DIY bus bars using twisted copper cable

[ScottWCO]

Hey gang -

I’ve got some LiFePo4 cells on order, and they’ll come with the usual set of bus bars and posts. But I’ll be building these packs to go into a van build, so beyond the usual concerns of the effects of expansion/contraction of cells on the bus bars and posts, there’s the added factor of vibration/rattling around.

I’ve been seeing where some folks have been using 4awg cables instead, crimping ring terminals on the ends, to handle both situations.

Lately I’ve been working part-time for a couple of friends who have a business making thermal transfer solutions for aerospace use, and much of what they make is made largely out of twisted copper cable. I chatted these guys up this morning about how well that material would work as a substitute for the usual bus bar, and they say it would be the equivalent of the 4awg cabling mentioned above.

I wanted to throw this out to the peanut gallery and get opinions, so have at it

 

[OffGridInTheCity]

I use 6awg soft drawn, stranded, bare copper wire for my 18650 pack bus-bars with good results. I think the key thing is you have to fabricate fasteners to your LifePo4 cells which is a lot of work compared to simple metal plates with screw holes. Other than the extra work - if bent a little between cells it should be flexible etc and work great.

 

[Colonel.lp]

Should work great as long as you have proper crimped lugs.

 

[ScottWCO]

I use 6awg soft drawn, stranded, bare copper wire for my 18650 pack bus-bars with good results. I think the key thing is you have to fabricate fasteners to your LifePo4 cells which is a lot of work compared to simple metal plates with screw holes. Other than the extra work - if bent a little between cells it should be flexible etc and work great.

Bare - no heat shrink? No brush-on insulation (silicone I think? I'm trying to remember what my guy mentioned when I quizzed him on the topic)?

 

[Batvette]

Get some copper pipe couplers, insert wire, smash them with a hammer and solder them. Youll have no issues other than lacking foo foo prettiness.

 

[Steve_S]

Chuckles, sorry but THAT is a huge can of worms... All Lithium Based Batteries are Millivolt & milliohm sensitive. The whole expansion & contraction thing is also terribly overblown, as long as the cells are Bound Together (Hand Tight Squeeze is GOOD ENOUGH) and taped with wide FibreTape or similar and put into a snug box/casing you won't have issues. 99% Of prebuilts (even Victron and such) use Hard Bus Bars.

 

[12VoltInstalls]

Bare - no heat shrink? No brush-on insulation (silicone I think? I'm trying to remember what my guy mentioned when I quizzed him on the topic)?

I don’t even like bare safety grounds
(well except where a bare safety ground increases the chance of clearing a fault. For that reason I like steel electric boxes in a shop or like in a jobsite trailer.

 

[HRTKD]

My two 4s 280 Ah LiFePO4 batteries use the standard bus bars between cells. I have a compression fixture on each battery. This in an RV trailer that sees some very rough roads. I've had zero problems with the terminal screws on my batteries coming loose.

As long as the cable you have access to can support the currents that the battery can produce, go for it. But don't use cable thinking it's better for your batteries (assuming you have the cells compressed).

 

[JJJJ]

I had a piece of heavy duty awg with soldered heavy duty copper lugs. Initially the results were encouraging charging at 10.5 amps. However after about an hour or so saw diminishing returns. Guess is that this was due to growing resistance. Went back to the bus bar.

 

[Colonel.lp]

I had a piece of heavy duty awg with soldered heavy duty copper lugs. Initially the results were encouraging charging at 10.5 amps. However after about an hour or so saw diminishing returns. Guess is that this was due to growing resistance. Went back to the bus bar.

How do you mean diminishing returns?

I've been using wire/lugs for busbars on an 2p4s of 280ah eve cells. Yes resistance is slightly higher, but 6 months of charging at 80amps(6hrs) once a week and no weird things going on at all, BMS voltages are milliamp correct, ∆ stays between 5 and 10mA.

I don't disagree that busbars are less prone to an issue, and will certainly go back to them when I find some flexible ones with a hole rather than a slot, bit properly made cables with lugs are not a disaster.