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Old 04-15-2009, 09:02 PM   #11 (permalink)
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you have to control the low sides too. and the 555 needs resistors and capacitors etc.

the fets come in quad packages so an avr and two chips would be three chips total for the microcontroller route (mosfets included).

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Old 04-15-2009, 09:12 PM   #12 (permalink)
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This is good stuff, guys. Thanks. Digesting & reading your code, dcb...
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Old 04-15-2009, 09:12 PM   #13 (permalink)
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Missed your description of the panel, nevermind!
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Old 04-15-2009, 11:26 PM   #14 (permalink)
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The correct way is to use a boost converter. However, not any common boost converter can be used as in a solar application, as it must attempt to regulate the *input* voltage as well as the output voltage. The reason is that solar panels are more or less current sources up to near their open circuit voltage. (Read about the photoelectric effect for more information, but the basic explanation is that the electrons knocked free by light have a certain velocity and therefore a certain amount of voltage difference they can overcome.) The boost converter should try to pull down the input voltage to the desired value as long as the output voltage is not too high. Use a potentiometer to set it to maximize efficiency. If the panel voltage is clamped too low, efficiency suffers as a lot of the electron energy is wasted. If it is let to go too high, the low energy electrons will not be able to make their way to your circuit. The optimum point is something like 13-18v for a 12v panel.
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Old 04-15-2009, 11:37 PM   #15 (permalink)
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In what sense is a boost converter the "correct" way? (Efficiency? Simplicity?)
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Old 04-16-2009, 12:12 AM   #16 (permalink)
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If I was wanting to do a 12V solar charger for 72V I would probably build the one dcb has listed. It is a simple circuit so that means there are fewer things that can go wrong.

Simpler is always better if it does the same thing as the more complicated circuit. But for my setup I will probably stick with the one I posted since it does continuous balancing of the batteries and swapping out the 555 in the circuit for an arduino could give me a lot more capabilities like measuring volts/amps and having a display show total KW used or something. I can never leave well enough alone it seems like
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Old 04-16-2009, 01:00 AM   #17 (permalink)
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Quote:
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In what sense is a boost converter the "correct" way? (Efficiency? Simplicity?)
Both simpler and more efficient. It is simpler than trying to switch the panel between the batteries and more efficient as well as it will allow the panel to operate at its most efficient output voltage. The efficiency gained by hitting the sweet spot is greater than the losses in the boost converter.
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Old 04-16-2009, 05:41 PM   #18 (permalink)
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Mike, any thoughts on "more current" meaning more electrolite stirring in the battery? Part of Darins idea is that it would be better to occasionally stir up the electrolite by applying more charging current individually, (i.e. by rotating which battery is being charged). Not sure how much current you need for that though.
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Old 04-16-2009, 10:14 PM   #19 (permalink)
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Mike, any thoughts on "more current" meaning more electrolite stirring in the battery? Part of Darins idea is that it would be better to occasionally stir up the electrolite by applying more charging current individually, (i.e. by rotating which battery is being charged). Not sure how much current you need for that though.
It is actually better to charge at low current than at high current. As for keeping the electrolyte mixed, it's a valid point for a stationary system but in the case of a car, just driving would produce enough vibration to keep it mixed.
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Old 04-17-2009, 04:42 PM   #20 (permalink)
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I think I'm with mike on this one, jack up the output voltage (or add three more panels) and/or build a solar powered desulfator, and optionally optimize the current draw from the panels (gets more complicated quickly though)

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