Solar Panel Voltage Regulator

replace flame with sun?

Do you really need solar concentrators and hence a panel control system for ammonia absorber system ?

The evacuated tube collectors are capable of generating quite high temperatures.

MPPT will set both the current and voltage to give some maximum power level. The battery also sets a specific voltage as a function of current. How do these get matched? Is a switching voltage converter required as part of the MPPT? It seems like a linear regulator would defeat the purpose of the MPPT.

It's a lot easier if you have only one thing to worry about. Measure the thing you want to control. For battery charging, all you need to know is the charge current.

Use a buck converter between the solar input and the battery. Set the duty factor of the converter. Measure the charge current. Change the duty factor. Measure the charge current. If it went up, change the duty factor in the same direction. If it went down, reverse the change in the duty factor. It will dither around the maximum current point. It will track changes in the input power. It will track battery state of charge. It will track clouds passing. I used a PIC processor and a Hall effect current sensor. No calibration...It just works.

You have to pile battery protection on top of that if you want to track voltage/temperature capabilities of the cells to limit (reduce) charge current below the maximum available. Just add temperature sensor to a PIC input. Add battery voltage to the equation. That does require knowledge of the cells and calibration of the sensor and some math in the duty-factor algorithm.

One does not imply the other. I'm told ammonia works on low level heat.

Vac tubes are concentrators of course.

NT

Plop a switcher in there then and sketch it up!

Cheers, James Arthur

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It's not that simple. A small panel is subject to intermittent shutdown or reduced output with passing clouds so the switcher has to intelligently rec over from undervoltage/power shutdown. MPPT is meaningless for a charger be cause its output voltage and thus power is constant for the most part, and that power draw has to be less than the MPP if the charger is to avoid back ing off its charging rate. For any given power draw there are two possible operating points for the panel: higher current at lower voltage, or lower c urrent at higher voltage, the two converging to a single solution at the MP P, as a function of insolation of course. This is the perfect setup for wha t used to be called "hunting."

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r reduced output with passing clouds so the switcher has to intelligently r ecover from undervoltage/power shutdown. MPPT is meaningless for a charger because its output voltage and thus power is constant for the most part, an d that power draw has to be less than the MPP if the charger is to avoid ba cking off its charging rate. For any given power draw there are two possibl e operating points for the panel: higher current at lower voltage, or lower current at higher voltage, the two converging to a single solution at the MPP, as a function of insolation of course. This is the perfect setup for w hat used to be called "hunting."

Of course, which is why I posted what I did. Bill asked for "simple," so I gave him "simple."

Stephen Woodward wrote up a slick little switching MPPT solar battery charg er in EDN IIRC, some years ago. If someone wants inspiration, that would be a good starting point.

Ah, here it is...

His circuit only charges to 2.35V (temp. compensated) per cell; he does not implement topping voltage and float voltages.

Cheers, James Arthur ~~~~~~~~ Is there some shortage of carriage returns in the world such that technical people *have* to run all their thoughts together in a single paragraph?

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d backing off its charging rate.

In a sensible world all available power is extracted from the panel, which is worked at MPP. Thus charger output is not constant.

panel: higher current at lower voltage, or lower current at higher voltage, the two converging to a single solution at the MPP, as a function of insol ation of course. This is the perfect setup for what used to be called "hunt ing."

NT

Only on your part.

What cell? Battery or PV?

Yes, a commercially available MPPT controller *should* do as you say.

The battery does not "set" a specific voltage. The battery voltage will change slightly depending on its SOC, age, chemistry, current, and temperature.

A switching regulator is required in the MPPT controller. A linear regulator will not work in the MPPT world.

Oh, it CAN be done all-linear, if you use a motor/generator/field-winding-control scheme. The power-handling is so easy with SMPS ICs that we forget there was a way to do it before switchmode power...

As an attempt to clear things up that was a complete failure.

The problem with that circuit is the constant current operation It seems more efficient to directly connect the panel to the battery to obtain maximum current from the panel and then just shut down when the battery voltage reaches max. That's why I proposed a relay. On the temperature problem, I could add a diode or 2 in the divider that feeds the comparator and compensate for temp. Not sure how to simulate temp changes with LTspice?

Just set the current limit to something higher than the panel can deliver. Or take it out completely if you want to live dangerously and trust Harry to never use another power source. (Not recommended, but the solar panel's a current source anyhow.)

If you want efficiency you'll need a switcher. Otherwise, here you go.

Cheers, James Arthur

Right. And a decent MPPT charger will accept a higher nominal voltage above the battery voltage to help with partial shading of modules (if enough modules are in series) and also IR drop in the PV wire. They are simple in theory but not real simple to make work well.

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or reduced output with passing clouds so the switcher has to intelligently recover from undervoltage/power shutdown. MPPT is meaningless for a charge r because its output voltage and thus power is constant for the most part, and that power draw has to be less than the MPP if the charger is to avoid backing off its charging rate. For any given power draw there are two possi ble operating points for the panel: higher current at lower voltage, or low er current at higher voltage, the two converging to a single solution at th e MPP, as a function of insolation of course. This is the perfect setup for what used to be called "hunting."

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That's not an MPPT charger, it's a constant current non-MPPT until the pane l insolation no longer supports full power output, at which point it starts tracking MPP. The schematic shown is an abomination, the explanation of ci rcuit operation is total horseshit, and it's full of a bunch of trims and o ffset adjusts that misrepresent it as a precision when in fact it's a touch y pos good for little more than a lab demo- if that.

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n or reduced output with passing clouds so the switcher has to intelligentl y recover from undervoltage/power shutdown.

power is constant for the most part,

void backing off its charging rate.

ch is worked at MPP. Thus charger output is not constant.

he panel: higher current at lower voltage, or lower current at higher volta ge, the two converging to a single solution at the MPP, as a function of in solation of course. This is the perfect setup for what used to be called "h unting."

Right and most apps, especially portable setups, will not have the panel on a solar tracker, so the incident radiation is only there in quantity for a few hours and fades otherwise. MPPT may save you from or lessen the need f or oversizing the panel.