Common pack design mistakes, how to avoid?

[spinningmagnets]

In my theoretical battery pack, the 8mm wide flat copper bars cross the 10mm wide nickel strips, so the contact area for 20A is 80 Sq mm.

This current needs to travel through 6mm length of 10mm wide pure nickel strip (0.20mm thickness) to get from the center of the cell tip, to the edge of the nickel-plated copper series bars.

Just a side-note, I found bare solid copper wire in 8-ga for 500-ft roll at $150, so...$0.34 per foot, which can be compressed into bar stock. Which is $0.04 per inch/25mm

1/16th inch thick (copper bar-stock/plate) is 0.065" thick, which is 1.6mm thick. that looks to be a fruitful hunting ground, since cutting it into strips of 8mm wide X 1.6mm thick is somewhere around 12.8mm squared in cross-section, equal to somewhere around 6.5-ga

edit, found 0.032 thick (1/32nd", 0.8mm) X .375" wide (9.5mm) copper bar stock, for 5-cents per inch/ per 25mm of length, so...0.8mm x 9.5mm = 7.6mm/squared in area cross-section, equal to 8.5-ga solid copper wire. https://www.etsy.com/listing/231678857/copper-flat-bar-stock-375-in-x-36-x
30mm long [1.2 inch] x (3 per P=group X 14S = 42 plus 6 for end caps ) roughly 60 inches? so a 14s / 6P pack would take $3 worth of bare copper bar for series connections equal to 8.5-ga (70A continuous?)

Here is same price, but narrower at 0.25-inch wide (6.3mm), and at 0.32-inch/ 0.8mm thick, its equal to 5mm squared / 10-ga (good for 50A continuous?)

Home DIY of the nickel-plating is always an option, but how to get a factory to make a thin nickel-plate? And at what price?

In the pic below, I just grabbed a pic from ES, and then drew-in two copper flat bars (for the series connection) where I would make the series connections (possibly nickel-plated and then soldered onto the nickel paralleling strips. The two red arrows point to how this builder only made the series connection with a single nickel strip of the same material and thickness as the paralleling strips:



These are high-current cells, so those single-path nickel series strips were being asked to handle 80A peaks...

 

[Matador]

I have recently been impressed by the PF cell, when used at 10A peaks. Imagine someone spot-welds six cells in-line, we solder thick copper flat bars in between every 2-cell group to make the series connection. Three series-bars connections from one 6-cell paralleled sub-group to the next. Copper is cheap, so we make them thicker than necessary. The distance from the center of one cell to the next is 20-ish mm, so each cells' 10A-worth of peak current only has to travel 10mm to reach a series connection.

Only 0.35 milliOhms according to this chart (0.20mm thick nickel strips flowing current a distance of one centimeter): viewtopic.php?f=14&t=84412&start=50#p1238471

10A X six paralleled cells is 60A peaks, which is what I am aiming for in an initial prototype. Of course the 30Q cell costs a little more, but at a rated 15A per cell, 6P would be 90A?

You can also make the calculation from my more complete table here (for future reference) https://endless-sphere.com/forums/viewtopic.php?f=14&t=84412&start=75#p1240322

Look under the "10 mm width" row--> then under the " 0.2 mm thick sub-row --> then cross check under the "Nickel" column.... You'll see that the value resistance value (printed in red) is 35.0 mOhm/meter (multiply that buy 0.01 m (that is 1 cm)). So for 1 cm of lenght, the resistance is exactly 0.35 mOhms (R = 35.0 mOhm/meter x 0.01 meter = 0.35 mOhm).

See picture below for how to read the table :


Just thought I'd make a usefull chart for resistances too, not just the "subjective" amapacities...

 

[Matador]

In my theoretical battery pack, the 8mm wide flat copper bars cross the 10mm wide nickel strips, so the contact area for 20A is 80 Sq mm.
Home DIY of the nickel-plating is always an option, but how to get a factory to make a thin nickel-plate? And at what price?

Well I don't know what they will charge you, but plating 5 to 30 microns thickness of nickel does not require a whole lot of Nickel metal from the electrode... and at aroung 5 USD per pound of metal Nickel, you can make a hell of a big electrode. A pound of nickel goes a looooooooooooooonnnnng way for plating copper.

Then you need Nickel ammonium sulfate hexahydrate((NH4)2Ni(SO4)2 . 6 H2O) cristals to make a nickel ion electrolyte solution (just dissolve the cristals in distilled water until the solution is saturated) ... One you have the electolyte solution, you can pretty much use it infinitly (as nickel ions are constantly self resplenished by the bare nickel metal electrode which make new Ni2+ ions into solution)...

The most expensive part of plating by a company is clearly for the labor, rather than for the equipement, chemicals and electricity bills.

 

[Hillhater]

Plating is cool but why wouldnt you simply spray the finished assembled pack with one of the protective coatings used for electrical equipment and motors etc,..like Scotch 1601/1602. ?http://solutions.3m.co.uk/wps/portal/3M/en_GB/ElectricalMkts/ElectricalSupplies/products/sprays-coatings/insulating-sprays/
That would prevent corrosion and add insulation also.

 

[Matador]

Plating is cool but why wouldnt you simply spray the finished assembled pack with one of the protective coatings used for electrical equipment and motors etc,..like Scotch 1601/1602. ?http://solutions.3m.co.uk/wps/portal/3M/en_GB/ElectricalMkts/ElectricalSupplies/products/sprays-coatings/insulating-sprays/
That would prevent corrosion and add insulation also.

Good point !

 

[madin88]

Surface area is also important for current handling. A nickel sheet which is equivalent to lets say 1mm² copper can carry much higher current, because it will not overheat due to the much larger surface area.
The nickel or steel sheets are welded to the cells, this means the cells will soak up most of the heat which is produced by the resistance of the welding sheets.

talking about "the connection between the cells will add ..% to the total resistance of the battery" would make sense.

IMO it is not about absolutely BEST conductivity, because if the cross section is large enough, the nickel sheets will not add much to total resistance of the entire battery.
IMPORTANT is the equal current flow through all cells. Here is where most mistakes are made. This is the most important thing, not as for example 0,2 or 0,5% lower total resistnace.

 

[mkp007]

Plating is cool but why wouldnt you simply spray the finished assembled pack with one of the protective coatings used for electrical equipment and motors etc,..like Scotch 1601/1602. ?http://solutions.3m.co.uk/wps/portal/3M/en_GB/ElectricalMkts/ElectricalSupplies/products/sprays-coatings/insulating-sprays/
That would prevent corrosion and add insulation also.

If you plate with nickel, it may make spot welding easier due the increased resistance. 2 for 1 hopefully (corrosion resistance + weldability).

 

[mkp007]

I know you are using data from reference tables, but i am struggling to understand why a microscopic plating thickness of Nickle on the surface of a copper conductor would cause its Ampacity to be reduced by 13%...?? For sure , its Conductivity would not be affected. Can anyone explain ?

Good point, and honestly, I don't know the answer. I just took the derating factor of 0.87 from the reference I gave before as cash.
Maybe Nickel has less termal dissipation ability than copper. Maybe this is what reduces the ampacity rating...

I don't think the derating applies to our DC voltage application. That's more for AC high frequency stuff. DC current will go with area of the conductor and not more on the outside of it. You will notice that cables used for high frequency communication is bare copper for that reason. Plated copper is good for our application.

Maximum Frequency for 100% Skin Depth: This data is useful for high frequency AC engineering. When high frequency AC is conducted by a wire there is a tendency for the current to flow along the outside of the wire. This increases the effective resistance. The frequency listed in the table shows the frequency at which the calculated skin depth is equal to the radius of the wire, and is an indication that above this frequency you should start considering the skin effect when calculating the wire's resistance.

http://www.powerstream.com/Wire_Size.htm

 

[mxer]

Thoughts on this pack?. Looks a work of art.

 

[Hillhater]

If you plate with nickel, it may make spot welding easier due the increased resistance. 2 for 1 hopefully (corrosion resistance + weldability).

just how much would that resistance increase ??
i doubt the difference in resistance through a few microns of nickel at the interface , would be significant.

 

[mistercrash]

Thoughts on this pack?. Looks a work of art.

16S7P if I see correctly. From the dimples at the spot welding points, it looks like 7 or 8mm X 0.15mm Nickle strips. The series connections connecting the P groups are irregular. I see some have up to 5 strips of Nickle making the series connection and others as low as just two strips. Let's say the 18650 cells are 3000mah and capable of a constant discharge of 3 amps per cell, times 7 is 21 amps. 5 strips of 8X0.15 Nickle could carry that load but anything lower is insufficient IMHO. And then there's the matter of this huge block of cells all held together by nothing more than the cell's heat shrink and the Nickle strips. Last, the pack is unfinished. What will carry the power out of the pack? The + and - terminations are not there. It looks like a battery I would have made 5 years ago when I started in the EV hobby.

 

[Voltron]

As you said, it's obviously not done yet, but the least I count is three strips per series connection...

 

[mxer]

Wow I've got alot more reading to do, I was going to follow this pack, back to the drawing board, thanks guys.

 

[parabellum]

If you plate with nickel, it may make spot welding easier due the increased resistance. 2 for 1 hopefully (corrosion resistance + weldability).

just how much would that resistance increase ??
i doubt the difference in resistance through a few microns of nickel at the interface , would be significant.

Nickel is blown to dust at this point, do not count on it. Those microns just evaporise, just count cooper with some "surface protection" which is kind of questionable (I am doing that my self in hopes but, it just cracks and comes off in any strain scenario, like bending. I use electrolysis.)

 

[Matador]

it just cracks and comes off in any strain scenario, like bending. I use electrolysis.

What voltage do you use during that electroplating ?

I've had the best result at low voltages using ripple-less DC sources (either from 18650 or lower voltages from alcaline 1.5 volts cells). Some people on youtube say DC from walwarts doesnt give as good a result because of the ripple, while plating at a too high a voltage will give a smooth layer of plating, and it's more prone to flake off.
I haven't tried from walwarts or other external powersupplies, but I've experience that higher voltages give poor results. A lot of people suggest 1.5V or 3.0V. For my purpose, 3.7 volts worked fine.

https://www.youtube.com/watch?v=Q8Xo43sfLgY 8)

 

[Matador]

Nickel is blown to dust at this point, do not count on it. Those microns just evaporise, just count cooper with some "surface protection" which is kind of questionable

Just to give you an idea those 0.1 mm nickel stips are actually just 100 microns thick.

Of course the plating can be just 3 or 5 microns if you don't plate for a long period of time, but if you're patient it's possible to plate 30 microns of Nickel over Copper with a low enough voltage (low voltage necessary for a smooth plating layer, especially for long periods of plating).

Check out Table 1 at page 9 of this "Nickel Plating Handbook" (very informative book btw). They do 50 microns nickel plating (50 microns) !
https://www.nickelinstitute.org/~/media/Files/TechnicalLiterature/NPH_141015.ashx

This guy also says he gets best results with low voltage and using batteries as the DC electricity source for electroplating
https://www.youtube.com/watch?v=Q8Xo43sfLgY 8)

 

[mistercrash]

As you said, it's obviously not done yet, but the least I count is three strips per series connection...

Yes you are correct, I missed seeing that third little strip. Three or four is still not enough IMO unless it's for a very low power application.

 

[mkp007]

If you plate with nickel, it may make spot welding easier due the increased resistance. 2 for 1 hopefully (corrosion resistance + weldability).

just how much would that resistance increase ??
i doubt the difference in resistance through a few microns of nickel at the interface , would be significant.

Nickel is blown to dust at this point, do not count on it. Those microns just evaporise, just count cooper with some "surface protection" which is kind of questionable (I am doing that my self in hopes but, it just cracks and comes off in any strain scenario, like bending. I use electrolysis.)

Vaporizing is good. As long as localized heat is being produced. It all comes down to localized heat.

As for the Ni flaking off, what was your surface prep technique? There are many ways to screw up plating and only one way to do it well. I recommend find a plating facility and have them do it for you. I believe the best prep is an acid etch, clean and dry in a non-humid environment and then plate.

Bending the copper strip after plating puts a lot of yield strain at that copper-nickel interface. I would not expect the plating to remain adhered in that situation. You must prevent bending the strip too much once plated.

 

[Matador]

Vaporizing is good. As long as localized heat is being produced. It all comes down to localized heat.

As for the Ni flaking off, what was your surface prep technique? There are many ways to screw up plating and only one way to do it well. I recommend find a plating facility and have them do it for you. I believe the best prep is an acid etch, clean and dry in a non-humid environment and then plate.

Bending the copper strip after plating puts a lot of yield strain at that copper-nickel interface. I would not expect the plating to remain adhered in that situation. You must prevent bending the strip too much once plated.

I went getto here :lol: , plating in my appartment (Story and pics here : https://endless-sphere.com/forums/viewtopic.php?f=14&t=60364&start=25#p1235640). My prep technic was sanding with sand paper to remove the oxide layer, 180 grit --> 320 grit, 600 grit (wet) --> 2000 grit (wet). Then used isopropyl alcool to remove any fingergrease, then plate in homemade Nickel acetate (for each 0.06 dm2 peace, I plated at 3.8 volts, current was around 10-15 mA, 12 hours of plating.... My nickel electrode was a nickel coin made of 99.9% Nickel (canadian coins between 1957 an 1981 I believe)...

I did not try to bend, but my stips are almost 1.8 mm thick (my build is bit unusual)

 

[parabellum]

What voltage do you use during that electroplating ?

Voltage is not only factor. There is conductivity of the electrolyte, electrode to electrolyte contact surface and distance between electrode and work piece. I used plastic container with 2 electrodes in opposite corners and place 5 strips in between. Used adjustable buck converter from 12v supply, regulated to ~4.5V. Strips near the electrodes plate really quick, one in centre takes for ever, but they behave identically concerned to flacking.

what was your surface prep technique?

Sanding with 400 sand paper. I did plating for corrosion protection in no weld pack, time will tell if it works.

 

[spinningmagnets]

From mkp007:

"Tin vs. Nickel - Nickel is not solderable, so any items that may need to be soldered to the bus bar wouldn’t stick to electroplated nickel. Forming, nickel is not as ductile as tin would be and therefore may crack under stress if bent. Tin is better than nickel as far as conductivity is concerned. Nickel can and will grow a heavy oxide that may prevent conductivity over time as the oxide is more difficult to break through than tin." (ref http://ppc1904.com/resources/faq)

Immediately, several posters pointed out that balance leads and even "thick copper wire" series connections have been soldered in the past, so solder works "well enough" connecting copper to nickel, BUT...my interest in posting this is that...nickel is expensive, and is slated to become MORE expensive as time goes on. Copper is cheap and works very well for parallel foil-strips, and also series current-bars. Corrosion over time is the issue of concern with copper, and tin is cheap. as far as resistance, we are only talking about a thin plating on a flat bar, that is bonded to the thick copper series-connection.

Lead-free solder is mostly tin, so...maybe if we "skin" copper series flat-bars with lead-free solder, we will have a useful style?

Lead-free solder melts at 220 to 300°C (depending on the formula)

The 60/40 alloy is one of the most common types of solder. The alloy contains 60 percent tin and 40 percent lead (tin is the first number in the label). The chemical symbols may also be included in the label such as "60Sn/40Pb" (tin is Sn and lead is Pb). The 60/40 solder has a melting point of approximately 360 degrees F and an electric soldering iron is used to melt and apply it. Flux-core 60/40 solder is a common choice for electronics work because it has a low melting point, it cools quickly and it "re-solidifies" quickly.

 

[Matador]

"Tin is better than nickel as far as conductivity is concerned." (ref http://ppc1904.com/resources/faq)

Well it's strange that they say that !

According to wikipedia tables, Nickel is 1.5 times more conductive than Tin :
Nickel Conductivity (at 20°C) : 1.43×10^7 S/m
Tin Conductivity (at 20°C) : 9.17×10^6 S/m

Ref : https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

But besides conductivity (which is not so much of an issue since the bussbar core is Copper), I understand that tin has a lot of advantages : more ductile than nickel, electroplating can be avoided simply by applying a coat of Tin solder using flux.

 

[spinningmagnets]

Thanks, I find so much conflicting info on the web.

If in fact "most of" the tin we find readily available (in low-lead solder) is slightly less conductive than "most of" the supposedly pure 0.20mm-thick nickel strips we buy from China, would a series connection copper flat-bar that is given a thin skin of high-tin solder conduct well enough (have reasonably low resistance) that its benefits will outweigh its drawbacks?

https://www.bluesea.com/resources/108

Perhaps the most interesting fact revealed by this chart is how low most copper alloy materials rank in relative conductivity. One might easily assume that alloys such as the brasses and bronzes, because they are mainly copper, are nearly as conductive as copper. This is not the case. The small percentages of tin, aluminum, nickel, zinc and phosphorus that make up these alloys degrade the electrical performance of the resulting alloy to a far greater percentage than their compositional percentage in the alloy.

One should not conclude from this, however, that brass should never be used in electrical applications. There are instances where the superior tensile and machining characteristics of brass make it a better choice than copper as long as the sectional areas are increased proportionately to achieve the conductivity that a copper part would have in the application. Size for size, however, copper is exceeded only by silver among the materials commonly used for electrical applications.

These guys rate conductivity as:

100__Copper
61___Aluminum
27___Zinc
22___Nickel
15___Tin
7____Lead

Common "lead free" solders have over a 95% of Tin in its composition, and the melting temperature is higher than older solders that are approximately half lead. Perhaps consider soldering the series flat bars onto the paralleling strips before they are spot-welded onto the cell ends? (using a jig to hold them in the exact shape needed?)

 

[mkp007]

'
This post may be of interest here: RC LiPo vs 18650 Cell High Power Packs https://endless-sphere.com/forums/viewtopic.php?f=14&t=84949

I don't want to derail this thread so please post comments there

 

[LewTwo]

You folks might want to look at copper 95% zinc 5% alloy. It is commonly used as very thin sheets in arts and crafts. Also used in munitions (think full metal jacket). It has excellent corrosion resistance, conductivity betweel aluminum and copper and it can be soldered with silver solder.