Testing the big 15 and 20Ah LiFePO4 cells is tough! *Pics*

[AussieJester]

I haven't heard any stories of failures either and more then 1,000 roadsters have been delivered.

Give it time

KiM

 

[cell_man]

Brain-fart: A large packs might benefit from plates that can pass coolant... Corrugated aluminum panels, perhaps.

Certainly would add to pack size and weight; but the benefits might surpass the penalties.

That's just the sort of thing I was thinking of. It wouldn't need to be very thick IMO to be effective if fans were implemented and 1 layer of the corrugated material every 2nd cell would probably suffice for most aplications IMO. Probably not so heavy also.

 

[voicecoils]

Reading these Energy density calculation i think we might take in acount the connection from one cell to another..
...
We should add the connection structure weight in the calculations.

We need to simply be clear in our discussions and comparison. To my mind, there are 3 categories to consider:

[*] energy and power density of the chemistry itself (ignoring the cell container)
[*] energy and power density of the cell itself (where a load could be applied directly to the terminals of a single cell)
[*] energy and power density of a complete engineered pack, with applicable BMS included (the pack is in situ, ready to operate in it's application)

 

[Matthijs]

Here you can see how the Dow/Kokam Ultra High Power modules are being build for the White Zombie using 30 ah Dow/Kokam cells.

http://photos.plasmaboyracing.com/album07

This must be the extra weight Doc is talking about.

 

[CroDriver]

I like Plasmaboys batt pack bat I wouldn't use the cell tabs as a structural part of the pack (he's obviously holding the cells using the terminals )

 

[galeson]

From reading through the text it appears that the picture of Plasmaboys pack has the side shown as the top. He plans to have the cells stacked up. Also note there is no provisions for cooling although the case was designed by Dow/Kokam itself.

 

[liveforphysics]

Cooling these cells really isn't going to be a concern guys.

For a drag racing application, I've dead-shorted these prismatic A123 cells for 10-15 seconds, and they don't melt. That's way harder abuse than they're ever going to take in a drag application, and then they get 15-20mins to cool down while you wait in line to get to make a pass again.

For a street EV application, if you want at least a 30minute run-time, this means the average C-rate on the cells is going to be 2C. You're going to have bursts of 20-30C during peak acceleration, and you're going to have times where it's coasting or braking etc, or just cruising along holding a set speed, and it will be cooling down during these periods.

I've done 1.5 minutes at 450amps on the fresh 15Ah cell, and it was warm, but not dangerously hot. That's 11.25Ah, which is 75% of the capacity of a 15Ah cell anyways, and that's taking it all continuously at 30C. I could have continued to discharge at 450amps, I just stopped because my loadbank was starting to glow red. lol

 

[liveforphysics]

Also guys, as far as the weight of the pack vs the weight of the cells alone, if you want to make as light of a pack as possible, you can simply stack the cells on top of each other, fold the tabs together, and solder them directly to each other, solder big leads to the ends of the stack to connect to the controller, and call it a day. This is a very reliable proven method to make a pouch cell pack, as evidenced by the millions of RC lipo packs that work fantastic using this type of construction.

These more elaborate methods are to make possible cell swapping needs, or pack re-configuration needs as easy as possible. They do not need to be done for an application where you're looking to absolutely minimize weight, like in an ultralight aircraft or something where an extra 2-3lbs of pack construction materials could be swapped for an ounce of solder and some kevlar straps.

 

[CroDriver]

Cooling these cells really isn't going to be a concern guys.

For a drag racing application, I've dead-shorted these prismatic A123 cells for 10-15 seconds, and they don't melt. That's way harder abuse than they're ever going to take in a drag application, and then they get 15-20mins to cool down while you wait in line to get to make a pass again.

Hmm, I heard that some crazy guy is going to race against gas cars in REAL races (not only drag racing) with this pack.

Here is what this crazy dude wanted to do with them:

(ignore the tab color on the last picture)

I hope that this will keep them cool

 

[liveforphysics]

Crodriver-

You will never be having a temp problem with a setup like that.

 

[AussieJester]

Hmm, I heard that some crazy guy is going to race against gas cars in REAL races (not only drag racing) with this pack.

Yeah he sounds like a right tool Co Driver what a twit, stay away from him man he will
get you into trouble

Seriously buddy, looks insane, is this a definate goer is it? IIRC your running ThunderSkys in
a car now is that correct? What car are you planning on dumping this pro-setup in mate?

Best of luck anywayz be sure to follow that when you start it!!

KiM

 

[CroDriver]

Hmm, I heard that some crazy guy is going to race against gas cars in REAL races (not only drag racing) with this pack.

Yeah he sounds like a right tool Co Driver what a twit, stay away from him man he will
get you into trouble

Seriously buddy, looks insane, is this a definate goer is it? IIRC your running ThunderSkys in
a car now is that correct? What car are you planning on dumping this pro-setup in mate?

Best of luck anywayz be sure to follow that when you start it!!

KiM

lol

Yes, I have TS cells in my car now but I'm building another car, almost from scratch. Just using the BMW "shell".

Two custom made motors, custom made differentials (AWD), two 400V/2000Amp liquid cooled controllers and a lot racing stuff. Should be fun to ride

I'm 90% sure that this cells will be used (Headway cells are in the 3D model because I was planing to use them before these cells became available).

I will probably make two separate packs, 4p112s each. One where the engine used to be, the other like in the 3D model

 

[AussieJester]

OH HELL YES!!! now thats more like it for a lecky car!!! Have you got a thread happening on it
on another forum? I recall there was a 'mate' of yours that came here briefly pissed a few off with a couple
comments he made, he had a kit car? was it? I saw a thread of that on another forum, if you have one too would like to subscribe to it too follow your progress...

KiM

 

[CroDriver]

I recall there was a 'mate' of yours that came here briefly pissed a few off with a couple
comments he made, he had a kit car? was it?

Eeehm, I can't recall that... Maybe you mixed something up...?

I saw a thread of that on another forum, if you have one too would like to subscribe to it too follow your progress...

KiM

I have a thread for the old BMW here:

http://www.diyelectriccar.com/forums/showthread.php/bmw-bi-moto-ev-project-28287p15.html

...but it seems like the pictures are not there anymore

I also have a thread about my GTM EV project here:

http://www.ffcobra.com/forums/showthread.php?t=229801

The kit is still somewhere on a ocean ship. I will open a thread when both projects are nearly finished

 

[AussieJester]

It wasn't you that did the pissing of people off bud, it was another chap also from Croatia he seemed to know you though.
He was calling Luke a kiddie racer or something along those lines...anywayz...no matter...

Cheers for those links mate...look forward to seeing this puppy happen! Best of
luck beating "White Zombie" too, thats a pretty quick lecky sedan, yours
definitely looks better so you got a start there hehee

KiM

 

[bigmoose]

Kim is thinking of a guy that went by "Jeff" I believe. He also offered for sale an A123 vehicle battery pack for $30,000 IIRC.

 

[CamLight]

Hmm, I heard that some crazy guy is going to race against gas cars in REAL races (not only drag racing) with this pack.
Here is what this crazy dude wanted to do with them:
<snip>
I hope that this will keep them cool

crodriver, what's the link for those pictures? I wanted to check out that guy's project but couldn't find it using the file names for the photos. Thanks!

 

[AussieJester]

Kim is thinking of a guy that went by "Jeff" I believe. He also offered for sale an A123 vehicle battery pack for $30,000 IIRC.

100% correct, and this is the thread in question...he has edited most of his post now but some can still be seen in other members replies where they have quoted him, sounded like a right wanker too me.

/off topic

KiM

 

[MitchJi]

Hi Luke,

Cooling these cells really isn't going to be a concern guys.

For a street EV application, if you want at least a 30minute run-time, this means the average C-rate on the cells is going to be 2C. You're going to have bursts of 20-30C during peak acceleration, and you're going to have times where it's coasting or braking etc, or just cruising along holding a set speed, and it will be cooling down during these periods.

I've done 1.5 minutes at 450amps on the fresh 15Ah cell, and it was warm, but not dangerously hot. That's 11.25Ah, which is 75% of the capacity of a 15Ah cell anyways, and that's taking it all continuously at 30C. I could have continued to discharge at 450amps, I just stopped because my loadbank was starting to glow red. lol

In a "street EV application" the cells would be enclosed and possibly pressed against each other. Do you think in that situation cooling won't be an issue?

The honeycomb aluminum between cells (even without fans), possibly with the holes vented would probably make a big difference. Probably not much weight. For an ebike the main issue might be space.

If the Turnigy Lipo packs don't get too hot with no spacers and the heat production and tolerance is similar plates might be overkill (on an Ebike).

 

[liveforphysics]

So, this is the reason why my FET setups kept exploding until I went to the 100ohm gate drive resistors with the 7.1v zenner clamp diodes. The inductive kickback is brutal! This is the reason why caps are so very important on things with FETs, and it's a damn shame I can't use them on a cell testing setup (because it would influence the cell performance readings).

Ok, I snuck my test-rig into work to have access to the $14,000usd fluke thermal imager, and took some very slick pics.

I layed out some engineering blueprints to protect the table, then setup the whole mess right on the 20ft long confrence table. lol

These are thermal tests from the minty fresh undamaged cells. I tested the 15Ah cell until I ran it to LVC, then swapped to the 20Ah cell, and ran it almost to LVC, but I had an unexpected problem with my test setup that you will see later in the pics. lol

The colors auto re-calibrate to fit the temp range, so blue might be 500deg if there are parts in the picture at 1000deg, or white/red could be -20deg if there are parts in the picture at -100deg, so you must use the temp tags to read the temps, or look at how the temp scale is setup for each indivdual picture.

This is 2 minutes at 150amps on the 15Ah cell. (5Ah, or 33% of cell capacity used)
97deg peak temp. Ambient temp was 77deg F, so 150amps for 2minutes just brings the cell up to human body temp, and all localized at the cathode. Pretty damn cool running cell.

I loaded the loadbank up to 300-315amps, and let it sit another 1 minute (Another 5Ah, 66% of cell capacity used).
107.7deg F temp peaks. Feels about Luke-warm to the touch in that cathode area, about body temp for the rest of the cell. Still very cool running for a cell getting hit with 20C discharge continously...

I was going to step up the discharge to 450amps for the last 5Ah left in the cell, but I was dicking around tweaking the manual focus and trying to range the camera that it all ready had another 30seconds at 300amps, so I just let it finish at 300amps to LVC. (Another 5Ah, ~90-100% of the cell used.)

At this point, I was pretty proud of how my setup was working, and I wanted to take a pic of the FETs.

Shoot! Barely warm! Little bastards were doing a hell of a job, and I owe that to BigMoose's advise about the higher resistance gate drive resistors and the zeners to protect gate bounce. Thanks Moose!

So, feeling pretty confident with my FET setup, and wanting to make the most of my time with the IR imager, I decided to hit the 20Ah cell with a worst case scenerio sort of situation. I did 600amps, 80% duty cycle (480amps PWM average), 10khz switching frequency.

So, it starts out humming right along, this was roughly 40seconds in (5.3Ah, 26% of the cell used), I didn't get a clean time marker when I started exactly. Oops! I decided to just run the cell into LVC and snap pics along the way. lol This is pretty much an absolute worst case scenerio jump in your EV and just stay wide open on max current limit from a full charge all the way to empty. lol If a cell can handle this, it can handle pretty much anything an EV is going to throw at it.

The FET bank was really making a strong humming sound, so I decided to snap another pic.

I could see the loadbank start to relax, and I could see waves of heat riseing off of it. lol I wanted to check on the FETs again.
WHOA! 371deg F FETs!!! Not good! lol I decided to just let it run it's course and see what happens though.

This was about 95% discharged, keeping up the brutal amp rate the whole time. Why didn't I run to 100% discharge? You will see why below.

The solder on my FET bank MELTED!!!! WHOA!!! Amazingly, I tested the FETs afterwards, and they still seem to work perfect! Notice that crazy delta-T between the copper and the FETs! Can you say thermal run-away? lol

 

[liveforphysics]

Anyways, I really crunched down on those terminals when I first suspected a poor cathode connection was causing the localized heating.

I really had those copper blocks cranked down tight on the cathode and annode. I don't think it was a poor connection causeing the localized heating, and it turned out to be localized in that area on both 15Ah and 20Ah tests. I'm thinking that just happens to be the area of highest resistance in the cell design.

This is actually a good thing.

It means we don't need heatsinks! We just need a simple heat-spreader plate to sandwich between each cell, and these things will be bulletproof against even the absolute worst case scenerio EV applications. Bicycles aren't even going to get these cells above body temp.

Very cool cells!

-Luke

 

[cell_man]

Great work luke

Pics are blocked again If they could be attached or send them by PM that would be great.

The cells seem to really like the pulsed load. They're some great figures for sure I think it's still important for anyone who does use these cells that although they have amazing capabilities you do need to keep within some boundaries or they can be damaged quite quickly, but as the limits are so high I can't think of many circumstances that would actually push them to those boundaries. I think as long as the temperatures are kept within limits and very high discharge rates that pull the cell down to 2.3V or lower (circa 30C) are not sustained for more than a few seconds, they will have a long and healthy life even in very high performance applications.

My personal feeling now is that they should be treated like a 15-20C continuous with the capability to deliver 30C plus for a few second bursts. As per the 26650s a cell temperature of no more than 60deg C should be strictly adhered to and better yet a little lower as when you really hit them very hard the temperature will continue to rise after the load has been removed and it's the internal temperatures that you are most concerned with. Also if you look at A123 26650s, independent tests I've seen suggest that the 30C rating given by A123 is a bit optimistic and a more reasonable rating of circa 18C is more realistic. The performance of the 15 and 20Ah cells appears to give very comparable C rating to A123 26650s but in a significantly more energy dense package with regards to weight and even moreso volume, not to mention the relative ease of assembly.... (but I'm pretty much there now) and finally cost. A123 26650s are presently circa 7USD on ebay a pc for 2.3Ah or 3.04USD/Ah as opposed to my price of 2.5USD per Ah. 26650s would have to be 5.75USD a pc to be the same per Ah price as the big cells.

Thanks again Luke

 

[bigmoose]

Luke, my hats off to you! Stunningly great test, the thermal images are priceless. Glad the FET switcher electrically held together. Sure appears that without any doubt these cells are the real deal

Ohhhh, how I love the aroma of high power electronics in the morning

Ah, I really like the thermal images Luke, can you share which model Fluke Imager that is? What's the interface to get the thermal images out of it? How flexible is setting up the image to print the localized temps over the thermal map? The more I look at your pix, the more fascinated I am with the images.

 

[gestalt]

I got a chance to go over one of the large packs that a123 uses and it seems that they sandwich the cell between two sheets of aluminum for heat syncing. and between each of those sandwiches ~~mmmm, lithium sandwich~~ there is a layer of a neoprene like material to allow for expansion. I was told that the cells can expand about 10%, have you seen anything like that in your tests?

 

[cell_man]

I got a chance to go over one of the large packs that a123 uses and it seems that they sandwich the cell between two sheets of aluminum for heat syncing. and between each of those sandwiches ~~mmmm, lithium sandwich~~ there is a layer of a neoprene like material to allow for expansion. I was told that the cells can expand about 10%, have you seen anything like that in your tests?

I haven't personally checked for that but I would be surprised if it was as much as that, but who knows. That might explain why the code number indicates a cell about 0.2mm thicker than I've found. So how many sheets of neoprene? I've made a bit of a list below showing how you might stack the cells if cooling sheets were added. Where does the neoprene go?

Cell
Alumimium
Cell
Aluminium
Cell
Alumium

Also roughly how thick is the Neoprene and how thick is the alumium sheet. Is the aluminium sheet insulated or just direcly onto the cell? However I would have thought you would only see expansion like that if pushed very hard. I'll have to get a bigger resistive load to check for that.

I have some big 2ohm loads that I've used on a 16S pack. They are only 750W rated so I'm running them well over spec, with about 25A at over 50V so 1.25kw a piece. I'll need about 10 of these to push a 16S pack to circa 200A (need lower resistance to allow for the sag). I wanted to make some test benches for checking cells before assembly into a pack and my idea is to make a simple method to tie say 8 cells together using a quick clamping method, then run them into a resistive load whilst monitoring the relative sag across the pack to ensure they work well together.

Thanks for the great info, really really useful