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[on:]

Hello,

I'm currently in the process of building a solar Maximum Power Point Tracker (MPPT) charger similar to Tim Nolan's one, http://www.timnolan.com/index.php?page=arduino-ppt-solar-charger.

Having read up on lead acid charging regimes, I noticed that the code used doesn't implement any form of topping or absorption regime whereby the voltage is regulated at a constant value and the supply current is slowly decreased to a trickle charge level. Being new to battery charging basics, I'm not sure whether this phase of charging happens naturally to a battery as it approaches full charge or is this manually done?

If the current is manually controlled, how could this be done with an Arduino?


Any help or information would be much appreciated, Thanks.

[Reply #1 on:]

I am new to arduino, but I do have a little knowledge about how batteries should be charged.

First, read this:  http://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

Second, get the detailed specifications for your batteries - the manufacture will usually tell you EXACTLY how to charge (bulk, absorb, float and equalize).

Bulk charge is normally dynamically driven based on voltage and current, absorb is often implemented as time bound, float is indefinite, and equalize is time driven (and only occasional)

[Reply #2 on:]

I have some experience with solar. Here is an Maximum Power Point Tracker for $20.

http://www.ebay.com/itm/MPPT-10A-Solar-Regulator-Charge-Controller-12V-24V-Autoswitch-Solar-Panel-/121013495990?pt=LH_DefaultDomain_0&hash=item1c2cf768b6

If you do make one with the Arduino, (not really intended for permanent outdoor use, proper housing is a must)please post back with results/how to. It would be interesting if nothing else. Good luck! Steve

[Reply #3 on:]

I made a charger using a TI BQ2031 IC and it regulates current at Imax until Vmax is reached, then regulates Vmax until current falls to a set percentage of Imax so for a 12 volt 4Ah battery I regulate current at 1C until voltage reaches 14.7 volts, and then maintain 14.7 volts until current falls to .25 amps.  Then I switch to a float charge of 13.5 volts to keep the batteries topped off.  When it is regulating the voltage at 14.7 volts, current will slowly fall as the battery charges.  For MPPT they have this app note:  http://www.ti.com.cn/cn/lit/an/slva378/slva378.pdf

[Reply #4 on:]

Nice!

[Reply #5 on:]

Yeh, I could easily go out and buy one, but where is the fun in that!?

I made a charger using a TI BQ2031 IC

Funny you should say that. I've actually got a free sample in the post as we speak. I also came across it in my research and it looks really neat! I'm planning on testing it too, however, I really wanted to be able to control everything through the Arduino rather than using R-C networks to configure the IC. Nevertheless, I'd love to see the schematic from your charger!
It was my hope that I could use the Arduino to basically mimic that same charging algorithm that the BQ2031 uses.

First, read this:  http://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

Thanks kev_rm, that link was really useful and informative too!

[Reply #6 on:]

Ive made a number of MPPT solar chargers, and you have the right idea with the various voltages and charge currents.
The practical problem that arises is that the input power to the charger varies over the course of the day and may vary
rapidly as clouds move over the solar panels so the tracker will be trying to maximise the power into the battery all the time.
Its quite possible that there simply wont be enough power available to provide the bulk charging and equalizing currents
when you want them, so you have to keep track of how much power was available to provide the required charging when you wanted it.
Is the battery that is being charged also being drained by some load, or is the Solar Charger just to keep a battery fully charged by trickle charging it.

[Reply #7 on:]

Is the battery that is being charged also being drained by some load, or is the Solar Charger just to keep a battery fully charged by trickle charging it.

Potentially both, but most of the load will generally be on during the evening.

[Reply #8 on:]

OK, so whats the relative drain caused by the load , compared to the size of the Solar Panels.
ie how much is the DOD of the battery overnite.

[Reply #9 on:]

...
Its quite possible that there simply wont be enough power available to provide the bulk charging and equalizing currents
when you want them..

I think that's a question of do you have enough panel, not how to charge. 

PS: "When you need them" does not apply to equalizing... this can be done every 2-6 months as time & energy allows.  (less frequently the better behaved your system is on your batteries)

[Reply #10 on:]

how much is the DOD of the battery overnite

Well at the moment i'm planning for a 30Ah load. I want to limit the DOD to 30% for prolonged battery life. Going by that, I'd need a battery rated at around 100Ah. Therefore, assuming an average daily insolation of 6 PSH a 200W solar panel should be enough to charge a battery (That doesn't take into account batt efficiency etc). 

What I'd like to end up with though, is an open source MPPT that can be adjusted to suit any kind of application or requirement.

[Reply #11 on:]

Atmel has a great app note for a battery charger reference design that they sell.  I considered using an AVR uC before finally settling on the BQ2031.  If you read through the whole thing cover to cover you will learn a ton about what you are trying to put together.

http://www.atmel.com/images/doc1659.pdf

[Reply #12 on:]

Hi.

Please, keep talking about this topic.

You might already know that some other people are working on that kind of project but I still give the following link in case :
http://www.freechargecontroller.org/index.php?title=Main_Page

http://thesolarpowerexpert.com/introducing-the-v4-charge-controller/

http://www.atmel.com/images/doc1659.pdf

Unfortunately, I'm a very beginner with ARDUINO and  I can't understand all the information given. But I'm very interested and I'm studying this project.

Please keep talking, sharing and giving your advice about it.

About what I know about the ARDUINO community, It would be much more active to share about the topic's link I've just given above on the ARDUINO forum.

I'm personally  looking forward a high voltage input (200V-250V) to 12V/24V output MPPT regulator. Not for the MPPT function but mostly to use high voltage and lower the line losses on solar panel and batteries' line and save cost on big and long copper wire. In that case; MPPT would just be a nice side effect !

Something like this would be nice !
http://www.dcsolutionsaustralia.com.au/renewables/solar-controllers-mppt/midnite-classic-200v-mppt-solar-controller.html

I have some experience with solar. Here is an Maximum Power Point Tracker for $20.

http://www.ebay.com/itm/MPPT-10A-Solar-Regulator-Charge-Controller-12V-24V-Autoswitch-Solar-Panel-/121013495990?pt=LH_DefaultDomain_0&hash=item1c2cf768b6

The one I'm talking about is not 20$. And the link doesn't even work in France !