The Electrodacus SBMS thread (SBMS0, DSSR50, etc)
- Thread starter Dzl
- Start date
To make a correction my 2 Tesla system is 2x 6s or 12s 24 volts system (parallel batter) and thus why i need to use 2 SBMS0s and series the automation which makes this a 12s system.
My system is properly protected with full control of over charging, under voltage, under temp charging, over temp shut down. I also have automation to mmain warming the battery in low temps.
Unfortunately the Electrodacus SBMS0 can not be configured for 48 volt systems, so you need to look at Tiny BMS, Chargery BMS, and Rec-BMS.
If you can do 2x6S for your 24V Tesla system, why not 2x8S (series-connected) LFP banks for 48V? All either SBMS would see is an 8S/24V system, no? Or am I missing something?
Sure you can do 2x 8s 24 volt LifePo. I thought you could do 2x 6s 48 volt Tesla or 2x 8x 48 volt LifePo the same way, but when you connect the batteries in series the SBMS0 is limited to 36 volts max so it cant handle 48 volts. I have no idea if you can wire the balance leads the same way and have it work with a 48 volt system. It may burn something up in the SBMS0. It would have to be tested, but i dont think it is possible,
Dacian has no plans to engineer a 48 volt 16s BMS as he says he cant match PV panels for the needed 60 volt charge voltage. So 48 volters need to purchase much more expensive 48 volt BMS systems,
OK, connecting some dots btw what you mentioned in this post and previous, and schematic you sent me. Each cell in your two 6S Tesla packs is 4.167V (3.6V nominal) for two 24V-ish packs (and 160Ah) ... connected to each other in parallel (for a total of 320Ah). One SBMS for each pack to balance cells within each. Packs connected in parallel to balance the two packs ... effectively balancing all 12 cells together, yes? For some reason I thought your 2 Tesla packs were connected to each other in series. Just not familiar w Tesla batteries. Suppose you can't do that because, while cells w/i each pack are balanced, the two halves could become unbalanced and SBMS couldn't see that.
How does the SOC reported on your 2 SBMS's work when you've got both EXTIO3s connected to your 300A load shunt and both EXTIO4s connected to your 100A charging shunt? Did you just configure each SBMS for 6S but double the Ah of the cells it balances (so each thinks it's measuring charge for a 320Ah bank)?
Last edited:
yes my 2 teslas are connected in parallel for 24 volts. A series connection would make it 48 volts. When a battery is in parallel and possibly at different SOC the two will equalize to each other over time. To aid in equal charging and discharging i have made sure all battery cables are of equal length to achieve equal resistance. The BMS will equalize any individual cell differences.
The SoC read out is equal on each SBMS. I do have separate 300 amp 75mv shunts for each battery and i have had some discrepancies on the readout of outgoing power so I may adjust my shunt box to combine both positive cables to one out going shunt and one incoming shunt and then to one 200 amp fuse.
Still a work in progress, but fully functional system and individual cell protection on 12s.
Tom
Following up on #s below and the apparent discrepancies noted by @BiduleOhm
>>This is what I wrote to Dacian<<
Looks like "Gain at PV Panel" is really "Loss at PV Panel" if you're using MPPT. Numbers seem to represent "what's the percentage loss if I'm on MPPT?" vs "what's the percentage gain if I'm on SBMS?" The gain for 60 cell panel is really 11.79% 4.77% 0.00% 0.00% (for 5C, 25C, 45C, 65C respectively) moving from SBMS to MPPT, not 10.54% 4.55% 0.00% 0.00%. Discrepancy is even bigger for the 72 cell: 34.43% 26.05% 18.09% 10.48% vs 25.61% 20.67% 15.32% 9.49%. A minor point but it's a little confusing to folks.
Also, how do you calculate "Gain after DC-DC"? Not sure what those #s represent.
>>His reply (edited slightly for clarity)<<
I probably added too many values to that MPPT gain table so I will try to explain what you see there.
An MPPT is nothing more than a DC-DC converter controlled by a microcontroller with a proper algorithm to get the max power point. Since a DC-DC converter it is not 100% efficient, there is some loss in the DC-DC conversion, usually 92 to 95% efficiency for quality MPPT (this is the DC-DC efficiency not to be confused with MPPT algorithm efficiency that some like to list as over 99%).
The so called Gain at PV panel is the theoretical extra power available if you had an ideal MPPT with 100% efficiency, while gain after DC-DC is the net efficiency after the MPPT/DC-DC converter efficiency is considered and I was very generous there and used 97% efficiency MPPT.
The SBMS uses just a solid state switch plus ideal diode and so since there is no DC-DC conversion and transfer efficiency is almost 100%, it is the same as if you where to connect the panel directly to a battery that, in the case of 8s LiFePO4, is always around 27V while charging until is fully charged, when it is above 28V. But that is just for a few seconds max minutes so most of the time it is 27V, thus the voltage used there in the table.
You can take the I-V curve for the exact panel I used there from the datasheet at get all those numbers I put in that table.
You will not use an MPPT with a 60 cell PV panel as it will most likely not work, other than in cold winter days, as for most MPPT, voltage of the panels need to be higher than the battery voltage so, if not, that gain will be 0% when panels are hot in spring, summer but they will perform much worse than SBMS with DSSR20
Of course you will be using 72 cell panels if you where to use an MPPT so that at least it will work all the time and you will have some small gains even if still far from a cost effective solution as I explained in the video.
Hope I answered your questions but if not feel free to ask for more clarifications.
So, there you go. Not much to go on to try to reverse engineer the calcs beyond what I was able to above. But at this point, we can go back and forth on the theory and data sheet calcs until the cows come home (oh wait, I think I hear them coming now!) So, alas, that is it from me on this topic until I see some test results.
>>This is what I wrote to Dacian<<
Looks like "Gain at PV Panel" is really "Loss at PV Panel" if you're using MPPT. Numbers seem to represent "what's the percentage loss if I'm on MPPT?" vs "what's the percentage gain if I'm on SBMS?" The gain for 60 cell panel is really 11.79% 4.77% 0.00% 0.00% (for 5C, 25C, 45C, 65C respectively) moving from SBMS to MPPT, not 10.54% 4.55% 0.00% 0.00%. Discrepancy is even bigger for the 72 cell: 34.43% 26.05% 18.09% 10.48% vs 25.61% 20.67% 15.32% 9.49%. A minor point but it's a little confusing to folks.
Also, how do you calculate "Gain after DC-DC"? Not sure what those #s represent.
>>His reply (edited slightly for clarity)<<
I probably added too many values to that MPPT gain table so I will try to explain what you see there.
An MPPT is nothing more than a DC-DC converter controlled by a microcontroller with a proper algorithm to get the max power point. Since a DC-DC converter it is not 100% efficient, there is some loss in the DC-DC conversion, usually 92 to 95% efficiency for quality MPPT (this is the DC-DC efficiency not to be confused with MPPT algorithm efficiency that some like to list as over 99%).
The so called Gain at PV panel is the theoretical extra power available if you had an ideal MPPT with 100% efficiency, while gain after DC-DC is the net efficiency after the MPPT/DC-DC converter efficiency is considered and I was very generous there and used 97% efficiency MPPT.
The SBMS uses just a solid state switch plus ideal diode and so since there is no DC-DC conversion and transfer efficiency is almost 100%, it is the same as if you where to connect the panel directly to a battery that, in the case of 8s LiFePO4, is always around 27V while charging until is fully charged, when it is above 28V. But that is just for a few seconds max minutes so most of the time it is 27V, thus the voltage used there in the table.
You can take the I-V curve for the exact panel I used there from the datasheet at get all those numbers I put in that table.
You will not use an MPPT with a 60 cell PV panel as it will most likely not work, other than in cold winter days, as for most MPPT, voltage of the panels need to be higher than the battery voltage so, if not, that gain will be 0% when panels are hot in spring, summer but they will perform much worse than SBMS with DSSR20
Of course you will be using 72 cell panels if you where to use an MPPT so that at least it will work all the time and you will have some small gains even if still far from a cost effective solution as I explained in the video.
Hope I answered your questions but if not feel free to ask for more clarifications.
So, there you go. Not much to go on to try to reverse engineer the calcs beyond what I was able to above. But at this point, we can go back and forth on the theory and data sheet calcs until the cows come home (oh wait, I think I hear them coming now!) So, alas, that is it from me on this topic until I see some test results.
*queue the curtain*
Still doesn't explain the gain at PV panel numbers... and that's what I was talking about.
It's not that I want to be picky, we're talking a 25 % difference here, and that was big enough that I saw it just reading the table.
Edit: and the gain after DC/DC is still incorrect as it's based on the other percentage.
It's not that I want to be picky, we're talking a 25 % difference here, and that was big enough that I saw it just reading the table.
Edit: and the gain after DC/DC is still incorrect as it's based on the other percentage.
Last edited:
*sigh* ok, last one for real this time ... I was able to reproduce his "Gain at PV Panel" #s in my email to him (see above). They're really "Loss at PV Panel" if you're already on MPPT and move to SBMS, not the other way around. I think it's more a language issue than a math one. The #s are correct if you flip the comparison (numerator/denominator) he's stating his #s represent. The differences, however, don't really impact his conclusion (at least the theoretical one) too much though.
Ahhh ok, now I see.
So, voluntarily using the opposite way around to make numbers look better while maintaining it's a gain in the legend... I'm truly disappointed to see that from an engineer, usually it's the marketing dept. who does that.
So, voluntarily using the opposite way around to make numbers look better while maintaining it's a gain in the legend... I'm truly disappointed to see that from an engineer, usually it's the marketing dept. who does that.
Last edited:
no ... just a language issue i think ... no deceit
I think you are assuming ill-intent/intent to mislead where there isn't any. My impression of Dacian is that he is quite a straight up, honest guy, open guy. I agree that chart is at best confusing and somewhat misleading, but I think as @Dhowman noted its just a simple mistake/poor wording. If he was trying to mislead, I don't think he would post the raw data that shows his mistake right next to the mistake.
I might be wrong, but I think the graph Dhowman posted is a screenshot from a 5 year old youtube video, which would explain why the chart hasn't been (and can't easily be) corrected. If I am wrong and the chart is posted somewhere, than I definitely think he needs to correct it.
I think he tries to address Dhowman's first question:
Dhowman said:
Here:
Dacian said:
But I think he misses the point about mistaking % loss and % gain.
We just had a few emails exchange where I asked him directly why the percentages in the video don't match what I calculated and he avoided the question by using the reverse formula to show the 25.6 % of the table was correct and saying that anyway it's irrelevant as it's for a -30 °C ambient temp and it's for the 72 cells panel (I used the 239/321 W example).
Yeah... excepted the problem is the same for all the percentages, whatever the temp or the panel.
I don't like when someone is trying to BS me, but oh well, I'm more disappointed than anything else, no point continuing. So I'll stop writing about the SBMS.
NB: that's just my personal opinion, feel free to think otherwise, I'll not hate you for that
Yeah... excepted the problem is the same for all the percentages, whatever the temp or the panel.
I don't like when someone is trying to BS me, but oh well, I'm more disappointed than anything else, no point continuing. So I'll stop writing about the SBMS.
NB: that's just my personal opinion, feel free to think otherwise, I'll not hate you for that
I think the choice between MPPT vs PWM is all about the wires, and not about efficiency. From http://www.bogartengineering.com/support/faq.html if you can match the panel voltage to the battery bank, the only situation when the MPPT beats PWM is in rare situations (low temp, low battery voltage, which might not apply with LiFePo4). So, my understanding is the only reason to use MPPT is to run a higher panel voltage so that the wiring coming from the panels to the charge controller is thiner/cheaper.
I have purchased the SBMS0 and 4 DSSR20s (16 12v 100w panels 2P2S 4DSSRS).
I don't like his WiFi solution though. It is an access point, which would be cumbersome to the point of useless. I would have to disconnect my phone from wifi, then connect it to the SBMS, then reverse that whenever I was curious about the battery and solar.
I emailed Dacien and he feels that it should be possible to develop new firmware for the WiFi controller (ESP20) that will enable it to work as a client. If anyone else wants this, or is eager to do, this please contact me. I am a pro software developer and plan on doing it. I don't want to have duplicated effort. Depending on what I find and do, I plan on making this solution available to others and/or Dacien.
FWIW, if I was designing a system today, I would do it like Dacien's but, I would make the SBMS0 headless. It would have no physical user interface. It would start up as a wifi AP. You connect to it, and using the browser, switch it to your existing wifi network. The browser/wifi would be the UI for controlling and monitoring everything.
I don't like his WiFi solution though. It is an access point, which would be cumbersome to the point of useless. I would have to disconnect my phone from wifi, then connect it to the SBMS, then reverse that whenever I was curious about the battery and solar.
I emailed Dacien and he feels that it should be possible to develop new firmware for the WiFi controller (ESP20) that will enable it to work as a client. If anyone else wants this, or is eager to do, this please contact me. I am a pro software developer and plan on doing it. I don't want to have duplicated effort. Depending on what I find and do, I plan on making this solution available to others and/or Dacien.
FWIW, if I was designing a system today, I would do it like Dacien's but, I would make the SBMS0 headless. It would have no physical user interface. It would start up as a wifi AP. You connect to it, and using the browser, switch it to your existing wifi network. The browser/wifi would be the UI for controlling and monitoring everything.
Sign me up!
Raspberry Pi is in the works for my system that would cover that functionality for SBMS, but would be nicer if it was a WiFi client vs AP.Would require a nearby WAN, which isn't always available on vehicle based systems which a lot of peeps use this for (cuz it results in a MUCH smaller overall SCC physical footprint). BT might be better. Both would be ideal. Animated screens like ones on Victon Phoenix display would be ... well ... nirvana.
Sign me up!
Would require a nearby WAN, which isn't always available on vehicle based systems which a lot of peeps use this for (cuz it results in a MUCH smaller overall SCC physical footprint). BT might be better. Both would be ideal. Animated screens like ones on Victon Phoenix display would be ... well ... nirvana.
I'm weighing adding a raspberry Pi to my system with Victron's Venus OS on it (this is why I was asking about whether the victron Smartshunt could be used on the positive side in that other thread). I'm not sure if its worth the trouble because most of the info and monitoring it provides would be redundant with the info the SBMS0 provides. But the Victron monitoring does have some advantages, I like the cleaner more intuitive visually intuitive monitoring screens, I like that the data can be viewed locally or remotely through VRM and I like the idea that there is a whole family of products designed to communicate with the VenusOS software.
It would probably provide very little actual utility on top of the SBMS, but I like to tinker, and I like gadgets, and I like data, and the cost of Pi is pretty minimal.
