A123 AMP20 Battery Pack Build...

[agniusm]

Good points here mate you'd need to consider if you will be pulling some juice. Your box is nice, clean job, but sharp edges one, poor heat transfer of perspex. You could fabricate aluminium box 5mm below tabs and than make 3mm perspex cover to protect from shorts.
My second opinion is that you made 2 mistakes in connecting tabs. First being putting brass blocs in between tabs, and second using one bolt. As mentioned before, brass is less conductive, twice the resistance of copper. So you have little surface area for proper tab contact + lots of resistance between cells. My other suggestion would be to drop a little soldering iron on balancing leads, i would not trust crimp only, there is vibration and something will get loose in time. For the tabs squash all 5P in between 2 brass blocks and use 3 x 5mm bolts. On the end connection just add 3mm copper flat bar this way: brass|tab|tab|copper flat bar|tab|tab|tab|brass and bolt it all together tight. Good luck

[SlyCayer]

Very nice! What size copper bar did you use?

Copper Flat Bar 3/4" X 1/4"

What are the outside dimensions of your polycarbonate battery box?

560mm X 230mm X 280mm

then I would be a bit worried about vibration, and what sharp edges might do to your cells.

No Worries, the white plastic you see is a very very soft plastic, and it will not "Scratch" the cells, I have tested it properly before doing it, but from your suggestions, I am thinking of buying some simple foam to put all around the cells.

ssooo... what car is it going into?

Electric Go-Kart 32Kw

It will give you much better clamping over the tab surface area.

EDIT... as I look closer, the heavy cables coming off of the blocks to put the groups in series should be connected directly to the tabs and not have a nut in between and NOT have the very small ring terminal between. That tiny ring terminal + the bolt (I assume brass?) will be carrying the full current of the pack, you should rely on direct surface contact of the high current parts without anything in between.

The bolts are Silicone Bronze, very close to same conductivity has Copper. The Bolts and Nuts will carry a 450A current for short period of time and from my estimation, the nut/bolt conductivity is as much as a 1/0 or 1awg Cable and it's only 1/4" thick...

I am eager to put this pack on the kart to see how it reacts... I will have a programmed BMS working with A/D Inputs and Relay, programmed directly on a tablet wirelessy with Bluetooth.

It will monitor all parallel group voltages, temperatures of certain connections and temp of cells, it will also have a built in GUI on the tablet for RPM, Speed and all the cells voltage and LVC and HVC lights.

[rwaudio]

I honestly don't know anything about silicon bronze but a quick search of it's conductivity say's it's 5-20% as conductive as copper depending on the type.
A 1/4" bolt with even 20% of the conductivity of copper is bad news at 450A.

Your battery box is beautiful and appears to be very well assembled, I hope you can take constructive criticism from the members here and visit other options before you blow some bolts off and either short something out or destroy those nice clear boxes.

If you don't take the warnings please mount a camera on the cart pointed at the boxes so we can at least watch them blow their bolts.

[The Mighty Volt]

I can't possibly comment on the safety of the pack build as I have never worked with these prismatics, but thanks for taking the time to upload the photographs. It looks good and builds like this attract interest and the helpful suggestions which come from same. Well done.

[deVries]

What are the outside dimensions of your polycarbonate battery box?

560mm X 230mm X 280mm

Thanks!

then I would be a bit worried about vibration, and what sharp edges might do to your cells.

No Worries, the white plastic you see is a very very soft plastic, and it will not "Scratch" the cells, I have tested it properly before doing it, but from your suggestions, I am thinking of buying some simple foam to put all around the cells.

I'm actually worried about your white plastic spacers. These spacers are *not* providing uniform pressure or support to your stacked cells. It is my opinion with the high vibration & turning forces driving a Go-Cart at high speeds that you will damage your battery unless you provide uniform pressure & support over the *entire* surface area against your "end cap" stacked cells. The white plastic spacers will do just the opposite of providing uniform pressure & support.

Use a good foam with minimal "soft" compression to act as a spacer and "compressor" between the polycarb & your entire surface of these end cap cells, that foam compressor could still be removable, otherwise I think you will damage your cells w/o that additional support over the entire surface area.

The A123 professionally manufactured modules with multiple cells *specify* that these modules provide *Uniform Pressure* against the entire cell surface area. Your module with white plastic is doing just the opposite of that specification, imo. This will likely damage your cells, imo.

Quoting from one of these A123 modules, perhaps used for the Chevy Volt, it states the module has: "• Uniform compliant compression system"

[acuteaero]

The bolts are Silicone Bronze, very close to same conductivity has Copper. The Bolts and Nuts will carry a 450A current for short period of time and from my estimation, the nut/bolt conductivity is as much as a 1/0 or 1awg Cable and it's only 1/4" thick...

Again, I'm with RW-

http://www.eddy-current.com/condres.htm

Bronzes range between 48% and 7% of the conductivity of copper, the silicon bronzes listed are lower, either 12% or 7%. Might want to recalculate your equivalencies there-

Seems to me that moving the lugs to be directly adjacent to the tab stack and adding a load-spreader to the outside tab instead of having it flying, clamped just under the washer and bolt would be easy things to do to eliminate the worst weak points in the design. Depending on the resistance of these spots in the pack you may be able to determine that they need attention by running some discharge and checking it afterwards with an IR thermometer or thermal camera- or you might blow it up on the first run!

Good luck- please consider making these simple modifications- I think they will be well worth it!

[SlyCayer]

I'm actually worried about your white plastic spacers. These spacers are *not* providing uniform pressure or support to your stacked cells. It is my opinion with the high vibration & turning forces driving a Go-Cart at high speeds that you will damage your battery unless you provide uniform pressure & support over the *entire* surface area against your "end cap" stacked cells. The white plastic spacers will do just the opposite of providing uniform pressure & support.

Use a good foam with minimal "soft" compression to act as a spacer and "compressor" between the polycarb & your entire surface of these end cap cells, that foam compressor could still be removable, otherwise I think you will damage your cells w/o that additional support over the entire surface area.

The A123 professionally manufactured modules with multiple cells *specify* that these modules provide *Uniform Pressure* against the entire cell surface area. Your module with white plastic is doing just the opposite of that specification, imo. This will likely damage your cells, imo.

Quoting from one of these A123 modules, perhaps used for the Chevy Volt, it states the module has: "• Uniform compliant compression system"

I will be using foam for sure, what foam do you recommend?? The foams need to be have some sponger but not to much, so it's hard to gauge what foam I should use... Foam that is used in high school gyms should work?

The bolts are Silicone Bronze, very close to same conductivity has Copper. The Bolts and Nuts will carry a 450A current for short period of time and from my estimation, the nut/bolt conductivity is as much as a 1/0 or 1awg Cable and it's only 1/4" thick...

Again, I'm with RW-

http://www.eddy-current.com/condres.htm

Bronzes range between 48% and 7% of the conductivity of copper, the silicon bronzes listed are lower, either 12% or 7%. Might want to recalculate your equivalencies there-

Seems to me that moving the lugs to be directly adjacent to the tab stack and adding a load-spreader to the outside tab instead of having it flying, clamped just under the washer and bolt would be easy things to do to eliminate the worst weak points in the design. Depending on the resistance of these spots in the pack you may be able to determine that they need attention by running some discharge and checking it afterwards with an IR thermometer or thermal camera- or you might blow it up on the first run!

Good luck- please consider making these simple modifications- I think they will be well worth it!

I will be changing the position of my lugs to be the first on top of my end string...

This simple change isn't so simple, to put this extra 1/4" copper bar between the cell will be hard because by putting an extra thickness, it will make my width of my pack over what my box was designed for and will great a cap between each parallel group since an extra 1/2" for both 1/4" bars per pack widens the whole pack by 4"...

I will have to rethink this and see what I can do.

[deVries]

I'm actually worried about your white plastic spacers. These spacers are *not* providing uniform pressure or support to your stacked cells. It is my opinion with the high vibration & turning forces driving a Go-Cart at high speeds that you will damage your battery unless you provide uniform pressure & support over the *entire* surface area against your "end cap" stacked cells. The white plastic spacers will do just the opposite of providing uniform pressure & support.

Use a good foam with minimal "soft" compression to act as a spacer and "compressor" between the polycarb & your entire surface of these end cap cells, that foam compressor could still be removable, otherwise I think you will damage your cells w/o that additional support over the entire surface area.

The A123 professionally manufactured modules with multiple cells *specify* that these modules provide *Uniform Pressure* against the entire cell surface area. Your module with white plastic is doing just the opposite of that specification, imo. This will likely damage your cells, imo.

Quoting from one of these A123 modules, perhaps used for the Chevy Volt, it states the module has: "• Uniform compliant compression system"

I will be using foam for sure, what foam do you recommend?? The foams need to be have some sponger but not to much, so it's hard to gauge what foam I should use... Foam that is used in high school gyms should work?

I've seen some very high density foam used for floor exercise mats. This type of foam is dense & not squishy like a sponge. This high-density foam could be ideal, since it does not flex easy & is slow to press in. A dense exercise mat foam may be ideal if it recoils to press back against the entire surface of the cell. Also, there is dense foam used for packaging too that could be cut and used in layers to build-up the ideal thickness. Perhaps even high quality Styrofoam or "carving foam" might be used too or in combination with these other materials to get the correct thickness & recoil against the cell.

Please document with more pictures your solution, since this will help many of us with our battery builds too. Thank you!

[acuteaero]

I've seen a lot of people use camping sleeping mats for battery pack padding foam. The stuff in particular is blue, about 1/2" thick and pretty dense. Available at walmart cheap (I've heard)- I bought mine at REI (less cheap...) According to 2nd hand reports it's even flame retardant (none of my battery packs using it have burned up...)

If you can exchange the three copper bars on the end for 3/16 thick ones (requiring bending the tabs closer to each other) then you can put a 3/16 bar on the outside without changing the outside dimensions of the assembly... As well, that end bar doesn't need to be conductive (except for the one under the end lug!), it just needs to spread the load from the allthread across the tab- you could use something like 1/8 or even 1/16 steel instead for more rigidity with less thickness- even giving it a bit of a curve beforehand to help spread the load most effectively. This is a bit of a similar concept to the one I employed on my recent pouch cell pack build. I used .062 spring steel strip. viewtopic.php?f=14&t=38761#p565974

-Henry

[liveforphysics]

I hope it works for you long enough to enjoy your project.

Here are some observations:

If you suspend any unsupported weight on the tabs of a pouch cell in a high vibration environment, the connection internal in the pouch between the aluminum positive tab and the aluminum foil layers will flex as the unsupported mass bounces around, the foils will fatigue, work-harden, and crack away from the tab internally. Anything connected to a tab MUST be mechanically supported if you wish for a long life on something. In the case of a go-kart, it might not get time to fail, and hopefully works out fine.



NEVER conduct through a fastener, and if you're going to for some reason, silicon bronze is the lowest conductivity type of bronze available. It's generally 1/10th or less the conductivity of copper (the stronger alloys often used in fasteners being 1/20th the conductivity). In a go-kart application, you'll be chassis limited to pulling high currents for short periods of time, so it likely won't be an urgent failure point, but it would be wise to check the tension on the nuts, as thermal cycles on relatively slippery bronze fasteners tend to walk the fasteners tension off.

Suspending a cantilevered cable/lug mass unsupported off the tabs is extremely poor practice, in a vibration test I can assure you it would tear the tabs off when the vibe sweep hits the natural freq of that suspended mass. Fortunately, for this go-kart application, it's unlikely to see more than a dozen or two hours of use, so hopefully it doesn't have time to fail.

The clamping area is almost non-existent for tabs on the edges. A 1mm piece of spring steel that is curved to have the concave side facing the tab that needs to be clamped and added to the stack-up would be a good idea for those edges. Similarly, in a future design, using 3 small fasteners, made of good steel (remember, your goal is to never conduct through them, just using them for the clamp load) would be a much better option.

Pouch bodies seem greatly under supported. When these pouches get warm (and they might never get warm if used in a go-kart), they become very soft, almost cooked pasta soft, and require good structural support to keep them from collapsing on themselves.

The box is huge and thick with lots of air space and polycarb is a good insulator. It would not work as an extended high current battery, fortunately, a kart can only use little bursts and cooling is unlikely to be an issue at all. For a kart, low weight is the whole reason they are quick. I think a stack up of cells with some thick aluminum end plates (over sized a bit so the bands dont touch the pouch stacks) tightly snugged band clamps strapping the assembly together would give you a good mechanical retention system that provides good pressure and is low weight. You could slide in 1/16" lexan sheets on the edges of the cells before strapping the steel bands down. Any place that ships equipment on pallets would be able to put some steel band clamps on for you.


Most importantly though, you made a pack! And It's going to get that kart moving and making smiles on your face, which means you're winning, and your future pack designs will be that much better.

[deVries]

I think a stack up of cells with some thick aluminum end plates (over sized a bit so the bands dont touch the pouch stacks) tightly snugged band clamps strapping the assembly together would give you a good mechanical retention system that provides good pressure and is low weight. You could slide in 1/16" lexan sheets on the edges of the cells before strapping the steel bands down. Any place that ships equipment on pallets would be able to put some steel band clamps on for you.

This seems like a much better solution than using foam pushing against the polycarb & cell "end caps" surface area. 4 threaded rods one for each corner of the end plates might work well too, *but* a picture of an A123 module shows 2 strap bands being used to hold the cells in compression attached to an end cap/plate at each end.

Luke, do you have any idea about what the surface pressure/compression should be on these cells when creating a stack of these aligned together? A123 states their modules meet some compliance spec for uniform compression of these cells in their module. Quoting from one of these A123 modules, perhaps used for the Chevy Volt (according to Doctorbass), it states the module has: "• Uniform compliant compression system"

[SlyCayer]

Hey,

Instead of foam I have been thinking about a 3/4" Plywood board the size of the cell with threaded rod in every corner(4)... 1/4" Rod, would that replace the foam to a certain extent?

[999zip999]

There is a lot of weight on the tabs with a vibration of a gokart. If you can take up the space side to side by the buss. It could be easier on the tabs. Ping uses black foam strips on top of the cells between taps under the connections yea that air space filled with foam strips. They have pre glued foam tape like the stuff used on doors and windows, it does look like that and is thicker ?

[SlyCayer]

the taps

Taps? What is a taps?

[deVries]

Hey,

Instead of foam I have been thinking about a 3/4" Plywood board the size of the cell with threaded rod in every corner(4)... 1/4" Rod, would that replace the foam to a certain extent?

As long as your cell edges along the outer perimeter edges of "the stack" are not touching the rods lengthwise & have a small gap, then wood could work too. (Though it may flex and bend more than a metal plate.) You need to be very careful to apply equal tension & make sure the rods are "locked" in place, so vibrations don't cause the rod-tension to come loose. I think the rod could be smaller diameter than 1/4" too, because I do *not* *believe* you want much tension on the rod. *IMO* you *only* want a "snug fit" and as little compression as possible... the cells may "breathe" by expanding & contracting over time... so only tighten just enough but do *not* squeeze that gel too much, IMO, as that may cause a short or damage the pouch over time.

When you mount your battery box onto the Go-Kart, will the cell stacks be in a vertical or horizontal position?

I'm guessing horizontal, so I would use a dense packaging foam along the underside of the cell stack to rest on and support the stack lengthwise. You could even use this foam to fill any gaps lengthwise along the vertical cell edges of the stack at least partially up the sides to add some slight pressure to dampen vibrations & add minimal lateral support.

If there is some way to mount the battery box to isolate it from external vibrations or dampen these, then that would be better than nothing too. Otherwise, you want the cell stacks somehow isolated from outside vibrations as much as possible.

There is a very good type of dense packaging foam used to ship expensive and sensitive electronics to protect these components from shock & vibrations. It is easy to cut & comes in various thicknesses to even 12" or 24" or more inches thick. It is grey-black in color. (Bubble-wrap might be used in some combination too.)

Remember, you must isolate the tabs from any vibrations or movements, otherwise the cells will be damaged in days or weeks or just hours of use.

(Make certain your wire and mechanical connections to the tabs or "bus bars" can not transmit vibrations into the flimsy tabs or to this "tab area" of the cells. )

[999zip999]

The tab's are thing's you don't want to tear off the top of your pack. Sorry for the miss key.

[SlyCayer]

My cells are positioned vertically where the tabs are sticking up.

If i use my 3/8 polycarb for my compression plate it will keep the box to a certain visual level.

I will also be mounting my boxes on some springs and the cells on 1" foam at the bottom of my boxes

[deVries]

My cells are positioned vertically where the tabs are sticking up.

Ok, then everything I wrote above applies, since your cell stack will be stretched-out horizontally, which is my meaning for my "horizontal" post just above.

If i use my 3/8 polycarb for my compression plate it will keep the box to a certain visual level.

Good idea!

I will also be mounting my boxes on some springs and the cells on 1" foam at the bottom of my boxes

Very good ideas worth trying. You do such an excellent job of posting your "photo documentary" that I hope you will show the same details as you proceed.

Most Excellent!

[SlyCayer]

Pack Update:

[deVries]

Once again, you do an excellent job of documenting your work with just photos. Excellent!

It will be interesting to learn how your design works for you over time... Please keep us updated on anymore changes & what you learn along the way... thanks.

You have gotten some suggestions with the "tab/bus bolts" that you did *not* change (yet?), so I guess you're going to test it with your connection method 1st

What wire size are you using to connect to the tab/bus bolts that lead to the controller? (Some have suggested *not* to connect the main power wires using the single nut/bolt.) Will it carry the load amps you will be drawing? Some wires have much smaller diameter size, so maybe these smaller wires are for a BMS, balancing, or charging?

Send us some picks with your mounting ideas on the Go-Kart & some action shots too.

Thanks!

[SlyCayer]

2/0 is the AWG I am using... 18AWG wires is for balancing and monitoring of my parallel strings.

I haven't done the change for the tab sandwich suggestion because The washer is about 0.68" in diameter and the 2/0" Wires are about 0.44" in diameter so the washer size should not affect anything is the wires are longer and create more resistance by it's actual size... Also any lugs used have about the same surface area has a 0.68" washer... Correct if this is wrong. I am only pulling 450 amps for now...

[deVries]

I haven't done the change for the tab sandwich suggestion because The washer is about 0.68" in diameter and the 2/0" Wires are about 0.44" in diameter so the washer size should not affect anything is the wires are longer and create more resistance by it's actual size... Also any lugs used have about the same surface area has a 0.68" washer... Correct if this is wrong. I am only pulling 450 amps for now...

Hopefully, someone with more "pouch cell" battery build experience can comment and help you with your above setup. There are experts that know about this on ES.

Someone give SlyCayer some help please...

Doctorbass, Sir Battman! The A123 Battery Appears in the Night Sky...

Can you help give SlyCayer some ideas for this?

In the meantime I'll just repost LFP's comments, which are expert advice too...

NEVER conduct through a fastener, and if you're going to for some reason, silicon bronze is the lowest conductivity type of bronze available. It's generally 1/10th or less the conductivity of copper (the stronger alloys often used in fasteners being 1/20th the conductivity). In a go-kart application, you'll be chassis limited to pulling high currents for short periods of time, so it likely won't be an urgent failure point, but it would be wise to check the tension on the nuts, as thermal cycles on relatively slippery bronze fasteners tend to walk the fasteners tension off.

Suspending a cantilevered cable/lug mass unsupported off the tabs is extremely poor practice, in a vibration test I can assure you it would tear the tabs off when the vibe sweep hits the natural freq of that suspended mass. Fortunately, for this go-kart application, it's unlikely to see more than a dozen or two hours of use, so hopefully it doesn't have time to fail.

The clamping area is almost non-existent for tabs on the edges. A 1mm piece of spring steel that is curved to have the concave side facing the tab that needs to be clamped and added to the stack-up would be a good idea for those edges. Similarly, in a future design, using 3 small fasteners, made of good steel (remember, your goal is to never conduct through them, just using them for the clamp load) would be a much better option.

[SlyCayer]

In the meantime I'll just repost LFP's comments, which are expert advice too...

Where in my whole battery pack are you seeing ANY current being carried by ANY fasteners?

[deVries]

In the meantime I'll just repost LFP's comments, which are expert advice too...

Where in my whole battery pack are you seeing ANY current being carried by ANY fasteners?

I don't think I wrote that you were doing that now, since *after* your first post of pictures which did show that you were using 2 nuts on that silicon brass threaded rod. You were asking a question I could not answer, so I posted for more help from someone else. I just repeated LFP's advice in the meantime. Sorry for any confusion...

[SlyCayer]

I don't think I wrote that you were doing that now, since *after* your first post of pictures which did show that you were using 2 nuts on that silicon brass threaded rod. You were asking a question I could not answer, so I posted for more help from someone else. I just repeated LFP's advice in the meantime. Sorry for any confusion...

I really thought I had missed a lug that was positioned over my nuts/washer/terminal connector so if I did, I really needed you to point out where...