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Busbar solder not sticking
#1
I have been using 12-2 Romex wire, removing the outer yellow casing, removing the ground wire that is wrapped in paper, and then stripping the other two wires of their insulation to get 3 strands of bare copper wire. 

I have been using 3 of the 12 gauge wires twisted together in my bus bars. The problem I have had with past packs, discovered when I had to dismantle a "underperforming pack", is that the solder does not appear to adhere tightly to the busbar.  I have tried scarifying the busbar with a file along the areas where the soldered fuse  wires go, but this has still occurred to some degree.  I am wondering is there is some sort of invisible coating on the copper wire that is preventing a good adherence of the solder.  In my new build, I am heating the busbar on the kitchen natural gas cooktop burner until it has a slight orange hue and then waiting until  that coloration disappears, leaving the bare copper with a slightly gray hue.  I am then using fine sandpaper to scarify the wire, and wipe off any dark residue.  Will see if this solves the issue.

Is anyone else having this problem, or taking similar steps to resolve?  Is there a better way?
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#2
If you've used a file to get the outer layer off, you probably need to add more flux and/or hotter iron. A 35W iron won't work. A 65W will struggle. Also the tip needs to be large, not the needle sized tip that is standard.
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#3
I also occasionally had similar issues with soldering fuse wire onto smooth solid core copper. Seemed like a solid connection, but somehow detached later on. I've since switched to using 7-strand 5.5mm^2 wire. Solder wicks and sticks much easier & better, and the wire is also much easier to handle (bending, cutting, etc).
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#4
I use.... 
* wire - 6 AWG Soft Drawn, Stranded, Bare Copper Wire  - https://www.wireandcableyourway.com/6-aw...-wire.html
* solder - Kester 24-6337-0027 Solder Roll, Core Size 66, 63/37 Alloy, 0.031" Diameter -  https://www.amazon.com/gp/product/B0149K...UTF8&psc=1 
* soldering iron (100w with flat tip as mentioned above) - Weller W100PG Weller Farenheit Heavy Duty Soldering Iron with CT6F7 Tip, 100 Watt, 700  Degree https://www.amazon.com/gp/product/B002I7...UTF8&psc=1


No need for scraping/cleaning/preparing-of-any-kind (rosin is in the solder) on either the busbar or the cells. 27awg (negative side) and 30awg (fuse wire side) wire solders up nicely to cell and busbar.  Have soldered 8,000 cells to date with some nearing 2yrs old and all is solidly attached / no corrosion / no problems. Unsolders/re-solders easily for maint. There are issues with DIY powerwalls, but this is not one I loose sleep over Smile
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#5
High Power high mass soldering iron and rusin core solder and There wont be an issue. 150w + is Good to have
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#6
(03-03-2020, 02:46 PM)drspeakman Wrote: I have been using 12-2 Romex wire, removing the outer yellow casing, removing the ground wire that is wrapped in paper, and then stripping the other two wires of their insulation to get 3 strands of bare copper wire. 

I have been using 3 of the 12 gauge wires twisted together in my bus bars. The problem I have had with past packs, discovered when I had to dismantle a "underperforming pack", is that the solder does not appear to adhere tightly to the busbar.  I have tried scarifying the busbar with a file along the areas where the soldered fuse  wires go, but this has still occurred to some degree.  I am wondering is there is some sort of invisible coating on the copper wire that is preventing a good adherence of the solder.  In my new build, I am heating the busbar on the kitchen natural gas cooktop burner until it has a slight orange hue and then waiting until  that coloration disappears, leaving the bare copper with a slightly gray hue.  I am then using fine sandpaper to scarify the wire, and wipe off any dark residue.  Will see if this solves the issue.

Is anyone else having this problem, or taking similar steps to resolve?  Is there a better way?
Hello Drspeakman,

I think you might be overheating the copper.  With soldering electric stuff, I don't get the copper that hot.  When I am working on copper plumbing or copper Air conditioning things, when I was learning I would overheat the copper.  I am not 100% sure, but it kind of sounds like you are overheating the copper.  When I would be using a torch with plumbing flux, if the flame gave off a green flame, it meant that I had overheated the stuff.  The only way I could get a good joint would be to let everything cool off,  Scrape off all the grey/black oxidation with wire brush, sandpaper, reflux it (plumbing flux not electrical flux), then reheat it and try not to get the joint as hot. 

So in your case I would scrape off all the black/grey stuff with a wire brush, and I would flux the joint with rosin flux or rosin flux with RA additives.  I would then heat it up with a powerful soldering iron, or torch, but only heat it up till solder flows.  After the solder flows, I would remove and add heat just to keep the solder flowing, not overheating it, and only keep the heat on till you get enough solder to flow through the joint.  If you use RA modified rosin flux, I would use alcohol to remove the excess flux from the joint.

Good Luck,
Rip
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#7
(03-05-2020, 04:22 AM)Riplash Wrote:
(03-03-2020, 02:46 PM)drspeakman Wrote: In my new build, I am heating the busbar on the kitchen natural gas cooktop burner until it has a slight orange hue and then waiting until  that coloration disappears, leaving the bare copper with a slightly gray hue.  I am then using fine sandpaper to scarify the wire, and wipe off any dark residue.  Will see if this solves the issue.
I think you might be overheating the copper. Rip

I missed this the first read through, and I agree with Rip. Don't use a cooktop gas for heating the wire. Fire is not a friend of wire soldering, especially for prolonged periods of time.

finishing.com Wrote:Between room temperature and 100 °C copper forms a thin Cu2O layer; at about 150 °C a complex oxide forms Cu3O2; and at 200-300 °C CuO forms. Significant oxidation occurs when CuO begins to form

This is in reference to direct heat to copper, not soldering. Placing the copper over an open flame is direct heat and causing super high temps in work. If it's changing color, you are waaaaay to hot for copper wire. Not only are you rapidly oxidizing the copper, you are also making it more brittle.

During the manufacturing process of house wire, there is no extra coating added to the wire before it's sleeved. However, there may be some residual oil that is used during the cooling process. If anything, a gentle sanding with the file would be plenty, but not really necessary.

I stand by what was mentioned before, you need a bigger iron to get the wire hot enough for long enough time for the solder to adhere to it. Otherwise, the copper will wick the heat fast away from the solder connection, making the solder actually partially solidify at the point of contact. This is called a cold joint.

You should have an iron that has a large barrel like this 100W iron:
 

Not using the standard thin barrel that you get from Walmart or a craft store.
Having an iron with a large tip also helps a lot
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#8
Thanks for all your comments.  Very helpful.  I am using the exact soldering iron recommended.  I believe in my early pack construction 2 years ago, I did not scarify the copper wire with a file over the soldered areas, and that is the culprit.  I have only disassembled 2 of the original 14 packs (100p14s) and that is when I discovered the issue.  I am going to continue using the Romex household 12/2 wire as I already have it, and make my own busbars by twisting 3 wires together, but I will no longer heat them up after initial production.  I am just going to scarify with a file over those soldered fuse wire areas.  Seems to be sticking very well right now.  I am building my second powerwall, and have 12 more packs to assemble. 

Next question is how what to do to connect up and use this second wall, ie do I need another Schneider Conext 4048SW inverter and PCM 60X charger, or can I connect both powerwalls in parallel and use my current nine rooftop (maxed out) 280 watt solar panels and inexpensive night grid power ($0.15 per KWhr) to charge up both packs as a single 48v battery, now just with double the amperage.  I am going to make a new post in the appropriate section to address this, as I know it is off topic, but feel free to respond here if you think you have a quick and simple answer. 

Thanks again, love this group!
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#9
Probably should create a 2nd thread for the 2nd question, but quick answer is:
You can parallel solar inputs and parallel battery banks. Inverter outputs cannot be paralleled unless they are smart enough to do so. This usually requires an interconnect between them.
Otherwise, 1 inverter runs one circuit panel, the other inverter runs the another circuit panel
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#10
Science experiment:

Created 4 small sections of busbar and soldered 3 small wires on each one, about same distance apart as would be between the cells in a pack, and all about the same length.

Bar #1 heated on natural gas burner on stove to remove any surface material

Bar #2 same as above, but scarified with a file over the areas soldered

Bar #3 no heat, no scarification, just soldered

Bar #4 no heat, scarified, then soldered

Result:  Only failure to stick well was preheated and not scarified busbar.  Stuck very well on untreated copper wire, scarified untreated copper wire, and on scarified preheated wire.  I am going to discontinue any pretreatment except to scarify with a file.

So, my next thought is that I may be causing the soldered areas to unstick when I am adding the extension to the busbars with a copper pipe butt splice.  I use a more malleable 10 gauge stranded copper wire to extend the busbars and then add Andersen connectors on the ends.  I use a blow torch to add solder into the ends of the butt splices after thoroughly crumping over the wires.  It may be this heating process to add solder into each end of the butt splice that is extending down the busbar and causing the soldered areas to loosen up.  At least this is my current working theory.  I am going to do this process first, and then do the soldering of the cells to the busbar as the LAST step, hoping this will eliminate the issue.
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