EVE-280 cells should these be clamped tight or spaced for expansion?

lance

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My two 4s batteries are in my bumper pull toy hauler (11k GVWR). I get down some rough roads, drive on some highly off-camber roads and look forward to getting into a camping spot that requires 4Lo. I had the opportunity earlier this year to verify that all the screws on my cell terminals were still tight. Only one screw required a small amount of tightening. I'm using no thread locker or lock washers.

Maybe one day I'll take the packs apart and see what the surface between the cells looks like. But based on the screws being secure after all I've put the batteries through, I doubt that I'm going to see any evidence of friction/movement between the cells.
While I've not done so yet with this battery pack in, I've already had the van down and up some pretty grinding, bouncing roads for extended periods..... believe me: I'm building my cabinet frames and everything anticipating some rough riding.
 

lance

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also yes I believe you don't want to keep these at a max state of charge for too long which is why you shouldn't top balance them and leave them at 3.65v for months.
I wonder if I should connect something to them and drain them down further; they're at whatever they shipped at... which I've already forgotten the number! But, memory is it was pretty high. There's still many months to go before they come online.
 

HRTKD

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I like the look/sound of that but, my understanding was that there was also a desire to have some air movement between the cells, whether for cooling or for heat transfer from heating pads in extreme cold.

Reports on the forum are that these cells don't heat up much unless you're pushing a high C discharge for an extended period of time.

The warming pads on my batteries do a good job of heating the batteries evenly. I have a temperature sensor for my BMS and the thermostat located in the middle of the battery and the temperature sensor for the Victron BMV-712 located on the last terminal in the battery. The temperature readings I see on both devices are often exactly the same. I've never seen them far enough apart to bother taking note of it.
 

lance

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Reports on the forum are that these cells don't heat up much unless you're pushing a high C discharge for an extended period of time.

The warming pads on my batteries do a good job of heating the batteries evenly. I have a temperature sensor for my BMS and the thermostat located in the middle of the battery and the temperature sensor for the Victron BMV-712 located on the last terminal in the battery. The temperature readings I see on both devices are often exactly the same. I've never seen them far enough apart to bother taking note of it.
Well, this is good to know, thank you. You're reminding me that the guy at the heating pad company, with whom I had a great conversation, has apparently dropped the ball on my design. I've got to reach back out to him and try to get it moving again.
 

Firstascent

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I wonder if I should connect something to them and drain them down further; they're at whatever they shipped at... which I've already forgotten the number! But, memory is it was pretty high. There's still many months to go before they come online.
I bet they're around 3.2-3.3 something volts. but keep in mind that could be like 25% or 70% state of charge haha. the curves is very flat in the middle so voltage isn't the best indication.

Do you have an inverter? if so you could do a top balance, assemble them in your 4S (or whatever size) pack, drain them down to 50-60% and then let them sit ready to go.

I would've done something similar but I didn't have a charger or inverter until a couple weeks ago when I started. But now I'm full swing ahead on my install.
 

Short_Shot

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I like the look/sound of that but, my understanding was that there was also a desire to have some air movement between the cells, whether for cooling or for heat transfer from heating pads in extreme cold.
Not necessary. In fact that would be bad.

Heating pads can just be stuck to the bottom or sides.
 
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lance

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I bet they're around 3.2-3.3 something volts. but keep in mind that could be like 25% or 70% state of charge haha. the curves is very flat in the middle so voltage isn't the best indication.

Do you have an inverter? if so you could do a top balance, assemble them in your 4S (or whatever size) pack, drain them down to 50-60% and then let them sit ready to go.

I would've done something similar but I didn't have a charger or inverter until a couple weeks ago when I started. But now I'm full swing ahead on my install.
Ah, yes of course. I, out of my relative ignorance on the topic, was conflating voltage and SOC. I do understand the long flat curve in the middle....

I do not have an inverter yet, no. Curious though: even if I did, and followed these steps you suggest, how would I know the batteries' SOC using that method?

I also need to check the amperage of the charger I bought next time I'm downstairs where it is at.... if memory serves me right, it was one recommended by Will on this site somewhere.
 

Firstascent

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Ah, yes of course. I, out of my relative ignorance on the topic, was conflating voltage and SOC. I do understand the long flat curve in the middle....

I do not have an inverter yet, no. Curious though: even if I did, and followed these steps you suggest, how would I know the batteries' SOC using that method?

I also need to check the amperage of the charger I bought next time I'm downstairs where it is at.... if memory serves me right, it was one recommended by Will on this site somewhere.
The most accurate way is using a shunt so you can accurately track how much you've used in aH. With that being said, voltage as we mentioned isn't the best measure of SOC, I'd think it'll at least get you close enough for storage. you just don't want them full.

good chance your charger is the same as mine haha. I got mine from amazon from one of Will's recommendations, I think it's a 30v/10a charger and was around $60 or so.
 

lance

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The most accurate way is using a shunt so you can accurately track how much you've used in aH. With that being said, voltage as we mentioned isn't the best measure of SOC, I'd think it'll at least get you close enough for storage. you just don't want them full.

good chance your charger is the same as mine haha. I got mine from amazon from one of Will's recommendations, I think it's a 30v/10a charger and was around $60 or so.
Yep. That's the one!

Interesting that the only way to know a battery's SOC is to monitor what's gone into it, and what's come out of it. I actually do have my shunt and bms (Shuntmon and Watchmon7) but, I'm nowhere close to prepared to take on setting them up. Hell, I don't even own the PC I'm going to need to run their software yet.... I'm a Mac guy here. I think I'll just sit on the batteries as they are....
 

Firstascent

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Yep. That's the one!

Interesting that the only way to know a battery's SOC is to monitor what's gone into it, and what's come out of it. I actually do have my shunt and bms (Shuntmon and Watchmon7) but, I'm nowhere close to prepared to take on setting them up. Hell, I don't even own the PC I'm going to need to run their software yet.... I'm a Mac guy here. I think I'll just sit on the batteries as they are....
Oh that’s funny!
Very similar setup here, I’m using Batrium as well except I have the watchmon4 with blockmon’s and the shuntmon as well. I am also a Mac guy but have a pc I keep on the side for the rare instances such as this haha. Soon Batrium will have their cloud software and I can’t wait for that.
 

Johannlog

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Is there a thread (or posts in this thread somewhere), that deal more specifically with how to compress cells to the desired 12 PSI? From what I have read so far there are a lot of assumptions on how/if it must be done and the effectiveness of compression. I am not sure what SOC my cells will be at when they arrive (I bought them from Amy) but apparently I won't really be able to determine precisely the SOC (using voltage) anyway, so should I just use tape and hope for the best?
 

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Bob B

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There is this one and also one about using a special foam, I don't have quick reference to the foam one, but you can probably find it with a search.
 

Shawn Hayes

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I’ve read a lot of posts/threads about compression. So many ideas and different ways to do it. I ended up using 5/16” aluminum plates with .20” hard rubber matting between plates/cells to give them a “firm” cushion when they expand and rebound when they contract. I used 1/4” threaded rods, 10 rods for each 16s pack, 4 packs of 4 cells, to apply pressure evenly as I could. I used the 12-psi (torque wrench) rule of thumb at 3.25 volts when clamping.
The one thing I never read was how much PSI was gained once you reached 3.65 volts? So tonight, I am charging up a my last 16s pack and had an idea.
When bolting together this pack, I inserted a blood pressure cuff between the middle cells on the end of the pack. I set the blood pressure cuff at 30 mmhg (millimeters of mercury) and started charging. Hopefully this will give me an idea of how much PSI is gained between 3.25v and 3.65v. So for every 1mm of mercury gained, I’ll divide by 51.715 to get the added PSI.
Now I I know this may not be scientific or the best idea ever. But since I was unable to find how much PSI would increase this was the best idea I could come up with to give me a good rule of thumb on the PSI gained.
Thoughts? Does anyone already know this? I assume each application may be different based on the materials used in the compression application.
 

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Firstascent

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I’ve read a lot of posts/threads about compression. So many ideas and different ways to do it. I ended up using 5/16” aluminum plates with .20” hard rubber matting between plates/cells to give them a “firm” cushion when they expand and rebound when they contract. I used 1/4” threaded rods, 10 rods for each 16s pack, 4 packs of 4 cells, to apply pressure evenly as I could. I used the 12-psi (torque wrench) rule of thumb at 3.25 volts when clamping.
The one thing I never read was how much PSI was gained once you reached 3.65 volts? So tonight, I am charging up a my last 16s pack and had an idea.
When bolting together this pack, I inserted a blood pressure cuff between the middle cells on the end of the pack. I set the blood pressure cuff at 30 mmhg (millimeters of mercury) and started charging. Hopefully this will give me an idea of how much PSI is gained between 3.25v and 3.65v. So for every 1mm of mercury gained, I’ll divide by 51.715 to get the added PSI.
Now I I know this may not be scientific or the best idea ever. But since I was unable to find how much PSI would increase this was the best idea I could come up with to give me a good rule of thumb on the PSI gained.
Thoughts? Does anyone already know this? I assume each application may be different based on the materials used in the compression application.
Cool setup and interested in your results.
Just one thought, you should at least use a washer in between the nut and the busbar
 

ken morgan

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I’ve read a lot of posts/threads about compression. So many ideas and different ways to do it. I ended up using 5/16” aluminum plates with .20” hard rubber matting between plates/cells to give them a “firm” cushion when they expand and rebound when they contract. I used 1/4” threaded rods, 10 rods for each 16s pack, 4 packs of 4 cells, to apply pressure evenly as I could. I used the 12-psi (torque wrench) rule of thumb at 3.25 volts when clamping.
The one thing I never read was how much PSI was gained once you reached 3.65 volts? So tonight, I am charging up a my last 16s pack and had an idea.
When bolting together this pack, I inserted a blood pressure cuff between the middle cells on the end of the pack. I set the blood pressure cuff at 30 mmhg (millimeters of mercury) and started charging. Hopefully this will give me an idea of how much PSI is gained between 3.25v and 3.65v. So for every 1mm of mercury gained, I’ll divide by 51.715 to get the added PSI.
Now I I know this may not be scientific or the best idea ever. But since I was unable to find how much PSI would increase this was the best idea I could come up with to give me a good rule of thumb on the PSI gained.
Thoughts? Does anyone already know this? I assume each application may be different based on the materials used in the compression application.
it ain't stupid if it works... and even if you cannot get an exact PSI figure, if you can get a percentage of pressure increase that could tell you a lot as well. there is no such thing as worthless data, it might not pertain directly to what you originally wanted, but it can still be used in one form or another.
 

Short_Shot

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I’ve read a lot of posts/threads about compression. So many ideas and different ways to do it. I ended up using 5/16” aluminum plates with .20” hard rubber matting between plates/cells to give them a “firm” cushion when they expand and rebound when they contract. I used 1/4” threaded rods, 10 rods for each 16s pack, 4 packs of 4 cells, to apply pressure evenly as I could. I used the 12-psi (torque wrench) rule of thumb at 3.25 volts when clamping.
The one thing I never read was how much PSI was gained once you reached 3.65 volts? So tonight, I am charging up a my last 16s pack and had an idea.
When bolting together this pack, I inserted a blood pressure cuff between the middle cells on the end of the pack. I set the blood pressure cuff at 30 mmhg (millimeters of mercury) and started charging. Hopefully this will give me an idea of how much PSI is gained between 3.25v and 3.65v. So for every 1mm of mercury gained, I’ll divide by 51.715 to get the added PSI.
Now I I know this may not be scientific or the best idea ever. But since I was unable to find how much PSI would increase this was the best idea I could come up with to give me a good rule of thumb on the PSI gained.
Thoughts? Does anyone already know this? I assume each application may be different based on the materials used in the compression application.
What is the "12psi rule of thumb"?

One does not make psi with torque without calculating the loading over the thread pitch.
 

Shawn Hayes

Learning Everyday
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Messages
127
Location
South Carolina
What is the "12psi rule of thumb"?

One does not make psi with torque without calculating the loading over the thread pitch.
Maybe so. However there seems to be a hundred ways people are doing this compression idea. Springs, this pressure at this SOC/voltage etc....
So I’m using 12 inch pounds on a torque wrench to tighten down my threaded rods. Maybe I should have said 12 inch pounds on a torque wrench instead of PSI...
But it’s not perfect, but should achieve compression without over compression. Hence the blood pressure cuff to see how much increase I get at 3.65v.
 

ken morgan

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to date I have only seen or heard of one member here actually taking the time and funds to build a pack with a pressure sensor. This is a poor mans way of at least getting an idea of what the delta is. if you see repeatedly that your pack experiences a 4 PSI inclrease then you know that you can tighten to xx without going over the 17PSI threshold (or whatever the current accepted value is). so good on you for trying. Do your thing and let us know the results. (not making fun of you I am serious).
 

Short_Shot

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Maybe so. However there seems to be a hundred ways people are doing this compression idea. Springs, this pressure at this SOC/voltage etc....
So I’m using 12 inch pounds on a torque wrench to tighten down my threaded rods. Maybe I should have said 12 inch pounds on a torque wrench instead of PSI...
But it’s not perfect, but should achieve compression without over compression. Hence the blood pressure cuff to see how much increase I get at 3.65v.
Oh. Yeah that makes more sense but does not readily convert to psi on the cell.

There's some simple math to do to figure that out but I'm neck deep in calc 2 homework
 

HRTKD

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There's some simple math to do to figure that out but I'm neck deep in calc 2 homework

Thanks for the reminder from the very distant past. Now I'm going to have nightmares tonight.
Eyecrazy.gif
 
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