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Gerhard Maier
Germany
873 Posts |
 Posted - 29/05/2008 : 11:02:38
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CanÆt add anything more than our experts about improving the MMM dynamos, but perhaps to the question:
"why was this not a problem in period ?".
Before we had the dip filament bulbs, with two different focused filaments in each bulb, I think to avoid dazzling the oncoming cars, the driver had to switch off the off-side lamp and dipping the near-side one.
So for quite a period of driving the headlights used only 36 instead of 72 watts. Nowadays with the dip filament bulbs, we have improved road illumination, but that requires the full 72 watts all the time when headlights are on.
Further to this, on photos of our cars, when they were new, I can only see one tail/brake light.
That again must have saved some additional watts !
Gerhard
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bahnisch
Australia
674 Posts |
Posted - 29/05/2008 : 11:43:06
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| By way of background, I had my F-type (12 volt) dynamo rewound (I believe that there are two different ways of rewinding them, each giving different charging characteristics eg output at low revs as against higher revs, etc) and was persuaded by the very elderly and much respected "sparky" to stay with the three-brush system. For some inexplicable reason (initially probably my incorrect wiring) it has never been very vigorous and never seems to achieve the seven amps that it was set at on the test bench prior to installation. Since I seldom drive at night, I admit that optimum dynamo output is really not a major issue in my case. The real point of this response, however, is to say that this car, along with other MG's that I own, are permanently connected to automatic battery chargers and I consider this to be the best solution to the whole question of dynamo output. I personally do not see a need to increase dynamo performance (with the extensive modifications that seem to be involved) when the batteries in my cars are always fully charged and the (admittedly meagre in some cases) dynamo output is able to keep the battery fully charged (at least in daytime driving) until I return home. I might say that I am not averse to modifications per se, in fact fellow enthusiasts will know that I have carried out some pretty major ones in my F-type, all in the interests of "driveability" and/or reliability. |
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Bruce Sutherland
United Kingdom
1564 Posts |
Posted - 29/05/2008 : 19:29:48
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Hello Andrew and all,
For another 'little' retirement job I've had to complete an electrical load analysis for a post war classic car to be fitted with an effective air conditioning system. The additional electrical loads in modern city traffic driving conditions were way beyond the output from the original equipment dynamo.
Out of interest I have adapted a current/modern electrical load analysis method from Bosch for my P Type.
The Excel spreadsheet I've written readily allows for different assumptions for the number of lamps/accessories, their power requirements/watts, also variation of factors for the duty times for intermittent loads (e.g. stop lamps, headlamps, radiator fan, etc., etc.)
You can play to your heart's content, but needless to say the empirical criteria (experience) used within the Bosch pro-forma to relate the total power (W) from the load analysis to their recommendation of the rated size (e.g. 55A) of the generator/alternator - the result is well in excess of 8-8.5A output from the Rotax/Lucas DDS14 fitted originally to P Types.
The net result is in agreement with the concerns of many, that for modern driving conditions including additional safety-related lighting now desirable, we would like to have more amps and more lumens per watt.
If anyone would like a copy of the Excel spreadsheet, please send me your email address.
Bruce.
email: brucesutherland@f2s.com |
Edited by - Bruce Sutherland on 29/05/2008 19:32:54 |
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Blue M
United Kingdom
1472 Posts |
Posted - 29/05/2008 : 21:06:06
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Can these automatic battery chargers be plugged into the two pin socket on the instrument panel? I am using quite high power headlamp bulbs ( 45/50) which I did not realise were using so much electricity.
Until now I also did not know that the faster you go the less amps are produced, which would mean driving on a motorway at about 30mph after dark. Rather you than me!
Ian |
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ajc
United Kingdom
49 Posts |
Posted - 29/05/2008 : 21:19:56
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Just to add my tuppence worth, I converted my everyday Volvo to use HID lamps....High Intensity Discharge.
These use 20amps to turn on but then drop to a mere 3 amps during operation....and are four times as bright as the old 55w halogen bulbs they replaced....
I chose the standard white colour rather than the blue ones one tends to see out and about...
I drive a lot at night and these have been invaluable, though the legality is somewhat questionable on older cars....My MOT station said though as long as the beam pattern is not affected he did not have a problem with them.
One item is the ballest box to ignite them....where to place on an older car....though these are getting very small now...like a flouro light starter motor.
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Edited by - ajc on 29/05/2008 21:24:10 |
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ags
United Kingdom
275 Posts |
Posted - 30/05/2008 : 00:45:32
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Hi All,
As a rider to the discussion on, "why was this not a problem in period?", something has occurred to me that really should have been first on the list. This is the extremely large increase in traffic from the Thirties until now. I was prompted by a newspaper article saying that there are more than 30 million vehicles on the roads of the UK now, and from memory (though I have not found a source), the number of vehicles did not exceed 1 million (UK again) until well after 1945. In other words your chances of encountering another vehicle are now about thirty times greater than they would have been, since the length of our roads has been increasing at a slower rate. I would guess that this difference in probabilities would be similar anywhere in Europe today.
Gerhard, you are quite right, a single tail light was legal in our country in the Thirties but has not been allowed here since some time in the Sixties (I think) and is certainly both unwise and illegal today. The same thing applies to the "dip and switch" system for headlights which you mention, though the date at which it fell outside the law might be different.
Bruce, I would really appreciate a copy of your spreadsheet, could you send it to the address in my profile, please.
Nick, I hope that you do not think me cheeky, since I asked you to contribute by name, but your argument is not correct. I hope that nobody tries the method that you have suggested as it is a sure recipe for dynamo destruction. Although I have quoted amps all through the discussion, as this is the parameter which is easiest to adjust, it is not the fundamental limiting factor. The balance of amps and volts does not matter at all to the dynamo - First Law of Thermodynamics "In any process the energy of the universe remains the same" - what is important is the energy which is the product A x V x Time = Watts x Time which is proportional to Joules = Energy. In other words if you are dissipating 15 x 12 W in your lamps in a given time then you must be passing the same 180 W through the dynamo in the same time and in fact even more because of the wasted heat.
The situation is even worse than I suggested in my first post, because I think that I overestimated the efficiency of our dynamos. The examples I used were based upon bicycle dynamos which are a special case being very carefully designed for high efficiency. In particular they rely on permanent magnets and so need no field windings. After further reading my current estimate is that our dynamos are no more than 40% efficient and might be as low as 20%. In other words for every Watt transformed into electrical energy four might end up as wasted heat. Reworking my first estimate and taking the lowest figure for efficiency it now looks as if my standard dynamo can disperse (9 x 12)/0.2 = 540W of waste heat in relative safety whilst (9.5 x 12)/0.2 = 570W is marginal or worse. (9 x 20)/0.2 = Calamity. "Please do not try this at home".
Yes Terry, I know the voltages will vary according to speed and load and that the currents quoted are suspect but it is all only intended as a first approximation to get a method for comparing different circumstances on a similar basis.
Bob L., your analysis concerning wire gauges and my own of sources for improvement omitted at least one cause of waste heat. This is the energy wasted in magnetic hysteresis in the armature core. As yet, I am still no nearer quantifying it all.
More technical ramblings from
Andrew Smith MMM571 |
Edited by - ags on 30/05/2008 11:34:27 |
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rbm
United Kingdom
141 Posts |
Posted - 30/05/2008 : 09:51:54
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I had discounted the HID lights system as this is 12V only, but as for amp drawn to lumens emmited it is at the top of the tree for systems we could use now.
Richard |
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Bruce Sutherland
United Kingdom
1564 Posts |
Posted - 30/05/2008 : 18:39:18
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Hi Richard,
Do you have details (detail drawings/dimensions) of the HID (gas discharge) light unit and its mating control box?
I suspect that a new reflector would be required and that and a housing for the control box would require designing.........I wonder if it could all be made to fit inside an LBD140 headlamp shell?
Do any of our German for French colleagues know any lighting design engineers at Hella, Bosch or Valeo? It would make an excellent project for some young graduate designers in their electrical design departments!
Other wistful engineering ramblingsāfrom
Bruce. |
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ajc
United Kingdom
49 Posts |
Posted - 30/05/2008 : 23:29:05
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The ones in the car fit straight into the existing light unit with no modification whatsoever....they even use the existing clips on the lights to hold them in the hole in the reflector.
I seem to remember Phillips make the smallest and most reliable ballast....
As for fitting into the MG lights I will have a look in the garage when home sunday as I have not looked at the lamps/reflectors for a few years so have no idea of the setup there. |
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bahnisch
Australia
674 Posts |
Posted - 31/05/2008 : 12:44:36
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| In my F2 Magna (replica), M-type and TC I plug the automatic battery chargers into the dashboard sockets. In my other cars I have made up little sockets (placed in easily accessible locations) using (cheap) parts obtained from one of those radio/electrical shops that seem to abound these days! This is far more convenient than finding a "hot" wire under the bonnet (as I used to do!) or worse, attaching an alligator clip or somesuch to the battery! These chargers only deliver a maximum of less than five amps even with the battery practically flat (which in practice never happens!). There are many benefits in keeping batteries fully charged. |
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