Introduction to battery pack design and building, Part-3

Introduction to battery pack design and building, Part-3

This third installment is usually concerning the special issues which are wanted when building a high-amp battery pack, plus…I’ll listing a number of the products and tools which are typically used to construct a pack so, let’s get started.

The spot-welders utilized by business to make ebike battery packs are giant and expensive, and it’s unrealistic to even think about them for the home garage DIY builder. This is essential because, there are lots of nations where it is still very troublesome to purchase an entire battery pack, because the most well-known pack sellers do not ship to many nations.

The principles for delivery an entire battery pack are complicated and they are getting worse yearly. Even in case you do manage to get a pack builder to ship one to you, it’s costly and dangerous. Plus, even probably the most successful pack producers don’t make packs in each potential shape and measurement.

Nevertheless, it’s still truly fairly straightforward to buy the person elements to build a pack, regardless of the place you reside (as listed in part-2, click on right here), and because of this resourceful storage DIY builders will proceed to assemble their own packs. That is the primary purpose I wrote this collection on pack-building.

The methods and materials which might be used have been steadily enhancing, however… I hope to document a number of the widespread “greatest practices” as they’re at present recognized, so as to help new lovers avoid the widespread costly errors on their first build.

Sunkko Spot-Welders

I simply can’t advocate any product from this model (I apologize to Sunkko, but…I have to be trustworthy). I only mention them in any respect as a result of they are so well-known, and they’ll present up immediately in any Google-search about “18650 spot welder”.

The most important take-away I discovered from researching them is that…the 220V version is slightly extra dependable than the 110V version (and the 110V model has a horrible document…Don’t belief me, analysis this yourself).

Many locations just like the EU and Australia are lucky to already have 220V AC because the default system in all houses. Houses in the USA are sometimes 110V, however remember it isn’t troublesome to get your garage wired up for 220V for an electrical clothes-dryer, and in addition many air-conditioning models within the USA also have a socket that’s wired for 220V.

A typical model of Sunkko spot-welder.

Because the 110V model and the 220V each draw roughly the identical amount of watts, the 110V model attracts twice the AMPS from the facility socket of your property, which frequently trips the breaker (15A is widespread in the USA, 110V X 15A = 1650W). Even in the event you do get the 220V version (and either discover a 220V socket someplace in your house, or have one added), the electronics for each are a recognized weak spot. If you have already got a Sunkko, here is a website with information on tips on how to improve it, and fix it when it breaks (click here).

The Malectrics Spot Welder

This “pocket spot welder” from Germany appears to be working very nicely, and it has many glad clients. The programmable brain-chip is the popular “Arduino Nano”. The welding pulse time might be adjusted from 1-milli-second, as much as 500ms.

Somewhere alongside the line, someone found out that when you had a big battery that was able to putting-out lots of amps, you possibly can add some sort of on/off change and timer to make a spot-welder out of it.

I have seen youtubes that did this the place they added a car-starter solenoid change as the on/off factor. The problem with that design is that a automotive starter solenoid change is a single physical change that passes all the full amps of the 12V automotive battery (12V X 200A = 2400W)…

The full energy (with no resistance in-line) can embrace an power as high as 800-CCA (Chilly Cranking Amps). If there’s an engine starter-motor in-line as a load (the “resistance” of the circuit), then a typical 4-cylinder engine would usually draw about 200A for a half second, and then it will settle into around 100A to continue spinning the engine.

Nevertheless, it is a “dangerous design” to make use of a automotive solenoid starter-switch because the on/off aspect in a spot-welder that is powered by a automotive battery. One of these change can sometimes completely weld itself into the “on” place, since it might usually ONLY cross 200A peaks, however “now” you might have removed the resistance of the automobiles’ starter-motor and the change is passing the complete 800A that the battery is able to.

That’s the sort of amps that may produce sufficient heat to soften nickel strips as a spot-welder. I solely point out this to point out that a widespread 12V automotive battery has proven to be enough to energy a spot-welding operation for 18650 cells.

Additionally…as a result of a car-starter solenoid is determined by two bodily metallic contacts to the touch [and then be pulled away by a spring]doing this might cause a really inconsistent amount of welding pulse-time (measured in milli-seconds, which is one-thousandth of a second)

So…what can we use as an on/off change that can handle excessive amps? and may be controllable to adjust the spot-welding pulse in thousandths of a second? Perhaps the standard and customary MOSFET semiconductor?

A “FET” (Subject Effect Transistor) is a intelligent sort of  transistor that can be used as an sign amplifier, or a diode, or an on/off change…relying on how it is configured in a circuit.

The Malectrics package is a precision timer that uses a gaggle of FETs [in parallel] to show on-and-off a LOT of battery current as a spot-welder. You’d additionally need to add a big [and fairly new] 12V automotive battery as the facility source, and the most typical mistake for a new builder is to make use of a “small and previous” automotive battery that they already had. In case you are utilizing the longest weld-pulse setting, and but you’re nonetheless getting weak welds? it is probably that the battery you’re using is weak.

12V X 800A = a pulse energy of 9,600W

If the Malectrics system interests you, their web site may be discovered by clicking right here.


Within the pursuits of full disclosure…once I first noticed the kWeld, I turned the primary USA vendor for them, as a way to velocity up the quantity of US-based customers. It appeared very progressive and promising, and I needed precise customers to beat on them to see if it had any weaknesses, and…the results have been impressive. I was retailing them for a few yr, and the company has grown rapidly, in order that they now have a “actual” enterprise companion to handle all US sales [18650 heat shrink & cell holders, inc].

At first glance, the kWeld appears to be similar to the Malectrics. So far as perform is worried, one spot-welding cable simply passes its present by means of a large fuse from the automotive battery submit to the spot-welding probe. The second battery submit passes it’s current by means of a gaggle of paralleled FETs that act because the on/off change, on its approach to the second spot-welding probe.

The kWeld prices more than the Malectrics, and here’s why. It makes use of a proprietary administration system for the electronics, which measures the current passing by way of the system in real-time. Which means if the input voltage slowly drops while you’re using the welder, the gadget routinely adjusts the heart beat timing so as to make sure that the full amount of power delivered could be very consistent from one weld to the subsequent.

It additionally has a battery-test mode to tell you if the battery you plan to make use of will be capable of do the job. The original version of the kWeld was specifically designed to be used with either a lead-acid automotive battery, or a 3S “Lithium Polymer” pack (3S, 11.1V nominal LiPo, 12.6V when fully-charged). Nevertheless, the suitable choice of LiPo packs is restricted to just a few specific models which are recognized to have very low resistance, and are capable of sudden excessive bursts of amps, without struggling any injury (look for the 3S battery designation “130C, 5000-mAh”…or more).

Between using the readily-available automotive batteries (regionally sourced, as a result of they’re heavy, and delivery can be costly), and high-amp LiPo packs, the early kWeld units developed an excellent status.

Nevertheless, virtually immediately…some clients requested the choice of utilizing super-capacitors (which often operate at lower voltages). The second version of the kWeld had its voltage vary widened in order that the kWeld will work with an enter from as low as 3V as much as 30V (many nominal 24V / 7S lithium packs have a fully-charged voltage of roughly 28V).

The “kCap” eight.2V supercapacitor financial institution as an choice. Some builders feel that automotive batteries are cumbersome and heavy, and some clients favor to avoid utilizing LiPo batteries, because of the worry of a LiPo battery hearth.

The kWeld is made by in Germany, and it is owned and run by an electrical engineer. Based mostly on the success of some lovers who used super-capacitors, Keenlab has designed and commenced producing a supercapacitor-bank choice which operates at eight.2V, plus an influence supply that can take your 110-VAC house current and supply the 8.2V at very high currents, so that the facility bank refills rapidly.

Although the manufacturing unit guarantee has limits, this welder has been used at eight.2V X 1900A for a pulse power of 15,500W

International kWeld clients can contact by clicking right here.

For kWeld clients situated in the USA, you’ll be able to contact Keith at “18650 Warmth Shrink and Cell Holders INC” by clicking here.

The kWeld North American Fb help group could be found by clicking right here.

Copper and Nickel Buses

In case you are proud of a ‘widespread’ ebike package, then you will also be proud of a standard ebike battery pack [my default recommendation for a battery pack is a high-quality 48V-52V pack, like the Luna Cycle packs, as of the summer 2019].

That being stated, perhaps you’re building an electrical motorbike, or perhaps a high-powered electric bike? You’ll NEED your pack to offer extra amps than a ‘widespread’ pack. 18650-format cells exist that may present 15A-30A (at present, Samsung 30Q and 25R, LG HB2, Sony VTC6). In case your pack design requires a high-amp cell like this, the design bottleneck would be the cell inter-connects, and the two pack collectors (the constructive and unfavourable terminals).

Pure nickel as a cloth (and spot-welding as an assembly technique) is the default bus-material selection for “widespread” cell interconnects (18650 / 21700 cylindrical cells). Nevertheless, when your design wants excessive pack-amps, the bus materials turns into a important design choice.

The widespread pure-nickel collection bus-ribbon has a width of approximately 8mm (1/third of an inch large), and it’s current-carrying capacity is measured by its’ thickness. Widespread battery packs (a 25A peak from 5P?) uses zero.15mm thickness for 5A per an 8A-rated cell. A zero.20mm thick nickel ribbon is widespread for the favored 10A rated “high-capacity” cells, like the LG MJ1, Samsung 35E, and the Panasonic GA.

Presently, the builders’ dilemma happens when utilizing a high-amp cell (15A-30A). I’ve seen builders using double-layers of nickel ribbon for the collection connections, but…I do not advocate that strategy. At larger amps, utilizing nickel as a bus-material finally ends up being more of a resistor than a conductor. By that I imply…it converts a LOT of battery watts into warmth as an alternative of carrying out work. Also, the 2 terminal collectors will experience voltage sag, so the builder won’t get the complete amps that they paid for through the use of genuine high-amp cells.

Utilizing MAGNETS!

This seems like a joke, however I assure you, this actually works. I wouldn’t use magnets on a nickel bus, as a result of nickel is just too stiff to evolve to the floor of the cell ideas. I feel that copper sheet is a really viable materials for 15A-30A high-amp cells, such as the 30Q, 25R, HG2, and the VTC6.

If you want to experiment with copper bus materials, I might begin with 30-ga, or probably 32-ga (sheet-metal gauge is totally different than the wire-gauges we are already conversant in). One mil is one thousandth of an inch.

0.20mm___8-mil__32 ga
0.25mm__10-mil__30 ga

These thicknesses of copper sheet are skinny enough that they can be minimize with scissors. Copper is mushy at these thicknesses, however an equal thickness of nickel could be very stiff.

Notice that this builder is using the extra heat-resistant fiber washers on the constructive ends. Additionally, he’s building the pack on a stiff plastic sheet over his workbench. The pack proven is 12S / 4P

In the pic above, the delicate copper sheet is being minimize to type bus-plates that present both the collection and parallel connections. Neodymium “button” magnets are surprisingly highly effective, and the electrodes of 18650-format cells are “nickel-plated steel”. Nickel has a really low quantity of magnetic attraction, however the metal cores on the cell-electrode ideas will strongly pull in the direction of these magnets.

Since magnets are also very strongly drawn to each other, the builder above has glued the magnets onto the copper sheet with a gel “tremendous glue”. It’s also possible to buy button magnets with a chamfered gap in the middle, which might can help you insert a flat-head screw from the cell aspect by means of the magnet, and screwed into some sort of aspect panel (perhaps 1/Four-inch plywood, or plastic kitchen chopping board?).

I might additionally advocate firmly attaching the bus-plates by some technique onto the plastic cell holders so the plates do not move around. I am advised the magnets maintain the plates firmly in place, but in a crash, I’m involved that they could shift around and probably brief out.

Spot-welding a Copper / Nickel sandwich

This can be a new improvement. There have been many experiments with copper bus-material that is nickel-PLATED within the hopes that doing so would permit it to be easily spot-welded. Nevertheless it isn’t readily available for purchase, and corporations like Makita, Milwaukee, and DeWalt use an expensive laser to weld them onto cordless software cells. This left residence DIY nickel-plating as a topic of many experiments, which have not labored out to date.

Lately, an anonymous youtuber has posted that for those who put nickel on prime of a copper ribbon, It spot-welds simply with the widespread spot-welders listed above (kWeld, Malectrics, Boss-Degree, Riba, and so forth). Right here is the link to the youtube, quick forward to 8:38 to see the copper welding half.

Spot-welding a nickel /copper sandwich onto an 18650 cell

The copper and nickel strips proven above are both zero.20mm thick, and 0.15mm thick nickel is reported to additionally work. Additional experiments are continuing to find out all the other thicknesses that might work. After seeing this, my research revealed that that is an previous metal-workers trick when making an attempt to spot-weld aluminum sheets to one another. Here is a link to a youtube video that exhibits the metallic sandwich technique getting used on aluminum.

There’s some hypothesis as to why this works, nevertheless it has been verified to work, so this is an thrilling improvement for builds whenever you need to use high-amp cells. An fascinating side-note is that some builders have ordered pure nickel up to now as a bus materials, and when it arrived…they discovered that they had been bought nickel-plated steel.

It was dangerous sufficient to get ripped-off, however now they had to anticipate genuine pure nickel to reach in a second order. Nevertheless, in case you or a pal have any nickel-plated steel ribbon just sitting on a shelf, the copper in a nickel-copper sandwich would carry the present, so the nickel a part of the sandwich might be the cheap steel-core ribbon.

Using high-amp flat pouch cells

Although I’ve sometimes seen large-format flat pouch cells on ebikes, and 18650 cells used on E-motorcycles, you will most often see it the opposite approach round. For many ebikes, 18650 cells remain straightforward to configure into a customized pack that matches an uncommon shape, and the performance and range of 18650 packs are often one of the best match for most ebikers, with pouch cells being the type of selection for E-motorcycles. A cylindrical 18650 cell is principally only a pouch cell that has been rolled up and inserted right into a metallic cylinder.

The higher the amps that these cells are designed to offer, the larger the tabs shall be, so the tabs won’t turn into a bottleneck to current. The bolt-holes within the tabs have been minimize by a standard workplace paper hole-puncher.

Nevertheless, despite the fact that utilizing flat pouch cells will drive the builder to use a pretty big rectangular shape because the building block of the pack, motorbike conversions typically need such excessive amps, that flat pouch cells are the only viable choice.

Once you determine that you may be using this format of cells, I consider that the cell-connections are literally easier to put together, compared to making high-amp spot-welds.

Flat laminated pouch cells, seen right here with vast tabs on the same end (on the left), or…large tabs on reverse ends (on the appropriate). The tab connections between the cells for flat laminated pouch cells are much simpler to reliably accomplish, in comparison with cylindrical cells like 18650’s, and 21700’s.

These flat pouch cells are being compressed on their side-faces, which helps to decrease the interior electrical resistance. The tabs shown have been spot-welded collectively. The pack proven is 12S / 1P

For those who add bodily compression on the side-faces of flat pouch cells, it’ll decrease the interior electrical-resistance. Doing that spreads out the current-flow more evenly across all the chemically-reactive inner surfaces. If half the interior surfaces have a poor contact, they may circulate less current and run cooler, but the surfaces with good contact will then be pressured to movement far more present than they have been designed for.

If this happens, then the interior “scorching spots” will cause the electrolyte in those places to “off fuel”, which results in a puffy cell look. The more fuel that is generated, the more severe this situation becomes (gasses forming inside will trigger delamination of the interior layers).

Utilizing only 20-PSI of compression drive is a lot better than nothing, and I’ve seen revealed reviews that pressures as much as 100-PSI may be useful.

Slicing plastic cell separator-sheets from the edges of an previous storage tub.

Within the pic above, I have bought some high-amp pouch cells, and I am tracing out the shape to cut cell separators, which can help to stop a short between the tabs when I’ve them on my workbench while I’m connecting the cell tabs.

The beginning of assembling a pouch-cell battery pack.

In the pic above, I’m using pouch cells to assemble a 12V suitcase pack to charge my telephone and laptop computer during a power outage, since I reside in tornado nation (and I formerly lived in earthquake nation). The additional-large tabs are a clue that I have chosen high-amp cells, and I have accomplished that so I may also use this pack to “bounce begin” my automotive, if needed.

I’m utilizing this chance to take pics of a number of elements of the pack meeting procedures that I feel are essential for brand spanking new builders. Please notice that I’m performing this activity on prime of a purple plastic storage bin lid, and beneath this cell is a inexperienced plastic cell separator (seen in the pic above the previous paragraph).

The tabs have been marked as +/–, nevertheless it was in very small print, so I used felt markers to make giant marks. I also used scissors to chop a tab-cover for the constructive tab, utilizing ziplock sandwich luggage as the cover-material. I then hooked up the ziplock plastic tab-cover with a piece of “low stickiness” blue painters tape which is straightforward to take away and in addition does not depart any glue residue.

Take notice that on this specific brand of cell, a small part of the top-right corner of the destructive tab has been reduce at an angle to make identification easier.

I found some aluminum flat-bars to use as tab-clamps, and these already had threaded holes. Remember that the tab-clamps might be product of metal if you would like, since they don’t want to hold current (the 2 cell-tabs are pressed collectively, skin-to-skin). I am purposefully using aluminum clamps to behave as a heat-sink. I beforehand believed that an aluminum plate that was situated inbetween the cells would draw inner warmth out to the sting as a cooling measure, but doing that leads to the surfaces of the cell-sides to run cooler than the cores.

If the varied areas inside the cell run hotter or cooler than each other, then that might additionally change the interior resistances of that cell. In depth research has shown that cooling the tabs will lead to probably the most secure and even inner temperatures in the lively supplies, while still drawing-out a number of the inner warmth within the lively layers of the cell.

It’s fairly straightforward to cut threads into a drilled gap on a 7075-alloy aluminum bar (click here for one choice). The 6061-alloy Aluminum conducts electrical energy better, but it is extremely gentle, and you may simply break a tap when using it as a bar-clamp materials to chop threads into a drilled hole.

In this software, I like utilizing threaded holes within the aluminum bar material (with a chamfered hole underneath the flathead screw-head) to permit the clamps to be as thick as potential, since utilizing a standard bolt-and-nut on a through-hole would require the clamps to be thinner. Since there isn’t any lock-washer to to scale back any attainable connector-loosening from vibration, I will use a thread-binding fluid, like Locktite.

This technique permits me to use clamp-bars which might be the same thickness because the cell. A collection connection is made between two cell-tabs, and the clamp type shown has two similar items, so the material buy calculations can be straightforward. One aspect of the two end-collectors clamps can be flat-bar copper, to offer the constructive / unfavourable outputs for the pack.

From LFP

This popped up in a current forum dialogue evaluating soldering buses to cells vs spot-welding. LFP (Luke) was the top battery pack engineer at Zero bikes.

“…This thread matter might be re-phrased as, is it better to hit yourself within the balls with a baseball bat, or a golf membership?

Firstly, using FLIR on shiny nickel surfaces is laughable, as a result of it’s one thing like 5-10% emissivity, so these temp values it’s reading are +or->100-degC of being useful for something.

Lastly, the temp on the top of the nickel is completely irrelevant, as the highest of the nickel isn’t the heat delicate area.

If you solder a can, after which reduce the cell apart, you will notice that the separator layer is melted together and deformed on the ends, and the can has excessive fuel strain, and the thermal decomposition breakdown merchandise of the carbonate esters within the electrolyte are going to cause it to age poorly and develop self-discharge from the impurities launched by that thermal breakdown.

If you spot-weld a can, it’s not the outer-side that matters in any respect. Not even related to talk about, or take a look at, or think about. If you reduce that cell aside, and you see the inside of the can, which was glowing red-hot steel (2500-degF) for the weld to be attainable, you see that the interior corrosion-resistant surface lining of the can is vaporized away, and in it’s place is carbon debris from flash boiling electrolyte carbonates, and now that carbon shall be polluting your cell to increase the self-discharge charges.

For those who’re going to attempt to spot-weld, you don’t do it based mostly on how the welds look externally, or how exhausting they are to [physically] pull off the can, these metrics are baby’s play to nail, and simply don’t matter with respect to making a pack that may final. You should tune the method by chopping open the bottom of every cell you bonded to and analyzing the injury to the top of the jellyroll, and look at the underside of the can floor for what kinds of thermal decomposition merchandise at the moment are poisoning your in any other case very pure electrolyte.

Soldering packs is for purposes the place you don’t care if it even works as soon as, and random self-discharge ranges are acceptable, and random failure in a short while is desired.

Spot-welding (to the bottoms of cans) is for whenever you don’t care about leaking electrolyte out of the can from the stress-risers in the heat-affected zone close to the weld fusion website (the place it was 2500 degF), and also you don’t care about having the corrosion resistance can-coatings remaining practical, and need to pollute your electrolyte with random carbon particles (think of setting your breakfast right into a frying pan at 2500 degF)…”

So, what technique do you have to use?

Properly…solely you possibly can determine what dangers you’re prepared to take, and what is going to fit into your price range. I only hoped to collect details about what materials and strategies are at present getting used, and to point out a few of the harmful pitfalls that new builders is perhaps stumbling into. I hope this has been helpful not directly, and I will update this Three-part collection as new info is available in.

Written by Ron/spinningmagnets, June 2019