Gauging Busbars Bus bars DIY

[wlfpck1]

I think I have found a $16 solution to my problem.

Copper 110 Flat Bar 1/4" x 1 1/2" x 12"-Long -- .25" x 1 1/2" Copper Bus Bar | eBay

110 Copper Flat Bar 1/4" x 1 1/2" x 12"-Long -->.25" x 1 1/2" Copper Bus Bar.

www.ebay.com

 

[HRTKD]

1.5" wide is probably wider than you need. 1" is closer to the ideal width.

 

[wlfpck1]

1.5" wide is probably wider than you need. 1" is closer to the ideal width.

https://www.ebay.com/itm/Copper-110...655172?hash=item469f612784:g:RvQAAOSwqqRdpMY6

this is better hoping it'll carry enough current for me.

 

[ArthurEld]

MSC 110 Copper 1/8 x 3/4 x 72 $36

 

[wlfpck1]

I'm back and got the flat copper 110 stock. Bus bars installed and still get warm and still seeing voltage drop when only pulling 200W at 12V. I'm slowly giving up on these cells.

 

[cinergi]

I'm back and got the flat copper 110 stock. Bus bars installed and still get warm and still seeing voltage drop when only pulling 200W at 12V. I'm slowly giving up on these cells.

Then you almost certainly have dirty cell terminals that need polishing (3000 grit sandpaper) and cleaning. Make sure you do the same to the bus bars. I speak from experience and it's alarming how easy it is to have a bad connection.

 

[upnorthandpersonal]

What @cinergi said: the aluminium terminals oxidize almost immediately on contact with air, and aluminium oxide is an insulator. Sand it gently, immediately put some Noalox or similar on it (very little), sand down the copper bus bar where it makes a contact with the terminal and try again.

 

[wlfpck1]

What @cinergi said: the aluminium terminals oxidize almost immediately on contact with air, and aluminium oxide is an insulator. Sand it gently, immediately put some Noalox or similar on it (very little), sand down the copper bus bar where it makes a contact with the terminal and try again.

Thanks I'll try this and update. I'm amazed at how hard it is to make a solid connection. I figured flat bus bar against flat battery terminal was sufficient. No one talks about this being a struggle with a DIY battery, I am wondering how common this is.

 

[Zil]

the rule is the rule, but you can calculate the resistor you get and the loss.
you could go for 30mmx6 for example.
a

Could you provide a link to this "rule"? Thanks

 

[wlfpck1]

Thanks I'll try this and update. I'm amazed at how hard it is to make a solid connection. I figured flat bus bar against flat battery terminal was sufficient. No one talks about this being a struggle with a DIY battery, I am wondering how common this is.

So I took another approach. I got 2/0 wire used it as bars. Tried to pull 900W with my kettle. After about 10 seconds the only issue was the screw circled in my picture getting extremely hot. Had to shut off my kettle. The other terminals and terminals did not get warm.

 

[HRTKD]

So I took another approach. I got 2/0 wire used it as bars. Tried to pull 900W with my kettle. After about 10 seconds the only issue was the screw circled in my picture getting extremely hot. Had to shut off my kettle. The other terminals and terminals did not get warm.

Stainless steel screws?

 

[wlfpck1]

Stainless steel screws?

Zinc

 

[RCinFLA]

A 2.4mm x 20mm x 50mm pure copper strap is 0.017477 milliohms. That is about 10x less resistance then internal resistance of a 280 AH LFP cell.

There are various grades of copper, 101 is best with lowest oxygen content.

When it comes from China I would not bet that straps are pure copper. Likely have Zinc and Tin alloy mixed in. (a.k.a.. Brass mixed in)
Brass has five times higher resistance then copper.

Aside from actual strap, the contact with compression bolt, oxidized aluminum terminal, its flatness and surface roughness can add more resistance then actual strap.

Probably the aluminum terminal surface deserves the most attention. More then the actual strap.

 

[Hedges]

The steel screw was hot, but NOT the aluminum lug?
If so, suggests poor contact at bottom of lug and current went through screw.

 

[RCinFLA]

A small washer will just pucker the strap pressure around the screw head. It is better to put a large outside diameter thick stainless steel washer under screw head to ensure full cell terminal uniform surface pressure between strap and cell terminal (fender washers).

A good future discussion would be how to clean the aluminum cell terminals to ensure any oxidized aluminum is removed. I don't think using emory cloth or sandpaper is a good idea as it may embed grit into aluminum terminal surface. White vinegar will clean off aluminum oxide but need to avoid getting it into screw thread holes and need to follow up with alcohol cleaning. Make sure everything dry before connecting.

 

[Ampster]

Vinegar would work on my aluminum buss bars. I use 3M pads and blow off grit.

 

[Ampster]

The steel screw was hot, but NOT the aluminum lug?

It would help to use NoAlox, which is designed for copper Aluminum connections like that.

 

[wlfpck1]

It would help to use NoAlox, which is designed for copper Aluminum connections like that.

I am wondering how companies that sell 12V LiFePo4 batteries already assembled avoid bus bar heating issues. I have seen tear down videos and know the guts of their batteries are not much different than what I have built. I wonder if they are soldering their bus bars directly to the terminals so they avoid bus bar connection issues...

 

[HRTKD]

I am wondering how companies that sell 12V LiFePo4 batteries already assembled avoid bus bar heating issues. I have seen tear down videos and know the guts of their batteries are not much different than what I have built. I wonder if they are soldering their bus bars directly to the terminals so they avoid bus bar connection issues...

That sounds like a @Will Prowse question since he's done the teardown of more batteries that I've ever owned. Solder can be brittle and I would be reluctant to do that on a battery that is used in a mobile environment.

 

[Ampster]

I wonder if they are soldering their bus bars directly to the terminals so they avoid bus bar connection issues...

Aluminum doesn't solder but i have seen some sonic welds.

 

[Will Prowse]

Yeah, most are welded. Unless you buy something from aliexpress. But usually they are sized properly. Most of the time they are actually oversized.

I haven't seen a busbar soldered to any cell terminal. Even nickel strips that are soldered to a bms, are still spot welded to the cells.

Probably sonic weld or those laser welders. I saw one at bigbattery factory, it's nice. That's the most common method for these types of cells and terminals.

Edit: I read the thread and I would start by cleaning the terminals and busbars as mentioned by RC in FLA and ampster. The current carrying capacity of busbars mentioned early should be fine. Seems like something is not clean. Also feel the terminals. If one is wiggling because of a bad weld, that might be your problem.

Some of the older prismatic cells (sinopoly) would break internally if you tightened them too tight, or had a ton of vibration without compressing them. I don't think it is a problem here, but I would inspect those terminals like crazy.

 

[Freep]

This was going to be my response, so no need to type it again. "Flat" is not flat. Sometimes the cheap route isn't so cheap.

Yeah sometimes you do what you've got to do. When my cells arrived they didn't include enough buss bars to put them in parallel. So rather than wait around I pounded some pipe.

Is there any consensus on a good source for high quality buss bars in the USA?

 

[HRTKD]

Yeah sometimes you do what you've got to do. When my cells arrived they didn't include enough buss bars to put them in parallel. So rather than wait around I pounded some pipe.

Is there any consensus on a good source for high quality buss bars in the USA?

I think the problem with finding bus bars for batteries is the terminal center-to-center measurement. The bus bar may have to be specific to that battery.

This is why some of us are making our own battery bus bars out of bar stock.

 

[Hedges]

Yeah sometimes you do what you've got to do. When my cells arrived they didn't include enough buss bars to put them in parallel. So rather than wait around I pounded some pipe.

Is there any consensus on a good source for high quality buss bars in the USA?

In the theme of DIY, here are a couple sources of copper bars:

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

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Ready-made, Blue Sea is among the sources (for battery & load cable connections, not linking individual cells).
I bought some from an eBay vendor/fabricator. But optimum hole spacing depends on your terminal size.

For linking cells, I'd like to see mechanical compliance, so as to not stress the terminals, especially considering swelling/clamping.
I observed some of the commercial images show a lamination of many thin sheets, with a slight curve.

 

[HRTKD]

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