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Forum Index : Microcontroller and PC projects : Solar BMS dev board ARM cortex M0
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electrodacus Newbie  Joined: 30/03/2014 Location: CanadaPosts: 39 |
I'm new on this forum. I live off grid since last year use solar and wind for power and store my energy in LiFePO4 batteries. There was no Solar charge controller for lithium so I build one. It will be open source and if enough people are interested (currently on Kickstarter) I will do video tutorials on micro controller programming (ARM cortex M0) in this case since this is what Solar BMS is using but is also the best microcontroller at this moment low power consumption low cost and high performance. There will also be hardware design tutorials including PCB design so you will be able to design a similar product in very short time with all the available information and tutorials. 8-bits microcontroller are history :) I designed my first dev board with AVR about 11 years ago back then it was the best option but is not any more. Here is a 3D rendering of the Solar BMS 
I will try to answer any questions you may have. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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bigmik Guru  Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Welcome Electrodacus, It looks very well designed.. Can you provide a few more details.. I cant believe that is a 3D rendering, even the screws are all at different angles. I assume (but just a guess) that BMS stands for Battery Management System..?? I have 5kw of Grid connected solar panels but when the `war begins' I might need to go off grid. Where does this connect and how does it work? What would I need to change from Grid to Off Grid? Besides a cubic metre of batteries? Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
I picked up on that too, but I'm pretty sure it is though. The black screws look artificial and the LCD is working without any wires connected. If you ever swap to totally off grid you'll likely need a complete change of attitude to electricity consumption or put in rather a large battery system that has to cope with "over night" and grey days. The life style change for us wasn't too difficult but if you are accustomed to "the comfortable life" where supply > demand, it can be a bit of a shock at first. Don't try and rely on wind power to fill the grey gaps as overcast days often mean calm days. David M. |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Mobi, It is really a point of interest as I cant see me really going off grid.. I sell my excess at 70c per kw and buy any I need at about 35c peak and 18c off peak so I, over the course of a year, pay nothing for electricity and chop about half of my gas bill (excess credits to pay that). In about 10 years when Victoria ceases the Premium Feed in Tariff (not available anymore) and I revert to what is now a measily 8c (less than 1/4 what they charge you for peak (seeing generation is ALWAYS peak time) I will have no interest at all in selling any.. I may even offer extension leads to my neighbors  (No I wont).
But I may look into a battery backup system to run the house overnight (storing our excess generation) but maybe that is too difficult/expensive to implement. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
Except for the LCD that is a photo from the real unit the rest is 3D. It will be quite a lot to say about the Solar BMS (Battery Management System) you can see full spec and more details here https://www.kickstarter.com/projects/electrodacus/open-sourc e-programmable-solar-bms-development-boa?ref=live But yes the idea is to replace existing solar charge controllers those that work with 12 and 24V Lead Acid with this Solar BMS and Lithium batteries. Most of the LiFePO4 batteries can do over 3000 cycles at 100% DOD and at the current cost are way less expensive than Lead Acid. The get around 10 to 15 cent /kWh stored during their lifetime still the most expensive part solar panels at 1$/Watt in my location can get to about 3cent/kWh over 25 years amortization period. I can go in to details on how this is calculated. I'm just preparing a video on the difference in cost between Lithium and Lead Acid the people still did not realized that Lead Acid is much more expensive for energy storage. A good way to reduce the battery size is to have also a wind turbine if there are good wind resources in the area. I live off grid since last year and I can manage with about 60 to 90kWh/month production is a bit higher at 100 to 120kWh/month but if not used is lost. I have under 1kW of solar panels and a 300W wind turbine but is both sunny and windy here in the middle of Canada. Dacian. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
Is not hard after you crate one screw just copy and paste and rotate random the screw to look more realistic. The LCD is the only one that is a photo from the real thing. Energy efficiency and conservation are an important step if you decide to go off grid. I'm originally from Europe where energy efficiency and conservation was more important so there is no compromise for me or life stile change. In my case overcast days are quite windy so it did help to have both but it depends form location to location. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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graynomad Senior Member  Joined: 21/07/2010 Location: AustraliaPosts: 122 |
This is a VERY interesting project. I've been living totally on solar for about 15 years, still AGMs but when they fail I might swap over to LifePo4. I've been meaning to develop something similar for ages but there are so many other projects to do. So I figured that if I wait a while someone else will do the work :) At first I though this gadget couldn't work because with these batteries you have monitor the voltage on every cell and I didn't notice the IDC connectors. Then I saw the header and "Cell 1 .. 8" so I assume those connections go to each cell. I take it electrodacus that you do not bother with equalising the cells, it seems to be a misconception that this is required after the first equalising which you can do manually. There is a forum dedicated to LifePo4 control, these guys have several DIY systems that involve the Junsi battery monitor. It all seems to work well but I think it's a bit of a bodge job and I'm sure that a dedicated box that does everything would be of real interest to them. One question, because of the different charging characteristics of LifePO4s it's common to have spare power available half way through the day or even earlier (a real shock to people with LA batteries) and people seem to like to dump that power into a hot water system or other storage device. Can you add a control output that can be used for such a purpose? PS: I'm also pretty keen on LPC processors, I (mostly) ported the Arduino core libs to an LPC1227 last year. Rob Gray, AKA the Graynomad, www.robgray.com |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
I also waited for someone else to do the work but it did not happen :) Yes I do monitor each individual cell and threshold are fully programmable so any type of Lithium battery will work. I also do cell balancing max 100mA but with timing not just simple thresholds so it can balance any battery size. There is a bit of imbalance on any battery my 100Ah LiFePO4 from GBS needs about 1 or 2Ah each 2 months but if I use this Solar BMS I will never need a manual balance except maybe at first installation. One important difference from car BMS is that this needs to work 24h a day not just when the car is running or charging and their BMS uses a lot of power mine is extremely low power at just 1mA with a 24V battery this is fully working monitoring the pack and updating the LCD. Is very common to have spare power actually I have right now at 11:16 in the morning but I use that for cooking most of the time. I cook with electricity and try to cook (mostly my wife :)) when is sunny so I use the power directly from there. But there is a optoisolated serial port and the TX pin can be used to control a FET or relay to divert power to a resistive heater if you need that. I use the ST version of ARM cortex M0 because of low power but other manufactures where quite close. I worked with AVR even designed a dev board about 11 years ago but now AVR is just history in my book :) Here is a photo of my dev board from 2003  http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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| Privatteer Newbie Joined: 09/06/2012 Location: AustraliaPosts: 39 |
Couldn't get link to work. Edit: But saw signature link afterwards. Unless the system is capable of detecting shunts running at max current or high cell voltage and backing off the charge I would say 100mA is not enough. The ones on my system are 800mA and they have failed once to keep up after several bad days of weather tripping the high voltage cell cutout. There has been a few times I've checked them and been indicating fully active. Then again going by image of unit and terminal size perhaps 10A max? Edit: OK 40A by youtube video. Have you considered 16 cell,48V systems? At this stage in Australia I would not say Lipo/LiFeP04 are cheaper but its getting a lot closer. It would be nice to see a system designed from ground up for lithium. FYI, LiFeP04 16 cells, Morningstar TS-MPPT-45, "evpower" cell shunts and a cobbled together picaxe high/low voltage disconnect. |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
I seen that the link to kickstarter is broken but you found the one form my website. How do you edit a post on this forum? I can't see any edit button. There is cell monitor for individual cell once a cell got to limit say 3.6V it will stop the charge and continue balancing at 100mA for the highest cell as long as it is in between the set limits for balancing and for a max time also programmed in seconds or minutes based on battery capacity. Balancing is a bit more intelligent so 100mA is more than enough for any battery size. Right now I have a 100Ah 8 cell GBS battery for my house and this I currently balance manually once every two months or so and there is no much difference between cells just over 1Ah between the highest and the lowest cell. Charge is done at max 0.35C and discharge between 0.5 and 0.8C under 2000W so there is no reason to have much imbalance. With individual cell voltage and charge disconnect there is no chance to go over the set threshold 3.6V or 3.55V if you prefer. So battery is absolutely safe. Each terminal is designed for continues 20A 3.3mm2 or AWG 12 conductor and there are two for charging so 40A and 4 terminals for load so max 80A continues. I got my LiFePO4 the A123 System two years ago form China at 19$ for the 20Ah cells and that make it 2.5x less expensive than the best Lead Acid during the life time I will soon have a video on youtube about is almost done. I took a look at picaxe. So are you cutting charging and discharging based on total battery bank voltage or individual cell? Thanks for the feedback. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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| graynomad Senior Member Joined: 21/07/2010 Location: AustraliaPosts: 122 |
Re balancing, I've not done any of this yet but on the LifePo forum I belong to a lot of people have and consensus is that you should manually balance when you first get the cells, after that there is no point. People have been running for long periods and tested each cell to find just a few mV difference. As I understand it they monitor each cell during charging and kill the current source entirely if any of then get to the max, repeat this for a while and eventually they all catch up. It may be quicker to balance but it's not as easy to do. Now all that said, AFAIK these guys do not have very sophisticated systems whereas a gadget like this could easily do some smart balancing which has to be better. Rob Gray, AKA the Graynomad, www.robgray.com |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
Is not a bad idea to do manual balance before you install the cells for the first time since there may be large differences initially. Batteries no matter how good have small differences in capacity and internal impedance so with no balance the difference between cells will get larger with each charge / discharge cycle. That is not a problem if you at least have a good BMS that monitors each cell and cut the charging discharging when any of the cell gets to the limit. The only problem is that in time it can be months you will lose some capacity because of the imbalance (your pack capacity is only as good as the lowest capacity cell). Then in some situations you can do manual balance very couple of months and that can be OK for some applications. But you still need a good BMS you can not just stay and manually monitor your cells for every charge and discharge. That will take a huge amount of time and you may not pay attention or forget to monitor and damage your cells. You probably don't care if your battery is just an 20$ RC battery but if is a few thousand dollar battery for an offgrid setup you will be quite sad :) Even a few hundred dollar eBike battery is not that cheap to afford a new one. In conclusion balancing is not vital and probably dose not take much time to rebalance manually every few weeks or months but individual cell monitoring is for sure necessary and manually doing that where you need daily charge is not an option. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All Well I am in the market for a new BMS for my caravan. It has 800 Watt of solar and 200AH of LiFePo4 batteries. Without reading all the info can you tell us what the expected retail price would be ? Regards Regards Hervey Bay Qld. |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
You did not mentioned how many cells in series if is lees than 8 then it will work great for you. The Solar BMS is currently on Kickstarter see this link Solar BMS on Kickstarter If for some reason the link dose not work then just search "Solar BMS" on Kickstarter There are a few options in there all include the 9% Kickstarter fee and international shipping. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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| Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All I have 8 cells configured in 4 sets of 2. Currently using 4 cell pairs monitoring. I can see some limitation on my side. When I use the Microwave in the van on the Inverter, it draws 150 Amp. This means that the Inverter is connected direct to the battery, and thus wont be part of any usage calculations. I have a Xantrex Lite for that at the moment. My current BMS wont allow the current that I have available, and so charging takes longer as a result. To be attractive to the RV market , charging current must reach 60A at least. We (Retired Grey Nomads) are not just using solar for a few led's and TV anymore. I use a standard Toaster in the morning (90 Amps) , my wife puts her porridge in the Microwave (150 Amps) , the coffee maker comes on at 50 Amps. And then some of us are using spare capacity to heat water (saves gas). If I had 60 amp capacity, then a couple of hours of full sunlight and I am back to near 100 % charged and I can survive a couple of cloudy days. I am like you, if I cant get a total clean solution, then I will build my own. At the moment there are too many parts to my system. Regards Regards Hervey Bay Qld. |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
I live offgrid and the Solar BMS is designed for my needs. The difference is that I have a 24V setup so current is half for the same power. 24V 80A is also enough 2000W for microwave, oven, cook-top of course not all at once but since I can use 2000W from the battery and inverter is 92% efficient I have exactly 1800W available at the AC outlet that is also the limit for all 110 - 120V devices. Solar charging is around 30A right now but again 24V 8s LiFePO4 If you can get an 24V inverter then you can probably convert to 24V and arrearage the cells for that. Of course this Solar BMS will be Open Source so if you want you can modify to fit your requirements for 12V but I think is easier to switch on 24V. Actual over current limits are set at 48A charging and 96A discharging so 40A and 80A can be used continuously with no problem. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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| graynomad Senior Member Joined: 21/07/2010 Location: AustraliaPosts: 122 |
I see this got funded Dacian, good luck with it. Despite not having much spare money right now I was about to back just to help get it over the line because it seemed to stall at about $7000, but it seems others were thinking the same and there was a last minute rush :) Rob Gray, AKA the Graynomad, www.robgray.com |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
Thanks for the support. Yes there where a few waiting for the last minute and some that increased the pledge. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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