ajw22
Member
- Joined
- Nov 16, 2018
- Messages
- 733
My PowerShelf project has come a long way sinceI started collecting 18650 cellsabout 2 years ago. This is the latest status (April 2020):
Background:
I've had my gridtied system with feed in tariff installed a few years ago, which unfortunately is nearly useless on cloudy days and entirely useless during the night.
At my companyI had a drum full of discarded powertool batteries,and decided to put them to good useafterstumblingacross a Youtube video featuring somequirkyAussie who built himself a powerwall.
Later switched to discarded ebike packs containing mostly 2Ah Sanyo cells. While not free, it's still cheap and there's a near endless supply.
While spendingseveral months harvesting cells as well as reading up on various projects, I figured that I'd need years to complete the full system I wanted. So the logical approach for mewas to construct a modular system that I could expand byadding PV panels / chargers / batteries / invertersas I went.
=== Overview of current status /[planned max]===
* [DONE!]9.44Wsolar panels
* [DONE!]3x eSmart3 60amp solar chargers configured to max total 120Amp
* Batteries in parallel: 6x 14s108p;nom 60kWh, 45kWh ACusable /[10x 14s108p, nom 100kWh]
* 6xChinese"Smart BMS 60A" with bluetooth,RaspberryPi3 + Grafanamonitoring
* 3x 1kW grid tie inverter with limiter /[4x 1kW]
* [DONE!] 1x 1.5kW emergency standalone inverter for during blackouts
=== The details: Solar panels===
Canadian solar 265W on 4x racks @6 panels. Connected in4p3s configuration. EacheSmart3 charger is attached to 2 DIY racks. Racks are securely anchored to the concrete.
=== The details: eSmart3 60amp solar chargers ===
The 3 devices areeachconfigured to charge ata maximum of 40Amp (combined total 120Amp)due to the limitations of the batteries, and57.12V(4.08V*14) to extend battery life. Quite happy with these units, though one cooling fan decided to disintegrate and needed to be replaced.
=== The details: Battery packs ===
Made of custom designed 3d printed parts. I compromised severely on the electrical design aspects to maximize the serviceability and ease of construction/replacement. I've made various improvements to the design, and it's now in the 9th Version. I've attached the source .SCAD file below. You need a free CAD software called OpenSCAD edit it (it's just a text file), render ("F6"), and save as .STL (File->Export->). Edit the bottom 10 lines to suit your needs, it should be pretty self-explanatory.
PRO:
* a pack can be taken out by undoing2 wood screws and disconnecting the XT60 connector. No need to fumble with theBMS lead as it'sintegrated into the XT60 connector.
* Apart from removing/reattaching the fuse wire,a cell can be replaced without tools simply by pushing them out. No prying apart, hammering, etc required.
* bus bar is made of just 1 length of partly stripped5.5mm^2 cable. No twisting, powertools or bending contraption required
* hardly any possibility of accidentalshorting, even during maintenance or whenbumping into itwith metal tools stuck all over your body.
CON:
* Cells will(dis-)charge unevenly under high load, so limited to 30A
* Cell voltage monitoring might be inaccurate under high load
=== The details: 18650 cells ===
Initially I started off with a free supply of oldpowertool batteries. Unfortunately, they typically are 1300~1500mAh low capacity/high drain cells - the exact opposite of what a powerwall needs. After exhausting that supply, I switched to old ebike cells. Now I almost exclusively use1800~2400mAh Sanyo cells.
I check the capacity and test for self-dischargeevery cell, but do not sort them in any way. My latest 108ppacks are built with basically randomly selected cells, although I try to put in some low capacity 1300mAh cells into the front ofevery pack. The packs generally end up with remarkably similar capacities, but if they do not, I can easily swap some ofthose low capacity cells with higher capacity ones(or vice versa, if the pack capacity is too large) to equalize capacities.
=== The details: BMS/wire harness ===
I useone Chinese 14s 60ASmart BMS purchased on Aliexpresson each battery. The sensor/balancing leads are integrated into the XT60/harness so as to simplify maintenance. There is a 30A fuse inline in the harness for extra safety.
PRO:
* Cheap
* Balancing can be set to start at any voltage and diff. Currently configured start if at3.9+V andmore than 0.015V difference.
CON:
* Can balance/bypass at only50mA. This is so farproving to be enough, except whenthere are faulty cells. On the plus side, faulty cells will not go undetected.
*Initial balancing / balancing after maintenance can take days, if not weeks.
=== The details: 1kW grid tie inverter with limiter===
I went with these instead of hybrid inverters, because I didn't want to rewire the whole house breaker. This just requires a dedicated line to the breaker panel and aclamp meter on the main line to prevent feeding back into the grid. At the moment I have 3 of those throttled to max 750W. While they do not feed back into the grid,they often do not share the load equally. They are currentlyconfigured to slow down / stop when the battery voltage reaches 48.3V (3.45V*14)
2019-11-26 update: The Inverters are now connected to the breaker boxvia a TP-Link HS105 Smart Wifi Plug. This allows the Raspberry Pi 3 (below) to disconnect the inverters during off-peak hours (11pm~7am, 1/3 price!)if the batteries are kinda low.I hope to implement a smarter system in the future that takes into account weather forecast data
2020-04-29 update: Changed the batteries low threshold during the winter months to 3.7v/cell. This allows the batteries reach 3.9V/cell on the occasional sunny dayand do some balancing.
=== The details: Raspberry Pi 3 + Grafana monitoring ===
This hasproven extremely useful. With the pack levelvoltage vs timegraph, I can easily see when a pack has developed a problem - even distinguish between a blown fuse, self-discharging cell, or reduction in capacity due to wear.
I've taken the snapshot below a day afterreplacing/ reshufflingsome cells. Not enough time for the balancer to properly top balance.
Background:
I've had my gridtied system with feed in tariff installed a few years ago, which unfortunately is nearly useless on cloudy days and entirely useless during the night.
At my companyI had a drum full of discarded powertool batteries,and decided to put them to good useafterstumblingacross a Youtube video featuring somequirkyAussie who built himself a powerwall.
Later switched to discarded ebike packs containing mostly 2Ah Sanyo cells. While not free, it's still cheap and there's a near endless supply.
While spendingseveral months harvesting cells as well as reading up on various projects, I figured that I'd need years to complete the full system I wanted. So the logical approach for mewas to construct a modular system that I could expand byadding PV panels / chargers / batteries / invertersas I went.
=== Overview of current status /[planned max]===
* [DONE!]9.44Wsolar panels
* [DONE!]3x eSmart3 60amp solar chargers configured to max total 120Amp
* Batteries in parallel: 6x 14s108p;nom 60kWh, 45kWh ACusable /[10x 14s108p, nom 100kWh]
* 6xChinese"Smart BMS 60A" with bluetooth,RaspberryPi3 + Grafanamonitoring
* 3x 1kW grid tie inverter with limiter /[4x 1kW]
* [DONE!] 1x 1.5kW emergency standalone inverter for during blackouts
=== The details: Solar panels===
Canadian solar 265W on 4x racks @6 panels. Connected in4p3s configuration. EacheSmart3 charger is attached to 2 DIY racks. Racks are securely anchored to the concrete.
=== The details: eSmart3 60amp solar chargers ===
The 3 devices areeachconfigured to charge ata maximum of 40Amp (combined total 120Amp)due to the limitations of the batteries, and57.12V(4.08V*14) to extend battery life. Quite happy with these units, though one cooling fan decided to disintegrate and needed to be replaced.
=== The details: Battery packs ===
Made of custom designed 3d printed parts. I compromised severely on the electrical design aspects to maximize the serviceability and ease of construction/replacement. I've made various improvements to the design, and it's now in the 9th Version. I've attached the source .SCAD file below. You need a free CAD software called OpenSCAD edit it (it's just a text file), render ("F6"), and save as .STL (File->Export->). Edit the bottom 10 lines to suit your needs, it should be pretty self-explanatory.
PRO:
* a pack can be taken out by undoing2 wood screws and disconnecting the XT60 connector. No need to fumble with theBMS lead as it'sintegrated into the XT60 connector.
* Apart from removing/reattaching the fuse wire,a cell can be replaced without tools simply by pushing them out. No prying apart, hammering, etc required.
* bus bar is made of just 1 length of partly stripped5.5mm^2 cable. No twisting, powertools or bending contraption required
* hardly any possibility of accidentalshorting, even during maintenance or whenbumping into itwith metal tools stuck all over your body.
CON:
* Cells will(dis-)charge unevenly under high load, so limited to 30A
* Cell voltage monitoring might be inaccurate under high load
=== The details: 18650 cells ===
Initially I started off with a free supply of oldpowertool batteries. Unfortunately, they typically are 1300~1500mAh low capacity/high drain cells - the exact opposite of what a powerwall needs. After exhausting that supply, I switched to old ebike cells. Now I almost exclusively use1800~2400mAh Sanyo cells.
I check the capacity and test for self-dischargeevery cell, but do not sort them in any way. My latest 108ppacks are built with basically randomly selected cells, although I try to put in some low capacity 1300mAh cells into the front ofevery pack. The packs generally end up with remarkably similar capacities, but if they do not, I can easily swap some ofthose low capacity cells with higher capacity ones(or vice versa, if the pack capacity is too large) to equalize capacities.
=== The details: BMS/wire harness ===
I useone Chinese 14s 60ASmart BMS purchased on Aliexpresson each battery. The sensor/balancing leads are integrated into the XT60/harness so as to simplify maintenance. There is a 30A fuse inline in the harness for extra safety.
PRO:
* Cheap
* Balancing can be set to start at any voltage and diff. Currently configured start if at3.9+V andmore than 0.015V difference.
CON:
* Can balance/bypass at only50mA. This is so farproving to be enough, except whenthere are faulty cells. On the plus side, faulty cells will not go undetected.
*Initial balancing / balancing after maintenance can take days, if not weeks.
=== The details: 1kW grid tie inverter with limiter===
I went with these instead of hybrid inverters, because I didn't want to rewire the whole house breaker. This just requires a dedicated line to the breaker panel and aclamp meter on the main line to prevent feeding back into the grid. At the moment I have 3 of those throttled to max 750W. While they do not feed back into the grid,they often do not share the load equally. They are currentlyconfigured to slow down / stop when the battery voltage reaches 48.3V (3.45V*14)
2019-11-26 update: The Inverters are now connected to the breaker boxvia a TP-Link HS105 Smart Wifi Plug. This allows the Raspberry Pi 3 (below) to disconnect the inverters during off-peak hours (11pm~7am, 1/3 price!)if the batteries are kinda low.I hope to implement a smarter system in the future that takes into account weather forecast data
2020-04-29 update: Changed the batteries low threshold during the winter months to 3.7v/cell. This allows the batteries reach 3.9V/cell on the occasional sunny dayand do some balancing.
=== The details: Raspberry Pi 3 + Grafana monitoring ===
This hasproven extremely useful. With the pack levelvoltage vs timegraph, I can easily see when a pack has developed a problem - even distinguish between a blown fuse, self-discharging cell, or reduction in capacity due to wear.
I've taken the snapshot below a day afterreplacing/ reshufflingsome cells. Not enough time for the balancer to properly top balance.