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Planning my 4S40P portable power station
#11
(08-29-2020, 02:10 AM)Korishan Wrote:
(08-28-2020, 08:47 PM)AndrewBrown Wrote: 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 bottom busbars.
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#12
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.
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#13
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.
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#14
(08-31-2020, 02:09 PM)ajw22 Wrote: 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

(08-31-2020, 06:44 PM)Korishan Wrote: 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
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#15
(08-29-2020, 02:10 AM)Korishan Wrote:
(08-28-2020, 08:47 PM)AndrewBrown Wrote: 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 another portable 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)

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)

As always, Thank you for your help
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#16
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
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#17
(09-02-2020, 08:44 PM)AndrewBrown Wrote: [...] 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.
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#18
(09-02-2020, 10:55 PM)ajw22 Wrote:
(09-02-2020, 08:44 PM)AndrewBrown Wrote: [...] 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
2)for how long - I have two batteries for drone (rated capacity of each battery 3850mAh, 60Wh)
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#19
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-Li...B01DYPY0E4

You can look up safe limits on a table like this:
https://www.powerstream.com/Wire_Size.htm
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#20
(09-03-2020, 01:41 AM)ajw22 Wrote: 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-Li...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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