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Old 13-03-18, 11:43 AM   #11
Lucien Nunes
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I'm not 100% sure that I understand the purpose of the exercise: Is the aim here to upgrade an existing 6V vehicle from dynamo to alternator while keeping it 6V? If so, what dynamo is presently fitted and what problems, other than the usual ones with 6V electrics, are you experiencing with it?

There are two ways to charge a 6V system with a 12V alternator:
a) Make the alternator generate 7.2V (charging voltage for a 6V system) instead of 14.4V,
b) Generate 14.4V and convert it down to 7.2V

Both are possible; I have done similar things, as in the past I have made all sorts of modifications and high-performance charging systems, including getting 120A out of a 16ACR Mini alternator! I have not specifically addressed 6V systems though.

Option a) involves two steps.
1) Replace the regulator with one that regulates at 7.2V, or fool / modify the existing one into thinking it's regulating at 14.4V when the alternator output is exactly half that.
2) Unless the alternator is running very fast relative to the crankshaft, up-convert a supply for the field winding that still requires 12V for full field strength.

Neither of these tasks is difficult with a bit of electronics knowledge, and the resulting add-on electronics would be small and could be hidden under the end cover of most alternators especially the roomy Lucas ACRs. The available output current would be approximately as per rating, maybe rather lower if 2) is omitted. The parts cost is very low - perhaps 40 on top of the original 12V alt. No rewinding or other major mods needed to the alternator itself.

Option b) involves a rather more expensive and bulkier box of electronics - a stepdown converter sufficient for the full output power - external to the alt. No modifications are needed to the alt at all. Most of the guts of the converter can be bought ready-made but some hacks may be required. The available output current will depend on the converter but could be up to maybe 1.5x the original alternator rating - a 34A 16ACR might offer 50A at 7.2V.

The simplest approach would be a) 1) only. In the past I have modified a CAV 130604 regulator to control an ACR type alternator to deliver a non-standard voltage; some extra mods would be needed to make it function on a 6V system but it can be done. I don't know just how fast the alternator would have to run to make charging effective - with a small pulley it might be just fine. In that case, you will need the alt, the regulator and a few changes of components in the reg.

a) 1+2) and b) offer the distnict advantage even over normal applications of the 12V alt, that its low-speed performance will be improved. In a 12V system, 14.4V is needed for full charge rate and 11V won't charge anything at all, yet 11V is plenty to continue charging a 7.2V system. Therefore, it might be possible to fulfil all the electrical needs of the car and continue charging even at idle, with no drop in system voltage.

Any benefits accrued over using a dedicated 6V alternator, if such exists, derive from the 12V unit's larger physical size and therefore spare power conversion capacity, when that capacity is harnessed at 7.2V. With skill and patience, an alternator could be re-wound to the lower voltage and with a suitable rectifier upgrade and regulator, would peform just like a genuine 6V alternator of approximately double the current rating.
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Old 13-03-18, 09:13 PM   #12
minorman
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OK Lucien. The idea started as a result of the road Vehicle lighting regulations (and other rules). With all the legally required lighting powers (e.g.30 + 30 watt headlights equals 10 amps alone) plus other lighting, windscreen wiper. petrol pump, ignition you can see the load is or can be high. My 1936 Morris 8 uses a 6 volt system with a Lucas C45 6volt dynamo. The Morris 8 has a smallish 6 volt battery box and the battery is a good fit in it. The limiting factor of the 3 brush dynamo is that it is totally unventilated so the cooling is zero and it is restricted to about a maximum of about 9 amps output to the battery and at this charge rate the field current needed to produce this charge is around 4 .5 amps. It gets very hot if you ask for more and the efficiency gets even worse. There are several constraints.

1. I could go 12 volt as some have done but I would need to relocate the battery.

2. I could use 12 volts and have say a 17ACR alternator to replace the Lucas C45 dynamo but it would not look right under the bonnet.

3. Where do I hide all the necessary high power gubbins to convert 12 volts to 6 volts ?

4. Nit pickers who decide that"it's not original" - yes they are everywhere and the fact that there were a couple of self tapping screws I used once "of the wrong type" which drew some caustic comments.

This started out as I thought 590 +vat was a bit steep to provide a converted dynamo that looks absolutely correct and produces enough power to drive everything plus actually charge the battery at night.
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Old 13-03-18, 09:23 PM   #13
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Are the regulations retrospective?

NHH
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Old 13-03-18, 09:38 PM   #14
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Led bulbs?

Dan
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Old 13-03-18, 09:43 PM   #15
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There seems to be a good supply of vintage-looking Bosch 6v alternators on ebay, or do the rivet counters object to them too ?

Phillip
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Old 14-03-18, 12:48 AM   #16
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What high powered gubbins ?
12 volt Dynamator, charge regulation is internal, you connect earth, power and one to charge light.
Battery, large motorcycle one (BMW R1150?) is probably all you need, or look at modern small batteries as fitted to new small cars (smart car one is tiny).
Change all bulbs to 12 volt, change flasher unit, if engine is a good starter you may get away with the original 6 volt motor, at least until the day you have to crank it forever to start.

Neil.
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Old 14-03-18, 08:01 AM   #17
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Unfortunately it appears the regulations are retrospective. Its a riveting read the road vehicles lighting regulations 1989. I don't think it has ever been tested in court but when the morris was built the headlights were of a lower wattage and there was only one 3 watt rear light. Now there have to be 2 rear lights and 30 + 30 watt headlights bulbs. The crazy thing is, pre a certain date (1986) you can theoretically only use filament bulbs of 30 + 30 watt because that's how the rules were written. LED bulbs were just a dream then. I have considered using replacement plug in LED bulbs and a few people do but the beam pattern is not that good, and the difference between main & dip can be variable between bulbs. Some modern cars do have LED headlamps and they are very good, particularly when the manufacturer has put an awful lot of money into design and development to get the beam pattern and focus right. Also, because the rules have never been updated from 1989 they are by default legal. I dont want to go 12 volt as this requires other changes beyond just light bulbs. e.g.petrol pump, fuel sender & gauge, trafficators, starter, ignition coil, wiper motor.

Re "the gubbins". If you use a 12 volt alternator say 17 ACR then it can produce up to 14.5 volts and a lot of amps. The sensing control unit inside needs to detect a varying battery voltage as the battery charges or discharges to control the output but ther isnt a 12 volt battery to see. If I put something like a power converter to transform the output to a nominal 6 volts then the sensing control in the alternator cant "see" the varying 6 volt battery terminal voltage to adjust its output. I presume the system at the best would probably be unstable or worse.

I will see if I can find an old vintage bosch alternator if there is such a thing. I thought I had found one on ebay at the weekend but the seller was doing the usual of mis advertising. i.e. alternator / dynamo ??? etc. A bit like advertising a NOT LISTER D engine when it is a villiers etc etc. For the moment I will just keep plugging in the battery maintainer each time I put the car back in the garage.
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Old 14-03-18, 08:47 AM   #18
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Quote:
Originally Posted by Hornet 6 View Post
Snip, if engine is a good starter you may get away with the original 6 volt motor, at least until the day you have to crank it forever to start.

Neil.
Forget the starter motor, we used to start our A35 by hand, it's all part of the charm.
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Old 14-03-18, 10:21 AM   #19
nickh
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Quote:
Originally Posted by air-cooled View Post
There seems to be a good supply of vintage-looking Bosch 6v alternators on ebay, or do the rivet counters object to them too ?

Phillip
I'm not entirely convinced that they really are alternators https://www.ebay.co.uk/sch/i.html?_o...or%22&_sacat=0 but even so would probably be a useful upgrade from the pre-war third brush regulated job.

NHH

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Old 14-03-18, 05:53 PM   #20
Lucien Nunes
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If for aesthetic reasons a conventional alternator is unacceptable, then none of the methods I mention in my post above are applicable. However, if it can be tolerated, and you definitely want to stay with 6V, then the three possibilities I outlined above are all technically feasible to the extent that I bet I could get one or other of them working within an hour or two of tweaking and testing.

Quote:
The sensing control unit inside needs to detect a varying battery voltage as the battery charges or discharges to control the output but ther isnt a 12 volt battery to see. If I put something like a power converter to transform the output to a nominal 6 volts then the sensing control in the alternator cant "see" the varying 6 volt battery terminal voltage to adjust its output. I presume the system at the best would probably be unstable or worse.
A traditional alternator regulator (i.e. not integrated with engine management) does not do this. It simply generates a constant voltage, regardless of the battery's state of charge or the running load from the electrical system. There are a few subtleties that are not worth going into here in the forum post, but in principle it can be made to function without a battery.

Quote:
Where do I hide all the necessary high power gubbins to convert 12 volts to 6 volts ?
I marginally favour modifying the alternator to produce 7.2V as all the mods can be hidden inside it, rather than converting 14.4 down, but if you convert you're looking at a module about 3x3x2 inches. For example: https://www.ebay.co.uk/itm/263222811096

I used to build things like this from scratch but now they are so cheap I buy them ready made and change a few critical parts to higher spec ones to improve reliability. That will feed your 6V system up to 20A at which point it will be consuming about 11A from the 12V side. It needs cooling but not a vast amount, the electrolytics, transistors and rectifiers could be re-oriented so that it fits in a finned heatsink case the size of a cigarette packet. As it has both current and voltage limiting, two modules would work in parallel to give 40A at 7.2V.

Quote:
There seems to be a good supply of vintage-looking Bosch 6v alternators on ebay
Quote:
I'm not entirely convinced that they really are alternators
Indeed they are not. Hailing mainly from Germany, I think it's a faulty translation of 'Lichtmaschine'.
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