DIY Silverfish Batteries

[stevet2233]

Hi All,

TLDR; Guess to put it as simply as possible my questions are:

1) How do I safely open/close the Silverfish Battery Cases once assembled

2) What size cells in what combinations of series/parallel will i need to craft a 48V 11.6 Ah and 499.2Wh battery (or something equivalent enough that it will also be safe for my bike)



I am relatively new to the whole e-bike thing, but I'm a mechanical engineer and have also been working with a lot of electrical stuff for years and feel confident in my ability to properly build a battery and attach a BMS(i build telescopes that get put on space probes and launched into deep space, i should be able to handle a battery haha), my main concern would be proper component selection, proper insulation/housing and the more specific electrical stuff to make sure the cells and layout i select will generate the proper voltage/current for my bike. My goal is to craft a backup battery, i haven't decided if i want it to be identical to my current one or have a longer life (current one seems pretty solid), price will likely determine this in the end

A secondary goal is to learn how to take the Silverfish batteries apart properly (shockingly difficult to find a guide online) to confirm the honesty of the seller (he told me they were samsung cells, id like to confirm this). The battery case looks like it has been opened, as the warranty label has clearly been ripped, but it also clearly has chinese on it, so it is totally possible that he opened it himself and replaced shitty chinese cells with quality samsung ones.

The bike I bought (prebuilt by a group of other enthusiasts) came with a silverfish style battery, which id like to continue using to avoid any other modifications. My current battery is 48V 11.6 Ah and 499.2Wh. I have found cases for these batteries which look like they are identical to what I have now and also places to buy quality cells, which is all great, and I fully understand how wiring/spot welding the batteries in series/parallel works and how to attach the BMS/where to get one, but i want to know if there is anything specific about the Silverfish cases i need to know about or any special insulation i need to worry about.

Thanks all!
Steve

 

[indianajo]

I'm a physicist with years of electronic test equipment maintenance, ending as a factory maintenance mechanic.
There is no way I'm direct welding a device that bursts into an explosion (extinguishable only with sand) if your penetration of the case is a little deep.
There was something about special zinc tabs that are low melting point. I found some on e-bay. Didn't buy them. Remember your welds have to withstand however many G your bike puts out plowing through a chughole. Those battery spot welders all over e-bay, they don't even have a inert gas shroud to protect the weld from oxygen. Whistling in the dark, IMHO. Yeah, people do it all the time on drone batteries. Drone batteries are tiny enough to fly. ebike batteries are heavy enough to burn down a package delivery truck, which is why you can't ship them back to the vendor. You're not hazmat shiper certified.
The **** batteries I bought were wrapped in 300 mm heat shrink. You cut it with scissors. You can buy new on ali, at least I did before they needed to know your DOB to sell to you.
Buying cells, beware of flashlight cells which can put out about .5 A, as contrasted with e-bike cells that can put out about 4 amps. Good luck on reading the datasheets, they are not something you can find on datasheetcatalog.com Good luck on even reading the part # unless you read mandarin. Or is it guangjouw? Wherever the ebike cell industry is located.
the 2 ****y scooter batteries I bought had 14 stacks to get about 50 A as specified in the datasheet. They were failing to put out 5 amps before collapsing to 20% of rated voltage.
I got a decent battery from luna. If you live in CA, grin tech is reputable. If in Hong Kong, Em3EV. I suggest you spend your time adapting a mount and connector to fit your current bike, then start riding.
If you want to **** with a dead/defective battery, do it next winter, outside in the freezing cold. Definitely not indoors, unless you own a test chamber that can withstand LIIon battery explosions. Not ****dy likely.

 

[harryS]

Almost all ebike batteries use spot welded nickel or nickel plated conductors. The good ones don't let the metal connects serve as the only structural members. They will have a plastic form, but the connects do keep the cells in place. Many of them use shrink wrap as a structural element. That's probably not good, as it can squeeze things at random.

I've got a silverfish battery. Never opened it. It should be obvious though. Probably a couple of screws hold the plastic endcaps. The cells will be in a wrapped bundle inside the aluminum center casing. I've opened up other types. Had to replace a BMS on one.

 

[stevet2233]

Yea @harryS that matches what i've read about assembling the batteries together(spot weld nickel tabs being used by everyone, including manufacturers). As far as the case goes, it looks extremely straight forward to open it up, there's 8 pretty prominent screws just begging the engineer in me to take them out, just wasn't sure if there was anything i more tricky on the inside or anything in particular i needed to watch out for before damaging my commute lol(other than basic electrical safety of course). I am a manufacturing engineer, assembly processes are my life, i can develop my own, but that occasionally results in destructive testing, or at least damage, which id like to avoid hahaha. Figured if there were any hidden secrets to the case it would be god to ask haha.

@indianajo , How else would you recommend efficiently connecting the batteries? Like Harry had said as well, from literally everything i've ever seen it appears that spot welding nickle tabs between the batteries is the universally accepted best method of assembling cells and that any quality cell (the samsungs, LGs and Sanyos of the world) should all be 100% safe to spot weld.

 

[harryS]

Found this, what appears to be a drawing, but it's probably accurate. There will be some kind of insulation protecting the cell electrodes from that massive short circuit presented by the case.

WHile the above shows the discharge port at the top, mine has the discharge connector in the bottom of the battery. There it sits against the bottle of the battery cable and gets jounced every time the bike hits a bump.

So I put a little foam padding under the battery so the contacts wouldn't bounce as much, and added some foam between the battery and frame to stop a persistent rattle. It's pretty quiet now.

 

[stevet2233]

Thats awesome, thanks @harryS this is pretty much exactly what I was hoping for, just something that shows me the main elements of what's actually in there and what would be possible for me to damage haha. I can definitely work with this!

Yea my discharge port is on the bottom as well and bounces like that occasionally, luckily i don't really ever get a rattle at all though. That's not a bad call with the foam, i actually have a perfectly sized strip adhesive backed neoprene rubber sitting in front of me right now to serve that same purpose haha.

And yea, i'd definitely be looking into insulation as well. I know of a setup you can get where you can make custom shaped cell arrays with hardware attached to it that allows you to make your cell layout and hold the cells in contact via the hardware(essentially screws pushing nickle plates against the terminals to keep contact), so you don't need to spot weld, which is great, but from what i saw it appears the set in only capable of making rectangular arrays, meaning it will be significantly larger and I don't think it would fit in the silverfish case The same company does sell the spacers you can use to keep the cells apart in a octagonal array, but you need to spot weld those. Whatever I end up going with, once its assembled it will be getting wrapped in insulating foam and then shrink wrapped at least 2 times

 

[tomjasz]

Head over to endless_sphere. Much better suited for these adventures. I have several welders from makers there. None of the drama the subject seems to illicit here. If you can’t find the threads message me. There’s also s great source for batteries. See thread by tumich for GA cells.

 

[indianajo]

None of the drama the subject seems to illicit here. If you can’t find the threads message me.

The drama has been documented on PBS news. Boeing has had a catastrophic LiIon battery failure in a 787. Tesla has had two catastrophic LiIon battery failures on camara. Several people have been killed by vapor devices. I'm so confident of LiIon technology, I don't mount it between my legs. It is out front 2' from my body. I tried to buy LiFePo4, but all I was shipped was 18 lb of garbage - twice.

 

[tomjasz]

The drama has been documented on PBS news. Boeing has had a catastrophic LiIon battery failure in a 787. Tesla has had two catastrophic LiIon battery failures on camara. Several people have been killed by vapor devices. I'm so confident of LiIon technology, I don't mount it between my legs. It is out front 2' from my body. I tried to buy LiFePo4, but all I was shipped was 18 lb of garbage - twice.

I dare say I’ve been involved in hundreds if not a couple thousand battery sales. Scores of builds and tracking at least a dozen battery build threads and sites. I charge and store in double walled and steel ammo boxes. But the numbers of catastrophic failures just don’t warrant that level of concern. To me. However I support and understand your take on safety. Like most risks, it can be mitigated. Every liIon fire i know of was user error.

 

[tomjasz]

Thats awesome, thanks @harryS

That’s harrys. Top notch advice. Another of the great help we get!

 

[stevet2233]

@Thomas Jaszewski thanks for the tip, ill head over there when i have the chance!

@indianajo i dont deny there are risks with literally any Li-Ion battery, but again ill ask, do you have an alternative, safer method, than the one that is universally used throughout the industry? As I mentioned, I am a manufacturing engineer designing and executing assembly procedures opto-electro-mechanical telescopes that NASA and other organizations put on space probes and launches into deep space, im pretty intimately familiar with how to safely assemble electrical devices and am confident I could safely build a battery, i just don't have the background on the proper battery selection to make the voltage/capacity combo i desire, which was what i was initially asking about.

 

[Nico2019]

Hi All,

TLDR; Guess to put it as simply as possible my questions are:

1) How do I safely open/close the Silverfish Battery Cases once assembled

2) What size cells in what combinations of series/parallel will i need to craft a 48V 11.6 Ah and 499.2Wh battery (or something equivalent enough that it will also be safe for my bike)



I am relatively new to the whole e-bike thing, but I'm a mechanical engineer and have also been working with a lot of electrical stuff for years and feel confident in my ability to properly build a battery and attach a BMS(i build telescopes that get put on space probes and launched into deep space, i should be able to handle a battery haha), my main concern would be proper component selection, proper insulation/housing and the more specific electrical stuff to make sure the cells and layout i select will generate the proper voltage/current for my bike. My goal is to craft a backup battery, i haven't decided if i want it to be identical to my current one or have a longer life (current one seems pretty solid), price will likely determine this in the end

A secondary goal is to learn how to take the Silverfish batteries apart properly (shockingly difficult to find a guide online) to confirm the honesty of the seller (he told me they were samsung cells, id like to confirm this). The battery case looks like it has been opened, as the warranty label has clearly been ripped, but it also clearly has chinese on it, so it is totally possible that he opened it himself and replaced shitty chinese cells with quality samsung ones.

The bike I bought (prebuilt by a group of other enthusiasts) came with a silverfish style battery, which id like to continue using to avoid any other modifications. My current battery is 48V 11.6 Ah and 499.2Wh. I have found cases for these batteries which look like they are identical to what I have now and also places to buy quality cells, which is all great, and I fully understand how wiring/spot welding the batteries in series/parallel works and how to attach the BMS/where to get one, but i want to know if there is anything specific about the Silverfish cases i need to know about or any special insulation i need to worry about.

Thanks all!
Steve

Hi,

Apart on the comments about mounting and welding/soldering, which is true to be a problem at home, I just wanted to provide you with a table fo different configurations of typical 18650 cells for you to see which would be the best configuration, and then there are other things to see like space, weight and how to assemble them

This is the chart

I hope it will help to see which is your best choice
Nicolas