My DIY battery storage system

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jonescg
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My DIY battery storage system

Post by jonescg » Sep 04, 2017 9:30 am

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
Another lead to lithium conversion. Too bad the scooters themselves sucked balls.
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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
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The scooter to be charged of an evening.
Plates on.jpg
My good scooter - 3 kWh onboard, 60 km range
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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.

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Re: My DIY battery storage system

Post by Monstarr » Sep 14, 2017 7:26 am

You can use a Meanwell ISI-500 MPPT charger & inverter with those LiFePO4 cells. They somewhat have the same charge voltage as lead.

http://www.ebay.com/itm/Mean-Well-350W- ... XQvV9SMITK

There are more on ebay btw.

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Re: My DIY battery storage system

Post by jonescg » Sep 18, 2017 8:23 pm

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

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Re: My DIY battery storage system

Post by jonescg » Sep 26, 2017 7:53 am

All of the cells ready and willing!
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Next step is to get some busbars cut up. Only needs to be about 1 mm thick, if that.

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Re: My DIY battery storage system

Post by jonescg » Oct 15, 2017 4:42 am

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
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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.

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Re: My DIY battery storage system

Post by jonescg » Oct 28, 2017 5:34 am

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.
Power cabinet 2.jpg
Next step is the busbars.

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Re: My DIY battery storage system

Post by jonescg » Oct 29, 2017 9:12 am

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
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Re: My DIY battery storage system

Post by jonescg » Nov 18, 2017 7:01 am

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
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Re: My DIY battery storage system

Post by jonescg » Dec 29, 2017 5:29 am

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
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Trays made2.jpg
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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.

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Re: My DIY battery storage system

Post by augidog » Dec 30, 2017 11:51 am

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Last edited by augidog on Jan 08, 2018 3:44 am, edited 1 time in total.

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Re: My DIY battery storage system

Post by fechter » Dec 30, 2017 1:10 pm

Are you going to compress the cells? Sometimes those will puff if run at high rates.
"One test is worth a thousand opinions"

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Re: My DIY battery storage system

Post by jonescg » Dec 30, 2017 8:23 pm

@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.

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Re: My DIY battery storage system

Post by amberwolf » Dec 31, 2017 2:13 am

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. :/

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Re: My DIY battery storage system

Post by jonescg » Dec 31, 2017 9:32 am

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.

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Re: My DIY battery storage system

Post by amberwolf » Dec 31, 2017 2:48 pm

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).

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