First battery build ever - some questions

[sean_cad]

I am building my first ever ebike battery.


It's a 20s4p configuration, with Molicel P42A cells. I have a 150A cont/375A peak ANT Smart BMS - I plan on limiting current on both the BMS and Controller to 80A peak.

I have the following materials:

1. 0.1mm pure copper sheet (3500mm wide)
2. 0.2mm x 8mm pure copper strip
3. 0.2mm x 8mm pure nickel strip

I did some testing and determined the 0.1mm copper sheet with 0.2mm pure nickel strip on top is the easiest and strongest weld. I had a hard time spot welding the .2mm copper.

...

My questions are

• Am I going to run into any issues having such an over specced BMS? It's a Smart BMS and can be turned down to 80A peak, as can my Fardriver controller.
• Do I need copper bus bars in my build? The 80A peak will rarely be pushed for more than a few seconds at a time. I will be mostly pushing very low power (1kW) average
• Is my cell layout the easiest for a first time build? (see image below) can you recommend an easier and more foolproof layout?
• What copper/nickel configuration is the best with the materials I listed above?
• Is using XT90 safe for discharge?
• Am I biting off more than I can chew?

 

[glennb]

Sounds like you're got a handle on it.

You could do it in 2x2 squares, instead of 1x4, so that the posive and negative are at the same end of the battery.

You might like to peruse the ongoing stainless steel copper sandwich thread in the battery forum. Seems substituting SS for nickel is all the rage.

P.s. pink BMS is pretty.

 

[sean_cad]

Sounds like you're got a handle on it.

You could do it in 2x2 squares, instead of 1x4, so that the posive and negative are at the same end of the battery.

You might like to peruse the ongoing stainless steel copper sandwich thread in the battery forum. Seems substituting SS for nickel is all the rage.

P.s. pink BMS is pretty.

Thank you, I'll will look into the 2x2 configuration, that seems light it might be easier. I'll also look into nickel plated steel strips, I agree they seem so much easier to obtain a strong weld combined with copper

 

[sternwake]

Stainless on top of copper allows the use of significantly less welder power to achieve solid welds, compared to nickel plated steel, or pure nickel

If one's welder is not easily able to weld the chosen thickness of copper under Nickel or nickel plated steel, then using stainless might make all the difference.

If one can weld copper under nickel plated steel or pure nickel at near their welder's max power, they can likely weld same copper under stainless using 20% less power and stress the welder far less, and achieve more consistent welds as well.

The reason All cell manufacturers say do not solder to cells and to spot weld instead is because of the heat, then using less welder power to achieve solid welds can only be beneficial, but to what degree is arguable.

I had struggled with a cheap underpowered welder and a desire for 0.15mm+ copper.
I tried all sorts of things to increase its ability, and had I been aware of stainless at that time I likely could have achieved my desires, but then would not now have a welder which can weld 0.3mm copper reliably, consistently, at well less that the welder's maximum power.

Nelvick's(Zeus-fl/Diy500ampdotcom) welding flux also lessens the welder power required.

My AwithZ P20B welder can weld 0.2mm copper, no sandwich no flux using 80% of its available power.
It can weld 0.2mm copper under 0.1mm stainless using 55% of its available power.
It can weld 0.2mm copper under 0.1mm stainless, using flux, using 38.5% of its available power.

0.2mm copper welded with no sandwich can be pulled off the cell with 50% less force than when it has stainless on top.



My nickel plated steel and pure nickel will likely never be used in any battery build ever again.

Some.might decide to use pure nickel as it can in theory increase the ampacity of the sandwich.
I'd argue thicker copper under stainless would be easier to weld, and offer less electrical resistance and have far less susceptibly to broken welds, should there be physical stresses on the busbars as there is in my Application, Esk8, where vibrations are extreme, and the P groups need to be able to flex with the board and enclosure.

 

[sean_cad]

Stainless on top of copper allows the use of significantly less welder power to achieve solid welds, compared to nickel plated steel, or pure nickel

If one's welder is not easily able to weld the chosen thickness of copper under Nickel or nickel plated steel, then using stainless might make all the difference.

If one can weld copper under nickel plated steel or pure nickel at near their welder's max power, they can likely weld same copper under stainless using 20% less power and stress the welder far less, and achieve more consistent welds as well.

The reason All cell manufacturers say do not solder to cells and to spot weld instead is because of the heat, then using less welder power to achieve solid welds can only be beneficial, but to what degree is arguable.

I had struggled with a cheap underpowered welder and a desire for 0.15mm+ copper.
I tried all sorts of things to increase its ability, and had I been aware of stainless at that time I likely could have achieved my desires, but then would not now have a welder which can weld 0.3mm copper reliably, consistently, at well less that the welder's maximum power.

Nelvick's(Zeus-fl/Diy500ampdotcom) welding flux also lessens the welder power required.

My AwithZ P20B welder can weld 0.2mm copper, no sandwich no flux using 80% of its available power.
It can weld 0.2mm copper under 0.1mm stainless using 55% of its available power.
It can weld 0.2mm copper under 0.1mm stainless, using flux, using 38.5% of its available power.

0.2mm copper welded with no sandwich can be pulled off the cell with 50% less force than when it has stainless on top.



My nickel plated steel and pure nickel will likely never be used in any battery build ever again.

Some.might decide to use pure nickel as it can in theory increase the ampacity of the sandwich.
I'd argue thicker copper under stainless would be easier to weld, and offer less electrical resistance and have far less susceptibly to broken welds, should there be physical stresses on the busbars as there is in my Application, Esk8, where vibrations are extreme, and the P groups need to be able to flex with the board and enclosure.

I have the AwithZ UF20B (10.5kW) - I've done some testing. It does not weld .2mm copper alone, it barely made a dent in it. However with .2mm pure nickel on top it did a decent weld, but I doubt it would survive vibrations from an Ebike.

I think I'll stick with either one of the two configurations:
.1mm nickel plated steel under + .1mm copper in the middle + .1mm nickel plated steel on top
or
.2mm copper under + .2mm nickel plated steel on top

My .1mm pure copper sheet is huge, so I can cut it to shape and try to achieve the maximum volume possible, hopefully this would be sufficient for 80A peak

 

[sternwake]

There are many reports of the AWZ Uf20b being able to weld 0.2mm copper under 0.1mm stainless, even some reports of it being able to weld 0.3mm under stainless, using flux, although that raises my eyebrow in doubt in the absence of proof.

The best conductor that is not silver, is copper.
I personally want only copper touching my cell contacts.

I want very strong welds that tear the sandwich when forceably removed, as a test of the strength of the weld and the welder settings

0.1mm copper by itself is very weak, and so is 0.2mm copper by itself.
However 0.2mm copper under nickel plated steel, or stainless steel is quite strong. It will deform the cell can when one tries to remove it, when welded properly.

It will require far less power to spot weld 0.2mm copper under stainless steel, than it will under an equal thickness of nickel plated steel. This is undisputable fact.

Using Pure nickel on top of copper, in my opinion, is pointless, unless nickel plated steel or Stainless is not available.

Triple stacking makes No sense, especially if it is not copper in direct contact with the cell. I have triple stacked when the first two layers were copper, and only did that as I did not have 0.25 or 0.3mm homogenous copper and was still experimenting, exploring the limits of my p20B welder.

Copper is the obvious conductor of choice.
The issue is that copper is very hard to weld without lots of power. Copper nickel sandwich was the original way to actually weld copper, years ago, and most everybody realized that copper nickel plated steel sandwich was even easier to weld. Stainless is another step above that. It is like the magic material of the spot welding world.

The arguments of dissimilar metal corrosion hold little weight IMO, as if moisture is on contact with these conductors there is far larger issues at hand.

Stainless steel is the most effective spot welding aid when placed atop copper.

There is no more effective copper welding aid than stainless placed atop it. Not nickel, not nickel plated steel, Stainless steel.

Maximizing the copper thickness below that stainless welding aid should be the goal of any battery build, in my opinion.

One can do the math and say 0.2mm pure nickel at X width is more than adequate to pass the expected amperage without overheating, but the fact remains that copper has 4 times less electrical resistance. 0.2mm pure nickel by itself is obviously easier to weld than 0.2mm copper, especially with low power welders from 2019, but this is 2026, and we have supercapacitor based spot welders with a plethora of power.

The top layer of any copper sandwich will be conducting very little of the current, as copper has 4 times less resistance as pure nickel, and 10x less resistance as steel.

A roll or sheet of 0.1mm 304 grade stainless steel is far less expensive than pure nickel, and with a decent pair of Tin snips is not difficult to cut.

The AWZUf20B is capable of welding 0.2mm copper under 0.1mm of stainless
You report 0.2mm copper under 0.2 pure nickel yielded weak welds. That is hardly surprising.

Before I got Stainless or flux, I was disappointed that I could not weld 0.2mm copper under 0.15 nickel at max power with my P20B. i could however using 0.1mm nickel plated steel.

Now with Stainless and flux I can get reliable consistent solid welds using under 40% of the welder's maximum power.
Stronger welds.
less heat entering the cell damaging the electrolyte in contact with the interior weld nugget.
0.2mm copper.
Win Win Win.

Stainless is a magical copper spot welding aid.
Period.
It's not really magic, just physics.

But the war on science, and logic, is strong, and alarmingly effective.

 

[HardWaterATX]

A roll or sheet of 0.1mm 304 grade stainless steel is far less expensive than pure nickel, and with a decent pair of Tin snips is not difficult to cut.

The AWZUf20B is capable of welding 0.2mm copper under 0.1mm of stainless

This is great information, I have a sunkko 709ad that was given to me and am about to embark on my first pack build and am a little nervous about the welder working out. I have about 6kwh of 21700 cells and don’t want to waste any.

 

[sean_cad]

There are many reports of the AWZ Uf20b being able to weld 0.2mm copper under 0.1mm stainless, even some reports of it being able to weld 0.3mm under stainless, using flux, although that raises my eyebrow in doubt in the absence of proof.

The best conductor that is not silver, is copper.
I personally want only copper touching my cell contacts.

I want very strong welds that tear the sandwich when forceably removed, as a test of the strength of the weld and the welder settings

0.1mm copper by itself is very weak, and so is 0.2mm copper by itself.
However 0.2mm copper under nickel plated steel, or stainless steel is quite strong. It will deform the cell can when one tries to remove it, when welded properly.

It will require far less power to spot weld 0.2mm copper under stainless steel, than it will under an equal thickness of nickel plated steel. This is undisputable fact.

Using Pure nickel on top of copper, in my opinion, is pointless, unless nickel plated steel or Stainless is not available.

Triple stacking makes No sense, especially if it is not copper in direct contact with the cell. I have triple stacked when the first two layers were copper, and only did that as I did not have 0.25 or 0.3mm homogenous copper and was still experimenting, exploring the limits of my p20B welder.

Copper is the obvious conductor of choice.
The issue is that copper is very hard to weld without lots of power. Copper nickel sandwich was the original way to actually weld copper, years ago, and most everybody realized that copper nickel plated steel sandwich was even easier to weld. Stainless is another step above that. It is like the magic material of the spot welding world.

The arguments of dissimilar metal corrosion hold little weight IMO, as if moisture is on contact with these conductors there is far larger issues at hand.

Stainless steel is the most effective spot welding aid when placed atop copper.

There is no more effective copper welding aid than stainless placed atop it. Not nickel, not nickel plated steel, Stainless steel.

Maximizing the copper thickness below that stainless welding aid should be the goal of any battery build, in my opinion.

One can do the math and say 0.2mm pure nickel at X width is more than adequate to pass the expected amperage without overheating, but the fact remains that copper has 4 times less electrical resistance. 0.2mm pure nickel by itself is obviously easier to weld than 0.2mm copper, especially with low power welders from 2019, but this is 2026, and we have supercapacitor based spot welders with a plethora of power.

The top layer of any copper sandwich will be conducting very little of the current, as copper has 4 times less resistance as pure nickel, and 10x less resistance as steel.

A roll or sheet of 0.1mm 304 grade stainless steel is far less expensive than pure nickel, and with a decent pair of Tin snips is not difficult to cut.

The AWZUf20B is capable of welding 0.2mm copper under 0.1mm of stainless
You report 0.2mm copper under 0.2 pure nickel yielded weak welds. That is hardly surprising.

Before I got Stainless or flux, I was disappointed that I could not weld 0.2mm copper under 0.15 nickel at max power with my P20B. i could however using 0.1mm nickel plated steel.

Now with Stainless and flux I can get reliable consistent solid welds using under 40% of the welder's maximum power.
Stronger welds.
less heat entering the cell damaging the electrolyte in contact with the interior weld nugget.
0.2mm copper.
Win Win Win.

Stainless is a magical copper spot welding aid.
Period.
It's not really magic, just physics.

But the war on science, and logic, is strong, and alarmingly effective.

Do you think pure steel strips are better than nickel plated steel? Or there isn't much of a difference

 

[sternwake]

Do you think pure steel strips are better than nickel plated steel? Or there isn't much of a difference

In terms of welder power required, I suspect there is little difference. It would depend on the thickness of the nickel plating and the alloy of steel used.

I have some Nickel plated 0.2mm copper and can tell no difference between it and non plated 0.2mm copper. Same welder settings, same results with either. The plating can be scraped off pretty easily.

 

[sternwake]

This is great information, I have a sunkko 709ad that was given to me and am about to embark on my first pack build and am a little nervous about the welder working out. I have about 6kwh of 21700 cells and don’t want to waste any.

I have no experience with Sunkko welders and cannot say what it is or is not capable of. The10.4kw Uf20B reports of sucessfully welding 0.2mm copper under 0.1mm stainless are from other users on this forum. I have the 14.6kw AWZ P20B and need 55% of its max power if i am not using welding flux and 38.55 of its power for 0.2mm copper under 0.1mm stainless using Nelvick's welding flux/ Brazing paste. Please note that this is not soldering flux. Some have overlooked this huge detail and say things like My flux dried out and was ineffective.

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