Terminating the 15Ah and 20Ah Cell-Man cells

[liveforphysics]

Luke,

The melting point of that silver solder is 655 deg C, which is 1211 deg F, so it'll be fine.

Jeremy

Ohh! lol. I totally missed that C . 1211f should be about perfect for melting point.
Thank you Jeremy!

 

[cell_man]

Just thought I'd better update with some pics of a pack that I assembled. It's a 12S 15Ah pack. It weighs in at approximately 5.2kg including terminations, BMS etc but without any mechanical protection for the cells. Termination parts weigh about 220g for this 12S pack so less than 20g per cell.

View attachment CIMG0645.JPG

View attachment CIMG0646.JPG



This packs dimensions are 222 * 156 * 81mm, not bad I reckon With this termination method it lends itself to easy add/modify BMS balance wires or change a cell. No special tools are required for assembly, just a little care and some time.

Also I really do think that many have overlooked the 15Ah cells. They are every bit as strong as the 20Ah cells at current levels up to at least 100A. It's only when you start to pull really serious current that the 20Ah cells will give noticeably less sag. The capacity is actually closer than the specs suggest as well. I ran my 15Ah pack to the BMS cut off today and it gave me 16Ah on the CA and that's running dual 25A controllers with dual Puma 500W motors.

 

[Ykick]

I'm ready to try some 15Ah pouches!

 

[chroot]

Make one 24s 72v 15Ah for me :lol:

 

[regmeister]

deleted

 

[Elithion]

I can get those interconnecting PCBs custom made but without a good method to solder the tabs

Soldering? Who said anything about soldering. Please reread the installation page:
http://lithiumate.elithion.com/php/install_cell_board_pouch_single.php#Installation

There is no soldering: it's just clamping.

 

[gestalt]

Yes, something along the line of a specialized A-clip, that way there is more flexibility when using various cell compression techniques. Ease of cell swapping would be clutch as well, I'm thinking of using a brass clip with the wires clamped on to the rear of the clip. Have a simple tool to release the clip.

 

[regmeister]

deleted

 

[cell_man]

I can get those interconnecting PCBs custom made but without a good method to solder the tabs

Soldering? Who said anything about soldering. Please reread the installation page:
http://lithiumate.elithion.com/php/install_cell_board_pouch_single.php#Installation

There is no soldering: it's just clamping.

Yeah your method using the clips looks very nice and quick. I was pointed towards some soldered pouch cells on your installation manual, which was why I had made that comment. You don't happen to sell those clips loose do you? I'd like to have a play with them to see how it works out. The only negative aspects I could possibly see to the clips is that they might take up a little more space than the clamping method I've made, also not sure there's sufficient space between adjacent terminations on a 1p pack with cells under 7mm thick. Thanks for taking the time to respond

 

[peterperkins]

I like the clip method as discussed previously, not sure if the elithion clips would work on the 15/20ah cells tabs?

I can't afford to invest £1000+ in getting some special clips made to the earlier spec unless someone want to contribute/help?

Any millionares on here?

Cell_Man's assembled pack looks nice.

I will need a 16 cell pack so may be interested in buying the bits to assemble 3 x 16 cell packs. Or I might just solder them and sod it!

What was the final consensous on the exact type/make of solder/flux reqd?

 

[regmeister]

deleted

 

[MitchJi]

Hi,

Be careful of rubbing and vibration!:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=17497&p=256874#p256590

I am pretty sure my Ping died from vibration and shock rather than heat. All bad cell groups were at the ends of the pack, and there were obvious signs of fluid leakage at the bottom of the pack.

Yeah, that's why I put foam liner at the bottom where the battery sits. (Or, if it's in a bag, I don't use anything because the bag material itself has "give" to reduce peak shocks and evenly distribute the forces.)

A layer of cork sheet at about 1/4 inch thick is a good dampening material - which I use in my pack.
Assuming you charge every 20 miles, that's only 250 cycles you had on your Ping. Significantly lower than the claimed 1000+.

I was using that interlocking foam they sell at Costco for playrooms and such. Tried to make it tight enough that the pack wouldn't move around. Even so, the constant jarrring somehow wore down the cells.

Lots of rubbing goes on inside the battery bag or box. Hopefully the shrink wrap used now will help with that vs the duct tape that was on the early packs.

That's why I make the super tight fitting inner boxes custom fit to my pings. There is just no movement at all, and all the rubbing goes on on the outside of the tight box. I have some areas on ping 1 that rubbed quite a bit of the aluminum box away, but remove the battery, and the duct tape still looks cherry.

On some nicad packs I have, it didn't take long to start putting some serious rub marks on the cell cans. I didn't protect them so good, and quickly realized I needed to do more, even with metal canned cells.

 

[liveforphysics]

A way to prevent cell/cell rubbing is the method used on all the RC packs. Double side tape between layers.

A bit of carpet tape can electricly isolate, and end any cell/cell chaffing.

 

[cell_man]

A way to prevent cell/cell rubbing is the method used on all the RC packs. Double side tape between layers.

A bit of carpet tape can electricly isolate, and end any cell/cell chaffing.

I didn't think cell to cell rubbing would be a problem if it was tightly packed, but yeah I don't suppose it can't hurt. I was more concerned about alumium sheets between the cells causing problems, but if they were gonna be connected to the outer case, sticking them to the cells would make it very difficult to get them correctly lined up. I've just used a sheet of plastic around each cell on the 3p pack as I didn't want to take any chances.

 

[olaf-lampe]

Hi Paul,
don't try to fix the cooling sheets to the outer case! Everything must have a way to 'breathe'. Some cells do change their thickness ~ 4-10% depending on SOC. I'm not sure about your's...
-Olaf

 

[oatnet]

I am building a 16s pack of the 16ah cells. The immediate use will be on my BMC V3 bike so probably only 50a discharge, but I'll fuse it for 200a. I have a custom padding idea in mind, and the battery box will be mounted to the upper stanchions of a boxxer fork so it should get pretty soft ride.

Since the clip idea first came up, I have been envisioning making clips from the plastic spines that slip onto cheap report binders. I figure a layer of heat shrink will keep the jaws of the spine closed firmly on the tabs, keep them from sliding off either end, and take a lot of the compression load off the plastic.

I finally got a few moments to work on them, so I put some tab condoms (heat shrink folded over and secured with painters tape) on a pair of terminals and gave it a shot. I rolled the tabs together around an 16ga balance wire, compressing each fold with pliers. I'll use a vice to compress them better when I want it "permanent". If the folds can't rotate, they should stick together.

I got a pack of report covers from Staples for $6. The report spines I remember from childhood reports were a bit thinner, but about the same depth. As you can see from the pics, they leave a large gap around the folded tab. I might just slice a dowel in half and use that to keep the folded tabs compressed and immobile. Or maybe I'll just wrap the tabs around the outside of a dowel, it would be gentler on the tabs but I think the folds keep everythink locked together.

cell_man, you mentioned that you polished the tabs. Was that to remove a coating, or just maximize contact area? BTW, the labels you put on the tabs (listing AH drained and IR) use a gummy adhesive and are difficult to get off. I guess the cells were taken to 100% DOD to get this data, something I would never do to them, especially on their virgin discharge, especially when they were going to be sitting a while. Maybe on my next order, maybe you can just charge them and make sure they hold a surface charge for a day or so?

 

[jonescg]

Hi Paul,
don't try to fix the cooling sheets to the outer case! Everything must have a way to 'breathe'. Some cells do change their thickness ~ 4-10% depending on SOC. I'm not sure about your's...
-Olaf

But how then would you conduct the heat out of the cells? And will they get that hot anyway? Hard to know what the cell swelling will amount to, but Paul, you were saying they don't change much at all?

 

[peterperkins]

What was the exact low temp solder people used to solder the tabs? Make? Supplier? Flux?

I might make a special tab solder clamp from a couple of 25-50w aluminium resistors bolted to two copper plates spring loaded so you apply paste between tabs. and grip them with the hot copper solder clamp thingy. Only the top edge or few mm needs to be soldered imo.

I'm still looking at the clip method but there is very little room between cells in my stack of 50 cells! So that's not easy.

 

[cell_man]

cell_man, you mentioned that you polished the tabs. Was that to remove a coating, or just maximize contact area? BTW, the labels you put on the tabs (listing AH drained and IR) use a gummy adhesive and are difficult to get off. I guess the cells were taken to 100% DOD to get this data, something I would never do to them, especially on their virgin discharge, especially when they were going to be sitting a while. Maybe on my next order, maybe you can just charge them and make sure they hold a surface charge for a day or so?

Yes I polish the tabs just to remove any oxidization and found this helped to reduce losses in the terminations. The cells came in pre tested, the labels were already fitted when I received them. I found the cells were generally around 50% SOC. I had a lot of cells there's a limit to how much testing I can do I'm afraid.

Your termination method looks very straightforward. It will be interesting to see how it works out.

What was the exact low temp solder people used to solder the tabs? Make? Supplier? Flux?

I might make a special tab solder clamp from a couple of 25-50w aluminium resistors bolted to two copper plates spring loaded so you apply paste between tabs. and grip them with the hot copper solder clamp thingy. Only the top edge or few mm needs to be soldered imo.

I'm still looking at the clip method but there is very little room between cells in my stack of 50 cells! So that's not easy.

I never had much luck with soldering the tabs. I believe the correct solder is 91% nickel, 9% zinc. I've seen places that advertise appropriate solder and flux for lipo tabs but I've not been able to get hold of any myself.

Hi Paul,
don't try to fix the cooling sheets to the outer case! Everything must have a way to 'breathe'. Some cells do change their thickness ~ 4-10% depending on SOC. I'm not sure about your's...
-Olaf

But how then would you conduct the heat out of the cells? And will they get that hot anyway? Hard to know what the cell swelling will amount to, but Paul, you were saying they don't change much at all?

I've seen it stated that they should be under compression and I've also heard mention of some swelling. I'll put a layer of foam in the pack to allow for some expansion and the sheets used are very thin so they would easily bend a little if required.

 

[olaf-lampe]

Hi Paul,
don't try to fix the cooling sheets to the outer case! Everything must have a way to 'breathe'. Some cells do change their thickness ~ 4-10% depending on SOC. I'm not sure about your's...
-Olaf

But how then would you conduct the heat out of the cells? And will they get that hot anyway? Hard to know what the cell swelling will amount to, but Paul, you were saying they don't change much at all?

The bad thing about swelling cells is, that they shrink when they get discharged. And that's the moment, when IR rises and cooling is most important ( if at all ) . They'd loose pressure to the fixed cooling sheets and that's it.

The best way to keep up the pressure is to have a compressable sheet ( eg. mousepad-stuff {what's the english name for it?} ) in the stack and everything else is free to move. That's why I suggested alu-foil to be crunched against the boxwalls.

The other 'bad' thing here is, that the cell connectors are one big block, and there will be a little stress on the tabs from swelling. If you check back on an earlier page, I suggested single cell connectors instead of a big block.
But it is still unknown, how much these cells tend to swell/shrink. So maybe you don't need to worry

Like the Americans use to say: been there, seen it, got the T-shirt...
Olaf

 

[Malcolm]

What was the exact low temp solder people used to solder the tabs? Make? Supplier? Flux?

This looks promising Peter, maybe try some on an aluminium takeaway container first?

"Alusol is a low temperature flux cored, lead bearing soft solder wire. It is available in 1 metre lengths at 0.9 and 1.5mm dia.
It will readily solder commercially pure aluminium and copper aluminium alloys. It is best heated with a soft propane flame."

http://www.cupalloys.co.uk/joining-aluminium-c100014.html
http://www.cupalloys.co.uk/alusol-15mm-dia-x-1-metre-i102.html

As for maintaining contact between aluminium heat conductors and the cells during expansion and contraction, my first thought would be to use spring loaded end plates to maintain a relatively constant pressure.

Foam rubber or neoprene wouldn't exert much pressure and would considerably add to the thickness.

 

[liveforphysics]

http://www.solder-it.com/shop/item.aspx?itemid=89

I bought a case of this stuff.

Right on each package it says, "for Lithium polymer battery tab connections."

 

[bonzo]

Guys,

I NEED your advice. I am looking at purchasing 64 of these cells, other than cell_man, as he said he is sold out.

Here are pix of the cells from the seller.....tabs are cut off, and holes have been drilled.

At an investment of over $3000, I am concerned, are these cells usable?

I am worried about terminating them this way, pulling 300amps through them,(16S4P) and heat melting the seal, or pouch.

Also concerned about lack of insulation between tabs and foil edge.

Should I buy these or pass on them?

Justin in AZ

 

[liveforphysics]

In a 4P arangement, it might work because it's only 75amps per cell connection point... but that seems like a very trouble-prone connection method IMO... I can see the foil tabs ripping, the glue of the foil packages getting warm and looseing the seal on the cells, etc.

 

[BatteryMooch]

For me personally, there's no way I'd buy those cells.
But, you'll have to decide how badly you want them.