Battery terminals not flat, raised outer edge. How to fix bad contact?

[Aridom82]

So i am discovering how essential is to have very good contact between the busbars and the battery.
The problem is that the battery terminal does not have a flat surface for the busbar to rest on. It has like a raised outer edge and when you torque the busbar in it just 'bites' a circle in it. See picture.
So how do you guys deal with this?
I was thinking in filing a little bit the outer edge and then putting a thin copper washer with some battery grease.
I am not sure that it will get it to work to the 160 amp target though.

 

[chrisski]

There is a thread on this forum from a couple years ago about using copper washers on the raised terminals on those batteries.

 

[Aridom82]

There is a thread on this forum from a couple years ago about using copper washers on the raised terminals on those batteries.

i am trying to find it with no luck

 

[SamDeleted]

Is it ACTUALLY making a bad connection? Can you test the resistance?

 

[chrisski]

Is it ACTUALLY making a bad connection? Can you test the resistance?

How would you test resistance?

 

[Aridom82]

Is it ACTUALLY making a bad connection? Can you test the resistance?

My ohmmeter is not sensitive enough to tell me milliohms.
I am asuming that is a bad connection because there is no full contact unless you torque the hell out of it.
Even if i measure a very low resistance, what happens when you put 160 amps through it?

 

[SamDeleted]

How would you test resistance?

Well I figured ohmes on a multimeter , unless that won't work for some reason...


Terminal to terminal
Length of the link bar
Terminal to end of link bar

With those three numbers you should be able to work out how good the connection is ?

 

[SamDeleted]

what happens when you put 160 amps through it?

Possibly a hot connection, maybe a bit of melting ?

 

[Hedges]

My ohmmeter is not sensitive enough to tell me milliohms.

Where there's a Will there's a way.

Even if i measure a very low resistance, what happens when you put 160 amps through it?

Possibly a hot connection, maybe a bit of melting ?

While putting 160A through it, just measure voltage with your meter and do a little math.

Voltage drop will show up faster than melting (most of the time). Temperature rise is the integral of power over time, divided by thermal mass (neglecting conduction, convection, etc. of course.)

 

[chrisski]

i am trying to find it with no luck

Strangely I can’t find the thread on either this forum or any info on Google. I think it was Michael B Caro who came up with the idea. I think his account got deleted and perhaps the thread got deleted with that.

If it’s the info is not available, perhaps copper washers was a bad idea.

 

[Aridom82]

While putting 160A through it, just measure voltage with your meter and do a little math.
Voltage drop will show up faster than melting (most of the time).

That is a bit scary. I think the best to do is try to improve the connection as much as possible, and then with the bms connected do charge/discharge test with incremental amps watching with my thermal camera.

I think the 1mm copper washer between battery terminal and busbar makes sense, i could electroplate them with nickel just a little bit to avoid the well known galvanic corrosion.

 

[ArthurEld]

I bet that makes great contact. You could sand it off but I think they did it like that on purpose.
I'm just guessing

 

[fafrd]

That is a bit scary. I think the best to do is try to improve the connection as much as possible, and then with the bms connected do charge/discharge test with incremental amps watching with my thermal camera.

I think the 1mm copper washer between battery terminal and busbar makes sense, i could electroplate them with nickel just a little bit to avoid the well known galvanic corrosion.

Aluminum has higher redustivity than copper but the studs themselves are already Aluminum.

The advantage of an Aluminum washer is that it is soft, so the steel ‘ridge’ will easily bite into an aluminum washer so that the stell entire stud surface is in electrical contact with the bottom surface of the aluminum washer.

Plus, a properly-sized aluminum washer will lose less contact area to the ‘slot’ in the busbar and will extend under more of the busbar end, so mm^2 of contact area should be higher than without a washer at either side (top and bottom) and overall resistance may actually be lower regardless of the added resistance from a thin layer of aluminum (even in the case that the ridge is not causing the busbar to only contact along the perimeter with no washer.

 

[Aridom82]

Aluminum has higher redustivity than copper but the studs themselves are already Aluminum.

The advantage of an Aluminum washer is that it is soft, so the steel ‘ridge’ will easily bite into an aluminum washer so that the stell entire stud surface is in electrical contact with the bottom surface of the aluminum washer.

Plus, a properly-sized aluminum washer will lose less contact area to the ‘slot’ in the busbar and will extend under more of the busbar end, so mm^2 of contact area should be higher than without a washer at either side (top and bottom) and overall resistance may actually be lower regardless of the added resistance from a thin layer of aluminum (even in the case that the ridge is not causing the busbar to only contact along the perimeter with no washer.

Ok, so putting an aluminum washer makes even more sense. I have a lot of it in my shop. I can make my own washers to the exact size and dont lose a mm2 of contact. No anodized stuff ofc.

 

[Brett V]

Thread 'Improving Contact Area on Welded Stud Pads'
https://diysolarforum.com/threads/improving-contact-area-on-welded-stud-pads.26869/

 

[Aridom82]

Thread 'Improving Contact Area on Welded Stud Pads'
https://diysolarforum.com/threads/improving-contact-area-on-welded-stud-pads.26869/

Aww wonderful stuff. Thanks!

 

[ArthurEld]

Thread 'Improving Contact Area on Welded Stud Pads'
https://diysolarforum.com/threads/improving-contact-area-on-welded-stud-pads.26869/

Lots of arguing in there. I saw someone said the studs come out. That would make it easy to file the terminal flat

 

[Aridom82]

Well i went through the whole thread. The basic idea is to put an aluminum washer with the center hole size that includes the 11 mm smaller base of the stud, so when you screw the busbar on top you have increased greatly the whole contact area. Just have to make the washer the same thickness of the exact difference in height. People were pointing out that is very close to 2 mm.

 

[Hedges]

That is a bit scary. I think the best to do is try to improve the connection as much as possible, and then with the bms connected do charge/discharge test with incremental amps watching with my thermal camera.

Thermal is slower to respond. Resistance (voltage drop) is instantaneous, and will change if contact is deteriorating.

Scary? Then start with less than 160A. Try to get at least 100 counts of LSB on your volt meter. Read watts or amps on inverter (assuming you don't have clamp ammeter) or measure resistance of AC load and voltage applied.

If mV counts start running up faster than battery voltage droops, abort the test and address the problem.


I would plug a couple electric radiators into the inverter; they can be set for 600/900/1500W each.

The advantage of an Aluminum washer is that it is soft, so the steel ‘ridge’ will easily bite into an aluminum washer so that the stell entire stud surface is in electrical contact with the bottom surface of the aluminum washer.

Hope there is no steel in the path, poor conductor. Only bolt itself should be steel. It may have a head under an aluminum cap.

 

[Brett V]

Lots of arguing in there. I saw someone said the studs come out. That would make it easy to file the terminal flat

Yeah, it had its moments. I originally came up with the crush washer idea but don‘t know if anyone ever tried it. I have a pair of 16 cell batteries with the round studs and have had zero issues. Each stud and mating surface on the bus bar was cleaned with 000 steel wool and alcohol. I used a calibrated dial type torque wrench, torqued to 10 nm. (I think)

The BMS is only good for 100 amps continuous so I can’t test more than that. Have pushed them enough to warm up a 1/0 cable and using a thermal camera, the studs and bus bars are at the same temperature as the cells.

I have 32 new cells with the flat square landing pad for the bus bars and plan to use the same procedure. it will be interesting to see if they behave any differently.