DIY BMS

[Mars]

I am not satisfied with the BMSs that are out there so I decided to make my own.

Here is a list of some of the features I would like:

1. Maintain battery balance.
2. Low temperature charging cut off.
3. High temp load shedding.
4. Display for all voltages (like the ISDT BattGo BG-8S Battery Meter).
5. Charge counting battery capacity display.
6. Amp and energy monitoring for solar charging, AC inverter load, DC loads.
7. At least three levels of load shedding.
8. Output data for monitoring via network connection.

Anything I am forgetting?

Mars

 

[svetz]

Hey Mars!

Interesting idea. Here's my wish list:

• Active balancing rather than resistance draining would be nice.
• Some sort of light/indicator to know while the charging cycle was active (always unsure when the charging cycle is complete)
• A health indicator for when/if the BMS dies.
• Low voltage cutoff
• Separate charging/discharge (some BMSes limit discharge amps as they have a common feed)

 

[Mars]

• Active balancing rather than resistance draining would be nice.

I thought about that for awhile and my gut feeling is that it is probably not worth it. I would like to collect some more data to test that assumption and quantify the actual energy that is wasted.

• Some sort of light/indicator to know while the charging cycle was active (always unsure when the charging cycle is complete)

9. Indicator when charging complete.

• A health indicator for when/if the BMS dies.

10. Heartbeat monitor on BMS

• Low voltage cutoff

That is part of 7. Load shedding. My idea is you start shedding non essential loads first and never get to the total low voltage cutoff. I want the BMS to stay running so when the sun comes up, the system will reboot itself. The last step of the load shedding would need to cut off absolutely everything.

• Separate charging/discharge (some BMSes limit discharge amps as they have a common feed)

I feel that is such an obvious requirement that I did not need to list it.

I did not mention it but my plan is to do this as an open hardware and open source (GPL) software project so others can copy it.

Mars

 

[anderm15]

Hi Mars,

I am also interested from the standpoint of learning. I would be interested in your progress as you work through this project.

My main goal it to build a BMS for a system that doesn't have a readily available charging source (stand alone battery, no solar or other charge source), so my requirements would be different mainly oriented around power consumption.

I would be interested in sharing sources, there is a lot that can be found on google but taking time to sift through everything is a bit overwhelming.

Do you plan to post through out the project? To GitHub potentially?

 

[Mars]

...
My main goal it to build a BMS for a system that doesn't have a readily available charging source (stand alone battery, no solar or other charge source), so my requirements would be different mainly oriented around power consumption.
...
Do you plan to post through out the project? To GitHub potentially?

That reminds me of another criteria.

11. Manage multiple energy sources including solar, utility grid, generator, vehicle alternator.

At this point, it is still just a concept. I don't have a good feel for how much effort this will be or exactly how it will be done. It could be just putting together a system using existing available components and existing software. If that is the case it would probably be just a web page with instructions on where to get the parts and how to set it up.

I plan to do more research this weekend and develop a plan.

I started taking a good look at the ISDT BG-8S as a potential candidate for collecting battery information. It has a data connection via BattGo. But unfortunately BatGo is proprietary and is not suitable.

A good candidate for the starting point is an active balancing chip set from either TI or Linear Technology.

Mars

 

[Aptiva]

Would using a Raspberry Pi's GPIO keys and WiFi/BT features be feasible for logging and control or are you trying to use something arduino based?

 

[Craig]

Im working on same sort of thing gonna start playing with some of these https://www.mouser.com/datasheet/2/698/isl94212-1529392.pdf

 

[Mars]

Would using a Raspberry Pi's GPIO keys and WiFi/BT features be feasible for logging and control or are you trying to use something arduino based?

My initial concept was to use an arduino for the basic BMS features and a Beagle Bone for data logging and load management part. But I quickly realized that I should start with a integrated circuit IC that includes basic BMS features. I am still collecting information on what type of chips are out there.

 

[Mars]

Im working on same sort of thing gonna start playing with some of these https://www.mouser.com/datasheet/2/698/isl94212-1529392.pdf

That is interesting. So how are you going to "start playing"? Buy an evaluation board?

 

[Craig]

That is interesting. So how are you going to "start playing"? Buy an evaluation board?

ihave the chips on order and one of these programmers to start playing with. https://www.aliexpress.com/item/32995692408.html?spm=a2g0s.9042311.0.0.21ba4c4dCAXh8G

I'm pretty positive im clueless on how to use this stuff but its all about learning anyhow.

 

[Aussiecroc]

Most of what you have described is in this product. Id love to know what others think. A mate of mine who lives close by has run his entire house using one of these and a bank of lifepo4 for 4 years now. No problems as yet. The data % yadayada it puts out is huge. Controller, battery meter, balancer, cut offs all in one.

ElectroDacus

 

[jezohare]

Most of what you have described is in this product. Id love to know what others think. A mate of mine who lives close by has run his entire house using one of these and a bank of lifepo4 for 4 years now. No problems as yet. The data % yadayada it puts out is huge. Controller, battery meter, balancer, cut offs all in one.

ElectroDacus

thank you for your info, its nice to know your mate has no problems with his electrodacus for 4 years. I just recieved 2 sets of SBMS0 & DSSR20 chargers which is a modular system not requiring any heatsinks / fans. I have not installed them yet. After reading the manual I just found out is its also compatible with victron mppt & several inverters so its very flexible.

 

[gnubie]

I was impressed with the SBMS the first time I saw one on youtube, BigClive channel was it I think. There's really only one thing to be aware of, they are PWM controllers, not MPPT.

 

[Aussiecroc]

@jezohare is it true that this new SBMSO turns the digital relays (is that what they are?) on and off many times a second (PWM?) and monitors that level according to how the batteries are going?

I know a group of RV and house guys here who get a plasmatronics pl20 to replicate it's action through arrays of panels being turned off and on the same as the 20 amp first array with ssr's - all going to the one battery. They believe that PWM is great for lifepo4.

 

[gnubie]

Interesting, RV with the limited space for panels is one place I would have thought that using a MPPT controller would be considered essential. PWM works but you are basically throwing power away by running the panels off Vmp, etc.

 

[John Frum]

1. At least three levels of load shedding.

Can you flesh this out a bit?

 

[Mars]

Can you flesh this out a bit?

As an example, I would want to shed water heating, refrigerator, water pump, lights, controls in that order.

 

[John Frum]

As an example, I would want to shed water heating, refrigerator, water pump, lights, controls in that order.

So the BMS has programmatic control of the load center breakers?