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| Solar panel regulator design question |
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| Seekonk:
Lots of questions. Think of the TL431 as an opamp, voltage reference and a transistor. You have to supply some power to run this. Everything works best if you stay above 2.5V. Drive it hard and it will go just under 2V. Input/reference is high impedance, but go over about 2.6V and it acts like a zener drawing current. Up to about 10ma and then it destroys the chip. Choose your voltage divider so that doesn't happen. It is an analog chip used to make linear power supplies, but the switching is fairly abrupt. 15K. I don't know how you do it, but I just guess since I don't know the resistance values of the boost converters voltage divider. It isn't critical, just need to drop the boost converters voltage just below that of the battery. That won't take much current. As said, the TL431 can't go to zero. An offset of a couple volts is needed and at least one diode so the circuit doesn't act on the boost converters voltage divider when the panel is above voltage. A traditional red LED is about 1.7V and is nice as it provides some indication, it still glows some when holding the panel at power point. This circuit is so useful in solar. |
| JoeP:
Right, I see. So when the PV is above 18V, the TL431 conducts, putting the diodes into reverse bias and making the boost regulator go to the voltage specified by its feedback divider (which should be about 30V), then when the PV is too low, the TL431 acts like an open circuit, allowing the 15K resistor to alter the boost's feedback divider so that the output voltage is lower (about 22V). The negative feedback then allows the TL431 to reach a sort of equilibrium. Is it safe just to connect this output to the battery via a diode? Thanks for all the help, and sorry for the questions. |
| Seekonk:
The nice thing about boost converters is they naturally isolate the panel from the battery. You still are powering the TL431 which is a little over 1ma and the controllers voltage divider. Or loose the power of a diode drop. Your decision. Here is the nice option, A cheap PWM can be added. This is one I use to maintain batteries. The buck puts out 14.5V to the PWM controller. It says 20V, but that was when it was connected to a grid tie inverter. |
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