A123 AMP20 Battery Pack Build...

[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. :wink: )

 

[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! 8)

 

[SlyCayer]

Pack Update:

 

[deVries]

Once again, you do an excellent job of documenting your work with just photos. Excellent! 8)

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. 8)

Someone give SlyCayer some help please...

Doctorbass, Sir Battman! The A123 Battery Appears in the Night Sky... 8) :lol:

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...

 

[SniperGaulois]

Amazing, very well thought out thing you made there. looks neat and organised to me! and the plexiglass/wood mix is very nice!

Of course i dont understand resistance in large batteries, i guess they need giant contacts everywhere.

for the copper clamp system, seems pretty efficient for sure. would be interested to see how much a simulation of one of those joints would heat up if you put 2000w through it, i think they can certainly handle 500-700 watts each, as long as the foil is thick enough not to weaken in the clamps!

 

[SlyCayer]

plexiglass/wood mix is very nice!

There is no wood inside my boxes at all, the wood you see in the picture is my working table...

how much a simulation of one of those joints would heat up if you put 2000w through it

I will be pulling 450amps from the battery pack, I will also use a thermal camera after my first run to check the temperature of my connections.

 

[deVries]

I will also use a thermal camera after my first run to check the temperature of my connections.

Good idea. Using a laser temp sensor or temp sensor to "spot check" or a wired sensor in potential "trouble spots" might be useful too.

 

[SlyCayer]

wired sensor in potential "trouble spots" might be useful too.

With my A/D Inputs on my Bluetooth board, I will have 8 sensors, 1 for temperature of motor, 1 for controller temp, 6 in my 2 packs(3 sensors per pack).

 

[megacycle]

Hi Slycayer decent size, nice.
Just a couple of points i found when researching pouch builds,
Being involved with bus connections everyday in my job,i researched bus connections to some extent
and it is'nt an abstract science.
http://www.copperinfo.co.uk/busbars/pub22-copper-for-busbars/sec7.htm#Busbar Jointing Methods.
Large overlapping joints are generally a waste of materials for one and there are standard clamping pressures for connections a lot of builds could possible use some kind of paralleled edge clamp for example.

Secondly seems most pack builds seem to favour a lot of flammable materials as if the case is mainly cosmetic
and therefore almost abstract again, i've been using a switchboard grade formica case and a steel frame surround.
At least if my MJoules go ballistic hopefully i might get a few seconds for a get away before i get a vital part burnt.

Thirdly good luck with it and looking forward to some tyre smokin video.

 

[texaspyro]

At least if my MJoules go ballistic hopefully i might get a few seconds for a get away before i get a vital part burnt.

Nope, Sir Edsel Murphy will wind up gobbling your dangly bits before you can say "Oh, crap!"

 

[megacycle]

At least if my MJoules go ballistic hopefully i might get a few seconds for a get away before i get a vital part burnt.

Nope, Sir Edsel Murphy will wind up gobbling your dangly bits before you can say "Oh, crap!"

Yep tex who am i kidding, might as well face the truth.
I'm sitting atop of, or strapped onto a bomb, YEEEEEEEHHHHAAAAA!!!!!!!!!!!!!!!! :lol:

 

[miro13car]

Since it is thread about building A123 20Ah cell pack.
It might help
If you look for tool to make holes in tabs.
I found cheap and very useful.
Bought in STAPLES office supply chain hole puncher by FISKARS brand.
It makes lovely holes in 20Ah pouch cell terminals.

 

[megacycle]

Anyone looked at http://www.te.com/catalog/cinf/en/c/11052/1009?PID=42403&RQS=C~11052.
foil terminators, could be good for tabs termiations.

 

[SlyCayer]

Since it is thread about building A123 20Ah cell pack.
It might help
If you look for tool to make holes in tabs.
I found cheap and very useful.
Bought in STAPLES office supply chain hole puncher by FISKARS brand.
It makes lovely holes in 20Ah pouch cell terminals.

Hmm, that's what I used...

Let me show you: http://www.amazon.com/Neiko-Power-P...87CW/ref=sr_1_3?ie=UTF8&qid=1336420828&sr=8-3

I built a jig using metal L brackets and wood to make sure all the holes in the cells we're all positioned exactly the same.