Homebrew MPPT

[fungus]

Is there any solar MPPT charger schematics on the web in the 10-100w range which dont involve programming PIC chips or any commercial MPPT chargers for around $50 in the 10-100w range?

[commanda]

I've got a circuit which i printed out off the web. The website is no longer in existence, unfortunately. It uses a 78S40 chip.

The simplest topology is a buck converter with the voltage sense on the input; ie the output of the panels. Adjust the regulation set-point to maintain this at the panels Vmp, usually about 17 volts for a 12 volt panel.

I could scan it and send it to you as a pdf if you want. Email me.

Amanda

[AbyssUnderground]

Does this work as well as an MPPT controller would?

[Ungrounded Lightning Rod]

That IS what a MPPT controller does:  Convert between volts and amps to run the source at maximum output.

For panels the maximum output is at a particular voltage.  So a regulator set up to adjust its load to drag the input to that voltage is what you want.

[altosack]

Don't disparage using a PIC (or other) microcontroller. It may take you a bit of time to learn, but it will be far cheaper than any other way of making (or, gasp, buying !) an MPPT solar charge controller, and you'll be able to use the experience for many other things.

If you want to go with a discrete buck converter (one of Amanda'a suggestions) you could do that, too. The MPP is usually 80% (in voltage) of the open circuit voltage, and the open circuit varies slightly with insolation, but mostly it varies with cell temperature (which is a factor of mostly insolation and ambient temperature). While it is great to dynamically track the MPP, if you just adjust it seasonally, you'll be most of the way there. When you decide to, you could always upgrade this buck converter with a microcontroller (not to directly drive the PWM, just to give the feedback to the circuit).

If you have no programming experience and want to make it a little easier on yourself, you could get a picaxe for a bit more money than than a PIC or AVR ($10-15 vs. $2-5); it's got an onboard BASIC interpreter. If you're interested in doing such a thing, I would be willing to help (I'd prefer a PIC or AVR, though), just post to the board.

Dave

[dinges]

Amanda, I'm interested in this schematic/design too. Still have got a 78S40 lying around somewhere. If you do decide to scan & convert it to pdf, it might be an idea to upload it to your files folder, so everyone that is interested has access to it.

[commanda]

I was just thinking the same thing myself. Will do it tomorrow when I get back to work.

Amanda

[ruddycrazy]

Hiya guy's,

           Well I have an AERL-900 MTTP hooked up to my house array and from heaps of research I reckon this unit is the bee's knee's in mttp's. Now to try and copy it would be a nightmare. Anyway it's hooked up to my 14 Kaneka Thin Film panels in series and inputs around 119 volts but the input in amps compared to the output is usually around 3:1 even on a cloudy day. I'm also interested in Amanda's design so if she would like to supply a schematic etc I could have a play.

Cheers Bryan

[annamathew]

   Hello sirmam

          My self Anna Mathew doing my BTech .

          Working for a seminar on MPPT.

        so I would be thankful for any  information related to this.

 I would like to have a basic study on this technology, solar boost 2000, how is it economical and so on

 Thank you

 waiting for a positive reply

[annamathew]

Hello Sir\ Mam

        HOw can we adjust the load for max. output .Is it at any other cost

[SamoaPower]

Here's a true MPPT converter that seems to fit your requirements.

http://www.elecdesign.com/Articles/Print.cfm?AD=1&ArticleID=6262

Keep in mind however, that this is not a multi-phase battery charge controller, it only maximizes power from the panels. I believe it could be used in conjunction with a charge controller.

[commanda]

Can't lay my hands on the complete article at the moment.

Here's a pdf of just the circuit which I did several years ago.

solar-mppt.pdf

I didn't design it personally, nor have I built it.

Amanda

[dinges]

Thanks.

[fungus]

Thanks for that commanda. Do you know what the inductor value should be?

[commanda]

Off the top of my head, no.

I seem to recall the original design was 12 volt and 10 amps.

If you go walter schmidt's smps calculator page, you can work it out; and even get some recommended cores with number of turns.

Amanda

[Opera House]

Switching regulator chips are like children.  Each is different, but they are all the same.  With a dual input type like the TL494, one sense input turns on the regulator at about 19V and the other can shut it down when the battery voltage reaches 14.  The transformer in a 250W PC power supply should be suitable for up to a 100W power supply (the reason so many of these fail).

It may sem like a great idea when the panel maximum is 19V and the battery voltage is 12V, but that difference is really too small to get the numbers everyone expects.  Between battery voltage rise, resistive losses to the panel, diode losses, and other internal losses of the regulator, it is hardly worth doing.  That is the reason they make the panels such a high voltage.  If you run the panels at 24V and convert to a 12V battery system, the numbers then look good.

I recently found a small 6V panel suitable for maintaining a 12V battery at my camp when I take in the big panels.  Have to design that in the next two weeks before I go back and it will use a power point boost.  One of a dozen or so projects that will be posted using old power and UPS supplies.

[fungus]

Well I put the numbers in and it came out with 41uh.

[fungus]

Actually it was 47.41uh