This may be a repeat message. if so I apologise. Oso did a great job explaining the application of alternators in hydro systems. I am familiar with about a dozen systems using alternators and can confirm that most have the regulators disabled/bypassed in favour of a Xantrex C40/C60's in diversion mode. A few use permag alternators or rewound (for slow speed) alternators. However the latter also use diversion controls on the output.
Rob Quoting oso954 <[EMAIL PROTECTED]>: > > > > > --- Manfred: > > > > You are attempting to draw on your car experience (watching a > > voltmeter) and trying predict how the alternator will react in a > > totally different usage. You would have a much better understanding > > if you were watching a bi-directional amp meter. > > > > You stated "I fear that a 70A alternator running at half its rated > > speed will definitiley NOT produce 50-55A, but rather will end up > > with insufficient voltage to put ANY current at all into the battery > > bank! It depends on the specific alternator, of course, but if it's > > rated at 6000rpm, I would not count on it being usable at all at > > 3000!" > > > > If you go to: > > http://www.balmar.net/PDF/Alternator%20Drawings/60- > > seriesdimensionaldrawing.pdf > > > > They have a wonderful drawing of their alternators in various > > amperage ratings. In The lower left hand corner are the output curves > > for them. The lowest line is their 70 amp alternator (also shown are > > 100, 120 and 150 amp alternators) > > You have to interpolate between the lines, but at alternator rpm (not > > engine rpm) their 70 amp can produce about 32 amps at 1800 rpm, about > > 38 amps at 2000, about 60 amps at 3,000, and finally reaches 70 amps > > at 5,000 rpm. This is a fairly typical curve for many alternators. > > To me, it is ridiculous to spin the alternator the extra 2000 rpm to > > pick up 10 amps, in this example. That extra 2000 rpm will > > significantly cut down the brush life. > > > > Note that this is what the alternator can do at those rpms, not what > > the regulator is telling it to do at any given moment. > > > > "The regulator in a car alternator is designed precisely to fully > > charge 12V batteries. Typically, the alternator output is regulated > > to 14.4V or thereabout." > > > > It is not designed precisely to fully charge 12V batteries. It is > > designed to fully charge ONE 12V battery of a specific size. It will > > vary the current based on the current state of charge of the battery, > > to recharge it as rapidly as possible without doing harm. Higher > > current rates used when the battery is in a lower state of charge. > > Lower current rates when the battery is at a high percentage of > > charge and is being "topped off". > > > > The regulator for a specific car will be based on the amp hour > > capacity of the battery that the manufacturer puts in the car. The > > Toyota Camry comes with a 65 amp hour battery. So if we are talking > > about bringing the battery from 95% to 100 percent charge and doing > > it at a 10 percent rate, the regulator will instruct the alternator > > to deliver 6.5 amps to the battery. It doesn't matter what speed the > > engine/alternator is turning at, that is all that will be delivered, > > because that is a nice slow rate to top off the battery. 5 percent > > of a 65 amp hour battery is 3.25 amp hours, the 6.5 rate will have it > > fully charged in half an hour. > > > > When you take that same alternator/ regulator and couple it to a 650 > > amp hour battery (or 10 batteries of 65 amp hours wired in parallel) > > the regulator cannot tell the difference. You are now 32.5 amp hours > > away from full and trying to fill it at 6.5 amps. It will take 5 > > hours of charging without any additional draw on the system to bring > > the battery to 100 percent. And because you are filling it at 6.5 > > amps, you are not generating the additional 30 plus amps that you > > could be generating with a smarter regulator, or one better sized for > > your battery bank. > > > > One solution is disable the internal regulator (or remove it ) and > > use another regulator or controller that is more appropriate for the > > larger battery bank. Another option is to lock the regulator into a > > 100 percent charge rate and then use a dump load controller and dump > > load to burn the excess generation beyond that which will fit into > > your battery bank and current usage at the moment. There are > > additional solutions, but those require an accurate picture of the > > loads on the system and time of use. > > > > Anyway, I hope that this explanation helps. > > Oso > > > > > > > > > > > > > > > > > > > > > > > > > Does your company feature in the microhydro business directory at > http://microhydropower.net/directory ? 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