0.15mm by 30mm nickel strip amps?

[houseofdreams]

Hi

I'm in the planning / designing process of building a 10s3p 18650 battery, or a 10s2p 21700, that decision isn't made yet. The max amps that will be pulled from this pack, will be 15A, so not a lot. (300W motor, with 540W peak)

Online you can find multiple sellers, using small 7mm wide strips but I'm reading a lot about the amp draw between the p-packs, so my idea was to buy a 30mm wide, 0.15mm thick nickel strip and cut it to size to fit my battery design.

I allready saw the table on this forum, with the thickness a width of the most popular nickel strips, but it stops at 10mm. Is it as simpel as multiplying these values?

a 5mm strip can handle 3.1amps, a 10mm strip can handle 6 amps, so I assume that a 30mm strip should be able to handle 18amps? Or doesn't it work like that?

Here is the idea of how I want to make it


Thanks!

 

[harrisonpatm]

You're probably referring to Matador's nickel strip chart, which I will link for other people just seeing this thread and wanting more info.

a 5mm strip can handle 3.1amps, a 10mm strip can handle 6 amps, so I assume that a 30mm strip should be able to handle 18amps? Or doesn't it work like that?

It does kind work like that, kinda. There are other factors to consider, namely that you conductor is thin and wide, but as a rule of thumb, the number you'll want to focus on is the cross-sectional area of conductor.

My suggestion would be to build for your planned discharge, plus 20-50%. You said it'll be max 15 amps? Build it for 25, and you'll never have to worry about your strips heating up.

 

[docw009]

You didn't mention capacity, but if range matters, so does capacity.

On paper, you'll see that a 3P 18650 can have 10,5AH while the 2P 21700 can have 10Ah, but in real life they run lower. I've built and own packs that fit these sizes. I think you'll do better with 18650's. My Sanyo GA packs run just a little under 2.9AH/cell when riding to LVC on my ebikes. My Samsung 50E is around 4AH/cell. So that's 9AH vs 8AH, at a higher cell cost, call it $40.

If I were to buy cells for another small pack, I would choose the 50S over the 50E. Your 15A controller would run the 50E at 70% of rated current. That drops to 33% for the 50S. I would expect better life with the latter as long as you don't go much over 15A. At current cell prices, about $1/cell more or $10.

 

[houseofdreams]

Another question I have, regarding this topic:

series connections between p-packs, should be calculated to be able to carry the max amp that the load will demand of the battery, correct?

So if my load demands between 9 and 15A, the nickel strip between each p-pack should als be able to carry 9 to 15A. If I than look at Matador's table, a 10mm wide, 0.15mm strip will only carry 6A.

Below is a picture of the (bottom of the) battery pack, that came with the device.



The green series connections are just done with a 10mm wide strip, only the "bridge" from one half to the other is done by 3 strips. This cannot be a good design then I assume? Or am I being too cautious?

A YT video that was allready posted on this forum in another topic, shows this image


This is kind of logical, but I haven't seen this being done in many battery building videos that are available online.

 

[harrisonpatm]

series connections between p-packs, should be calculated to be able to carry the max amp that the load will demand of the battery, correct?

Yes

The green series connections are just done with a 10mm wide strip, only the "bridge" from one half to the other is done by 3 strips. This cannot be a good design then I assume?

I would agree, that no, this isn't the best design. Not impossible, but could be designed better.

A YT video that was allready posted on this forum in another topic, shows this image

This is kind of logical, but I haven't seen this being done in many battery building videos that are available online.

Because while, logically, stacking in this matter ensures enough material to carry the current, in practice this means you have a quadruple stack of nickel in one place. DIY spot welding packs is already difficult enough to make consistent current paths, and adding a quadruple stack is asking for more failure points.

Browse the copper-nickel sandwich thread and see if any of those variations is doable with your equipment.

 

[houseofdreams]

Browse the copper-nickel sandwich thread and see if any of those variations is doable with your equipment.

I see a lot of mentions of k-weld's in that article, so I assume a less capable spotwelder will not do the trick, so I think that's not an option for me. I'm not planning to build lot's of battery's, so I don't think spending 170$ on a spotwelder is going to be an option.