I think parts of this conversation would be better moved over to the Heltec BMS thread, or start a new topic with your questions, we are taking this conversation pretty far off topic in the SBMS thread.
The Electrodacus SBMS thread (SBMS0, DSSR50, etc)
- Thread starter Dzl
- Start date
That's understandable, their website is pretty shitty and feels like an afterthought. But the post directly above yours had the correct, direct link to the Active Balancing BMS. Hopefully that helps clear up any confusion.
Here are links to the Active Balancing BMS:
Heltec Store on Aliexpress
Heltec Store on Alibaba
Back to the topic of the SBMS0 I recently learned became aware that while the SBMS0 has low temperature protection, charging and discharging cannot be set or controlled separately which significantly limits its utility.
In his usual style, Dacian has a well reasoned but narrow and rigid argument as to why low temp disconnect is not the proper way to solve the predicament of LFP in low temps (he feels avoiding low temps, insulating, and/or heating are better solutions). While I don't disagree with his logic (actually I was fairly swayed by it), I don't think his argument eliminates the usefulness of low temp disconnect as a safety measure, and protection layer. This will not be a problem for many people, but I do hope this is addressed in future iterations of the SBMS0.
Some relevant info here and also in this thread (read the second link if you want to here Dacian's reasoning).
In his usual style, Dacian has a well reasoned but narrow and rigid argument as to why low temp disconnect is not the proper way to solve the predicament of LFP in low temps (he feels avoiding low temps, insulating, and/or heating are better solutions). While I don't disagree with his logic (actually I was fairly swayed by it), I don't think his argument eliminates the usefulness of low temp disconnect as a safety measure, and protection layer. This will not be a problem for many people, but I do hope this is addressed in future iterations of the SBMS0.
Some relevant info here and also in this thread (read the second link if you want to here Dacian's reasoning).
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sremick
Mostly competent. Knows enough to be dangerous
I'm planning on incorporating heating system in my kit to address this. While I don't ever expect to have the kit exposed to conditions that would require it, I like the failsafe of having it there just in case. I have a number of thin-film 12V heating elements that will go in-between the cells, which will be controlled by PID code on the Arduino along with separate temperature sensors (although the Arduino will also be getting temp info from the SBMS itself to do with however I see fit).
Likewise, a PWM fan will also be controlled by the Arduino to handle cooling if things get too hot inside the kit, with the speed ramping up proportional to how hot it is (preferably not running at all under normal conditions). Both the battery temps and the SBMS temp will be taken into account with this.
childcarepro
New Member
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- Jul 5, 2020
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Yes, let's get back to the topic, people! ?
I agree with you, while it is clearly better not to freeze your cells, it's even better-er to be sure that if you DO freeze your cells, you don't permanently damage them by charging them while frozen.
I also agree that SBMS0 (123SmartBMS has this limitation too, I learned) should only disable charging, not discharging, while below 0 Celsius, since only charging is harmful to the battery while below 0. [Well, much more harmful than discharging.]
michael d
off-grid solar pilgrim
yes. I am in process of assembling the Electrodacus SBMS0 system. I will be using a pair of 10 gauge wires from each set of 2 60cell 250watt panels to the Electrodacus SBMS0, 20 of the Electrodacus DSSR20 via the Electrodacus (2x) Electrodacus DECT16. the 10 gauge PV wire is going to cost a lot. For 40 panels(2 panels in parallel) 75 feet each run that is 20 runs of 10 gauge wire to the DECT16 which means (20x2x75=3000feet) 3000feet of PV wire for the 40-panel array. this part cost $1249 shipped but I bought 2000 feet red 10 gauge PV wire and 2000 feet black 10 gauge PV wire, 200 feet bare copper#6 wire, plus a 250-foot roll of thermostat wire. PV wire is expensive. could save a lot of the PV array is closer to the Electrodacus components and battery bank. I chose not to put the array closer to keep away from children (or other people) and safety issues and the view was also an issue for my location! 40 panels x250watt = 10,000 watt array. more later
Trying to understand your system. Do you have a link or spec for the 60 cell, 250W panels?
In another thread you mentioned 327W panels.
michael d
off-grid solar pilgrim
michael d
off-grid solar pilgrim
1 sbms0, 2 dect16's, 20 dssr20's cost $877.06 including shipping.Thanks for telling us the cost of the wires in a real world example
What's the cost for the SBMS0, DSSR20's and DETC16's?
michael d
off-grid solar pilgrim
michael d
off-grid solar pilgrim
(40) 250watt 60cell panels shipped to me cost $2340.80 these are used w/o defects.
michael d
off-grid solar pilgrim
michael d
off-grid solar pilgrim
8x3.2=25.6; 25.6x280ah =7168; each 280ah cell wired in parallel 1st so you get 7168x2=14336 capacity on 8s 24 volt sbms0.
This is getting a bit off topic, but have you done an analysis if the 60-cell panels with Vmp = 30V will work with a 26 to 28V battery?
I have some doubts it will work at elevated temps (50C panel temperature). The operating voltage of the panel when in pwm mode is a tad below Vmp. The 30V is reduced by temperature and the long cable drop.
You really need a Vmp of 34V
I have some doubts it will work at elevated temps (50C panel temperature). The operating voltage of the panel when in pwm mode is a tad below Vmp. The 30V is reduced by temperature and the long cable drop.
You really need a Vmp of 34V
60 Cell panels are what Dacian Recommends for his DSSR's
I have been curious about this for a while but never looked into it. I had always heard 60 cell panels were never popular pre MPPT as 36 cell or 72 cell panels were considered optimal for 12 or 24 volt systems with PWM type controllers. But Dacian seems to feel that 60 cell panels are optimal for his system (is this a difference in his design, a difference in battery chemistry that affects voltage, or maybe just a different design theory).
Can anyone shed any light on this? Why does Dacian consider 60 cells optimal for 24v when the rest of the industry considers 60 cells too small (or have I misunderstood something).
Well, 2x75' of 10 AWG will drop 2.47 V @ 16.54 A which is 8.2 % of 30.3 V.
Can someone tell me how spending 1000+$ on wires and almost as much for the DSSR20's + SBMS0 + DECT16 (and we still need to add 20 breakers/fuses + all the things you need to manage and connect 40 wires...) to end up with more than 8 % losses in the wires only is a superior solution to having fewer and thinner wires with a MPPT SCC which will be as or more efficient, harvest more power on cloudy days, be easier to install (40x 10 AGW wires doesn't sound fun to manage...), and be cheaper? did I miss something?
michael d
off-grid solar pilgrim
I am hoping to go to 60 feet long runs. but time will tell. the 72cell panels would have been better for the distance in all reality(i already caught that in my research).
I might be able to move a few components to shorten my length. I do not always make the best 1st choices, but I do not claim to be an expert in electricity either but have primarily worked with 120 240 house wiring. the bms monitoring/management is new to me but the Chinese bms's that I reviewed had many problems with little to no support. I am using 16 of 32 280ah lifepo4 cells for this with 24-volt components. the voltage drop on the wire was an issue potentially but I am working to remedy that issue. I do not have any real data at this time.
I do believe the Electrodacus SBMS0 without the mppt is the way to go; though. time will tell with more data. just sharing what I am doing. helpful critique is always welcomed. thanks all. snow in melting so outside I go to work. bye
each run is 75 feet of red positive and 75 feet black negative wiring. I never calculated the voltage drop exactly yet but did know 60 feet or less was better. there are a few components I could move a bit. I am using a ground mount so don't want to ruin all my view. already cut down trees for better solar siting.
I might be able to move a few components to shorten my length. I do not always make the best 1st choices, but I do not claim to be an expert in electricity either but have primarily worked with 120 240 house wiring. the bms monitoring/management is new to me but the Chinese bms's that I reviewed had many problems with little to no support. I am using 16 of 32 280ah lifepo4 cells for this with 24-volt components. the voltage drop on the wire was an issue potentially but I am working to remedy that issue. I do not have any real data at this time.
I do believe the Electrodacus SBMS0 without the mppt is the way to go; though. time will tell with more data. just sharing what I am doing. helpful critique is always welcomed. thanks all. snow in melting so outside I go to work. bye
each run is 75 feet of red positive and 75 feet black negative wiring. I never calculated the voltage drop exactly yet but did know 60 feet or less was better. there are a few components I could move a bit. I am using a ground mount so don't want to ruin all my view. already cut down trees for better solar siting.
Don't know what's he thinking? Ask him to join the discussion.
Back in the "old" pre mppt days, when pwm controllers were used for 12V LABs, it took some engineering effort to determine 36 cells was optimum for a 12V panel, powering a 12V battery. Nothing has changed. If you have 24V battery you need 72 cells when operating pwm.
A 60 cell panel doesn't have enough voltage headroom. In order to charge the battery, panel voltage needs to be greater than battery voltage. The 60 cell panel has Vmp = 30.3V. That's specified at room temperature. Since the panel is less than 20% efficient, about 80% of solar radiation goes to heat the panel. The temperature coefficient of panel voltage is about -0.34% per deg.C. If there's a modest rise of 25C, voltage drops by: 0.34 * 25 = 8.5%. Vmp drops to 30.3V * 91.5% = 27.7V
10 awg cable has 1 mOhm/ft resistance. 150 ft gives 150 mOhm resistance between panel and battery.
Charging current is dependent on panel voltage, battery voltage and line resistance:
I = (Vpanel - Vbattery) / Rcable
If the cells are at 3.2V then charging current is:
I = (27.7V - 8 * 3.2V) / .15 = 14A
The two panels in parallel have the capability of supplying 16A, but due to cable resistance and small voltage headroom, charging current is reduced to 14A.
If cells are at 3.3V charging current is 8.6A
If cells are at 3.4V charging current is 3.3A
