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DIY laptop powerbank project

  • Ignatus Friday, February 24, 2017 6:09 PM Reply

    First of all, I’d like to give a big SHOUT-OUT to all the great minds and kind-hearted DX members who have supported me and other electronic enthusiasts in the past :


    @Desolder
    @sheepish
    @ozOzo
    @cyclist
    @gasbag11
    @matrix-neo


      




    WARNING/ SNOOZE ALERT :


    Just skip this novel if you are one of the persons who brainstormed with me in the past anything in regard to this project and just read the second post 




    Okay, here a recap of how it all started what happened so far:



    I needed a powerbank to operate (not only charge) a MacAir laptop, which consumes up to 45Watts @ 14.75V under full load. However, I use this laptop only for light work and I measured  with the help of SKU: 414035 that on average the laptop consumes only 15-20W.


    Since 18650 Lipo cells are the easiest to come by, I soldered a first prototype from just three, brand new Samsung 18650 cells rated at 2600mAh each, in series to a boost converter SKU: 214310.

    samsung2200.jpg



    WARNING/ DISCLAIMER: It is dangerous to directly solder Lipo cells and should be avoided. You are not only risking to harm yourself, but you can potentially destroy the cells as well. The cheapest, usable spot-welder with acceptable results on Ebay costs just $120 and is a good investment. If you decide to use a hot iron to solder LIPO cells DO IT AT YOUR OWN RISK!  



    Anyhow, my Lipos, the laptop and I survived and I went ahead to gather more materials to build a larger, more sophisticated powerbank.

    Unfortunately, the manfacturer of the powerbanks that contained the Samsung cells wasn't very consistent. Those powerbanks costed me approx USD 20 each and contained 5 Samsung cells = $4 per cell.


    After one initial test-order, I ordered 2 more powerbanks. Unfortunately, they contained cells of a differnt make (LG) and I decided to look elesewhere. I even managed to return the cracked open powerbanks to the manufacturer and got a refund.



    I then sourced locally 2x SKU: 456170 for $30 each. These XIAOMI power banks were for me the only way to be somewhat sure that the Lipo cells are of good quality, recently manufactured and not fake.

    Xiaomi provides some scratch-label verification code that can be checked online for authenticity. Since these MI power banks are most of the time even cheaper than buying the cells individually, it was a no-brainer.


    This MI powerbank contains six LGABF1L1865 cells rated at 3350 mAh each.

    Awesome deal at $5 per cell and 750mAh more capacity each than the Samsung ones.


    xiaomi_powerbank.jpg




    If you are gentle when removing the cells from the plastic housing, you won’t have to solder or spot-weld them later and can just solder the overlapping nickel tabs.



    So, I got two MI packs and ended up with twelve individual LGABF1L1865 Lipo cells. I then cut the twelve cells apart and created a 3s4p configured battery which would provide 12.6V fully charged, which is pretty close to the desired 14.75V for my Macbook air... or at least so I thought in the beginning of this never-ending DIY journey.


    For testing purposes, I connected this reconfigured pack to a 3s battery protection board

    SKU: 255211 and from there to the boost converter SKU: 214310 .

    It worked fine for a bit, but sometime during one of the tests I accidentally connected the battery with reversed polarity to the protection board or to some wrong solder pad. I don't remember the datails apart from the fact that the the 3s protection board blew-up. -No explosion, just some “magic smoke”.


    Luckily, I also ordered previously one 4s battery protection board SKU: 255209.  After the mishap with the burned out 3S protection board, I tried to modify this 4S board to make it work as a 3S protection board (following instructions from @Desolder) .

    I don't recommend this mod. I destroyed this board too when I tried to modify it (ground one pin). My soldering iron is a bit too big, my magnifying glass too weak and my sweaty hands too shaky.  Also, it seems there are some differences in the smd components between the two versions:

    3svs4s.jpg


    Anyhow, during the whole process of destroying two battery protection boards, I realized that a 3s battery configuration would not be an efficient powerbank for my laptop’s approx.15V requirement.

    A 3s4p Lipo battery configuration provides 12.6V when fully charged, 11.1V nominal Voltage and will shut off at around 9.6V. That also meant that this pack would have to continuously boost the voltage to 14.75V  and therfore, the DIY powerbank would drain very fast.


    The next logical step was to re-arrange the 3s4p battery to a 4s3p configuration, since I already owned twelve Lipo cells and thought that I wouldn’t need more.


    A 4s3p pack would provide 16.8V when fully charged, nominal 14.4V and die at around 12.8V.
    -These values are much closer to the required 14.75V for the Laptop and seemed like a slightly smarter choice.


    I placed a few more orders for 4s battery protection boards SKU: 255209 as well as an automatic Buck-Booster SKU: 258020. Unfortunately, I read only far too late that somebody complained about RF frequencies interference of this Buck-Booster. I then placed another order for an automatic Buck-Booster SKU: 297691 and this one seems to be working great, although it does cost more/double.


    I also ordered two of the percentage-based, capacity meters SKU: 424105. Yes, two units. I love to have spare parts laying around :)

    Once the new Buck-Booster and the 4s Battery protection board arrived I connected everything in a test set-up.

    Unfortunately, I then had to discover that battery meter SKU: 424105 can not display the remaining battery capacity while a load is connected.

    The user ( @Sheepish ) suggested that I could use an automotive relay SKU: 289783 and a reset switch. Whenever I press the button switch, the powerbank circuit would stop powering the laptop and connect to the battery meter to show the remaining capacity. -As soon as I release the pushbutton switch, the capacity tester's display would shutdown and the laptop would get power again. -Nice idea!


    So, I placed another order for the relay and this time also ordered DX’s smallest 4S Lipo charger SKU: 433805 (great suggestion by user @Desolder), which I intent to incorporate into/inside the DIY powerbank. I like that it has zero buttons, there is nothing to press or to select to start charging, only the charging wattage might be a bit too low for this big powerbank.


    I also found at another source a different battery capacity meter. That meter displays the battery's percentage based on measuring resistance and can display the remaining battery capacity while a load is connected to it.

    So, I might use that one instead and utelize the automotive relay only as an on/off switch.







    Edit: fixed some grammar errors and typos.

    Posts(183) | Reviews | Tip post

    post edited by Ignatus on 2/25/2017 at 3:12 AM
  • Ignatus Friday, February 24, 2017 6:10 PM Reply


    After the Chinese New Year celebrations. Finally some of the long-awaited items from DX and other sources arrived (not all items are in the picture):

    charger_arrived.jpg


    While I was waiting for DX, I also bought locally another twelve Lipo cells.

    Now I got here 24x LG 18650 cells all ready to be wired up for a 4s6p 20Ah powerbank.


    24cells.jpg


    So, all is great now, right?

    Well, yes and no:


    mrbean.gif


    -My better half received from me a new Laptop on Valentine’s day.

    Unfortunately, the run-time is bad. She gets max 4 hours out of it when video editing and it draws around 60 watts at 20V/3A under full load.


    Now, I could either build one dedicated powerbank for each of us or we could share one. Since the DIY powerbank is somewhat heavy and not super cheap either, I’d prefer to share one and invest into a large 100W or 150W solar panel.


    So, all deceisions to-be made depend on competent feedback which I hopefully receive from you guys, please?



    QUESTION A.)  1 or 2 boosters

    One solution would be to use two different buck-boosters which use the battery-pack simultaneously. This setup would severely stress the battery protection board SKU: 255209 and requires some copper heatsinks and maybe even a tiny fan.

    However, I’m not even sure if this is possible. Can I connect two buck-booster boards to one battery-pack? One of them would be adjusting the output voltage to 20V for the new laptop and the other buck-booster to 14.75V for my old laptop. Would they somehow interfere with each other?





    QUESTIONS B.) in regard to buck-booster and Watts


    To make the powerbank work efficiently with the new second, additional laptop power requirements I would need to once again increase the cell configuration.

    This time to 6s6p = 22.2V nominal / 25.2V when fully charged and use automatic Buck-Booster SKU: 297691 and a 6S BMS (protection board with load balancer/charging-circuit integrated, from another source) .

    So, if I set the output voltage to just 15V via the potentiometer, what happens to the excess voltage? Is it dissipated as heat?

    My question is basically: Do I waste the 10Volts?

    Or in other words:

    Considering that I’m using the automatic Buck-Booster:


    Would I get a longer run-time from the hypothetical 6s6p 22V nominal pack using a hypothetical 15V 4A laptop = 60 Watts vs. using the 20V/3A Laptop = 60W ?


    Is here only the Watt consumption relevant or also that the voltage output is modified by the buck-booster ?



    QUESTION/S  C.) in regards to resistors and potentiometers:

    I 'd eventually like to built a proper enclosure for my DIY powerbank and I can't use a mini screwdriver to adjust the output voltage on the tiny trim pot whenever one of us needs to plug in.


    trim_pot.png


    I’d like to desolder the one that is on the Buck-Booster and replace it with some sort of “Rotary switch with detents” or preferably something smaller. A 10 position slide-switch with detents?

    Or maybe just a more user-friendly/accessable, such as a larger potentiometer?

    I found this one with 10 detents and a breakout-board that has space for resistors. - Kind of a commercialy available, semi-DIY rotary-switch potentiometer.


    rotaryswitchpoti2.pngrotaryswitchpoti1.png



    Unfortunately, it is relatively huge when keeping the DIY powerbank's to-be builld box/casing in mind. If anyone can suggest a much smaller sized solution, I’d be very happy to hear about it.


    Also, how close to the PCB do I have to place the new potentiometer, since any wires would introduce resistance, would it be smarter to use insulated nickel strips instead of wires?

    If I choose another potentiometer instead of that aforementioned rotary switch, I’d like to avoid needing to make e.g. 40 turns just to change 10V in output variance. The trim pot on the Buck-Boost converter is rated at 0.5W and 100K Ohms.

    My general fear with using a rotary based potentiometer is that vibration during transport might change the output voltage unintentionally, and I don’t want to incorporate another voltage display into this battery pack.


    I'd love a rotary switch with resistors or a potentiometer with detents that have a proper “click” to them when moving to a new position/ selcting a different voltage.

    Assuming that I either order the rotary switch with detents or maybe even find a sliding switch with 10 positions, or DIY a rotary switch and hook up some resistors:


    It would be nice to plan a bit ahead this time and have a broader range of output voltages. Let’s assume from 24V in 1V decrements down to to 12V.


    A setup like this would allow me to potentially connect/charge /operate all type of gadgets e.g. my 12V Sony bluetooth speakers, Wife’s laptop 20V, my laptop almost 15V etc..


    What type of calculation do I have to make for choosing the right resistors when upgrading to a 6s Lipo or staying with the 4s pack considering that I am replacing a 0,5W 100K Ohms trim pot.



    EDIT:

    On a second thought, it would most probably be easier to calculate needed resistor values with a fixed scenario and more easy if we just have 10 equal 1V decrements/ steps.


    Variables to work with are:

    hypothetical 6s battery

    24V max output desired

    14V lowest output desired

    0,5W 100K Ohms trim pot currently in use



    If the current trim pot would be at it's highest point of resistance when putting out 14V,


    to get a 1V output increase, the first resistor would need to be 90K Ohms

    to get a 2V output increase, the second resistor would need to have a value of 80K Ohms

    to get a 3V output increase, the third resistor would need to have a value of 70K Ohms


    etc.... ? Or am I totally off track?



    So, I'm just guessing:


    a.)The current trim pot might be adjusted anywhere around the middle right now (50K Ohms?)  to output 15V... scratching my head.....


    b.) ... mhhhh...... there must exist a mathematical formula that I can rely on?



    Okay , that's all for now. I look forward to actually using this powerbank one day.



    Edits: fixed Grammar/ sentence structure, typos and major edit to the resistor section.



    P.S.: I start to wonder if I will actually be happy once this project is complete. I seem to enjoy creating problems and finding solutions

    Posts(183) | Reviews | Tip post

    post edited by Ignatus on 2/25/2017 at 4:28 AM
  • sheepish Top 10 Forum Poster Friday, February 24, 2017 7:13 PM Reply

    Is that one of the Monkees?


    Edit - apparently yes; Peter Tork.

    DX has found a new way to deceive customers:
    Use reviews for different products that have not been bought
    by the person who wrote the review.
    http://club.dx.com/forums/forums.dx/threadid.1462252
    Posts(23529) | Reviews | Tip post

    post edited by sheepish on 2/24/2017 at 7:15 PM
  • Ignatus Friday, February 24, 2017 7:17 PM Reply

    smiles Hello @Sheepish


    Yep, that is Peter Tork

    Posts(183) | Reviews | Tip post

    post edited by Ignatus on 2/24/2017 at 9:00 PM
  • gasbag11 Top 10 Forum Poster Saturday, February 25, 2017 12:07 AM Reply

    Yep, that is Peter Tork


    WOW! He certainly aged well.  lol


    Btw, thanks for the kind words, but it's up to sheepish and desolder now. I know nothing about electronics. 

    ALWAYS ask questions about a specific item on its
    page. Scroll down and click on "Post a new topic".
    Posts(11518) | Reviews | Tip post

  • Ignatus Saturday, February 25, 2017 5:08 AM Reply

    Hi gasbag


    Nice to see you again !


    Yeah, I slowly feel bad asking these many questions knowing that we have here mainly two electronic geeks who are investing their free time. I'll have to check for some online courses, I just have too many exciting electronic project ideas floating in my head.


    Lols at "aged well".

    Found another snap. At least one of those two really knew how to play the guitar


    petertorkmiami1967.jpg


    Okay, I'm drifting way off topic here again :)

    Cheers.

    Posts(183) | Reviews | Tip post

  • sheepish Top 10 Forum Poster Saturday, February 25, 2017 7:38 AM Reply

    The cheapest, usable spot-welder with acceptable results on Ebay costs just $120 and is a good investment.


    One of those would be very nice. I wonder when DX will list one.


    I love to have spare parts laying around :)


    I've decided I do too. It's not because I order stuff and forget why I ordered them by the time they eventually arrive.


    Unfortunately, the run time is bad. She gets max 4 hours out of it when video editing and it draws around 60 watts at 20V/3A .


    Video
    editing can be very power hungry. A very quick calculation indicates
    that's about right, assuming an actual 3350 mAh per cell and a
    buck/boost regulator efficiency of 83%. Lower actual capacity would give
    a higher efficiency.


    I’d prefer to share one and invest into a large 100W or 150W solar panel.


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

    DX has found a new way to deceive customers:
    Use reviews for different products that have not been bought
    by the person who wrote the review.
    http://club.dx.com/forums/forums.dx/threadid.1462252
    Posts(23529) | Reviews | Tip post

  • sheepish Top 10 Forum Poster Saturday, February 25, 2017 7:51 AM Reply

    Can I connect two buck-booster boards to one battery-pack?


    If
    they're powering separate laptops I don't see why not. Six of those
    18650 cells in parallel should be able to supply at least 36 A. Just
    keep an eye on the heat.


    If you're going to go for more
    than four cells in series I have a feeling you need to be extra careful
    about keeping them balanced and protected (based on comments on
    Candlepower Forums regarding multicell torches).


    So, if I set the output voltage to just 15V via the potentiometer, what happens to the excess voltage? Is it dissipated as heat?

    My question is basically: Do I waste the 10Volts?


    It's mostly not wasted. If the buck/boost driver is a good one then you'll get >90% of the input power converted to the right voltage, thus <10% lost. I personally view the loss as a cost of getting the right voltage rather than as waste. High driver efficiency is highly desireable.


    I found this one with 10 detents and a breakout-board that has space
    for resistors. - Kind of a commercialy available, semi-DIY rotary-switch
    potentiometer.

    Unfortunately,
    it is relatively huge when keeping the DIY powerbank's to-be builld
    box/casing in mind. If anyone can suggest a much smaller sized solution,
    I’d be very happy to hear about it.


    How about something like sku.5660? (Sold out, sadly.) Connected in the right way would give four selectable voltages. If you have it in a box a silicone tailcap could be inserted into a drilled hole to make it look nice and be somewhat water resistant.

    DX has found a new way to deceive customers:
    Use reviews for different products that have not been bought
    by the person who wrote the review.
    http://club.dx.com/forums/forums.dx/threadid.1462252
    Posts(23529) | Reviews | Tip post

  • ozOzo Top 10 Forum Poster Saturday, February 25, 2017 8:33 AM Reply

    Hi Ignatus,
    I'm really chuffed to be included in such august company as those above, especially in an Electronics thread no less! As the only knowledge I have on that subject has been taught to me by gasbag11, neither of us qualifying as 'great minds', I conclude we are thought of as the 'kind-hearted' ones... for which I thank you.

    There is little I can contribute apart from encouragement in what appears to be an interesting project but as I am subscribed, I will be following your progress with interest. Any further education I gain will be a bonus.

    Worldwide 4G bands list:
    http://en.wikipedia.org/
    wiki/List_of_LTE_networks
    Worldwide 3G bands list:
    https://en.wikipedia.org/
    wiki/List_of_UMTS_networks
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  • Ignatus Saturday, February 25, 2017 8:42 PM Reply



    @sheepish


    Spotwelding:

    The cheapest, usable spot-welder with acceptable results on Ebay costs just $120 and is a good investment.

    One of those would be very nice. I wonder when DX will list one.




    Sorry, but my guess is:

    Most probably that will NEVER happen or DX will demand an outrageous $299. They seems to focus on smaller sized, easy to handle/ship items and on high profit margin, hot-selling goods such as cellphones.

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


    However, if you like/need/ want  a spot welder… Check this out:

    There is a German guy who built a 12V DC car battery based, handheld sized, arduino controlled spot-welder and wrote an Instructable.


    EDIT : REMOVED LINK


    Just Google for: DC spotwelder aruduino



    He suggested using a 48Ah car battery and I already own large 150Ah 12V lead-acid, inverter-battery which is catching dust. So, for me that handheld spot-welder is a cute solution and it got raving reviews too.




    DX shipping delays:


    I love to have spare parts laying around :)

    I've decided I do too. It's not because I order stuff and forget why I ordered them by the time they eventually arrive.



    I know where you are coming from, I’ve received In January 2017 a tiny $2 item that was part of a larger DX order placed in September or October 2016. -I barely remember what I ordered the item for and totally forgot about having ordered it in the first place when it arrived.



    A bit off-topic:

    However, once during Jan 2017 I was actually pleasantly surprised. A $130 DX order placed in end of December was shipped with DHL global and reached me in just barely over 14 days.

    I was full of joy and wrongly assumed that DX followed my one year old advice to offer DHL as a shipping method.

    Therefore, I soon placed another $30 or so order, which was then unfortunately sent out via the Netherlands/Dutch postal system instead of DHL Global, took almost 1 month to reach me and could only be tracked on the day of the delivery.


    I have to admit that after the last DX order, I’ve moved away from DX for the majority of my orders. Nowadays, I’m only ordering here products if I can’t find them on another site.

    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.

    My other supplier sells 95% of the time only products they actually have in stock and truly ships out to their local post-office within 48 hours. Usually, latest by day 4 I can start tracking my parcels. My electronic-parts orders over the past 2 month are totalling around USD300 and was not spent on DX, but on that other site.

    I also save a lot of time and a little bit of money,  getting many times 100% the exact same products as on DX at a lower price,without constantly needing to request DX to do price-matches here, which may or may not be honoured.

    In the past, I’ve sent in multiple price match and product requests. All I got was a reply that they value my suggestions and offered multiple times $1 or$2 in points or coupons.





    Back to the project:


    Run-time:

    Unfortunately, the run time is bad. She gets max 4 hours out of it when video editing and it draws around 60 watts at 20V/3A .

    Video editing can be very power hungry. A very quick calculation…
    .



    My apologies, I wasn’t very accurate with my explanation.

    My wife’s laptop’s internal battery lasts about 4 hours when doing regular work and around 2 hours when editing videos, and of course video editing happens at a much slower rate when compared to being plugged into AC mains due to the CPU’s speed-stepping feature.

    I haven’t tried yet connecting her new laptop to my DIY powerbank, because:

    a.) I should either upgrade the 4s6p pack to a 6s6p pack or

    b.) built one dedicated 6s6p powerbank just for her new Laptop and

    c.) most importantly I haven’t even put my 4s6p pack together yet.- It’s still all in parts.



    Heat:


    Six of those 18650 cells in parallel should be able to supply at least 36 A. Justkeep an eye on the heat.


    I will add a 10A or 15A automotive blade fuse at the output of the whole pack.


    If I build a larger 6s6p powerbank next time, I may add a temperature probe, sensing circuit and display. Additionally, I may also add a small fuse-wire with a 1A rating between each parallel 18650 cell, similar to what Tesla does … if one of the 18650 cells goes bad, the pack stays safe.






    Charging:

    …more than four cells in series I have a feeling you need to be extra careful about keeping them balanced.


    Each 18650 cell, in 2 of the 4 individual 6p units was measured for resistance and I’ve matched the cells as close as possible. The other two, 3.7V 6p units I left as purchased. The manufacturer seems to have already done an awesome job matching cells of similar resistance when building the powerbanks that I harvested for this project.

    Additionally, each of my 4 individual 6p packs is balance charged via the Lipo balance charger sku:

    This particular balance charger seems a little underpowered for my 20Ah DIY battery and will be a pain if I have to wait for 30 hours of continuous sunshine when charging via solar panels. However, it’s alright for charging via AC mains right now and I’ll see what can be done about it in future.




    Resistor/ Poentiometer/ Voltage divider issue:



    How about something like sku.5660 External link? (Sold out, sadly.)…



    Nice idea, although the product description is missing. I assume that each button-push would create a different resistance. Anyhow, it is sold out and I also need something that provides me a bit more fine grained control than just 3 settings when replacing the 100K Ohms pot based potentiometer on that buck-booster PCB.

    Therefore,the search for a good potentiometer solution / pot alternative continues. I might just add a larger, more user-friendly 100K Ohms potentiometer and a Voltage meter with display. -That saves me the headache to try to calculate multiple resistor values ( a not easily mastered feat with my limited knowledge as an electronics novice) to control the buck-booster.

    Additionally, it saves me the hassle of searching & ordering or even custom crafting a rotary switch with detents and a breakout-board for resistors.





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    post edited by Ignatus on 2/26/2017 at 9:44 AM
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