My Programable Solar BMS for any Lithium cells and Supercapacitors

electrodacus
electrodacus Registered Users Posts: 3
in Advanced Solar Electric Technical Forum #1
Hi, This is my first post here.
I'm an electrical engineer that recently build an off-grid house.
I decided to use LiFePO4 for energy storage since that is at the moment the best solution from the cost of storing energy point of view but there are many other advantages that I can go more in to details if someone is interested.
The problem was there is no Solar charge controller that can work with Lithium batteries so I decided since I have the knowledge to build my own.

Since I invested so much especially time I decided I will build a few of them for others if there is interest for it.
It was designed to fit my needs so it can work with 3 up to max 8 cells in series (that is what I use I have 8x 100Ah cells in series) so about 24V DC
It can work with any type of lithium battery since it has fully programmable parameters.
For solar off-grid weight is not important so LiFePO4 are probably some of the best and extremely safe I have mine inside. Or lithium-ion charged at only 3.92V are a good solution since you will only use 60% of they rated capacity if you charge them at 3.9V compared to 4.2V but the benefit is that they last 8x longer (8x the number of charge discharge cycles at 3.9V) and thus becoming about 5x more cost effective / kWh of energy stored and can last probably close to 20 years of daily use.

Here is a presentation video that I made for Kickstarter and is already submitted but I think they will ask me to change it since it has a 3D rendering and some people may confuse that with the real product.
I just found out after I spent one week to make the video anyway is a good 2 min presentation with the futures of the Solar BMS
https://www.youtube.com/watch?v=EZt1oJ3n7jY

And for those that want more information here is a longer 38 min video that I made with the beta sample I'm currently working on.
http://www.youtube.com/watch?v=PSYo8Jkq8S0

What do you think ? I will love to here your opinion even if you are not interested in this solar controller
It was designed as a replacement for the 12V/24V Lead Acid controller that everyone still uses.
I hope to soon make a video explaining with facts real numbers why Lithium is better than Lead acid for energy storage.
If you think you have a great Lead Acid battery that can compete with Lithium let me know the manufacturer and model so I can include in my comparison.
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Comments

  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #2
    Re: My Programable Solar BMS for any Lithium cells and Supercapacitors

    I was wondering when something like this might come along. The main problem i see is one of scale. Off grid folk, at least full time off gird) tend to use pretty big gear. Battery banks in the 400+Ah, system voltages of 24V or 48V. (so 16 cells is a must).And the one defining factor, an inverter. Those inverters draw in the vicinity of 100-300A, with surges much higher.

    How important is it that all loads go through the load terminals? If the BMS simply monitors the individual cells and can sound an alarm, but cutting off the inverter on a low cell, clearly wont work if it isnt routed through the load port. This is a common problem with all small charge controllers, and why no proper off grid charge controller has a load port.

    Your design looks more suitable for cabins and RVs and the like, DC loads, small inverters etc.

    Mixing the charge control and BMS is ambitous. Are you sure that all of those functions embodie the decades of experience in charge controllers in the field? Companies like midnite have taken years to get these products, tested, UL/ETL listed and brought to market in a comprehensive manner. UL listing seems as important if not more so for lithium in that often peoples household insurance depends on it.

    This sounds like a good project, and ive got various bits gear from you over the years, so i do wish you well with it. BTW welcome to NAWs.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #3
    Re: My Programable Solar BMS for any Lithium cells and Supercapacitors
    electrodacus wrote: »
    The problem was there is no Solar charge controller that can work with Lithium batteries so I decided since I have the knowledge to build my own.

    Cool stuff - I wish I had the skills to build like that, although I have reservations about the terminals ability to handle current. Welcome.

    Solar charge controllers do just fine now, like my Xantrex and Morningstars. These are simple pwm's, and all you need to do is set the voltage properly. The more expensive Outbacks and such can also be programmed to handle lifepo4. Note that commercially, Genasun is one example of existing mppt solar charge controllers designed specifically for LiCo02, and Lifepo4, so you'll have some competition.
    Or lithium-ion charged at only 3.92V are a good solution since you will only use 60% of they rated capacity if you charge them at 3.9V compared to 4.2V but the benefit is that they last 8x longer (8x the number of charge discharge cycles at 3.9V) and thus becoming about 5x more cost effective / kWh of energy stored and can last probably close to 20 years of daily use.

    STOP IMMEDIATELY.

    You are talking about Lithium-Cobalt voltages, and not Lifepo4 voltages. You will HURT your lifepo4 bank with the voltages shown. It is EXTREMELY important not to be vague about your chemistry. I sure hope you are not charging your lifepo4 GBS cells to those voltages, or you now have a lithium-plated pile.
    I hope to soon make a video explaining with facts real numbers why Lithium is better than Lead acid for energy storage.
    If you think you have a great Lead Acid battery that can compete with Lithium let me know the manufacturer and model so I can include in my comparison.

    I love Lifepo4, but you have an uphill battle on your hands as it does not make sense in every instance at this time. Review Bruce Schwabs powerpoint presentation found online - but we're talking about batteries to be used in house-banks, and not model RC planes or e-bikes.

    I suggest you demo with those GBS batteries you have sitting on the back shelf, and not with the hobbiest type stuff which is covered well elsewhere (like rcgroups forums)
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #4
    Re: My Programable Solar BMS for any Lithium cells and Supercapacitors

    Im confused ?? """My Programable Solar BMS for any Lithium cells and Supercapacitors """" ????? Battery cells AND Supercapacitors.???

    The terminals look capable of about 20a at 24v ?? ..I think there are far superior terminals strips available. Its virtually impossible to put wires above #10 under those screws successfully.

    3.92v is to high a charging voltage.. 3.9 should be a cell balancing set point. And a full charge set point of 3.6v.

    We have been experimenting at work with a prototype LIFEPO4 cell charger to cover 12 to 48v and 100a. Its taken about 6 months so far. The problems its not as simple as it seems to get them to work 100% with cell sizes from 10ahr to 200ahr.. Im not going into what we have found here. Just saying the charger needs to be able to alter certain paramaters when charging different cell sizes.
    We have found mostly the reasons now that car manufacturers are using cells below 10ahr..

    For very small systems below 50ahr total battery size a good PWM solar charger works perfectly. very easy to set and forget. Ones like the Chinese cops of the old Steca ones.. .. You only need add a simple low voltage cut off switch to stop any cell going below 2.3v... In fact I have not found a MPPT charger that will do as well. If there is it hasn't been given to me to test and verify
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #5
    Re: My Programable Solar BMS for any Lithium cells and Supercapacitors

    CooL stuff ! Nice videos, too.

    Keep up the good work.
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #6
    Re: My Programable Solar BMS for any Lithium cells and Supercapacitors
    john p wrote: »
    3.92v is to high a charging voltage.. 3.9 should be a cell balancing set point. And a full charge set point of 3.6v.

    Are you sure 3.9 isn't a typo? Together, assuming balance, that would take a nominal 12v / 4S pack up to 15.6v (massive lithium plating) where 14.4 / 14.6 is about the norm for lifepo4 for a full charge, which usually isn't necessary. 90% SOC (14.10 or so) is just fine, as that last 10% contains very little power.

    Or are you purposely driving a bms overvoltage and shunting / diverting current all around?

    Part of the issue may be the quality of your cells and/or if the manufacturer / distributor is custom testing each cell for both capacity and internal resistance and matching them. That takes more resources, time, and money. My contention here is that a 12v / 4S (or 8S for 24v) that does not contain carefully matched cells to begin with, seems to need a fulltime bms to make up for the loss of factory quality on the end-user side.

    End user matching solely by voltage is ballpark if the internal resistance is not matched from the factory as well.
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  • electrodacus
    electrodacus Registered Users Posts: 3
    #7
    Re: My Programable Solar BMS for any Lithium cells and Supercapacitors

    So many question.
    I hope to clarify as many things as possible. Thanks all for the feedback.
    I also see the thread was moved to a different category.

    zoneblue
    I was also expecting someone else to do something like that so I can use I will have payed anything not to waste so much time.
    It is designed for my offgrid house and it works for me but I know most people want way more power here.
    40A charging and 80A discharging is about as much as you want with 12V and 24V systems mine is 24V
    400Ah battery is no problem for the SBMS4080 as long as the solar array is within 1000W and load or inverter max 2000W overcurrent protection is actually set at 48A charging 96A discharging and shortcircuit can be set as high as 192A and fully programmable delays for both current limit and short circuit.
    My max load on inverter is 1800W AC inverter efficiency 92% at this load so it will work perfectly for me and this works at most a few hours a day for cooking the rest of the house is on 24V DC.
    The main chip takes care of the battery I can not give as of now more info on that the 32bit ARM microcontroller is for programing the main chip reading and displaying data and measurements on the LCD and maybe data logging.
    I worked 6 years in R&D designing airbag control unit for cars I know a lot about safety electronics but getting certification for this will to much money compared to the level of interest so it will not happen at least not unless a larger company wants to take my design and build in much large volume.

    PNjuntion

    Is what I use now a programmable PWM controller but is not fine no cell monitor or balancing and no capacity measurement not a great idea.
    This is not a business I designed this for me since there is nothing on the market. I've seen Genasun and is not the same thing is just a simple PWM controller no BMS.
    This is a fully programmable BMS so any type off battery will work not just LiFePO4 over 30 parameters can be changed see the 38mint video for more details.
    It can go as low as 0.8V for use with supercapacitors and as high as 4.8V for any possible future Lithium chemistry.
    There is also cell balancing all the time and yes max charge voltage for LiFePO4 is 3.6V not more you can set 3.54V if you want (fully programmable)


    John p
    See the answerers above is a fully programmable BMS so any type of Lithium will work with custom parameters there will also be some predefined parameters for most common chemestry.
    The connectors can handle 20A (300V) but are 4 used for battery 4 for load and 2 for PV all positive the negative is common and conected outside.

    boB
    Thanks for watching the video.
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