18650 pack safety

[cwah]

Hello,

I'm building my 18650 pack made of 14s14p pack:

It's going to be 196 cells made of NCR18650PF


I could use the 18650 brackets but I wanted something more compact. I save about 10% space without bracket.

I grouped them by series so that in case of chaffing there won't be short. Between each serie, I've added 3 layer of tape plus glue to minimise chafing. However it significantly increase the pack width...

Hopefully I won't have any issue!

 

[beast775]

Im guessing you need to go far ..

 

[Nobuo]

Hello,

I'm building my 18650 pack made of 14s14p pack:

It's going to be 196 cells made of NCR18650PF

I could use the 18650 brackets but I wanted something more compact. I save about 10% space without bracket.

I grouped them by series so that in case of chaffing there won't be short. Between each serie, I've added 3 layer of tape plus glue to minimise chafing. However it significantly increase the pack width...

Hopefully I won't have any issue!

Hi, not bad job!, too much energy in such compact space is fantastic

are you using pure nickel or nickel plated steel? also what is the thickness and wideness?

I just want to indicate a little appreciations. There are some potential dangerous spots depending on how the final insulating wrapping and installation will be made.

On the anodes I marked in the bottom red circle a tail of unnecessary nickel strip that is better if you cut to avoid a possible short, and on the upper red circle other piece of nickel that is bended in a sharp cutting bad position.

Also in blue circle I marked cells anodes where should have a spacer, or a little extra insulation.

These are neither a must, it all depends of the final build. (all for 18650 pack safety)

Thanks for sharing!!

 

[Nobuo]

This is an example of a 26650 Lithium manganese Dioxide (Li-Mn02) cell anode "self-short", and it is scaring dangerous

[youtube]nL2TT3darhY[/youtube]

 

[fellow]

His are Panasonic NCR18650PF, different animal. Probably among the safest cells out there. If you can make them pass 80'C, you are probably a magitian.

You can see the PTC safety "bulge" close to the plus pole. And that's only one of the many safety features it has.

193 cells, that's good for more than 135km on my ebike! My guess is 10kg, or thereabout. One can use the shrink tape in various dimensions to prevent damage due to vibrations. Glue seems effective too. I use PVC tube as an air shock absorber, but I form cells in cylinders (8s1p, 13s1p or 18s1p for example) and then put together. This way I'm not limited to their 7 cm width.

Nobuo: That deathcell looks like a terrorists wet dream !

 

[999zip999]

Be careful of the buss strips shorting on the positive end. I like using a gasket on the positive end. Lot's of stored energy.

 

[littleskull99]

Will you need a bms with these cells? Thanks

 

[The fingers]

This is an example of a 26650 Lithium manganese Dioxide (Li-Mn02) cell anode "self-short", and it is scaring dangerous

One of those set off in those gopher holes would sure get rid of them pests in a hurry. :wink:

 

[fellow]

Will you need a bms with these cells? Thanks

No need for BMS with Panasonic NCR18650PF. I'm using it without BMS (but with LVC set in controller) for more than one year. Those cells may (or may not) have "zero technology", but it is unwise to let them discharge down to 0V. Use the LVC set to 3.0-3.5 V/cell. There is not much energy in them under that voltage anyways. Upper limit is 4.2V, some people use 4.1V to make them live even longer. You may even check each cell periodically just to be at the safe side, it takes only few minutes.

 

[dnmun]

very poor quality of the spot welds. the guy has warned you about the short that is gonna happen so you should pay attention to him.

 

[Nobuo]

Will you need a bms with these cells? Thanks

No need for BMS with Panasonic NCR18650PF. I'm using it without BMS (but with LVC set in controller) for more than one year. Those cells may (or may not) have "zero technology", but it is unwise to let them discharge down to 0V. Use the LVC set to 3.0-3.5 V/cell. There is not much energy in them under that voltage anyways. Upper limit is 4.2V, some people use 4.1V to make them live even longer. You may even check each cell periodically just to be at the safe side, it takes only few minutes.

Maybe BMS it would be not completely necessary in this case with those cells, for avoiding a low voltage damage, if they stand as well as it supossed to do the under volting,

but once a paralleled group will get unbalanced with a higher Voltage, then the rest of the pack will be not fully charged because the charger will high voltage cut too soon.

So even in this case a BMS do a interesting job maximizing the capacity. with the great feature to limit the max amps continuous discharging and get more efficiency.

There are no reasons to use a 18650 pack without BMS as it is only a 4% - 8% cost invest with a completely significant role.

there are more appreciations to take into account: http://liionbms.com/php/about_bms.php

 

[cwah]

Yes I know the spot weld are not that nice... i'm using the chinese cheap one I had for 200usd.

the little extension I've let them on purpose so that I can easily solder sensing wires without warming the cell. I'll cut to shape after that...

Good idea not to have a bms...


So apart from the spot weld and little extension, it feeels quitr vibration proof?

 

[mfj197]

Cwah, is this for your 11 mile each way commute in London!? If so, why are you building a pack that big? I'm commuting 20 miles each way into London and using a 10s4p pack of the same cells you are using. Yes I am recharging at work because I use half the capacity on each leg, but 11 miles each way would easily be doable.

 

[cwah]

Because I'm not a super cyclist like you and the road is full of potholes...

I had an accident which lead to stiches on the head few months ago with a hybrid bike and now I aim for safety and comfort

 

[DrkAngel]

3" duct tape, form fit to parallels, allows in series to fit tightly with durable insulation between different voltage parallels.
I then stabilize entire build with clear boxing tape that allows visible inspection of all tabs and wires.
Reasonably sharp multimeter leads can poke through boxing tape for voltage confirmation-testing.

But in 8 years of 18650 pack building, I have never encountered any "rub through" instance. I always wrapped cells, serial and parallel, tightly together with clear boxing tape.

Considering the potential ... better safe than sorry though ...

 

[cwah]

Do you mean you have never put any insulator between each serie amin 8 years and never had any issue?

 

[littleskull99]

Do you have a link to purchase these cells? Thanks.

 

[DrkAngel]

Do you mean you have never put any insulator between each serie amin 8 years and never had any issue?

Yes.
See -DrkAngel Battery Builds - Roundup

 

[cwah]

Your bike is in a vibration prone environment and you have a difference of potential separated only by a layer of shrink wrap... and a bit of glue?

I think it's like the safety belt, most of the time you won't have accident, but if one day it happens you'd be happy to have it.

I'd be worried that if any of the glue comes loose, the whole pack is subject to failure.. or worse.

 

[cwah]

Do you have a link to purchase these cells? Thanks.

Nkon.nl. they do good price when you buy bulk

 

[district9prawn]

I have a couple of 18650 packs built just like this with tape and glue rather than cell brackets. Has been fine for over a year.

 

[cwah]

The pack now:
I protected each serie with tape to protect against short:

I tapped the whole to avoid wires chafing or even the nickel strip may touch other things:

Then used a long jubilee clamp to secure the cells.

And created my bag out of heavy duty tarpaulin:

 

[Nobuo]

Now looks better, beautiful packaging!

How much amps are you feeding with the controller?

does it include a BMS installed?

 

[cwah]

Only 35A for now. I'll have shortly a 50A controller coming... but my aim was more range than power. At peak power (1700W) I'm using about 1C discharge for the cells... they shouldn't even be warm :lol:

I have crazy 22 miles commute and sometime over 40 miles to do in a day. Considering I'm using about 40wh/mile, I can sometime use more than 1600wh without charging, which is almost depleting my pack.

The goal is obviously to only do shallow discharge, and charge the cells to 4V so that it last as long as Tesla's 7 years warranties ones!

I'm not using BMS, but I'll connect sense wires to 2 cell logs:

Extended directly in front of my handlebar! Much better I think

 

[Xer0]

90% battery, 10% tape!

btw, does it makes sense to use single cell protection?
by either a round pcb or just a simple ptc fuse on each