Kapton tape or heat shrink?

[donn_]

I need to insulate a bunch of 26mm cells, both A123 and Emoli, for use in C sized tubes.

What's best for minimum thickness, while still adequately isolating the cell's case from the body of the light?

Please specify type, in both cases.

I'll probably order the material from McMaster-Carr.

Thanks in advance,
Donn

 

[donn_]

No opinions?

 

[leeleefocus]

If it was me i would use heat shrink unless it will not fit. Most types of tape will keep the diameter smaller than the heat shrink but the heat shrink should give a much nicer looking and more robust finish.

 

[LuxLuthor]

Donn, the problem is you have very little tolerance in a stock Mag C. Heatshrink is more durable and protective than Kapton, but almost all of it that you will find is in a 5 mil (.005") thickness. 5 mil is about 0.14mm when it comes to shrink I have measured...but is doubled since it is on both outside measurements of battery diameter.

Typical Kapton comes in 1, 2, & 5 mil, but that does not include the adhesive layer. When you overlap edges--which is almost impossible not to do unless you go back with an Xacto knife and trim all edges flush--it will go beyond what you expected. Furthermore if you have a tight fit, sliding the Kapton covered A123 or Emoli 26xxx size cells in/out can easily tear and fuse-flash-weld inside.

Removing the sleeves from A123, I get about 25.78mm diameter. Emoli 25.88mm.

With a layer of "1 mil" Kapton on my Emoli it goes up to 26.15mm where there is edge overlap. That is also just about the same I.D. of the stock Mag C. The A123 has a tiny bit more clearance, but again it is not enough for me to use them comfortably--including frequent removal for charging.

For the safest operation, either you need someone to bore out the Mag C, & use heatshrink, or move to the Mag D.

 

[donn_]

Thanks!

I have some Stock C hosts, bored for shrink-tubed A123s coming in whenever the Ano GB finishes up, and those are the lights which will be using these cells.

I use 1" poly tube with o-rings for D tubes.

What about the material for the heat shrink? McMaster lists several different varieties.

 

[Mr Happy]

Excuse me if I just interject a small question here. But isn't a stock Mag anodized -- thus insulated -- in the inside? If you bore it, presumably that now leaves it conductive (unless re-anodized after boring)? This may be inconsequential, but it occurs to me that boring may substitute one weakness for another...

 

[LuxLuthor]

Mr. H,,

That is a good question. I actually do not know how good & reliable over time regarding electrical insulation from the anodization by itself...but with cells that can output 50A in a dead short, I don't want to test it, or worry about any scratches that are hard to see in a dark tube. Mainly boring was a consideration because the cells with shrink or overlapping Kapton will NOT fit, or the Kapton tears before long, and they get stuck.

Donn, you need 2" shrink (1.5" will not fit). You can either get it at CBP, or there is a thinner, clear version here that some of the RC guys use. If I was making a pack with Lithium cells, I would use balance taps...which is another concern with small C Mag body. These do not get out of balance as much as other cells, and don't have the explosive/fire risk, but series charging them can lead to imbalances. Worst case, after 10-20 charges, remove the shrink, check cells, & reshrink.

Edit: Donn, here is that post I was looking for that seems to be right up your alley that was from the RC Groups forum link, and he is not installing balance taps.

 

[Mr_Light]

Since you don't need heat resistance, why wouldn't you use something like clear packing tape which is wide, thin, and cheap?

 

[LuxLuthor]

Why do you think there is no heat issues? You can charge these A123 cells at 10Amps to nearly full in only 15 minutes.

 

[donn_]

Hi Lux,

That second link starts out with what looks like the pack I just dissected. Have you started on yours yet?

Anyway, I'm not going to be building packs or sticks, just wrapping the individual cells. They'll be charged individually, in a 2-place "Joe Charger" for now, and hopefully one with more cell capacity in the future.

 

[LuxLuthor]

Donn, yeah I have been using these cells since last year. I have probably bought 25 of them from various sources.