My DIY battery storage system

jonescg

100 MW
Joined
Aug 7, 2009
Messages
4,213
Location
Perth, Western Australia
I have converted several lead-sled scooters to LiFePO4 over the years, including these shitty E-max "Sport" scooters.
Emaxsport Pb to Li 001.jpg

They worked, but they only do 55 km/h, take a calendar month to get there, and they're really badly made. So after years of them not selling, I ended up picking up a couple of them for very little. I recovered the lithium I put into them and will be using them to make a load-shifting system for charging my scooter (which is not shit).

Future powerwall.jpg

The scooter to be charged of an evening.
Plates on.jpg

I hope to rig the solar panels on the shed to charge the 6 kWh LiFePO4 battery, so I can then dump charge from it to the scooter at night.
 
Thanks for the tip!
I have a couple of ways of doing this, and they cost about the same. But going down the MPPT charge regulator / inverter route might be the best for an 'off-grid' system.

Got two more scooters to rip apart this weekend :D
 
All of the cells ready and willing!

20170926_202906.jpg

Next step is to get some busbars cut up. Only needs to be about 1 mm thick, if that.
 
Only a little bit of progress to report - welding up a nuggety little cabinet to house the cells. I want it to be self contained. There's room for another 2 cells in parallel (8 kWh total).

Power cabinet.jpg

The aim is to have two lower shelves filled with cells and the upper shelf with the inverter and battery charger. If I had an inverter/charger I'd hook the battery right up to it, but I don't. So for the meantime I'll just charge it off the mains while the sun shines (set a timer from 9 am to 3 pm) and use the inverter to run the scooter charger.
 
Well the shelf part is complete. I'm going to put two sheets of 9 mm plywood down and glue them together for added strength.
There's room for about 8 kWh of these cells (I only have 6 kWh) but with any other chemistry you could probably fit closer to 16 kWh.



Next step is the busbars.
 
Just going to get these laser cut from 3 mm aluminium since that's what the terminal posts are made of.
Sure, I could drill them myself, but sending a file by email and picking up finished busbars is so much easier...
Power Cabinet Busbars.jpg
 
I got the aluminium busbars made to suit 9 cells in parallel, since that's what the cabinet can easily fit. I figured at the time I could just leave them there and populate them as I get more cells...

...but then I got greedy :twisted:

So I'm buying another 45 cells. It's not the ideal situation as I didn't want to spend too much on this battery, but what the hell. 9 kWh is more useful anyway.

Busbars going on sml.jpg
 
Little bit of progress today. I made some trays which I can assemble the battery on before lowering it down onto the shelf and pushing it in. You would need a friend on the other side as there's about 50 kg there.

One shelf nearly ready.jpg

Trays made2.jpg

I'm going to have to run the cables up the left hand side to the upper shelf (fuse, isolation switch, inverter/charger etc). I figure 9 strands of 12 gauge wire would be heaps.
 
@Augidog - haha, the scooters were had for a song. I got three 2 kWh scooters for about $2000. The batteries were the best part of them; the scooters themselves were total rubbish. To be honest, increasing the capacity from 6 kWh to 9 kWh was mainly about using the volume available. The cabinet is the size of a small TV cabinet I guess, so I might as well use the space fully. That, and the fact that 9 kWh is a fairly useful amount of storage. 6 kWh might be a little on the small side, especially in an all-electric household.

I picked up a 2.2 kW solar array, complete with 4 kW grid-tie inverter for $1100 off Gumtree (like Craigslist, but shittier). This included most of the rails and mounts, but I had to buy a few extras to make it work. Maybe another $100 in cable etc. But for a battery-buffered 2 kW solar system, it's pretty good going. Longer term I think I will get a hybrid inverter which can use the battery for the afternoon/evening shoulder period and still have grid export capability.

@Fechter - I've build a small timber tray which will hold the base of the cells firm, and the busbars will to a pretty good job of holding the tops in place, but I will also throw a bit of strapping around them too. I will have 180 Ah here, and at absolute worst, I'd be pulling 0.5 C on a really heavy load like the stove. So I think they should be fine. LiFePO4 is one of the more heat-tolerant chemistries too, which suits our climate here.
 
FWIW, I have some Thundersky 60Ah cells that swelled right up just recharging them at a low low rate, after only a partial discharge at a low rate. :(

I'd read over and over that they need compression, but hadn't bothered because of the rate I was going to use them at. Now I know better. :/
 
Some of these cells have already swollen a little from their life as a scooter battery, but not so much that I can't terminate them or anything. Plus they were manufactured by GBS about 4 years ago, so they're definitely a better generation of LiFePO4 cell than anything in yellow.
 
I don't doubt that. ;)

FWIW, my swollen ones still work--I just dont' trust them unattended, or enough to use them at any rate higher than a few amps. (they are sometimes used to power my audio amplifier for the music studio, or other "automotive 12v" uses around the house).
 
The last 48 cells have arrived. I'll spread these out amongst the old cells in an effort to sort of 'equalise' their capacities and impedance.
Going to be a fun weekend of making cables and lugs!

20180125_080824.jpg

And yes, I'll be recycling all those copper links since I don't need them.
 
I have terminated both trays of cells. Next step is to lower them into the cabinet (with the help of a friend) and wire it up.
9 kWh terminated_sml.jpg
 
Still don't have a strong helper for the shelf-shuffle, but I worked on the main DC isolation board. Switch, fuse, terminal busbars and current shunt. I might make this end the DC distribution board too - if I ever wanted to power stuff on 48 volts I can run several circuits back to a fuse box on this side.
Switch location.jpg
The inverter and charger will go to the other side.
Rivnuts in.jpg

I put M6 Rivnuts into the steel frame for covers which will keep it clean and tidy. Not sure what material I will use, probably just plywood. I can also power some fans for keeping the cells cool if need be - this way I can put filters on the incoming air.
 
Finally got it together today. I moved the shelves into place on my own - only 46 kg each, and I didn't have to move them very far. I did it while wearing my safety boots! (Truth be told, I was barefoot :lol: )

Battery complete.jpg

The two half packs are joined by 9 x 4 mm2 cables with ring lugs. The final + and - leads have to come from the other side. I didn't have the room to put them up the opposite side - bit of a design fault at the time of construction, but this does work, even if it's messy. The 9 x 4 mm2 leads are terminated inside a single 70 mm2 terminal lug which was crimped using a hydraulic crimper. When you have the right tool for the job, life is easy.

48 V dist board.jpg

The - side goes through a 125 A fuse first, then to a 200 A max, 50 mV shunt, then a busbar. The + side goes through a manual isolation switch to a busbar where I've fixed a small 6 position fuse box. There is still room for another 50 mm2 cable to bolt onto this to the inverter (which has it's own fuse). The 6 fused circuits can be used for lights, fridges, motors, scooter chargers... whatever. I wanted to make sure this was a complete, 48 volt, 180 Ah off-grid storage unit ready to go. Never forget your fuses!!!

Next step is to fit the charger and do a final balance charge.
 
I bulk charged up until the first cell went over 3.65 V (watching closely while stripping copper wire for recycling) and used the BC168 after that. Took most of the day, but we're sitting pretty with all cells having been taken to 3.65 V each. They're probably going to settle at about 3.5 V each overnight.

I will eventually buy some balance boards which trim the cell voltage down to 3.55 V each. Same as I have on my scooter: https://evparts.com.au/ev-power-bms/bms-cell-modules/lfp-voltage-balance-board.html
I will also have to get a dedicated bulk charger but I also don't want to spend too much money since I plan on getting a decent inverter/charger which couples with the solar array. Might get one of these:
https://evparts.com.au/charging/ev-pfc-chargers-1-5kw-pfc/chg-a-16c-25a.html

At least I can take it with me under the seat of the scooter for longer trips. The current charger is the original sealed-lead charger and it goes a little too high I think (59 V max). As a home charger it's not too bad, but I make a habit of turning it off after it's done charging.

Longer term I will probably fit one of these: https://www.outbackmarine.com.au/victron-smartsolar-mppt-150-100-mc4?gclid=CjwKCAiA-9rTBRBNEiwAt0Znw6LpLeNWMTkZ85lrxGb14ruQPPbR7xn4OJcaEANdJB9GDUUlHlA6sxoCbx0QAvD_BwE
And find myself a decent inverter for running the house.
 
Fame! :lol:
http://www.abc.net.au/news/2018-02-07/what-could-happen-to-electric-vehicle-batteries/9398100
 
Rube said:
jonescg said:
Fame! :lol:
Not as good as your sultury radio voice :D

Just for you mate :)

http://iview.abc.net.au/programs/abc-news-wa/NU1808W033S00

Starts at 12:27
 
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