MPPT Solar regulator DIY

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William_H

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For those a bit handy with a soldering iron I have cobbled up what might pass as a MPPT regulator for small solar panels.
The essence of the regulator is a Maxim device MAX787
http://www.alldatasheet.com/datasheet-pdf/pdf/73794/MAXIM/MAX787.html the PDF data sheet from this page has most of the circuitry and is quite simple.
It is intended as step down regulator for12 to 40v down to 5v. It is easy to fit a potentiometer (variable resistor) the wiper of which goes to pin 1 the top to output and bottom to earth. This makes it a variable voltage output regulator which can be adjusted to 14v or whatever regulated voltage you want for your battery. Unfortunately it requires some more volts than about 16v to get a regulated 14v for battery charging. No problem if you have near 20v from a solar panel.
So hopefully the regulator will suck about 18 volts or so from solar panel at best current point (max power) and provide 14v at a slightly increased current. Unfortunately less the inefficiencies.
The potentiometer could be adjusted or use a switch to give bulk charge or trickle.
Any way I have installed it here at home with 30w of solar panel. It seems like it might work OK but benefits I am not sure of. A cheap regulator anyway.
You may be lucky and get Maxim to provide free samples of the MAX 787.
You might want to fit a UC3906 Gell Cell Charge controller to control the regulator so giving 3 stage charging.
http://www.alldatasheet.com/datasheet-pdf/pdf/29407/TI/UC3906.html
Anyway any one interested or know more about MPPT than I do please let me know. olewill
 
I've thought about using the MAX1771 for a similar thing:

http://pdfserv.maxim-ic.com/en/ds/MAX1771.pdf

It's a bit twitchy (I'm using it to step up 12V to 200V at the moment!) but remarkably efficient. It will boot-strap itself up from very low input voltage, too.

What I don't know is how one tracks the max power point (I can see how to make an efficient voltage regulator).

I think the voltage for maximum power will vary with the amount of light falling on the panel, so this somehow needs to be built into the circuit. I think that you need to regulate the input demand for the regulator as if you left it to its own devices, it could draw enough current that the output voltage of the panel starts to collapse and causes the converter to draw even more current, dragging the panel down to low / ~zero volts.

I would be interested if there is some neat analogue way of tracking the MPP without having to resort to mapping things into a PIC, etc.

Andy

Just found some light reading.
 
MPPT regulator

The MAX1771 looks like it is designed for boosting voltage so might be good for a small battery to battery charger but not good for solar regulator. In solar you generally have a higher voltage 19v that needs to be transformed to 14v for battery charging.
Now this MPPT thing. Thank you for your interest I really don't know how or if the MAX 774 would suck the power from the panel at MPPT. Obviously only with a large or flat battery would all the power of the panel be needed. The input capacitor of the regulator would charge up to the panel voltage and be sucked down by the switch then the capacitor would again be charged. How does it know when to stop sucking so avoid pulling the panel voltage down. Perhaps you are right. It could get carried away pulling panel voltage down.
I wish I understood more about it hence the post.
It does I think seem to be working OK so I must try loading up the output to see what happens to panel voltage. I will let you know. thanks olewill
 
for what its worth I bought a cheap 'buck' regulator off ebay for a few quid the other day - one of these direct from hong kong jobs. I bought it to power a monitor that needed stabilised 12vdc input but they might be of use to you. Its up to 30v input and variable output, about 90-95% efficient which seems about right from what I have seen. This would, I beleive, to an extent go some way to using the excess voltage of the panel to give a gerater charge current at 13-14 volts. obviously it needs a delta of about 1.5v in the input to output voltage to work. I guess you could take 2 of these regulators, set one to a bulk charge voltage, the other to absorption voltage and either have them switched in or out automatically or even manually do it with switches.

you have got me thinking now. I have bought the maplin dual battery solar controller. this just switches panel in and out at predetimined voltage. maybe I will try the buck regulator between the panel and the controller. use it to reduce the output of the panel down to say 15 or 16 volts. might liberate a few more milliamps!

cant try it now im overseas but will have a go and report when I get back.
 
MPPT

Thanks to all the responses. Clearly MPPT is not as simple as I imagined. The described device is working but clearly not in any sort of MPPT mode. Unfortunately the Silicn Chip/Jaycar controller is for higher power than I have but thanks for the links. olewill
 
William_H said:
Thanks to all the responses. Clearly MPPT is not as simple as I imagined. The described device is working but clearly not in any sort of MPPT mode. Unfortunately the Silicn Chip/Jaycar controller is for higher power than I have but thanks for the links. olewill
Click to expand...

There are so many designs and products for regulators and charge controllers its astounding. Some work for some others not, some are simpler than others as you by now fully realise. I have been using a very simple circuit which cost me almost nothing to built and its been doing its job for a couple of years.

You can see the circuit I used here:

http://infomultiverse.com/diy/elect...r-power-regulators-and-charge-controllers.php

Its really easy to build.
 
temptress said:
Nigel I disagree with you. This is a discussion forum and if someone has something to add then IMO go ahead...
Click to expand...
Up to a point, I agree. Perhaps a couple of months while we still remember what was going on. More than that and it is better to start a new thread, with a back reference (for example a quote) to the original thread if required. The danger with a resurrected thread this old is that people may read the OP, then try to answer. This wastes everybody's time.

The only exception to this suggestion is when the OP wants to update the thread with new info.
 
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nigelmercier said:
Up to a point, I agree. Perhaps a couple of months while we still remember what was going on. More than that and it is better to start a new thread, with a back reference (for example a quote) to the original thread if required. The danger with a resurrected thread this old is that people may read the OP, then try to answer. This wastes everybody's time.

The only exception to this suggestion is when the OP wants to update the thread with new info.
Click to expand...

Again not so. That's your opinion and you are welcome to it. It is not the way things work.
 
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