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Old 19 December 2008, 14:49   #1
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Alternator Output

Hi All

Anyone know the best way to measure rated current output from engine alternator?

I want to check the output current versus RPM. I guess a variable load of some type is required while monitoring the alternator voltage??

Cheers

Tim
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Old 22 December 2008, 08:30   #2
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Quote:
Originally Posted by Talos View Post
Hi All

Anyone know the best way to measure rated current output from engine alternator?

I want to check the output current versus RPM. I guess a variable load of some type is required while monitoring the alternator voltage??

Cheers

Tim
What engine is it for? You can buy clamp on ammeters which are pretty good, they just go over the battery lead and measure what the draw is. If its a Mercury/Mariner i have lots of info on outputs from alternators!
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Old 22 December 2008, 11:53   #3
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Current depends on load, up until the alternator cannot meet the demand. Do you mean voltage, by any chance?

jky
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Old 22 December 2008, 12:08   #4
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It's easier to get the numbers from the alternator and ask the manufacturer.
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Old 22 December 2008, 15:42   #5
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Thanks Guys

Basically i know what the output should be from manufacturers data, but what you get after time is usually not the same thing

I imagined that you have to increase the 'load' on the output (while monitoring the current with an clamp meter), until the volage across the alternator falls outside spec, at different revs. This is the point that the output current is max

Tim
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Old 23 December 2008, 08:33   #6
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The regulator wont behave properly without a battery connected, in fact the excessive ripple voltage can kill the regulator.
the usual way to test an alternator is to switch all electrical loads on for a 5-10 minute period to take the "surface charge "off the battery, and drop the battery voltage down to 12 or so volts,
once the battery is suitably slightly flattened, start the engine and rev it to the approx speed that equates to the speed the alternator is rated at. the alternator should put its maximum rated current into the battery (which is regulated by magnetic saturation of the core) briefly, then as the battery voltage rises the current should fall.
by the time the voltage gets up to 14.4-14.8 volts the voltage regulator will take over and the current should have dropped to a couple of amps.

You cant really use a dummy load its to complicated to be worth bothering.
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