Recently there was a battery shipped to me that was built by a third party. My customer bought this battery from someone and didn't get a product that was up to snuff. In fact, its pretty much a nightmare in there. I have been tasked with fixing this pack, but before i do, i want to share it's brokenness in hopes that something can be learned here.
What i would like to do in this article is not to harp on the drama of this incident, but instead try to use one of the many failed FISA products shipped as an example of how not to do something. In this case, how not to build an electric skateboard battery. FISA, btw, means Fuck It, Start Over. This pack is a prime example of one that was fucked and should have been started over.
Why do i want to pike this work on the road side for all to see? Because it could have gotten somebody injured or killed. The battery pack is the heart of the whole board. Almost every aspect of the board's performance is directly affected by the battery pack. It shapes the character of the board in the way a soul shapes the character of a human being. You can use all manner of clever programming and power management tricks in the motor controller, but ultimately what determines if your board is mediocre or totally bitchin' is weather the pack can deliver the power when it is needed. You could have the nicest motors and controllers in the world but a shit pack is going to make your ride seriously lame.
So without further ado, lets meet the star of the shit show here. Below is a collection of images of this essentially non-functional and potentially dangerous battery pack. We have carefully removed the thread reinforced packing tape that was used to jacket the pack so as to preserve whatever is happening underneath it. Traditionally PVC heat shrink is used to polish off a pack, but tape is acceptable for a DIY pack you build yourself in your garage for your own board. This is not DIY, however, and it was sold as a product. So in my mind, it is completely unacceptable in this case to use packaging tape.
Above we see all manner of blasphemy. The nickel is too narrow and too thin. There is even a tear where the balance lead was soldered between the cells and broke the nickel surrounding the balance lead solder weld completely. Never mind the balance lead that detached from the nickel completely due to terrible soldering. And oh, the terrible soldering.
Dear Skatan that's a fucked up solder joint. And that wire. Look at that mess above this sentence and tell me you want to pay for that kind of quality. And i can only assume that the rabid baboons who built this pack to escape a government facility probably thought they were building a bomb, so it didn't matter if they soldered like shit and stripped the wires with their teeth. And there's a nice little gash in the balance lead just waiting to short on something. Maybe this actually is a bomb.
Yes, that nickel has a chunk torn out of it. That balance lead was probably the best solder weld in the bunch since it managed to tear that nickel chunk right out of the connecting rail between two P groups. It's torn because the nickel is too thin and too narrow, and the lack of either spacers or hot silicone fill between the cells to prevent cell movement which puts stress on both the welds and the nickel itself. There is a fuck ton of vibrational stress in a pack when you're on a rolling skateboard. To tell you everything i've learned and everything i do to build a pack is a whole separate series of posts, but rest assured, this pack would have been dead within a week had it not been practically dead on delivery already. Not to mention it was probably built by feral children afflicted with various debilitating diseases that deprive them of all sensory perception who were given the cells and some nickel sticks and told to make a seat cushion that must one day catch fire.
Mother of lead poisoning that solder joint is fucking terrible on the positive lead. Covered in spikes and absolutely no evidence of proper flow, this is the work of a seriously underpowered iron and a lack of both flux and skill. Most likely a lack of patience as well. That positive lead really does look like it was stripped with teeth instead of strippers, all kidding aside. And that's just fucked up, yo.
And what the hell is that giant loop for? If that's the bridge between the twin 5S rails than just kill me now. Why the fuck is there a gash in it? Maybe the customer tried to tie something into it like a BEC or a volt meter or something, but i doubt it because the strands are frayed and there's no sign of solder. This bridge should have been made of nickel anyway, just directly joining the twin rails would have made a more compact pack and would have been the proper thing to do if the adjacent cell polarity allowed for it. And in a 10S pack it would. 12S is a different story, i use a 10awg jumper because the P groups in question aren't oriented that way. But you can be damned sure its not hanging loose out of the pack and isn't gashed open.
Oh I know! lets just half solder half tack this one part and then splatter paint the pack with tin for funsies. The nickel is all over the place to begin with, then the solder is just flung on there. I want to write an entire paragraph of linguistically titillating sarcasm directed at this atrocity but i'm kind of sad. Somebody bought this thinking it would make their board go the way they wanted it to. And it didn't, because it's total shit.
What should have happened here
So now that we've eviscerated this pack along with its builder and sold it piecemeal to the hungry fans of my eloquent writing, Let's discuss what went wrong here.
First, the soldering iron. If you are planning to do shit like this and not just limit yourself to soldering headphone wires or other super thin gauge wire back together, you need a decent iron. At minimum, you need a 60 watt station. I'm not going to tell you which one to get, but you can find reasonably priced (as a hobbyist, not a manufacturer) stations on the internet available within the US that can do 480 degrees C and are more than capable of getting even shitty solder to flow beautifully with flux. That's not what was used here. The iron used here wasn't hot enough and the solder didn't flow correctly. Instead it chunked and became a frustrating mess, which is why its all over the goddamned pack like splatter paint. Hot lead splatter paint witing to short some shit when the pack vibrates it loose and it starts travelling around the pack.
Next, we have the nickel strips. They're too thin and too narrow. Skateboard batteries carry a lot of current. They have too. If you're making flat packs like this, you need 10mm wide nickel minimum and it needs to be 15 mils thick. That's .015 inches, not millimeters. And if you're doing a flat pack, again, like this one, you should probably double it up. This nickel was too thin and too weak to provide any manner of structural support at all. Never mind that it doesn't have what it takes to deal with the current required of a decent DIY board. It's going to just break physically and cause a short and possibly a fire if the cells are shit.
Speaking of weak nickel, to add to the problem no in-fill of silicone or cell spacers were used. One or the other is acceptable for a production pack, but just relying on tape to hold 15 cells in a row like this is stupid. If you need a compact flat pack, use black hot glue. ITs harder than the clear stuff and will prevent cell movement within the pack, reducing stress on the nickel and decreasing the likelihood of tears or broken welds.
On a more trivial yet still somewhat important note, its was sold wrapped in packaging tape. That's just lame. 180mm heat shrink is available anywhere. Ebay it or buy it from me, i don't care. Just fucking use it. And maybe put a sticker on it with your brand. Presentation matters too.
The most heinous crime in this pack, however, isn't the terrible soldering or the choice of nickel or the lack of any real structural reinforcement to mitigate damage due to vibrations. All of these sins are the children of a much bigger, darker issue. The most important ingredient in building a pack that you are planning to sell to a paying customer is patience. This pack was built in a hurry by somebody who didn't care about what they were doing. That is the sin to end all sins. You can't build the heart of your ride in a hurry. You need to research best practices. You need the right tools. You need to talk to people and find out what works and what doesn't. You need to buy a commercial pack, tear it down, and take notes on what is good and what is questionable, then ask more questions from experts.
You have to take your time. You have to take frequent breaks because mental fatigue from BZERP BZERP BZERP (the sound of a tack welder being used with a lot of repetitive motions) for hours on end is a real thing. You need to check what you've done every step of the way and be ok with having to start all over if you did something dumb. Again: there is mental fatigue, and there is repetitive motion. Those things should be taken seriously. Walk away now and then and do something else for a few minutes. Then come back and glance over everything to make sure nothing was missed the last time you looked.
Shipping garbage like this is inexcusable, and riding around on a board with this pack in it would be suicide. At best some kid fucked up a bunch of packs and "oh well i'm sorry mom and dad." At worst somebody could get killed by trying to use this in their board.
There is no free lunch, there are no shortcuts. Do it right or go home and find out how to do it right.