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DIY powerwall in uninsulated garage
#1
I'm in the beginning stages of planning my 48v DIY powerwall (harvest/used 18650s). I'm thinking of putting them in an enclosed rackmount server cabinet and placing that in my detached garage which is not insulated. The garage walls are made up of 6 feet of cinder blocks (pony wall) then 2 feet of wood framing that meets the open rafters (all wood). I'm in Seattle, so we're looking at a typical range of low 40's to high 70's degrees Fahrenheit with once in a while extreme temps at mid 20's and high 80's, respectively. On really hot days I've measured the garage's temps to be about 5 to 7 degrees hotter than outside.

Based on this setup and considering insulating the garage might not be an option (insulating over the concrete perimeter would make this 2 car garage, a 1 car garage), what's the next best thing I can do to help prevent the powerwall's performance from suffering during the colder and hotter temps??



P.S. - The solar panels will likely be installed on the garage roof, that's why I'm thinking of placing the powerwall in the garage. Also for safety reasons, in case the powerwall catches fire (yes, I will be fusing the battery, but still, you never know) - that building would possibly burn down, but not the house.

P.P.S. - The reason I'm thinking of building the powerwall in a rackmount server cabinet is that the steel enclosure would hopefully better protect it and/or contain it in the event of an earthquake (instead of flying off the wall in a wall mount setup). Plus I can get cabinets for as low as $50 and they're 28" deep which means more cells in parallel and longer battery run time.
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#2
(02-07-2020, 08:08 PM)crashintoty Wrote: I'm in the beginning stages of planning my 48v DIY powerwall (harvest/used 18650s). I'm thinking of putting them in an enclosed rackmount server cabinet and placing that in my detached garage which is not insulated. The garage walls are made up of 6 feet of cinder blocks (pony wall) then 2 feet of wood framing that meets the open rafters (all wood). I'm in Seattle, so we're looking at a typical range of low 40's to high 70's degrees Fahrenheit with once in a while extreme temps at mid 20's and high 80's, respectively. On really hot days I've measured the garage's temps to be about 5 to 7 degrees hotter than outside.

Based on this setup and considering insulating the garage might not be an option (insulating over the concrete perimeter would make this 2 car garage, a 1 car garage), what's the next best thing I can do to help prevent the powerwall's performance from suffering during the colder and hotter temps??
Congratulations on building a system.  I've had A LOT OF FUN!!

Battery University ( https://batteryuniversity.com/learn/arti...mperatures ) has this table:


My DIY powerwall is under the house and ranges from extreme low of 45F(7C) to 80F(27C) extreme hi and I haven't had any issues - especially since a DIY powerwall typicall implies fraction of 1C charge/discharge per cell.    In my case I rarely break 300ma/cell and in the 90-200ma/cell (charge/discharge range) most of the time.  

Personally, I wouldn't worry about  "....typical range of low 40's to high 70's degrees Fahrenheit...".   And a sophisticated BMS (like Batrium) with temp settings can protect against any rare/extreme events with automatic cut-off.   I live in Oregon and familiar somewhat with Seattle weather - I would not think you would get unexpected extreme temps until global warming has a few more years to take affect Smile
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#3
I'm in Australia and don't experience temps that cold, but we get plenty hot. With the inverters on inside one of my sheds it gets to 50deg c a few times, just run a fan over batteries and inverters and an exhaust fan. Cold is worse for them I believe.
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#4
Between 40F and 80F degrees is the sweet spot for 18650 Li ion. No special insulation required, except maybe for excessive humidity in your climate. Maybe modest ventilation to moderate temperature in the garage, especially if you have inverters in there too. My two cents.
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#5
A low wattage incandescent light that can be turned on in cold weather would help with humidity and the temperature. low in cabinet let the heat raise. a 25 watt appliance bulb should work.

later floyd
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#6
Wow! I'm a bit shocked - I was expecting to here this is a bad idea, I have to insulate the garage, I have to somehow insulate the cabinet itself, etc. This is a pleasant surprise!

I've got a ton of spare PC fans, so I can finally put them to use.

As for the low wattage incandescent light bulb idea - the cabinet isn't fully enclosure or seal, it has a mesh/perforated/grilled door and ceiling and the bottom is open - does the light bulb idea still help with humidity and temps?
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#7
From my experience just this week for freezing cold weather:
1. Make sure temperature sensors are calibrated. I've had one of my BMS trip because it was off by 3 degrees, thought it was freezing, and shut the battery off.
2. Keep charger/inverter/batteries in one enclosed space (within reason -> overheating). The inverter/charger waste heat will keep the battery warm.
3. Solar may not supply enough power to run the inverter through the night. Use a small Grid->battery charger in the evenings to keep temperatures above freezing. Works best if you have cheap off-peak rates. I've set my 10A charger to run from 11pm~7am.
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Modular PowerShelf using 3D printed packs.  50kWh and growing.
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#8
Your battery can withstand some freezing temperatures, as long as You do not charge the batteries while frozen.

Some Make/brands will survive charging at minus 5C but I had a whole batch of Panasonic cells that died while I charged at minus 3C.

ChrisD
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#9
(02-08-2020, 02:16 AM)crashintoty Wrote: Wow! I'm a bit shocked - I was expecting to here this is a bad idea, I have to insulate the garage, I have to somehow insulate the cabinet itself, etc. This is a pleasant surprise!

I've got a ton of spare PC fans, so I can finally put them to use.

As for the low wattage incandescent light bulb idea - the cabinet isn't fully enclosure or seal, it has a mesh/perforated/grilled door and ceiling and the bottom is open - does the light bulb idea still help with humidity and temps?
    PC fans might  supply enough  air movement to prevent the batteries from freezing. The light bulb idea wouldn't work in an open mesh cabinet.
 Make a magnetic roll down insulated cover for the door?  
 Later floyd
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#10
crashintoty:

ChrisD is right: overheating can probably be managed with some fans but the greater risk of damaging your batteries is operating (particularly charging) the powerwall in subfreezing temperatures. I think Seattle sees some times below 32F on clear winter days. But, as you noted, the garage is +5 to +7 degrees from ambient, so freezing risk is mitigated somewhat. In any case, BMS should be set to shut down charging if the cells are below 32F.

As also noted above, lithium cells can withstand freezing without being damaged so long as they're not actively used in that state (kinda the opposite of lead acid, now that I think about it). As for the other extreme, likely the inverter or charge controller would over-temp/shut-down before the cells reach max temperature specs in your situation.
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