Hello people, i’m kinda new on this, I’ve made my first diy esk8 and i have a problem, i full charge the battery, and after seconds of using, it dies. The battery is 10s2p with BMS. I use an ebay ESC. The output shows 38v, but if i start to use the motors, the V goes down immediately.
Where did the battery come from?
I made it from LG 18650 cells, first i charged them with a module and then i made the pack
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You are definitely using the correct charger? That pack should output 42v on full charge so if the charger is saying full at 38 then that could be the problem. Without a detailed look at the pack its hard to speculate really. Bms is wired for charge only I assume?
Multi meter time my friend. Check the charger output and carefully check the batteries true voltage and then go through your bms wiring to check the individual p packs. One could be way out of balance and the charger is trying to balance it which happens after the charge cycle on most chargers. Check for safetys sake though that all your voltage readings are correct.
The charger says 42v at the output, so i assume it’s ok. BMS just for charge? What do you mean? (Sorry I’m a begginer).
I started testing all the cells, they all are at the same V, and the wiring is ok too. The output of the bms is the same as the pack itself, but when i start to run the motor on the tip speed, it decreases immediately, just in matter of seconds, and then it turns off.
I’ll attach the connection scheme.
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The diagram above shows its wired for charge and discharge and since your probably pulling more then 35 amp the bms is cutting off.
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And what should i do? I just checked with the multimeter and the cells aren’t charged fully (all of them in 3.8v) and the charger stopped charging, i seems that the bms is cutting the charging.
This is courtesy of the wonderful gent who is our own @mmaner
Got the lot in there for you. As @M.Hboards said your bms is cutting off because it should be wired for charge only. Rewire it and you should be fine.
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Thanks dude, today I’ll change the connection. Is the mosfet switch really necessary? Because i don’t have it. And there i can’t see well, but there is the black wire (near the red ones) connected to the negative of the battery, isn’t it?. Thanks you for your help again
What LG cells are they? not all 18650’s are created equal. try bypassing the BMS for discharge, and only using it for balancing. As you are only getting to 38v it’s likely you have a failed cell in there. oh and that layout is for focboxes with a separate eswitch. Those dinky ebay escs have the switch built in.
I would also be curious what cells, 10s2p isn’t much either. The switch is not necessary for you either but on the other hand, you won’t have a huge amount of performance out of an Ebay ESC anyway.
I would question the battery build - what exactly is it and where are the pictures haha sounds like you’re missing a group
You don’t have to take the whole diagram as a template bro. Just take what you need from it. Its just a nice clear wiring diagram for the charge only mod you need to do.
Here you all have my set (it’s a prototype, i haven’t finished it, and please don’t hate me for the wiring haha). I didn’t use a spot welder because i don’t have one, and i know i didn’t use the best products, but please understand me, i live in Argentina and everything is very expensive haha. However, the wiring is OK, and now i changed the connection like you said and for discharge is still happening the same, the V go down in seconds.
Is it maybe too weak for 2 motors? May i build more parallel groups??
Soldering can damage cells if you get too much heat into them. Measure the voltage between each group. Should be close to equal. Then measure under load. And what exact cells are you using?
I charged them and they where all between 4.1 and 4.2v, so i assume they charge equal. The cell has LGDAS31865 K206G254A6 written on it. I just ride the skate in the minimum velocity and it worked fine, then passed to medium and it turned off 
Search the net for the max discharge rating on those cells. Not all 18650s are the same. Tje discharge rating on these is less than half an amp. Peak is 3.2 amps. Throw these into a portable usb charger and look for some decent cells. You want something thats minimum 15amp discharge for a 2p battery for eskate. That pack is a flare waiting to happen
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Dont bypass the BMS for discharge. You have 2p groups, so even if the cells can do 15A (which they cant since the datasheet says 3A max) thats withing limits of BMS. If the BMS is cutting then thats to protect the cells. If you pull more than 35A from these cells you are gona have a ‘‘fun’’ time
Ok people, i understood, i don’t want to transform my skate into a wood fire. I’ll change them, what brand or type do u recommend?
I know that this has already been found but -
This is a great resource for looking up cells you have or are looking at BTW