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Buss-bar Sizing

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LanduytG

Solar Enthusiast
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Apr 19, 2020
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I will have my 12 new 280ah cells Friday. Not sure of the quality of the buss-bars they send with the cells. In the event I don't like them I will make my own. With 280ah cells in 4s the current would be divided across all 4 cells, am I correct on that? If not then a 280amp buss-bar would be at least .250 thick if using 1 inch wide copper material. To me it makes more sense that it would be divided across the 4 cells so 70 amp bars so .125 one inch wide would be plenty.

Greg
 
The battery cells are connected in series, thus the current doesn't change and remains at 280amps for 1C load , the cuircuit voltage adds up and multiplies x4 per cell.
 
I have 64 x 280Ah LiFePo4 cells arriving from Amy in the next month. They will be used to replace my existing 48v 1000Ah OpzS FLA bank that is reaching EOL. Having substantially increased our power requirements since I built the system 10 years ago we now look like needing a peak current capacity of around 500A. This seems to be almost in the crazy range compared to most of the discussions here, but it seems to be well within the capacity of these Eve cells. I have a large (for me) investment in my existing outback 48V system which makes me reluctant to move up the voltage ladder just now. My current plan is to have two banks of 2P16S with a balancer/bms on each bank ( 2P16S2P, if I understand the nomenclature) but to also have the ability to run off either bank individually if issues occur. This leads me back to the topic of this thread, Can anyone assist me in deciding what would be appropriately sized interconnections between the series cells to support up to 500A from a single bank, and, does it really matter what size the 2P cross-connection bars are, assuming the smallest it will be is one of the ones Amy is sending with the cells.... (25x2mm I understand).

My proposed layout for a single bank:

LiFePo4Bank.jpg

Thanks for any help.
 
Fyi, kenz...the terminal on these batteries are not centered from the end and the sides. IE. the terminals are not the same distance from the side as they are from the end. The buss bars only work with the cells side by side. If the batteries are placed inline the bus bar is not long enough.

This was frustrating to me that they wouldn't design them to be symmetrical.
 
I would suggest you make 4x 48 volt batteries each with its own bms.
fuse and shunt each battery individually.
Then fuse and shunt the aggregate.
You 500 amp draw would be 125 per battery or 166.666666667 off 3 in the case that one is offline.
As for charging .5c is 560 amps and .2c is 224 so it should be easy to get a charge rate that is optimal for 4 and acceptable for 3 batteries in the case that one is offline.
 
Nice system! I notice how when you turn the corner that there is only one connection instead of the normal two. That would be the weak point. If like they say, the bus bars only work side by side, then you'll need a lot of doubling up on such joints and testing to make sure there aren't heat issues.

I'm not sure what stacking would look like but I had it in my head that the bus bars were 100a rated, but 5 (9 in reality) high seems a bit much.

So maybe separate systems or separate batteries with balance connections between them.
 
As I mentioned on other threads, am using 1/4 x 1.25 aluminum to avoid weak spots. My breaker is 125 Amps but the extra aluminum is to draw heat away from cells. To me the supplied buss bars are too narrow for the posts and the long slots reduce surface area further. I wanted surface area for conductivity.
 
Ampster said:
As I mentioned on other threads, am using 1/4 x 1.25 aluminum to avoid weak spots. My breaker is 125 Amps but the extra aluminum is to draw heat away from cells. To me the supplied buss bars are too narrow for the posts and the long slots reduce surface area further. I wanted surface area for conductivity.
Click to expand...


Just got my cells today and I have to agree the busbars are on the light side. I will be doing something different.

Greg
 
Thanks for all your input. I guess the 4 x 48v batteries is the best approach, though I had been hoping to save a bit of money on the balancers by doing 2 in parallel. Thanks for the heads up newbostoncons, and Ampster, I'll look into Aluminium bars as an option since the price for flat copper seems to be quite steep here in NZ. I'm now moving into the what BMS/balancers to use, but I'll raise that elswhere. Thanks.
 
Ampster said:
As I mentioned on other threads, am using 1/4 x 1.25 aluminum to avoid weak spots. My breaker is 125 Amps but the extra aluminum is to draw heat away from cells. To me the supplied buss bars are too narrow for the posts and the long slots reduce surface area further. I wanted surface area for conductivity.
Click to expand...
From which angle is heat buildup a concern at this battery terminal point?
What I mean is, is the concern the battery's overall size (say 280aH, 24v, 6720w)?
Is it the amps to the inverter or SCC, like 40a, 60a, or 80a?

Or is it your personal draw or load. Like you have an inverter that is capable of providing you up to 40a 120v ac, but your demand rarely exceeds 20a.

Which figure impacts the buss bar design?
 
In fact, you've got me looking at my manual for my LV2424 now, and according to these cells are too big. Is that the case? How could that be? Can ideal buss bars impact whether my design passes or fails?
Screenshot_20200621-123813.png
 
ecualibrium said:
From which angle is heat buildup a concern at this battery terminal point?
What I mean is, is the concern the battery's overall size (say 280aH, 24v, 6720w)?
Is it the amps to the inverter or SCC, like 40a, 60a, or 80a?
Click to expand...

ecualibrium said:
and according to these cells are too big. Is that the case? How could that be? Can ideal buss bars impact whether my design passes or fails?
Click to expand...
The battery size 28kW was determined by my need for reserve (3 days) My breaker is 125 Amps and my wire is 4/0. No magic math, just a guess based on infrared photo I saw of heat focusing around terminals. My design is way overkill which may wow the inspector.
 
Ampster said:
The battery size 28kW was determined by my need for reserve (3 days) My breaker is 125 Amps and my wire is 4/0. No magic math, just a guess based on infrared photo I saw of heat focusing around terminals. My design is way overkill which may wow the inspector.
Click to expand...
How far are you moving the ac once inverted? What size wire? I still hope to move mine hundreds of feet, and the guys on here seemed to think if I used 6awg I should be good to move 120v for 20amps. But using online voltage drop calculators, it seems I may need as large as 1/0. Which would be insane and completely unaffordable.
 
Ampster said:
The battery size 28kW was determined by my need for reserve (3 days) My breaker is 125 Amps and my wire is 4/0. No magic math, just a guess based on infrared photo I saw of heat focusing around terminals. My design is way overkill which may wow the inspector.
Click to expand...
You can't use a infrared camera to look at shinny surfaces. It will just give you a temp of what is reflecting off the shine. It is called emissivity.
You can put black electrical tape on the bus bar to get a more accurate reading.

What is Emissivity? | Fluke Process Instruments

Emissivity is defined as the measure of infrared energy radiated from an object. It can be measured from 0 to 1, when emissivity = 1 it is called blackbody, reaching thermal equilibrium.
www.flukeprocessinstruments.com www.flukeprocessinstruments.com
 
While you can't get an absolute reading on low-emissivity surfaces, you can get relative readings off the rough edges and adjoining materials enough to gather intuition about where the heat is being accumulated. (And, perhaps more importantly, whether one connection is getting substantially warmer than the others.)

When I point my flir camera at my battery, the nickel-plated bus bars show up as useless mirrors, but all of the adjoining materials, threaded posts, etc, have enough emissivity to make it easy to see what is going on.
 
ecualibrium said:
How far are you moving the ac once inverted? What size wire? I still hope to move mine hundreds of feet, and the guys on here seemed to think if I used 6awg I should be good to move 120v for 20amps. But using online voltage drop calculators, it seems I may need as large as 1/0. Which would be insane and completely unaffordable.
Click to expand...

"Hundreds" is pretty vague. How many feet? 6AWG would be fine for 200 feet of 20A at 120V.

There's also not one single, acceptable voltage drop for all applications. What drop is acceptable for your application? (What are you powering? What device is your AC source?)
 
nebster said:
"Hundreds" is pretty vague. How many feet? 6AWG would be fine for 200 feet of 20A at 120V.

There's also not one single, acceptable voltage drop for all applications. What drop is acceptable for your application? (What are you powering? What device is your AC source?)
Click to expand...
More like 300ft, one way.

But it will only be powering, charging devices, led lights, a computer... actually, desk fans and a studio refrigerator, maybe a low wattage micro, will be the largest draws. All "hot" things will use propane power.
 
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