Building a pack with 33140 Gotion 15ah cells

[mattman]

I have some of these Gotion 15ah LiFePo cells I want to build into 24v packs.

Has anyone worked with these? The terminals are copper, so I guess I could spot weld or solder to them. I have a spot welder and nickel strip, considering buying copper strip. I guess there are challenges welding the dissimilar metals. Any input? Thickness / width of copper or nickel? Any other tips?

My plan is to have these on hand, and ready to plug in to an APC BR1350MS UPS unit (1350VA / 810W output), so that in the event of a power outage that lasts longer than the AGM batteries in the unit, and have a switch to select my external pack. Since the output amps of the UPS would be low, I would not need the strips and wiring to handle nearly the amps the cells can put out.

 

[OffGridInTheCity]

I have some of these Gotion 15ah LiFePo cells I want to build into 24v packs.

Has anyone worked with these? The terminals are copper, so I guess I could spot weld or solder to them. I have a spot welder and nickel strip, considering buying copper strip. I guess there are challenges welding the dissimilar metals. Any input? Thickness / width of copper or nickel? Any other tips?

My plan is to have these on hand, and ready to plug in to an APC BR1350MS UPS unit (1350VA / 810W output), so that in the event of a power outage that lasts longer than the AGM batteries in the unit, and have a switch to select my external pack. Since the output amps of the UPS would be low, I would not need the strips and wiring to handle nearly the amps the cells can put out.

Did you get these from BatteryHookup? I see they are listing them.

I've always soldered my 18650 cells with good success. A solder like this - https://www.amazon.com/dp/B00DE2QVIG - doesn't need tinning and doesn't corrode, even after 8 years the packs in my powerwall are perfectly OK.

You'll need at least a 100w iron like this - https://www.amazon.com/dp/B002I7X7ZS Maybe more but doesn't look like it to me.

I first apply a dab of solder on the cell ends and then come back and solder on the fuse wire -> buss, and this technique has not damaged any of the 14,000 cells I've soldered up.

Looks you like need 16s and some kind of holders or wrap to keep the (metal?) cell skins from actually touching as they may be the negative? / you don't want shorting thru the skins.

Let us know how it goes - pics always welcome.

 

[mattman]

Did you get these from BatteryHookup? I see they are listing them.

I've always soldered my 18650 cells with good success. A solder like this - https://www.amazon.com/dp/B00DE2QVIG - doesn't need tinning and doesn't corrode, even after 8 years the packs in my powerwall are perfectly OK.
View attachment 33777
You'll need at least a 100w iron like this - https://www.amazon.com/dp/B002I7X7ZS Maybe more but doesn't look like it to me.
View attachment 33778


I first apply a dab of solder on the cell ends and then come back and solder on the fuse wire -> buss, and this technique has not damaged any of the 14,000 cells I've soldered up.

Looks you like need 16s and some kind of holders or wrap to keep the (metal?) cell skins from actually touching as they may be the negative? / you don't want shorting thru the skins.

Let us know how it goes - pics always welcome.

Yes, I did. I am thinking of getting more. Should be 8s for 24v, right? I am thinking 8s5p. I am looking at some pre-tinned, copper strips here. Wondering if I could spot weld on a low setting. I bought one of the super cap spot welders from BH, have not used it yet.

Pure Copper Tinned Solar PV Solder Tabbing Strip Bus Bar Flat Wire Ribbon | eBay

Heavy Duty Tinned Copper Tabbing Wire. Great alternative to nickel tabbing wire for 18650's, etc, when you want to solder instead of spot weld for zero resistance. Tinned copper makes soldering easy and safe.

www.ebay.com

I think I could use fairly thin strips for parallel connections, the a thicker busbar for the serial, right?

I was considering connecting eight sets of 5p, then putting some insulation between each row of 5 I want to series with the next. I found some 38mm spacers, but only in China so far. Don't really want to wait for them.

Thanks for the info / links.

 

[OffGridInTheCity]

Yes, I did. I am thinking of getting more. Should be 8s for 24v, right? I am thinking 8s5p. I am looking at some pre-tinned, copper strips here. Wondering if I could spot weld on a low setting. I bought one of the super cap spot welders from BH, have not used it yet.

Yes, 8s for 24v

Pure Copper Tinned Solar PV Solder Tabbing Strip Bus Bar Flat Wire Ribbon | eBay

Heavy Duty Tinned Copper Tabbing Wire. Great alternative to nickel tabbing wire for 18650's, etc, when you want to solder instead of spot weld for zero resistance. Tinned copper makes soldering easy and safe.

www.ebay.com

I think I could use fairly thin strips for parallel connections, the a thicker busbar for the serial, right?

Sure. For example, a 'battery' for me is made up of 100p units using 30awg (fuse) wire -> buss. The buss is 6awg. The idea is say... 50a on the bus and 50a / 100cells = 0.5a per cell -> buss - e.g. each 0.5a cell connection to buss doesn't need a thick connection but the buss needs to handle the whole 50a.

You can do the calcs for you're situation, you can lookup mm2 of the 'think copper' to verify the amps it can carry on a wire guage chart like this - https://www.powerstream.com/Wire_Size.htm - see the mm2 column.