Maximum Power Point Tracking and solar charging lithium

[Jonathan in Hiram]

So now I have the 100W flexible solar panel and about 1 kwh worth of 18650 cells wired up into two 6s12p pack which I run in series for 12s12p. In the future I'll probably be going to 13s12p and possibly even 14s12p.

After doing quite a bit of research into charging from solar panels to lithium it rather looks like I'm going to have to "roll my own" MPPT and charger, while searching I've found some quite interesting things. If you want to charge a battery of lower voltage than your panel's normal operating voltage there's a nice and easy circuit that uses a single comparator and some capacitors with a FET switch and appears to be a manually set maximum power point device, in this case to drive a motor but I see no reason a battery couldn't be charged instead with some minor changes in the circuit.

http://www.suburbia.com.au/~mickgg/minimax/minimax.htm

This one is probably the most interesting MPPT design I found, it uses an analog multiplier to calculate the product of voltage and current to naturally seek the MPP.

http://www.control.aau.dk/~jdn/edu/courses/11-2/best11/.../smpptfpa.pdf

And here is another analog MPPT design, I like this one since it uses only the simplest of parts but seems rather clever.

http://www.electroschematics.com/9718/solar-boost-converter-mppt-charge-controller/

I watched this entire series of videos by someone who is designing an Arduino based MPPT and has successfully marketed a PWM solar controller, it's got a lot of good information in it even though the bloke's pacing and delivery is a bit slow. I'd like to try an analog version before I get into digital I think though.

[youtube]MSz4-cr3EJw[/youtube]

What I'm stuck on more than anything is what MOSFET and inductor to use. I found a switching boost regulator calculator and have designed a 17V in 52V out regulator on it but have no idea if it's actually going to work.

http://www.daycounter.com/LabBook/BoostConverter/Boost-Converter-Equations.phtml

http://www.daycounter.com/Calculators/Switching-Converter-Calculator2.phtml

 

[JoeBaker]

That's a lot of excellent home work you did there. But if your not too hard up for cash these charge controllers work well.

http://genasun.com/products-store/mppt-solar-charge-controllers/mppt-for-lithium-batteries/

i have been eyeballing a GV10 for when i convert my radio batteries from AGM to LiFe.

But the 48 volt one could very well charge a ebike battery and there is a custom voltage option as well.

I should point out i have never bought one of there products but i have seen one of there lead acid boost MPPT charge controllers running off a 36 cell 100 watt panel charging a 48 volt golf kart and it was doing its job very well. in fact i don't think i had ever seen the thing need to be plunged in other then to equalize the pack.

As for my self I'm in the planning stages for a long range rig. And solar charging will be part of my charging system unless someone plants a current bush next to my fishing hole, i figure solar is the only logical way to go other then a small gasoline generator..

 

[Jonathan in Hiram]

That's a lot of excellent home work you did there. But if your not too hard up for cash these charge controllers work well.

http://genasun.com/products-store/mppt-solar-charge-controllers/mppt-for-lithium-batteries/

i have been eyeballing a GV10 for when i convert my radio batteries from AGM to LiFe.

But the 48 volt one could very well charge a ebike battery and there is a custom voltage option as well.

I should point out i have never bought one of there products but i have seen one of there lead acid boost MPPT charge controllers running off a 36 cell 100 watt panel charging a 48 volt golf kart and it was doing its job very well. in fact i don't think i had ever seen the thing need to be plunged in other then to equalize the pack.

As for my self I'm in the planning stages for a long range rig. And solar charging will be part of my charging system unless someone plants a current bush next to my fishing hole, i figure solar is the only logical way to go other then a small gasoline generator..

Unfortunately I've already spent the next couple of month's entertainment budget on the flexible solar panel so I can either wait or see what I can do myself for a few dollars. Since I posted this thread I've found some more DIY MPPT work going on, there is a Yahoo group on MPPT and something called "Ardubuck" that's a buck MPPT controller based on an Arduino microcontroller. I enjoy the creative process anyway, I built my own pack from used laptop cells I got from the electronic scrap dealer and so on..

I've done some modeling of the switching booster in LTspice circuit simulation, after a bunch of fooling around with component values, switching frequency and duty cycle it says that this circuit will put out almost 1.4A @ 52V when fed with the entire output of the 100W solar panel I have. The 0.3 ohm resistor in the input circuit is to model the current/voltage output of the panel and the 38 ohm resistor on the output side is to model the load of the battery at 52V. I haven't found a good model of a power MOSFET in LTspice yet so I'm using a bipolar transistor as the switch, MOSFET should make it work even better with greater efficiency.

When I get this section of the circuit built and working correctly I'll move on to the control system, ordering of parts begins this weekend.

 

[JoeBaker]

well i for sure want to keep fallowing your work on the subject. I'm looking at probably a few years until i have play money for my next build since I'm knocking out a 5K credit card bill that i blame my car on.

In any case the charging system i was planing on building will use 3 or possibly 4 of the 48V Genisun charge controllers. So if you get this worked out it would save me a good bit of coin on the build. But i have to admit most my experience with working on electronics is with vintage glowing glass bottles so something easy to fallow would be nice.

 

[Jonathan in Hiram]

well i for sure want to keep fallowing your work on the subject. I'm looking at probably a few years until i have play money for my next build since I'm knocking out a 5K credit card bill that i blame my car on.

In any case the charging system i was planing on building will use 3 or possibly 4 of the 48V Genisun charge controllers. So if you get this worked out it would save me a good bit of coin on the build. But i have to admit most my experience with working on electronics is with vintage glowing glass bottles so something easy to fallow would be nice.

I know the feeling all too well..

I learned electronics in the glowing glass bottle era myself, I was fixing the family B/W TV set starting at about 12 or 13 or so, pull the tubes out and run them to the drug store to put on the tester, find out which one went bad this time, I probably replaced a half dozen of the 12AX7.

If you are planning on a 12V lead acid setup for batteries the series of videos I linked to in my first post is brilliant, the author uses an Arduino to build an MPPT charger and he has put all the code, schematics and so on up online so you can duplicate his efforts easily. From my research I think each panel should have its own MPPT controller, Arduinos are dirt cheap these days and you don't need all the bells and whistles, there is a nearly microscopic version called an Adafruit Trinket that costs $7 in singles and more than likely has plenty of power to do an MPPT controller.

Here's the complete schematic of the Arduino MPPT buck controller from the videos, Juilan's blog is here.. http://www.256.co.uk

 

[JoeBaker]

I learned electronics in the glowing glass bottle era myself, I was fixing the family B/W TV set starting at about 12 or 13 or so, pull the tubes out and run them to the drug store to put on the tester, find out which one went bad this time, I probably replaced a half dozen of the 12AX7.

lol Yeah I'm not old enough to remember vacuum tube electronics in common use. And never have seen a tube driven TV with my own eyes. But i think between my room mates and i we have a good 6 or 8 12AX7s in rigs or as NOS (New Old Stock) spares since there easy to get. We also have a bunch of spare 6146As and Bs laying around since it seems we both have rigs that use them. But this list can take up a page or two of tubes we have or need spares of :wink: But yeah in the wold of ham radio tubes haven't quite died out. Example my Hallicrafters SX101 i payed almost nothing for and its still quite capable after new caps, tubes, and my friend alining it. So bottom line is good short wave receivers have never been cheep and give a kid a old clunker there going to make it work in the absence of a shinny new rig

 

[Jonathan in Hiram]

I have one of these 600W DC-DC boosters and have been doing some experiments with the 100W flexible solar panel and my 12s12p 18650 pack.

http://www.amazon.com/gp/product/B00KA2S1DG/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

In full sun with the panel perpendicular to the light I can put up to about 70-75 watts into the 12s battery at ~48V but the adjustment is critical to get maximum watts. The adjusting potentiometer is a 20 turn unit and in 1/16 of a turn you can zip right past the peak power reading on my wattmeter connected between the DC-DC converter and the battery. Just the act of putting the screwdriver in the pot slot will throw the reading off and it changes fairly quickly as the battery voltage increases, a feedback loop would really help keep it in the sweet spot for charging.

Here's the test setup being fed from the solar panel off to the left and going into the bike on the right, the big meter is reading panel volts and the wattmeter is reading 53.1W in at 1.1A and 48.4V, the input voltage from the panel is a little high at 17.65 volts which has dropped the output to the battery nearly 20W below what it can reach with careful tweaking.

I've decided to unsolder the gate lead of the MOSFET switch in the booster and trigger it with an optoisolator driven by the Arduino that Amazon tracking says is to be delivered tomorrow. I've already downloaded MPPT code for the Arduino and this method keeps me from having to reinvent the wheel with designing and building a switching booster. If I can't get the MPPT to work I can always just solder the gate lead back into the board and use it as it is now.

My bike does just under 15Wh/mi at 21 mph, that means every hour in full sun should give me about four miles of 21 mph riding. Two hours of full sun would suffice to get me to the grocery store and back and four hours would get me almost anywhere in my town and back.

 

[mountain biker]

dude your awesome...thank you...so then

I noticed that company also makes a constant current and constant voltage one too for about 36 bucks...the amazon add suggests you get two in parallel...

now your voltage will move around constantly right..but your current stays the same with this..is that correct....don't bms battery systems have a range for charing the lifepo4 like 24 to 44 volts at around 2 or 3 or 4 amps. right???new to this whole idea....working on first build and working on a bug out bicycle with electric winch.

 

[mountain biker]

sorry on this one then your output voltage varies but your output amps stay the same... is that right? so with the variance in the sunlight on the panel...this means that voltage on output will change? love to know sorry to ask such simple questions... but man its all so confusing...

 

[Jonathan in Hiram]

sorry on this one then your output voltage varies but your output amps stay the same... is that right? so with the variance in the sunlight on the panel...this means that voltage on output will change? love to know sorry to ask such simple questions... but man its all so confusing...

Solar panels are current sources, not voltage sources, at a given illumination level and temperature as you draw more amps from them the voltage drops, there is one point where the amps times the volts (watts) is at a maximum, for my particular cell it's a little over 17 volts at full sun, at that voltage the panel will be putting out a bit over 5.5 amps.

The problem is as the light level changes the optimum current and voltage change, mostly the current but the voltage moves a bit, this confuses the converter which is designed to work off a voltage source and remember a panel is a current source. Also as the battery charges it's voltage raises and the converter also gets a bit confused by that.

For the converter I've found a good source on Ebay that ships from the USA for a low price and gets it to you quickly.

http://www.ebay.com/itm/Boost-DC-DC-Converter-Power-Supply-Step-up-Module-10V-60V-to-12V-80V-600W-10A-/321532341458

I found the best way to use one of these is to connect the solar cell and turn the voltage up to your max battery charge voltage and then turn the current adjustment down until it gets a stable amperage reading into the battery. Put a switch between the panel and the converter so you can quickly turn it off and back on because sometimes the converter will shut off if it starts oscillating the voltage and won't turn on again until the input power is turned off and back on.

Once you get the converter and panel in your hands and hooked up to your battery it will become more clear to you as you play with the settings, you'll also need a wattmeter at least on the output side so you can see what changes as you turn the controls.

 

[kfong]

Nice ebay find Jonathan. Where did you get your flexible solar cell? I will be looking into a solar setup for my van next summer. Just in the planning stages for now.

 

[Jonathan in Hiram]

The panel came from Ebay too.. The deals seem to change fairly regularly there.

 

[mountain biker]

http://www.ebay.com/itm/Lithium-Charger-Step-down-5A-5V-32V-to-0-8V-30V-power-supply-module/370707642205?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D25880%26meid%3D7f8b18eb26f548c683a005a859c2ecf0%26pid%3D100005%26prg%3D10819%26rk%3D6%26rkt%3D6%26sd%3D400789936463&rt=nc

what about something like that? major questions...36 volt battery for lithium ion does this seem to light...I think it stops around 35 volts or so...

ive read somewhere on this forum that a guy hired a electriacian to to do a step down convertor..i wonder if you get over 36 volt like 60 volt or so and then step down would that make your charger more stable....?

 

[mountain biker]

http://www.ebay.com/itm/DC-DC-400W-6-40V-to-8v-80v-10A-Boost-Converter-Step-up-Module-Power-Supply-CC-CV-/111177068259?pt=LH_DefaultDomain_0&hash=item19e2ab6ee3

this is a step up converter but it says constant voltage constant amp control....

the capicator on the side says 100 volts....
I don't know...

 

[Jonathan in Hiram]

http://www.ebay.com/itm/DC-DC-400W-6-40V-to-8v-80v-10A-Boost-Converter-Step-up-Module-Power-Supply-CC-CV-/111177068259?pt=LH_DefaultDomain_0&hash=item19e2ab6ee3

this is a step up converter but it says constant voltage constant amp control....

the capicator on the side says 100 volts....
I don't know...

The capacitor rating has to be higher than the maximum the converter can put out .. 80V

 

[Jonathan in Hiram]

http://www.ebay.com/itm/Lithium-Charger-Step-down-5A-5V-32V-to-0-8V-30V-power-supply-module/370707642205?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D25880%26meid%3D7f8b18eb26f548c683a005a859c2ecf0%26pid%3D100005%26prg%3D10819%26rk%3D6%26rkt%3D6%26sd%3D400789936463&rt=nc

what about something like that? major questions...36 volt battery for lithium ion does this seem to light...I think it stops around 35 volts or so...

ive read somewhere on this forum that a guy hired a electriacian to to do a step down convertor..i wonder if you get over 36 volt like 60 volt or so and then step down would that make your charger more stable....?

The questions you are asking indicate to me that you don't know enough to be successful at this now. There is a really steep learning curve with all this and a lot you have to know quite well in order to make it work.

Not trying to be insulting, I'm sure there are things you are expert at which I know little about. Get some electronics training under your belt somehow and this will make a lot more sense. I was an experienced electronics troubleshooter when I came to ebikes and it wasn't all straightforward for me to learn either, took a while in particular to wrap my head around how motors really work.

 

[mountain biker]

no offense taken...you actually have sent me on the right path..been looking a lot of stuff up online. and I appreciate it.... so what about the step down convertor..you would have to get your volts up beyond the battery charge capacity but would this help you keep the machine from shutting off....I also noticed the frequency was different you mentioned that when your step up device started oscillating the same voltage you ahd to shut it off....

or quite simply....how s your project going

if you use your set up and you just leave it on..you said sometimes you have to turn off and on the power from the solar cell a switch and then it starts charging again.

what if you use a 6 volt or 12 volt sealed lead acid battery..like the ones that are used for deer stand camereas. I think everyready makes them and they are in the hunting section of Walmart..they also have a solar charger set up for them...could you use them as a buffer.... solar charger to switch,,maybe relay switch,,, to 12 volt then to buck up convertor to help stabilze the power reading...

and I apologize to ask you these questions but man your one of the few that have actually helped me understand this stuff...if it wasn't for you I wouldn't even of heard of a buck convertor or I may of found one a year or two later...you have expotentially helped my learning curve... talking to you is like that john trevolta movie where john trevolta is the space alien mining for gold on earth....battlefield ad I think.... I feel like the human in the learning machine talking to you....now I don't think your john Travolta I think you are like the learning machine in the movie...and I thank you for that.... man if you got any ideas let me know...I thank you...a nd I thank everyone on this topic..

 

[mountain biker]

this is for the boost one...man that price tag is heavy...off grid ebike/mppt station??? 105 to 305 watts power,,,run it for three hours then you get one hour of fridge time???... use any panel you want....
this is for custom voltage...they don't have an off the shelf 36 volt it seems like....12 24 and 48 roughly..
GV-Boost | 105-350W Solar Boost Charge Controller with MPPT for Lithium Batteries
http://genasun.com/products-store/mppt-solar-charge-controllers/

GV-Boost | 105-350W Solar Boost Charge Controller with MPPT for Lithium Batteries


The industry's most efficient boost controllers. These controllers boost lower-voltage solar panels up to charge higher voltage lithium batteries up to 48V nominal
8A 12/24/36/48V Boost MPPT Controller •99% Peak Efficiency
•Continuous MPPT
•Marine-Grade
•Advanced electronic protections
•5-Year Warranty.


Price:$320.00