To use or not to use BMS?

Discuss hardware related to the VESC such as the NRF nunchuk.
Quezacotl
Posts: 24
Joined: 05 Apr 2017, 11:06
Location: Finland

To use or not to use BMS?

Postby Quezacotl » 06 Apr 2017, 21:30

Hello!

I have found mixed results about people using BMS with VESC. And nothing too clear.

Since i have this problem of battery dropping way too early, i were thinking that what if i use BMS only for charging, and let VESC drop the battery when it's too low.
Is VESC reliable enough for battery monitoring? What i should take in caution? And what settings?

I have 36V/5Ah (10S5P) battery (max about 15A) with this kind of BMS:
Image

rew
Posts: 904
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: To use or not to use BMS?

Postby rew » 07 Apr 2017, 09:11

I used a BMS like that for a while. My batery is pretty bad: It will drop below 3.3V per cell when still at 90% State Of Charge.

The BMS would then cut off the VESC and refuse power until it was charged again. Not convenient when you're 10 miles from home.

I've been driving without BMS for several months now. A couple of weeks ago I checked the balancing again (after months of use) and it was quite perfect. It would be better if I do this more often, but it seems I don't get around to doing it often enough. On the other hand, my battery seems to cope.

Quezacotl
Posts: 24
Joined: 05 Apr 2017, 11:06
Location: Finland

Re: To use or not to use BMS?

Postby Quezacotl » 07 Apr 2017, 20:34

Okay, i will try to bypass the BMS too and use it only for charging.

My battery is also a "bad", because it's made from used laptop cells. I have tested them each with 3A discharge current and matched all the cells, all about 1000mAh.

What settings and battery do you have?

rew
Posts: 904
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: To use or not to use BMS?

Postby rew » 08 Apr 2017, 13:30

I have 10S of 10Ah nominal ebike cells. They should have around 7Ah of capacity remaining.

I use 34-32 as the "soft battery cutoff" region. I have 20A nominal motor current, so at 33V I can request a maximum of 10A motor current.

Quezacotl
Posts: 24
Joined: 05 Apr 2017, 11:06
Location: Finland

Re: To use or not to use BMS?

Postby Quezacotl » 09 Apr 2017, 21:35

Okay thanks.

I just finished building my enclosures for battery pack and controller. Now they are weather-proof.
Now i just need to test, test and test until i get all the settings optimal. I have 9+9km travel to work, so i can test and tweak all things well. :)


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