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Double stacking bus bars question

Tyler702

Desert dweller, quiet prepper
Joined
Aug 20, 2020
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I've read posts regarding folks double stacking bus bars.. presumably those bars that aren't quite as thick and robust. I've recently received bars with my 200Ah cells that I would consider to be in that category. I can nearly bend them with thumb and forefinger. (See pic, with a penny for comparison) My question is, is there an inherent issue stacking these things if there is a slight air gap along the length of the bar? Obviously at the posts, they're compressed together nicely, but they don't make absolute full contact sandwiched together along and in between the posts.
One solid thick bar is best practice I know, but in the interim, if I double or even triple stack these, which I have room to do, is there any problem I may see in the short term? Short term being 6 months or so with moderate to med cycling of my pack.
Thanks.
 

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Airgap shouldn't hurt anything.
The bowed shape should reduce stress on cell terminals.
Some busbars are a stack of similar pieces.

Are those aluminum? Tinned copper?
If aluminum, scrub off oxide and use some sort of corrosion inhibitor or dielectric grease between each mating surface (just the ones under pressure.)
 
Thx Hedges. I took a chance at the Ninthcit cells from Amazon and the bars they included were weak, in my opinion, but they claim they're 100% copper. Tinned I suppose..idk.. But like I said, bendable with thumb and forefinger with a little effort. I'm happy to double or triple stack em..I've got plenty of post space. I was just concerned about air gaps between them and if that created a problem.
 

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The gap between laminations isn't a problem. Multiple strips laminated makes it more flexible, less force on terminals. Even if cross section is less than the (insulated) wire you would typically use, may still be fine. Heat is generated, but because busbar is short the heat conducts to terminals and has more surface area to escape. See how much temperature rise at operating current.

Are those studs already attached to the terminals? Should be stronger than the tapped holes people were stripping. I don't know for sure the contact surface, but assume it is bare aluminum rather than tin plated. If aluminum, needs oxide scrubbed off and corrosion inhibitor applied. Tinned copper on aluminum isn't as bad as bare copper on aluminum. I would rather see tinned aluminum than bare. Best would be if aluminum busbars were welded between terminals but that takes other equipment nobody's going to have for DIY. (Some get pre-assembled packs done that way.)
 
Many people do double up the busbars, quite often I have seen That style of busbar doubled and with a small screw in the centre tapped through them for the BMS Leads, as well as flat busbars as well. BMS leads do not require a big connector and sometimes that can even introduce some issues which are a royal PITA to chase down.
 
Are those studs already attached to the terminals? Should be stronger than the tapped holes people were stripping. I don't know for sure the contact surface, but assume it is bare aluminum rather than tin plated. If aluminum, needs oxide scrubbed off and corrosion inhibitor applied. Tinned copper on aluminum isn't as bad as bare copper on aluminum. I would rather see tinned aluminum than bare. Best would be if aluminum busbars were welded between terminals but that takes other equipment nobody's going to have for DIY. (Some get pre-assembled packs done that way.)
Yes, these have laser welded studs. I'm not sure what the surface of the terminals are though. They have a "quasi" shiny look to them but not as shiny as the bars, so idk. I was going to work on my own diy pure copper bars, bare, but you're saying bare copper bars on an aluminum surface might not be optimal? Is that because of corrosion down the road? And could that be mitigated by applying a conductive inhibitor? Dielectric grease I think I've heard mentioned around here before? Fwiw, this will be a stationary pack not mobile, and I'm in Nevada, so very dry and low to no humidity year round.
 
Tinned copper is better. If you added additional layer of thin copper busbars on top, those could be bare. It is just copper to aluminum that is the bigger concern.

Would be nice to know if the new terminal surface was tin or aluminum. Some contact resistance or chemical tests could identify. Wouldn't want to scrub tin off, but if aluminum oxide I would want to remove that.
 
Tinned copper is better. If you added additional layer of thin copper busbars on top, those could be bare. It is just copper to aluminum that is the bigger concern.

Would be nice to know if the new terminal surface was tin or aluminum. Some contact resistance or chemical tests could identify. Wouldn't want to scrub tin off, but if aluminum oxide I would want to remove that.
Honestly I'm not sure what the surface is. I'll send the seller an inquiry. I'm not prepared to test it at this point..not too familiar in that area anyway. If it's tinned, leave it be, if it's aluminum, I guess adding some contact grease would be in order if I end up using my diy bare copper bars.
 
Caution, dielectric grease is not the same as Noalox or Ox-Guard, do NOT use that. OxGuard/Noalox only and a very tiny amount to cover the contact surfaces and NEVER EVER use them on the screws/bolts because it affects not only the power BUT also skews any form of Torque readings (it is a grease after all). You just cannot slater it on.

Virtually all terminal faces on cells have a thin wax to prevent corrosion during storage & shipping. If holes are tapped for bolts etc, there will be cutting oil residue. Both of these can hamper the reading by the BMS resulting in inaccuracies that create further issues. This also means using a Q-Tip with alcohol to clean out the holes too. This is Experience Talking.
 
Caution, dielectric grease is not the same as Noalox or Ox-Guard, do NOT use that. OxGuard/Noalox only and a very tiny amount to cover the contact surfaces and NEVER EVER use them on the screws/bolts because it affects not only the power BUT also skews any form of Torque readings (it is a grease after all). You just cannot slater it on.

Virtually all terminal faces on cells have a thin wax to prevent corrosion during storage & shipping. If holes are tapped for bolts etc, there will be cutting oil residue. Both of these can hamper the reading by the BMS resulting in inaccuracies that create further issues. This also means using a Q-Tip with alcohol to clean out the holes too. This is Experience Talking.
Good to know. Fortunately my cell bolts are lazer welded, so no issue there, but yea, applying grease carefully and ONLY to the contact surface and NOT on the bolt or nuts will be my plan of attack. I wonder if this Noalox is available at my local Ace Hardware or home depot. Ill check it out. Thanks for the helpful guidance!
 
Either NoAlox or OxGuard are usually available at Auto Suppliers (Like UAP) I bought mine at HomeDepot and it's not expensive either. If memory serves a big tube was $5 or so. Laser Welded Studs are the best way to go, just ensure the threads are clean.
 
The "bus bars" pictured in the first post of the thread sure look skimpy to me. How thick are those?
Not very. I don't have a caliper to measure, but I put up a pic of 2 of them on edge with a penny sandwiched in-between. They ARE tinned copper, but yea, pretty thin. I'll likely double stack em' till I get better ones.
 
Not very. I don't have a caliper to measure, but I put up a pic of 2 of them on edge with a penny sandwiched in-between. They ARE tinned copper, but yea, pretty thin. I'll likely double stack em' till I get better ones.

Double? Heck, I double stacked my bus bars, each of which has to be at least twice as thick as the one in your picture. If you're drawing high amp loads, I wouldn't trust those bus bars.
 
Double? Heck, I double stacked my bus bars, each of which has to be at least twice as thick as the one in your picture. If you're drawing high amp loads, I wouldn't trust those bus bars.
Agreed. Doubled for now, but once the pack gets put into use, I'll definitely have proper bars in place. Right now, I'm waiting on the other 4 cells to get my 8S hooked all together. So no major loads at all at this point.
 
I think copper, even thin, will safely carry a lot more current than you might think. Take a peek at a relay (open frame or in clear shell) and note how skinny the flexible braided wire is.
Measure length, width, and thickness with a ruler (estimate what fraction or multiple of 1/16" thick it is) and compute resistance.
You can either look up bulk resistivity of copper, and multiply by length, divide by width and thickness. Or calculate cross section, scale resistance from a table of copper wire cross-section and resistance.

See how much apparent cell voltage is lost at intended current. see how much power is lost.

A handful of busbars is going to be less voltage drop and power wasted than a long fat battery cable. I think it will work until you feel like replacing it.
 
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