12S7P flexible battery pack

Hey guys, I have been looking in the last couple of months for someone to built me a flexible battery pack for my Trampa Urban Carver and since I couldn’t find anyone willing to ship the pack to Canada, I have decided to attempt and build one myself. I aim to have the longest range possible (30+ miles), so I chose to build a 12S7P pack. I know that it may have been a better choice to try and build a smaller pack in my first attempt, but I believe I made enough research and took cautious measures in order to build this beast… and hopefully with your help, I’ll manage to nail it. :slight_smile: I decided to make this thread, hoping that I will benefit from some more experienced builders pro tips and I also hope that this topic will help other enthusiasts building the pack they desire.


Bellow you can find the layout I designed for this battery (the measurements are just my estimations and not the actual size of the pack). If you have any suggestions to improve this, please let me know. Also, if you guys could recommend me a good BMS that I could use and a 5-7 Amp charger, that would be great… Since I haven’t decided for a spot welder yet, I am opened to suggestions for this as well. Cheers!



Damn that’s a big pack but everything is possible. I got this spotwelder and it works perfectly fine and the price was also okey:

Which cells are you going to use? I think bestech has the best bms because I guess you gonna use a lot of amps with this build?

I have now a 10S 60A smartbms with bluetooth and it’s so handy, in like 5sec I can check everything of my battery pack, every seperate voltage, current, temperatures… This is the 12S 60A version:

I just really this bms and it works fine for me.

@bartroosen12 Yo man! Thanks a lot for the suggestions! I kinda avoided building my own spot welder, mainly because I thought I would have to use scrap parts… like microwave transformers, etc… but seeing your recommendation, I think I just changed my mind… :smile: The smart BMS (something that I didn’t know it even exists) seems like a very appealing options, especially since I like to take advantage of every feature that technology has to offer. As for the cells, I already bought the Samsung 30Q 18650 3000mAh 15A… just because I have noticed that most of the builders use these cells…


30Q is perfect! If you’re going to use 2 vescs and put them on 25A battery current each, so a total of 50A max, the smart bms will be fine. If you want more power you can go for the bestech bms. I have made a 10S4P with 30Q cells. IMG_20180724_095458 I think a lot of people on this forum use this spotwelder.

That looks neat!!!

For now, I’ll only use one vesc, put I plan to upgrade to twin soon… thanks for the tip! :wink: The smart bms you recommended will do perfectly, I think… but just in case, do you have any idea how to order from bestech?

As for the spot welder, I am thinking to go with this one, since for the diy one I will need to buy the car battery. https://www.amazon.com/dp/B073GWKSYL/?coliid=I1V0IHI31QGG2E&colid=2G0W31ZK8PG54&psc=0&ref_=lv_ov_lig_dp_it


Kudos for taking on the challenge of building your own battery pack! If you haven’t already done this, I recommend also on addition to of course reading as much as possible on the forum about building the pack, also hit up lots of YouTube videos, especially for how to wire up the BMS and balancing wires etc… Triple check everything before you make your welds. You know the saying, lol, ‘measure twice, cut once’. Definitely applies here, especially since electricution and fires can be very serious. That’s a HUGE battery pack to be running through one VESC and one motor. You’ll definitely need to make sure you get your settings right or you could easily fry both :wink:

Also, you saved yourself a TON of money here. A 12s7p battery pack from a pro builder easily would cost you anywhere from $850-$1000 I imagine your costs for the pack with BMS, charger, anti-spark, voltmeter, etc… Around $400-$450, so just by building this yourself, the spot-welder has more than paid for itself, and you can use it again to build as many as you want, or sell it off and get that second motor with that money :slight_smile: Best of luck!


@uigiroux Thanks mate! I watched a few tutorials on YouTube and I also ordered a book DIY Lithium batteries… plus with the help of other tutorials that I plan to watch and with your suggestions, I hope I will manage to make the battery. I’m planning each step very careful, especially since it is my first time doing this, but, honestly, I didn’t give too much thought to the settings, yet. If you could please explain more what could be the potential causes of frying your VESC or both, that would be awesome. Or a link where I can find more information would be cool as well. Yup… the price and the shipping issues are the things that pushed me in trying to make my own pack. Plus, I like building my own stuff, so being able to build my own batteries, could be an awesome achievement. Cheers!


Hey guys,

It’s been a while since I posted an update, so here are the 12 packs almost completed. I’ll soon start to spot welding all the cells. 1536287349257


I attached bellow a layout explaining how I plan to do the parallel connections as well as the series connections. For the parallel connections I will use 8 x 0.15T Pure Nickel strips. As for the series connections I plan to use the Trampa cables with their bullet connectors. Not so sure about the bullet connectors though, I just thought it would be a cool thing if I could detach the packs anytime I want… do you guys think I should use them or not?


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I would only put them if you really need to disconnect each group, and don’t forget to put heat shrink after connecting

More connectors = more losses and more things to get loose

@Pedrodemio Thanks for the suggestion! I don’t really need the connectors, they just would’ve made my life easier during the building process, but I think I can do just fine without them.

Regarding the BMS, I am still having a hard time deciding between these two:


I know that Bestech should be better, but the first one would fit perfectly in my enclosure. I’m pretty sure I could find space for the Bestech one, but it will be quite tight. So what do yoy guys think? Is Bestech that much better that I should try squeezing it in there?

You can definitely get away with a 12s8p flex pack.


@neiru37 I know mate… but I have an Urban Carver so my enclosure is smaller than yours. Btw… where did you buy your enclosure from?

I checked your tread… awesome build man!

I have an HS11 deck (which is basically a holy pro without the holes) that gives me an area of 690mm x 230mm under the deck to mount an enclosure:


Your street carver has an area of 690mm x 215mm:


My enclosure measures about 8 inches, or 203mm wide so I think you’ll be able to mount the same enclosure on the street carver.

I got my enclosure from @Eboosted’s shop: https://www.eboardsperu.com/product/trampa-hs11-holypro-35-ds/

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Do not use hot glue. It gets soft at high temperatures and the vibration stresses go through your welds.

I recommend medium ca. BSI brand stuff is my personal choice.

If you really want something with a little more give then try amazing goop or any silicone adhesive sealant. The reason this is better than hot glue is that it can withstand hot temperatures and not come undone yet it is easy enough to undo if you really need to. CA is pretty much permanent unless you rewrap the cells

Actually there’s high temperature hot glue you can use for, well, high temperature applications.

Thanks a lot guys for all the information! Regarding the hot glue, in the tutorials that I watched, no one had specified anything about the type of glue, so I was wondering if it is such a big deal, or can I get away with the standard one I used, since the packs are already assembled?

@PXSS Could you please post a link with the glue you recommend?

@neiru37 Yes, the Carver deck has 690mm between the points where the deck changes its angle, but the sides are shorter, so I only have 610mm for the enclosure. Anyways, I send a message to eboardperu asking them if they plan to do a double stack enclosure for the Urban carver deck.


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The problem with hot glue is how flexible it is. Specially when hot, as it does soften a little at temperatures above 60c. It isn’t an issue in most applications but when spot welding batteries, you do not want any flexing between cells as that translates into strain at the welds and eventually the vibrations will break them.

I use CA which is the generic term for super glue, krazy glue, or whatever you may know it as. I use medium CA particularly as it is thicker than standard super glue and gives you a few seconds of work time instead of drying up immediately.

Here is the one i recommend from amazon: https://www.amazon.com/Bob-Smith-Industries-BSI-133H-Insta-Cure/dp/B07GBYJN2G or this one https://www.amazon.com/dp/B0166FFCHS This one is even thicker but also comes with accelerator which dries up the glue instantly upon application.

Good luck with your build!