Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
can't get bigger spot welder, can I layer strips instead?
#1
I picked up a couple of 38120L LiFePo4 based batteries packs (flat top Headway) and I'm trying to replace the dead cells with good spares. The batteries use 0.5mm nickel strips, spot welded to make the pack (24v, 8s2p). I don't own a spot welder and the biggest readily available spot welder (Amazon) can only weld up to 0.25mm pure nickel strips (0.15mm if using the welding pen, which I'd have to use to weld in the center of the pack). To achieve the thickness and some of the strength of the current 0.5mm welded strips, can I simply spot weld 0.15mm x 10mm pure nickel strips together (also, what's readily available to me via Amazon) layering 4 strips on top of each other and shifting each weld 4 to 5 millimeters left/right for each layer (to avoid undoing the previous layer weld)??


P.S. - As per the application, these packs are likely going to be used in an e-bike or with an inverter to power part of my house temporarily (we have a winter storm coming this weekend so we're expected a power outage).
Reply
#2
You can but it greatly reducera current since ut all reliefs on that first weld.
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
Reply
#3
(01-08-2020, 05:40 AM)daromer Wrote: You can but it greatly reducera current since ut all reliefs on that first weld.

If I could get my hands on 0.5mm pure nickel - could I weld the same spot a couple of times until the strip is secure to the cells? If that won't work, what's the best I can do to build/re-build 38120L based batteries with a 0.25mm limited spot welder?
Reply
#4
You cant weld thicker at all. Best is to get hold of a proper welder. IF you need that high current out of the battery the spot weld need to sit properly.
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
Reply
#5
Or maybe do a couple of solder joints?
Running off solar, DIY & electronics fan :-)
Reply
#6
you can potentially solder but thicker strips = more heat and stress. Its also a bit difficult to solder nickel strips.
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
Reply
#7
I was thinking maybe use a short bit of copper wire, soldered to cell & nearest nickel strips? Eg like many folk use for their 18650 pack busbars?
Running off solar, DIY & electronics fan :-)
Reply
#8
(01-10-2020, 05:18 AM)Redpacket Wrote: I was thinking maybe use a short bit of copper wire, soldered to cell & nearest nickel strips? Eg like many folk use for their 18650 pack busbars?

Thick copper is very difficult to solder to cells in a way that won't create too much heat on the cell. Brass strips would be easier to solder, though they are less conductive than copper obviously and soldering to cells is still a bad idea in general.
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)