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12 volts from 6 volt dynamo

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12 volts from 6 volt dynamo

Posted by David Cooper at October 08. 2012

Al Osborne has written the piece in the technical section of this site in which he discusses the merits (and otherwise) of regulating 12 volts instead of 6 volts from a standard dynamo.  Date was 1999 - and things like LED bulbs and newer regulators are now around.  Is the essay up to date?

I'm currently trying to get a prewar 16H (with magdyno) back on the road and in the shopping list is the battery - and indecision rules as usual.

I need to find a cosmetic battery box, then a battery to fit it, and a new regulator (only because the original has not been tested for decades).  So it is immaterial to the cost if I use 12 or 6v.  I imagine LED pilot and back lights are the way to go - so the only power drains on electrics are the headlight and panel light.  Any advice welcome, please?  Can I even get a 12V battery to fit a t-shape battery box?  I feel a browse around Kempton Park might be useful at the end of the month - but only if the specialists are also there.

 

I live in London - and although I don't expect much night riding in the city I don't want to rule it out.

Re: 12 volts from 6 volt dynamo

Posted by Gordon Johnston at October 08. 2012

I converted an E3L to 12 volts by fitting an American-made 12V armature and field coil. Works of art, especially the spiral-wound silver soldered armature. I am very wary of taking a bog-standard dynamo and sticking a 12v regulator on it. There are not enough windings and the wires are rather thick. What can happen (and I have the evidence in a box) is that the extra heat in the dynamo can melt the solder holding the commutator segments which let go and fly out, seizing the dynamo. If you run up a 6v dynamo without the regulator, it will produce up to about 20 volts but theay were built to produce a regulated 6 volt output - tinker with that at your own risk. Just make sure you use decent wiring, have a separate earth wire to everything and take a look at the whizzy new 6 volt bulbs. Gordon. Oh, I can recommend solid-state regulators.    

Re: 12 volts from 6 volt dynamo

Posted by David Cooper at October 08. 2012

Thanks, Gordon.  I recollect something about the drawbacks of low voltages are mostly in things like contacts - the lower the voltage the more exotic the contacts in switches and plugs should be.  So computers use gold, and 6 volts needs silver, and 12 volts is OK with copper - or something like that.   But neither Lucas nor Norton used silver contacts... 

I wonder why 12 volts would get hotter?  Current should be half that for 6 volts for the same power.  But I suppose dragging more power from it at high revs with halogen bulbs etc might cause problems?

Re: 12 volts from 6 volt dynamo

Posted by Gordon Johnston at October 09. 2012

I didn't explain the heating as I don't understand it either - but I was informed by someone who really understands these things that it is the case - and I have the exploded dynamo to prove it. For 12 volts, you need lots of thin windings. For 6 volts you need fewer, thicker windings. It's a consequence of insufficient numbers of turns of winding I think which causes the problems trying to get 12 volts from a 6 volt dynamo. Of course you can change your E3H for an E3L on your magdyno. Same voltage, more watts. I had better read Al's bit on dynamos or he will be on me like a ton of bricks for spouting forth on subjects I don't know a lot about...

Re: 12 volts from 6 volt dynamo

Posted by lionel_yexley at October 09. 2012

It's the amps Gordon.  Like comparing a 30 Watt Vox with a 100 watt Marshall :) If you run a dynamo up to 12V when it was designed (using the term VERY loosely!) for 6V you double the potential amps too.  There's a much greater volume of smoke to pass through it (See current RH for technical info about the smoke. Ooh!  "Current"? is that a pun coming on?)

Cheers, Lionel

Re: 12 volts from 6 volt dynamo

Posted by Gordon Johnston at October 10. 2012

Ah yes, it's the old power = I squared R thing, innit. Double the I (or amps) and you get 4 times the power, or watts, or in this case heat to melt the solder holding the commutator segments in place. Sorry, have been under the weather with man flu and the brain has turned to porridge. Don't know if either the Vox or the Marshall could compete with my bagpipes when it comes to disturbing the peace... Gordon. 

Re: 12 volts from 6 volt dynamo

Posted by iain_brown at October 10. 2012

Hmm, well there is a least one person out here running an E3H at 12V. LED pilot light and tail light and a solid state regulator (Hawker).

Not that i have done a great number of miles, longest run is 160km (100 miles) so far, but no troubles as yet.

From memory Paul Goffs website seemed to suggest it was ok so i took the plunge.

The new Shorai batteries are tiny and fit easily in an old style battery box - they may only be available in 12V though?

 

Previously wrote:

Ah yes, it's the old power = I squared R thing, innit. Double the I (or amps) and you get 4 times the power, or watts, or in this case heat to melt the solder holding the commutator segments in place. Sorry, have been under the weather with man flu and the brain has turned to porridge. Don't know if either the Vox or the Marshall could compete with my bagpipes when it comes to disturbing the peace... Gordon. 

 

Re: 12 volts from 6 volt dynamo

Posted by David Cooper at October 10. 2012

Still waiting for Al to take the bait!

One of the benefits of using higher voltages is that bigger power can be carried by smaller wires.  Watts = volts x amps.  For 36 watts at 6 volts we need 6 amps, but for 36 watts at 12 volts we only need 3 amps.  So at 12v there should be less strain on commutators, switch contacts and wiring...in theory.

 

Anyway - it's 'only' a 16H and I suspect it won't rev high enough often enough to reliably provide 12 volts.  And since it won't be doing 70mph along the A3 I expect I shall stick with original 6v.

Re: 12 volts from 6 volt dynamo

Posted by alan_dawes at October 10. 2012

Sorry, have been under the weather with man flu and the brain has turned to porridge. Don't know if either the Vox or the Marshall could compete with my bagpipes when it comes to disturbing the peace... Gordon.

Get some whisky down you Gordon.

Re: 12 volts from 6 volt dynamo

Posted by joe_gibbs at October 12. 2012

Hi all, I ran a 6volt dynamo regulated to 12 volts on my old Ariel 350 for about a year to work and back (30 miles a day) all through the winter. The main problem was the load with a 55watt headlamp and led tail lamp would just about balance at about 36 mph. SInce a lot of the unlit roads are 30 restricted I had to push the old bike on the unrestricted parts to give the battery same charge. Never had any dynamo heating/reliability problems though. I switched to a 12 volt armature and field coil and it now balances at below 30pmh, much better  the regulator is a solid state thing I built myself. Hope this helps.

Joe G.Previously wrote:

Sorry, have been under the weather with man flu and the brain has turned to porridge. Don't know if either the Vox or the Marshall could compete with my bagpipes when it comes to disturbing the peace... Gordon.

Get some whisky down you Gordon.

Re: 12 volts from 6 volt dynamo

Posted by ashley_cutler at November 24. 2012

Nothing wrong with 6V providing all connections, contacts and earth points are good. I use a 6V halogen from Goffy and it works a treat giving a better light pattern than my commando. As for regulators, look up Dynamoregulators.com (based in Hampshire) they are designed to regulate better and at lower revs, you can also select the Voltage and current to be controlled of some the models. I use one on my Puch SVS that has 6V Noris Lund dynamo, it is current regulated and gives out just shy of 7.2V on tickover. 

Re: 12 volts from 6 volt dynamo

Posted by alan_osborn at January 21. 2013

Hello All,

'ere we go again. Most of the above makes sense (for once) Making the 6V dynamo give 12V-first you will need more revs to get to the charge point. A 12V Field coil will help get to this point sooner (than if you continued wit the 6V Field coil) 12V armature is not recommended as the extra wattage will eventually cause a burn up if you exceed the wattage of the E3L by much, 60 watt is what it was designed for, most dynamo men say 70W is tolerable-more-you are on your own. LEDs yes you can save 5 watts or so from the back light. Better/halogen 6V fine BUT the Halogen principle is designed around the higher voltage 12V) Also modern!!! Wipac Quad optics H4 etc  (Had them since the 70s....)have a much more accurate focus point within the reflector than the old pre-focus units, so converting to a decent headlamp unit would always be a good idea. 6V can be made to do 'the job' but as is said here, attention to decent/new switches, decent wiring. proper earthing etc. Even going up one size on cables all round can be good.

Battery-don't get a small one 5 Ahr is the minimum for safety. Don't get Burglar/fie alarm battery, with the square corners and Luca/spade terminals, these will fail early. Only use batteries that are intended for Automotive use! If all else fails buy a Honda!!!!

Al Osborn.

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