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.
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.
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.
