13S15P Battery Pack Build

[etienne]

I received some additional parts, some extra Nickel strips, connectors and cables.

Before soldering the BMS and the connecting cables, I first had to add some more nickel strips. The series connection will have to carry a lot of power (300A, as we know) so I need to make sure that the nickel strips can carry all this load. At this point I added (spot welded) a second layer on top of the first, which you can see in this image:

A quick safety tipp: When spot welding, there may sometimes be some sparks, so definitely wear some googles! Not to forget the gloves, when handling the battery in general.

It took about 90 minutes to cut and add the second layer. I may need to add a third layer, but I don’t have any nickel left, so I’d need to order some more…

This is what the battery looks like as of now (you can see the 12V car battery with the arduino controller, that turns the car battery into a spot welder, in the back:

[etienne]

Current going through the nickel strip - information also for myself

(thickness x width of nickel strip)

0,1mm x 5mm = < 2,1A (optimal) / ~ 3,0A (acceptable)
0,1mm x 7mm = < 3,0A (optimal) / ~ 4,5A (acceptable)
0,15mm x 7mm = < 4,7A (optimal) / ~ 7,0A (acceptable)
0,2mm x 7mm = < 6,4A (optimal) / ~ 9,6A (acceptable)
0,3mm x 7mm = < 10A (optimal) / ~ 15A (acceptable)

(source: How Much & What Size Nickel Strips Should You Use? Q&A#4 - YouTube )

[etienne]

So on my 13S15P Setup I am using 15 series connections with a double layer of 0,1mm pure nickel strip.

However the first layer is that combined strip that makes the series AND parallel connection at the same time (see the last photo in this post: 13S15P Battery Pack Build - #25 by etienne ).

The width for the series connection of that combined strip is 7mm,
whereas the single strip that I added as a second layer is 8mm wide.

Since I don’t have data for 8mm width (see above post), I assume that 15x 8 is the same as 17x7 (well, almost).

So in total, I have 32 series connections of 0.1mm x 7mm nickel strip (between two cells).
Since each strip can carry (optimal) 3A (and as an acceptable limit 4,5A) the battery as it is of today can carry 96A (optimum) or up to 144A for a short term.

Shit, that’s not enough for the 300A-needs. I probably need to solder some copper wire on top, if I don’t want to keep welding another few hundred nickel strips…

any comments from the Pros?

[1066]

@etienne , if I use 3 layers of : Freies Verschiffen 18650 batterie reiner nickel streifen 18650 zelle nickel band 0,15*27*5000mm nickel gürtel verwendet für 18650 batteriehalter|belt belt|belt freebelt b - AliExpress
…wouldn’t I have 45 series connections of .15mm pure nickel? 45 * 7.0A(burst) = 315A Max.

I’m not an electrical engineer, so, I may be completely off and not looking at this correctly. I know I don’t need the extra layers with the parallel connections, but the “all in one” strips look easier to me.

Thanks for your help. Your build looks really good!

Bill

[etienne]

Bill, using this sort of Nickel strip three times on top of each other would be “too much”

That’s because this “combined” nickel strip provides the series AND the parallel connection at the same time. So you would not only triple the series connection, but also the parallel connection, which only has very little current passing through. You’d be wasting material and adding unnecessary weight (even though it’s not much).

See again my photo. For the first layer, I used the combined nickel strip, for the second layer and the last parallel connection I used the single type nickel strip.

[1066]

@etienne , I understand that tripling the parallel is a waste, but I was just trying to figure out an easier way (less cutting and positioning) to cover the 300A series load. Your build has been excellent, so, I plan to follow your lead. Keep up the good work!

Bill

[etienne]

Bill, uhhh, that puts a lot of pressure on me, if you wanna follow along. (don’t blame me, if it’s not working out )

by the way, your calculation:

@1066

wouldn’t I have 45 series connections of .15mm pure nickel? 45 * 7.0A(burst) = 315A Max.

is correct. however the 315A is the “acceptable” current, not the “optimum” … this could still cause some hazard if you’re going full throttle for a long time … I am not sure, just thinking.
Any my problem is, that I have already started with obviously too thin strips… I should have done the calculations earlier

I am not an electrical engineer myself, I just have some basic knowledge about electronics, a good common sense, and I bought that book “DIY Lithium Batteries” that I mentioned before here in this forum (it’s a really good read).

The cutting and positioning is very very easy! You just cut the strip using a wire cutter and the positioning is done with your fingers. The plastic thing that keeps the cells in place also helps you positioning the strips.

So for my project, I am short of 204 A current carrying capacity between each series connection.
This is, see above, because my first and second layer of Nickel Strips can carry 96A so far only.

This product (22.54€ |0,2x8x100mm 100 pcs/lot Reine Nickel Platte Band Streifen Blätter 99.96% für 18650 power batterie pack spot schweißen spot schweißer|sheets|sheet strapssheet plate - AliExpress ) 100 pieces of 100mm length 8x 0.2mm pure Nickel strip (I need 25mm length, so each 100mm piece can be cut apart into 4x 25mm pieces) can carry a little over 6,4A per strip. (this is the table in an earlier post talks about 0.2x7mm, whereas this product is 0.2x8mm)
To be safe, let me calculate with 6,4A:

so 204A divided by 6,4A = 31,875 pieces. that’s roundabout two layers per parallel group (15 cells per parallel group = 15 connections, 2 Layers = 30 connections).

The above link is a set of 100 strips, each cut into 4 pieces makes a total of 400. For an additional double layer to make 180 connections I need 360 pieces, so I’d be good to go if I order one package.

… and just thinking again, If I do all the calculations with the “acceptable” current instead of the “optimum” - then one additional layer of the 0.2x8mm would be enough

[1066]

I’m with you on your idea and calculations. Since I have not started yet, it would be good if I could find the nickel tape in .2 instead of the .15 for my first layer. The thicker first layer tape plus two layers of .2 strips would give me about 288A optimal. I would be comfortable with that. The problem is that I have not been able to find the pure nickel “H” tape in .2mm. …but I am going to continue to look!

[MayMayDay]

For the LG HG2, you’re getting 45Ah @9.36kg (just cell weight), so let’s say 11kg after strips, packaging, BMS, etc. ~223Wh/kg (this considers charging the 18650s to 4.2V per cell).

Compare this to 12S2P (4x Bonka 6S 22Ah) @10.2kg and 44Ah. ~217Wh/kg

Your Wh/kg are almost identical, even though liion is supposed to be more energy dense than lipo. Am I missing something? The lipo route seems to save a lot of pain and burning.

[etienne]

I did not doublecheck your calculations, but they are probably right.

The decision to go this way was not because of energy density.
It was more of a safety and economical decision (don’t remember exactly, but you can recharge the Li-Ion probably a thousand times - you can’t do that with the Lipo’s).
The original thread as to why I am going this route is here: How about 18650 Li-Ion battery pack over the Li-Po packs?

[1066]

Just for information, I did find .2mm pure nickel “H” battery tape. That should give you 6.4A (optimal) & 9.6A (acceptable) :

https://www.aliexpress.com/item/1M-0-2-7-27mm-battery-pure-nickel-strips-High-purity-99-96-lithium-nickel-belt/32884596669.html?spm=2114.search0104.3.30.1fb813c8EpmWY5&ws_ab_test=searchweb0_0,searchweb201602_4_10152_10065_10151_10344_10068_10130_10342_10547_10343_10546_10340_5724715_10548_10341_10545_10696_10084_5724015_10083_10618_5724315_10307_5724215_5724115_10059_100031_5725015_10103_5724915_10624_10623_10622_10621_10620,searchweb201603_13,ppcSwitch_4&algo_expid=300c4af0-5a5e-4ab8-aabb-ed7675db6f22-3&algo_pvid=300c4af0-5a5e-4ab8-aabb-ed7675db6f22&priceBeautifyAB=0

What a url!

[etienne]

@1066

I did find .2mm pure nickel “H”

great, but too late for me
I am still waiting on the 100m long 0,2mm thick Nickel strips, they’ll probably take another two or three weeks to arrive by China SnailMail.

In the meantime I started to solder the control wires to the Battery:

The black wire connects with the main negative pole of the battery, the red ones the positive poles of each parallel group.
The main positive pole has two connecting wires, had to be done according to the BMS instructions.

[etienne]

On the right, you can see the connectors. I had to push in the cables myself, so I only used the amount of cables that I really needed, 13 red cables, one for each positive pole, plus one additional black and red for main positive and negative pole.

The BMS is good for a 24S setup, so I have 11 red cables that were not installed, hence the second white connector is almost “empty”

[etienne]

the “control cables” will actually measure the voltage of each parallel group and then do the balancing if needed (that’s what the BMS is for in the first place).

Soldering them onto the nickel strips was quite easy. I have a professional soldering iron that goes up to 450 (degrees Celsius, I guess)

It is important that the soldering iron is not applied too long, as there should be as little heat as possible reach the actual cell. Not really difficult, it took maybe two seconds of applying heat and solder to each connection.

[etienne]

For the main positive and negative discharge wires, that will actually connect the battery with the OpenPPG,
it is going to be a different story. I have purchased 8AWG cables and I plan to solder two of each onto the battery.

Here I did a test to actually solder the 8AWG wire to a piece of Nickel Strip:

I am not so happy with this… it does not look very good of a soldering job - but I had to apply the soldering iron for quite a long time, with a lot (and I mean a lot) of solder going into this.
The solder vanished mainly into the wire (stranded wire / litz wire, not sure what the right term is)
and only after it was satured, the solder also went onto the nickel strip.

I did apply some solder to the nickel strip first, then onto the 8AWG wire, then I combined both together - the connection was very weak, I could pull it apart with not even two fingers… So I added more heat and more solder, which all got “sucked up” by the litz wire until finally a good connection, that I could not pull apart with my fingers again, was established…

This worries me a bit. Soldering onto the cells IS NOT RECOMMENDED, as heat destroys the cells, that’s why I did the whole spot welding thing in the first place… but now I need to connect the discharge wires thoroughly over the whole length of the nickel strip… this may be a whole lot of heat for the cells…
not sure how I’ll do this, yet.

[etienne]

@MayMayDay I am hat 10,26 Kilograms for the whole battery as of now.
I still have some nickel strips missing, and a bit of solder is still to be added, maybe a sort of case (but the bonkas may need one as well.)
I don’t think it will reach 11kg, maybe around 10,5kg without a case:

[dpack (David)]

Very cool!

My apologies if you answered this already… how much flight time do you expect to get from this setup?

[jjooeehunt (Joe Hunt)]

As an idea for the soldering the main wires. Is it possible to solder like you have to a short piece of h-strip and make a really good connection. Then spot weld this h-strip to the pack?

[etienne]

@dpack

how much flight time do you expect to get

see here: 13S15P Battery Pack Build - #11 by etienne (Post number 11)

@jjooeehunt

Then spot weld this h-strip to the pack?

yeah, this is probably what I am going to do. I need to make sure that the series connection of this additional H-strip is also strengthened with extra nickel, though

[etienne]

still waiting for the extra nickel, can’t do much more without it.

The BMS comes with 4 thermistors, which I’ll need to stick into the battery pack into 4 different spots across the pack. Not sure yet how I’ll do it, as the pack is already complete…
Anyways, I started to solder some thin wires to them, so that I can connect them with the BMS

I added a drop of hot glue in the area where the cables are soldered to the thermistor’s pins, so that they can’t touch each other.