The BSA A7-A10 Forum

Technical (topic titles must be descriptive) => Lucas, Ignition, Charging, Electrical => Topic started by: trevinoz on 07.04. 2009 07:13

Title: 12 Volt Vs 6 Volt Generator
Post by: trevinoz on 07.04. 2009 07:13
I recently rewound an E3L generator to 12 volt specs just to see the difference.
The armature has more turns of wire at 0.7mm compared to 0.8mm.
The field coil has 50% more turns at 0.6mm compared to 0.7mm.
At the moment I don't know what speed I tested it at as I don't have a tachometer but hope to borrow one in the future.
The data is as follows :- Open circuit voltage -  23V
                                 Regulated open circuit voltage - 13.7V

I connected a 12V 60/55W Halogen headlight to the regulator and got the following results:-
                                 55W filament - 13.8V
                                  60W filament - 13.6V
                               60 & 55W filaments - 8.4V
I then repeated the experiment with a 6Volt generator which I had rewound and found the following:-

                                   Open circuit voltage - 13V
                                  Regulated open circuit voltage - 12.75V
                                   55W filament - 9.7V
                                   60W filament - 9.4V
                              60 & 55W filaments - 7.1V

From this it can be seen that the 6V generator needs to be run a lot faster to be in any way effective as at my test speed the voltage didn't reach the regulator set point and the high wattage lamps loaded the generator excessively, would probably be OK with a lower wattage lamp.

The 12V rewind seems to be the way to go for anyone using their bikes at night as a decent Halogen lamp can be used.
By the way, this generator is yet to be tested on a bike, all the above was done on the bench.
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: groily on 07.04. 2009 08:39
That is fascinating data Trev.
I've been playing a lot with dynamos and regulators recently (largely inspired by the ability to do so conferred by Manormike's oh-so-excellent DVR2 regulators) and have come to broadly the same conclusions.
The theoretical max to be derived from one of these generators, without increasing the internal heat generated in the field, is close to 140 watts; but only at the cost of not-useful compromise. To get that, it takes a fine-wound field coil ('12v' in the vernacular) with a thick-wound (ie '6v' as per original), armature winding. To get the thing to cut-in point takes a handful of rpm - close to 2000 - and it won't be regulating properly until closer to 3000 rpm. Ergo not a lot of use in normal riding. And the output is theoretical - I haven't tried to measure it, as it's a noisy business holding throttles at 3000rpm plus in the shed.
However, the use of an original thick-wound armature and original field at '12v' does give around 80 watts reliably, at the cost of some heat having to be dissipated in the field after Cut-in rpm and before full regulation kicks in. This would load the field a lot on long-lkegged machines habitually driven between those rpm, especially in built-up areas. In fact, the internal load at those rpm can be more than the dynamo is rated to cope with, although they seem to work OK - I have been running one machine in that configuration for over 20 years with various regulators of the early electronic type, but now a DVR. No melt-downs despite the absence of current regulation, as in all these applications - fingers crossed for the next 20 years.
I have one original 6v set-up (on my A10) which is OK and supports a 35W halogen just fine as you'd expect.
And I have one machine in this experimental hybrid 'fine field thick armature' mode, which may be OK for the summer for a country boy who seldom rides in heavy traffic, but I'll have to swap the field coil back to original or get a fine-wound armature for the autumn, to get reasonable cut-in and regulation rpm. These dynamos also run with DVR2s.
My only whinge with the fine-wound fine-wound mix is that you are stuck with 60W nominal output obviously (but the big plus is you retain the original cut-in rpm). But it would support a 45/40W halogen OK as long as the magneto is retained of course.

All depends how badly we want lights for what we do. I unfortunately need them often, to the point that I regularly take something with an Alternator when in doubt.

I was interested a few weeks ago, talking to Gary at SRM when ordering up a fine-wound filed coil for the hybrid experiment, to learn they they are looking at ways of getting more out of the original E3L generators, presumably because they are finding people overload the '12v' 60 Watt set-up. They apparently want to try to find some extra oomph, but it's hard. I think I heard him say that they are also going to be, or are, stocking DVR2s - but not sure about that. I for one never cease to extol their merits - to the point of boring people to death. And that's having had mechanical regs, JG ones, Podtronics ones, you name it. The DVR2 is the best I've had yet.
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: RichardL on 07.04. 2009 18:39
With only the most miniscule fraction of Groily's experience, I, too, extol the DVR2.

Richard L.
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: Richard on 07.04. 2009 18:52
I to use Mikes regulaters on both of my A10's owerthe Super rocket has one of Shaun Hawkers belt drive kits which drive the dynamo at a faster speed I have a 23w side light fitted for daytime running if required and a 45/55w halegeon headlamp bulb and a led rear lamp, I supported this with a 9ampere battery and have had exellent results
Let me know how you did your volage test and I will try and test my S/R the same and report the values.
The old Flash still has the chain drive and on slower engine speeds there is a difference
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: Dynamo Regulators Mike on 09.04. 2009 15:41
Thanks for the kind words about the DVR2 regulator chaps. You?re making me blush. *red*

Interesting thread this is shaping to be. Shame about the lack of speed data Trev. Due to the characteristics of filament lamps power is not proportional to the applied Voltage squared. A rule of thumb may be applied that power in a given lamp is actually proportional to v raised to the power 1.6. Also note that many if not most auto bulbs are rated at 13 V.

Ignoring the details of the maths  *conf* this suggests that your 115 W nominal load (at 13 V) drops to 43 W at 7 V, i.e. just over 6 Amps. On my test rig I measured about 7 Amps at 7V for a 60/55W headlight bulb, so the approximation seems not far out.

The point is that a standard E3L dynamo should be very happy at this loading. Lucas spec gives 8.5 Amps at a very modest 1,850 to 2,000 rpm dynamo (not crank) speed. A true load of 115 W on an E3L at 7 V would likely result in a pretty rapid meltdown. But it can happily run a 60 W headlight (halogen or not) at 12 V, with its standard 6V windings and a DVR2, without excessive speed, and indeed electronic ignition as well.

Do you know the resistances of the field winding used  in you tests, Groily and Trev? A few more truns on both field and armature would seem to be better for a 12 V conversion, but data on the available variant windings does not seem to exist.

There is no getting away from a dynamo?s output being proportional to its speed, and the number of turns in the magnetic field. Practical limitations to output include mechanical strength of the armature, winding and brush resistance (heat dissipation), and magnetic saturation field strength. Maybe SRM can come up with something radical, using modern steels, smaller air gaps, efficient cooling, rare earth magnets or whatever. Meanwhile they are indeed now stocking  the DVR2.

Title: Re: 12 Volt Vs 6 Volt Generator
Post by: snowbeard on 09.04. 2009 17:46
ok, I am barely following this conversation, so please speak slowly...  ;)

I still have the all original setup, E3L, 6V battery, mechanical regulator (that apparently still works!) and whatever bulb was in the headlamp when I got it (it lit up so I didn't mess with it much) 

I have obviously variable lighting with rpms, it drops to very low when stopped at a light, and I can see it brighten when I rev the engine.  I have nominal light for riding at actual riding speeds, it works for town but a dark night on a long road I can only imagine will be terrifying.

with the money I'm putting into my head, I hope to do some distance rides, theoretically still in the daylight, but we all know how well theory holds. 

what sort of things can I do to help out my headlamp for night riding?  maybe a better 6V bulb?  better gel battery?  I currently have the 6N11A1B for a battery.

can your DVR2 reg pull more out of this original system Mike?

sorry to be slow, but my first thoughts were simply to get 'er running, now I'm hooked and might as well make 'er reliable too!
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: beezalex on 09.04. 2009 18:29
I guess it all depends on how good your eyes are, but the 6V lighting on my flash is adequate with the DVR2 (Add my name to the list of people recommending it) and a standard lucas bulb.  I must also say that I find the lighting much better on a dark road than in town because your eyes don't adjust well to low light levels when there are a lot of other cars and ambient light.  That said, when I ride my Royal Star with 12V 55/60W halogen lighting, it's absolutely stunning how well my path is lit, so it all becomes relative I guess.

BTW, if your lights get dim at idle after riding for a while, you battery's bad. 
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: snowbeard on 09.04. 2009 18:46
ah, I suspected as much. I had the seat off and noticed some corrosion around the terminal, so I cleaned all that up and checked the water/acid levels. they were very low, so I topped up with some fresh acid.  I may need to just step it up and buy a new battery, eh? it's only a year or so old tho.

 I'll see what it holds now with new fluid, I have a tender that I was using also, which did appear to give it full charge and go green after a night. 

so does the DVR2 do more than a working mechanical? or is it just a more reliable modern replacement when the mechanical goes south?
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: beezalex on 09.04. 2009 19:00
I'm going to guess that if you battery was cooked out, you regulator isn't regulating very well.  You should definitely check to see if the voltage output is going above 7.5 volts.  If it is, that's going to be rough on the battery.

The DVR2 offers better regulation than the original, mostly because there are a lot of tradeoffs that are made in the mechanical regulator that constitute losses.  The DVR2 also has no moving parts to wear out because it is fully solid-state and if you, at some point change your mind, it's easy to reconfigure for 12V.  On top of that, I found that with the current exchange rate, it's cheaper than the podtronics or a new mechanical regulator.
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: snowbeard on 09.04. 2009 19:10
hmmm. it could be that the mech isn't working now, but it was when I got the bike up and running at first. haven't checked for a while, I'll look into that as soon as I get her back together...  one more thing.*conf*

thanks Alex!  *smile*

Hey Mike, can I order your DVR2 direct? or should I just go thru a supplier?  maybe I should just get two since I need one for the super rocket basket as well, maybe I need one for my Royal Enfield Hornet 250 as well!!  yikes!
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: beezalex on 09.04. 2009 19:23
I'll do the advertising bit for you, Mike, if you can enlighten us on that other thread about the current regulating characteristics of the DCR2, cause I gotta be honest, I don't know about that particular one.

Snowbeard, here's the web addy:

I got mine in about a week.  Great service and a solid article at a reasonable price. *beer*
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: olev on 09.04. 2009 22:58
Thanks Trev & Groily, Thats the best write up on on these generators I've come across. It will be interesting to hear what happens when Trevor sticks his generator on a bike and takes it for a decent thrash at night.
Is the alton an alternative? Are they reliable?
The ability to drive a quality electronic ignition (if there is such a thing) with a good headlight sounds attractive to me.
Happy Easter everyone, cheers
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: groily on 09.04. 2009 23:15
Don't know the resistance across my fine-wound field coil Mike as I didn't measure it. Sorry. A small handful of ohms I assume.
It was what SRM supplied, while I was in daft 'play' mode, trying to see what the effect of having a fine field and coarse armature would be in practice (and trying to reduce field load after cut-in and before full regulation). Result, unhappiness for fairly predictable reasons - but the ammeter suggests it produces some useful and very sustainable oomph at high rpm. I think the ideal would be a fast-turning dynamo with a field coil with something more than the windings of the '6v' standard one, but fewer then the '12v' coils available from SRM, Feked etc, with a standard wound armature. But it all depends what conditions we ride in, eh? In the sticks, where revs are available, no problem; in town, another story, as the old cut-in issue rears its head. And on whether the mechanical side of an E3L can handle it too, as you say elsewhere. I expect I'll melt something soon, but it's interesting in the meantime.
Glad to hear that SRM are indeed stocking DVR2s . . . my ears do work, even if listening remains an option! And I'm sure you'll pick up the 'current regulation' queries in the adjacent thread and put us to rights . . .
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: trevinoz on 10.04. 2009 03:28
Hi all,
        the resistance of my field coil is 5.6 ohms and consists of 450 turns of 0.6 enamelled wire, the original 6V coil consists of 300 turns of 0.7
The armature now has 20 turns per coil of 0.7 wire in lieu of the original 13 turns of 0.8. It was a tight fit but I managed. The field coil is somewhat larger but fits with no fouling.
I have been rewinding these generators for over 40 years, I learned as an apprentice and had to apply my skills to keep my Flash on the road as I kept burning out armatures, not knowing anything about the black art of regulators.
Thankfully I applied myself to the regulator mysteries and now strip and rebuild them.
I will supply the speed data some time in the future when I get hold of my mate's tacho.
As an aside re the DVR2 regulator, I overhauled a 1920 Vauxhall generator which had a rudimentary control system consisting of a cut-out and 2 sets of field coils which could be switched manually when charging required, one set of fields seemed to oppose the other. I have no idea how it was supposed to work and in fact the fields were all burnt out.
I asked the owner to get a regulator and he supplied a DVR2 which I fitted inside the cut-out box.
It has been in service for about 12 months now and has had no problems.
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: RichardL on 10.04. 2009 03:33
I think this is mostly meant for Snowbeard, considering his/your apparently imminent purchase of DVR2 regulator(s). I don't know if you saw this under another topic. if not, you might find it amusing. It shows how I mounted my own DVR2.

Richard L.
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: Dynamo Regulators Mike on 10.04. 2009 10:34
Good (Friday) morning all. Or Happy bun day as my wife says.

Snowbeard: as Beezalex said main advantage of using a DVR2 (or other electronic unit?) at 6V is fit and forget reliability. Voltage regulation is accurate promoting long battery life. You can purchase direct with card/PayPal on the website. (Note to moderators: he did ask)

Thanks for the field winding details. I am inclined to the belief that the double resistance field winding is a bit higher than ideal as well. Something like 30% extra turns ought to give adequate Amp.Turns for near saturation flux at 14V without wasted current. Resistance would be about 4.5 ohms. My estimate is that about 20% extra armature turns ought to provide a good compromise between maximum safe output current and higher cut-in speed. This based on same maximum armature dissipation at with standard 6 V, about 6 Amps 80W.

Result of the increased turns should be similar cut in speed as with Hawker 3:1 belt drive, but no fear of over revving dynamo if using sustained high engine revs (which I don?t). Less power available though. But another point is that Lucas output rating is for a nominal power, at defined modest speed. Not at all the same as maximum safe available power which as far as I know is not mentioned anywhere by Lucas.

I don?t know too much about the current limiting characteristics of the mechanical regulators, but  the 2 bobbin regulators has a series winding to reduce V reg at higher current drains. No idea how well this works in practice. Presumably the 3 bobbin types perform much better in this respect.

Cheers all
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: BSA_54A10 on 10.04. 2009 11:46

1) forget the battery tender. They do a reasonable job on trucks & tractors but seem to cook motorcycle batteries.
I use an old mechanical time switch ( you know the ones you use to fool the burgulars) . I set it for the smallest time interval which is 15 minutes, plug the battery charger into i and have never had a problem in the past 20 years.

2) modern batteries are a real work of art about 40 % of the weight of the old ones and about 5% as durable.
Once the generator is working properly a high discharge gel cell is the way to go. If you need the higher capacity then get 3 spiral wound single cell batteries and run them is series. They will actually fit in the old battery hole.
Once a new battery has been allowed to go dry it is next to impossible to get the plates to activate ( they oxadize when exposed to air and passivate if allowed to go dry. God forbid if you ever short one out this will usually cause the battery to fall apart internally

3) clean up the terminals every where and then apply either grease or something to prevent them corroding you can loose 2 Volts ( or more ) from dirty terminals and on a 6V system that is a real large amount.

I won't go on about the ganged spade & liquid electrical tape but I can not sing their praises enough. I slap the liquid electrical tape on just about every contact & terminal that I will not be regularly undoing it is real good stuff provided you did a good job cleaning the contacts before application.

Now as for lights.
I fitted a VW reflector ( from an old Kombi wagon ) into the back if the Lucas lamp . This allowed me to use the QH VW 6 V 35/45 W headlamp globe and I would never change them a truely brilliant light that had run without problem for over 10 years till I finally killed the engine.
The lamp was then transferred to the WD B40 after a dozen or more old Lucas prefocus globes parted company between the glass & base and gave another 12 years brilliant service till it was stolen ( with the rest of the bike). These bikes were daily transport and I can only remember changing the globe once. Down here in Oz the VW globe is still current stock  but Lucas type globes come only from specialist shops.
Title: Re: 12 Volt Vs 6 Volt Generator
Post by: trevinoz on 26.04. 2009 23:52
I finally got around to measuring the  test speed of my generators.
Unloaded is approx 2900 RPM and loaded would be slightly lower.
With 11 tooth generator sprocket, this equals 2367 engine RPM.
With 13 tooth sprocket, equals 2788 engine RPM.
Road speeds are approx. -  A10 SA - 39 MPH,  A10 PL - 40 MPH,  A7 SA - 34 MPH,  A7 PL - 35 MPH.
Pre '49 long stroke bikes with the E3H generator which has a 13 tooth sprocket, - 41 MPH.
The 12V generator reaches the regulated voltage before this speed but the 6V doesn't reach regulation.