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48V/280A LifePo4 powerwall - BMS recommendation
#11
Thanks OffGridInTheCity and gauss163 for your advice.
Yes I plan to let a little space between each cell and put 2 or 3 computer fan to cool down the pack, take air from outside (I have to make a hole inside the wall) and extract the warm air from inside the box on which I will put the battery cells.
All will be managed according to temperature sensor inside the box and fans will be start/stop automatically.
Air conditioner will be the last solution if the temperature goes too high.
Limit the SOC is also planned, maybe not to go higher than 75%

And what about the minus temperature, in our region the minimum temperature can reach minus -10°C but I think that internal cell temp can prevent from freezing
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#12
(07-29-2020, 06:31 AM)duclos_laurent Wrote: And what about the minus temperature, in our region the minimum temperature can reach minus -10°C but I think that internal cell temp can prevent from freezing
Typically - you must not charge below 0C (32F) else you'll do damage - the greater the charge the greater/faster the damage.   There is such as a thing as some 'special' LifePo4(s) that go a bit lower but I'm guessing you don't have those - but of course you should look up the specs for your cells. 

Its a curve down to 0C rather than a sharp drop-off.   This graphic gives a visual - https://www.researchgate.net/figure/Opti..._327966044

You should be able to easily find a BMS with low temp cutt-off to help you protect the battery bank.
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#13
Yes purchased BMS (https://www.ebay.fr/itm/8S-20S-Smart-Lit...4576370062 - 300A version with LCD) have temp sensor but I have to check if a parameter for minimum temp can be defined but I see that inside the bluetooth app for the BMS, otherwise, I can purchase a mirror warm-up system (https://fr.aliexpress.com/item/400099008...web201603_)
to put under the cell, system also connected to temperature sensor and usable with domotic
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#14
Be aware with this bms. Max charging Rate is 50Amp, even wehren discharge is 300 Amp!
30kWh 5x 14s80p with 5x40A China BMS. 14kWH LiFePo4 is in production.
1 x Fronius Symo 8.2 with 28 Jinko 340Wp panels east/west. 3 x Victron Multiplus II with Cerbo GX
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#15
I thought if you had a Multiplus or other regulated charger inverter, you wouldn't need a BMS. If its fused/Breaker and monitored by charger settings (short absorption) then all you need is a balancer which you could do manually every couple of weeks.
Just causing trouble and baiting Gauss....
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#16
You need something that controls voltage on cell level. Multiplus doesn’t care about that, it just stops charging at the set voltage...
30kWh 5x 14s80p with 5x40A China BMS. 14kWH LiFePo4 is in production.
1 x Fronius Symo 8.2 with 28 Jinko 340Wp panels east/west. 3 x Victron Multiplus II with Cerbo GX
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#17
(07-29-2020, 06:31 AM)duclos_laurent Wrote: Thanks OffGridInTheCity and gauss163 for your advice.
Yes I plan to let a little space between each cell and put 2 or 3 computer fan to cool down the pack, take air from outside (I have to make a hole inside the wall) and extract the warm air from inside the box on which I will put the battery cells.
All will be managed according to temperature sensor inside the box and fans will be start/stop automatically.
Air conditioner will be the last solution if the temperature goes too high.
Limit the SOC is also planned, maybe not to go higher than 75%

And what about the minus temperature, in our region the minimum temperature can reach minus -10°C but I think that internal cell temp can prevent from freezing

Outside air can bring humidity & lead to cell corrosion problems.
My large LiFePo4 packs don't seem to dissipate noticeable heat on charge or discharge. They are in metal battery box cases &l I have a DS18b20 temp probe in there.
I log battery + outside temps 24/7 - the cells slowly follow (lag behind) outside temps vs anything to do with charge or discharge.
Temps here are typically 5C to 35C with occasional hot days 45 ish. The cells have always been inside this range.


Now the inverter & 3x MPPT chargers, yes, they get warm & need some fans....
Some graphs:
Running off solar, DIY & electronics fan :-)
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#18
(07-29-2020, 06:31 AM)duclos_laurent Wrote: Thanks OffGridInTheCity and gauss163 for your advice.
Yes I plan to let a little space between each cell and put 2 or 3 computer fan to cool down the pack, take air from outside (I have to make a hole inside the wall) and extract the warm air from inside the box on which I will put the battery cells.
All will be managed according to temperature sensor inside the box and fans will be start/stop automatically.
Air conditioner will be the last solution if the temperature goes too high.
Limit the SOC is also planned, maybe not to go higher than 75%

And what about the minus temperature, in our region the minimum temperature can reach minus -10°C but I think that internal cell temp can prevent from freezing

You do what you have to do to keep the batteries cool but ambient is fine unless you live in the desert where your average temp is 40C. Hbpowerwall goes over 40C in his shed over the hot australian summers. Tesla powerwalls have been installed outside as well. Is it optimal? No but nothing in this world is optimal. Having it inside the house is optimal but increased risk to safety. A few hot summer days will not kill your batteries. The key is to install it at a location where it's shaded and not exposed to direct sun. My shed is located under a shade and the box is insulated. The temp inside is only slightly higher than outside temps. Humidity is not a concern unless you live in the swamp it's probably within working parameters. My shed contains the inverters as well so the heat generated dehumidifies the shed at night when the fan isn't running as much. During winters it must not drop below 10C. Batteries must never get below 0C. Heat generated from my inverters work well to keep it within these parameters. You lose capacity if you are running at lower temps but it's easier to add heat during winters with spaceheaters, etc.
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