Terminating the 15Ah and 20Ah Cell-Man cells

[flip_normal]

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.

As I understand it steel and aluminium have a tendency to electrolyse when in contact with each other, especially in humid conditions, and eventually produce a high resistance connection. You could use adhesive kapton tape on the outside faces of the tabs and solder the balance wires directly to the tabs. I like the simplicity of disassembly offered by this method, as long as the clips are supported to prevent stress on the tabs this would probably be my preferred method of connection.

EDIT: The balance wires could be terminated with an aluminium strip and the tabs folded with the strip slipped into the sandwich prior to the clip being attached, thus avoiding any soldering to the tabs. Support could be provided by a sheet high density foam with rectangular holes cut out for the clips to recess into.

 

[cell_man]

Made a bit of progress today and have managed to address some of my concerns namely weight and hopefully ease of manufacture and assembly. The jury is still out on the last 2 points.... This method adds about 250g to a 16S pack so much better than the last effort. Alternative materials would help this but this stuff is amazing at dealing with heat. There is absolutely no way this stuff will burn or melt. I was using 2 pieces of this material to clamp the alumium terminal (don't worry will be copper once I have got a chance to get some in) in a vice whilst I tinned it with a huge soldering iron I have (circa 200W and no temp control) and it just marked the surface a little.

It's not assembled yet and I need to change the fixings for countersunk but you should be able to get the idea. I'm now thinking a nut and bolt might be the best solution after all. Maybe even put the nuts on the inside No problems stripping threads, can probably go down a size on the fixings and it's quite easy to isolate the nut to prevent shorts. These fixings are pretty good but they have a tendency to split the material due to the small size of the pieces I'm screwing into. A bigger pilot hole would likely reduce this though.

I'm tieing both the 16S BMS and the Icharger balance leads into this pack so I can see what's going on wit the cell voltages and see how they react under load ect as each cell has capacity and internal resistance values. Should give me some insight into how the variation in parameters effects the pack balance. Packs are supplied with cells matched to the minimum capacity variation from my available cells and is generally less than 0.1Ah max difference.

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As you can see in the pics I've folded the tab over but the folds are not so tight so it shouldn't make too much of a mess of the tabs. There didn't seem to be any reason to tie across the pack so the termination has been split with the added bonus of reduced weight and it doesn't strain the section between the tabs as much now. A 0.5mm section of alumium sheet has been inserted alongside the tabs for balance wires. I think it needs a few refinements here and there but I think the basic idea is sound. I will have to get some more resistive loads to enable testing a complete 48V pack to at least 100A if not 200A and try logging the discharge with and without a fixing through the tab. That should determine once and for all if an additional clamp through the tab has any effect.

Hopefully it's almost there and then I start on the box, cooling panels and then the arrangement for packs with 2 or more parallel cells. Lots to do...

 

[cell_man]

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.

As I understand it steel and aluminium have a tendency to electrolyse when in contact with each other, especially in humid conditions, and eventually produce a high resistance connection. You could use adhesive kapton tape on the outside faces of the tabs and solder the balance wires directly to the tabs. I like the simplicity of disassembly offered by this method, as long as the clips are supported to prevent stress on the tabs this would probably be my preferred method of connection.

EDIT: The balance wires could be terminated with an aluminium strip and the tabs folded with the strip slipped into the sandwich prior to the clip being attached, thus avoiding any soldering to the tabs. Support could be provided by a sheet high density foam with rectangular holes cut out for the clips to recess into.

Not ruling anything out for the future but with the materials to hand and an idea of how to address some of my earlier concerns I had a go with the above. I'm on a bit of a tight schedule for this so really need to get something ready ASAP. I can knock this up myself and should be able to get them manufactured at a reasonable cost even on fairly small quantities if i choose to. We could probably do it all in house to be honest with abit of thought how to speed up the machining with a few jigs etc which would avoid all the setting that I had to do for each hole or cut on this prototype. My Girlfriend is complaining she's bored

 

[galeson]

I like this solution best. It will make it easier to build parallel pack packs.
How about using barrel bolts for the fasteners. You could epoxy the female end into the board and it would save you the countersinking, and there wouldn't be the problem with the bolt spinning if you ever needed to disassemble. The outside would then be nice and clean. You can get the bolts in brass. stainless aluminum or even plastic.

 

[cell_man]

I have actually been looking at inserts and was planning to put the insert on the cell side, so just a countersunk bolt head on the outside facing out. But the space bewteen adjacent cells is small, so you need to be very careful with fixing size etc. I still need to make a positive terminal and a few adjustments are required to the clamping terminals but it's not bad IMO. I've actually isolated the bolts from the cells by heat shring and electrical tape when the former ran out. It turns out the tape is probably better at this task as it's stronger.

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I may look at using a single piece of material to bolt over the assmbly as the very small sections used for each clamp put a lot of strain on the material used. That way I could stick with very thin material for an initial clamp to keep everything in palce but then bolt onto the clamps from above. This would also negate the need for holes in the tabs which I am against if at all possible.

As soon as I can get hold of the right type solder I'm also going to offer soldered packs. A lot of work goes into a termination method like this. It shouldn't be the only option as many do not require it and will be put off by any additional cost.

 

[olaf-lampe]

If you want to use a huge plate for clamping all tabs at once, why don´t you put silicone thermal pads between the tabs and the plate? This way you could use a solid aluminium plate for cooling and it could also work as top- part of the housing. Of course you must be very careful there is no conduction path.
-Olaf

 

[cell_man]

Hi Olaf,

I'm starting to think a simpler approach is necessary. I've made up a simple clamp today that is used on each termination. It didn't work out quite as planned but I'm thinking that I may have stumbled onto something. I'm now starting to think 1, 2 or even 3 holes through the tabs is maybe required and will make the whole process easier and therefore cheaper. The method needs to be fairly easy to implement because people do not want to pay for fancy termination methods plus the cells are so good you will not need to be dismantling the pack anyway I've done some load tests on a complete 16S pack monitoring the cells using a pair of Cell Log8S and it's shown me that you really do need to have a good clamping force across the entire tab or you get some voltage drop on that cell.

Also checking 1 of the 16S 80A constant BMS and all looks good so far. I had a bit ofa scare earlier when I connected the charger. I don't know if anyone's notced but they seem to have the convention that L is negative and N is positive. There are IEC plugs withred and black cables harwired this way and most of the cheap e bikes seem to use them Anyway with no instructions as to the polarity of the charger and the fact this charger only outputs voltage when it detects a battery is connected I stupidly assumed that the brown wire was positive and blue negative...... wrong Blew the charging plug to bits and thought I'd trashed both charger and BMS, but luckily it seems it's just the plug that took the hit, so lesson learned, hopefully....

I promise to have these packs ready for sale this week at least as shrink wrap packs and I will work on an enclosure method that I have seen which should work out very reasonable too. Will also try soldering some packs and will offer both options. Will keep the costs as low as possible even if it means I'm working for buttons initially till I can get someone else who is willing to work for buttons instead. Not so difficult to find the latter in China but combined with a good ability to put together slightly complicated electronic parts to a consistent high standard is not so easy. Don't worry I've got no intention of starting a sweat shop anytime soon, but a typical salary for someone who works in Starbucks in 1 of the most expensive cities in China is about the same as 2 or 3 cups of that coffee they sell all day....

 

[thomas]

Tried to do a little prototype compact 4s box. The plexiglass was just what I had around, some other plastic material that is easier to machine would be better.

Done in a hurry and with hand tools so please ignore the poor finish

The bolts through terminals is not really ideal Ill change it to clamp style probably with one bolt through the middle.
The box is made so it puts a little pressure on the foil edges of the cells and theres less than 0.5 mm air at the end of the stack. Not really compressed but the cells are held by the box and not by the tabs.
Needs some bms wires also.

only 1 cell on the pictures (only one I got )

 

[curious]

cell_man - you are getting close to what I suggested before. I agree - just use a common G10 plate to cover/clamp tabs, it will have better rigidity than individually cut pieces. Also you do not need as many bolts to compress the plates, certainly less than 2 per tab.

For certain very high current applications (not typical ebike) it would be prudent to use cell tabs as heat pipes and sink the heat from tab joint through a thin layer of 1/31" G10 to a common heatsink/chassis/whatever...

 

[gestalt]

thomas,

That is an awsome bat box, tough and simple. why not try some polypropylene sheet, cheap and easy to machine http://freckleface.com/shopsite_sc/store/html/polypropylenesheetthreequarterinchthick.html. I wonder if you can get the same material somewhere else in black though.

 

[cell_man]

Tried to do a little prototype compact 4s box. The plexiglass was just what I had around, some other plastic material that is easier to machine would be better.

Done in a hurry and with hand tools so please ignore the poor finish

The bolts through terminals is not really ideal Ill change it to clamp style probably with one bolt through the middle.
The box is made so it puts a little pressure on the foil edges of the cells and theres less than 0.5 mm air at the end of the stack. Not really compressed but the cells are held by the box and not by the tabs.
Needs some bms wires also.

only 1 cell on the pictures (only one I got )

Hi Thomas,

you know there's lots more waiting for you here

The box looks good but i would suggest an additional section on the clamps so that you are actually compressing the maximum surface area of the tab. I did some tests on the assembled pack shown previously and there was a couple of junctions that were giving higher volt drop under load than others. They were tight but not tight enough. You really do need to have a strong uniform pressure over a good area of the tabs to minimise losses and I'm starting to think bolts through the tabs is the only reliable way to achieve that.

cell_man - you are getting close to what I suggested before. I agree - just use a common G10 plate to cover/clamp tabs, it will have better rigidity than individually cut pieces. Also you do not need as many bolts to compress the plates, certainly less than 2 per tab.

For certain very high current applications (not typical ebike) it would be prudent to use cell tabs as heat pipes and sink the heat from tab joint through a thin layer of 1/31" G10 to a common heatsink/chassis/whatever...

The problem is that as soon as you cut slots in the material it looses alot of the required strength just where it is required. I'm starting to think that simple individual clamps for each juction will suffice for typical high powered E bike and it will still be DIY if necessary or maybe stick withe something like the latest version but with bolts through the tabs to ensure a good contact. I also think solder will be fine too. Both options will also add very little size or weight to the pack (moreso soldering) and reduce time and therefore costs. I'm starting to think a nice enclosure that everyone can see is a better way to spend my time than fixing terminations that nobody sees

 

[olaf-lampe]

A flat shaped individual clamp tends to bend, but what if you take something halfround. That would be much stiffer. The diameter should be a little smaller than the distance between the tabs you want to connect. You bend the tabs around the lower clamp from both sides. Than screw/press the upper clamp on it. No need of bolting through the tabs anymore. And you have smooth bended tabs that will not get stressed by vibrations a.s.o.

My boss will kill me, if he ever reads this
-Olaf
PM me for a nice 3D drawing I`ve made a while ago

 

[cell_man]

Hi Olaf.

I'm curious to hear more but what I'm visualising would need to be machined very accurately IMO, maybe I've got it all wrong though. I've sent that PM and a dwg would be great

Hi Thomas,

I wasn't as positive about your design as it deserved, it looks great and puts my efforts to shame. I'm sorry I've been giving myself a few bad days, trying to do too much and getting nothing done instead Will do my best to break that habit bad

 

[olaf-lampe]

Hi Paul,
I have to dig a bit in my archives to find the drawings. About accuracy: the good thing of the (half-)rounded shape is, it's flexible in the radial direction and stiff in the axial direction. But it's a bit more engeneering than just cutting and drilling.

-Olaf
<edit> Couldn't find the 3D but here is a sketch...

 

[thomas]

Paul my design would require some cnc milling I wouldn't want to make a bigger pack with all the manual machining that would take

Got acces to a manual mill so Ill try to knock up a box out of some PP sheet. Will mill out a slot in the sheet for each cell like crodrivers setup and bolt each sheet together.

Olaf that doesn't look too complicated think Ill steal that

 

[cell_man]

Paul my design would require some cnc milling I wouldn't want to make a bigger pack with all the manual machining that would take

Got acces to a manual mill so Ill try to knock up a box out of some PP sheet. Will mill out a slot in the sheet for each cell like crodrivers setup and bolt each sheet together.

Olaf that doesn't look too complicated think Ill steal that

It sounds like you have a similar problem to me. I like to make hard work for myself too I've got yet another version of the termination coming and I think it will be a winner and add only about 5mm to the length of the main body of the cell with light weight, will enable the pack to be easily split, hopefully not too much work and have no live parts to short out. I've got it down on paper and will have something knocked up within a day or 2. No bolts throught the tabs is also a strong possibilty but tests will have the final say. Worst case an M4 bolt through the tab is not the end of the world IMO.

The hard to find solder will be here in a day or 2 so I'll see how that goes. I'll need to knock up a kind of heat sink arrangement for the tabs to prevent excessive heat reaching the cells but it's not so difficult. I had a try on a cell and a big piece of copper clamped to the tab stops pretty much all heat.

Hi Olaf,

I do like the idea and will keep it in mind for the future, but I think it will require close tolerances on the clamps to ensure a uniform pressure across the entire tab and that level of machining is beyond me at the moment. Thanks for taking the time to send the pics, much appreciated.

 

[thomas]

What is the reason for the extra parts for the bolts? Wouldn't it be easier to just make the whole upper clamp the same shape as the bolt clamp so only two parts need to be made for one tab connection?

I would guess only the upper clamp is copper to save weight and the lower and bolt clamps are alu?

 

[curious]

Olaf's clamp can be made from a standard fiberglass rod for the bottom part and a half-tube (cut with dremmel) for the upper part. Inner radius of the half tube should be larger than rod radius by the thickness of two tabs. FG tubing/rods are readily available from kite building stores.

A more sophisticated option would be to use steel tube for the bottom part of the clamp and run non-conducting coolant through all clamps

 

[cell_man]

Olaf's clamp can be made from a standard fiberglass rod for the bottom part and a half-tube (cut with dremmel) for the upper part. Inner radius of the half tube should be larger than rod radius by the thickness of two tabs. FG tubing/rods are readily available from kite building stores.

A more sophisticated option would be to use steel tube for the bottom part of the clamp and run non-conducting coolant through all clamps

You're free to order a few cells and show me how it can be done I'm just concerned that if you are dealing with 2 rond surfaces unless they are exactly the right profile when also considering the tab thickness, you will get high pressure points and low pressure points unless there is enough give in 1 of the materials to allow for this. Going this route now would also mean completely re thinking the whole connection method and delay things considerably. There are lots of ways to successfully achieve this but most people will not accept an over engineered solution that is therefore costly for the sake of what? No holes in the tab or a 100g weight saving. You should see how others link similar cell mechanically, think 3 or 4 bolts with washer straight through the tab, no more, finished... It's taped up and hidden away in some heat shrink...


Termination will not generate any more heat than the tabs are already producing and there is at least 15mm of insulated tab material between the cell body and the exposed surace of the tab and you would need a lot of heavy material in the tab for it to effectively sink any heat and I'm dubious as to whether this would actually result in any appreciable gain in performance.

I hope I haven't come across as arsey as this thread has in fact helped me immensely to move towards a solution I'm happy ticks all the boxes, but I do need to get something workable ready ASAP.

 

[CamLight]

Just tossing out a wild idea...
For the hemispherical mounting clamp, how about using copper/brass wool between the top part of the clamp and the sandwiched tabs? That is, the orange stuff in Olaf's diagram is the brass wool. It would compensate for not-perfectly-matched tube halfs and ensure connections over many points and surfaces of the two tabs. And it conducts electricity and is very resistant to heat.

Otherwise, use a dense neoprene foam strip, perhaps 1/6" -1/8" thick, as the orange material. This stuff would ensure perfect compression along every bit of both tabs as long as the neoprene never gets fully compressed. There are neoprenes foams that can take any temperature those tabs might see but even the standard foam goes to 158F and those tabs will never be at that temp for long. And you can get the foam in rolls with a self-adhesive back!

 

[olaf-lampe]

Just tossing out a wild idea...
For the hemispherical mounting clamp, how about using copper/brass wool between the top part of the clamp and the sandwiched tabs? That is, the orange stuff in Olaf's diagram is the brass wool. It would compensate for not-perfectly-matched tube halfs and ensure connections over many points and surfaces of the two tabs. And it conducts electricity and is very resistant to heat.

Otherwise, use a dense neoprene foam strip, perhaps 1/6" -1/8" thick, as the orange material. This stuff would ensure perfect compression along every bit of both tabs as long as the neoprene never gets fully compressed. There are neoprenes foams that can take any temperature those tabs might see but even the standard foam goes to 158F and those tabs will never be at that temp for long. And you can get the foam in rolls with a self-adhesive back!

Good idea to put something conductive between the clamps, but don't forget how narrow the whole story is.
I also thought about copper paste ( seem's to be nonconductive ) or graphite powder ( is conductive, but how can it be spread evenly )
The latest and greatest idea came overnight, but I have to sketch a picture to describe it. It only takes one (copper) tube and the pressure would be spread evenly over the whole surface and I only need 1 bolt from sideways.
Stay tuned...
Olaf

 

[olaf-lampe]

Here are the sketches of my new simple tab clamp.
It's made of a copper/aluminium tube with a slot on both side. The slot starts and ends with a drilled hole to take care of stress caused by compression. The compression part is a silicone/rubber tube with nut/bold and washers on the ends.

Installation is simple : you guide the battery tabs through both slots and insert the silicone assembly. Then tighten the bolt until you have a nice pressure on the tabs. It works the same way as on some Dremel tools.

Of course the position of the slot is the critical part. Also smooth edges are mandatory.

http://img651.imageshack.us/img651/2540/fullpipec.jpg
http://img36.imageshack.us/img36/7748/fullpipe2.jpg

-Olaf

 

[cell_man]

Hi Olaf,

imageshack is blocked in China Any chance you could attach or forward to my email or PM

I've got my latest and greatest effort so far pretty much ready. Will post few pics tomorrow when it's finished. I tried the solder but wasn't happy with it if I'm honest. By the time you have taken care to sink the tabs, avoid any shorts, prepare the tabs etc etc I think a mechanical solution would have been time better spent. However I may not have the best soldering iron, maybe too hot and the solder I was supplied is maybe too corrosive. I used standard solder in the end. As long as the tabs are adequately sinked by clamping them down onto metallic bars, the heat doesn't reach the cells. So until I can find a good alternative solution mechanical clamping is gonna be the way I go.

I think you'll be presently surprised by my latest effort. It's quite a departure from previous efforts and seems to tick all the required boxes, apart from maybe it's still quite a bit of work... but definitely less than previous efforts and functionally superior too. My idea is not a half cylinder like yours but does have some similar ideas.

 

[heathyoung]

Blocked - pah. Download firefox for your browser, and install TOR - bypass the blocks.

 

[liveforphysics]

Hi Olaf,

imageshack is blocked in China Any chance you could attach or forward to my email or PM

I've got my latest and greatest effort so far pretty much ready. Will post few pics tomorrow when it's finished. I tried the solder but wasn't happy with it if I'm honest. By the time you have taken care to sink the tabs, avoid any shorts, prepare the tabs etc etc I think a mechanical solution would have been time better spent. However I may not have the best soldering iron, maybe too hot and the solder I was supplied is maybe too corrosive. I used standard solder in the end. As long as the tabs are adequately sinked by clamping them down onto metallic bars, the heat doesn't reach the cells. So until I can find a good alternative solution mechanical clamping is gonna be the way I go.

I think you'll be presently surprised by my latest effort. It's quite a departure from previous efforts and seems to tick all the required boxes, apart from maybe it's still quite a bit of work... but definitely less than previous efforts and functionally superior too. My idea is not a half cylinder like yours but does have some similar ideas.

I'm working on refining a soldering solution. I also had trouble getting heat quickly spread out over the wide and thick cell tab. I'm making a custom iron the uses a pair of heated copper blocks to clamp upon the cell tabs. When I get a setup refined that works quickly and ensures a perfect connection every time, I will mail it off to you.