a little over 3 Watts worst case.

How is it that the DVR3 & 4 run so cool?

These regulators do not use a diode to perform the cutout function, which is to prevent current flowing back into the dynamo from the battery at low or zero speed. Instead of the usual diode they use high current transistors which only switch on and pass current when the dynamo voltage is greater than the battery voltage. This technique allows the power lost in the cutout element to be reduced to well under half that seen in most electronic regulators on the market. This is a key part of what we mean by "cool and efficient". Low heat dissipation aids reliability and it also allows for very compact size in the regulator.

Does the charge/ignition warning light still function with your regulators?

Yes. The 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 output to the battery.

The ammeter on my mag-dyno machine shows a decent initial charge which falls rapidly as things "warm up". What is happening?

Referring to the ubiquitous Lucas MO1 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. When stood for a period the friction returns to a maximum and may be enough to again drive the dynamo at charging speed. This shows as an unusual falling ammeter reading.

Does the DVR2 suit both Lucas E3L and E3LM dynamos?

Yes, it also works fine with the lower power E3H and E3HM versions.

Will your DVR2 suit:
a. The Lucas MC45L dynamo fitted to my Sunbeam / Scott?
b. A Lucas C35SD dynamo on my Ariel Square Four?

Yes, in both cases.

Is the DVR2 suited to the Miller dynamo fitted to my Vincent / Velocette (etcetera)?

Yes, as long as field is wired to earth and original cut-out removed.

View Miller with DVR2 datasheet (Adobe Acrobat PDF format)

Is a DVR3 suitable for use with the 3-Brush dynamo on my pre-war car?

What is the maximum power output of the DVR2?

Maximum output is not really limited by the regulator. 75W for 6V system and 100W for 12V system is safe for the regulator.

What voltage can I expect at the battery using the DVR2/3/4?

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.

How do I polarise ('flash') 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 should be seen. Your dynamo is now polarised NEGATIVE earth, simple as that.

(Swap POSITIVE and NEGATIVE in the above to polarise for POSITIVE earth)

This procedure 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 a good idea to stick a prominent reminder near to the battery when the vehicle's earth polarity has been swapped, to avoid future polarity sensitive connection problems.

How can I check the output from my dynamo?

Shunt Field 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 show the polarity of the output. 6V or 12V should be seen on the meter at a speed equivalent to perhaps 30 mph on the road.

For a Series Field 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.

My dynamo checked out OK, but I get no output from my DVR2 (or 3). Why?

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 startup 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.

Do you advise changing a 6 V set-up to 12V?

Many 6 Volt dynamos on both motorcycles and cars work perfectly well at 12 V with no changes. The benefits of going to 12 V include better lighting and easy parts availability. The downside is that charge balance will take place at typically 30 % higher speed; no problem for cruising but could be around town. More power will be available at 12 V as a result of lower heating in the armature (half the current for given power). The DVR2 allows swapping to 12 V and back to 6 V by a very simple wiring change.

Is it worth rewinding a 6 V dynamo for 12 V operation?

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 (at least 50% more power available). Reliability may suffer and the initial cut-in may be delayed where the residual magnetism is low. The DVR2 gives much more output at lower speeds than some (puzzlingly) popular regulator units in any event; at least one competitor will actually discharge the battery at low speed. So it is worth trying the lower cost & hassle DVR2 upgrade first.

Will I benefit from fitting a larger capacity battery?

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.

Will I benefit from fitting a voltmeter or voltage monitoring device?

Spend your cash on an ammeter that works well instead. They do not all flicker wildly all the time if the charge regulation is good. A voltmeter will sometimes show a misleading high reading despite the battery being shot. Ammeter current gives a clear indication of the charge at a given time and is a better option in a dynamo system.

Will the dynamo start up with a completely flat battery?

Yes, the DVR2 will start with a very low battery. 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.

Wouldn't I be better off installing a modern (expensive) alternator alternative?

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 adequate charging is possible at all times for normal electrical loads.

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

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

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