Compressing cells in your battery builds is questioned in this video.

[fafrd]

People have to take off the panels and racking to replace shingles. Some of them will put up the latest.
Solar farms replace panels every 5 years. I don't think they treat them worse than we do.

I think the key is whether you have need of additional power or not.

A solar farm can always sell more power and has already made the full investment in a racking system covering the full available area.

So once the 5-year depreciation-cycle on their existing panels has been reached, it makes total sense to replace all old/fully-depreciated panels with new more powerful panels.

For a home-user, if they are roof-space limited and want more power, the same logic applies (though without much concern regarding depreciation, merely budget).

But if you are already getting all the power you need, there is no reason to upgrade to more powerful panels - you can free up some roof space, but so what? (you’ve already spent money on the racking system, so that’s a sunk cost).

 

[ArthurEld]

I think it is better to limit the expansion with a little pressure when the cells are fully charged.
I want some flexible busbars but I don't want to make them.

 

[ArthurEld]

I think the key is whether you have need of additional power or not.

A solar farm can always sell more power and has already made the full investment in a racking system covering the full available area.

So once the 5-year depreciation-cycle on their existing panels has been reached, it makes total sense to replace all old/fully-depreciated panels with new more powerful panels.

For a home-user, if they are roof-space limited and want more power, the same logic applies (though without much concern regarding depreciation, merely budget).

But if you are already getting all the power you need, there is no reason to upgrade to more powerful panels - you can free up some roof space, but so what? (you’ve already spent money on the racking system, so that’s a sunk cost).

I just think they did the math and replacing panels every 5 years makes sense. It would probably make just as much sense if I did it. That's all I'm saying

 

[Bob B]

I just think they did the math and replacing panels every 5 years makes sense. It would probably make just as much sense if I did it. That's all I'm saying

My guess is that they can take a tax credit by depreciating them over a 5 year period .... at that point they can sell the old ones an make a little and start over with new ones. That makes it good for us being able to find used panels in good condition for cheap.
Without the depreciation benefit, it probably wouldn't make sense.

 

[cinergi]

You'd probably get a double benefit from reducing the range .... but I don't know if the expansion is linear across the SOC range .... @cinergi did some testing and may have more detailed information.

@Metalophile
The cells expanded way before 100% SoC. Charging to a lower VPC won't help.

 

[fafrd]

My guess is that they can take a tax credit by depreciating them over a 5 year period .... at that point they can sell the old ones an make a little and start over with new ones. That makes it good for us being able to find used panels in good condition for cheap.
Without the depreciation benefit, it probably wouldn't make sense.

Exactly. Also, a production facility has a maintenance schedule and rarely wants to deal with the upkeep of old equipment. By switching everything out every 5 years, they maintain uniform infrastructure and minimize downtime for maintenance and repairs.

Makes total sense for a business.

Less for those of us trying to protect against rate increases by locking-in our own captive supply...

 

[cinergi]

At what C rate?

C rate had no effect on amount of expansion in my tests.

 

[Gazoo]

One dangerous issue I see with these batteries is terminal threads failing.

If one has used a thread locker I think the terminals will fail before the threads do. The maximum 8nm force as noted in the EVE spec sheet isn't a whole lot. It is axial force but as far as we know when @fhorst accidentally put pressure on his stud, the terminal sunk into the cell causing an internal short. As the cells expand and contract there is stress on the terminals unless using braided busbars or cables. When the cells expand they are capable of much more force than 8nm.

Some of my cells arrived with undulated (uneven) sides. When I first hooked them up to parallel top balance the busbars barely reached. I have squared them up as best I can to make an 8S square pack so my plywood is even across the cells. I am going to redo the whole pack using either braided bus bars of cables for the interconnects, use light compression at a full SOC, and call it a day.

 

[ArthurEld]

My guess is that they can take a tax credit by depreciating them over a 5 year period .... at that point they can sell the old ones an make a little and start over with new ones. That makes it good for us being able to find used panels in good condition for cheap.
Without the depreciation benefit, it probably wouldn't make sense.

I can't even count it as an expense.
I will get the 26% this time though.

I probably will replace my panels next time I replace my roof. But it depends on what is available then and how much it costs.

 

[HRTKD]

C rate had no effect on amount of expansion in my tests.

So State Of Charge matters more than the rate of charge?

 

[cinergi]

So State Of Charge matters more than the rate of charge?

Indeed. I don't think rate matters at all - I measured no differences between .05C and .5C - it was always the same 2mm at the bottom in a 4s configuration.

 

[fafrd]

If one has used a thread locker I think the terminals will fail before the threads do. The maximum 8nm force as noted in the EVE spec sheet isn't a whole lot. It is axial force but as far as we know when @fhorst accidentally put pressure on his stud, the terminal sunk into the cell causing an internal short. As the cells expand and contract there is stress on the terminals unless using braided busbars or cables. When the cells expand they are capable of much more force than 8nm.

Some of my cells arrived with undulated (uneven) sides. When I first hooked them up to parallel top balance the busbars barely reached. I have squared them up as best I can to make an 8S square pack so my plywood is even across the cells. I am going to redo the whole pack using either braided bus bars of cables for the interconnects, use light compression at a full SOC, and call it a day.

I decided to go with 2/0 welders cable and lugs for exactly this reason.

Expanding/contracting cells + rigid busbars = a great deal of mechanical stress.

Either rigging the cells up so each is free-standing or using a flexible interconnect that can easily move with the moving cells seems like the safest solution...

 

[ArthurEld]

If one has used a thread locker I think the terminals will fail before the threads do. The maximum 8nm force as noted in the EVE spec sheet isn't a whole lot. It is axial force but as far as we know when @fhorst accidentally put pressure on his stud, the terminal sunk into the cell causing an internal short. As the cells expand and contract there is stress on the terminals unless using braided busbars or cables. When the cells expand they are capable of much more force than 8nm.

I agree that thread locker makes the studs much stronger. They can handle more side pressure and more torque with loctite.
I'm not sure the jury has made up it's mind about fhorst's short. The heat could have made his terminal sink in. I think there may be other possibilities as far as what caused his short.

Some of my cells arrived with undulated (uneven) sides. When I first hooked them up to parallel top balance the busbars barely reached. I have squared them up as best I can to make an 8S square pack so my plywood is even across the cells. I am going to redo the whole pack using either braided bus bars of cables for the interconnects, use light compression at a full SOC, and call it a day.

 

[Gazoo]

I'm not sure the jury has made up it's mind about fhorst's short. The heat could have made his terminal sink in. I think there may be other possibilities as far as what caused his short.

Well that's true, but 8nm isn't very much. What did we get ourselves into...

 

[fafrd]

I'm not sure the jury has made up it's mind about fhorst's short. The heat could have made his terminal sink in. I think there may be other possibilities as far as what caused his short.

I agree that we ended up with a short-list of 2 or 3 possible causes for his unfortunate failure.

On the other hand, I think we are all pretty much in consensus that the terminals are the Achilles-Heel of these 280Ah LiFePO4 cells...