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LTO Powerwall
Quote:just need to make the rest of them

And a few spares just in case Wink
Why make 1 when you can build 2 for the twice the price.

Nice setup you got there. Overhangs are nice, as long as they are supported. Here in Fl we'd have to pull those overhung ones down as we get hurricanes. Though, I'm sure they could be set up in such a way they could be taken down quickly (we usually have at least a few days warning, sometimes a week)

For the axials and the DB connectors, make a jig where the fuses are held in place. Wink
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Where the panels are overhing they are not exposed to the wind so unless we get a bvery bad storm they will stay put. I had thought the extreme option would be to put a couple of wooden battens across and then put a weight on if there was a storm. Would more likely just move them onto the top of the next panel in the roof, fortunately we don't get hurricanes very often (40yrs or more).

For Florida I would just lay them flat on the floor or propped up with a brick or two to let the rain wash off, take the bricks out in hurricane alert.. as long as they don'g get over grown they would probably do just as well as on a roof and a lot cheaper to install (and clean).

Only takes a couple of frustrating minutes shuffling the fuses around to get them in place, like that old game with the ball bearing to get into the center of the maze.. I have not lost it and thrown one out of the window yet... Thinking about a jig and the only way to hold them would be a couple of thin strips with cuts in for the wires for the fuses to sit in because the fuses are touching each other... hmmmm...
(07-19-2018, 01:10 AM)completelycharged Wrote: ... I have not lost it and thrown one out of the window yet...

Yet Tongue
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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Been a while and finally installed the last cells after they had been sat on a shelf for nearly a year.... so now just under 36kWh.

The last 3 packs are "temporary" works in progress until I hook up some additional leads to allow each of the parallel sets to be connected for balancing or monitoring and add the rest of the case. They lack the separate breakers but they are in series with another pack with the 100A breaker in, so all ok... still needs a bit of tidying up..

The busbars (aluminium) with the "whatever colour cabling was available at the time" installs has berformed quite well.

While experimenting trying to trip a 100A breaker, a couple of long leads and a bit of steel plate to experiment on.... I could only get 325A before the end of the cable would dissapear at 14.8KW... 8AWG / 10mm2... and the breaker would not trip because the fault current was not high or long enough.

The intesting bit was the wattage lagged the volts and amps on the dispaly refresh interval... guess that's another made in China "feature".

Resting voltage was 47.23V so at 325A and 45.48V on the same meter that gives a battery to busbar resistance of 5.08 milli Ohm.
jdeadman likes this post
Thanks for introducing me to the site. A lot of information here of great interest it's much appreciated.
completelycharged likes this post
Bit of an update now the packs have been running for over a year and 12kW (6 packs) have done some miles travelling off-site.

Retrospectively the choices I made on approach in review are :

1. Choice of pack size of 11s
My choice of 11s was biased towards being compatible with anything designed for 48V based on lead-acid voltage range equivalence. This however ends up with the low voltage level seeing some inverter units reduce output due to low voltage (still within lead -acid range) so a 2x12s (24s) build would avoid this if a specific inverter model because the upper voltage range. That said the lower inverter ouptut sort of helps self regulate the depth of discharge so no real issue.When looking at the upper voltage range for 12s this starts to create issues if equipment is only intended to be lead-acid compabible as 12s woudl see 15.6V equivalent, compared to 14.3V if charged to 2.6V (higher than needed....)

2. Choice to build as separate 11s packs
Best choice out of all, for my situation. My need was for the ability not to be stuck with 48V and have the option to go 24V or any multiple of 24V upwards (72V or 96V is my next plan). The smaller packs make them useable separately and still easy enough to lift until I'm about 60.

3. BMS choice - none to date (installing one in the next few days).
Maybe I was fortunate with the cells and avoided disaster out of luck. The charge controllers I found out reset their voltage level settings if the DC rail is disconnected overnight and will then try to over-charge the pack (cought because I was working next to the volt meter at the time). Low voltage cut-out on the inverter units works well and the large pack size means any small vampire drain would take days to cause any cell to discharge below 2V and even then a zero volt cell is not an issue, the real problem is if any cell becomes a negative voltage forced discharge. The cells, however do seem to self balance if they are kept within the 10-90% range, howeve that is just my perception and lack of accurate voltage readings, however over a year this seems to hold true. I have never had to pull a single cell up/down only the 24V pack level cause by adding/removing packs.

4. Choice of 100A breakers on the packs
Still considering this one as I have not managed to trip a breaker "yet" even with a near short on one pack that warmed up a 10mm2 cable to near burning hand temperature in a couple of seconds.... I have opened up one breaker to have a look inside and not particularly impressed, so at the moment I'm more treating these breakers as simple isolator switches.

5. Build approach with aluminium plates / wooden boxes
Best choice, although this was distorted for me because I had access to equipment which would make the separate plates and drill the holes out. This did make the build process a lot easier and consistent so that the boxes could be stacked in any arrangement (impact on cable lengths needed to connect / join packs). Venting was not really needed as I don't run a pack more than 0.25C and is a risk as a falling cr*p collector. The double wall sides make for full terminal isolation so no stray wire accidents (less can be said for the fronts with one incident....)

6. Using 15 pin D-connectors for external BMS bookup
Works really well for packs (for manual or permanent monitoring), however this involves a lot of wiring and I mean a lot as each pack has 12 active wires and with 18 packs that's 216 wires, or 432 connections just to get out the box with over 100m of cable. 2m balancing leads need over 400m of cable, if using singles with another 432 solder joints. all in around 1500 solder joints.

7. Hot glue
This is a double edged sward, a big win overall. Building with hot glue makes for great wire positioning and terminal insulation (flashover and accidental shorts due to debris) but makes any repairs a complete pain, so make sure you don't have to replace or repair any connections (note the glass fuse choice below).

8. Pack breaker size 100A
The packs are 2kWh and 80Ah so the thought was to go for just over 1C in breaker sizing as this would allow for each pack to be run at 1C if used separately. The alternatives at the time (in my mind) were either 63A or 125A so my thought was 125A was too high (don't like the I2R losses with current up this high) and 63A just seemed too low for a couple of packs on thier own for 48V, however, given the use to date I would have gone for 63A breakers.

What would I change if building again ?
1. Pack breakers - double pole so that both sides are isolatedin the box
2. 63A instead of 100A pack breakers
3. Glass fuse integration in the packs for D-Connectors (blew up one socket !)
4. Small balancer per pack (still the plan)
piglet likes this post
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......

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