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DIY laptop powerbank project

  • Ignatus Saturday, February 25, 2017 8:44 PM Reply

    I'd like to know your thought regarding DX's solar charging controllers.

    The long answer:

    I have neither had any experience with DX’s MPPT devices nor with charging Lipo batteries via solar power. Based on a quick look, all DX’s solar charging controllers seem to be engineered for Lead-Acid batteries and one can’t use them directly for Lipos.

    The whole process to charge custom-sized Lipo batteries from solar power seems to be a somewhat complex topic and I’ve spent many hours online, reading about various approaches.

    I’ve come accros people who created MATLAB simulated models of the panels, doing extensive calculations and building complex custom-made charging circuit -that are just way over my head.

    I’ve also seen commercial MPPTs for multicell LiFePO4 batteries, DIY hacks with Super/Ultra Capacitors, DIY Arduino controlled Lipo compatible MPPTs, modified Lead-Acid MPPTs and other custom designed solar Lipo chargers.

    - The solutions that people have come up with are purely mind-boggling to me.


    I like simple things.

    My initial idea was that I would seemingly, oversize when choosing the solar panels.

    Possibly 2x75Watts or 2x100 Watts panels in series to create 34-36V, then use a large buck-boost converter such as SKU: 358336 or the one that I still have laying around as spare part SKU: 258020

    Both let me adjust CC as well as CV output. Then I’d feed that to the tiny 20 Watts Lipo charger SKU: 433805 which is connected / built into to my 4s6p Lipo pack or feed it directly to the real/better BMS of the yet to-be build larger 6s6p Lipo pack.

    -If that doesn’t work out for reasons unknown to me, I’ll experiment with one of those $20-30 MPPT devices. I would try to connect a buck-booster to the  MPPT’s 12V load terminals which in turn then connects to my Lipo charger.

    Unless somebody knows better and shares his/her knowledge, my only solution is to order some large solar panels, an MPPT, a large buck or buck-boost converter just to be safe / have a spare and start testing under real-world conditions.




    The just slightly shorter answer :):

    It is premature for me to try to come up with a workable and efficient solar Lipo charging solution at this point.

    My foremost priority is to complete the 4s6p powerbank project and be able to charge it via AC mains.

    The 2nd goal is to test and try incorporate this little miniature 3”x3”, 150 Watts peak, nasty square wave AC inverter into my DIY powerbank.


    AC.png



    The 3rd goal is to modify a timed auto-cut off circuit for no-load conditions and build it.

    The 4th goal is to build a decent looking and durable case.


    Solar charging is placed somewhere towards the end of my to-do list and before I get to the solar project my wife will nag me to build a powerbank just for her.


    -I consider myself lucky if she doesn’t demand that I immediately convert our car to an all electric drive as soon as my little powerbank works ;)


    On a second thought … that ^^^ would be an interesting project!



    Okay, massive writing exercise again today.  That’s all for now and I do have two requests for product recommendations, please:


    a.) I’m in dire need of lead based solder. Anything tested and proven to be of superior quality here on DX?

    b.) Also, I’d like to purchase an oscilloscope to measure ripple of switching power-supplies, AC inverter/s etc..  Something dead simple for me as a novice to operate and so low priced that it doesn’t hurt if I blow it up.

    -I can always upgrade to a $600-$800 unit when I get to the electric car conversion and can then justify the expenditure to the Chief financial officer of my household (my wife) .

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    post edited by Ignatus on 2/25/2017 at 9:02 PM
  • sheepish Top 10 Forum Poster Sunday, February 26, 2017 5:33 AM Reply

    They seems to focus on smaller sized, easy to handle/ship items and on high profit margin, hot-selling goods such as cellphones.


    I bought a bench power supply from DX at a pretty reasonable price compared to getting the same thing locally. I was surprised that it got sent by courier, but I guess that's how it is for bigger heavier items.


    I’ve waited some years for them to list a hub-motor for bicycles,
    suggested and requested it multiple times without any positive outcome.


    I was thinking of those just yesterday! There was an ad in yesterday's newspaper for a fat-tyred electric bike and I started thinking how it would be much cheaper to convert an ordinary bike myself.


    Thanks for mentioning that spot-welder project. Sadly, since that German guy is selling a kit, linking to that page is breaking the forum terms of use.


    I’m tired of never knowing if DX has the item/s actually in stock which
    they sell to me and I hate to be contacted 10-14 days later when they
    let me know that some of the items that I’ve already paid for are not in
    stock.


    DX needs to listen to these complaints, and start being stricter with suppliars who do not have readily available stock.


    I was looking at a non-MPPT device for charging lead-acid, and thanks to you I know know what MPPT is. Are they worth the extra expense? For my purposes (a bit of top-up while camping) I suspect not.

    Remembering 30 years.
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  • matrix-neo Moderator Sunday, February 26, 2017 11:22 AM Reply

    when you start talking about higher wattage power banks with several cells i would look into 7.4v or 14.8v li-po cells for the main reason sheepish bought up i.e balanced charging, otherwise it gets complicated, and once you talk about 1 or 2 devices powering laptops maybe consider a deep cycle lead acid battery, particularly if a solar panel is involved

    Resistance is futile-give in to DX gadget craving!
    also a voluntary mod-be nice please!
    Have an enquiry? https://cs.dx.com/ticket/index


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  • sheepish Top 10 Forum Poster Sunday, February 26, 2017 11:58 AM Reply

    i would look into 7.4v or 14.8v li-po cells


    With those voltages they would be 2 or 4 cell batteries. Each lithium ion cell is 3.7 V (or lithium iron phosphate cell 3.2 V). So those batteries should be balance charged too.

    Remembering 30 years.
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  • Ignatus Sunday, February 26, 2017 1:23 PM Reply

    @sheepish

    DX shipping heavy items:

    A spot welder weighs around 12 pounds , plus foot switch , some accessories and packaging = maybe around 15 pounds in total.

    Alright , I stand corrected in regards to DX not shipping heavy items. If they’ve sent you a big bench power supply they could easily ship other things as well.

    I’ve also just seen one that sells for just $89 on the rainforest site, with mixed reviews. That’s the lowest price I’ve ever seen one for in my life.



    Electric Bicycles:

    Plenty of fun, but not a cheap hobby.

    Fat tyres have too much friction and consume too much battery.

    One can convert most bicycles without too much effort. If it is an aluminium frame. it better be a really thick, strong frame, I’ve only converted steel based frames of BMX bicycles in the past.

    Also, depending on the wheel size and rider’s weight a suitable hub motor must be chosen.

    For a regular mountain bike, from any of the large retail chains,  with 26” wheels and a 160 pound rider:

    I’d recommend a 1000 Watts rear-wheel hub-motor running @ of at least 48V. Range costs money, but 20 Ah are nice to have available.  



    Forum rules:

    Well, I’ve deleted the link for now. Solely because it was too much work to write that insanely long forum post and I would’t want somebody to delete the whole post.

    I’ve checked the BOM that was supplied with the Intructable and that German dude also mentions it somewhere else - it’s almost as if he is running a Non-profit organisation.

    I don’t know what the forum rules say. Does it state that one can not link on the DX forum to a website which may or may not contain links which lead to other websites that sell something?

    The link provided by me was just for a free Instructable / non-commercial website that describes in detail how to DIY that arduino based spotwelder. The spot welder itself  is not being sold on that website.

    There does exist a link on that Intructable to a different website that sells the spot-welder at cost price /zero profit for all the people who were crying that it is too complicated to solder one together and program it from scratch.

    The intructable webpage I linked to is clearly not a commercial for profit venture and doesn’t sell anything.

    If that is against the forum rules, it won’t take long until DX issues a gag order forbidding us to even mention any products or services that are not sold by DX.



    Quote: " DX needs to listen to these complaints, and start being stricter with suppliers who do not have readily available stock."


    The real issue here seems to be DX’s greed for profits and bad inventory management.
    I think, DX should only list products that are truly sitting on their own shelves in their own warehouse.


    Good inventory management is a LIVE and constantly updated system.

    Anyhow, 95% of all important suggestions fall onto DX’s deaf ears. That is why I moved elsewhere for my orders, but I still love the DX forums :)




    Do I need an MPPT?

    I can not answer that question without knowing the size and voltage and set-up of your solar panel/s and the type/chemistry and size of your battery.

    But basically, yes! You need something to charge or connect a load to solar panels!

    An MPPT is like a gearbox. It connects the wheels to the engine and transfers the power according to a well calculated distribution system.

    The issue with directly connecting a solar panel to a battery is that the battery would pull the panels voltage down to the same level as what it is by itself.

    A good MPPT measures in certain intervals how much voltage is available from the panels. Then converts that to the needed voltage to charge the battery and lowers or raises the co-related amps, all based on the constantly varying output of the solar panel/s.

    However, I somewhat doubt that a $10 or similarly low priced  MPPT such as   SKU: 431777  is actually as good or even better than some of the more expensive buck / boost converters here.

    I also read that there are many fake MPPTs out there (even on the rainforest site) that simply act as a terminal connector. -Just an empty box with (screw) terminals for the wires that does what it should not do - directly link your battery to the solar panel.

    So, just keep in mind that most MPPTs are meant for charging lead acid batteries and at the same time most of them provide another terminal for running a low amp 12/24/48 V load.  

    If you want to charge  Lipos via solar you may need something else than a standard MPPT that sits between the solar panel and the Lipo to regulate output and charges the Lipo battery.

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    post edited by Ignatus on 2/26/2017 at 1:25 PM
  • Ignatus Sunday, February 26, 2017 2:24 PM Reply

    Hi matrix-neo, nice to see you here.


    Well, as sheepish already correctly pointed out, currently  there is no such thing as a 7.2 or 14.8V Lipo cell .- Those are Lipo cells connected in series that create those voltages.


    However, you mentioned WATTS in your post. And this is something that I agree to, to a certain extend.


    There are better ways to create high Ah, large sized, Lipo battery packs than spotwelding like me 24 cylindrical 18650 batteries into a 4s6p arrangement. The issue is that with this arrangemet the individual cells in the 6P packs can obviously not be balance charged.


    I could have purchased 4 large Lipo pouch cells with a massive capacity.

    Many sellers on ebay sell second hand Nissan Leaf (and Chevy Volt battery) packs and individual modules.


    A single Nissan leaf Lipo cell is rated at 32.5 Ah and 3.75V nominal.

    Four of these in series would sort me out. -Just need to find protection board or BMS and a charger that can handle these babies.


    Cost for a second hand module with 4 cells costs around $75. Unfortunately, it is hard to find new ones.


    Here a single Nissan Leaf module. Each contain 4 of those 32.5 Ah cells.

    The four cells are electrically configured as 2 in series and 2 in parallel.



    leaf1.png


    Here a single Nissan pouch in comparison to a 18650 cell:



    leaf 2.png



    Quote " maybe consider a deep cycle lead acid battery"


    Yeah, I doubt that a deep cycle lead acid battery is something that I'd like to stuff into my bags for hiking or bicycle touring.

    -Not even when driving to a campsite with a tent and stuffing all into my car.



    My current Lipo based 16.8V , 20Ah battery pack weighs about 3 pounds.


    A somewhat comparable 12V  20Ah sealed lead acid battery weighs 12.4 pounds
    !           


    If I add custom build, thin film 150 watts solar modules, sewed into a foldable fabric that would maybe add another 3-4 pounds.


    -That's about the maximum weight that I'm comfortable with lugging around in power related  gear.





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    post edited by Ignatus on 2/26/2017 at 2:36 PM
  • sheepish Top 10 Forum Poster Sunday, February 26, 2017 2:46 PM Reply

    sku.431777  makes no claim to be a MPPT solar controller. I don't know why you say non-MPPT devices like that one "does what it should not do" because as far as the battery is concerned MPPT just increases solar panel output power a little. An article I read this afternoon mentioned in summer it typically makes a 10-15% difference, in winter a bit more.


    The cheapest MPPT solar controller I can see on DX is sku.454921 at $23.91. It has such a fake CE rating it doesn't even use the China Export logo.

    Remembering 30 years.
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  • sheepish Top 10 Forum Poster Sunday, February 26, 2017 2:56 PM Reply

    ... a 4s6p arrangement. The issue is that with this arrangemet the
    individual cells in the 6P packs can obviously not be balance charged.


    The voltage of the six cells in parallel is the same, and they have the same chemistry, so they will have (very close to) the same state of charge. If a cell develops a greater (or lesser) capacity than the others it'll try to hold a higher (or lower) voltage under load and will end up simply providing a greater (or lesser) share of the total current. So it's not a problem unless a cell is badly faulty, for example short circuits the other cells.

    Remembering 30 years.
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  • Ignatus Sunday, February 26, 2017 4:36 PM Reply

     Quote " sku.431777   makes no claim to be a MPPT solar controller"


    I agree, my fault to refering to that sku. Sorry, I didn't check properly!



    Quote: "Because as far as the battery is concerned MPPT just increases solar panel output power"


    A real MPPT decouples the battery from the panels.

    It also converts the Voltage and Amps to the most efficient Volt to Amp ratio to charge a Lead acid battery. So, if you do own a Lead Acid Battery then I'd recommend to invest in an MPPT.


    How do you top up your lead acid battery at the moment with the solar panel? Solar panel to battery charger, then charger to battery?


    In an MPPT, appart from increasing the power efficiency, you also get a free inbuilt lead-acid battery charger.



    Quote:" I don't know why you say non-MPPT devices like that one "does what it should not do"


    I just wanted to warn you. I read on several websites that many of those cheaper $20 MPPT devics don't do anything at all. Many are fakes or just plain faulty.


    Also, as far as I understand differnt MPPTs are designed for differnt type of solar arrays.

    A solar array can be configured to deliver several hundreds of Volts, to be able to provide DC voltage over long distances/ wires.


    Quote:" An article I read this afternoon mentioned in summer it typically makes a 10-15% difference, in winter a bit more."


    A decent MPPT can increase efficiency upto 40%  depending on climate and charge state of your batteries among many other to-be considered factors.


    Quote: "The voltage of the six cells in parallel is the same, and they have the same chemistry.."


    I agree 100% !  That is also why I charged each of them and then measured each cell's resistance when building the six-parallel cell packs and put into each pack only cells of similar resistance.



    However, a portable 4s powerbank made from Nissan Leaf pouch cells with a total  32.5 Ah capacity would increase the nerd-factor by 10



    Greetings,

    Ignatus





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  • Ignatus Sunday, February 26, 2017 4:48 PM Reply

    Hello @ozOzo,


    I'm sorry for saying so late Hello and Welcome to this thread!


    I'm just always very exhausted after writing those extremely long and detailed posts .


    Electronic nerd or not, all kind-spirited souls deserve a loud shout-out and a BIG THANK YOU!



    More love, light and positive vibes to you.


    Greetings,

    Ignatus






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