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Fully Programmable Solar BMS ( Battery Management System ) Learn to program microcontrollers and HW design video tutorials
Open Source
Fully Programmable Solar BMS ( Battery Management System ) Learn to program microcontrollers and HW design video tutorials
Open Source
Fully Programmable Solar BMS ( Battery Management System ) Learn to program microcontrollers and HW design video tutorials Open Source
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    1. Dacian Todea 3-time creator on

      Hi David,

      Any supercapacitor will work. You will need to use at least 6 preferably 8 with a capacity no smaller than 200F. I think there are 350F available from maxwell at digikey and mouser and there are some 400F not sure what brand. Of course the larger the capacity the better but just for test a few hundred Farad will work.
      They are great for tests since they can discharge and charge fast so you can see how the limit's work but are relatively expensive. You may also use some old laptop cells if you have around those 18650 type.


    2. David Jenkins on

      Finally got my Solar BMS released from customs (it arrived in Germany over three weeks ago). I looks really good - now I need to get some supercaps to play with before looking at LiFePo4.

      Does anybody have any recommendations for supercaps suitable for testing the Solar BMS?

    3. Dacian Todea 3-time creator on

      Hi Eddie,

      Unfortunately the label is the same do to cost. Internally the power board is different with smaller mosfets and higher value shunt resistors for more precise current measurement on the SBMS1616.
      I still have to find the time to install my main SBMS (I only have one on the secondary system working fine in the last two months)
      I need to do quite a bit of work before installing the main SBMS.
      Today I just remade the installation for the house heating since winter is already here. That will probably have also a SBMS with modified software to control the propane heater based on water temperature. I will probably add some photos with that setup later today.


    4. Eddie Kinlen on


      I received my two Solar BMS's today and am looking forward to adding them to my application. I will let you how it goes. I did notice that one package says SBMS1616 and one says SBMS4080, however, the labels on the BMS case on both state SBMS4080. Was this a error, a bonus, or is just that the label is the same for both due to cost? Either way, considering I am in the Middle East the shipping was quick. Looking forward to testing and any of your future applications. I would also like to see a video of your home system with the BMS installed (The Final Product).


      Eddie Kinlen

    5. Dacian Todea 3-time creator on

      Thanks Danny,

      Yes others have mentioned the size. I'm thinking on a new version that will be able to handle 100A for both charging and discharging almost double the power while reducing the size even more. The TDP will be about the same at around 20W at full load.

    6. Missing avatar

      Danny ter Haar on

      Just received my 2 bms's. /me so happy ;-)
      Even though I watched your movies, they are way smaller than I anticipated .
      About 2/3 of the size I thought that they would be.
      This project is absolutely the best project I have participated in.
      More features available than promised and delivered on time.
      Thank you Dacian!
      Please drop me a note when you are doing another project!

    7. Dacian Todea 3-time creator on

      Hi Danny,

      Is not about the voltage level in the supercapacitors since that will never get higher than the open circuit voltage of the PV panel. Is about the fact that supercapacitors do not work in the same way as the PV panel and are not current limited.
      When I connect the PV panel to a battery the current will be limited to no more 10 to 20% over what is specified on the PV panel label as SC current.
      Supercapacitors are more like a battery with even lower internal resistance so they will output almost unlimited amount of current when connected to a battery that has a different voltage level.
      Any existing solar controller PWM, MPPT or any other type for any battery type will not work with supercapacitors attached to the solar panel in the way it was described there
      But also as important as the above problem is the fact that they will not help in any way capture more energy. There is no equivalent between an MPPT and the supercapacitor pack and you will not get any additional energy production with the supercapacitors attached in that way.
      I will advise against doing this experiment but if you intend to do this make sure you are careful the instant high energy that can be released from the super capacitors can be quite high and even melt cables instantly.
      You can see this as if you want to connect a 36V lithium battery pack to a 24V Lead acid battery, Not the best analogy but quite similar.
      I'm just printing the shipping labels right now so you will get the SBMS soon.

    8. Missing avatar

      Danny ter Haar on

      " and when you reconnect the charging " why would you disconnect anything ?
      maybe add a bleeding resistor with a relay (powered from the supercaps) to get dangerous voltages out of the caps ?
      I think it's a great way to use maximum power instead of mppt.
      Will experiment with it once I have a setup going.
      thanks for the feedback. Looking forward to receiving the bms

    9. Dacian Todea 3-time creator on

      Hi Danny,

      The supercapacitors are cool. I was playing with them for about two decades but that buster cap applications makes no sense there is nothing helpful about that. In fact is quite a bad idea to have them in parallel with a solar PV panel.
      When battery is fully charged and solar controller stops charging those super cap will charge to the open circuit voltage of the solar PV panel and when you reconnect the charging a huge amount of current will try to go in to the battery tripping the overcurrent protection (if it exist) on some solar controller this may damage them permanently.
      But even more important is that this will not help in any way to get more energy from the panels.


    10. Missing avatar

      Danny ter Haar on

      Just found this, might be a great idea to use in addition as a replacement for a max power point charger:…
      Source for supercaps:
      I just ordered a kit

    11. Missing avatar

      Danny ter Haar on

      Do you know you are the first and only project this that I backed this far that actually is delivering within the specified planned range ?!
      Kudos !!

    12. Missing avatar

      Danny ter Haar on

      Sorry, should have checked you google+ page.

    13. Dacian Todea 3-time creator on

      Hi Danny,
      There is progress. I work on building the units. It takes quite some time to build all but I will ship in October as I promised.
      I will start shipping probably around middle of October maybe sooner is hard to estimate how long it will take since I build all units at once. Is easier this way than build each individual unit completely but is harder to estimate when I will be done.
      You can see some photos with the progress on my google+ page. Last photos are from a few days ago. Here is the link

    14. Missing avatar

      Danny ter Haar on

      Any progress to report ?

    15. Dacian Todea 3-time creator on

      From what I remember your LiFePO4 batteries will be separate form the starting battery so as long as the temperature is to low for normal charging there will be no charging done.
      Both solar and alternator charging have the same limitations in the sense that if you only use a very small portion of the available current the rest is wasted energy.
      Loading the alternator will increase by an insignificant amount the fuel consumption.
      All battery chemistry will suffer if charged at low temperature Lead Acid even more than Lithium.
      No amount of charge current is acceptable at low temperatures but a small current usually less than C/30 will not do much harm.
      But that current is 10x lower than normal temperature charging current so it will take 10x more to charge the batteries.
      Since both solar and car alternator are available a few hours/day at best wasting time charging a battery at 10x lower current is not a good solution in my opinion.
      Charged at 0.03C a LiFePO4 with extremely small internal resistance will have no self heating to speak of.
      Say you have a 12V 100Ah battery bank and you charge them with 30A nominal current PV panels is winter and you have a 4h / day of sun you can charge at 3A for 4h so the equivalent of 12Ah or you can heat the battery for one hour with 30A x 12V x 1h = 0.36kWh of energy and then charge them for the remaining of 3h about 90Ah
      I suggest you get smaller cells and connect them in parallel so you can heat them much faster do to smaller individual thermal mass.
      By the way I just "finalised" the USART data logging for the SBMS.
      I just made a post about on google+ here is the first generated csv file
      Just a fast charge discharge cycle of 8 series connected hybrid ultracapacitors that I use for development with a data acquisition interval of 1second.

    16. tigerbus on

      I think "usually" might have different definitions in different applications :) just think about a car in winter. You stop it in the evening, outside temperature is like -20celsius and then you start it in the morning. Thus cold batteries and immediate power from the alternator. That's my standard case :) in other automotive applications severe limiting if charging current is pretty common, because this way you can gently heat up the chemistry from within. Getting heat into a cell structure like those thundersky ones is really hard. Takes a long time and it's unevenly distributed so you have to have even more time to actually let it settle. Battery packs with heating and climatisation in plugin-hybrid concepts use this method to shorten the heating procedure while waiting for the combustion engine to actually produce warm coolant which can be used to heat the battery :)

      How are you limiting the current through your FETs? Simply by switching off?

      Have to think some more about climatisation of cells before I actually make the jump towards this technology. Your devkit will be the base for some experiments :)

      For me the whole thing only makes sense, if I can save some significant amount of weight in the final setup compared to standard battery technology like lead gel cells.

    17. Dacian Todea 3-time creator on

      tigerbus, I understand you have special requirements but usually battery low temperature is not the case. Batteries are usually stored living spaces where temperatures never get below freezing. And if they do charging of lithium batteries is not recommended at any current. Max charging current on most LiFePO4 or LiCoO2 is around 0.3C that will allow for a decently fast charging in a sunny day. If battery temperature is under recommended charging temperature the charging is usually extremely restricted so much that it will make no sense charging a full charge will take weeks at that current limit.
      A better way that I know you also mentioned before and is used by others is to use a battery heater (use the power form the solar panels directly on the heater so that battery temperature gets to optimum and then you can use the full charge current).
      Yes you can use those GPIO at any speed they are microcontroller GPIO pins that can work up to a maximum of 50MHz over 1000x faster than any PWM charging.
      And PWM current limiting is not a good option for Lithium batteries at any temperature.
      At low temperature is extremely bad since you reduce the average charging current but the pulse current is full solar panel output.
      Sorry I did not noticed your comment before. There are no proper replays or notifications for this comments.

    18. tigerbus on

      Btw, the output could of course only be used to drive some external CC limiting device, so the question would be: are the two logic pins you introduced fast enough for PWM? Or can they be set to analogue output?

    19. tigerbus on

      Dacian, no problem at all, just wanted to check whether you got carried away with some details or everything is on track :) with no hardware you can do some software work I suppose? I noticed that I will probably need current limiting according the the batteries datasheet at certain temperatures, e.g. at very low temperatures a very small charge current to heat up the cells and then slowly increase charge current. I remember we've been talking about pogrammable true/false cutoff limits.... I think I would need to implement more sophisticated limiting for charge and discharge at different temperatures e.g. as two lookup tables for allowable current over temperature. Not necessarily programmable via the menu, since that should be set only once according to the batterie's datasheet. So if you are bored.................... ;)

    20. Dacian Todea 3-time creator on

      Hi Martin, Project is a bit slow. I ordered the PCB's some time ago they are ready and hope they will be shipped today it will probably not be a fast shipping one or two weeks.
      I have most of the components ordered and received.
      Most was from Digikey but I have some from Mouser sitting in custom since last week not sure why.
      Still the project will probably be ready well before the estimated delivery date.
      Sorry I do not provide more regular updates. I will do a photo with the PCB's as soon as I get them and post an update here when that happens.

    21. tigerbus on

      Hey dacian, how is the Project coming along? :) cheers!

    22. Dacian Todea 3-time creator on

      Danny, I understand that in some applications there is limited space but even then getting a better spec panel will be less expensive than an MPPT. A panel that is 18% efficient instead of 16% will do more than a very good MPPT and last for at least 25 years.
      Still we are talking about an average of 10% at best based on climate. You can get more than that by just using more efficiency equipment (I'm referring to what you connect as a load to your system).
      Considering my system I use in average only 60% of what I'm producing the rest is wasted. I can probably redirect the other 40% to heat water or something like that but if I do not need that then it will still be wasted energy.
      Time is valuable I will not recommend investing time in an MPPT unless is something that you enjoy as a hobby and not just for the gain of having an MPPT.

    23. Missing avatar

      Danny ter Haar on

      Thanks for the ultra fast extended answer. Pricing has come down quickly, but I bought solar panels at $0.8/watt in 2012 already (wholesale). There are conditions where PPT does make sense: eg on an RV on any other situation where you have limited space for solar panels. I think the technique used in the arduino project could be easily integrated for hobbiest when they use your setup. Li-on batteries are so much better in charging/discharging cycles at higher current. Given the idea of your open source setup, i wanted to share this for future experiments based on your setup. I have 2 setups where I have limited space for panels, and would like to implement this. Will do some experimenting in the future when I get around to it and will give feedback as soon as I have some. Thanks again for your quick reply.

    24. Dacian Todea 3-time creator on

      Hi Danny,
      Yes the Solar BMS will never implement MPPT.
      There are a good reasons not to implement MPPT and the most important has to do with economics.
      This was a great innovation not that long ago when the cost of implementing MPPT made sense considering the savings (an average of 10%) and the cost of solar PV well over 10$/W. It actually made sense down to around 5$/Watt.
      If you can make an DC-DC converter with good enough efficiency and a cost low enough to make sense at 1$/Watt panels then that will be great but there are limitation on how inexpensive you can make an efficiency DC-DC converter and I do not think is possible.
      Is funny that when the MPPT was introduced and it made economic sense people did not understood how they can recover all that extra they payed for an MPPT controller.
      By the time they understood the benefit the price of PV went down so much that it was not longer any benefit.
      That arduino solar MPPT is designed for just around 5A and 12V battery with very good cooling (larger heatsink or fan) you may be able to use a 100W solar panel that is 10x less that the 1000W Solar BMS was designed for.
      Now try to calculate the cost of the parts used on that 100W MPPT there is a part list in there since is open source.
      Just the 3x power mosfet are about 4.2$ in large quantities 1000pcs from digikey.
      Then there is a MAX4173 in there another 1.4$ and IR2104 about 1.3$ then there is the coil another 1.4$ all this in 1000pcs or more (remember I only had 58 bakers without the extra cost of MPPT)
      Now try to build 1000W DC-DC converter based on that design and you will see that component parts alone will get in to the 100$ range and then you need to add the extra shipping from Canada to international destinations for those around 1.5kg more and that is an additional 80$ for the lowest cost option.
      All this dose not include engineering cost or take in consideration low volume.
      In my case MPPT will not save anything since I use 60 cell panels. But let assume I will have used 72 cells panels (not sure why I will do that 3x 72cell are more expensive than 4x 60cells and the 3x72cell will produce 10% less power even with an MPPT than 4x 60 cells without MPPT)
      I produce about 1000kWh/year from my 3x 60cell panels so I will produce about 1200kWh/year with 72cells say I get a huge 15% extra with the use of an MPPT that is around 180kWh/year. That MPPT will need to work for 30years to recover just those 180$ in raw materials and shipping and that is extremely unlikely.
      Cost/kWh used was 3 cent/kWh that is the cost that a 1$/watt solar cell gets his money back in my location over 25 years.
      I did made a lot of exaggerations in the favour of the MPPT and it still not even close to be competitive.

      Sorry for the long answer. (I hope it makes sense)

    25. Missing avatar

      Danny ter Haar on

      Hi Dacian.
      I know this project is not intended for and never will implement PPT.
      Just found this project which does and imho the extra hardware is really simple and reasonably simple. Comes with schematics/source code for arduino.
      Just wanted to share it with you/all backers:…
      Maybe in a future project ? ;-)

    26. Daniel Farley on

      Thanks for the update :-) and the kicad files.

    27. Missing avatar

      Danny ter Haar on

      Thank you for the update. I think it is all wonderful news/upgrades. Very happy !
      Much appreciated !

    28. Dacian Todea 3-time creator on

      Hi Daniel,
      I will look in to those links and see what I can do.
      I'm hoping to have all PCB's modified by the end of this week. I will still need to use the old laptop for that. There is to much work to move everything to the new machine and I will do that after I order the PCB's and components.
      I had an old Samsung 32GB SSD that I was testing since that uses just 500mW vs 9W min for the 3.5" HDD that was there. I try to reduce the idle power on the new machine as much as possible.

    29. Daniel Farley on

      Hi Dacian,

      One idea would be to set the documentation as a wiki as that will allow a way for all of us users to contribute to it. And as its open source it would be good for helping develop extra capability's of the unit to have it open like that. have a look at the opensource hardware project, where there is lots of people helping others with the unit and moding it etc...

      Good luck on the laptop upgrade... i have just gone through that my self... new one has a SSD it is amazing what difference it has made.


    30. Dacian Todea 3-time creator on

      Thanks Daniel I will make sure that next update will also be posted here.
      Currently I'm upgrading my old laptop and I will need to move all the file on the new one.
      Danny I will try to make also a written document but not sure where I will post that. I do not have time at the moment to create a blog on my website.
      In the end I will probably do a short pdf manual explaining just the basic connections and how to set the Solar BMS.
      In the meantime I will probably still make videos relating to progress. Probably next update will be by the end of next week when I finalize the changes on the PCB's.

    31. Missing avatar

      Danny ter Haar on

      Dear Dacian.
      Positively meant feedback:
      All the information in your 41 minutes youtube video could be written in text with screen shots to explain stuff. It would take less than 5 minutes to read (for me)
      I think you are introducing a lot of overhead with your video's.
      Could you consider putting things in writing instead of video recording next time ?

    32. Daniel Farley on

      Hi Dacian Todea, im also happy to hear about how things are going :-) Thanks for the update.


    33. Missing avatar

      Danny ter Haar on

      Thank you! I am glad to know there is a (future) possibility to communicate with the unit! I would appreciate announcements here (or through kickstarter email update service) that a youtube update is available. Thanks again for doing this!

    34. Dacian Todea 3-time creator on

      This comment section is not that great since there is no replay button and I will probably be the only one getting an update when someone posts in here.
      I will try to update as often as possible. The things I worked in the last few days where probably boring for an update. I try to finalize the component list that will be used so that I can start changing the layout for the next sample.
      There will be a USART communication port optoisolated as it is on the beta but not sure I will get the time to write a software for it (I will probably do but do not want to make any promises) then you can connect a USB to USART adapter and do data logging on a tablet or a PC.
      I will do most of the updates on youtube. There is only one video made since the project ended not sure you have seen that one.
      I can also announce the update here but not sure if people will want to get an update every week if they are not extremely interested in the progress and just want the board when is ready.

    35. Missing avatar

      Danny ter Haar on

      Is it possible to incorporate some kind of extension bus to which later eg a serial or usb port could be connected for monitoring ? I know we barely made the first goal, but I would like very much to have some kind of monitoring capability.

    36. Missing avatar

      Danny ter Haar on

      How often will you be providing us with updates btw ?

    37. Missing avatar

      Rich P on

      Congratulations !!

    38. Dacian Todea 3-time creator on

      Hi Julian,

      Look at the spec there is an address pin so that two of this IC can be used one master and one slave so you can use 16 cell.


    39. Julián Dela on

      Thanks! I was interested to see if the IC could be scaled up to 16 cells, unfortunatelty seems like not with this one.

    40. Dacian Todea 3-time creator on

      Hi Julian,
      Yes I will do a video with all details soon but that IC is the ISL94203


    41. Julián Dela on

      Now that the project has been definitely funded, can you say which IC you are using for the battery monitoring? Thanks!

    42. Dacian Todea 3-time creator on

      Hi Danny,

      An MPPT controller may last more than 5 years if is well build and used at only a fraction of is total capabilities.
      Say you use that 80A flexmax at only 40A than it will probably last 3 to 4x more than if used at 80A but since you get an oversize unit it will cost more.
      Heat is what will degrade the electrolytic capacitors but check any electrolytic specification from large and quality manufacturers and you will see just a few thousand hour of use before fail.
      A grid tie inverter is a totally different story since that already has all the hardware needed for MPPT you can not do that without that option so all you need is the MPPT algorithm.
      As for the shipping cost that my vary from country to country. If you check Canada Post website you will see that a >2kg international parcel (other destination than US) will cost at least 80 to 100$ vs 20$ for a 200 to 400g parcel.

      Like I mentioned before my Solar BMS can not be upgraded to MPPT just with software
      It needs a DC-DC converter and that is extremely large and heavy for 40A 1000W converting this to an MPPT will be a total redesign way larger and with a huge heat-sink will look quite different.
      In the summer is when you get the lowest performance out of an MPPT since the solar PV panels are hot and the voltage will drop. In cold and sunny days you get the best performance out of an MPPT. Average over a year will never get you more than 15% and that is the important number when you do a cost benefit analysis.
      About the battery video.
      The 100% was used for calculation simplicity. And you can discharge a Lithium battery 100% that is how most manufacturers do the tests.
      For Lead acid this is not recommended but for calculation purposes is the same thing see the cycle life graph for that Trojan 100% DOD 800 cycles then 50% DOD 1600cycles so the total energy stored during the life of the battery will not be different in that calculation since you multiply 800cycles x 100%(1) or 1600 x 50%(0.5)
      That comparison as I mentioned in the video was kept simple so not extremely accurate so people can understand the calculation.
      If I will have used more accurate and complex formula the Lead Acid will have looked way worse.
      LiFePO4 is by far the lest expensive energy storage option (including just chemical batteries) available today on the market.
      OffGrid is really small today not a market for the big players but there are already grid connected options form Sony, Bosh and SMA just to name a few all with LiFePO4 batteries and 10 to 20 years warranty some claiming over 7000 full cycles.
      I can provide you with links if you are interested in this option.


    43. Missing avatar

      Danny ter Haar on

      I have a couple of flexmax 80 running for 5+ years, no problems what so ever. A friend of mine has flexmax 60 & flexmax 80 running for 10+ years. I tend to disagree with your life suggestion. I have 3 solar setups at the moment: a 5 kWatt inverter connected to 48 volt lead acid battery bank, includes MPPT inverter. A grid tie only 3kWatt inverter with 2 strings with each MPPT, with 3600 watt DC solar panels connected to it. And 6 micro inverters, again with MPTT. So have been in service at my place 5+ years. The 3kWatt grid tie only is transformerless to the grid, does have HF transformer for the dc-dc chopping. I am pretty sure it will outlive the 10 year factory warranty. A friend of mine repairs solar inverters and most problems he encounters are the dc -> ac part that gets fried. Most often by lightning strikes etc. I don't share your vision that it would be unreliable, much more weight/shipping. SInce you already have a uprocessor in your design, it would be the ultimate plus for a (future) V2 of this project. But since it will be open source, I might have a go at it myself in the future. In the summer you can easily gain 30+% extra power from MPPT. I think that is easy ROI over your investment.
      Your design with 24 volt might be too limited for what I have in mind. I really want higher voltage, maybe even up to 96 volt DC. I do not agree with your calculation about 5x costs of MPPT over 25 years. Same goes with your video about the batteries. If/when you discharge batteries to 100% you are killing batteries, no matter what chemistry. I think if you would take different calculation parameters, if would still be in favor of Li-Ion but not with the margin you gave in your example. I hope this projects advances, I am very much looking forward to it.

    44. Dacian Todea 3-time creator on

      Hi Danny,
      MPPT is an obsolete technology because of the current cost of solar PV panels.
      Main component on an MPPT charge controller is a DC-DC converter and for my solar BMS with 24V battery and 40A charge current you will need a 24Vx40A ~ 1000W DC-DC converter you can imagine something like that will make the Solar BMS at least 10x heavier and larger 200g at the moment vs at least 2kg just the international shipping alone can be 70$ to 100$ more then the components of the 1000W DC-DC converter will not be cheap large electrolytic capacitors and big coil.
      If you have a desktop you probably have a large 200 to 1200W power supply that is also a DC-DC converter and a bridge rectifier.
      Also a good MPPT will not last for more than 5 years of daily use because the heat will degrade the electrolytic and they have a finite life so you will need a few of this during the life of the solar panels over 25 years.
      Now usually an MPPT will improve the power collection by about 15% or less depending on climate at your location.
      This 15% can be more easily and economically get with just adding 15% more solar panels like 150W additional to the 1000W and they will cost around 150$ at 1$/Watt and last 25 years.
      My controller dose not use any electrolytic caps so it will last the life of the panels over 25 years.
      In contrast you need about 5 MPPT controller during 25years life of the panel each cost at least 100$ for the components (large Heatsink + large electrolytic caps + big inductor and other components) then there is the shipping also 5x this will never be able to compete with 150$ of solar panels but it was a time not long ago when solar panels where over 10$/Watt and then the MPPT made sense.
      As for the other part yes is possible to make this work with 16 cells 48V but it will be about double the size and weight more expensive mosfets an additional battery IC and of course some software change it will probably add another 60 to 70% to the cost in low volume.
      I designed this for me and 24V was what I needed for the offgrid house and other projects that I have in mind (a low speed solar vehicle and a garden robot maybe more in the future). Luckily it will be open source so anyone can add changes to this design.
      And by the way the solar tracking is also obsolete because of the drop in price for solar panels :)

    45. Missing avatar

      Danny ter Haar on

      I have been googling/reading about DIY mppt. How hard would it be to implement something like that in a future version ? And up the battery voltage to 48 volt and Voc to 120 volt ? :-) That would be an absolute killer in the market imho.

    46. Missing avatar

      Danny ter Haar on

      Things like would make a charger like this way more interesting in the future over here in california

    47. Missing avatar

      Timothy Geisler on

      I am hoping even if they don't answer they decide to test a unit. I also posted on a group of Kickstarter backers on FB. All we can do is try and hope.…

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