Stuart: Havent tried passive cooling yet but i have heatsinks on the bench for it and you could use conformal coating with heat dissipating capabilitites. The later could also be protection towards moisture if needed.
If you want to sustain 100% colling based on the resistors some kind of added capability to cool is needed.
@daromer that looks exactly what I want! Thanks! So would you recommend I connect it to half the battery pack to give it the 24v it needs for power or an external power source? Would this cause much draw from the half that’s connected and cause the cells to become unbalanced? Or is the power draw so minimal it won’t make much difference?
Also, the standard Arduino relay boards give enough current to trip the breaker?
The ABB units need about 6-9A inrush current. The relays on the normal Arduino boards should be able to cope with that.
No they wont get out of balance. You draw this current during 250ms when the breaker trips. So just hook the breaker up to half the pack through the Relay 
Thanks for your help so far! Last question (for now 
), I’ve seen some breakers from midnite solar, 200a for around $120 brand new. Which route should I go? used ABB or the midnite solar ones new?
Cant say which one is best for you. I dont have access to midnite where i live and havent tested them. For me the ABB units are rock solid but they are also very big. I have both S5 and S3 here and the S5 is a beast!! 
Found some mounts on thingverse and redraw some bits to get them on a dinrail, attach the antenna and make it modular, still need to do some redrawing and modifications
Ufffff 2700 forum messages! half a live to read all!!!
Please please improve github with some how-to. 
So my questions: sorry if was asked previously…
-Not clear if 680mA can balance large packs (100 18650 cells… 200A aprox). Why not upgrade MOSFET to support more current?
-Best approach for my powerwall will be split in two: 14s 100A, so: I need two controllers or only one can manage two strings.
Thanks
The MOSFET can support over 6Amps, however how do you dissipate the amount of heat that will generate?
Only you can determine if the balancing current is enough for the size of the battery you are constructing, as you mention you can split larger packs down into multiple strings. Up to 4 are supported on the current controller (16 with the new experimental software).
The ESP8266 doesn’t have many IO pins, most are already used hence the PCF chip - this also allows higher current on the pins and also removes the possibility of destroying the ESP chip when driving external devices.
Thanks @daromer, went with the s3, although shipping to Australia doubled the price sthink it will still be worth it
You have my attention! Care to elaborate on other features and timing of beta release, along with timing for the new controller?
Had a module which seemed to ever so slowly drain the battery it was attached to…can it be caused by my not so pretty solderwork on the attiny?! What also caught my attention was that this module was always
3 degrees warmer then the rest (also when i measured temp with an ir thermometer.
Screenshot_20201222-200856_Parallels Client|690x326
I’m also very curious about this. Would be interested to know why the external 2.048V reference was selected over the internal 2.2V reference.
From the datasheet [http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-8495-8-bit-AVR-Microcontrollers-ATtiny441-ATtiny841_Datasheet.pdf]
Internal 2.2V reference voltage can be in the range of 2.134 to 2.266 V (quite a large % difference)
Additionally, the power supply to the ATTINY needs to be higher than the voltage reference for it to work.
The V4.21 design uses a 1.25V reference (0.5% tolerance), which is able to measure lower voltages of cells to support different cell chemistry.
Would be interested to see the results
So I suppose if one was planning to calibrate the ADC readings and only read cell voltages > 2.2V then the internal reference might be fine? Thanks for the info Stuart.
Perhaps, I don’t rate the internal reference on any of the ATTINY chips, the reference voltage bounces around with the supply voltage - the exact thing you don’t want.
Yeah, good point. Looking at the datasheet (the ATTiny85 in my case) the voltage reference does indeed drift quite a bit: https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-2586-AVR-8-bit-Microcontroller-ATtiny25-ATtiny45-ATtiny85_Datasheet.pdf (page 191). I suppose you could try and compensate for that curve in software a bit but that’s not ideal.
Are you referring to the TL432 here (which I see in the jlcpcbassembly branch)? Looking at the datasheet (http://www.unisonic.com.tw/datasheet/TL432.pdf) I’m not totally clear on how much current it is constantly drawing from the cell. I would guess it’s “Minimum Cathode Current for Regulation” which is 0.6-1mA and that seems quite high to me.
Looking at the LM4040 (which I see in the master branch) - the operating current is bit lower at 45-60uA (https://www.ti.com/lit/ds/symlink/lm4040-n.pdf page 7) which seems more acceptable for smaller packs of cells.
What sort of acceptable idle current draw are you aiming for with v4? Thanks for walking through all this with me - appreciate your insights!
