permanent magnet alternator
Posted: Sun Feb 18, 2007 10:22 pm
Some may recall my question regarding results of an attempt to reduce the voltage drop between the regulator/rectifier output (white wire) and the battery.
At full output measured in the output wire from the regulator/rectifier at 13.9 volts and dash voltmeter reading just over 13 volts, there was 0.7 volts drop between the output terminal of the regulator/rectifier and the battery positive.
"Aha!", I thought, "Here's an opportunity to reduce the voltage drop which should increase the charging system output.
A 12 gauge wire was soldered in parallel with the output wire and connected to the battery side of the starter relay. (Effectively to the battery positive)
On retest there was zero voltage drop but the alternator output remained at 13.0 amps and dash voltmeter at just over 13 volts.
I was mystified for some time but a call to an old buddy who teaches power generation clarified the issue. I should have explained the effect on my own as I am quite aware of the current output, self limiting characteristics of alternators but as with all things which one is not using frequently.....
The reason is that the KLR alternator is capable of 13.9 amps at which point the counter induction of the stator begins to reduce the magnetic field strength of the armature so much that the output current falls off. This I knew but wasn't bringing into the question.
This effect is the reason that automotive alternators utilize a single element regulator which limits voltage rather than requiring a two element regulator to limit both voltage and current as is the case of DC generators.
(DC generators also use a third element to prevent reverse current because they don't use diodes but that's not pertinent)
What I did not know is that the regulator is likely designed to take this into effect such that the designers likely used fairly light wire between the regulator and battery knowing that some voltage drop would have no effect on current delivery. The risk I take in reducing the voltage drop between regulator and battery is that they may have taken this voltage drop into account as an assistance to regulating voltage. Removing the effect of the lighter wire could have a detrimental effect on the regulator life so I will remove the heavy wire.
Note that this has nothing to do with reducing voltage drop to other loads on the bike by use of relays.
Klaus & I have been talking about this problem and came to the conclusion that this effect was not an Ohm's Law problem but were stopped at that point.
Thanks for your help, Klaus. Drop by and I'll by the coffee.
Norm
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