A Final Word on Bypassing BMS for Discharge

Us 7mm antispark bullets. If it rattles loose no spark

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Best would be to direct solder the motor. No risk of hardware failure.

Iā€™m using XT60 after the fire incident, no more spark if they become loose

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That too :wink:

hey there i really need your help and you seem like the right person to go to for it ;))

ive had an electric skateboard that served me well, until its cells died after the bms drained it. I got new cells and an exact same BMS, with the only exception of it not having an on/off switch. Do you think its alright to forgo to on off switch and leave my board on all the time? thank u so much

Hard to say not being familiar with what bms your using now. If left on, I would keep an eye on your packā€™s voltage periodically and make sure that the battery isnā€™t draining too low. You definitely want to have the Vesc or Vescs disconnected while storing your board. If your going to store it for an extended period and checking the voltage regularly is not possible then charge the battery to storage voltage and disconnect it from the entire system.

By storing for a long period you mean not using it for a long period of time and leaving it on, or using it regularly and leaving it on all the time

I donā€™t think itā€™s a good habit to leave the board on as eventually you might forget.

Fun fact: did you guys know that the eBay esc has an automatic turn off feature that turns the board off after being on for a while

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Either storing it for a long time or simply not using it for a long time. Itā€™s basically the same. You should never leave the the whole system including the Vescs on while your not riding it. Leaving the bms connected while in storage will depend on the characteristics of the bms. If your going to store your board for a year or longer then I would recommend a storage charge and disconnect the battery from everything.

I am considering bypassing bms because this issue i will explain below.

Would anyone know why the bestech12s bms would cause me to have an early low voltage cutoff? Usually around 44.4V. 12s5p to bestech 12s bms(HCX-D223v1) to 80 amp antispark (from eskating.eu) to dual focbox to dual TB6374. Running 60A motor max 30A battery max. voltage cutoff on focbox start set to 41.0V and end set to 39.0V. Note all cells are verified at 3.7V

antispark link https://eskating.eu/product/anti-spark-power-switch/

bms link https://eskating.eu/product/12s-bestech-bms-80a-12s4p-5p/

Any input would be great as i would like to go for a ride without unexpected cutoff and support hasnt been of much help yet. hopefully they will get back to me with more info.

Since your running 5p you can go a max of 100A battery current but thatā€™s not realistic. Iā€™d say 65A is good. You cutoff values are insanely high tho. The cutoff end is at 2.8v/cell so that is 33.6v and cut off start is around 3.1v/cell which is 37.2v.

Once i trust the battery wont cut off i will probly up the amps. I just read that you dont want to take cells below 3.2v using Samsung 30q i will try lowering the battery cuttoff on the focbox and see if that fixes anything. i will try maybe 38v start and 34v end to be conservative(i may be overconservative with current set up) but my issue is that its cutting off at 3.7V per cell or 44.4V overall. anyway ill try that and see how she goes

The only way to test would be with a current load (not the VESC) to see if it is the BMS. If it is, the BMS will cut at 44.4v under load. The anti spark shouldnā€™t have anything to do with the issue

so just went for a ride had an issue at the same point in my ride. finished ride with 3.7v or 44.4v after setting battery cutoff on focbox to 38v start and 34v end.

Maybe there is a pack with lower voltage than the others or sagging a lot more than the others, this will cause the BMS to shut down the power in order to protect the lowest P-Group from reaching a pretty low/dangerous voltage.

Unmount your battery and meassure all voltages now.

yah i check all voltages after atleast every other ride everything is ballanced even when the cutoff occurs ill stop in the middle of the road open it up and check on the spot and everything is still ballanced. unless like you say one is sagging more than the rest i would have to have a monitor on each individual cell during the ride to notice that. i track all my rides with ackmaniac and havnt noticed anything out of the ordinary there. i did bypass bms last night and had no cutoffs and more torque. altho i would really like to figure out this bms thing as i like the idea of the extra protection on discharge

I had a similar problem and it turned out I had broken series connections in my pack. Most of the time it would work but when it did not the BMS shut down the board. I bypassed the discharge and the board would cut out for a second then recover. After I fixed the pack, I reinstated the BMS to discharge also. Who made your battery?

i built it so it will deffinetly be worth checking but i havnt had any issues after i bypassed discharge. still gonna check it all out tho to be sure. thanks

@makevoid Sorry for the bump, but can you give me some advice on my current build? Iā€™m pretty new to electronics in general, but keen to learn. Iā€™m looking to put a dual Turnigy Aerodrive SK3 - 6374-149KV Brushless Outrunner Motor onto my A/T rig, these motors specify a max loading of 70a, So does that theoretically mean they might want to pull 140a through the ESC/BMS/battery under full load?

Iā€™m probably going to put a focbox in there, and I have a 10s5p LG HG2 pack which I understand can draw 100a continuous easily, so Iā€™m trying to spec up a suitable charge/discharge BMS to run the whole shebang, but running into space issues in the enclosure, so Iā€™m curious what is the lowest amp BMS I could consider that will do the jobā€¦

Well, after a lot of thinking I can confirm the real cause of the fire on my Trampa was the lack of fish paper between pgroups