12S7P battery for Trampa. Help me with the build

Thanks. There is fish paper between the p groups and they are also welded together with hot glue. After it is finished it will be wrapped with Hudy battery tape and shrink wrapped.


More progress. 20181122_091159

I have another question concerning the BMS (Bestech D140 12S) I will use it as a charge only, so the load will not be connected to the P(-). Before I plug in the balance cables, I have to connect the B(-) correct?


Also it seems I must not connect the B(-) balance wire, is that correct? It seems strange they would include a pin that should not be used.

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Take a multimeter and measure the resistance between B- and the first pin. It’s 0ohm, means they both connected via pcb intern. That’s why you don’t need to wire up the first balance pin from the jst plug.

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Looking good, wish my welds were this clean

For less work you could completely skip one of the parallel connections on each group, doing it only at the ends of the battery, they aren’t/shouldn’t be carrying any current anyway, and having them doubled does no improve current handling


I wired my D140 bms like this board







And it fits :sunglasses:


You would not believe what gave me grief. The freaking heat shrink. Nkon did not have the size i wanted in stock so I got a huge one that tried to make it work. It did after 2 failed attempts and my OCD compels me to change it at the first opportunity. Now that is see all that empty space I think I should have gone for a 12s8p or 9p. :joy:


I know that and for the D140 there is continuity between the B(-) and the first pin. However I have read about a lot of BMSs going up in smoke if the balance leads are connected before the B(-). Connecting the B(-) separately ensures that even if I connect the balance connectors in the wrong order, I will not damage the BMS. I am not sure about that but since the manufacturer suggests that way of connecting, I figured it would be better to follow his instructions.

I didn’t said anything about the connection order. Just that the B- is connected via pcb with pin b- pin and that this is the reason why it doesn’t need to be wired. What you can also see in the schematics

Aaaannnddd finished…




Looks super nice :+1:

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Thanks man. I took it for a test ride today. Power is lacking and the motors are overheating. My guess is that the drag from the enclosed belt drive is causing it but I need to research it more.

Oh that’s not so good to hear. How your motor max settings? Maybe they too high?

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Motor max is 55A. I wanted to increase it but since it is overheating now with temperatures around 10-15C imagine what will happen in the summer. I definitely need to figure this out.

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Hope you are sorted now! Nice Chat! Please note that carbon is conductive. The BMS wants to be protected against getting in touch with the carbon.

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Thanks Frank. Really enjoyed it.

It is not seen in the pictures as I did that later, but I wrapped the BMS in kapton tape and then shrink wrapped it before actually installing it in the monster box. I will post a picture later this afternoon.

if the bms has only positive on the balance leads, there’s no chance of short circuit or anything so it doesn’t matter on bestech bmms or d140 what comes first

What do you mean by only positive? As long as you have difference in potential there is always a chance of a short circuit.

As promised, a photo of the BMS.:wink:



I would like your opinion on the series connections. Right now I have 7 x 8mmx0.15mm strips between p groups. I am aware of the various tables concerning nickel strip ampacity and according to this post in endless sphere my series connections are good for 7x5A=35A. https://endless-sphere.com/forums/viewtopic.php?f=14&t=68005

My objection lies in the fact that according to my logs my battery sees currents over that value only for a few seconds.

Do you think I should double my nickel strips on the series connections?

So right now you have 7 layers of 8mm wide and 1.5mm thick nickel strip?