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Slight OT ; Car alternator failing?

Hi all,

I recently had to buy a battery for my girlfriends car, it failed with the cold temperatures lately (battery was also nearly 5 years old). In order to get warranty on the battery i had to go down to the shop to check the charging system in the car. The guy hooked up an analyzer did some tests (starting voltage, battery voltage unloaded, battery voltage loaded,...) and goofed up the first time; when the analyzer asked to load the battery and run the angine at 2000rpm he took a while to find the rear window heater and by the time he had the engine revved up the analyzer sayd he had completed this step. Result was that the analyzer said that there was a problem in the charging system, that alternator voltage was to low when it's loaded. Of coarse there was I said, the car was idling when the analyzer said to run at 2000rpm. The guy was starting to make an appointment to replace the alternator, but I convinced him to take the test over. This time he did it right but then there was another problem, the analyzer said that there is a to high diode ripple. I couldn't help feeling that I was being fooled and refused to leave the car behind to replace the alternator. Now I would like to check the ripple myself, how much ripple can the battery take, quite a lot I presume? Am I right that I can check this with a multimeter set on AC voltage, or should I use a scope? Btw, test results from the analyzer said that voltage unloaded was 13.65V, and loaded 13.20V, those are quite normal values I presume?

PS : Sorry if I blabbed along the whole story, for those who hate long stories, the main question is : what's the maximum ripple a car alternator may produce?

Reply to
Billy
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[snip]

An alternator is an AC machine with 3-phase full-wave rectification, so the ripple is fairly small, even with a resistive load, barely noticeable with a battery attached. However, open diodes will show up as excessive ripple.

Sounds to me like the technician at the shop you chose doesn't know diddly-squat. Find another place that can test alternators... preferably one that doesn't *sell* them.

A five-year-before-death battery indicates to me that the charging system is most likely in good condition. I rarely get more than two years on a battery here in Arizona... the heat kills them.

(If you are moderately electronically capable: measure the neutral terminal with an average-reading voltmeter... it should be precisely

1/2 of the battery voltage. *Any* fault will cause this voltage to deviate from 1/2... I designed a fault-light system for GM eons ago that does this test.)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

I think its a 2-phase, at least mine (you can see some my mods on my site under electronics at the end ... :-)))

-- Regards, SPAJKY ® & visit my site @

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Reply to
Spajky®

How many diodes? On this side of the pond we have six diodes, 3-phase (Y-wound) winding.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

I have only 2 of them here; IMHO you have much bigger car than mine needing stronger generator to fill up your much bigger accumulator ... :-)

-- Regards, SPAJKY ® & visit my site @

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Reply to
Spajky®

[snip]

I have never seen an alternator that didn't have 6 diodes.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

IMHO for 3-phase alternator is enough 3 diodes: coils connected star topology (common is +) & 3 other ends connected thru diodes to GND (-) ... no need for 6 ones ...

-- Regards, SPAJKY ® & visit my site @

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Reply to
Spajky®

[snip]

Do it however you like. You asked a question, I answered. I am an expert on alternators, check my patents on my website.

You somehow don't like my answers. Ask no more.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Ok, I will ... :-)

:-)) , this is agood one ...

-- Regards, SPAJKY ® & visit my site @

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Reply to
Spajky®

Not really. If you only use three diodes you need heavier field windings, and the DC output will have more ripple. Using full wave rectification is cheaper, and gives better performance.

--
We now return you to our normally scheduled programming.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

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