Weird bus bar idea

cinergi

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The is no heat.

You can see that each 16S is on 2 rows and parallel is between each every 2 cells , please open the image and see the connections of batteries and also on the end are the inverters. Also for better balancing inverters will be moved at series ends, now they remained from first 2 series of 200Ah and i just added 2 more series of 16s of 310Ah. The setup is for long therm storage and load is not too high. Also using 2.5mm2 balcing with WAGO allows me to add up to 5 x JK Active BMS to work in parallel. I consider having all batteries as one pack and connecting4 or more inverters to the same pack better than using separate pack for each inverter (not possible with parallel setup also, so it should be same battery pack).

Heat is irrelevant to the discussion. Telling me that you have no heat does not mean that this configuration will perform well (whether it's short-term or long-term).

I did look at the picture. I spent a lot of time studying your picture. Please assume good intent on my part; my points still stand - I do not recommend this configuration. It's still your choice but I recommend flat bus bar connections and balanced power flow. You appear to even have different size cells in parallel.

Have a look at what I found with terminals that were apparently dirty (but there was no visible indication it was dirty, there was no heat, and there were no performance problems):

That particular issue would have, over time, caused issues. I *guarantee* you have the same issue with your current configuration. You have different C rates throughout your entire pack which will age the cells differently which will cause balancing issues that no amount of active balancing can correct.

If my reasons still aren't clear, I'm happy to clarify further. You asked for input - I'm giving it to you.
 

elvis_asaftei

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Heat is irrelevant to the discussion. Telling me that you have no heat does not mean that this configuration will perform well (whether it's short-term or long-term).

I did look at the picture. I spent a lot of time studying your picture. Please assume good intent on my part; my points still stand - I do not recommend this configuration. It's still your choice but I recommend flat bus bar connections and balanced power flow. You appear to even have different size cells in parallel.

Have a look at what I found with terminals that were apparently dirty (but there was no visible indication it was dirty, there was no heat, and there were no performance problems):

That particular issue would have, over time, caused issues. I *guarantee* you have the same issue with your current configuration. You have different C rates throughout your entire pack which will age the cells differently which will cause balancing issues that no amount of active balancing can correct.

If my reasons still aren't clear, I'm happy to clarify further. You asked for input - I'm giving it to you.

how can I identify by using ohmmeter the problem ?
 

cinergi

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how can I identify by using ohmmeter the problem ?

One way would be to measure the DC voltage from the right-most positive cell terminal to the left-most for each parallel set of cells while under load. This will show you the voltage drop. It's not as accurate but should be sufficient to show a relatively significant drop.
The different-capacity cells is harder to measure the drop ... you'd need to charge into the top knee or discharge into the bottom knee and measure the voltage differences ... get the pack relatively discharged and then charge it fully. Is your State of Charge meter calibrated to the sum of all your amp-hours? (e.g. 200 + 280 + 280) or did you use the lowest common denominator (e.g. 200 + 200 + 200)?
It would be ideal to measure current but you won't be able to get a clamp meter around those bus bars.

I guess we're a little off-topic for this thread.
 

elvis_asaftei

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One way would be to measure the DC voltage from the right-most positive cell terminal to the left-most for each parallel set of cells while under load. This will show you the voltage drop. It's not as accurate but should be sufficient to show a relatively significant drop.
The different-capacity cells is harder to measure the drop ... you'd need to charge into the top knee or discharge into the bottom knee and measure the voltage differences ... get the pack relatively discharged and then charge it fully. Is your State of Charge meter calibrated to the sum of all your amp-hours? (e.g. 200 + 280 + 280) or did you use the lowest common denominator (e.g. 200 + 200 + 200)?
It would be ideal to measure current but you won't be able to get a clamp meter around those bus bars.

I guess we're a little off-topic for this thread.

I will check. I will also buy an DC clamp meter devs use I have only AC . If connections are good the current will flow only in series if I move the inverter on extremes and cells will not get unbalanced. Setup is for long therm storage not short term
 
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Leon

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6061 aluminum in the annealed state has slightly lower resistance than in the T6 state, so annealing doesn't do anything negative.
Regarding the cable connections, I made up these:
View attachment 55277

So that the distance from the cell terminals to the shunt connection is pretty close to equal.
That looks great, and I could make something like that at home (I really want a CNC plasma cutter).
 

Leon

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Let's use the water analogy for current flow. Your bus bar mounting hole is the drain hole. And the battery terminal the drain pipe. The water flows towards the drain hole. The water(current) will fall over the front edge of the drain( bus bar hole) and wrap around all the way around to back side, filling the pipe(terminal post).

Shown on your sketch, the 2 middle terminals look much more robust than the 4 on the corners. You can easily implement this design change to make all 6 terminal post Drain profiles match. The same applies to rounded corners, no current will make it into the hard 90 corner. But this would be unreasonable to do well with hand tools.

These are second order effects, but the key point is symmetry, its very important in high power delivery to minimizes system imbalances.

Note to Self: Make friends with a beer drinking plasma cutter owner.
Thanks for the explanation. It's nice that it makes intuitive sense.
 

Leon

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Here is my progress so far. I decided to split the pack in two so I get two small hernias rather than one big one.

Side panels are 17mm structural ply, couple of coats of paint slapped on. A piece of 12mm ply forms a base, attached to one side only at this stage.

DSC_0901.JPG

Cells are separated with some clear shelf liner material, 0.8mm thick across the bumps, half that in between. The texture is fine enough that I'm not worried about uneven pressure. PVC maybe? I put some sheets from the covers of plastic sleeve binders between the cells and the plywood, polypropylene I think. Some more shelf liner is under the cells, on top of the 12mm ply.

M8 threaded rods hold everything together. They are awkwardly long in case I get around to sourcing 20 springs. Probably not worth it with only 3 cells in a row. I've covered them with clear vinyl tubing between the boards.

DSC_0903.JPG
 

elvis_asaftei

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Here is my progress so far. I decided to split the pack in two so I get two small hernias rather than one big one.

Side panels are 17mm structural ply, couple of coats of paint slapped on. A piece of 12mm ply forms a base, attached to one side only at this stage.

View attachment 55403

Cells are separated with some clear shelf liner material, 0.8mm thick across the bumps, half that in between. The texture is fine enough that I'm not worried about uneven pressure. PVC maybe? I put some sheets from the covers of plastic sleeve binders between the cells and the plywood, polypropylene I think. Some more shelf liner is under the cells, on top of the 12mm ply.

M8 threaded rods hold everything together. They are awkwardly long in case I get around to sourcing 20 springs. Probably not worth it with only 3 cells in a row. I've covered them with clear vinyl tubing between the boards.

View attachment 55404
What are the benefits of having the cells pushed from sides ? What is the force applied ?
 

elvis_asaftei

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Messages
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Here is my progress so far. I decided to split the pack in two so I get two small hernias rather than one big one.

Side panels are 17mm structural ply, couple of coats of paint slapped on. A piece of 12mm ply forms a base, attached to one side only at this stage.

View attachment 55403

Cells are separated with some clear shelf liner material, 0.8mm thick across the bumps, half that in between. The texture is fine enough that I'm not worried about uneven pressure. PVC maybe? I put some sheets from the covers of plastic sleeve binders between the cells and the plywood, polypropylene I think. Some more shelf liner is under the cells, on top of the 12mm ply.

M8 threaded rods hold everything together. They are awkwardly long in case I get around to sourcing 20 springs. Probably not worth it with only 3 cells in a row. I've covered them with clear vinyl tubing between the boards.

View attachment 55404
Why do you use expensive small cells in parallel and not large 310ah cells because it is half the price.
 

Leon

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What are the benefits of having the cells pushed from sides ? What is the force applied ?
These prismatic cells expand and contract during charging and discharging. Eventually this causes some sort of breakdown internally, reducing the life of the cells. Compression reduces this problem somewhat. The issue is extensively discussed on the forum.
 

elvis_asaftei

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These prismatic cells expand and contract during charging and discharging. Eventually this causes some sort of breakdown internally, reducing the life of the cells. Compression reduces this problem somewhat. The issue is extensively discussed on the forum.

is this happening also at lower than 0.2C charging and discharging rate ?
 

Leon

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is this happening also at lower than 0.2C charging and discharging rate ?
I think it's less of a problem at lower rates, not sure of the numbers. Plenty of info on the forum. I suggest doing some reading to see if it applies to your system.
 
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Gazoo

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is this happening also at lower than 0.2C charging and discharging rate ?
It does with my 280ah EVE cells. There is much discussion regarding cell compression so I am not going to go into it here. But I suggest you start your research here. And search the forums.

It looks like you could rearrange the busbars so they all lie flat against the cells terminals. Cinergi is absolutely correct.
 

elvis_asaftei

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It does with my 280ah EVE cells. There is much discussion regarding cell compression so I am not going to go into it here. But I suggest you start your research here. And search the forums.

It looks like you could rearrange the busbars so they all lie flat against the cells terminals. Cinergi is absolutely correct.

Yes, you are right, I will use alternate top bottom on bus-bars … like that all will be flat . thanks
 

elvis_asaftei

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Wha
Here is my progress so far. I decided to split the pack in two so I get two small hernias rather than one big one.

Side panels are 17mm structural ply, couple of coats of paint slapped on. A piece of 12mm ply forms a base, attached to one side only at this stage.

View attachment 55403

Cells are separated with some clear shelf liner material, 0.8mm thick across the bumps, half that in between. The texture is fine enough that I'm not worried about uneven pressure. PVC maybe? I put some sheets from the covers of plastic sleeve binders between the cells and the plywood, polypropylene I think. Some more shelf liner is under the cells, on top of the 12mm ply.

M8 threaded rods hold everything together. They are awkwardly long in case I get around to sourcing 20 springs. Probably not worth it with only 3 cells in a row. I've covered them with clear vinyl tubing between the boards.

View attachment 55404


what is the maximum amount of pressure (without damaging the cells or valve explode )that can be used to flatten swollen batteries ?

A31BA55D-147E-4634-9439-5FD4A88D7D43.jpeg
 

Bob B

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Sep 21, 2019
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3,389
what is the maximum amount of pressure (without damaging the cells or valve explode )that can be used to flatten swollen batteries ?

For a normal pack build .... 12psi is ideal and anything 17 and over is worse than no pressure when it comes to increasing life cycle ...... but ..... this is not a standard situation and I don't know for sure what the answer is.

For more answers about cell compression, you should do a search and .... do your research as Gazoo suggested.
 
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