Power wall location and safety question

J

Jeremy Choy

Member
Joined
May 10, 2017
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60
Hi Everyone,

I plan on jumping with two feet into the powerwall after building 52v e-bike batteries. I'm looking for a way to make my commuter bike 100% emission free and save a bit on electricity bill with a grid tie. mainly an expensive hobby I just want to start playing with.

Problem is with winters it gets to -31f. So placing the powerwall outside is a challenge which many probably don't have to deal with. I'm curious how many people have these in their home or in their attached garages. It's a lot of power. I'm fairly comfortable with electronics, plan on making a custom monitoring forvolt and temperature, and havecut offs. depending on capacity, I will not run the cells below 3.2 or charge above 4.1.

I plan on a 14s50p (100ah) (buying those ebay hoverboard batteries, new all the same brand/type/cap)

I was planning on placing everything in my workshop in the basement in a steel enclosure. just curious on your opinions vs. trying to make an enclosure outside and then having to build a climate controlled enclosure.

Thanks in advance
 
I would never put a home built power wall in your house or garage. Never. I think there are a few people here with smaller packs who have done steel enclosures, maybe one of them could offer advise here.

Those are some pretty extreme temperatures though. This past winter, I ran my powerwall outside for the first time in the cold. The temps bottomed out around 12f if I recall correctly. It still ran fine even though people don't recommend going below 32f. My best suggestion would be a separate insulated tool shed or something where you can keep it warmer than the ambient air temp.
 
Not saying it's entirely safe, but i have mine in my house in a metal enclosure. There's a lot of steps you can do to increase the safety, fusing, limiting voltage, etc. I also top mine out at about 4.1. Down the road i do plan to build a shed to house everything.
 
Thanks for the response to my rhetorical question. I think ultimately I like my house and batteries will go in a shed.

if I can't get a reasonable temperature in the shed, I will run it for 3/4 of the season and store the batteries indoor Nov-March not connected. I will switch the solar from parallel to series and tie it directly into a grid tie inverter.

I just have to dig a trench and run my power from the batteries into the house to the grid-tie. more work, but safer.
 
JeremyChoy said:
Thanks for the response to my rhetorical question. I think ultimately I like my house and batteries will go in a shed.

if I can't get a reasonable temperature in the shed, I will run it for 3/4 of the season and store the batteries indoor Nov-March not connected. I will switch the solar from parallel to series and tie it directly into a grid tie inverter.

I just have to dig a trench and run my power from the batteries into the house to the grid-tie. more work, but safer.
Click to expand...

I am just beginning, have couple hundred cells tested and charged, still waiting to get more charged/tested. Will begin building soon. I have a 16 kW grid tied solar system for 5800 square foot house. Spins meter backwards most days.

Was interested in Tesla Powerwall 2 x 2 until was told the installed price would be more like $18k. Not an option. So going to try this out and see what happens.

Have only 2 options for placement of my DIY Powerwall. One is inside the garage beside my 2 SolarEdge inverters (attached to main dwelling), not so safe, and the other is on the brick wall outside of the garage. Would need to run conduit up the wall, through attic, and eventually to the inverters. If I did this, would have to design and construct a large box enclosure, probably with something like Hardie cement/fibersiding, costs around $65 for 4 x 6 feet panels. Would have to be deep enough to house everything (packs/inverter/etc), and some sort of weatherproof cover/doors to keep it all dry, and may need some sort of ventilation system to keep air flowing to keep it from overheating.

Wonder if anyone else has done this yet? If so, what size, enclosure would be adequate? Thinking about 14 packs of 80 cells each to start, but would like to have the option of tripling that amount as time goes by.
 
I don't think I'd sleep well with a DIY storage system inside or attached to my house.

I'm starting small, but it may grow. Just an off grid system to run a single 300w 240v pump (also considering a 24v pump to skip the inverter). I considered making a cabinet up against the boundary fence near the pump to minimize the cable run, but I've got a couple of good size garden sheds on cement slabsonly 6m from the pump, so will probably use one of those.

For those without the space, I've been wondering about the curbside utility cabinets you see around the place. In Australia for example the FTTN cabinets being deployed for the National Broadband Network. I've got no idea where to source them or how much they might be though.


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I am somewhat confused by some of the responses to safety with regards to a DIY install. Are you telling me that all these lead acid systems people have installed in their home are much safer than the 18650's? What steps should be consider if we do want to put it in our garage? I mean fusing all the cells is the first step. A system monitor that would shut the battery system down if it reached a certain temperature.... Some type of fireproof enclosure.....

Lets have this discussion. I know one thing I have learned, you MUST have a switch to turn off the batteries on the outside of your home in the event of a fire.
 
RobertBaumer said:
I am somewhat confused by some of the responses to safety with regards to a DIY install. Are you telling me that all these lead acid systems people have installed in their home are much safer than the 18650's? What steps should be consider if we do want to put it in our garage? I mean fusing all the cells is the first step. A system monitor that would shut the battery system down if it reached a certain temperature.... Some type of fireproof enclosure.....

Lets have this discussion. I know one thing I have learned, you MUST have a switch to turn off the batteries on the outside of your home in the event of a fire.
Click to expand...

Lead acid batteries don't spontaneously ignite....
 
John said:
RobertBaumer said:
I am somewhat confused by some of the responses to safety with regards to a DIY install. Are you telling me that all these lead acid systems people have installed in their home are much safer than the 18650's? What steps should be consider if we do want to put it in our garage? I mean fusing all the cells is the first step. A system monitor that would shut the battery system down if it reached a certain temperature.... Some type of fireproof enclosure.....

Lets have this discussion. I know one thing I have learned, you MUST have a switch to turn off the batteries on the outside of your home in the event of a fire.
Click to expand...

Lead acid batteries don't spontaneously ignite....
Click to expand...

Additionally, nobody wants to be responsible for telling you that what you're doing is safe enough to put in your garage, then be sued because your house burns down. Just be safe and put them outside. Is it worth risking your home/family to store a few kw of power inside rather than out?
 
Lithium don't spontaneously ignite, either. They must be damaged to ignite. Either physically or electrically they are damaged. Overcharging is the most common failure
 
Korishan said:
Lithium don't spontaneously ignite, either. They must be damaged to ignite. Either physically or electrically they are damaged. Overcharging is the most common failure
Click to expand...

And I would like to add, by a LOT, not by 0.05v. I had 1680 cells hit 4.4-4.5v last week for a couple of days and not one single cell blew up, vented, etc. Probably halved their remaining lifespan, but that's about it.
 
Has anyone seen a 18650 spontaneously combust without help from a heat gun? I am curious, really... this is a good topic... Let's say you live in a neighborhood where people might walk away with your batteries, then what? Unfortunately I do not live in the outback.

1. So far I have learned that I will double fuse.
2. Monitor the batteries and have a shut down mechanism in the event of trouble.
3. Design and/or buy a fireproof enclosure that includes a cooling system.
4. Take extra precautions with wiring as to not shorting.

others
5. Do not carry batteries up a ladder (Daniel)
6. Deploy Halon system in garage, would also help to remove unwanted pests.

5 & 6 are jokes......

-Bob
 
while i am not against point 6, at least not entirely, we all know what would end in there too...
 
A halon or similar setup would not keep a cell that has already super failed into fireworks from keeping the burning process going. The only way to really "stop" an ignited cell is to quench it. Suck the "heat" away from it. The electrolyte is what catches fire and it is like welding underwater, it carries it's own Oxygen in the chemical makeup. So a halon wouldn't suffocate it. So, if you wanted to put an external additive to stop the fire, as mentioned in another thread, sand would be a good medium as it not only contains the flame, but also sucks a lot of heat away from it. Also, you could use a compressed noble gas (not compressed air, obviously, as it has O2 in it) and douse the cells in flame. Ie: you could use liquid nitrogen or even CO2 (CO2 I'm not completely sure about, however, I think the CO2 bond is stronger than the ignition process and could suck enough heat out)
 
I suspect that a monitoring software would have to be smart enough so that if you lost a pack and your voltage dropped off my 3.7, your charger would not continue to charge as if you did not loose a pack.....

Example: 14s would be 51.8v nominal, so if you lost a pack, I would think the charging software would shut off at 48.1v.

I would be very interested, I believe we might have some members who work with Raspberry Pi computers, I would like to see what would become of that.

-Bob
 
If the packs are in Series, then a lost pack will make a huge difference in readings. The BMS would/should detect a short within the pack arrangement. The voltage wouldn't drop down like that.
However, in parallel, you'd have a similar situation as Dan had with his failed pack. The BMS would need to monitor each pack individually via a shunt (imho) and when that failed pack starts sucking large amount of current, disconnect the pack.

Remember, Series Adds Voltage, Parallel Adds Amperage.

But yes, Rob, the BMS should be smart enough to do disconnections based on these measurements. My BMS is going to have several layers of protection and monitoring. Not only are the packs going to be shunted and monitored, but the series connections within the packs will be monitored as well. It will have control to disconnect a series in a pack, a whole pack, or the whole system, depending on what's going on.
 
that sounds quite expansiv, and watch who is saying that^^ i wonder if a fuse would do the same....
 
MajStealth said:
that sounds quite expansiv, and watch who is saying that^^ i wonder if a fuse would do the same....
Click to expand...

The whole reason why I'm doing it this way is because my cells won't be soldered together. They will be slotted in cell holders. This way I can determine what cells are going bad and pull and replace them. This also allows me to do micro-stats on the packs. I can get a lot of information gathered about the recycled cells. I'll be able to plot the life cycle of almost "every" cell by doing it this way.

I almost want to put in even more checks to monitor each cell. But I don't know if I want to go quite that in depth yet. It may end up that way, depending on how I actually assemble my packs. I haven't decided that yet.

And, it's not so expansive as that's how a lot of EV's are set up. They can tell what cells are bad and be able to replace just those cells and keep the whole pack in place. Also, if a cell goes bad before they get back to the shop, the BMS disconnects that cell from the pack so it's not drawing the whole string down.
 
mike said:
Korishan said:
Lithium don't spontaneously ignite, either. They must be damaged to ignite. Either physically or electrically they are damaged. Overcharging is the most common failure
Click to expand...

And I would like to add, by a LOT, not by 0.05v. I had 1680 cells hit 4.4-4.5v last week for a couple of days and not one single cell blew up, vented, etc. Probably halved their remaining lifespan, but that's about it.
Click to expand...

Mike, Korishan,

Agreed. But to my knowledge there is nothing you can do to a lead-acid battery to cause it to burn (yeah, they generate hydrogen, but venting removes that risk). 18650s are filled with flammable substances and have the ability to self-ignite, thus must be treated accordingly.

-John-
 
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