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I was using the report to show that modern alternators had high outputs even at low engine revs. Due to the difference in pulley sizes between the alternator and engine the alternator would be running at quite high output even at tick-over. Revving the engine would make very little difference to the approx. 14 4 volts already being output. |
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The term output is ambiguous. Whilst alternators have a relatively constant voltage output vs engine RPM, their current output is related to the RPM by curve that roughly has the form of Imax(1-e^-(k*RPM)). The maximum current output is available at around 2500RPM. It is the current that carries charge from the alternator to the battery meaning that the charging rate is dependent on RPM roughly in accordance with the shape of the above formula's curve. |
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But the report doesn't show what you say, quite the opposite, the charts / graphs, 3 & 7, I mentioned previously actually how low the output, in amps is at low engine revs Talking about the difference in pulley sizes is irrelevant, the article and graphs are talking about output at engine speeds, RPM, not at the alternator rotor speed, RPM. You are comparing apples with oak trees ! MSS explains the voltage, current thing excellently. |
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Alternator output ( voltage ) is a straight line graph and is related to rpm when not being being controlled by a voltage regulator. As I said, the regulator controls voltage in the car's electrical circuits but not current which varies according to demand. As more items are switched on the voltage input to the armature varies.--This variation changes the strength of the armature's magnetic field. The armature has about 6 amps being fed into it to give maximum output.---Perhaps even up to 100 amps or so output. This input ( 1 to 6 amps. ) is what varies the current coming out of the alternators field coils which are bolted to the inside of the casing. Your 2500 speed is vague as you don't quote a specific alternator type or output. All my input ( information. ) is specific to the types of alternators fitted to the R75. PS. Merry Xmas.-----:snowball::new_year: Ooooops. nearly forgot.--;) ( Which vary very slightly according to the make and model fitted. ) It would also be nice if you explained what the letters mean in your complex formula. |
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Read the title underneath it.---It says alternator speed.---:duh: PS. I'm sure everybody has heard of --"oak apples"--Lol. Plus, you've left a word out in your first sentence. |
Got to go now as my coach has just turned into a pumpkin.---:D---And those mice can run faster than I can.--( What with my stick and all. )
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[QUOTE=Ducati750cc;2910403]A bit technical in parts but otherwise not bad.
Remember when you said......... " Fast tick over to put a charge into a nearly flat battery is no better than just letting the engine tick over.--The modern alternators will hold 14.4 volts even at tick over.-- " And I said .........."Fast tickover compared to idle tickover to put a charge into a nearly flat battery is the same you say. Can I suggest you experiment on your suggestions with a modern alternator with both a voltmeter and an ammeter connected. Then come back to report that the amps produced is exactly the same at both idle and a high idle. " Could I suggest you read the PDF, taking note of Fig. 3 and Fig. 7 where you will find that there is a noticeable increase in current output at higher idle ( fast ) speeds Just found your post. Five amps is a reasonable regulated charge rate both by the alternator or a battery charger. Any more than that and the battery will start to overheat and lose water vapour from the electrolite. The level of electrolite will start to fall reducing the amount of the plate taking part in the chemical action. Capacity is therefore lowered by overcharging. On the car the battery is shielded from engine heat by having a casing around it. Engine heat too can cause vapour loss making the battery less efficient.---:shocked: I believe you are looking at the capabilities of an alternator and not what it is actually doing when in a controlled operation on a car. |
Good thread this one and we might be closing in on the factual truth. I really enjoy these kinds of searches.----:chat:
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It's a bit late now but I'll see if I can make it less enjoyable for you tomorrow. :laugh:
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