My First 48V 6.5KWh Li-Ion Powerwall 🥰

italianuser

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Feb 25, 2020
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Final thoughts before starting:

- This heat is disrupting my chargers LOL today it's 36°C (96.8°F) outside and 28°C (82.4°F) inside; Liitokalas just switch off, a 12V 2A transformer just burnt out. So I'm switching power sources to two used PC PSUs which can output 12V at 7A each and I'll use them outputting 4A. Added big external fans.

- My cells come from different sources: two vendors (500+400 cells) and notebook batteries (250 cells). I want the four 14s20p batteries to have the most similar cell distribution possible, so I won't only divide cells by capacity and IR but also by model. For e.g. I have 200 Samsung 22F and 200 UR18650AA Sanyos: I'll divide them equally in the 4 packs, 50 Samsungs each and 50 Sanyos each.

- Final choice for series connections: nickel plates, strips, copper busbars? First choice is 16mm2 copper busbars for each battery, cells fused with 35AWG tinned copper, spot welded. Haven't got to test spot welding again (maybe I'm too scared after my last test LOL), if that fails I'll go for welding (I love welding!).

- I made the cooling/heating system with ESP8266 and got the DS18B20s working in OneWire configuration; an ESP8266+14 DS18B20 for each 14s20p battery; fans and Peltier cell switch on/off when temperature thresholds are reached; using IRFZ44N for giving them 12V current (I might use two MOSFETs because they get terribly hot with all the heatsink). I'll mount two cooling/heating systems (primary and backup) because temperature is critical. Looking for any other possible SPOF (single point of failure). So 12V power source for the system will be double, too: my old small solar system as primary source, grid as second source.

ESP8266-temperature-control.jpeg
On the left ESP8266, center MOSFET with heatsink for powering cooling, in front of MOSFET three small DS18B20 temp sensors.

peltier-12V-3A.jpeg
Peltier cell 12V 3A; I'll try cooling using this and a set of fans to distribute cool air.
 

ajw22

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Nov 16, 2018
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- I made the cooling/heating system with ESP8266 and got the DS18B20s working in OneWire configuration; an ESP8266+14 DS18B20 for each 14s20p battery; fans and Peltier cell switch on/off when temperature thresholds are reached; using IRFZ44N for giving them 12V current (I might use two MOSFETs because they get terribly hot with all the heatsink).
View attachment 25465

Nice start. The problem with your MOSFET getting hot is because you're applying a too low Gate voltage. If you look at the datasheet for the IRFZ44N ( https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d ), the "Gate Threshold Voltage" is 2.0~4.0V - so at 3.3V the MOSFET is _almost_ off and essentially acting like a complex and expensive resistor. If you want to use the IRFZ44N, you need to apply at least 5V to Gate, ideally closer to 10V.

These should work much better at 3.3V Gate voltage:
 

italianuser

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Nice start. The problem with your MOSFET getting hot is because you're applying a too low Gate voltage. If you look at the datasheet for the IRFZ44N ( https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d ), the "Gate Threshold Voltage" is 2.0~4.0V - so at 3.3V the MOSFET is _almost_ off and essentially acting like a complex and expensive resistor. If you want to use the IRFZ44N, you need to apply at least 5V to Gate, ideally closer to 10V.

These should work much better at 3.3V Gate voltage:
I must say, I wouldn't have searched that! Very good info, I'll find an easy way to raise up that 3.2V coming out of ESPs pin, shouldn't be too difficult. Yes, I did think it was strange that a 49A rated IC heated up with only a small load. I won't change IC because I have a box of IRFZs so it's good to have suggestions to use it better. I'll update the schemas asap (y)
 

ajw22

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I must say, I wouldn't have searched that! Very good info, I'll find an easy way to raise up that 3.2V coming out of ESPs pin, shouldn't be too difficult. Yes, I did think it was strange that a 49A rated IC heated up with only a small load. I won't change IC because I have a box of IRFZs so it's good to have suggestions to use it better. I'll update the schemas asap (y)

Here are some classic approaches to increase Gate voltage when using a low voltage controller, method#1 being the most obvious.
The Gate can take up to 20V, so you can use your main 12V source for the gate - Don't forget the ~10kOhm pull-up resistor.

It shouldn't be difficult to steal a NPN transistor from old junk electronics, don't forget the base resistor missing in the diagram.
But if you have surplus IRFZ44N's, you could use that instead of the BJT transistor - the low 3.3V gate voltage in this role will be plenty to overpower the pull-up resistor without overheating

The only issue is that the main load could switch on briefly until the microcontroller boots up and sets the IOs properly... probably not a big issue in this case.
 

italianuser

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It shouldn't be difficult to steal a NPN transistor from old junk electronics, don't forget the base resistor missing in the diagram.
Yes, I'll use a transistor, I have quite a few. The resistor is maybe a bit hidden on the left side, connected to the green wire.
But if you have surplus IRFZ44N's, you could use that instead of the BJT transistor - the low 3.3V gate voltage in this role will be plenty to overpower the pull-up resistor without overheating

The only issue is that the main load could switch on briefly until the microcontroller boots up and sets the IOs properly... probably not a big issue in this case.
Oh that does happen, not a big issue. As soon as I try the complete prototype with full load and all sensors I'll share the schematics and PCB layout. Thanks!
 

ziporah

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Apr 26, 2021
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@italianuser be careful you don't get condensation with those peltier elements. I used to have them in one of my old amd athlon overclocked gaming rigs (those were the days) to freeze the core to death when overvolting and overclocking, but the problem was always condensation and isolating the cold side so there was no water (condenstation) on the mainboard and cpu. I wouldn't want your carefully tested and crafted packs to get rust from oxidation. You might get a set of DHT-22's and put it on the inside and outside of your enclosure to detect large differences in humidity.
 

italianuser

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@italianuser be careful you don't get condensation with those peltier elements. I used to have them in one of my old amd athlon overclocked gaming rigs (those were the days) to freeze the core to death when overvolting and overclocking, but the problem was always condensation and isolating the cold side so there was no water (condenstation) on the mainboard and cpu. I wouldn't want your carefully tested and crafted packs to get rust from oxidation. You might get a set of DHT-22's and put it on the inside and outside of your enclosure to detect large differences in humidity.
So true, we were talking about this today with another member of the forum. I have a couple of ideas for condensation, I must do some deeper research. In my mind I have a few things: a smoother software algorithm to lower temperature because the goal isn't to refrigerate like a fridge (most applications on the web show this) but to control temperature <n> degrees per time-frame; air-flow; double-enclosure; choosing a correct position for the peltier cells.
DHT-22, ye nice, I'm adding it now to the schematics, thanks (y)
 

Wolf

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Sep 25, 2018
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BME280 and or BME680 can be used also especially if you get the right includes and write some good code. I have a BME680 in the center of my battery box and it can calculate, obviously temp, humidity, barometric pressure but also sense any VOCs. I also have 4 DS18B20s on 4 corners of the box giving me well rounded temp readings. The VOC sensor on the BME680 is so incredibly sensitive, if a mouse farts in the shed it will pick it up. So If I detect a serious change in the AQI the sensor spits out, it is time to investigate to see if I have any issues. I may also incorporate a smoke sensor into the mix. The MQ-2 is quite a good all around sensor, requires nothing to speak of for code yet gives an early warning and is very sensitive. Could also tie an alarm in with it I suppose.
Dew point can be calculated by temp, humidity, and pressure so condensation can be avoided that way. Also good airflow will eliminate most of that. I initially had a DHT-22 as my main sensor but the reaction time was a bit to slow. I guess I was impatient. So I have the BME680 sensor calibrated with proper code and it controls my heating and ventilation system. If you are going that route get the expensive versions as in https://www.mouser.com/ProductDetail/619-28061 worth every penny in reliability. In my case I am not using Pelletier units but just airflow. 4 servo motors control 4 flaps, 2 on the lower sides of the box and 2 on the top of the box, also at the top of the battery box I have 4 5000 RPM 180mm fans PWM speed controlled by temperature with each of the fans hall sensors reporting to the ESP32 which is the control unit for the whole project. All of the parameters, of course, reporting to an influx database and visualized on grafana. 450 lines of code with a external watchdog and OTA reprogrammable if necessary. I even had to install an external antenna because the inside of the box is lined with a heat and cold reflective insulation and the WI-FI was spotty.
Left upper DS18B20 sensor is offline right now. As I am in Europe I cant fix it yet. Soon.:p
Wolf
1624448730993.png
 
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italianuser

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@Wolf your graphs are so inspiring. I'll go for DHT-22 for now, I found a very good study, conducted over a 12 month period Test and Calibrate DHT22 Hygrometers. Also, smoke/gas sensors are a good idea, it's quite a time that when I leave the lab and close the door I think I must mount some detection system and the MQ series seem to work well; I have one mounted in the kitchen but it's only active when the alarm system is on.
 
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