Author Topic: 12v the big question  (Read 3399 times)

Online groily

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Re: 12v the big question
« Reply #15 on: 19.10. 2010 23:20 »
Understand all that worthy ambition Chaz.

But there are Big Buts . . .

Point One:
a)You don't want and can't have a rectifier with a dynamo - you're producing dc already because that's what dynamos do, thanks to the commutator, which is a mechanical rectifier.
b) Rectifiers go with alternators, which don't have commutators and produce AC which needs converting because there's no such thing as an AC battery even if sparks and lights can run off it.
c) You want a dynamo regulator and cut out.
d) The simple fact that you're negative earth is not a reason for putting a Japanese alternator system part in there. It won't work, I promise. A dynamo regulator manages the dynamo's output (D) by controlling the dynamo's field coil input (F). Dynamos are very elegant devices in that they serve up power according to demand rather than according to simple rate of rotation, so the regulation has to be designed to match output to electrical demand. Totally different principle from an alternator, whose output, unregulated, would be solely dictated by rpm. The means of regulation in an ac regulator are completely different from a dynamo's.

Point Two: the idea of getting better lights when the dynamo's going to be overloaded because of ignition loads doesn't stack up.

You have to start from first principles.
Your DC system produces a nominal 60 watt maximum safe output.
That's 10 amps at 6 volt, 5 amps at 12. Yes, fewer amps with higher voltage because watts equals volts times amps.
Your Rita/Boyer/what the hell? ignition option will consume 2 amps at least at 12v.
That's 40% of the dynamo's current rating (amps) and will leave you with a mere 3 amps or 36 watts of power, at full 'regulated' rpm, for everything else.
The tail lamp and speedo take maybe 8 of them, leaving 28.
If the sidelight up front stays on with the headlamp, that's another 5W-odd gone, so 23 left.
(LEDs can reduce this a bit, but not enough.)
At engine rpm between about 1000 ('cut-in' rpm) and below about 1800 ('regulating' rpm) the dynamo is feeding the whole output from D into the field coil, F, unregulated.
Under full load, ie lights on and ignition on, that's a lot of load on a small generator.
Above about 1800rpm the regulator, if you had one, would manage the field input to prevent a meltdown in the armature, but it wouldn't maintain system voltage because the loads are too high for the dynamo's capacity.
The battery would gradually lose charge as it would be making up the difference.

The 'big question' here is not how to pick from some mix and match menu of attractive-looking options regardless of what you've got, but is whether the basic electrical system on your machine can properly support what you want to do. It can't, it really can't.

You need a good dynamo, a decent voltage regulator and cut-out, whether mechanical or solid state and I favour the latter, and, for choice, a magneto (or other independent spark generator). Or, you need an Alton alternator with its own built-in regulator, if you want to have powerful lights plus electronic ignition. 12v on its own is no magic solution, nor is a solid state regulator, and least of all is electronic ignition. Which is not, IMHO, likely to do anything useful for a '56 A apart from flatten the battery and maybe fry the dynamo.
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Online groily

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Re: 12v the big question
« Reply #16 on: 19.10. 2010 23:32 »
Thanks  a lot Wilko.
AC volts? Any tips on who makes? I read elsewhere .22mf dV/dT greater than 1000, dF less than .05%, etc and avoid metallised polyester as the dielectric will fail at some point . . . . Self-healing being a finite thing.  A mystic art. Fingers crossed for the ceramic things I've now got in 2 mags (which are working fine so far). IIS say they've sold 6000 of these expensive things they sell, and zero failure they know of. Anyone in a position to contradict that? 
Have another ceramic one coming from the US to compare - but the prob is can't tell when they're going to fail till they do! All good fun. But far easier were the armature redesigned to allow routine replacement (like on some of the single cylinder mags), but about 60 years too late!
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Bill

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Re: 12v the big question
« Reply #17 on: 20.10. 2010 07:59 »
In reply or addition to Groily's last post, you can get more than 5A and thus more than 60W, from an E3L dynamo regulated to 12V, but at 12V it doesn't do any useful charging below 2000rpm, which of course means the battery goes flat in traffic.

I found you can run a dynamo quite successfully at 12V, so long as you have a front pilot light for in town and so long as you are not depending on it to power electronic ignition. You might get off with powering points with a dynamo and battery.
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Offline chaz

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Re: 12v the big question
« Reply #18 on: 20.10. 2010 18:33 »
if you dont mind, Im sitting in the wings reading the debate, very enlightning *respect*
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Offline iansoady

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Re: 12v the big question
« Reply #19 on: 21.10. 2010 11:30 »
Ive looked through many web sites and dealers pages in search for the answer.

Well you did ask.....

There are (at least) as many opinions as there are people to give them. I can only say what's worked for me for 40 years. But I know there are other equally valid solutions.
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Online groily

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Re: 12v the big question
« Reply #20 on: 21.10. 2010 19:48 »
You did Chaz, as Ian said! And there are lots of options, some of which have been mentioned, which work really well. That particular one won't.

TT you're dead right as usual. As I think I might have said earlier on - 80W odd are available without overloading the field if we're talking 12v-converted original Lucas windings. And of course you're right about the cut-in speed, iffy in town . . . but I have one such, which works OK because I'm a country bumpkin. Fine-wound coils sort that, but we're back to 60W safe max.

Having said which, what total utter complete moron crushed a pair of alternator wires between a pair of primary cases this morning and made such a b**** of everything he couldn't go for the planned blast. . . ?
His excuse is he was looking for something interesting to do. She didn't really manage more than half a smile.
Luckily, by end of day it was sorted.
But it's going to rain tomorrow.
And France has no Gas/Petrol or any other combustible materials, so that helps no end.
What are the penalties for pouring central heating oil into a diesel car?
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Bill