looking at the pro's and cons of converting to 12v.
There are several ways, the most expensive is changing the dynamo for a 12v alternator.A cheaper option seems to be swapping the 6v regulator for a step up converter,a DVR2, Digiten and several other makes are advertised on the web.
Has anyone done this? If so,what make did you use and what were the results? Thanks.
Hello,
I have used : DVR2,. Positive Earth.
This is working like charm. Dynamo is still old Lucas 6V. All works fine. but easily I get 12V to charge my battery. Only really low rpms take juce from battery to lights.
I just wish I was not sticking to positive Earth and take negative earth unit. LED bulb selection would be far wider.
Overall I would recommend DVR2
Dan
I have used DVR2 regulators on all my dynamo equipped bikes for years. Change to neg earth asit makes it easier to get bulbs.
I too have DVR2 and stuck with +ve earth on my 'scrambler' and with freshly rebuilt Dynamo and new battery get 13.5v across the battery at surprisingly low revs.
The dynamo on my ZB32 was knackered and needed rebuilt. I did so using 12V armature and field winding and DVR2 regulator. No problems in last 3 years.
Can't go wrong with DVR2 regulator, it's the only one that will charge a battery even if it's flat, fit and forget.
I have both sides of my engine open in order to set up the gearbox (see other thread). Might there be any advantage in fitting a 12V alternator while the engine is open anyway?
Your 6V alternator is quite capable of running 12V system although if you are upgrading it would better to fit a 2 wire alternator intended for 12V which will provide more power. Or, if you want to splash out go for a 3 -phase alternator (https://rexs-speedshop.com/product/high-output-12-volt-lucas-3-phase-alternator-kit-with-pme-regulator/).
You have all persuaded me that the DVR2 is the way to go.
Although I have been 'spannerin'bikes since Pontius got his pilot's licence,electrics have been a mystery to me.
My B31 is positive earth, to change to negative earth is it simply swapping the battery leads and ammeter leads over and wiring in a negative earth DVR2 to the manufacturer's instuctions?
Don't laugh,I have been spoilt by years of Japanese bikes and have largely forgotton what it's like to own a proper British bike.
You'll need to flash the dynamo too.
Do what you said re the change. If you don't know how. To flash the dynamo for correct charging take the lead to the dynamo f or field and flash it against the live terminal of the battery, this will then change the polarity of the dynamo.
You don't need to convert to negative earth - nothing wrong with sticking with +ve earth, yes your choice of LED bulbs can be more extensive but the DVR2 and decent dynamo (again you do not need to change the dynamo armature to skinnier wire that the 12v conversion uses) the 6v dynamo will be fine, unless you plod around at <2000rpm in town, similarly the stock 6v Lucas Altette horn works just fine too.
That's interesting re DVR2 positive earth.LED bulbs are polarity sensitive, but am I being thick here.
Pos earth the juice comes up the black wire and down the red the opposite of negative earth.Is it possible to simply swap the wires over on a negative earth auxilliary LED light.
Another thing puzzling me is the amps produced.The 6v dynamo on my B31 is given as 60w which is 10 amps,just enough to balance all the lights.Converting to 12v,does that mean that the amperage doubles?or the wattage doubles?or neither.It rather seems like getting something for nothing.
Quote from: Janacek on 31 Jul, 2025, 23:51 That's interesting re DVR2 positive earth.LED bulbs are polarity sensitive, but am I being thick here.
Pos earth the juice comes up the black wire and down the red the opposite of negative earth.Is it possible to simply swap the wires over on a negative earth auxilliary LED light.
Another thing puzzling me is the amps produced.The 6v dynamo on my B31 is given as 60w which is 10 amps,just enough to balance all the lights.Converting to 12v,does that mean that the amperage doubles?or the wattage doubles?or neither.It rather seems like getting something for nothing.
Some LED bulbs are configured that they will work both negative and positive earth but most are polarity sensitive and require a negative earth.
Your dynamo at 12V is probably still 60W but a 12V bulb draws ½ the current of a 6V one. A 36W 6V bulb draws 6A but a 36W 12V bulb only draws 3A. So out of your 10A available there would still be 7A left to power everything else.
Regarding LED's, the bulb polarity is important when the body of the bulb is grounded to the frame via, for example, the rear lamp assembly. This is where negative earth might be an advantage if there is better bulb availability. For an auxiliary light that has two wires and is not electrically connected to the frame, bike polarity is not an issue.
In theory, a 6v dynamo controlled by a 12v regulator could generate double the power. In practice however, there are several limitations (winding resistance, heat dissipation, rotation speed, age, construction, etc) that effectively limit the output to not much more than the originally specified 60 watts.
If you convert a 6volt dynamo to 12 volt you can expect a realistic 80 watts as an output.