# A123 pack Idea



## skooler (Mar 26, 2011)

Just realised that if I reverse the bolts so that the head is countersunk into the plywood, nothing will protrude on the bottom of the 'layer' reducing the risk of a short against the next layer.

hmmmmmmm.


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## Ziggythewiz (May 16, 2010)

I like the simple approach. I'd add a lockwasher and nut between the bar and the plywood so you're not relying on the firmness of the wood to maintain the electrical connection.


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## rwaudio (May 22, 2008)

skooler said:


> Just realised that if I reverse the bolts so that the head is countersunk into the plywood, nothing will protrude on the bottom of the 'layer' reducing the risk of a short against the next layer.
> 
> hmmmmmmm.


I like the design, but I would use metal top and bottom for the clamping force. I wouldn't put something "soft" in there. I've played with a few packs and I use some clamps when charging. If I slide it on and it's tight/won't fall off, but the screw isn't tightened HARD. The connection heats up an insane amount. I believe that's why Jack R's packs kept blowing up is because of the pathetic attention to detail and method that he was using to clamp the cells. I would clamp the tabs then attach them to the plywood.


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## skooler (Mar 26, 2011)

Thanks both, agreed, wood is to soft to be part of the clamping force.

I am now thinking that the head of the bolt is countersunk in the plywood to avoid shorts.

The thread of the bolt then protrudes the other side of the plywood.

Next the first aluminium bar is tightened to the plywood using tapped holes in the bar, this is not part of the clamping force - its just part of the same bolt that isnt being used.

Cell tabs are then placed above this bar.

The next aluminium bar is placed over the threads and tabs, it has two 6mm holes that are not tapped.

A lock washer and nut then complete the clamping force.

I can draw it if needed!

Thoughts?

Cheers

Mike


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## Ziggythewiz (May 16, 2010)

I don't think I quite follow.

I don't think any of the aluminum needs to be threaded, just bolt head > washer > bar > tabs > bar > washer > nut > plywood > washer > nut


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## kakheath (Jan 7, 2012)

skooler said:


> My initial thought is that I dont like the idea of stacking all the cells up next to each other because of the risk of a short.


To aid in the handling, monitoring, testing and removal etc, I was planning to make 4s5p modules out of mine and connecting a series of 25 of these for my pack in the car. These could be used as an equivalent replacement for a normal 12V battery and or charged / tested like one until I assemble the complete pack. My plan was to place the cells together standing straight up like the attachment below. Can you help me understand your comment about there being a possibility of a short?


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## skooler (Mar 26, 2011)

kakheath said:


> To aid in the handling, monitoring, testing and removal etc, I was planning to make 4s5p modules out of mine and connecting a series of 25 of these for my pack in the car. These could be used as an equivalent replacement for a normal 12V battery and or charged / tested like one until I assemble the complete pack. My plan was to place the cells together standing straight up like the attachment below. Can you help me understand your comment about there being a possibility of a short?


I like the idea, 12v 'subpacks'.

I just really dont like the idea of the series cells being seperated by a small piece of plastic. (The white material in your picture)

I'm probably being completetly over cautious though!

It does seem to use space much more efficiently though.

Cheers

Mike


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## kakheath (Jan 7, 2012)

skooler said:


> I like the idea, 12v 'subpacks'.
> 
> I just really dont like the idea of the series cells being seperated by a small piece of plastic. (The white material in your picture)
> 
> ...


This is my first EV so I do not claim to know what I'm doing here. I've just been following the builds of others an experimenting some myself. 

The white plastic pieces could be any size. If one wanted to increase their size for protection, it's quite easily done at very little expense. This was one of my power supply packs for testing my individual cells, but I liked it so well that I thought I would use something like it in the car. The white pieces were just an experiment. They are made from molding trim from Home Depot. 

I have purchased HDPE for when I build the car modules. This should have better protection at high temperatures and provide a more solid feel when tightening the outer clamps. I was concerned that thermal expansion would be a concern and had made a design that used an inner spring to keep tension on the module cells in case the white pieces softened, but have now abandoned this idea with the use of the HDPE material. I thought I would torque the outer clamp nuts and then re-torque them after a cycle or two to see if the thermal effects are significant or not.

Your comment on the short got me thinking whether the pack weight should rest on the bottoms of the cells or should I try to have the them hang from their tabs. This is probably a good question for another thread though.

I like the Flatinum layout concept from an efficiency standpoint, but will the connections still be accessible? Are you going to stack multiple sets of the 6s3p modules on top of one another and how were you planning to monitor them?


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## skooler (Mar 26, 2011)

kakheath said:


> This is my first EV so I do not claim to know what I'm doing here. I've just been following the builds of others an experimenting some myself.
> 
> The white plastic pieces could be any size. If one wanted to increase their size for protection, it's quite easily done at very little expense. This was one of my power supply packs for testing my individual cells, but I liked it so well that I thought I would use something like it in the car. The white pieces were just an experiment. They are made from molding trim from Home Depot.
> 
> ...


I see it as very unlikely to short but possible.

I also see your point about the pack weight being supported by the cells. the way I would look at this is that each cell is supporting its own weight, and the weight of the clamp.

I planned on running individual cables from each cell for monitoring. 

Yes the modules will be stacked one above the other.

Cheers

Mike


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## Guest (Mar 17, 2012)

Don't hang the weight of the cells by the tabs. Support the from the bottom or the side in case of the flat type layout. My plan is to shrink wrap each cell before putting them together. A bit of extra precaution against shorting the cells edges. It makes for a wider package but provides extra protection to the cell prior to assembly.


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## Brute Force (Aug 28, 2010)

Don't use materials that melt or burn in the construction of your battery pack! That means no plywood or HDPE (or other thermoform plastics). Consider using GPO3, also called electrical grade FRP. Relatively cheap, and ideal for the job.

Also consider using multiple small screws for the tab connection. It spreads out the load over a wider area which makes for a better electrical connection.


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## rwaudio (May 22, 2008)

I'm working with the tabless cells, and I don't think you have to worry about shorts between cells or package sides/bottoms. I have to remove the "packaging" to expose the remainder of the cell tabs for connection and the packaging is insanely strong but flexible (allows for pack swelling without compromising the containment). I have to literally grind through the plastic, then aluminium then plastic layers with a 120grit sanding wheel to reach the tab. It would take a very large amount of cell movement over a very long time to ever wear through all of the layers of the casing, so as long as you eliminate movement within the pack by whatever method you choose, there should be no problems. The amount of movement required to wear through a cell would probably fatigue and break off a cell tab long before you had casing issues.

I agree with gottdi though, don't hang the cells by their tabs. Ideally attach the cells in groups, then support those groups and if possible also support the tabs/clamps whatever you are using for connection. If there was a weak link in the cell I would say it's probably the aluminium tab so keep it all supported and you will be fine.


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## skooler (Mar 26, 2011)

Brute Force said:


> Don't use materials that melt or burn in the construction of your battery pack! That means no plywood or HDPE (or other thermoform plastics). Consider using GPO3, also called electrical grade FRP. Relatively cheap, and ideal for the job.
> 
> Also consider using multiple small screws for the tab connection. It spreads out the load over a wider area which makes for a better electrical connection.


I have always been under the impression that it takes a lot of heat to get wood to catch, and plywood is very dense. Around 200c in the open is a figure I seem to remember. 400-500c with limited oxygen

These will be in 'sealed' boxes with very little ventilation and therefore oxygen supply.

FRP is a quite expensive in the UK.

Does anybody else think that using plywood is a bad idea?

Perhaps a heat resistant paint would be a good idea?

Cheers,

Mike


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## rwaudio (May 22, 2008)

skooler said:


> I have always been under the impression that it takes a lot of heat to get wood to catch, and plywood is very dense. Around 200c in the open is a figure I seem to remember. 400-500c with limited oxygen
> 
> These will be in 'sealed' boxes with very little ventilation and therefore oxygen supply.
> 
> ...


If your pack actually hit the ignition point of plywood all of your cells are probably toast anyway, they don't like it over 65C. Will you have a way to monitor temperature in the box? I would say that is more important safety concern than using a potentially flammable material near the cells. Half your car is flammable so unless you have a completely fire proof box you can never eliminate the risk. If you did have a source or temperature for ignition I believe the cells would be much more dangerous than a piece of wood. That said my battery box is steel and aluminium (with foam insulation) and not wood. I had contemplated putting an MDF subwoofer enclosure in an unused part of the battery box but decided against it due to vibration.


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## Ziggythewiz (May 16, 2010)

Plywood isn't that flammable. If anything it may be helpful as it will smolder long before it flames.


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## skooler (Mar 26, 2011)

Ziggy and rw,

Thanks for confirming my thoughts about the suitability of plywood.

I'm going to go for it. Hopefully I can order everything next week.

I will take lots pictures and maybe a video and post them up here.

Brute force,

I think I may add another bolt to the Centre of each clamp to help spread the load.

I'm going to go for the design in my first post just turning the bolts around and adding another in the Centre, will also add some industrial type straps to stop the cells moving. Hopefully I can order everything next week.

I will take lots pictures and maybe a video and post them up here.
Cheers,

Mike


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## MN Driver (Sep 29, 2009)

Drywall is a great fire rated material. Certain types of foamboard are too which would help with insulation against the cold too. I think Thermax is fire rated in certain thicknesses, might be worth looking at.


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## somanywelps (Jan 25, 2012)

MN Driver said:


> Drywall is a great fire rated material. Certain types of foamboard are too which would help with insulation against the cold too. I think Thermax is fire rated in certain thicknesses, might be worth looking at.


Drywall handles moisture VERY poorly.


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## skooler (Mar 26, 2011)

Last couple of questions.

I'm thinking of having 3 m6 bolts per clamp, should this be enough for spreading the force and for torque? Would m8 bolts be more suitable?

Also I plan of having 6 tabs in each clamp, will this be too many? Should I add another bar?


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## rwaudio (May 22, 2008)

skooler said:


> Last couple of questions.
> 
> I'm thinking of having 3 m6 bolts per clamp, should this be enough for spreading the force and for torque? Would m8 bolts be more suitable?
> 
> Also I plan of having 6 tabs in each clamp, will this be too many? Should I add another bar?


I would try and keep all the tabs together, M6's are fairly strong in that respect. I just moved to M5's to clamp 3 tabs. I found in the smaller sizes the amount of torque you can apply is sometimes the limiting factor to a bolt size vs the strength of the bolt itself. (2.5mm allen head on an M4 vs 4mm allen on an M5 of a slightly different style for example).
With M8's you might be decreasing the surface area more than required given the torque you need, depends on the clamp design too though. I'm guessing the 3 bolts don't all go through the tabs?


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## skooler (Mar 26, 2011)

rwaudio said:


> I would try and keep all the tabs together, M6's are fairly strong in that respect. I just moved to M5's to clamp 3 tabs. I found in the smaller sizes the amount of torque you can apply is sometimes the limiting factor to a bolt size vs the strength of the bolt itself. (2.5mm allen head on an M4 vs 4mm allen on an M5 of a slightly different style for example).
> With M8's you might be decreasing the surface area more than required given the torque you need, depends on the clamp design too though. I'm guessing the 3 bolts don't all go through the tabs?


I'll draw what I'm thinking and post it when I get home.

I was thinking about brute force's comment about spreading the clamping force when I mentioned 3 bolts. It'll probably OK with just 2 bolts and won't lose any surface area (increasing resistance) but yes all 3 bolts would go through the tabs.

I think I'll go with countersunk m6 bolts with 4mm allen heads.


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## rwaudio (May 22, 2008)

skooler said:


> I'll draw what I'm thinking and post it when I get home.
> 
> I was thinking about brute force's comment about spreading the clamping force when I mentioned 3 bolts. It'll probably OK with just 2 bolts and won't lose any surface area (increasing resistance) but yes all 3 bolts would go through the tabs.
> 
> I think I'll go with countersunk m6 bolts with 4mm allen heads.


due to some inconsistent results with countersunk M4's I'm switching to M5's with Nord-locks. 

If you wanted even clamping force I would increase the thickness of the clamp material before adding a 3rd bolt.

Spend some extra time with the tightening of your countersunk bolts, it took me awhile on my 12v test pack to get everything 100% (running it through a couple charge cycles while measuring the cell impedance with the PL6) It will quickly point out a high resistance connection as a cell group with high IR. (or simply something different that the other cell groups) It's very important to put the balance wires in the same place with the same connectivity on each cell group though to get valid results.


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## Brute Force (Aug 28, 2010)

Evenly distributed force is more important than higher localized force. You want to maximize the contact area to minimize the contact resistance. Using three M4 screws with belleville washers to maintain a constant compression force is the direction I'm considering.

I maintain that the plywood is a bad idea. Wood just does not have properties consistent with safe and reliable use around high energy electrical circuits. Please do more research on the subject before you commit to this path. While you might get away with it, I'd really hate to hear that your project burned to the ground because plywood was cheaper than FRP.


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## major (Apr 4, 2008)

Brute Force said:


> I maintain that the plywood is a bad idea.


That's a no-brainer.

I haven't viewed this thread until just now. I agree. Do not use wood.

Another thing........Do not rely on compressed plastic or composite material to clamp a high current connection. This obviously includes wood. Your connection will fail eventually. Make all high current connections using metal parts for the clamping force structure. This includes threads for the fasteners. 

Securing the high current components to an insulated structure must be done with a secondary fastener, not the primary clamp.

Advice from many with many years of experience. Take it or leave it 

major


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## skooler (Mar 26, 2011)

major said:


> That's a no-brainer.
> 
> I haven't viewed this thread until just now. I agree. Do not use wood.
> 
> ...


Damn! 

Major, you and Brute Force have made this difficult for me!

I really respect your opinion on the forums so I am going to have a rethink...

I have always been under the impression that it takes a lot to get wood to burn. If the cells and/or connections are getting to a temperature that will ignite plywood then I think the wood catching will only be a side problem!?

Please feel free to prove me wrong/ convince me otherwise.

Any suitable suggestions on another material?

FRP is quite expensive in the UK

Drywall/plasterboard is bad with damp and breaks to easily.

Aluminum honeycomb and sheet is too expensive.

Lexan and polycarbonate are also quite expensive and probably not stiff enough to stack. I would probably need to go quite thick making it more expensive.

Acrylic is too brittle.

Any ideas?


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## jr dragster (Oct 11, 2010)

If you used alum or steel then you have to insulate it so plastic of some kind might work out cheaper in the long run?


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## major (Apr 4, 2008)

skooler said:


> I have always been under the impression that it takes a lot to get wood to burn. If the cells and/or connections are getting to a temperature that will ignite plywood then I think the wood catching will only be a side problem!?
> 
> Please feel free to prove me wrong/ convince me otherwise.


Perhaps you didn't understand. It is the high current electric connection which needs to be clamped solid with metal parts and fasteners without relying on any plastic or composite. You can use non-metal for the enclosure and/or separators. Just do not screw the tab clamps into the non-metal material to squeeze them together. 

If this is your typical EV, the C rates should be in a range which will not cause excessive cell heat. And the tabs or other high current connections will stay within moderate temperature range if they are properly clamped. It is when the connections are improperly clamped which will cause them to become loose and then they overheat and fail sometimes causing fire.

I think fiberglass is a good candidate for enclosure.


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## skooler (Mar 26, 2011)

major said:


> Perhaps you didn't understand. It is the high current electric connection which needs to be clamped solid with metal parts and fasteners without relying on any plastic or composite. You can use non-metal for the enclosure and/or separators. Just do not screw the tab clamps into the non-metal material to squeeze them together.
> 
> If this is your typical EV, the C rates should be in a range which will not cause excessive cell heat. And the tabs or other high current connections will stay within moderate temperature range if they are properly clamped. It is when the connections are improperly clamped which will cause them to become loose and then they overheat and fail sometimes causing fire.
> 
> I think fiberglass is a good candidate for enclosure.


Hi Major, sorry I misunderstood, Thankyou for clearing that up

I am not using the wood as part of the clamping force.

I am simply using longer than needed bolts and using the excess to attach the clamp to the plywood or whatever else I decide to use.

Just to confirm, do you see an issue with using plywood to support the cells and clamps? 

I see it only being an issue if the clamps are not up to scratch?

Cheers,

Mike

Thankyou for clearing that up


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## major (Apr 4, 2008)

skooler said:


> I am not using the wood as part of the clamping force.


This diagram shows you compressing wood to secure the clamp.



skooler said:


> This shows how the clamps hold the tabs and how the bolts also hold the the cells to the plywood.


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## skooler (Mar 26, 2011)

major said:


> This diagram shows you compressing wood to secure the clamp.


It does look like that!

The idea is that the lower of the 2 clamps will be tapped - meaning the clamping force is between the bolt head and the bottom clamp. If needed a nut could be positioned between the clamp and the plywood.

The remaining length of the bolt is used to secure it to the plywood.

Does that make sense?

I will redraw it at some point today.

Cheers

Mike


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## skooler (Mar 26, 2011)

Anybody got any ideas on how to integrate a BMS?

Looking at mini BMS so I can re-Use the modules when I switch to a prismatic pack.

Cheers

Mike


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## Ziggythewiz (May 16, 2010)

Just wire it in between your support layer and the bolt. Or add another bolt between the clamp bolt and the support layer.


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## puddleglum (Oct 22, 2008)

I've been reading this with interest. I have a couple of noobie questions, though. Since it seems that temp., both high and low, has a significant effect on performance and life expectancy, does there need to be any consideration for ventilation between cells or at least groups of cells? Also, do these cells need to be compressed to keep them from swelling? Are any of you planning for active heating or cooling of your packs?


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## Guest (Apr 9, 2012)

puddleglum said:


> I've been reading this with interest. I have a couple of noobie questions, though. Since it seems that temp., both high and low, has a significant effect on performance and life expectancy, does there need to be any consideration for ventilation between cells or at least groups of cells? Also, do these cells need to be compressed to keep them from swelling? Are any of you planning for active heating or cooling of your packs?


Compressing does not prevent swelling. It can hide swelling until you release the pressure. Do not over charge or over discharge period. If you do that they will not swell. 

As for cold cells you should have some sort of insulation and as for heating, so far no one has had any trouble with overheating the cells. Some even put in sensors to allow a cooling fan or coolant to run once the cells got to a specified temperature to protect them from over heating. In two years the cooling has never come on and the system does work. Insulating is more important than cooling as far as the batteries are concerned. If your still concerned you can install a thermostat that will turn on a cooler. Bet it never comes on. 

Pete


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## Elithion (Oct 6, 2009)

skooler said:


> Anybody got any ideas on how to integrate a BMS?


You basically have 2 options:


Distributed (electronics on the cells)
Non-distributed (electronics elsewhere, spaghetti wires to the cells)
 For a distributed solution, there's only one off the shelf BMS with cell boards specifically designed for pouch cells. However, with some ingenuity, you can shoehorn cell boards meant for prismatic cells onto pouch cells.

For a non-distributed solution, any non-distributed BMS will work, because the format of the cells doesn't matter: wires go from a central box to each and every cell. Specifically:


Simple analog BMS (tells you nothing), such as Clean Power's MiniBMS (centralized version)
Sophisticated digital BMS (tells you who, what and why), such as the Orion BMS


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