6 or 8 weeks, ISTR. I was away at short notice. My other cars were OK. I knew batteries lose their charge but didn't have time to disconnect anything.
The $64,000 question is;
Is the sequence of events I have described impossible or merely unlikely?
I already knew it was unlikely since I'd previously jump started dozens of cars (and at least one since) with no problems and had a memorable WTF moment when I saw the red battery charging light on the dashboard.
The only difference is that I'll be less likely to offer help with jump leads in future in case someone decides I owe them an alternator.
In your original post you suggested it was likely:-
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From: Subject: Re: easy way to generate an ac signal Date: Wed, 24 Oct 2012 17:20 Newsgroups: uk.d-i-y
The diodes get fried if you try to jump-start a car with a flat battery, so that someone's dad will probably have a car alternator with fried diodes in his shed that you can modify to get the AC out.
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If you have friends like that I'd avoid helping them at all.
When you said I should have sought professional help, I undersood that I should have got a 'professional' mechanic, rather than an enthusiastic amateur.
So what did you have in mind. I should have got a mechanic who was CEng IEE? Or that I should have got a doctor to jump start it like in Casualty? Or a clergyman to read the last rites over it? I'm sorry if I misunderstood you.
Yes, I did say that. Mea Culpa. I should have said "...could get fried". I'd have been more careful with the phrasing if I'd known it would be so contentious.
In fact I've started two cars since then, both for strangers, with no subsequent alternator problems. I'm nice like that.
So are you going to answer that question or continue dodging it?>
ry had enough charge, then turn both off and disconnect the jump leads.
So how is jump start any different from reconnecting a battery you have previously disconnected? And how do you start the engine if the battery is flat.? Nothing you say makes any sense.
Car alternators are modified so that the normal sine wave is "clipped". The modification is the strange shapes of the pole pieces on the armature/rotor which distorts the magnetic field it generates.. This means that there is less ripple on the rectified DC. This prolongs the life of lights. It also means the alternator is less efficient due to increased iron losses. It also means as it doesn't generate a sine wave, it is useless for the purpose advocated by some people here who don't seem to understand how electrical machines work..
Rpm. field current, and voltage have no bearing on the wave form. A sine wave is a sine wave is a sine wave. It either is or it isn't.
"Clipped" Can you give a reference for that Harry?..
Really?..
Well where do you want to define that then at the output terminals or pre rectification and relative to where in the windings and under what test conditions..
Its clear you have never worked with alternators, or built regulators for them, and don't have a clue to their characteristics.
I cannot believe you say that the waveform, and here you haven't even specified if this is the rectified current output or voltage output waveform, is independent of rpm, field current or output voltage.
I have never argued that the claw type field alternator ironwork might create a modified sine wave, but I can assure you that stator leakage inductance will go a long way to smooth out current ripple. You also haven't considered the battery impedance in further smoothing of output voltage. Low voltage filament lighting also has sufficient mass to further smooth any variation in temperature from a minimal voltage ripple.
Regarding whether a sine wave is a sine wave is a sine wave, Catnic took to court a number of manufacturers who were infringing their patent. Although the patent used "vertical" and their opposition were using off vertical sections, ie at a slant, even in the pedantic world of patents, Catnic won. In other words if it looks nominally sinusoidal, it probably is.
If you can produce real alternator waveforms, which aren't clipped by rectifying load (ie no load), that are near square then I will be impressed.
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