he got it going by writing me first
Around 23:40 we exchanged some PM’s and then it suddenly stopped…
hummie uses fusion360 and apparently he has some problems exporting (to any format). Probably one of the hidden features of fusion360?
@hummie, If you can verify if you can open a dxf with LibreCAD, then it’s fairly sertain I can also import it in KiCad.
Local time here in Europe is now 01:47 and it’s time to put one ear on a pillow for the next bunch of hours for me.
5.5 fat traces with balance traces ( no outline) v1.stl (36.8 KB) 5.6 26650 pcb Drawing v1.pdf (124.2 KB) 5.7 holes.dxf (138.2 KB) 5.7 holes.pdf (105.0 KB) 5.7 pcb w traces v1 Sheet1.dxf (150.1 KB)
We hope you put those files public on purpose…
At this moment I have a preliminary draft of your PCB.
The files you posted are not of much use to me.
The DXF files are scaled. the stl file is a “blob” which I do not know how to handle well. The PDF file has measurements, but there are lots of inconsistencies.
So I had to do some guesswork to make a PCB out of this.
I assumed the outside diameter of the PCB is 500*143mm (or is that the size of the pads?)
Instead of trying to scale and convert your DXF files I just took some coarse measurements, rounded most measurements down to whole millimeters and converted it to a native KiCad project.
Sizes I used for the pads:
- 31 * 160mm
- 73 * 78mm
- 31 * 80mm
I have put SMD pads on both top and bottom, and stitched them with rows THT pads.
I also had to make other guesses.
First guess is to what this PCB is actually used for.
I guess it’s for very big battery packs with a lot of 26650 cells.
I guess that each pad is for 6 cells.
I guess that 6*12 = 72 of these 26650 cells are stacked between 2 PCB’s.
I guess that multiple of these stacks form a larger complete pack.
I guess there may be hundreds of these 26650 cells in a complete battery pack.
Are these guesses correct?
What is the current rating of this battery pack? I guess that each (0.7mm) via is good for about 2 to 3 Amps, but have not researched it thoroughly.
At the moment the long pads have 122 via’s and the square pad has 112 via’s.
Some of the work I’ve done:
I started with making a schematic:
The schematic is of course very simple.
A connector (2.54mm spacing) for the sense lines, and 3 sizes of pads. I also added labels to the wires for ease of PCB routing.
After that I made custom footprints for the Pads.
Pads are on Top and Bottom of the PCB, and Top and bottom are stitched wit via’s:
I have also made a custom footprint for the “slots” and placed an array of them on the PCB. At the moment each slot is 9*1mm.
In KiCad’s 3D viewer it looks like:
As you can see I have not routed the board yet, KiCad is yearning for me to replace the white ratsnest lines with real tracks.
You put all the tracks on the same layer, Is it OK if I put some on the top, and others on the bottom?
But I will only route the board once the exact dimensions and locations of the pads are clear.
The easiest way is to have an DXF file of only the object. scaled 1:1 and inclusive the board outline (Is it 500x143, or is that the size of the outline of the pads?
Also, I think it’s now time to discuss my “fee”.
What is this design worth to you?
It took me a few hours, most of it was trying to understand what exactly you want to make, and some of it was to refresh some info of how to do things the KiCad way.
What is it worth to you to have this design in a quick manner?
What sort of production are you going to make of this? How many of these battery packs will you make?
At the moment I’ve put about 5 hours of work in it, inclusive communication and figuring out how to interpret the files you posted here.
Since you offered to pay for this design, I want you make a fair donation to the KiCad project for the worth of this design to you.
You can make a donation through:
https://funding.communitybridge.org/projects/kicad
I’m not sure, but I think this donation is tax deductible, but if that’s important to you, i’ll leave the details for that for you to figure out yourself.
I am also having difficulties with sizes and dimensions, because different files you made public here have different measurements.
For example:
- I would have expected 1:1 raw objects, no title blocks and such.
- Pdf says: 161.06mm long. (Top left pad)
- Stl says: 162.50mm long.
- Dxf says: 107.35mm long.
- PDF says: Pads 31mm wide, while the Stl pads are 30mm wide.
- Stl is only file with “accurate” measurements, but does not have board outline.
- Weird scale factors on drawings.
- It also seems logical you want rounded corners on the PCB. Maybe the same radius as the 26650 cells?
- How about the “ears” on the 2 short pads near the connector for the sense lines. are those important? (I can add them easily)
- Is my idea of via stitching around the edges OK? Do you want more or less via’s, and where do you want them?
- I am also not sure of the exact locations of the slots. At the moment I’ve set the pitch between the slots to 27.41mm. Is this an important measurement? If it is not important, then I prefer to work on a grid of whole millimeters. KiCad itself is not very good with measurements, and with whole millimeters it’s easier to work on a grid.
- On the pdf you have a measurement of 11.6mm Is this the center distance between the slots, or is this measurement for the distance between the pads?
- When the design is finished, is it OK if I post the whole project here, or do you want to keep it private (Then I’ll PM it).
I think it’s also a good Idea if you install KiCad.
KiCad is an open source program and this won’t cost you anything. Then, when you view the project in KiCad you can determine if it’s OK, and I can make adjustments before making the final Gerbers. (Or you can make the Gerbers yourself with a few mouse clicks).
Also, having the complete design as a KiCad project makes it easier for you to adjust the design for a different sized battery pack.
Last:
I’ve removed the border and titleblock of “5.7 pcb w traces v1 Sheet1.dxf” and then scaled it with a factor of 1.5, and now it fits reasonably well on the PCB. But I do not know if this scaling is correct. Ideally I ant a .dxf file with:
- Outline of the PCB.
- Location and size of all pads. (Is roudning to mm OK? Can all the “Long” pads be the same size?)
- Location and size of all slots. (Is rounding to mm OK?)
- Location and size of the connector.
- Circles for diameter and location of the 26650 cells. (these are not always exact the same size)
Is it possible the battery cells are in some ridgid frame with fixed dimensions? If so, is there a datasheet? (Post it)
Also some notes about your tolerances would be nice.
Are sizes of the DXF a maximum, a minimum, or plus and minus some distance.
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Now I realize the intention may be differently.
Could it be that just 2 of these PCB’s will form a single battery pack?
It may be a good Idea to use the back of the PCB to make series connections between the cells.
Maybe you want smaller pads on the back of the PCB to solder wires to?
Another idea is to put 2 holes near the connection of the sense wires.
If your intention is to solder the wires directly in the PCB, then some form of stress relief is required. with holes through the PCB, you can put tie-raps through the holes to secure the cable. (The cable may not bend at the solder connection. It is a stress concentration point).
Maybe these cells are supposed to be glued together.
Soldering is uncommon for Li-Ion.
Let me know your requirements and I can make adjustments.
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I have had experience with doing something like this. What amount of current do you want to draw out of the battery?
If it is more than a few amps then i highly suggest you go a different route than using a PCB.
The team i worked with made the experience that you really need copper inlays to be able to handle even currents in the order of 20 Amps. (Mainly because you really need to ensure that there is very little voltage drop within your battery pack as you otherwise draw differing amounts of power from your cells). Soldering to such copper inlays gets however really tricky.
And as soon as you use copper inlays you basically can also directly use nickel plated plates (same material as the strips that come out of your cells) laser cut to your desired shape allowing you to even have thin strips protruding bend over to make soldering easier or even better have them spot welded. Solder thin wires directly to these plates to then get the protection circuit and don’t forget to include space for temperature sensors.
And separate the different voltage zones by use of plastic plates (can be glass fiber reinforced plastic if you want the same component to add more mechanical stability).
For pure series connections there is an even simpler solution. Place your cells next to each other but rotated such that the minus pole of one cell is always near the plus pole of the next one. Tape them together by use of fire resistant tape (to be on the save side). Then solder them together without anything else in between. For mechanical strength put large shrink tubing on top of that.
This is how most commercial battery packs are made (the one for RC cars, planes, …)
You can also place rubber strips around the connection points to reduce the chances of short circuits in the case of mechanical damage to your pack (for example if it is dropped). The least you should do is put tape over them.
You can also buy one cheap pack and dissect it to see how it can be done.
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In his other post hummie plans to use 2OZ copper for this board.
There are also no connections on the back side. Top and bottom are symmetrical, which gives 4OZ copper total. I also assume the connection on the back will be in the middle, which helps current spreading and reduce voltage drops.
I do not know what’s going to happen with the back of the board.
A photo of a similar finished battery pack would be nice.
Also, is 5 hours of design time normal for a board like this?
What would be a fair price for such a board?
At the moment I don’t even know if this is for a mass produced commercial product, or a one-off hobby project.
Comments from any forum readers welcome.
The problem with battery backs is that you have very little room for voltage drops. Especially if cells are connected in parallel. A few mV can be a surprisingly high difference in state of charge depending on exact battery type and of course where on the SOC curve you are. This can lead to different amounts of ageing of the affected cells which leads to a reduced lifespan for the whole pack.
Using inlays or metal plates in combination with good electrical connection between the plate and cell (best option welding) goes a long way to reduce these problems.
Equally important is to ensure the mechanical arrangement allows for the current paths to be as equal as possible for all cells. Plus good temperature regulation to ensure all cells are as close in temperature as possible (inner cells might get hotter without special care as they are isolated from the environment by the cells next to them).
And of course a proper balancing and protection circuitry combined with proper charging regulation and correct battery dimensioning for the expected discharge profile.
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I have no experience myself in battery pack design.
Just tried to do the best I can with the info I have.
For all I know hummie may be planning to solder solid 12x12mm copper bars over the backside of the PCB with M8 bolts to secure thick wires for his battery pack. It’s all speculation, I can only wait for hummie’s response.
I simply shared my experience with making battery packs for different electrical vehicles (see my profile background image to discover three of the vehicles i was involved with)
For reference: The batteries i made ranged from a few Wh (12s1p) to 20kWh (108s20p).
Also you are not responsible at all to make decisions for this project. The original reporter must decide what technology they use to connect their batteries. They are responsible to calculate (or better simulate) how the expected application current will affect the voltage levels. And if they lack the knowledge to make this decision than they are responsible to reach out to others who have the skills necessary.
hi. i emailed you asking if you were interested in doing this battery last night and didnt hear back and found someone else to do it! i offered you one of the batteries done, with the (36) 26650 a123 batteries welded to it, but i didnt hear back from you and …this other guy has it almost done and i offered him the same.
as far as making money from selling these i do plan to do that. i jumped into buying 480 of these A123 batteries off batteryhookup.com.
if any of you are interested in a complete battery with this board welded to the cells i’ll do it for you for the cost of the parts and shipping alone. i more so sell electric motors i make and this for experimental fun for me to try and sell down the road. i imagine ill want to change something! the last ones i sold at just my cost.
the simpler version i made before which have been used for a while. i think on the pcb is safer than maybe any other way and it flexes without stress on connections and can take the current fine, and makes assembly much easier.
Ive had another version of this made and i figured the math on the conductivity of 2oz copper mirrored on top and bottom connected by vias and it was good. this version has even more copper with the fat traces being even fatter. i spot weld nickel to the cells and then weld the nickel tab to the board and while others say you shouldnt weld to the board it seems to work well being easier and faster than soldering.
john
After a bit of fiddling around I found your mails in my spam box.
I do not use that mail address much and apparently the filter for that mail address is a bit more aggressive than for my normal mail.
I also have no interest in a battery pack. I have no use for it myself. My main interest was (ans still is) in promoting KiCad and use of KiCad.
Shipping a bunch of Li-Ion cells to Europe would also have been a prohibitive factor.
My design is of course much better then the design from that other guy, because it’s a complete KiCad project, complete with custom pad etc it is easily modifiable to other battery pack sizes. And without having to make a mechanical drawing of the thing first.
I also have my reservations about spot welding the nickel tabs to the copper of the PCB. Metallurgy is a complicated science and I don’t know how nickel and copper mix together. These packs will probably also see a lot of abuse and copper is not very strong and the small spotwelds create stresspoints, especially if they also need to hold the weight and G-forces of (moving) the whole skateboard.
To me it feels like a wasted afternoon.
Ah well, shit happens.
You’re still free to make a donation to KiCad if you wish though.
The board I designed is also quite different from the pictures you posted.
The board I designed is for 12 cells in series and 3 cells parallel, and with 2 rows of cells on the board next to each other. I see that now.
If I had known that I would have designed the PCB differently.
I would simply have made a footprint with 2 pads for a single battery, and put 32 of the same footprints on the PCB and added some zones.
For the next time. Try to reconsider before you use a mechanical CAD program to design a PCB. PCB programs are much better at that.
thats what i want. 12 in series and 3 parallel as you did it. i dont understand how you would have more simply done it with a footprint with 2 pads for a single battery but sounds interesting.
hate to think its a waste of time for you and i know people will want it maybe you can open source the design or something. its what i want and this other guy isnt even done it but i got pulled by him when i didnt hear back from you and now here we are with you done it and him almost done.
but…the project isnt really done and next would be to incorporate balancing circuitry on the board for the 12 in series. something like this:https://www.thunderheartreviews.com/2020/03/hx-jh-004-4s-12v-lifepo4-balancer.html
all the bits are labeled there. maybe its easy for you guys but beyond me. i do think of it as the final step in doing this, getting balancers in the middle instead of doing the plug at the end. do you think that would be possible to fit? i imagine so.
Putting the balancer on the same PCB as the batteries is a very bad idea for a skateboard.
Everything bends and flexes on a skateboard, and the (SMD) resistors and capacitors are made from ceramics and are very brittle. They break easily when the board is even slightly bent.
Also, the PCB now has the same size as the batteries, and adding the balancing circuit would make it bigger, and harder to fit under a skateboard. If it’s connected via a cable or connector you can put it in a separate box, safe from mechanical abuse and moisture.
I am also missing charging terminals. Are these supposed to be from wires soldered to the board?
Also, I assume you want to use a charging current of several Amps. How is that going to combine with balancing circuits which can only balance 60mA? Trying to increase the thermal properties by sticking a piece of aluminimum on it is also far from “best practice”.
Ok maybe ur right and would be too much stress on the board for bits. The bending is not much but does sound risky
At least they’re lithium iron cells n hard to burn
I was thinking could sneak the balancing between the cells. 9mm wide x like 450mm room. But if u think not safe…unless someone else disagrees I’ll forget it.
Charging and discharging will happen through the ears beside the balance plug. From math I did long ago the main fat traces should be equivalent to maybe 12awg and the balance traces good for at least three amps. Which is unlikely.
like those vehicles @Rene_Poschl
The balancer circuit from your link to thunderhart has 62Ohm series resistors.
4V / 62 = 64 mA, an that is the maximum balancing current that will flow with this circuit.
You could design a 26mm high (or less) circuit for the balancing, and then as long as needed, and glue it vertically between the 2 rows of battery cells. solder some wires directly to it (more reliable then connectors), and after testing, glue it together with silicone chaulk.
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