harrisonpatm
Member
- Joined
- Jan 5, 2022
- Messages
- 222
I said in a different post regarding humidity that I would post in a month when I have it assembled, but I realized it's probably beneficial to post now and get feedback on things that I might be able to easily change while it's still disassembled.
I've been lurking and learning on the forum for over a year while I process and gather used 18650s from computer repair stores that give them to me. That was my first goal of the project: I didn't want to spend any money on cells and see what I could accomplish under that constraint. My budget is high on time, low on actual currency. In the past year i've built several small packs for various uses, of various levels of success. I was always waiting to see what kind of size and build I would eventually want for my whole house powerwall. I eventually came across this user's post and decided to take my inspiration from there; I really liked the use of small p packs added a little bit at a time to increase system capacity without having to rebuild the physical storage. This way I could keep collecting my free batteries and add them to the wall when I get decent ones, a little bit at a time, and eventually could have enough for the whole house.
I went with 24p packs, average cell capacity of 2100mah-ish, in 14s strings. By the time I had my design figured out, I had enough to start the build with 2 strings, giving my roughly 4.8kwh of storage right off the bat, depending on the level of discharge I go with.
The batteries would have to live outside. I eventually got enough salvaged wood from pallet boards and disassembled shoe store shelves to build a sort of mini outdoor shed, with enough space to eventually store 4 strings total. Wood got water- and fireproof treatment, salvaged tin roofing and scrap FRP from my (restaurant) work for extra layers.
I have holes in the front for ventilation in the summer to dump excess heat. They've got a layer of bug screen over them for debris, 3d printed housings for PC fans go on on half of the openings, and 3d printed regular vents go on the other half for static air movement. I had originally planned to install the fans on the top half, pulling air out of the box and away from the batteries, and the static vents will be on the bottom for return air. Does that sound ok? Or is there another configuration that would work better? I have 8 holes for now, and currently have only 4 fans from my scrap pile of matching size and voltage. If I can get 4 more matches, I would probably add them in, via new 3d printed shrouds, to have 4 fans blowing air in, and 4 blowing air out. Then come wintertime I'll physically plug up and insulate the holes to keep everything in there toasty.
I left gaps in front and behind the batteries because I currently don't exactly know how to warm the batteries in the winter. Some sort of heating element, some sort of insulation, haven't decided yet. I had unexpected success early making a heating bed for my 3d printer project, and it got me to thinking about some ways that I can DIY the heating for the batteries. I have about 6 inches on all sides of the batteries that I can use later, when I decide what I'm doing. In fact, that's mostly what's putting the project on hold for now: I'm waiting for the weather to warm up enough to let me put the batteries outside without having to heat them. Then I have 8 months to figure out my winter plan for next year.
My house doesn't use that much electricity, around 6-12kwh per day, so if I can eventually get enough cells to fill up the storage, it could have enough for 1-2 days of use, which would be nice. But to start, the primary usage of the powerwall will be backup energy storage for my electric motorcycle conversion. I only have 500w of solar for now on the south side of the house. Last year those were used to charge the bike directly via MPT-7210. It worked fine, but charging was inconsistent, and I could only charge when the bike was plugged in, so the panels were doing nothing if they weren't actively charging the bike. Now with a powerwall setup, and a more efficient true MPPT controller, they will be charging the batteries all the time. I will then use a boost converter when the bike needs a charge, to step up the nominal 48v of the powerwall to the 24s LiFePO4 of my bike.
If bike charging works for awhile and I still have excess power that can be used, I plan to wire an output to my house via a 48v to 12v buck converter to directly power a few things in my living room: LED house lights that are already on 12vdc anyway, charging phones and computers, kids toys, internet, ect. I have no plans for a 120v inverter yet; i don't have enough panels or battery capacity to necessitate it. But I gave myself enough physical space in my fuse box, and on my busbars, to add one later if I am able to install more panels.
That's it for now, just waiting on warmer weather to actually install the batteries into their space, they're already balanced and ready to go, everything is wired and fused as much as it can be. Let me know if you have any questions, or if I left anything out. Looking forward to comments! Thanks in advance.
Edit: I realized that I don't have a pic currently of how the series busbars work, but they're directly inspired from the build I liked to in the beginning of the post. Every time I add a string, each pack will be connected in parallel via series busbars, which are already connected to the balance wires on the BMS. So any future capacity additions should work without having to rebuild anything.
I've been lurking and learning on the forum for over a year while I process and gather used 18650s from computer repair stores that give them to me. That was my first goal of the project: I didn't want to spend any money on cells and see what I could accomplish under that constraint. My budget is high on time, low on actual currency. In the past year i've built several small packs for various uses, of various levels of success. I was always waiting to see what kind of size and build I would eventually want for my whole house powerwall. I eventually came across this user's post and decided to take my inspiration from there; I really liked the use of small p packs added a little bit at a time to increase system capacity without having to rebuild the physical storage. This way I could keep collecting my free batteries and add them to the wall when I get decent ones, a little bit at a time, and eventually could have enough for the whole house.
I went with 24p packs, average cell capacity of 2100mah-ish, in 14s strings. By the time I had my design figured out, I had enough to start the build with 2 strings, giving my roughly 4.8kwh of storage right off the bat, depending on the level of discharge I go with.
The batteries would have to live outside. I eventually got enough salvaged wood from pallet boards and disassembled shoe store shelves to build a sort of mini outdoor shed, with enough space to eventually store 4 strings total. Wood got water- and fireproof treatment, salvaged tin roofing and scrap FRP from my (restaurant) work for extra layers.
I have holes in the front for ventilation in the summer to dump excess heat. They've got a layer of bug screen over them for debris, 3d printed housings for PC fans go on on half of the openings, and 3d printed regular vents go on the other half for static air movement. I had originally planned to install the fans on the top half, pulling air out of the box and away from the batteries, and the static vents will be on the bottom for return air. Does that sound ok? Or is there another configuration that would work better? I have 8 holes for now, and currently have only 4 fans from my scrap pile of matching size and voltage. If I can get 4 more matches, I would probably add them in, via new 3d printed shrouds, to have 4 fans blowing air in, and 4 blowing air out. Then come wintertime I'll physically plug up and insulate the holes to keep everything in there toasty.
I left gaps in front and behind the batteries because I currently don't exactly know how to warm the batteries in the winter. Some sort of heating element, some sort of insulation, haven't decided yet. I had unexpected success early making a heating bed for my 3d printer project, and it got me to thinking about some ways that I can DIY the heating for the batteries. I have about 6 inches on all sides of the batteries that I can use later, when I decide what I'm doing. In fact, that's mostly what's putting the project on hold for now: I'm waiting for the weather to warm up enough to let me put the batteries outside without having to heat them. Then I have 8 months to figure out my winter plan for next year.
My house doesn't use that much electricity, around 6-12kwh per day, so if I can eventually get enough cells to fill up the storage, it could have enough for 1-2 days of use, which would be nice. But to start, the primary usage of the powerwall will be backup energy storage for my electric motorcycle conversion. I only have 500w of solar for now on the south side of the house. Last year those were used to charge the bike directly via MPT-7210. It worked fine, but charging was inconsistent, and I could only charge when the bike was plugged in, so the panels were doing nothing if they weren't actively charging the bike. Now with a powerwall setup, and a more efficient true MPPT controller, they will be charging the batteries all the time. I will then use a boost converter when the bike needs a charge, to step up the nominal 48v of the powerwall to the 24s LiFePO4 of my bike.
If bike charging works for awhile and I still have excess power that can be used, I plan to wire an output to my house via a 48v to 12v buck converter to directly power a few things in my living room: LED house lights that are already on 12vdc anyway, charging phones and computers, kids toys, internet, ect. I have no plans for a 120v inverter yet; i don't have enough panels or battery capacity to necessitate it. But I gave myself enough physical space in my fuse box, and on my busbars, to add one later if I am able to install more panels.
That's it for now, just waiting on warmer weather to actually install the batteries into their space, they're already balanced and ready to go, everything is wired and fused as much as it can be. Let me know if you have any questions, or if I left anything out. Looking forward to comments! Thanks in advance.
Edit: I realized that I don't have a pic currently of how the series busbars work, but they're directly inspired from the build I liked to in the beginning of the post. Every time I add a string, each pack will be connected in parallel via series busbars, which are already connected to the balance wires on the BMS. So any future capacity additions should work without having to rebuild anything.
, congrats! you seem to have everything in the right place. The heating system is a good idea, I'd go for a double system, with a backup heating in case any component of the primary should stop for any reason; could be a manual or automatic backup system but I wouldn't sleep OK without that.
