This could be interesting

upnorthandpersonal

Administrator
I might put a spring washer there, but I'm not expecting the compression to be accurate - I just need some compression since it's better than no compression. I don't think I exceed 18 psi in any case. I also assume some elasticity in the threaded rods and the insulation foam between cells (not pictured).
But who knows, I might change my mind :)
 

svetz

Works in theory! Practice? That's something else
Short Version: You're probably fine, but compression springs are cheap

Long Version
... some compression since it's better than no compression....
But, also from that link, no compression is better than exceeding 18 psi. If you tensioned them while they were at their maximum temperature you're probably fine. But, you might be losing the advantage of compression while they are cooler.

If you tensioned them while cool, you might have a problem. As long as you torqued them appropriately, then the insulation (not shown) is probably inconsequential (that is it's probably already as compressed as it can be).

Thermal expansion/contraction is normal. The more cells there are in a row the greater the effect is. The threaded rods aren't going to expand/contract much as they're not subject to the same thermal loads (and different materials expand/contract at different rates).
The Case
for Springs

1620045014087.png

Let's say each of the 8 cells expands and contracts 0.25 mm, so with 8 cells in a row that's 2mm overall. If neither the cell nor the bars were compressible the pressure would be enormous. I suspect since it hasn't failed, that the wood has an indent where it was compressed under thermal load.

Still not convinced? How about Compression Springs are cheap at $2 to $8 each?

Not positive about the calculation, but I suspect you take the surface area of the battery and multiply it by the psi. For the sake of example math, let's say the two rows of cells have a combined surface area of 300 in² you'd multiply by 15 psi to get a total force of 4500 lbs. Divide that by 4 bolts to 1125 lbf per bolt. Springs are usually rated in lbf/in and a length. So a 3" 100 lbf spring compressed 2" is applying 200 lbf. Here's a $35 pack of 5 springs that are 2" and supply 838 lbf/in, or 1125 lbf at 1.34". So, when the batteries were hot you could torque them down. As the batteries cooled, the springs would keep pressure on them. Shop around, longer springs would apply more constant force.
 

upnorthandpersonal

Administrator
Yes, I've done the calculations before (in metric though ;)

As I said, I might change my mind and add them. I probably have some in the lab somewhere...
 

cinergi

1.21 Jigawatts
NOTE: The expansion/contraction of the cells is not due to temperature, it's due to SoC. So even at constant temperature, there will be changes in cell size. (I have a spring-based fixture so I know this from direct experience). (EVE 280Ah cells; Lishen 272's are a whole 'nother matter)
 

tmstr

New Member
How's the setup doing?

I'm building a mobile home to a 7.5T truck and looking for cheap solar panels from China. Thanks for the tip of Yangtze Solar Power. Right now discussing with them about 600W panels. They also have 700W panels but said that the production time is very long. Roof space is quite limited so I'm trying to maximize it :D Already ordered 16*310ah batteries for 48V setup and Daly BMS.

Greetings from Finland! ;)
 

upnorthandpersonal

Administrator
Terve :)

Set-up is doing great. Too much power this summer - let's see how autumn and winter go. Those panels perform as advertised, I'm happy with them. They look good as well. Batteries are performing as expected for a year already. No issues, and the BMS performs even better than expected - I really thought I would have destroyed it a couple of days ago, but it keeps on doing its thing. Same with that MUST inverter and charge controllers. I've really pushed them, and they seem to hold it together much better than anticipated.
 

houseofancients

Solar Addict
Strangely no real proof of those backdoors was ever forthcoming. :) That's not to say Hauwei doesn't produce horrifically bad firmware at certain product levels. It does. 3rd party audits have found mind bogglingly bad things such as multiple different versions of flawed libraries being used, within a single product.

At the sort of level I was talking about in my last post, China isn't cheap anyway. It's a myth that China is cheap. It's cheap if you want cheap crap. If you want something done properly in China, it can be a bit cheaper than the more familiar Euro/USA etc names, but not a whole lot.
same cant be said for cisco and juniper which did have all sorts of holes and backdoors in them
 

rhino

Solar Addict
Where did you get that MUST 6kW inverter? Their alibaba store seems to have minimum order of 10?
 

Leon

Solar Enthusiast
Inspired by these bus bars, I've ordered some tinned braid from China. When it gets here, I'll document the process I go through to make them.
 

upnorthandpersonal

Administrator
So after running this system for a little over a year now, I thought it would be a good idea to give a more in-depth status report. Let's go over all the components of the system.

- Solar panels
I am extremely happy to have gone with these large 500W ones. Not only do they perform as they are supposed to, they look good: the 'massiveness' of them together with how it simplified (in my case) the ground mount design is a great bonus I did not expect when I got them initially. Having a large panel also simplifies wiring, needs less mounting hardware, etc. They went through several storms in the mean time, and a very long and cold winter without any issues.
20210821_180344-jpg.61111


- Batteries
Cells are perfectly fine. The insulated box I made for them keeps them at temperature. I've not noticed any degradation. I don't know how many cycles I've put them through, but they have been close to empty during winter months, and close to full over summer. They're not being pampered; when I need the power I will deplete them, and when I'm processing wood for winter, or drying berries/meat or canning I will use the power 24/7 also in summer.

- BMS
This is the one component I really thought would be too cheap to be true, and I bought a few spares just in case since I thought for sure I would blow at least one. I had a couple of instances where I blew a 225A Class T fuse on the battery that I thought for sure would have destroyed the (100A rated) BMS. To my surprise, they survived my shenanigans. They've been running 24/7 for a year now without a hiccup. The spare ones are still in the box, unopened.

- Charge controllers
100A charge controllers hooked up to panels that can and do provide that amount of power. No issues what so ever. I only wish they came in a higher voltage version. Nothing much else I can say: power comes in, power goes to the battery, day after day, never an issue.

- Inverters
The high frequency one I stopped using and is a back-up now, stored away. It could handle most of the loads, but in the end did have some problems with specific inductive loads. Surprisingly, not the 1kW well pump, but the 150W or so ventilation system. The rest was no issue, but compared to the low frequency one the only advantage I see is the lower self consumption.
While the low frequency inverter is no Victron, it's a beast. 6kW, heavy as I don't know what, plug in everything I have at once (ventilation, well pump, waste water fan, pressure vessel, compressor, coffee maker, saw etc.) and it happily hums along at full load. Never an issue starting anything I hook up to it. It has a self consumption of around 50 to 75W, which while higher than a low frequency inverter isn't really that high either.
In addition, I made sure I could get spare parts; I ordered a spare power board and control board and had it shipped using FedEx from China. Cost: 150$ including $80 for shipping, one week delivery time. I swapped the components to make sure I can fix it if needed, and this was a breeze. So nice to have a device one can service at this price.

- Bus bars and MG Chemicals 847
Yeah, I'm using my self made braided ones and they're in my opinion still the best. I might be biased ;)
I also really like the MG Chemicals 847 between the bus bar and terminal. I've not had connection issues at all, nor do I have any issues with the BMS balance leads. The 847 really seems to 'unify' or 'equalize' any potential issues from not having perfectly flat bus bars, or differences in resistance contact from cell to cell. For me, after a year now, this is perfect.


Conclusion: seriously, this is boring. I would have at least expected something to blow up, not work as advertised. I was hoping to be able to have multiple posts with stories... but no. Maybe I should do even cheaper components next time. Can't start a YT channel with this stuff :)
 
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Fusion is the future

Solar Enthusiast
Make your bush bars self from alu strip, make then 2 x the square diameter as from copper and you have even a lower resistance and it is a lot cheaper .
 
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