The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Mosin on 30.09. 2009 16:11

Title: 6v - 12v Conversion
Post by: Mosin on 30.09. 2009 16:11
In an attempt to make my A7 more useable as I return home from work in the rapidly darkening evenings, I am seriously considering upgrading from six to twelve volts so that I can fit brighter lights. I live in the middle of nowhere so getting plently of good long runs at speed in is not a problem at all, but not being able to see where I am going on unlit country lanes very much is.

Having read up on the subject as much as I can find on this forum, would I be right in thinking that all I need to do is fit

A new regulator (DVR2 seems to be the preferred one)
A 12v battery
A new set of bulbs
A new horn?

I am aware that it may be necessary to fit something like the SRM dynamo belt drive kit, but is there anything else that I need to know? Also, does anyone have any make/model numbers for a suitable sized 12v battery for my bike?

My plan is to fit LEDs in the tail lamp etc thus giving me the maximum amount of power possible for the headlamp. Does that sound like a reasonable plan?

Any thoughts people might have would be most welcome.

Title: Re: 6v - 12v Conversion
Post by: rocket man on 30.09. 2009 21:04
hi mosin ive got a 12 volt conversion on my bike i have the dynamo
kit from srm also have 2 6volt small batteries dry cell   in unison podtronics
regulator it works very well but i also have an optimate charger as
well wich keeps it fully charged when im not using her not sure you need to change your horn

Title: Re: 6v - 12v Conversion
Post by: Dynamo Regulators Mike on 30.09. 2009 21:14
Hi Mosin

Sounds like you may well benefit greatly from 12 V conversion and better lighting.

I run my A10 with a 60W halogen headlight. I would not recommend this for everyone. I believe the E3L dynamo is well up to providing the power, and of course the DVR2 is perfect for the job. But the weak link is the dynamo drive. I have gone through a number of belts on my setup in just under 10k miles. To date I have been using a Hawker belt kit which is nicely made with some thoughtful touches, such as spanner flats on the dynamo pulley and threaded extractor holes on the larger pulley. But you need to ensure that not a trace of oil can get onto the cogged V belt used or it slips. A decent level of belt tension is important and I found tension needed to be adjusted quite often (about every 1,000 - 1,500 miles). However I have a suspicion that my pulleys may have been from a faulty batch, and the grooves not made quite deep enough which would make for belt slip as well.

I would be very interested to hear how people get on with the SRM timing belt option. I have heard from a couple of sources, both with some commercial interest, that sudden loading can strip belt teeth. Some up gearing of the dynamo is provided. I recall our Groily having problems with the taper slipping with this kit.

After going through 2 belts on mine I decided to try a polyurethane belt as a replacement. Before fitting I ensure that the belt would not bottom by cutting the groove a bit deeper. This type of belt works beautifully on my regulator test rig at room temperature. But the belt shedded its teeth on a long hot run in Holland at the international recently. Presume this was due to heat softening - polyurethane only rated to 85 C according to manufacturer (don't know if that is absolute maximum or beginning of derating load).

I believe that the dynamo pulley is actually too small in attempt to give maximum gear up for lowest speed output. But reverting to lower ratio reduces one of the key belt benefits. Then you would not need the benefit so much on an A7 as your revs will be higher for a given road speed.

It occurred to me that anodising the pulleys might help to reduce slip by increasing friction and reduce wear should occasional slip occur. But it may be that only a wider belt and larger dynamo pulley would provide a cure.

As far as a battery is concerned you don't need anything large or expensive. A low cost autojumble wet 5.5 Ah one has lasted me 4 years which seems to compare well with others I know. Well designed LED stop/tail light good idea, and you shouldn't need a new horn.

Title: Re: 6v - 12v Conversion
Post by: bsa-bill on 30.09. 2009 22:04
I have said this before so sorry if I bring about a bit a dejavu.
I have a SRM belt conversion and can only praise it, due to a mistake on my part the dynamo drive chamber filled with oil, this came to light many hundreds of miles after the rebiuld when oil started to run out behind the cork gasket at the dynamo, so the belt had been running in oil for probably most of that time and had continued to drive the dynamo, this is where a toothed belt sytem scores I think.
The cork washer supplied that goes behind the large drive pulley is quite thick and does need to be squashed up in order for the taper to bite on the pulley, friend of mine cut the cork washer in half to achieve this - not sure if thats a good fix or not.
 Also the toothed belt supplied is reinforced with wire/nylon cords

All the best - Bill
Title: Re: 6v - 12v Conversion
Post by: Richard on 30.09. 2009 22:59
Right oh now my two penny's worth,
You will need a belt drive conversion so that at slower revs your dynamo runs faster so keeping a charge to the battery.
The tension should be tight that means no give on the belt, I purchased a hawker kit and his instructions were to fit it tight then after a couple of hundred miles retension it then it will not have to be touched, so far after a few thousand miles this has proved to be the case. It is easy to do just twist the dynamo using the holes around the end plate which are there for doing just that then tighten while still holding the tension on.
The battery really needs to be as big as you can fit in the battery tray I have an 11 amp hour battery that just fits in this will hold enough for those journeys at night when you will use more amps than you can replace on slower journeys.
Using a 28watt side lamp for town use where a really bright light is not required will also save on the amps with an led tail and stop lamp this will also help, this is what I have on my S/R along with a DVR (I think thats correct, a manor Mike one from the BSAoc) however I am running a 45watt headlamp as I think that using a 60watt although the dynamo is rated at 65watt I beleive is going to lead to problems with early dynamo failure as it is working it to hard whilst night riding and I think I am correct in saying that they are not rated at 65watts for continuos useage.
Also changing the headlamp reflector and glass for a Wipac with a H4 type lamp will give a better light beam and spread.
It may be worth speaking to Paul Goff as he is well up on being an expert on this subject as he sells and also rides a bsa A10 his link is below
Hope this helps

Title: Re: 6v - 12v Conversion
Post by: Dynamo Regulators Mike on 01.10. 2009 10:03
It's a bit of an old chestnut, but the E3L dynamo is rated 60 W, presumably continuous, by Lucas at 7 Volt output. This is equivalent a safe design current of 8.5 Amps (at a modest 2,000 revs). The same safe current, heating wise at 14 V out (12 V nominal) is double the power.

Now ohmic heating in the armature is not the only limitation to safe output, for example field dissipation, bearing loads and brush sparking will all effect reliability. But there is some consensus that 80 to 90 W is safely possible in the longer term. (I would be very surprised and delighted to find a trustworthy survey of long term reliability at 12 V high output not dominated by anecdotal evidence.)

No, for me the drive is the weak link with my 60 W lights plus 20 odd Watts for Boyer. Dynamo ok but belt drive marginal. Timing type belt seems the way to go if teeth not stripped in the longer term by sudden load switching.

Title: Re: 6v - 12v Conversion
Post by: groily on 01.10. 2009 11:58
Most evidence is anecdotal unfortunately . . .
 . . . but for what it's worth I've been running an AMC twin at 12v for over 20 years and a lot of cumulative miles, standard windings, nowadays with one of Mike's DVR2s. There's no way of stepping up the gearing on a pinion driven unit and I ran it in London for several years with a 60/55W halogen. It was fine, although heavy traffic and low revs did obviously tend to drain the battery a bit. Before that, when it was still 6v in the 1970s, I ran a 60/55W light as well - and it lasted for ages until the dynamo eventually said 'Enough!' and threw wires off the commutator. After the conversion to 12v, I used a JG reg, which was as good as you could get back then (and still works). But not as good as the DVR2 in my opinion. Dynamo output is perfectly adequate. That bike has its magneto - so I've never had to think about powering a Boyer unit as well (which might worry me a bit, not having Mike's skills with electrickery!). Nowadays it's on a 45W halogen in a Cibié concave reflector, which is awesome. The only thing I used to find, less so now with the DVR but still now and then, is that it sometimes needs a good handful of revs to get the dynamo to cut in. That could be because of the traces of oil that tend to work their way into the dynamo on that bike, or maybe the level of remanent magnetism is a bit low?

On another AMC twin I have recently put in a '12v' so-called armature and field, so 60W max safe output, and it supports a 45W lamp easily with an old fashioned tail, same as on the other one. Also with a mag and a DVR2. Works fine, and of course cut-in revs are as per original, which is the point of it. I am beginning to prefer this set-up - winter will tell me if I really do - April is a way off!

My A runs at 6v, also with a DVR, and more modest 35W halogen, standard tail lamp (and magneto of course). It would support a 45W easily, same as the others, but I have an aversion to lots of amps doing the rounds if I can help it. The lights aren't bad at all but that Cibié spoils me for anything, even moderns. The toothed-belt drive (SRM) has needed no adjustment (and the compartment isn't full of oil!). I installed it with enough slack to twist the belt to vertical from horizontal, which I think was what I was meant to do. However, the taper on the drive pulley went awol early on as Mike mentioned and I used the original steel dynamo drive sprocket centre set in the reworked pulley to sort it. No problems since.

Overall, I trust all three bikes to illuminate the road and to charge. All have fuses here and there and I run them all positive earth, just so I don't muddle myself up when playing. It's interesting having one of each of the three main variations on the E3L theme, and I'd say they're all OK if they're properly regulated and if the harness and battery are OK. But I definitely prefer 12v, and when the A needs a battery, I'll convert that too. Meanwhile, I'm very grateful to Mike for having come up with a great box of tricks.
Title: Re: 6v - 12v Conversion
Post by: trevinoz on 01.10. 2009 21:50
I am curious as to why the chain drive is being discarded in favour of , it seems, unreliable belt drives.
I have always used the chain and still do. All of my associates use the chain. We do not have any problems with chains as long as they are in good condition.
I put in a new one on every rebuild.
Maybe I don't put in the miles to warrant replacing the original drive.
Title: Re: 6v - 12v Conversion
Post by: Richard on 01.10. 2009 22:08
the belt drive system steps up the drive speed to the dynamo,
I have a 12 volt system on my plunger A10 but still have the chain drive and the difference to charging the battery when the lights are on and at slower speeds is noticeable, I have not had a problem with the belt drive pulley yet and It has been on the bike a couple of years now, I think that if they are put on securley in first instance and the belt is tight then they should be trouble free.
As for my previous post I bow to mike's superior knowledge  *respect*and as such may put a brighter headlamp bulb (lamp whatever)  Mike can I send the repair bill to you when I burn the dynamo out *smile* *respect* (only joking).
As for the battery I still think the way to go is to fit the largest amp/hour one that will fit in the space, much better for getting home if and when the dynamo or charging circuit fail
Title: Re: 6v - 12v Conversion
Post by: bsa-bill on 02.10. 2009 09:04
I had no end of trouble with chain drive when I had my first A10, went through three in a year or so, although we did not have liquid grease and such to hand in 61/62.
Of course my chian fitting skills at age 18 might have been somewhat short of requirement *smile*

All the best - Bill