Terminating the 15Ah and 20Ah Cell-Man cells

[cell_man]

Fellas I've now now made a prototype of my proposed termination method which uses only non conducting material apart from some m4 bolts to hold it all together. Here's a few pics. Please ignore the fact that the sections are different width. I need to get some more 5mm sheet and will ensure all sections are of course identical depth.

Here are a few pics:

I've added sections of 0.5mm aluminum at each junction to allow balance wires to be added. The alumium could be changed to either stainless steel or copper as required. I think stainless may be the best bet due to it's strength. If the little tab breaks off the pack would need to be broken down to replace it.

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This shows the order of the pieces used. Divider is approx 2mm and the clamping sections are approximately 5mm thick. Together, with the tabs and 0.5mm balance tab insert, the total thickness is just about spot on for the 15Ah cells. Would be straightforward to adjust the termination pitch thickness as required.

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I've also done some tests with 2 cells connected in series using the non conducting clamps with bolts immediately at the edge of the tabs. I made a quick check of the difference an additional clamp in the centre made (by tightening a G clamp down onto it). It made a significant difference, about 0.2V additional voltage drop at that termination, so bolts through the tabs are necessary IMO My main concern with using non conducting tabs at high current is the loss of any heat sinking effect metalic terminals would have. The tabs are very thin and do actually get very hot at high discharge rates. IMO the heat will be coming from 2 sources, firstly generated by the resistance in the tab material and secondly from within the cell itself. I do not have concrete figures just yet but I feel non conducting tabs are more than adequate for constant current of circa 100A or a bit more with significanly higher peaks, but when sustained high loads are required a different approach is sensible. I'm concerned that not allowing the heat from the tabs to be adequately dissipated into the terminals may cause problems within the cell allowing core temperatures to get too high. If you think about it, the tabs do actually make a great heat sink and they are directly connected to the core of the cell that actually requires cooling the most. Maybe that is part of the reason for making them so thin

I'm also playing with putting some aluminium sheets between the cells to aid cooling. However I'm starting to think that this method cannot adequately cool the cell in the centre. I mean I'm sure it will help a bit, but due to the relatively large distance from the centre of the cell to the edge where the sheets can actually disipate the heat. I'm using quite thin aluminium sheet (0.5mm) so it will quickly adjust to the cell surface temperature but will not draw much heat out of the cell with access to cooling air. Thicker sheet will help but that defeats the point of such an energy dense cell IMO. To effectively dissipate heat from the entire surface of the cell I feel it is necessary to space some aluminum sheets apart by a small distance to allow cool air to be blown through the gap. If something like this was implemented on every 2nd cell that should be enough. If there was a honey comb sheet available, that would work well IMO. Water cooling would of course be better and would allow the cell temperature to be controlled in both directions, to get some heat into them on cold days and dissipate heat when being pushed.

Probably a bit difficult to make out what going on in these pics with the mass of cables.

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This was a previous version of the termination method which used metallic clamps and which would allow the terminals to act as a bit of a heat sink.

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I think I'm gonna have to configure a resistive load sufficient for say a 16S pack with at least 200A capability or better a bit more. As with everything on these cells what at first seem quite straigtforward quickly turns into a bit of a ball ache, but I'd rather make sure I've covered all the bases before sending out packs that are not properly thought out and implemented. These cells are not cheap and it would be a serious tragedy if I were to put together a pack that damaged the cells in some way. If you're gonna do something, I reckon it needs to be done right

[CamLight]

Great work!
I'm very anxious to see how this evolves.

[cell_man]

Thanks John,

I can see more test equipment on the horizon It's never ending. It's like that never ending hill, you get to what you thought was the top, only to discover yet more hill

I might not have all the data to back up my tests, but with a fairly sensible approach I should be able to get some ball park figures and decide on conservative discharge levels for the different termination styles.

I'm happy to do these tests, at least it gives others who have bought these cells some more insight into the termination so that hopefully any avoidable issues are avoided. These super overkill termination methods I've seen on some builds are now starting to make a bit more sense. Even if they are not required electrically, the cooling they offer to the terminals/cells can't do any harm.

[adrian_sm]

so bolts through the tabs are necessary IMO

Looking at the two photos below gave me an idea that will achieve the same result, without cutting holes in the tabs.

If you combine the two methods for a full pack you wouldn't need to modify the tabs, but you could still get the centre clamp on the tabs.

The idea would be build the pack with all the clamp/spacer blocks as per the first image.
But then have a separate clamp/s that clamp, like the g-clamp, but across the full stack of cell tabs and non-conductive blocks.

Maybe one clamp for the left side, and one for the right. This clamp would have to be made from metal for strength purposes, but could be fully lined in non-conductive plastic sheet on the tab side to avoid any shorting issues. To keeps things compact this clamp block would have to be sized appropriately for a specific stack of cells. But 12S,16S,24S might keep most happy.

It is probably only suitable for low power applications, as I agree at full power the heat will need to be managed better. But maybe that can be handle by extracting it from between the cells as you have mentioned.

Not sure if the above makes sense, but what I have in mind is essentially a low profile g-clamp across each termination bank.

Just my two cents worth. Keep up the good work.

Adrian

[cell_man]

Hi Adrian,

thanks that is a good idea, but it may not be required after all. I ran some more tests and I think I had neglected the tighten BOTH screws down on the offending termination I will run some more checks to make sure anyway.

As a slight variation on your suggestion, how about:

If you notice on the pics I will be putting 3 bolts through the full assembly to keep it all together, so could maybe have a plate top and bottom (same material I have used is sufficient IMO, it's very strong and stiff) and an additional bolt that pushes down at the mid point of the terminations at the top and bottom of the stack.

I will try to finish off the terminations for a 16S pack tonight. I've already cut the pieces, just need to drill and tap the holes. Should be able to get it all put together today or maybe tomorrow. I've received some 16S BMS and wire 1 up and see how it manages using a bulk charger. Here are some pics of the BMS, it's rated 80A constant but can accept significantly more for bursts.

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[Dingo2024]

Hi Paul,

Not trying to cause more problems/issues ...as I appreciate optimising the termination method IS time consuming; but is the ultimate aim to produce complete packs which have the BMS and cells housed inside a protective 'box' and look similar to an orthodox car or motorcycle battery? i.e. not duct tape or shrink rap

thanks,

Ian

[cell_man]

Hi Paul,

Not trying to cause more problems/issues ...as I appreciate optimising the termination method IS time consuming; but is the ultimate aim to produce complete packs which have the BMS and cells housed inside a protective 'box' and look similar to an orthodox car or motorcycle battery? i.e. not duct tape or shrink rap

thanks,

Ian

Hi Ian,

yes, a protective box is the ultimate aim but I will offer a shrink wrap (no duct tape ) pack initially, maybe with some protective panels to prevent damage and then look to get a box sorted out. I know a place that can supply simple aluminium boxes to whatever dimensions are required so I'll get a sample ordered and see what they are like and they are not so expensive either. However it would be nice to be able to do something a bit clever like something that can mount in the triangle of the frame or a seat post mounted pack, or whatever, but it all takes time and quite a bit of work to put them together. I've got a couple of different slide on boxes but they are a bit small at only about 140mm wide so that rules out the standard 1s I've seen. The other problem is that a mass produced box is pretty cheap so it's hard to compete on price but I'll try to keep things as reasonable as possible.

However, first things first, I need to get the simple pack sorted first and go from there. IMO the terminations are 1 of the more tricky parts of the pack, so I'm hoping when the time comes to do an enclosure it's not gonna be as much of a PITA as the terminations have been so far....

Cheers
Paul

[oatnet]

Phenolic plastic might be a good material for thos protective panels you mention.

[cell_man]

Phenolic plastic might be a good material for thos protective panels you mention.

I had a quick look at the material properties and yes it does look suitable. You don't happen to know the Chinese name for it do you ?

[nicobie]

Why not use Formica? I used it on my Ping packs and it worked out real nice. Cheap, attached with hot glue gun and is easily removable with a hot air gun. I've got pics if anybody is interested.

[CamLight]

cell_man, Check out G10 epoxy material too. IIRC, it's less expensive than FR-4. I've always loved using Delrin too but I don't know it's upper temp limit. Incredibly easy to drill and machine (easier than Nylon 6/6) and great for the more structural components.

[cell_man]

Thanks guys for all the great suggestions

There is an area not so far from me were I source almost all my tools and materials. I'll see if these materials are available. I'm also quite concerned about adding too much weight. I don't want to ruin that great energy density figure by careless packaging.

Will look at making a simple aluminium enclosure, it may work out better and I could maybe use that duct tape after all, but inside of course. I think I'm now pretty close to having something ready and will put together some 16S 15Ah and 20Ah packs at first and maybe some 12S when the BMS becomes available.

I still need to work out the positive and negative terminals of the pack which will be made from copper but I have some ideas for them that should work out pretty nice.

Thanks for your patience and I'll do my best to have something nice ready ASAP. Good things come to those that wait

[galeson]

It looks to me from the exploded view of plasmaboys battery pack that there is no provision for cooling at all. The case is lexan (not particularly good thermal conduction) and he is planning to have very high pulse usage as well as drive the white zombie on the street.

[cell_man]

Not as much progress today as I would have liked but at least have some ideas about how to implement the terminals. I drilled a 4mm hole which was a tight fit for the tinned cable and clamped it using an M4 bolt. The copper bus bar is 8mm thick. Ignore the larger hole, 2nd from left, this was originally a terminal from my test load which has now found a new home.. .

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The BMS is fitted with double 10AWG high temperature cable hence the reason for 2 holes on the terminal. I'm debating whether to drop the double termination and bring it to 1 point. It's a real PITA drilling all those deep and quite narrow holes into solid copper bar. A crimped connector and bolt may be another option to reduce the machining. A single tapped hole maybe 10mm deep seems quite apealing after knocking up those clamps.

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This 1 is a bit rough around the edges. The tabs haven't been cut down, the sections are all odd sizes and I haven't tightened the hole assembly down just yet. Need to get longer M4 bolts before I can proceed much more. I'm thinking a different thread on the bolts used on the clamps. If re used a few times the thread can give on the clamps. I've only had it happen once while tightening a clamp down, but still. Will have to have a look for some different bolts with maybe a deeper thread and a tap to match. Does anyone know much about bolts that are suited for this type of material? Another option is to go up 1 or 2 sizes on the clamping bolts, but that makes space a bit tight on the 15Ah termination.

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Here are the sections that make up the terminals in order that they assemble. As mentioned please look beyond the slightly rough edges. I've got the right tool now to do a nice clean and accurate cut on this material.

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Still a way to go but I think the basic idea for the terminations is almost there, at least for the more moderate power packs anyway. When i say moderate I'm talking circa 100A constant and much more for bursts. It may well be that this is sufficient for higher current too but will need to do a few checks first to confirm.

[MitchJi]

Hi,

My main concern with using non conducting tabs at high current is the loss of any heat sinking effect metalic terminals would have. The tabs are very thin and do actually get very hot at high discharge rates. IMO the heat will be coming from 2 sources, firstly generated by the resistance in the tab material and secondly from within the cell itself. I do not have concrete figures just yet but I feel non conducting tabs are more than adequate for constant current of circa 100A or a bit more with significantly higher peaks, but when sustained high loads are required a different approach is sensible. I'm concerned that not allowing the heat from the tabs to be adequately dissipated into the terminals may cause problems within the cell allowing core temperatures to get too high. If you think about it, the tabs do actually make a great heat sink and they are directly connected to the core of the cell that actually requires cooling the most.

If thats an issue why not use aluminum for the short thick blocks that contact the tabs? Make it a little narrower than the other pieces so they are recessed (sort of like BigMoose's ridges). If aluminum contact on both sides is required maybe use two thinner pieces, one on each side of the tabs.

I've also done some tests with 2 cells connected in series using the non conducting clamps with bolts immediately at the edge of the tabs. I made a quick check of the difference an additional clamp in the centre made (by tightening a G clamp down onto it). It made a significant difference, about 0.2V additional voltage drop at that termination, so bolts through the tabs are necessary IMO

If that is still an issue maybe aluminum blocks will bend less reducing the need for clamps. If necessary I think clamps would be better than holes in the tabs. I think "ears" protruding from the middle of the outer blocks with bolt holes (Nylon bolts would be great if they are strong enough) would probably do it.

Will look at making a simple aluminum enclosure, it may work out better and I could maybe use that duct tape after all, but inside of course. I think I'm now pretty close to having something ready and will put together some 16S 15Ah and 20Ah packs at first and maybe some 12S when the BMS becomes available.

I think a non conducting enclosure will be better.

[patrickza]

That looks like a headway BMS, did you get it from Headway or somewhere else? I have the 24s version, and I've never managed to trip it. Apparently the 24s version is 100A continuos and 400A burst, might just be enough for the power hungry guys. The work well too, keeps things nicely balanced if you use a good charger. I don't recommend the headway charger, they don't have a decent CV mode for balancing (I have two and they both behave the same). I've had far better results using my kingpower charger from ecitypower. Also I've found that on a 24s pack I need a minimum of 88.1v to get everything balanced perfectly.

[cell_man]

Hi,

My main concern with using non conducting tabs at high current is the loss of any heat sinking effect metalic terminals would have. The tabs are very thin and do actually get very hot at high discharge rates. IMO the heat will be coming from 2 sources, firstly generated by the resistance in the tab material and secondly from within the cell itself. I do not have concrete figures just yet but I feel non conducting tabs are more than adequate for constant current of circa 100A or a bit more with significantly higher peaks, but when sustained high loads are required a different approach is sensible. I'm concerned that not allowing the heat from the tabs to be adequately dissipated into the terminals may cause problems within the cell allowing core temperatures to get too high. If you think about it, the tabs do actually make a great heat sink and they are directly connected to the core of the cell that actually requires cooling the most.

If thats an issue why not use aluminum for the short thick blocks that contact the tabs? Make it a little narrower than the other pieces so they are recessed (sort of like BigMoose's ridges). If aluminum contact on both sides is required maybe use two thinner pieces, one on each side of the tabs.

I've also done some tests with 2 cells connected in series using the non conducting clamps with bolts immediately at the edge of the tabs. I made a quick check of the difference an additional clamp in the centre made (by tightening a G clamp down onto it). It made a significant difference, about 0.2V additional voltage drop at that termination, so bolts through the tabs are necessary IMO

If that is still an issue maybe aluminum blocks will bend less reducing the need for clamps. If necessary I think clamps would be better than holes in the tabs. I think "ears" protruding from the middle of the outer blocks with bolt holes (Nylon bolts would be great if they are strong enough) would probably do it.

Will look at making a simple aluminum enclosure, it may work out better and I could maybe use that duct tape after all, but inside of course. I think I'm now pretty close to having something ready and will put together some 16S 15Ah and 20Ah packs at first and maybe some 12S when the BMS becomes available.

I think a non conducting enclosure will be better.

Hi Mitch,

this material is actually very stiff and seems to bend less than an equivelent piece of aluminium. The only stumbling block I've now run into is the fact that the amount of material used means it actually weighs a bit too much. I'm gonna look at an alternative method which will use less material but requires some moderate bending of the tabs which is not a major problem IMO. I'm also going to look at just soldering the tabs but need to get hold of the correct solder ect. Tried to find some today but no joy. I need to do a lot more tests before making any assumptions and my comments are often a bit of thinking out loud. Maybe should consider what I put down in writing a bit better so don't take anything I've said above as fact

Regarding enclosure material, I think that as long as the tabs are properly isolated the case shouldn't have an impact but I do hear what you're saying. However aluminum sheet is hard to beat for a simple enclosure when the low weight, fairly straightforward manufacturing and reasonable cost are considered. A nice injection moulded case is great if you've got the numbers, just not there just yet.

That looks like a headway BMS, did you get it from Headway or somewhere else? I have the 24s version, and I've never managed to trip it. Apparently the 24s version is 100A continuos and 400A burst, might just be enough for the power hungry guys. The work well too, keeps things nicely balanced if you use a good charger. I don't recommend the headway charger, they don't have a decent CV mode for balancing (I have two and they both behave the same). I've had far better results using my kingpower charger from ecitypower. Also I've found that on a 24s pack I need a minimum of 88.1v to get everything balanced perfectly.

No not headway. They do not make BMS anyway so must be bought in. This unit is a 16S but the PCB can accept max of 20S if fully populated. When did you get the BMS?Thanks for the info

[olaf-lampe]

You could use smaller strips to crimp the tabs together. You´ll end up with the same contact resistance when you press harder on a smaller area.( compared to pressing the whole tabs together with a lower pressure per sqmm). Let the remaining tabs stick out and get some fresh air. Saves weight and improves cooling.

-Olaf

[cell_man]

You could use smaller strips to crimp the tabs together. You´ll end up with the same contact resistance when you press harder on a smaller area.( compared to pressing the whole tabs together with a lower pressure per sqmm). Let the remaining tabs stick out and get some fresh air. Saves weight and improves cooling.

-Olaf

I'm going to try a different arrangement which should reduce the material used significantly. I quite like the cooling effect of all those tabs poking out like you mentioned, but how about the sparks that will fly when you short them..

Gonna try getting some zinc solder also and try soldering the tabs but there doesn't seem to be anywhere to source zinc solder in China believe or not. I'm starting to think Lukes suggestion was right all along, why is he always right.. Soldering the tabs together is looking like a tempting option compared to cutting god knows how many clamps and screwing the whole thing together. Ping packs aren't exactly DIY and that doesn't seem to have done him any harm

[flip_normal]

Hi cell_man, not sure if this has been mentioned but, if you do decide to solder the tabs it might be an idea to clamp them at the base of the tab with some of that fat copper bar you've got whilst applying the solder (if it's possible to do without shorting anything) might help to divert excess heat away from the cell innards, then cool the tabs off with a damp rag as soon as the solder has set. I wouldn't fold the tabs before soldering as this would make dissasembly more difficult. Hope this helps, keep up the good work.

[peterperkins]

Could we use a special sort of very stong bulldog clip to clip cell tabs together?
Some sort of machine spring clip with flat faces and a special tool to spring it open and release it onto tabs when in position.
BMS wires can be soldered to the clip or have a 1/4" spade terminal built into clip.

[liveforphysics]

I wanted to be sure using zinc solder to connect tabs wouldn't be an electrical point of high resistance that could cause tab heating.

I just worked the numbers on the electrical resistance of zinc being used to connect the tabs.

It turns out, zinc is a pretty damn good conductor. Copper is 16.8nOhm/m, Zinc is 59nOhm/m, and our normal solder base, lead, is 208nOhm/m, and tin is 109nOhm/m. Zinc solder is an electrically superior solder to our 60/40 lead/tin electronics solder.

If you lay a 4.5mm path of zinc all the way across the tab, you've got a connection that equals half the resistance of the tab material itself, meaning it would be generating less heat at the connection than the tab itself, and I've all ready found these tabs to be incredibly capable when it comes to handling extremely high currents without getting warm.

I would recommend setting up to solder the tabs just like it would be done with an RC LiPo pack, except scaled up a bit. A couple of 1/4" copper bars on a little spring clamp, and solder paste. The little copper bar clamp is very handy, because it not only holds the tabs together, but it makes a thermal sink/barrier from the soldering heat on the tabs ever reaching the temperature sensitive parts on the inside of the cell. Trim the tabs as desired, apply a little smear of the the solder paste on the outside area of one tab, put the clamp on the area of the tab as close to where it enters the foil package as possible, but not where it blocks the area you need to apply heat to solder the tab. Then hit the outside part of that tab with as intense of heat as you can manage. Most people use flame, but I don't like the tendency to oxidize the surface, so I use a hot gun. lol, I remember I could throughly melt the solder paste in LiPo cell pack construction in roughly a 2-second heating period by covering the back (air inlet) side of my heat gun until the coils went from red, to bright orange (just takes about 5 seconds, so be careful you don't melt your heating element!), then releasing my hand at the same time I would direct the little chisel tip of the heat gun onto the tabs. 2 seconds later, you could see the solder completely wet and flow, I pull the heat gun away, and keep my fingers on the area the tab enters the foil pouch. If done correctly, you could hardly even feel the tab on the back side of the heatsink get above room temperature. This was all for working with LiPo cells that have 1/4" wide aluminum tabs though of course, but I can't think of why the same process couldn't simply be scaled up for connecting these monster cell tabs.


This stuff is pricey for it's tiny quanity, but it's just flux with 85% zinc micro-balls, and 15% aluminum micro-balls. It melts at a low temp and is super easy to work with for doing LiPo tabs. There are of course many larger quantity aluminum solder pastes available, but just for experimenting, this stuff is pretty common to find in hardware stores and things. I would think it, or something like it would be available in China.

http://www.amazon.com/Aluminum-Solder-S ... B0017T0U3U

[cell_man]

Hi cell_man, not sure if this has been mentioned but, if you do decide to solder the tabs it might be an idea to clamp them at the base of the tab with some of that fat copper bar you've got whilst applying the solder (if it's possible to do without shorting anything) might help to divert excess heat away from the cell innards, then cool the tabs off with a damp rag as soon as the solder has set. I wouldn't fold the tabs before soldering as this would make dissasembly more difficult. Hope this helps, keep up the good work.

I've had a bit of a look into how to do the soldering and yes I would use some kind of clamp to as a heat sink to prevent excessive heat reaching the cell. I hear what you're saying about folding the tabs though, good ponit. Getting the solder etc is a bit tricky but I'm on the case. My first choice hoever would be a mechanical method and hopefully i may have somthing that will work well in the pipeline. Much less weight, size etc. Will reveal when it has been transferred from the back of this scrap of paper into reality. Also found a better solution for fixing that doesn't require any thread tapping and is much stronger. I couldn't strip the thread when I tried so definitely up to the task. We may be getting closer....

Thanks Luke for sharing your knowledge and experience yet again Hopefully can come up with a method to solder quite soon. If I could offer both a mechanical and solder method it gives the end user a choice at least. The solder should definitely take less time and parts so would be a cheaper alternative.

Thanks all for your comments

[liveforphysics]

I need to order a big stack of cells to use for my 100mph project bike, and for the bike builds for my parents, and I will experiment with soldering methods until I get something that is optimal for soldering these large cell tabs.

[cell_man]

Sounds Good Luke

I'll do something for you on the cells Luke as a bit of a thank you for all your efforts