need help parallel and series the lipo to BMS

[splitfire]

i just got my BMS and wanting to connect my lipo packs . i have 21s 3p 15000mah 9pcs 6s and 3pcs 3s all of them are 5000mah....ok heres what i did, i connect all the power wires to series to make 87v.....everything is good. I connect the balancing leads from each group of series lipos to the other group. i just connected 1pcs 6s on each group..it works ok ...Now i tried to connect the 2nd balancing lead of 6s in each group it goes BANG!! balancing leads burnsout and melted. I know cannot connect the balancing leads in parralel from the same group in series coz that will go wrong....i dont know why did this happen....i am pretty sure that i connected the 3pcs 6s balancing leads from 3 different group of series lipos, not the same group....
Do i need to connect the power wires first in parallel before connecting the balancing leads in parallel? or it doesnt really matter which comes first? any Idea what is the safest way to connect them without burning something like fuse? small wire?

 

[wesnewell]

If you had done it right, you would not have gotten a bang.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=39666
http://scriptasylum.com/rc_speed/lipo.html

 

[dogman dan]

To me, the easiest way to avoid this is to pair up packs in parallel first. Then you have pairs of packs with just one balance lead. Then, you start making series connections with the main leads.

as you series, the last balance wire of each pack connects to wire 0 (the negative balance lead wire) of the next one.

Very easy to confuse which lead goes where, as the pile of spaghetti gets bigger and bigger.

 

[splitfire]

Hi Dogman dan thanks for the info . I am going to pack up my batteries I will start weld all the balancing leads in parallel. Do I need to parallel my power wires too? Can you pls give me a wiring diagram. And also dont know how to connect then in my bms I have 21s lipo in total 3x 6s and 3s .. 6s has 7 leads a total of 21 plus 4 leads coming from 3s so I have 24 leads going to a 21 leads input bms.

 

[dnmun]

do you not understand that the black wire in the JST plug goes to the bottom of the first cell in the pack? that is connected to the top wire in the JST plug of the lower pack.

it is best to remove all of the pouches from the shrink wrap and build the battery up as a 21S3P pack and put it all in orthogonal compression. use 1/8" hardboard for the end plates. put it in compression with some wood clamps from harbor freight. then wrap with long zip ties to hold it in compression. mount it in an enclosure which is able to maintain the compression on the entire pack and do it uniformly across the entire end plate.

remove all of the sense wires, remove all of the large connectors at the top and bottom of each pack and solder the tabs together where the lower pack joins to the upper pack at B0.

connect your 3S at either end where the tabs line up with the tabs in the following or preceding pack.

then connect all of the pouches in parallel with small 24 AWG wires and then connect the 21S sense wires to each of those parallel connections.

verify the polarity of each connection in the sense wire plug before connecting the sense wire plug to the BMS.

 

[splitfire]

Thanks dnmun. Yeah better to connect the tabs when connecting them in series . Can you show me pics. I know ive seen you pics somewhere were you unwrap the batteries use a clam and solder the leads . I just cant find it again or pls send me the links. Thanks

 

[splitfire]

Thanks dnmun. Yeah better to connect the tabs when connecting them in series . Can you show me pics. I know ive seen you pics somewhere were you unwrap the batteries use a clam and solder the leads . I just cant find it again or pls send me the links. Thanks

 

[dnmun]

lost my pictures when i had a disk crash but found a few left in the camera.

 

[splitfire]

Cool. Thanks for the pics. I already assembled my packs. And did not go bang . I just dont know what gage wire to use for power cables #10 or #8. Is it thick enough?

 

[dnmun]

if you have the 8 and have terminals or can get some andersons on it. but 10AWG will handle 90A surges and 40A all the time.