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Negative connection off a parallel busbar - top middle or bottom?
#1
I was about to make up 5 of these packs (4s14p) for my sons electric motorcycle conversion (Lead to li-ion 20s14p) and recall an article indicating that I should take the connection from the opposite end of a parallel busbar due to the energy moving from + to - accross the series and so both connection being on top could put more starin on the top cells in each parallel.

Unfortunately after questioning myself and whether I just made that up in a dream, I can no longer find the source for the logic, so my question is should I go with a or b, or something else.

Thanks in advance for your help and if anyone has a link to any decent articles (or search terms I can use in Google :-) 

   

The bus bar will be connected with axial fuses
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#2
Oposite on all high drain. No doubt There IF you want it to last. Its all about resistance
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#3
I'm struggling to get my head around which end is opposite because if I have two U bus bars on the back end then surely a will be the very opposite of the chain (last cell in the U on the back will be the one at position a)

and conversely if I have two n bus bars then b would be last in the link.

Man I can confuse myself so easily :-)

is there anywhere where I can read about this?

I found this great article (its not the original one I thought i read or dreamed :-)

Its by spinningmagnets so its really well written and almost describes my situation with regards to adding a copper wire over the end collector of the 10p (pos and Neg)

this article is describing a 5p pack with red wired end connector (towards the end of the article)

https://www.electricbike.com/introductio...-design-2/
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#4
OK so I have up loaded the latest build photos, in essense I have the series being joined together using the U bus bars and the straight bars at either side are the end connectors for taking the higher load.

does this sound right?
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#5
The two pictures with the wires & connectors look right.
The one with the white words added looks wrong.

Like daromer says it's about the resistance & any path through any cell being equal.
Running off solar, DIY & electronics fan :-)
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#6
(05-24-2020, 05:59 AM)Redpacket Wrote: The two pictures with the wires & connectors look right.
The one with the white words added looks wrong.

Like daromer says it's about the resistance & any path through any cell being equal.
That's cool to have re-affirmed. During the process of banging my head and  going around in circles, i tried to sketch out the pack if it was just a straight pack of 2x28 batteries and how I would link them, I realised i needed to flip that U in the white writing photo for least resistance.

Although the copper is overkill for joining the Parallel cells it is needed to link the last/first in the series (this is my takeaway from the spinningmagnets article) and is also necessary in taking the load at + and - positions.

I'm now content with my pack and will fuse the cells to the bus bars and attach 4s Balance leads before balancing and installing into the project motorcycle.
Thanks for you reply, it can be a lonely world out there when your not too sure :-)
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#7
If it's an electric motor bike, currents will be significant so you may not have enough copper!
How many amps will the motor draw?
Running off solar, DIY & electronics fan :-)
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#8
(05-24-2020, 11:27 AM)Redpacket Wrote: If it's an electric motor bike, currents will be significant so you may not have enough copper!
How many amps will the motor draw?
It claims max peak at 30Amp its 72v and I believe a 2500w motor, the copper is 4mm2 so for the tiny length (15cm) I believe its fine upto 42A continuous i'm more concerned with the 14p battery pack delivering 2A/cell i'm using, 1amp fuses as I find these to blow around 4amp. 

The motorcycle is a Junker that my 17 year-old has taken an interest in re-building, all basic stuff but as he is in Curfew mode (All under 20yr olds in Turkey are under permenant House Curfew) its given him a project to keep busy. other than asthetics and the battery pack we're a few more days away.
The Motorcycle will be a run-about going no more than 25mph there will be some slight uphill riding which may get close to peak but i think its ok.

A friend that was using the KWeld Spot Welder managed to Over Voltage charge the Turnigy Battery Imax setting was 4s not 3s so I'm Still trying to identify an alternative power source as the turnigy will not deliver anything over 300a now, My car battery tests at 900a through the KWeld but after the first fuse weld at 18.5J it drops down to the mid 700's and reports under current.  

Thanks for your interest, onwards and upwards
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#9
(05-23-2020, 11:13 AM)mbladen Wrote: OK so I have up loaded the latest build photos, in essense I have the series being joined together using the U bus bars and the straight bars at either side are the end connectors for taking the higher load.

does this sound right?
The answer to your poll is ... NONE OF THE ABOVE
Not ... a)
Not ... b)
Not ... c)

Instead of the U-Shaped connectors ...
I would have completed the full rectangle shape
This reduces the max amps flowing in this bus to ~50% of your design = less voltage drop

Instead of connecting both wires ( #1 & #2 ) of the XT-60 connector to one end of the straight bus ...
I would connect wire #1 about 1/4th between (a) & (b) & wire #2 about 3/4th between (a) & (b)
This significantly reduces the max amps flowing in the straight bus to ~25% of your design = lower voltage drop
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#10
But making a rectangle would cause uneven current distribution in the cells....
Eg the current would tend to want to flow in the cells in a straight line between negative & positive wires.
Your description way would likely be better but still some unevenness.
Keeping the "U's" as discussed shares the current flow best.
Running off solar, DIY & electronics fan :-)
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