schroederjd
Solar Enthusiast
- Joined
- Nov 12, 2020
- Messages
- 175
Hi Everyone,
After spending the last 2 months building my battery (48v, Lishen 272Ah cells, build thread here), I'm considering abandoning the TinyBMS s516 that I'm currently using. I like a lot of the features of the TinyBMS has, but it has a few quirks that I'm struggling to get around. Rather than shell out another $250 for a replacement TinyBMS (which may not behave any better than the last one), I'm considering a different option. After reading through a few of the 'full' DIY BMS threads, I'm confident that option is way beyond my skill/knowledge level. I do love the idea of controlling things with a ESP32-based MCU (or similar). And that has lead me to the option of using an off-the-shelf 'smart' active balancer for the cell-level voltage measurement and balancing, and the MCU+relays for protection features.
Here's where I'm at with the design. I would really appreciate any feedback on this.
Functional Requirements:
As previously stated, cell-level voltage measurement and balancing would be performed by the balancer. The newest version of the JK balancers have the option for RS485 communication. Thanks to upnorthandpersonal, I've already got the RS485 protocol, so it should be fairly straightforward to get the cell-level information from the balancer to the ESP32. The other key inputs for the MCU would be the current readings (from the LEM HOYS) and temp readings (from the thermistors). Those would go through the ADS1115 16-bit ADC (not for the extra bits, but because the ESP32's internal ADC is pretty terrible). Load and charging disconnects would be separately controlled by the ESP32 using the relays listed above, likely driven by optocouplers. The 5A relays would be wired in series with the inverter on/off switches to disconnect loads in the event of LVP event (and to allow for remote shut-down of the inverters). The 40A relays would go on the positive side of the incoming PV lines (one for each MPPT) to disconnect charging in HVP or LTP events. Battery box heater would also be controlled by the MCU.
Anyway, i'm still pretty early in the design process, so would very much appreciate feedback.
Thanks in advance.
After spending the last 2 months building my battery (48v, Lishen 272Ah cells, build thread here), I'm considering abandoning the TinyBMS s516 that I'm currently using. I like a lot of the features of the TinyBMS has, but it has a few quirks that I'm struggling to get around. Rather than shell out another $250 for a replacement TinyBMS (which may not behave any better than the last one), I'm considering a different option. After reading through a few of the 'full' DIY BMS threads, I'm confident that option is way beyond my skill/knowledge level. I do love the idea of controlling things with a ESP32-based MCU (or similar). And that has lead me to the option of using an off-the-shelf 'smart' active balancer for the cell-level voltage measurement and balancing, and the MCU+relays for protection features.
Here's where I'm at with the design. I would really appreciate any feedback on this.
Functional Requirements:
- At least 1A of balancing current (the quality of my cells is questionable, at best...)
- NLT 80A continuous charge current, NLT 150A continuous discharge current
- Separate-port operation with an all-in-one inverter/charger
- Cell-level low-voltage load disconnect
- Cell-level high-voltage charge disconnect
- Low-temperature charge disconnect
- Remote monitoring by Wifi, minimally including individual cell voltages, pack voltage, SOC, pack current, pack temp, and ambient temp
- Component 1 - JK 1A Smart Active Balancer ($118)
- Component 2 - ESP32s Development Board ($12)
- Component 3 - LEM HOYS 100-S/SP33 Current Sensor ($33)
- Component 4 - ADS1115 Breakout Board ($7)
- Component 5 - Crydom 48V/5A DC SSR (3x $22)
- Component 6 - TE 200V/40A DC SSR (2x $51)
- Component 7 - NTC Thermistors (3x $1)
As previously stated, cell-level voltage measurement and balancing would be performed by the balancer. The newest version of the JK balancers have the option for RS485 communication. Thanks to upnorthandpersonal, I've already got the RS485 protocol, so it should be fairly straightforward to get the cell-level information from the balancer to the ESP32. The other key inputs for the MCU would be the current readings (from the LEM HOYS) and temp readings (from the thermistors). Those would go through the ADS1115 16-bit ADC (not for the extra bits, but because the ESP32's internal ADC is pretty terrible). Load and charging disconnects would be separately controlled by the ESP32 using the relays listed above, likely driven by optocouplers. The 5A relays would be wired in series with the inverter on/off switches to disconnect loads in the event of LVP event (and to allow for remote shut-down of the inverters). The 40A relays would go on the positive side of the incoming PV lines (one for each MPPT) to disconnect charging in HVP or LTP events. Battery box heater would also be controlled by the MCU.
Anyway, i'm still pretty early in the design process, so would very much appreciate feedback.
Thanks in advance.