Planning my 4S40P portable power station

AndrewBrown

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May 26, 2020
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image_venfdf.jpg
Greetings,

Could anyone help to figure it out with schematics for batteries layout and soldering busbars?
Please see the attached picture. I assume that all POS and all NEG should be connected in the manner that a have attached, but this is only from the top. Could any know how these cells should be connected on the bottom side of this pack?


Andrew
 
floydR said:
No picture attached
Did you click on picture after it uploaded in image uploader.
Aslo use preview to verify the picture is in the post.
later floyd


Sorry, my bad. Picture attached
 
Nope, all wrong. You have Pos Pos, Neg Neg, Pos Pos, Neg Neg. nope. It'd be Pos, Neg, Pos, Neg. Basically what you have drawn is a 4s40p


Please read the FAQ located on the main home page.
 
Korishan said:
Nope, all wrong. You have Pos Pos, Neg Neg, Pos Pos, Neg Neg. nope. It'd be Pos, Neg, Pos, Neg. Basically what you have drawn is a 4s40p


Please read the FAQ located on the main home page.
Yes, you absolutely right it was a typo. I have drawn 4S40P. In this case, I also allocate cells in the wrong order, right?
 
if you're going with 4s40p, then you the drawing is "sorta" correct. The drawing is 3s40p. (misspoke earlier)

Just connect 2-Pos and 2-Neg that are adjacent to each other (ie, row 1, 2, 3 & 4), and then on the flip side, you add the next section starting with row 3 (ie row 3, 4, 5 & 6).
 
Korishan said:
if you're going with 4s40p, then you the drawing is "sorta" correct. The drawing is 3s40p. (misspoke earlier)

Just connect 2-Pos and 2-Neg that are adjacent to each other (ie, row 1, 2, 3 & 4), and then on the flip side, you add the next section starting with row 3 (ie row 3, 4, 5 & 6).

Could you please check.
image_xhwaku.jpg
Am I right?


Korishan said:
if you're going with 4s40p, then you the drawing is "sorta" correct. The drawing is 3s40p. (misspoke earlier)

Just connect 2-Pos and 2-Neg that are adjacent to each other (ie, row 1, 2, 3 & 4), and then on the flip side, you add the next section starting with row 3 (ie row 3, 4, 5 & 6).
What do you think about this option? Can I do this way, is this right?



image_zoadym.jpg
 
The first one won't work, you'll create shorts. I highlighted the issues. Unless these were supposed to be alternating top/bottom.

The second one is better. Assuming the blue lines are the bottom side. Just a little tweaking. You should have more than 3 bus lanes. I would say minimum of 4, and go with the widest strip you have. Also the strips that run the length of the parallel groups should also be as wide as possible to fit the space. You don't want any hot spots from restricted current flow. If you think of current flow as water flow, you'll better able to visualize were the restricted flows would be at.


image_xjtufw.jpg
 
Korishan said:
The first one won't work, you'll create shorts. I highlighted the issues. Unless these were supposed to be alternating top/bottom.

The second one is better. Assuming the blue lines are the bottom side. Just a little tweaking. You should have more than 3 bus lanes. I would say minimum of 4, and go with the widest strip you have. Also the strips that run the length of the parallel groups should also be as wide as possible to fit the space. You don't want any hot spots from restricted current flow. If you think of current flow as water flow, you'll better able to visualize were the restricted flows would be at.


image_xjtufw.jpg


Few more questions with your permission.

1. If busbars will be1/8" Thickness, 1/4" Width - is it enough?
2. To be honest I didn't catch regarding "Just connect 2-Pos and 2-Neg that are adjacent to each other (ie, row 1, 2, 3 & 4), and then on the flip side, you add the next section starting with row 3 (ie row 3, 4, 5 & 6)" .Is it possible to show on the drawings?


Thank you in advance




 
AndrewBrown said:
1. If busbars will be 1/8" Thickness, 1/4" Width - is it enough?
2. To be honest I didn't catch regarding "Just connect 2-Pos and 2-Neg that are adjacent to each other (ie, row 1, 2, 3 & 4), and then on the flip side, you add the next section starting with row 3 (ie row 3, 4, 5 & 6)" .Is it possible to show on the drawings?

1) That would probably be sufficient, yeah. It's about cross sectional volume to carry current. With 1/8 x 1/4 would give you approximately 105A capability. Remember, current will flow through the "entire" string of cells, not just added up at the ends (this is voltage). That would give you a very good margin to keep hot spots down. You could even go with a thinner material perhaps and still be fine. A 1/16 x 1/4 would give you about 70A.

2) Basically it's what your second drawing is. The blue lines connect the opposite side. The only reason I said 4 rows was because you had 2x20 arrangement. Had you had 1x40, then I'd said connect rows 1 & 2, 3 & 4, on the one side, and connect 2 & 3, on the other side. For each section of the series, you connect Pos to the Neg of the next section.
 
Korishan said:
AndrewBrown said:
1. If busbars will be 1/8" Thickness, 1/4" Width - is it enough?
2. To be honest I didn't catch regarding "Just connect 2-Pos and 2-Neg that are adjacent to each other (ie, row 1, 2, 3 & 4), and then on the flip side, you add the next section starting with row 3 (ie row 3, 4, 5 & 6)" .Is it possible to show on the drawings?

1) That would probably be sufficient, yeah. It's about cross sectional volume to carry current. With 1/8 x 1/4 would give you approximately 105A capability. Remember, current will flow through the "entire" string of cells, not just added up at the ends (this is voltage). That would give you a very good margin to keep hot spots down. You could even go with a thinner material perhaps and still be fine. A 1/16 x 1/4 would give you about 70A.

2) Basically it's what your second drawing is. The blue lines connect the opposite side. The only reason I said 4 rows was because you had 2x20 arrangement. Had you had 1x40, then I'd said connect rows 1 & 2, 3 & 4, on the one side, and connect 2 & 3, on the other side. For each section of the series, you connect Pos to the Neg of the next section.

I have added two more bus bars, one from the top and one from the bottom.What do you think?
P.S. Blue - it's bottombusbars.
image_gnanki.jpg
 
Yeah, that's about it. And agree with ajw22. With this current view, the "Main" connections are on the bottom.

Also, the bussbars are "technically" the long strips that go the length of the parallel connections and the interconnects are the other bars.
 
ajw22 said:
Not important, but... "Main POS" and "Main NEG" are reversed. Would have been very obvious during construction... you're connecting the main cables to the bottom of the cells, not the top that's visible in the diagram.
Thank you for your advice. I am really appreciated it


Korishan said:
Yeah, that's about it. And agree with ajw22. With this current view, the "Main" connections are on the bottom.

Also, the bussbars are "technically" the long strips that go the length of the parallel connections and the interconnects are the other bars.
Thank you very much. I am really appreciated it
 
Korishan said:
AndrewBrown said:
1. If busbars will be 1/8" Thickness, 1/4" Width - is it enough?
2. To be honest I didn't catch regarding "Just connect 2-Pos and 2-Neg that are adjacent to each other (ie, row 1, 2, 3 & 4), and then on the flip side, you add the next section starting with row 3 (ie row 3, 4, 5 & 6)" .Is it possible to show on the drawings?

1) That would probably be sufficient, yeah. It's about cross sectional volume to carry current. With 1/8 x 1/4 would give you approximately 105A capability. Remember, current will flow through the "entire" string of cells, not just added up at the ends (this is voltage). That would give you a very good margin to keep hot spots down. You could even go with a thinner material perhaps and still be fine. A 1/16 x 1/4 would give you about 70A.

2) Basically it's what your second drawing is. The blue lines connect the opposite side. The only reason I said 4 rows was because you had 2x20 arrangement. Had you had 1x40, then I'd said connect rows 1 & 2, 3 & 4, on the one side, and connect 2 & 3, on the other side. For each section of the series, you connect Pos to the Neg of the next section.



Could I ask a few more questions:

1. I also have to build anotherportable power pack on cells LiFePo3 32650 (4S6P) 36Ah with BMS. My question is: can I use Nickel plated strips for connection? What is cons pros for this type of connection? (pls see attached picture as example)image_qcrmmf.jpg


2. What gauge of wires (pos and neg) do I need for a load?

3. Am I understood correctly how to wire BMS in my case? (pls see attached picture)image_zncbkz.jpg


As always, Thank you for your help
 
1) You can use nickel strip, yes.
Pros are it's very easy to install, quick, and efficient.
Cons are you better practice on discarded cells first to get the settings right. You don't want to blow a hole in good cells.

2) yes, looks correct
 
AndrewBrown said:
[...] pack on cells LiFePo3 [...]

2. What gauge of wires (pos and neg) do I need for a load?


Again not important, but it's LiFePO4 (Lithium, Ferrum (Latin for Iron), Phosphor, Oxygen x4), aka Lithium-Iron-Phosphate.


2.)The design planning should have started with considering (1)what you want to power, and (2)for how long. That dictates the needed (1)wire gauge and (2)number of cells. So what are you planning to power with this power station?
Note that the BMS can probably handle 30A only very briefly without extra cooling.
 
ajw22 said:
AndrewBrown said:
[...] pack on cells LiFePo3 [...]

2. What gauge of wires (pos and neg) do I need for a load?


Again not important, but it's LiFePO4 (Lithium, Ferrum (Latin for Iron), Phosphor, Oxygen x4), aka Lithium-Iron-Phosphate.


2.)The design planning should have started with considering (1)what you want to power, and (2)for how long. That dictates the needed (1)wire gauge and (2)number of cells. So what are you planning to power with this power station?
Note that the BMS can probably handle 30A only very briefly without extra cooling.
1)what you want to power - I am planning to use this power pack for charging batteries in the field for my DJI drone
[size=small]2)for how long - I have two batteries fordrone (rated capacity of each battery3850mAh, 60Wh)
[/size]
 
You'll have to look at the DJI charger - it will state things like voltage and current it requires. Put in the values in this calculator to figure out the cable thickness required for an acceptable energy loss (<1%?).
https://www.calculator.net/voltage-drop-calculator.html

Also strongly recommend wiring in a fuse, just in case. Cheap BMSs are known to fail. The fuse should be rated +20%~+100% higher than what the charger requires, but lower than the safe limit of the cables, so that the fuse burns out before the cables do.
https://www.amazon.com/10-Pack-EPAuto-Line-Holder/dp/B01DYPY0E4

You can look up safe limits on a table like this:
https://www.powerstream.com/Wire_Size.htm
 
ajw22 said:
You'll have to look at the DJI charger - it will state things like voltage and current it requires. Put in the values in this calculator to figure out the cable thickness required for an acceptable energy loss (<1%?).
https://www.calculator.net/voltage-drop-calculator.html

Also strongly recommend wiring in a fuse, just in case. Cheap BMSs are known to fail. The fuse should be rated +20%~+100% higher than what the charger requires, but lower than the safe limit of the cables, so that the fuse burns out before the cables do.
https://www.amazon.com/10-Pack-EPAuto-Line-Holder/dp/B01DYPY0E4

You can look up safe limits on a table like this:
https://www.powerstream.com/Wire_Size.htm

Thank you, I will order these fuses.
However, I looked on my future battery pack and this fuse and couldn't figure it out In which place I should add this fuse?
I assume that fuse should be somewhere on POS wire, right?
 
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