A123 20Ah Pressure Thoughts--and bits for experiments.

[agniusm]

Had some 10mm PP sheets around so i went ahead and knocked up dirty prototype. Looks like it would work very well with nice aesthetics when done properly:

Perhaps someone who received samples could post where the strapping slots are on A123 compression plate (measured)?

 

[docnjoj]

Beautiful work as usual Agnius!
otherDoc

 

[wb9k]

Beautiful work as usual Agnius!
otherDoc

Seconded. Agniusm, your stuff looks great. I've been meaning to say it for a while....

 

[whatever]

if the end plate has a curved outer profile, it will distribute the pressure evenly across the cell, some sort of parabola, I made one out of foam today for my 48v20ah pack, quick and easy to shape foam

 

[icecube57]

Cellman wouldnt give up the heatshrink? Maybe I asked for too much. I was willing to pay... bummer.

 

[999zip999]

Maybe he doesn't know you are the black LFP.

 

[nicobie]

This thread is great by the way, lot's of good ideas, and knowledge sharing.

Yea. It's why I spend a bit of my time here digging for nuggets.

Glad to see you posting. It seems that some here have pissed off Luke and it looks like he might be history. I can't understand why some people get pissed off just because folks like you and Luke can't be spilling the beans on the latest and greatest batteries and ESPs. Have you seen what shit LFP has taken because he didn't review some tiny homemade 450A RC controller?

You both have to be careful about pissing off the corporate lawyer bean counters that control the $ (think FETs with abnormal input signal). :lol:

I wish it could be all for free for everybody.... but one has to pay his/her bills. I Really appreciate you Batteries Guys helping out when you can and acknowledge the fact that you have to follow your company's rules. jesus. H. christ, somebody has to bring home the bacon.

Ask -methods. He has walked the walk. One stubborn dillweed who has earned his strips.
............

Yes Luke, there really is a reason for not sharing (USA shit patent system). Just think of the Chinese business model.

 

[megacycle]

That controller you mentioned, just been put through it with one happy punter, finally, phew.
http://www.youtube.com/watch?v=0gKtMUTnjQo

 

[ejonesss]

i just posted over at http://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&p=785864#p785864 about another idea and now to think about it may be in the wrong place

Since even pressure is required, my immediate thought is to put something inflatable to press evenly on each endplate. How hard would it be to use a couple of car or truck inner tubes to make a well sealed bladder for each end to fit the shape of a cell? What I like is that the pressure is adjustable, measurable, evenly distributed, and can maintain a near constant pressure regardless of SOC. Plus air doesn't weigh much at 5-10psi.

John

A mechanically constrained inflated bladder system sounds pretty good. That's clever, I like it.

If you've got a closed cell dense foam of a material that remains elastic, and you crush it, it behaves similar to a bunch of little bladders all constrained in a sheet of silicone rubber (or whatever material).

 

[agniusm]

OK. I have looked again into those sensors. This one: http://www.phidgets.com/products.php?product_id=3103_0 max pressure is 1Mpa. According to this: http://answers.yahoo.com/question/index?qid=20100121034848AAJa1gM
1Mpa equals 150psi max and the minimum is 10.3kpa which I assume is 1.5psi. So I would think it falls in the right brackets to measure compression of our battery pack. With the cost of 6usd is cheap enough to leave it inside for occasional recheck. Perhaps my thinking is wrong if someone with the knowledge wants to jump in and comment

P.S. attached data sheet, looks good to me, 10kg per 1cm^2 so more than 3 tons per our cell area

 

[wb9k]

OK. I have looked again into those sensors. This one: http://www.phidgets.com/products.php?product_id=3103_0 max pressure is 1Mpa. According to this: http://answers.yahoo.com/question/index?qid=20100121034848AAJa1gM
1Mpa equals 150psi max and the minimum is 10.3kpa which I assume is 1.5psi. So I would think it falls in the right brackets to measure compression of our battery pack. With the cost of 6usd is cheap enough to leave it inside for occasional recheck. Perhaps my thinking is wrong if someone with the knowledge wants to jump in and comment

P.S. attached data sheet, looks good to me, 10kg per 1cm^2 so more than 3 tons per our cell area

Very interesting. Not a precision device, but that probaby doesn't matter here--within reason. Can you buy reasonably small quantities?

 

[agniusm]

I think I can get precision by putting it between 2 cells and adding 350kg whatever weight and measuring resistance, then just replicating tension to get the same resistance value course checking for result consistency. You can get those single units but I must search for them in europe as from usa they would charge 40-100usd for .5g shipmet.

 

[megacycle]

Is that 5% tolerance for fixed loads.
No temperature compensation, states 0.15%per degC.
Guessing maybe overall tolerance value of +/- 5% of measured force starting out at say 25 degC.
E.g. 0.5psi either side of 10psi.
Should be ok for not going extraterrestrial.

 

[agniusm]

I thought so too given 10-25psi margin for error. 15 psi would be a safe bet.

 

[wb9k]

Sounds good to me!

 

[megacycle]

Can a decent digital multimeter read volts on the FSR in a voltage divider, instead of op amps?
Could make a simple, cheap set up.
Would be good if they made an FSR with approx dimensions of a cell, would be on the custom wish list.

 

[steelmesh]

Anyone see these cheap sensors, maybe I can try to embed a couple of these in my pouch packs and see what happens. Sandwich the sensors between a couple thin sheets of stainless I guess.

http://www.tekscan.com/flexible-force-sensors

 

[steelmesh]

Had some 10mm PP sheets around so i went ahead and knocked up dirty prototype. Looks like it would work very well with nice aesthetics when done properly:

Perhaps someone who received samples could post where the strapping slots are on A123 compression plate (measured)?

I picked one of these up with some stainless ties last week, it works well getting the ties tight http://www.amazon.com/gp/product/B002IWX71M/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1

 

[ejonesss]

looking at the image https://www.technologyreview.com/sites/default/files/legacy/auto_x600.jpg it looks like the bands go around the pack 1/4 the way down and 1/4 the way up from the bottom if you see the grooves in the side of the image



also what keeps the cells from puffing out on the sides or at least the sides from bulging?

Perhaps someone who received samples could post where the strapping slots are on A123 compression plate (measured)?

 

[agniusm]

Can a decent digital multimeter read volts on the FSR in a voltage divider, instead of op amps?
Could make a simple, cheap set up.
Would be good if they made an FSR with approx dimensions of a cell, would be on the custom wish list.

I think you dont need to. Just measure the resistance with multimeter

 

[megacycle]

If you don't want to scale the set up, as resistance decreases with force, if you want scale it and straight onto a dvm display, it might be better to measure the vd across a precision resistor in series with fsr.

 

[agniusm]

Dont see the real use getting it onto display.

 

[megacycle]

I expect it's an individual thing, if you just want set and forget, but if you want to monitor changes during heavy charge/discharge at differing ambients or experimenting and don't want to work out what the reading means, you can scale it using vd.

 

[deVries]

Had some 10mm PP sheets around so i went ahead and knocked up dirty prototype. Looks like it would work very well with nice aesthetics when done properly:

Perhaps someone who received samples could post where the strapping slots are on A123 compression plate (measured)?

After you cut the groves just how easy is it to flex the PP. If you can bend it, then I doubt you can apply equal pressure over the surface area of the cell. It will flex downward into the cell where the grove is and flex up elsewhere. As you can see from the post in the other thread, the pics clearly show large ribbing sections in both directions on the A123 plates which will definitely apply much more equal force over the entire surface area of the cell.

See:

Just how flexible is that PP after you've cut those groves???

 

[megacycle]

PP would deform with temperature and even though it's flame resistant would melt and probably smoulder/ catch fire.
I've used Lexon before, for jobs, it was exensive and got not were near the strength of phenol sheet which can be totally fireproof too, not as light because it needs to be dense and probably as cheap or cheaper.

Doing grooves to make it comply with the tab kit and strap looks good, but it's follows a theme of function follows form.