How do I size bus bars for my LiFePO4 280Ah cells?

chrisski

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Is this 4 hours to electroplate a single bus bar? A bit more detail please. I would hope theres a way to do several at once.
Bars plated instantly.

The nickel solution took 4 hours to make. That is a one time only deal and should last forever.

Here’s a thread I did a couple days ago. I think plating is in post 2.


 

PeteW

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Bars plated instantly.

The nickel solution took 4 hours to make. That is a one time only deal and should last forever.

Here’s a thread I did a couple days ago. I think plating is in post 2.
Thanks very much, I'll dig into this tomorrow. It looks like it will be very informative.
 

PeteW

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I got between 205 amps and 209 amps when I looked 1/8” X 3/4” copper.

I guess the question I have is, do you size the busbars no wider than the terminals? My 25 ah cells have terminals that are 3/4” wide, so that is perfect for them. if I put a wider busbar, it would overhang the flat area the busbar is supposed to attach to.

I hope is going well with your cells.

I do not know how wide the contact surface for the 280s are. Mine just came in today (excited!!), but it will be until Monday before I can unpack them.
You want the busbars at least as wide as the terminals. Wider will give lower resistance but it also exposes more metal for short circuits.

I was getting ready to measure and order the copper and this stopped me in my tracks. I know I'm taking forever. It's long story.

So, here are a couple pictures (below) of the top of my batteries. The terminals stick up quite a ways from the top of the battery, I'm taking a rough guess, but I don't think 1/4" would be an exaggeration. the surface area of the terminal where the stud sticks out is about a 7/16" diameter. Is this going to be a problem?

PXL_20211106_050417574.jpg

PXL_20211106_054812552.jpg
 

chrisski

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You want the busbars at least as wide as the terminals. Wider will give lower resistance but it also exposes more metal for short circuits.
I was getting ready to measure and order the copper and this stopped me in my tracks. I know I'm taking forever. It's long story.

So, here are a couple pictures (below) of the top of my batteries. The terminals stick up quite a ways from the top of the battery, I'm taking a rough guess, but I don't think 1/4" would be an exaggeration. the surface area of the terminal where the stud sticks out is about a 7/16" diameter. Is this going to be a problem?
I am going to use them this way. We are not the first people to put these together and I hope to hear form others with those terminals. There’s been probably at least 10,000 of these batteries delivered, so I hope to hear something,

I have the same cells and will use the busbars that came with the 280s. I have not been able to put the battery together since my RV the battery will be installed are going in is in the shop to repair damage caused by a tire blow out.

1636203037982.png

I was concerned when I saw this also and contacted someone who is using these cells in a house (non-mobile) application and he pulls 200 amps from the batteries and pushes up to 150 amps into them. He said they were warm, not hot, but did not use them in a fixed not mobile.

That and what was said earlier about busbars being as wide as the terminals means I am going to use these. I won’t have a situation with mine where I will pull more than 100 amps per battery out of them.

I think I will need one or two extra busbars and I will use 3/4” X 1/8” at least or perhaps 3/4” X 1/4”.
 
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Steve_S

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I was concerned when I saw this also and contacted someone who is using these cells in a house (non-mobile) application and he pulls 200 amps from the batteries and pushes up to 150 amps into them. He said they were warm, not hot, but did not use them in a fixed not mobile.
This is ME, and this was done during the Hard Thrash testing process I ran this srpring. These tests were to determine the Failing Edge cases and fail over process, as I'm 100% Offgrid, quite remote and totally rural and can be snowed in for days, so I have to know what the system will/won't do.

Clarification required. I run 3x280AH & 2x175AH LFP for 1190AH/30.4kWh @ 24V and this is Residential, non-mobile. Because the Battery Bank is such a size & layout, it never collectively sees High Amp use... I consider <100A low use and when it's split with 5 packs, it's not much strain at all. BTW: 2x 280 use screwed terminals, 1x280ah has welded studs.

The Thrash Testing involved the full bank but also single pack full loading (charge/discharge) I pushed up to 0.5C to all packs and pulled to 200A from the 280's & 175A from the 175's. NB: The 175's are EV LFP, NOT ESS LFP, they came from the "Shunbin Disaster" and a slightly different cell. My system is also built to handle 300A, so BMS/DCC etc are all 300A Rated.

Default Busbars shipped by most vendors are 2mm thick by 15mm or 20mm wide with slotted holes. Most people double the busbars and that works out perfectly. Do understand that Amps put out by a battery pack is the Collective Amps from the cells... folks forget that important nugget.

I have made my own busbars with 110 Copper Bar Stock, and even went Big & Heavy and that was a costly lesson ! (copper != Cheap) and with all the testing and hard abuse level stuff, I found that Doubled Busbars at 4mm Thick x 20mm wide can handle it fine. Applies to BOTH Welded Studs & Screwed in Terminals.

KICKER: Technically, the screw/bolt should not be depended on for delivering current (the normal default) BUT a Welded Stud is reconsidered as integral to the terminal and as such can / does carry current to bars. I KNOW, but it's the Welding that changes the rule as such.

A TIP - Important for Mobile Especially. People, Split Ring Lock Washers are K.R.A.P. ! Please for Goodness Sake, use Stainless Serrated Washers !!!, they grab, hook in and stay put ! People have failed to listen to this, suffered issues and then came back to be told AGAIN and once done their problems went away and they NEVER COME BACK TO SAY SO ! (they say so in PM cause they don't wanna look dumb for not listening in the 1st place) Don't be one of them !

Tin Plated Bar Stock is available just not easy and you will pay a premium.
Do not use Crap Copper, use C-110 at least.
You can use Aluminium but use no less than 4mm x 20mm.
With Tinned Bars, you do not "have to" use Noalox/OxGuard but you can (marine environment best to use).
NB: Use only a very tiny amout of oxguard (very thin fil, no buildup), NEVER EVER on the threads (it is a grease).

BMS Sense Lead Tip !
These buggers cause many a lot of headaches ! Folks, you have no idea, it is a major issue. One SIMPLE SOLUTION but takes extra time, Tap a small screw hole into the busbar & using a very short self-taping screw to attach the sense leads to Busbar and NOT the terminal post. FYI/BTW, all proper Commercial Packs do it this way, rather than attempting to attach to terminals which can through values off... Remember these BMS' are Super Sensitive, they work in Millivolts & Milliamps and it really takes very little to throw them off.

Hope it helps, Good Luck.
 

chrisski

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Tap a small screw hole into the busbar & using a very short self-taping screw to attach the sense leads to Busbar and NOT the terminal post.
Thanks for the detailed write up.

I like the idea of doing of drilling And tapping. Next for me would be to find the specific ring terminal for a .5 mm wire that will work with any of the 4 or 5 crimping devices I have.

The small 26 AWG wires do not crimp very well for a M6 or M8 battery stud. I have my technique of using the open end 6.2 mm or 6.3 mm Ring terminal to fit on a 6 mm stud, but the crimp device is designed to crimp wires that are 2.5 mm, not the .5 mm wire size. If the correct .5 mm crimp device is used, ruins the M6 ring terminal. So, crimped with a .5 mm wire crimped with a 2.5 mm tool will pull right out, so to finish the job, I use pliers. Has worked fine for me, but my BMS leads are only 2 months old. Not sure how this will hold out over time.

I had also considered drilling and soldering the 26 AWG wire. Although easy, its a rather permanent solution and makes it hard to troubleshoot if anything goes wrong.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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I crimp everything, stopped soldering as it creates issues. A Small ratcheting crimper does it nicely, was only $20 or so.
I got quality Ring Terminals for all that from a local Raspberry Pi + Supply House (so much cheaper than anywhere else).
Simple enough to tap a tiny hole through the busbar and just use a self-taping screw (I use Hillman Brand tinned screws)
 

chrisski

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use Stainless Serrated Washers !!!
For between the nut and stud, Do you recommend a serrated washer with shallow teeth like this:
25B15E1F-A13E-4674-BD07-BE088C7C26A8.jpeg
Or one with deeper teeth similar to a star washer:
6F3128C9-532A-4477-8860-7ACBA1FCD903.jpeg
Thanks as always.
 

PeteW

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I have the same cells and will use the busbars that came with the 280s. I have not been able to put the battery together since my RV the battery will be installed are going in is in the shop to repair damage caused by a tire blow out.
Oooh, that sucks, been there! I had the front tire explode on the curbside which in turn blew the rear tire (dual axle setup) which then did some very destructive stuff to the rear aluminum panel behind it. I have a 29' 1992 Airstream. After reading a lot of positive reviews by others I up-sized my rims from 15" to 16" and changed from radial ST tires to radial LTs. Airstream now offers this as an upgrade on their higher end models.

This is ME, and this was done during the Hard Thrash testing process* I ran this srpring. These tests were to determine the Failing Edge cases and fail over process, as I'm 100% Offgrid, quite remote and totally rural and can be snowed in for days, so I have to know what the system will/won't do.

*Hard Thrash Testing, I'm unfamiliar with this, or maybe just this reference, can you or someone point me to some learn'n, please.

Default Busbars shipped by most vendors are 2mm thick by 15mm or 20mm wide with slotted holes. Most people double the busbars and that works out perfectly. Do understand that Amps put out by a battery pack is the Collective Amps from the cells *... folks forget that important nugget.

*When you say Collective Amps, are you referring to total watts, (A x V = W)? Please don't misunderstand my questions as being facetious or disingenuous, they aren't. I'm genuinely trying to learn something, but I'm very inexperienced and barely hanging on by my finger nails. ;)


I have made my own busbars with 110 Copper Bar Stock, and even went Big & Heavy and that was a costly lesson ! (copper != Cheap) and with all the testing and hard abuse level stuff, I found that Doubled Busbars at 4mm Thick x 20mm wide can handle it fine. Applies to BOTH Welded Studs & Screwed in Terminals.

I was supposed too, but did not receive busbars. I even paid for a number of additional busbars to handle doubling and battery configuration, etc. The person who facilitated my purchase has promised to make this right and I'm pretty sure he'll follow through, but there continue to be shipping issues and I need to move forward. Thank goodness the cells arrived safely and great condition, at least as far as I've been able to determine without busbars.

Based on some welcomed advice from FilterGuy I'm planning on buying 110 copper 1/8 x 3/4", which seems more than adequate to handle 150% of the 139A should I ever require so much power. I can't imagine it.

A TIP - Important for Mobile Especially. People, Split Ring Lock Washers are K.R.A.P. ! Please for Goodness Sake, use Stainless Serrated Washers !!!, they grab, hook in and stay put ! People have failed to listen to this, suffered issues and then came back to be told AGAIN and once done their problems went away and they NEVER COME BACK TO SAY SO ! (they say so in PM cause they don't wanna look dumb for not listening in the 1st place) Don't be one of them !
The Ochoos Toothed Serrated, they bite in and lock well.

I just purchased SS serrated flanged hex nuts, are you guys advising against these? As said, I'm building this battery for a travel trailer.

1636238538697.png


BMS Sense Lead Tip !
These buggers cause many a lot of headaches ! Folks, you have no idea, it is a major issue. One SIMPLE SOLUTION but takes extra time, Tap a small screw hole into the busbar & using a very short self-taping screw to attach the sense leads to Busbar and NOT the terminal post. FYI/BTW, all proper Commercial Packs do it this way, rather than attempting to attach to terminals which can through values off... Remember these BMS' are Super Sensitive, they work in Millivolts & Milliamps and it really takes very little to throw them off.

Thank you for this, it seems like a good and prudent suggestion.

Thanks. I’ll use those and on the nut add Loctite 242 Blue, the low strength version.

Thanks for this, I was thinking along the same lines. :)
 
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Horsefly

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*When you say Collective Amps, are you referring to total watts, (A x V = W)? Please don't misunderstand my questions as being facetious or disingenuous, they aren't. I'm genuinely trying to learn something, but I'm very inexperienced and barely hanging on by my finger nails. ;)
I'm not sure exactly what @Steve_S was meaning to say, but the Amperage out of the pack is - by definition - the Amperage that is passing through each of the serial cells.
 

chrisski

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I just purchased SS serrated flanged hex nuts, are you guys advising against these? As said, I'm building this battery for a travel trailer.
I received serrated hex nuts from the seller included in the battery. This is an RV installation and I plan to also use the toothed serated and Blue Loctite. That is after thoroughly cleaning the contact area on the bus bar and battery.
When you say Collective Amps, are you referring to total watts,
We'll see what he says. I took that to be the total amp output from his battery pack. I may draw up to 200 amps of power max, but with two batteries, that will be 100 amps from each battery pack, so I will make sure my busbars are at least rated for 100 amps.
Thanks for this, I was thinking along the same lines
I am going to be extremely careful since this Loctite might be non-conductive. To keep it off the bus bar and battery contact area, I will put the busbar on first, then the serrated washer, and then put a small dab on the serrated hex nut. Then I will screw on and torque. Seems to be different opinions on Loctite.

My other small battery pack that I use on a small inverter for a milkcrate solar generator, a 24 volts, 50 ah lithium, I used no Loctite. That will not rattle around.
 

PeteW

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I am going to be extremely careful since this Loctite might be non-conductive. To keep it off the bus bar and battery contact area, I will put the busbar on first, then the serrated washer, and then put a small dab on the serrated hex nut. Then I will screw on and torque. Seems to be different opinions on Loctite.
Based on your reference to conductivity I did some research. I'm afraid what I found was that Thread lock IS, as you suspect, non-conductive and a definite no-no. Here's a link to the google page I pulled up and found several good pieces on why it's a bad idea. Thank you again, I'm very glad you mentioned the possible conductivity issue because I was definitely planning to use a thread locker and now I will stick to mechanical means such at serrated nuts and star washers.
 

PeteW

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'm not sure exactly what @Steve_S was meaning to say, but the Amperage out of the pack is - by definition - the Amperage that is passing through each of the serial cells.
We'll see what he says. I took that to be the total amp output from his battery pack. I may draw up to 200 amps of power max, but with two batteries, that will be 100 amps from each battery pack, so I will make sure my busbars are at least rated for 100 amps.

This is helpful guys. Thank you.
 
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