Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
3 parallel battery with one external bms
#1
This is my first post in here. Thank you for all the members information sharing that help me to start my electric vehicle journey.
I'm building 20S9P, 20S12P from recycled 18650 and 20S2P from recycled 26650. The BMS i'll be using is 20S 72V 100A BMS

I'm thinking about connecting 3 battery in parallel and using one BMS that is connected to the 2 or 3 battery with the balance lead that go to the 2 or 3 batteries. Is this possible? What do you think about this setup? I'm trying to save cost by using only 1 high amp bms, or is it better to use 3 separate bms?

Thank you for your help and information.
Reply
#2
(07-31-2020, 02:17 PM)chronosteam Wrote: This is my first post in here. Thank you for all the members information sharing that help me to start my electric vehicle journey.
I'm building 20S9P, 20S12P from recycled 18650 and 20S2P from recycled 26650. The BMS i'll be using is 20S 72V 100A BMS

I'm thinking about connecting 3 battery in parallel and using one BMS that is connected to the 2 or 3 battery with the balance lead that go to the 2 or 3 batteries. Is this possible? What do you think about this setup? I'm trying to save cost by using only 1 high amp bms, or is it better to use 3 separate bms?

Thank you for your help and information.
Yes you can.   @DIY Tech & Repairs even did a youtube  -  https://youtu.be/sGj9UrfEcAw
Note: This bothered me as I'm imagined the sense leads burning up under load...  but other discussions on this over the last couple of years indicate that the 'main power' will flow thru the bus/terminals of the batteries rather than the sense wires - so it works great. 

Of course you can't have the different battery/cells with wildly different voltage level when you 1st join the sense wires as that might burn them up as they do the initial balance.
Reply
#3
(07-31-2020, 03:09 PM)OffGridInTheCity Wrote: Yes you can.   @DIY Tech & Repairs even did a youtube  -  https://youtu.be/sGj9UrfEcAw
Note: This bothered me as I'm imagined the sense leads burning up under load...[...]

Another remark: at 11:51 they show a 30Ω load of 3 series'ed small aluminum-housed 10Ω 100W resistors - see below.

[Image: HioQu.jpg]

Many beginners are not aware that the power ratings on such small power resistors presume that they are mounted to much bigger heatsinks (here typically a 12 x 12 x 1/8 inch aluminum heatsink). Without any heatsink they need to be derated ("free air rating"), i.e. in free air with no heatsink typically they can only handle 40-50% of their rated power. So in the video they can only handle 40W each, so 120W total (only a bit above what he's running them at, so they will get extremely hot, see below).

Further, the standards used for such power ratings permit them to rise to about 350°C (662°F), and they may actually get near that hot when pushed to their limits, so even a moments touch can lead to severe burns (but it will take a little time to reach full temperature). If you exceed the power ratings for long periods then they can violently explode, ejecting shrapnel - something you don't want to be near (esp. if you are not wearing safety goggles - like the video author).  So be careful with such (high) power resistors - be aware of their design limits.

Below is an excerpt from a Dale Vishay datasheet showing typical free air deratings (RH100 is their 100W models).  A good introduction to these matters is Ohmite's Resistor Selection Application Notes.

[Image: yQQdO.png]
Reply
#4
Super now that we have the Resistor lesson out of the way let's get back to assisting the OP with his question about
"connecting 3 batteries in parallel and using one BMS"

Yes The 1 BMS for  the 2 -3 battery packs should work just fine as OffGridInTheCity mentioned.

Do be aware of the chemistry differences between batteries as in ICR (low drain) and INR/IMR (high drain).
Additionally IR can have a significant effect.
In small p packs like this it can make a big difference in longevity especially if pulling more than 1A per cell and also discharging below 3.5V.
See my thread on behaviour of cells in parallel.

Wolf
For Info Google Drive

Great ABB shunt breaker seller River City Industrial
Great prices and superb service.
 [Image: em2566%20(1)__19172.1521541365.jpg?c=2]

Not your average Wolf       
            Cool
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)