Hi All
I have just had my dynamo converted to 12 volt All new bits
which is the best regulator to run with it?
Is there a electronic one, I can use but i want it look right
Have looked on the jolly interweb But a little confused
Any help would be great

Location: United Kingdom

The best electronic one is the JG regulator supplied by Dave Lindsley (Google Dave Lindsley), a friend bought two 48 years ago for his RP saloon (one to fit one spare under the seat) and suffered one failure over the years which was replaced FOC. However they are a lot more expensive now, about £100, and I'd heard he no longer does them.
Alternatively try our cherished suppliers, or check out the Cornwall Austin Seven Club website for the details of their system. I can't recommend my system as it is no longer available, but again I bought a few, half to fit half to go under the seat as spares. If you go the electronic route I'd definitely recommend buying two one to fit, one as spare because you can't fix a black box of electronics at side of the road.

I should have added that it also depends on how your dynamo has been rebuilt, there are a couple of ways of connecting the dynamo field depending on the type of regulator.

I too found the sea of info very confusing when first considering 12v.

It depends somewhat on what has been done. Electromechanical regulators seem unsuited for several reasons including
1) the switching action may rattle the timing gears
2) cannot handle the very high field current unless this otherwise restricted (ie series resistor, field rewound for 12v etc. Normally fed at 4 or 5v, 12v trebles the current, 9X the heating effect!!))
3) may accentuate sparking of 3rd brush if retained.
4) if a voltage only type, difficult to avoid exceeding 8 or so amps output for protracted periods if battery flat and heavy lamp load etc. (For some reason beyond me many report that the condition does not cause trouble, whilst it wrecks dynamos normally.)

As for all the electronic regulators they are all too complictaed for me, a mere ex one time radio technician. Others will advise. I gather some specialists rewind the field and provide a suitable voltage and current limiting regulator; this would seem to be the ideal.

Of course the very basic conversion as recently described by Steve Hainsworth involves no regulator. But your 3rd brush may now be disconnected.

Bob Culver

Location: Auckland

Location: Piddle valley, Dorchester.

Hi John, if you wanted to keep the installation looking nearer original I have a quite rare 12volt version of the Lucas cf1 type type cut out available, surplus to requirements as I went down the alternator route with my special.
Regards Ian.

Location: Worksop Notts

My dynamo has just been rebuilt by Paul Baker of Smartpower.
12 volt with a new regulator which can be fitted inside a normal cutout to maintain an original look.
After 20 years the dynamo and nik plevan cutout finally gave up.
Andy

My dynamo has just been rebuilt by Paul Baker of Smartpower.
12 volt with a new regulator which can be fitted inside a normal cutout to maintain an original look.
After 20 years the dynamo and nik plevan cutout finally gave up.
Andy

Can anyone explain to me what is actually done to a standard Austin dynamo when it is ' converted to 12 v' or ' re-wound for 12v ' ?

Having never had this done I don't have any idea!

Malcolm

Location: Cornwall UK

For the Dave Lindsley JG regulator the third brush is removed and the field is connected to the D & F terminals.
Some electronic regulators such as the one I use(make unknown, bought locally 30 years ago & closed down when the owner died.) have the third brush removed and the field connected to the F terminal and earth. I also use a CF1 cut out modified to 12 volt by the addition of a 32 ohm resistor. Each car has 2 regulators, one in use & one spare under my seat where they have been for 30 years.
I previously used a three brush dynamo and a 12 volt CF1 cut out with a Mini heater rheostat as a variable field resistor.
I don't know exactly what Classic Dynamo & Regulator conversions do but I believe they fit new field coils with a higher resistance-more turns of thinner wire.
I have no idea what the Nik Plevan arrangement was or any other system.

Interestingly the company below market a so called 'Dynator' - a 50 amp race alternator inside a dynamo case to replace the 6v or 12v Lucas C45 dynamo on a 1930's Morris 8. Although the Austin 7 is not currently catered for, the page does say that they "are more than capable of copying an original dynamo which we do not currently manufacture and producing a custom Dynator".

Not cheap of course, the Morris 8 one is £447, but none the less interesting.

http://www.wosperformance.co.uk/products/dynators/

http://www.ccw-tools.com/product.asp?P_ID=47120

Jeff.

Location: Almost but not quite, the far North East of England

Hi Malcolm

Like you I frequently encountered the expression "converted to 12v" but it was difficult to trace anyone who could provide datails. The expression is used to cover anything. Some, in defiance of all theory, claim to just feed the field directly through an electromechanical regulator and declare the system 12v! I eventually contacted a former auto elctrician who had modified several Sevens and eventually established that he fitted a field series limiting resistor, much as the simple Cornwall scheme recently described.

It is common with pre war Chevs to replace the field coils with those from a 12v, a more correct solution.

Any electronic regulator, assuming it controls via the field, will have some means of limiting peak field current.

Those contemplating alternators and other ultra high wattage device need to bear in mind those trace lubricated skew gears. Modern oils are marvellous but not magic.

Bob Culver

Location: Auckland

Jeff. This looks like a neat way to have the best of both worlds. The price is a bit steep but if it is reliable then it might be just the thing for someone who is concerned about keeping the original look. Thanks for posting the links.

One question I would have is how well are they cooled? Don't alternators have a sizeable fan which is needed to cool the diode?

Anyone got one?

John michael Knight

Hi All
I have just had my dynamo converted to 12 volt All new bits
which is the best regulator to run with it?
Is there a electronic one, I can use but i want it look right
Have looked on the jolly interweb But a little confused
Any help would be great

Location: United Kingdom

John is your dynamo still three brush or rebuilt as a two brush? If two brush the electronic regulator can,as mine is be fitted out of sight under the dash.The existing wiring can be cut within the harness to give the appearance of being original.

Location: Piddle valley, Dorchester.

Hi Paul Thanks for your comment's My dynamo is 3 brush
I live in Blackpool
Regards John.

Location: United Kingdom

Ray, that's just what I thought, as I also own a 1936 Series I Morris 8 Tourer - unfortunately I don't have a spare £450 to splash out on a Dynator!

It appears as if the unit being offered for the Morris 8 includes a new fan-belt pulley wheel incorporating fan blades. Neither the Series I / II or E Eights had fan bladed pulley wheels on the dynamo, just plain ones, though the 1948 to 1953 MM Minor which also used the Morris 8 Series E side valve engine did have a fan bladed dynamo pulley, so it must be possible to fit the Dynator to the earlier models.

On the Austin 7 the stumbling block is definitely going to be the fan and possibly the gear drive both ends - on the Morris 8 the dynamo is driven purely by the fan-belt.

Jeff.

Location: Almost but not quite, the far North East of England

This is a subject that always creates much conversation amongst owners.
Just how many amps does a Seven actually need when converted to 12v? Certainly not 50 or anywhere near that figure.
The C35 in standard 6v 3 brush form is rated 11a, 66w. So, we convert it to 12v and 2 brush. If we do it properly then the Dynamo will run efficiently, cooler and will only output when called to. If we rate it at 8a that gives us 96w or a 50% increase. Rate it at 11a gives us 132w or more than double the output in Watts. 96w is enough to power 2x 36w headlamp bulbs, 2 tail lamp bulbs, 2 side lamp bulbs and a dash panel bulb along with a wiper motor.
132w will do the same but with 45w headlamp bulbs and current to spare so in reality 9-10a is all that is required at 12v to give decent lighting and battery charging. All this without putting extra strain on the skew gear, the cars a,meter and switchgear or on the cars wiring. The dynamo will run cool enough to avoid any over heating problems (remember, I said properly converted to 12v, not a conversion that uses fields designed for a 6v 3 brush system and a 6v armature. A dynamo should be properly converted with its armature and fields suitably rewound using modern materials).

Connect it to a decent electronic regulator through a suitably sized fuse and you'll be rewarded with trouble free charging providing your cars wiring is in good condition. The fuse not only protects the regulator but the dynamo as well. A good electronic regulator will have field current limiting circuitry to limit the output of the dynamo to its maximum safe output, i.e. 8 or 11a. The dynamo will only ever provide a charge when it's required to such as with lights on or after a start up.
It will always compensate for the applied load but once the battery is full, it will stop charging so it's normal to be motoring along in daylight with the ammeter reading zero. The same goes for night driving. At normal road speeds with lights on, the ammeter will read zero. A charge will be shown immediately after a stop at say traffic lights whilst the dynamo replaces current used by the lights while at tickover. The ammeter will be seen to drop gradually back to zero.

An alternator rated at 50a. That's 600w. An alternator can only produce that sort of current if it is adequately cooled by a ram air system (fan and large cooling slots) that "rams" air over the internal parts including the big diode to keep them cool.
Seven dynamos have no fan nor any way of being able to add one. The dynamo is bolted to a hot engine. It has no cooling slots so is a sealed unit that will cook itself. The unit is very small (3.5" diameter) so cooling becomes even more of a problem.
Last year alone I had half a dozen people ring me with problems after having a dynamo converted to an alternator.

One chap spent £800.00 having his Lagondas dynamo "professionally converted on to have it last just 180 miles, expiring on the M4 in the dark. He pulled onto the hard shoulder and did what we would all do. He removed the cover band to investigate and to be greeted by a red hot mess. According to the company that converted it, he had voided the warranty by removing the cover band. They wanted nothing more to do with it. He contacted me and sent me the unit asking me to convert it back to a dynamo for him. It had been so modified inside that it couldn't be converted back and was in reality - scrap.
He then had to pay nearly £500.00 for another dynamo in non working condition and give it to me to assess.
It needed a full rebuild costing a further £500.00. £1800.00 spent in total when £500.00 would have sufficed in the first place.
I gave him back his 12v 3 brush 12a dynamo converted properly to 12v 2 brush capable of outputing 15a. Another happy customer.

Another spent a lot of money on a similar alternator conversion to 45a only to watch his wiring loom melt when a fault caused by switch gear and an ammeter designed to handle around 12a was forced to handle 40a or more under fault conditions. No fuse was fitted so the weakest parts of the system, the wiring and switch gear melted causing tremendous damage.
The car was a rare and expensive 20's Sunbeam tourer but the same thing could happen to any car.

Yet another customer bought a C40 lookalike. Purpose built 45a alternator inside. He bought 4 over a period of 2 years and each one failed. He's now reverted back to a proper C40 with electronic control and is happy.

Even ex VW Beetle 6v dynamos that are converted to fit older cars inc Sevens can cause problems under fault conditions.
They're capable of outputting 45a but on a Beetle they have a fan to cool them and cooling is further aided by the air cooling of the engine. I have a 6v 16a (96w) rated dynamo on the bench now from a 1925 Essex. It's had an armature 2 brush conversion and was connected to a 6v 45a Beetle regulator. The owner converted his headlamps to take 50w bulbs, added a USA made electric fan and an electric water pump. His dynamo stopped charging one night. It's thrown ever bit of solder from its comm and the armatures winding is down to earth after trying to supply nearly 40a. The previous owner who did the Dynamo/regulator conversion must have thought that 40a was less than 45a so would be OK. How wrong.

We now have LED bulbs to fit our cars. They give brighter lights with much less power consumption.
Up until now brighter lights meant demanding more current from the dynamo to get them.
This is no longer the case. We can now get brighter lights and lower the demand on our dynamo.
The dynamo has less load so runs cooler and more efficiently.

I hope I've cleared up some of the doubts and questions but if ive missed anything, feel free to ask.

Peter

Location: Saxilby

Excuse the spelling. The predictive text took over and I didn't check the draft.
Amongst other errors, armature should read amateur!

Location: Saxilby

Hi Peter,

Am I correct in thinking that the amount of current flowing in the field coil is controlled by the third brush?

Am I also correct in thinking that for any given load an increase in volts reduces the amps?

I fail to see why increasing the voltage through the field coil and reducing the third brush output would be detrimental to a standard Austin Dynamo but then I don't have a degree in electronics nor am I in the trade selling or refurbishing dynamos.

I should point out that my car has been 12 volts for almost 15 years, is in daily use, has gone from Cornwall to Scotland in three days and several other long trips, has 55w/60w headlights but has never shown any problems with heat or otherwise. Am I just lucky?

Location: Cornwall UK

Hello Malcolm, your low speed charging and cut in speed will be higher if you are using a 6v armature at 12v.
You are correct in saying that increasing voltage reduces current but a 6v dynamo is built to run at its most efficient at 6v.
The number of turns and the thickness of wire used greatly influences cut in speed and the ability to hold a load especially at lower speeds.
If one size fitted all then all dynamos would have been built the same regardless of voltage. The differences in field resistance are many and varied, dynamos were made to suit various vehicle characteristics including engine speed and load.

Most of my work is standard rebuilds and two brush conversion. I am a firm believer that with the advent of low power consumption LED bulbs, a 6v system in good condition is plenty adequate. Converting to 2 brush gives the dynamo and battery an easier time too. There are those that prefer 12v. I talk people through both options and some change their minds about going to 12v and have their dynamo rebuilt as a 6v 2 brush machine controlled by an electronic regulator.
A well designed electronic regulator will lower the cut in speed of a dynamo. This is good news for all but especially owners of low revving cars or cars with dynamos driven at engine speed.

I do 12v conversions for the Seven, Model A Fords and for some vintage and also post war American cars amongst others with the emphasis on building an efficient unit.

Most dynamos that come in to my workshop are original units that are absolutely worn out, are as found or have been given a hard life by someone winding the 3rd brush right round in a vain effort to squeeze more out of it. 6v units are the most abused.
All but a few need totally rebuilding.

Peter

Location: Saxilby

Hi Peter

Very interested in your comments. The experienced do not always share their knowledge.

Just to avoid confusing anyone, the rated output is the gross output and not the net less coil current, as registered by the ammeter with all electrical devices off. Is 11 amps rating for the 35M bolted to the hot engine as Sevens, or free as others? (I used to drive 60 miles home on weekends and return on Sunday night. The trip ended with a mile long flat out 35 in 3rd climb. When garaged the whole engine was far too hot to touch, right to the end of the dynamo!)

It only recently dawned on me that my car has been fitted with a 4 pole DEL dynamo. How does the output ability of these compare with the 35A and M?

Every dynamo I have worked on has had a severely cooked appearance with no surplus solder! But many work nonethelss, often after resoldering some commutator connections.

The end of life for many is determined by shallow commutator. If very thin the ends curl out, often with intriguing effect. Do you acquire new commutator units from somewhere?

Presumably if armatures are rewound for 12v, reduction of gauge must be very slight.

Bob Culver

Location: Auckland

Looking through all the posts, the original question is not really answered. It seems that John's dynamo retains the 3rd brush yet he mentions an armature and field rewound for 12v, which seems an unlikely combination (and expensive!). The regulator supplier really needs to know the exact setup before recommending a regulator.

And I am not sure that Malcolms questions were answered fully either. For most purposes can forget the supposed regulatory effect of the 3rd brush and think of it just as an adjustable source of volts. Normally the 3rd brush possibly feeds 5v max to the 1.5 ohm field, about 3 amps. If this current is much exceeded the field winding may burn out. Doubling the 3rd brush voltage, as for 12v, doubles the amps, 4x the heating! Fed directly from the dynamo output voltage is higher still (7v,13v). The peak field current has to be restricted in some way, somewhat crudely with a resistor, better still by rewinding the field, or more refined with a regulator, with the added advantage of high field current at low dynamo revs. And best of all field rewound and a regulator.

Apologies to those who knew all that.

Bob Culver

Location: Auckland

Location: Teignmouth

Bob,

Pity you have got you sums wrong!!

Doubling Volts halves Amps for any given load.

Lower amps means less heat !

Malcolm

Location: Falmouth UK

Quote
Rate it at 11a gives us 132w or more than double the output in Watts. 96w is enough to power 2x 36w headlamp bulbs, 2 tail lamp bulbs, 2 side lamp bulbs and a dash panel bulb along with a wiper motor.
132w will do the same but with 45w headlamp bulbs and current to spare so in reality 9-10a is all that is required at 12v to give decent lighting and battery charging. All this without putting extra strain on the skew gear,

Peter,

Just to avoid any doubt, the dynamo is a device to convert mechanical power in Watts to Electrical power in Watts, so if we double to output (assuming the same efficiency) then we need to double the mechanical power to produce those watts, and that power has to be transferred through the gears.

Cheers

Marcus

Location: Auckland NZ

Hi Fellahs

I hope this doesnt cause more offence, but for those who have forgotten 5th form science

volts=amps x resistance
amps =volts/resistance, so if the field voltage is doubled, the field current doubles
watts(power or heat)= volts x amps, or amps squared x resistance, or volts squared/resistance
taking the last the field fed from 3rd brush normally say 25volts/1.5ohms watts. On 12v this becomes 100/1.5 watts.
With an added 1.5 resistor reduces to 100/3, 33watts, half lost uselessly in the resistor. Quite a waste when the original lamps only 18w each.

It is the current squared x resistance which causes the heating of the armature. If it can be persuaded to operate at 12v near twice the watts output can be obtained for the same armature current. One merit of 12v operation.

For a load fixed in watts, current does reduce as volts increase. But most devices do not behave like this, they just draw more current and soak up more watts. If a 36 watt 6v bulb is changed for a 36 watt 12v bulb, then the current does halve.

Advancing to the 6th form the magnetising effect is the no of turns x current. Assume say 100 turns, normally 100xabout 3.3 amps. 330 ampere turns. The volume of steel is such that it may not get hugely more magnetised even if the ampere turns are increased. If field rewired for 12v can increase the resistance by using more turns of lesser conducting area so that the ampere turns remains 330; current will be reduced, and less power wasted cf the in line resistor arrangement. The lesser current draw enables the dynamo to produce useful output earlier.

All laboriously answered on the presumption that the questions were not a wind up, as I am so often accused of!

Bob Culver

Location: Auckland

Sorry Bob

Why has my conversion worked for 15 years without burning anything out and without the dynamo temperature being any different than a 6v system??

When you reduce the output using the third brush ( as in a 12v system ) you are reducing the load ( and heat ) in the dynamo, no matter what voltage is used 6v or 12v if you try and take too much out of the dynamo you will cook it! As you need half the amps at 12v than you do at 6v to power the same wattage of load then the output from the third brush is reduce in a 12v system.

If what you are saying is true then I should have destroyed many dynamos over the last 15 years.

Sorry but the practice does not match up to your theory!

Location: Falmouth UK

Location: Teignmouth

Malcolm, I share your frustration. I was only 8 years old when I learned that double the volts meant half the amps.

A little knowledge can be a dangerous thing

Stuart Palmer

Location: Teignmouth

THE 'POOR MAN's' 12 volt Conversion.
To convert to 12volt operation follow these instructions.
1. Check that the 6V installation is working OK
2. Remove 6V battery.
3. Change all bulbs to 12V
4. Replace ignition coil to 12V type
5. Remove cut out and insert 40ohm 2 Watt resistor in series with the control winding
Re-install cut-out as before.
6. Install suitable 12V battery (neg polarity)
7. No need to modify starter motor or horn
8. Check that you have done all he above correctly
9. Turn on ignition and start engine.
10. Check ammeter. If reading the wrong way round, reverse connections on rear.
11. Adjust third brush as before to obtain suitable charge rate. Usually reduce.
NOTES
1. Wiper motors will work on 12V, but probably with reduced life. Best find a 12V
wiper.
2. To retain petrol gauge accuracy fit voltage regulator type 7805 or similar. Cost
about 30p.
3. Trafficators, Best to change to 'flashers',which people under the age of 60
understand.
4. These instructions apply to the C35 type dynamo, but the same principles apply to
the DEL and DFL types. (DEL dynamos suffer from having the half charge resistor
within on field coil which is often damaged as a result)

Now isn't that easy, and no knowledge of ohm's law is required.

ERRORS & OMISSIONS ACCEPTED

I'm now off for the weekend. Any Queries or explanations to Bob Culver

Location: Moonraker country

Life's too short for that Vince.

Location: Wessex

Spot on Vince !!!

12v with very little cost, a reliable and simple system which is totally in line with the original method of battery charging.

Nothing wrong with adding all the bells and whistles to make the Austin more 'modern' but strictly not necessary.

Malcolm.

Location: Falmouth UK

Just a thought, Malcolm. You say your car was converted to 12 volts 15 years ago. At that time quite a few cars were converted primarily because the poor old A7 dynamo was not up to the requirements for night driving and at that time it seemed like a reasonable idea. Today, however, with LED lighting available, I can't quite see why we would need to change anything other than the headlamp bulbs.

Or am I missing something?

That was exactly my point in the earlier thread Ray, and I still don't see why there is such an obsession with trying to get the dynamo output to match the lighting consumption. Practical experience says that even with the third brush set at a quite minimal charge rate you will still get several hours running with all the lights on. Makes sense to me that running with a conservative 3rd brush setting will not cook your dynamo, or battery and will reduce the load on the skew gears which seem to be the main concerns. Sure if you regularly do long night runs and heavily discharge your battery it wont last that long, and in situation such this or where lights are needed 24/7, alternatives may need to be considered. Although I have not personally had the need to use them yet, LED technology continue's to improve and would now appear to provide a sound solution.

Location: NZ

Ian, while I have your attention please could you explain how the skew gears are affected by the voltage output of the dynamo? I am quite happy to admit to not knowing something.

Thanks.

Hi Ray,

There is more to converting to 12v than better lights.

The ease of obtaining replacement bulbs, including LEDs ( cheaper !! )
Cheaper batteries;
Better engine performance due to better spark;
Easier starting, particularly in cold weather;

and

This is only my belief, overcomes the stale modern fuel problems.

Added to this is the fact that the modern motoring world is geared to 12v and if you buy any appliance or accessory that uses battery power then it will be 12v.

I would agree with anyone who wants to stay 6v, if it works for them then that is fine, however, if you want to go 12v then that is fine as well.

I do get a little touchy when people say it can't or should not be done or that it will damage your dynamo, without any practical experience or evidence to that effect.

Lets live and let live!!

Location: Falmouth UK

With the esoteric discussions on electricity making my head hurt - I assume that as the dynamo (generator) electrical load increases the drive load also increases - although I wouldn't have thought a few amps extra would be enough to cause the drive gears to fail - seizing the distributor drive will do this.

Tony.

Location: Malvern, Melbourne, Victoria, Australia.

Malcolm, thank you for your clear answer. I don't use my car enough to worry about changing from 6 volts. I personally have never had a problem with starting in cold weather and the spark seems perfectly satisfactory so long as I have a good earth.

I also happen to have a plentiful stock of 6 volt bulbs but as I seldom venture out in the Swallow after dark I don't think that would be an issue for me either !

As to the cost of 6 volt batteries; they are not cheap I grant you so there you are at an advantage.

I couldn't agree with you more about individual choice and when it comes to technical issues, I personally tend to listen more than I speak; after all, we have two ears and one mouth for a reason!

Malcolm, I don't think anyone is saying that you should or should not convert to 12v, I certainly am not, simply that in many cases it is completely unnecessary. I agree wholeheartedly that we should live and let live, it is not a personal attack providing balance to the arguments for and against a pursuing particular route. As with many things Austin 7 much folk law has built up over the years that could lead the unwary to believe that modifications developed to overcome specific issues are required for all cars, often that is simply not true. I have been asked to assist a number of enthusiasts over the years who have got into trouble by over complicating life because they have read this or that and taken it out of context. To my cost I must admit I have also been guilty of making similar mistakes in the past, and probably will do again in the future. That is where this forum can be such a great resource, you usually get a good number of responses, some for, some against, some from armchair mechanics and some from people who get out and use their cars and share their experiences. It is up to you the reader to draw your own conclusions but you need to hear both sides of the argument to do so.

Ray, as Marcus made note of, a dynamo converts mechanical energy into electrical energy, reduce the electrical load and you reduce the mechanical energy required, thus less load on the skew gears. In my opinion, and remember this is only my opinion, most Austin 7 in use today will be quite happy with the dynamo set for only an amp or two winter charge rate (forget the summer rate). You wont melt anything and your battery will be much happier as there will be less likelihood of overcharging it. If on occasion you do happen to be out after dark you will have several hours to get home where you can then connect your battery up to charger.

Location: NZ

Thanks for your advice, Ian. I hadn't thought of the dynamo in terms of converting mechanical energy into electrical energy. I suppose it just never crossed my mind and you have opened my eyes, so to speak. That's what is great about this forum; we none of us know it all.

My conversion to 12 volts was carried out in the mid eighties, before the advent of LEDs and when I used the car to commute into Manchester. One of the main reasons were a ready supply of free batteries from modern cars when they were having difficulty turning over large modern engines in winter and yet had plenty of life left for a Seven. In the winter the battery in the Seven that wasn't being used was refitted into our Ford Cortina giving it 2 batteries. Now Ford Cortinas were seriously difficult to start on a damp winter morning, not ours with 2 batteries it was first time every time. Presently the battery in my Seven started life in a 2001 two litre Peugeot diesel and was moved to my Seven in 2009. Whilst the battery in Sue's Seven started life in No 2 daughters VW Beetle in 2003 and moved into her Seven in 2013. Our third Seven actually has a new battery in it. During the winter the batteries are removed from the two Sevens that are laid up and are kept on the bench for easy access for charging and for connection to an inverter to power the central heating when there is a power cut. This takes about 50 watts, less than one of Malcolm's headlights.
The other reason was the non constant flash rate of 6 volt indicators- a thing of the past with LEDs. So whilst the technology is available for me to convert back to 6 volts, there is no financial incentive especially with the developing unreliability of the electricity supply.
I always understood that the rated output of a Lucas C35 dynamo was 8 amps, where I found this piece of information is lost in the mists of time, to me that is carved in stone and not to be exceeded.

John michael Knight

Hi Paul Thanks for your comment's My dynamo is 3 brush
I live in Blackpool
Regards John.

Location: United Kingdom

Now that my Forum access is recovered or restored, the following is a repeat of the essence of a reply emailed to Malcolm, for the possible interest of others.

No matter how carefully I prepare comments, seem to be misinterpreted, or offend someone! I have never said any arrangement wont work, just that some simple conversions often claimed either defy physics, or some key factor is not mentioned, or some feature unknown to me and not explained by others operates to avoid trouble.

I note Vince operates 12v with no field limit resistor, but winds back the third brush. If the field limited to say 6v the situation is much as original and the field should be OK. The added virtue that there is no power wasted, but without some exploration with a meter it is difficult to know just how much power is being fed to the field, whereas a resistor guards against excesss.

Vital essential provisos are often not mentioned which is why conversions are often so confusing. Some claim to connect the original 6v field directly to the 12v output and live! Power approaching the full original dynamo output would then be sunk into the field winding!

I think several readers confused reference to the field winding and the watts absorbed by it, with dynamo output. With the field, all watts supplied to it go as heat of the winding and any resistor, if any.
The armature situation is different from the field, the watts input come from the mechanical drive and the watts output is dissipated externally. It is just the armature current squared x armature resistance which produces damaging armature heating watts. Thus whether 6v or 12v heating is much the same for the same current, whereas the output watts is doubled, the whole basis of power output increases with 12v.

The total power generated is near output volts x gross armature current, the latter 2 amps more than the no load ammeter reading (coilo cars) plus field current, say 13 amps, about 90 watts at 7v. Probably needs twice this in mechanical watts to drive. If all stepped up to 13v with the same amps the power to drive also more or less doubles, which the gears will certainly notice.

I know this repeats points others have already made but it is all together.

Malcom’s simple Cornwall scheme and as advocated by Steven Hainsworth works reliably because field current is substantially as original, and the dynamo output amps are kept modest.

Bob Culver

Location: Auckland

not about regulators . but have just seen your youtube clip of silver 7 special .i think i now own that car AOK --- could you email me and perhaps answer a few querries for me
many thanks
clive

Location: United Kingdom

not about regulators . but have just seen your youtube clip of silver 7 special .i think i now own that car AOK --- could you email me and perhaps answer a few querries for me
many thanks
clive

Location: United Kingdom

Having run Sevens since the nineteen fifties I have had my share of dynamo problems. I have long understood that the Lucas C35A dynamo is rated at 9 amps, and the C35M is the only one rated at 11 amps. What change may have been incorporated to achieve this I don't know.

Location: just north of Cambridge

I enter a state of glazing over as soon as people start getting all technical with electrickery so it was with a start that I woke up reading Vince Leek's beautifully simple explanation of a 'Poor Man's 12v conversion'.

Please Vince, could you expand on this bit and give us an 'idiots' guide' on what one must do step by step to achieve Step 5. Photos would be great if at all possible.

5. Remove cut out and insert 40ohm 2 Watt resistor in series with the control winding
Re-install cut-out as before.

Location: North Herts

I like to keep it all very simple and stick with the original 6 volt system.
Saving a lot of issues using standard parts and setup.
The batteries that we have now are super performance.
Dynamos that are rewound with the newer wire are much better as the wire coatings are superior.
The trick for me with the dynamos is to keep the charge rate down to a sensible level, this seems to give a very reliable piece of kit.
I do not worry about a discharge with all lights on, as I am using like most of you a 80 amp hour battery.
How long do you need to drive in the dark ?
I drove three hours fully light the other night - enough for me.
And are your reflectors beautifully re silvered with the headlamp bulbs focused ?

Location: The Centre of the Universe

Very well said Nick, I am completely agree with everything you say, and with the addition of LED the reasons for converting to 12v simply no longer stack up, I never really felt they did in the vast majority of cases either. I have always had complete reliability with 6 volt systems, but then I have only been driving Austin sevens for 30 years or so and still may have not have discovered all their failings!

Location: NZ