can't get bigger spot welder, can I layer strips instead?

wattwatt

Member
Joined
May 21, 2018
Messages
55
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 use0.5mm 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 weldup 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 achievethe thickness and some of thestrength of the current 0.5mm welded strips, can I simply spot weld 0.15mm x 10mm pure nickelstrips together(also, what's readily available to me via Amazon) layering 4 strips on top of each other andshifting each weld 4 to 5millimeters 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).
 

daromer

Moderator
Staff member
Joined
Oct 8, 2016
Messages
5,565
You can but it greatly reducera current since ut all reliefs on that first weld.
 

wattwatt

Member
Joined
May 21, 2018
Messages
55
daromer said:
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?
 

daromer

Moderator
Staff member
Joined
Oct 8, 2016
Messages
5,565
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.
 

Redpacket

Well-known member
Joined
Feb 28, 2018
Messages
1,265
Or maybe do a couple of solder joints?
 

daromer

Moderator
Staff member
Joined
Oct 8, 2016
Messages
5,565
you can potentially solder but thicker strips = more heat and stress. Its also a bit difficult to solder nickel strips.
 

Redpacket

Well-known member
Joined
Feb 28, 2018
Messages
1,265
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?
 

LithiumSolar

Administrator
Staff member
Joined
Oct 8, 2016
Messages
2,393
Redpacket said:
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.
 
Top