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Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 26 2016 12:59pm
by spinningmagnets
The "go to" material for the paralleling strips has been pure Nickel, because..."that's the way the big companies do it", and...they must know what they are doing, right? It turns out that most factory battery packs put out low amps, so Nickel is "acceptable".

The high electrical resistance of nickel means that it is easy to spot-weld the parallel and series strips onto the cell groups. Once we decide that we want high amps from a medium-to-small battery pack, the resistance of nickel becomes a liability. It is also an annoyance that pure nickel strips are expensive, and they are slated to become even more expensive in the near future. What are our options?

I have recently become convinced that pure copper flat bars are the only reasonable material for the series connections between the paralleled sub-pack modules. There is a thread exploring the use of spot-welding copper strips to make the parallel connections (easily DIY'd from using tin-snips on locally-acquired copper sheets). ... 14&t=84680

The series connections can cheaply be made from a very affordable DIY spot-welder using a salvaged Microwave Oven Transformer (MOT). ... 14&t=85023

I started this thread to raise awareness of the option of using brass sheet as the paralleling strips, and to also consolidate any info that we may find out about this possibility.

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 26 2016 1:00pm
by spinningmagnets
From ES member kdog in Hobart, Tasmania, Australia
...I have just finished spotwelding up a little 2s2p pack...I did it in 0.20mm brass to see how it would go (Plain old yellow brass, C260, iacs 27%). It welded easily, not quite as easy as nickel but close. I'm practicing for a large upcoming build (21s10p of 30q's) to see if brass will substitute for nickel. Any combo of nickel, brass, copper will weld together, so that's good...

...The only real advantage over nickel is cost- conductivity is marginally better, but It's about 1/3 [cost] of nickel and readily available in 100-300mm wide. Copper welds to nickel very well, in fact I prefer putting down nickel first to give the can a bit more protection from fickle coppers' inevitable blowouts.
As a general rule, the cheap and available brass is an alloy of roughly 3/4 copper, and 1/4 zinc

In the copper-spot-welding thread, it was mentioned that because of the low resistance of pure copper, it takes very high currents to make copper hot enough to form a weld. It is the low price of copper and its low electrical resistance that makes us want to use fat copper wire on an ebike power system, and thick copper flat bars for the series connections on the battery pack.

The series connection must carry the full pack current, however the parallel connections only need to carry the cells max current a short distance, if we place a series flat bar in-between each pair of cells to intuitively provide equal current-sharing in all of the packs cells. If 0.20mm thickness of pure nickel has proven adequate for most parallel busses (0.008-inch, 8-mil, 32-ga), then upgrading to brass (at double the thickness) is a cheap and easy way for us to make our own parallel bus-strips from locally-sourced brass sheets. Info from poking around the web:

iacs, if pure copper has an electrical conductivity of 100, then...

red brass:_______C230_______(85% Cu / 15% Zn)___conductivity 37/100
yellow brass:____C260_______(70% Cu / 30% Zn)___conductivity 28/100
pure nickel:____________________________________conductivity 22/100

machining brass__C330/C360___(yellow brass with 3% lead to make less brittle, <1% of iron to stiffen)
naval brass:_____C464_________(60% Cu / 39% Zn / 1% Tin), poor conductivity, highly resistant to corrosion, expensive
German silver:___C770_________(55% Cu / 27% Zn / 18% Nickel), poor conductivity, good resistance to corrosion, affordable

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 26 2016 4:24pm
by kdog
Any addition to pure copper lowers its conductivity rapidly in the first few % of content. The high copper alloys- usually>95cu, still have substantially reduced conductivity. Their thermal conductivity is usually reduced in a linear fashion and tensile strength goes up.
The following alloys are probably excellent contenders for battery builds, being able to substitute for nickel +/or copper.

IACS____Alloy#____spotweld?___ alloy additives listed as a %, all alloys listed have copper as the remainder, typically 95%+

80_____C18145_____Good_______(0.2 Chrome, 0.2 Zinc, 0.1 Zr)
80_____C18141_____Good_______(0.3 Chrome, 0.2 Tin, 0.1 Aluminum, = or less than 0.1 each of Zr, Mg, Si)
65_____C19170_____Good_______(1.0 Zinc, = or less than 0.1 each of Ni, Sn, P, Fe, Pb, Si)
60_____C40410_____Excellent___(0.7 Tin, 0.5 Iron, = or less than 0.1 each of Pb, Zn)
45_____C64750_____Excellent___(2.0 Nickel, 1.0 Zinc, 1.0 Iron, 0.5 Tin, 0.4 Silicon, = or less than 0.1 of P, Mg, Zr)
40_____C70250_____Excellent___(3.2 Nickel, 1.0 Zinc, 0.7 Silicon, 0.2 Iron, 0.2 Magnesium, 0.1 Manganese)

above this line: expensive
below this line: cheap, and readily available

37_____C23000________Fair_______red brass_____(85.0 Copper, 15.0 Zinc)
28_____C26000________Good______yellow brass__(70.0 Copper, 30.0 Zinc)
10_____Stainless steel__Good

For reference pure copper rated below poor and yellow brass (mentioned above) is good.
Still haven't found a supplier for any of these alloys... If anyone is in the industry and wants to give me a lead :wink:

[moderator edit to rearrange selections in order of conductivity]

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 26 2016 5:44pm
by Matador
Here a good table for electrical properties of metals and metal alloys
They state conductivity, resistivity and %IACS values : ... sistivity/

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 26 2016 11:31pm
by kdog
Can someone in the USA, please go to wirejewelerycom on eBay, buy a sheet of their red brass. I've verified that it is actual red brass ; c23000, iacs 37%, fair for spotwelding) it in all different thicknesses
I just can't swallow $30au for shipping for one tiny sheet.

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 27 2016 8:27am
by spinningmagnets
He has "red brass" sheets in:

__20-ga__0.032__0.80mm___6 X 6 inches, also available as 6 X 12 (mm =152 X 304)

(red brass is 37/22 the conductivity of nickel, about 70% better. 0.25mm thickness is 25% better than the common 0.20mm busses, so 0.25mm red brass can carry twice the current of common 0.20 nickel, or...the same current with half the waste-heat)

Nickel____0.008__0.20mm ... pg=&_from=

$8 USD, 30 Gauge 0.010 Dead Soft Red Brass Sheet Metal - 6x6...paypal me $10 USD, and I will pay any extra expenses that come up for shipping, PM me your address.

USPS hard envelope is listed as 6 X 10, and can hold a sheet of 5.5 X 9.5

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 27 2016 1:16pm
by spinningmagnets
Conductivity comparison, iacs electrical conductivity chart rates pure copper at 100:

Numbers are approximate, but...if pure nickel electrical conductivity is 22/100, and red brass is 37/100, then red brass is 15/100 better, so 15/22 is 68% better?

Tack on another 25% of that total because 0.010-inch/0.25mm thickness is about 25% thicker than 0.008" / 0.20mm, so the available 30-ga red brass sheet can carry roughly double the amps of 0.020mm pure nickel.

Allowing for minor production variations, we could still count on red brass having 1/3 the current capability of equivalent pure copper cross-section of wire. 8.0mm wide strip X 0.25mm (30-ga sheet) = 2.0mm squared = a physical 14-ga wire (but at 1/3 the current)

19-ga wire made from pure copper has a cross-section of 0.60mm squared (1/3rd of 2.0mm squared). A chart on the web rates 19-ga pure copper (equal in conductivity to "2.0mm squared" red brass) is 14A continuous (maybe 28A temporary peak?). If there is one copper series flat bar between each cell-pair, then red brass would provide 28A continuous per cell-pair, so 4P would be 56A for the pack, and 6P would be 84A

Of course with so many variables, the peak amps are more related to how hot the busses are actually getting (how often each rider is drawing peak amps). But with the PF cell providing 10A per cell (60A for 6P), red brass is a winner. The 30Q cell has been providing 15A per cell peak. which is only one amp over the continuous rating of red brass parallel strips (90A peak for 6P).

If the cell's peak amps rating is near the busses continuous rating, I am satisfied that this is worth investing in. I am told the cell temps should never exceed 140F (60C). If I made a mistake in the calcs, or I missed something important, please post up...

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 28 2016 7:58am
by Hillhater
What is the real concern with these conductors..volt drop, or overheating issues ??
With the short distances involved, i doubt voltage drop will be significant compared to the overheating risk ? which case, the actual surface area of the strip is equally important as its cross section area.
A wide thin strip will dissipate heat better and operate cooler than a narrow thick strip of the same CSA,and material.

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 28 2016 8:42pm
by spinningmagnets
There is really nothing to be concerned about. I suspect nickel will rise in price sharply sometime in 2018, and if yes...what are the next best options? Even the more common "yellow brass" has some of the benefits listed below, but...

Compared to pure nickel, red brass is:

1) 68% more conductive per volume (less resistance, if you want a high-amp battery pack.)
2) Cheaper right now (1/2 the price?), and also likely to remain cheap over time (made from abundant copper and zinc).
3) In theory, red brass should be much easier to spot-weld onto the ends of 18650 cells, compared to pure copper ribbon.

On the other hand, nickel is very corrosion resistant without needing any additional treatments. If you are building battery packs locally, and nickel parallel strips are working well for you, please continue to do so...

If you like using nickel, stock up now. The current oversupply is making nickel about as cheap as it can get. The main global use of nickel is in the production of stainless steel. There are only so many nickel mines, and they are producing as much as they can. Demand for stainless steel is projected to rise by 2018, creating a shortage of nickel. If the price of nickel rises (and it might not, who knows?) you can either pay more then, or switch to red brass...

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 29 2016 2:43am
by amberwolf
The only concern I can think of with brasses vs nickels is the corrosion of brasses is faster / more severe under the same conditions, vs nickels.

In places like here in Phoenix I wouldnt' be worried about it, but in humid areas, especially coastal ones, I would guess that as long as surfaces are treated (dielectric grease, or vaseline, or some other coating, etc) after building it, it'd probably be fine.

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 29 2016 9:20pm
by spinningmagnets
My initial read up on spot-welding copper/brass indicated that tungsten rods are readily available at affordable prices, and since they have a very high melting temperature, they didn't "stick" to the pieces like conventional spot-welding probes.

However, just found a reference where a DIY'r used "carbon arc electrodes", and even said that graphite can be cheaply sourced and easily shaped as the tips. he didn't say why, but the tungsten guys said the rods have high resistance so they get very hot, even glowing if there isn't enough wait between welds. maybe the carbon rods have less resistance, but also don't stick to the work-pieces? [the carbon pieces were short and just at the tips of the spot-welding probes, the cables were thick copper stranded wire] ... en-Copper/

I found videos of Sunstone's new Orion 250i spot-welder. Specifically made for spot-welding copper and/or brass onto 18650' to the price? I have bought many cars in my life for less. I don't expect them to be helpful in determining the best voltage/amps/and pulse timing.

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Nov 29 2016 9:46pm
by spinningmagnets
Page 298, "Copper and copper alloys" By Davis
Resistance welding of specific alloy groups
Copper and copper alloys having electrical conductivity higher than about 30% IACS (see table 18) are the least well-suited for resistance-spot, projection, or seam welding, mainly because of severe electrode pick-up. Thin copper stock can be welded using electrodes faced with RWMA class-13 (tungsten), or class-14 (molybdenum), but surface appearance is poor, and frequent electrode maintenance is required. A tinned coating on wire or sheet is helpful in welding copper.

Low and high-zinc brasses
The low-zinc brasses are difficult to weld, although easier than copper, and are subject to electrode pickup. Welds made in these brasses may lack strength, principally because of comparatively high electrical conductivity (32% to 56% IACS). The high-zinc brasses have an electrical conductivity of 27% to 28% IACS, and can be both spot and projection-welded over a wide range of conditions. Electrode pickup can be a problem, unless weld time, welding current, and electrode force are properly selected.

Excessive electrode pickup and blowthrough of the weld may occur when long weld times, high energy input, and low electrode forces are used. Yellow brasses (C268 and C270) are less susceptible to electrode pickup than cartridge brass except when long weld times and high energy input are used. Electrode force should be sufficient to prevent arcing or expulsion of molten metal, to which these alloys are subject because of their 30% to 40% Zn content, which boils at 905C (1665F). As shown in table 19, the recommended electrode force, when using electrodes having a face diameter of 4.8mm (3/16-inch) is approximately 1.8 kN (400-lbf)...

...electrode forces lower than those needed for welding low-carbon steel are used. But extremely low forces, which can cause electrode pickup and weak welds, should be avoided. Low electrode force can also cause high-zinc alloys to flash or burn through
Many of the sunstone spot-welding youtubes are short on raw info, but one of them stated their machine was using 5-lbs of force before it would pulse on copper...
Selection of process
Weldability of the work metal often determines which process should be used for a given application. Some of the coppers and copper alloys can be spot-welded, but not seam-welded because of high conductivity, and not projection welded because of low compressive strength of the projections at elevated and seam welds can be made in work metal as thin as 0.025mm (0.001-inch). Spot-welding of metal as thick as 3.2mm (0.125-inch) has been reported for copper alloys. Projection welding is best suited for work thicker than 0.50mm (0.020-inch).

The current used for resistance welding of copper alloys is much higher than used for welding low-carbon steel. Therefore, the electrode must have high electrical conductivity to minimize heat build-up. the Resistance Welding Manufacturers Association (RWMA) Class-1 electrode materials (typically tungsten or molybdenum alloys, containing copper and cadmium) are sometimes used for welding copper and high-conductivity brass. Class-2 materials containing copper and chromium, are used on low-conductivity brass, bronze, and copper-nickel alloys. Electrodes must be sufficiently liquid-cooled to minimize sticking to the work material, and to prolong their life. Tip contours must be carefully prepared, and the electrodes must be properly aligned.

The use of projection welding frequently can increase the quality of joints in high-conductivity alloys because current can be concentrated where needed. Distortion and electrode pickup are minimized because the electrode contacts a large area of the work metal. Projection welding may be preferred when the components are self-locating, or to simplify fixturing, or improve dimensional accuracy

26-ga yellow brass, $9 per 6 X 18 inches [will also affordably cut into smaller pieces for minor fee] ... rasSW.aspx

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 02 2016 1:14am
by spinningmagnets
I have ordered some 30-ga red brass, and some 28-ga yellow brass sheet. Both have approximately the same current-carrying capability, and are capable of pulling the amps that are at the upper end of what the best 18650 cells are capable of.

30-ga___0.25mm___0.010-inch___red brass, higher conductivity, but harder to spot-weld onto 18650's
28-ga___0.30mm___0.012-inch___yellow brass, lower conductivity, requires thicker ribbon for same current, but spot-welds easier than the red

If anyone has a spot-welder (whether factory-made or a DIY MOT style), I want to encourage experimentation with these, and I will send you a free sample to test if you are interested. The higher the copper content, the more current is needed (using very short pulses), and...pressing the strip down onto the cell-end firmly is something that is definitely required. The volts, amps, pulse length, and applied pressure are the questions I hope to find the answers to. ... fo/BR6060/

I am intrigued by the C40410 alloy mentioned by kdog. The conductivity is an excellent 60/100 (1/3rd better than red brass), and the "spot weldability" is rated a "Excellent". It appears a tiny trace of tin, iron, lead, and zinc added makes it spot-weld much better than pure copper (less than 1% each). Only problem is that I can't find anyone who makes a finished product out of it. Certainly no sheet-metal of a specific thickness. If I was a large battery pack manufacturer, it might be worth it to have some C40410 made up, and sent to a metals shop that rolls raw materials into sheet-metal.

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 08 2016 8:01pm
by spinningmagnets
Found a link in the "spot-welding copper" thread, concerning which type of tungsten probes to use
"...2% Thoriated (color code: red)
Preferred for their longevity and ease of use, 2% thoriated tungsten electrodes are the most commonly used electrodes today...These electrodes can be used for AC welding, and they are exceptional for DC electrode negative (straight polarity)...You should use a pointed and/or truncated tip...for DC welding processes, and also when welding...on thinner materials (those ranging from .005- to .040-in)...
The above quote is discussing TIG-welding, but I felt it had some useful info that might transfer over to spot-welding brass/ least as a starting point, from which to compare other future experiments. ... ig-welding

"Spot Welding Copper Strips to 18650 Battery Cells" ... 14&t=84680 are interested in 2% Thoriated Tungsten rods as spot-welding probes, here is some info on the diameters of the available rods.


Fechter has suggested that inserting a tiny short tip into a thicker copper rod would aid in conductivity and also cooling the tungsten tip, therefore I "think" a useful first experiment would be with the thinner tungsten rods. for the thinner rods, perhaps slice a lengthwise groove in the copper rods' tip, and clamp the thin tungsten in it? (as opposed to drilling a 1.0mm hole)

.040 ... Sw3ydVxaew

1/16 ... 1967679595

Sampler, 4 pieces, different diameters ... SwgQ9Vzy4U

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 09 2016 4:23am
by kdog
I found a producer of speciality copper alloys in US, they do some foils on my list including c70250. . I emailed them about retailers that buy their stuff and they gave me a contact- Insulectro in CA ( lake forest) ive emailed them regarding samples. I'm really really hoping they will be able to help. That was a couple of days ago. No word yet.
Fingers crossed

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 09 2016 11:50pm
by spinningmagnets
I now believe that common spot-welders will work if we use pure copper that is plated with nickel. I looked into covering copper with stainless steel plating (which I didn't know was possible, but it is), and although it works, nickel has half the resistance/twice the conductivity of stainless. If we are only plating nickel, the actual volume of nickel is tiny, so cost will likely never be an issue. Nickel strips can even be salvaged out of old battery packs (cordless drills, ebike packs, etc).

The salvaged nickel can be pretty twisted and chopped up, and it won't matter because it is only the raw material for plating. I have used a dremel with a thin abrasive wheel to cut nickel tabs in the past, works well...

"DIY nickel-plating onto copper connectors to cells" ... 14&t=85310

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 10 2016 5:57am
by kdog
Haven't heard back from the first company regarding copper alloys in foil... But I've found another specialty copper alloy producer, again in the US, who has a sweet range. I emailed them just a few moments ago.
Let's say that it goes well and I want to order a reel of a particular alloy...
Is anybody out there keen to go in cause the MOQ will prob be big for our purposes..maybe 20kg. Bear in mind I've no idea on cost at this stage, and it would be far better to have a US person to receive the goods ( if it comes to that)
Just wondering what the interest is....

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 10 2016 10:22am
by litespeed
I would definitely be insterested as I'd like to really explore these options. I've been so slammed at work and with Christmas coming haven't had time to order some thin copper to try that yet. My reasoning for wanting a less resistance material is from my current (pun intended!) pack of VTC3's. I have a 20s15p of Koinion cells (a true 10C cell that most rate as a 20 amp continuous cell.) and regularly pull almost 200 amps from them with my QS205 3.5T/MaxE combo. I loose about 10 volts on a fresh pack which I believe is from the nickel strips. I still can get 20 + amps easily from the pack which makes me think it's the strips that's the bottleneck.

Before I go to the expense of a new pack I want to figure out what is the best for me to use. I plan on either Sony VTC5's or Sanyo 25R in the same 20s15p and want like all of us do....virtually no voltage sag.

I feel, after trying thicker copper that with my equipment that this brass will be a better option. I think pure copper is always going to have to be used with very specific equipment as in $10,000 +....for that kind of money I'd rather just buy another toy.

So spinningmagnets if you have some samples you want me to try with my 800WS CD welder then I'll bite and we can see what develops with kdog's inquiry.


Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 10 2016 7:41pm
by spinningmagnets
litespeed, PM me your address, I'll send some 30-ga red brass and 28-ga yellow brass sheet to you for $10 to cover postage

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 11 2016 9:56am
by Volts
anyone try conductive glue as an alternative to spot welding, was thinking it might work better then welding as the heat from the welding process will increase the internal resistance of the battery, plus the silver electrical epoxy should be more conductive?


Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 11 2016 3:23pm
by amberwolf
couple relevant threads in this list, just searching on "conductive glue" in the first post (there are other threads with different search terms I dont' recall) ... mit=Search

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 12 2016 3:35pm
by ewinters
What about something like this cooper shielding tape, with conducive adhesive?

Enviado de meu XT1580 usando Tapatalk

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 12 2016 5:07pm
by ewinters
I was wondering if I could make P groups by simply sticking 1 or 2 layers of this cooper tape. They have corrosion protection and some have 2 sided conductive adhesive.

Enviado de meu XT1580 usando Tapatalk

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 12 2016 7:23pm
by kdog
been investigated before
glue is high resistance=heat equalls failing glue=more heat etc
now you have bits of copper floating around in you pack looking for a terminal to short to...
hehe you can try it!

Re: Brass for spot-welding 18650 parallel cell groups?

Posted: Dec 12 2016 10:24pm
by spinningmagnets
I've seen this copper foil used for low volts and low amps. Since it is flat, you can run it behind paneling to power speakers, etc...

I see the adhesive is advertised as being conductive. i don't know what that could possibly be used for, but anyone who wants to experiment with it can buy a small amount and test it for how many Ohms of resistance the adhesive side has.