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

[floatingdog]

The beer mug in the picture is a nice touch. LOL. Thank you and all those working so hard on this effort for sharing the adventure. When you are done, credibility, capability, and quality will not need to be debated. ES is a really remarkable community.

Best wishes for your success,

John

 

[swbluto]

I've tested many of these cells and they all have performance which is far above the above figures when measured on my resistive load. I've already posted lots of pics of the cells under various load conditions. Also I have been instructed that these cells should never been loaded to under 2V so I would say that the cell under test has already been seriously damaged as stated by Luke and is therefore no longer performing properly.

Now lets say that even if a 26650 A123 cell has a slightly better C ratings than these prismatics, that does not take into account the much higher energy density of the prismatics and the form factor of the prismatics makes the volume much smaller than a pack built from 26650s. Not to mention the ease of pack building. A 16S pack of 20Ah cells is 110mm high, 165 wide and 227 long (not including terminations). How big is 16S, 9p (144 cells) of 26650s?

I would say a sensible approach to sizing a pack is to base it around 10C. This would give you plenty of headroom for higher peaks and also give you a more reasonable range. 10C will after all only give you 6 minutes usage. I will try to do some more tests on the resistive load and you can see the typical voltage sag at more reasoable loads. 30C is great for dragsters, but come on how useful is it in real world situations. A very high C rating just means that at more reasonable loads, the sag is is much reduced as is the heating.

There are plenty more cells if anyone has test equipment that can adequately check a 20Ah cell. They are welcome to contact me to obtain a couple of cells for test.

Liveforphysics just admitted his testing results were done with the heavily abused cell, so we just need more representative independent testing. I also think the cell tests should be performed on a cell after it's been cycled to break it in. It seems that's coming in due time, so don't worry much. They already show they have performance far above the typical EV cells.

 

[cell_man]

Thanks fellas

I hope my comments were not taken as any form of critism for Lukes great effort to get these cells tested for which I am eternally grateful. It's just that some are taking figures out of context and making incorrect assumptions IMO. I have every faith in these cells, that is why I put my life savings into buying them in sufficient quantity to make the price as good as is possible, plus working pretty much every hour of the day to get get them put together into a really good finished product.

I appreciate all the advise and information that I have been given by ES members and have used it to help steer my way I'll continue to listen and do my best to ensure that whatever I offer meets or exceeds expectations and is continually developed and improved. I really have a passion for this and it's about much more than making money for me, I can assure you. Pretty much any money made in the forseeable future over my costs will be ploughed back into the business to help it grow so that I along with others who wish to contribute can offer more and better solutions in the future. I use an Ebike as my daily transport, we've still got bare concrete floors, no doors in any of the rooms and presently using a shitty little fan heater to keep my feet warm..... 50$ a cell is not gonna get me into a big S600 Merc any time soon...

All the best
Paul

 

[MitchJi]

Hi Paul,

I thought my images already posted using a resistive load would give some idea of the cells capability but I'm now thinking that I'm best to dump another 3000USD into a test system that can test to 2000W.

I think that's totally unnecessary.

 

[AussieJester]

Hi Paul,

I thought my images already posted using a resistive load would give some idea of the cells capability but I'm now thinking that I'm best to dump another 3000USD into a test system that can test to 2000W.

I think that's totally unnecessary.

Couldnt agree more Mitch...

Personally i think theres been enough testing, i wouldnt be wasting another cent on equipment Paulif some body else is willing to so be it, their choice, IMHO you have gone above and beyond already sending cells out free of charge for impartial tests, not that I bother reading a word of the technical garb when it comes to batteries bores me to tears, if Luke says they are the real deal, thats good enough for me...

KiM

p.s the new method for securing the tabs (pcb board material) IMO is alot better than the original method also, best of luck getting these mass produced to save you $$$ too

 

[cell_man]

Hi Paul,

I thought my images already posted using a resistive load would give some idea of the cells capability but I'm now thinking that I'm best to dump another 3000USD into a test system that can test to 2000W.

I think that's totally unnecessary.

Thanks Mitch, I might hold off on it for now, but I'll need something soon. I can get a professional version of the CBA with 2000W capacity, but that's not really enough for a big assembled pack. Is there any way to use something like the CBA in series with a large resistive load, so that the CBA can adjust the load, but the majority of the dissipated power goes into the resistors? The icharger 208B has this facility but on a much smaller scale than is required.

I've got resistive loads that can pull about as much current as is possible out of a single cell and they can be adjusted for even higher current if required. This is not a fancy test, just a simple resistrive load but AFAIK it is a valid test.

I personally think that the max C rating is less important than the voltage sag at a more reasonable 10-15C. I've just now fixed to get 10pcs of A123 26650s sent ASAP and will have some comparisons made between the 2 cells types within a few days. Even if the prismatics fall a little short of the absolute max C rating, I'm very confident that at more reasonable discharge rates they will be comparable.

Even if I don't get the test equipment right now, I'll be getting something very soon. I don't like not having the right tools for the job. With a proper piece of test equipment I'll be able to do cycle tests on completed packs and include test data with every supplied pack.

Thanks Kim.

Sorry Luke for posting so much on your thread. I just wanted to address some of the points and to let people know that I am listening and will do whatever is required to assure people that these are the real deal 8)

 

[AussieJester]

I just wanted to address some of the points and to let people know that I am listening and will do whatever is required to assure people that these are the real deal 8)

^^^ this is the kind of attitude that will get you alot of respect and business IMO, more the pitty more suppliers don't adopt this line of thinking ....:: big thumbs up::

KiM

 

[cell_man]

Fellas,

I've only just viewed the video that was previously posted and I can state with 100% certainty that cell is not functionaing correctly. All the cells I have checked have had less than half the voltage sag that cell is displaying for a given current.


View attachment CIMG0204.JPG

View attachment CIMG0201.JPG

Here are 15Ah tests again but witrh greater load. Notice the current clamp has exceeded it's 400A max rating. Initially the cell delivers 400A plus at 2.61V and then after some time it drops to 2.40V but still delivers 400A plus. These tests were done after I had learned a couple of tricks from Docbass, which are namely, to take a little charge out of the cell before hitting it really hard, letting it get a little heat in it and giving it a few hours after charging, before running any tests.


View attachment 3

View attachment CIMG0264.JPG


Here are some pics from 20Ah tests

View attachment CIMG0250.JPG

View attachment CIMG0251.JPG


The cells I tested were not treated specially and not even cycled more than 2 or 3 times before subjecting them to these tests. However they have always been kept under pressure whilst testing and charged to 3.60V. I didn't want to but in too much on this post but I do think that those videos do not give a true picture of how these cells perform. If someone will host a video of my tests or put it on youtube please let me know and I'll forward it.

Tomorrow I will buy a higher rated current clamp and show what 400A plus actually is. I've calculated circa 550A by measuring the current on a single resistor in the above test rig, then determining the total current through all the resistors. The tab voltage was circa 2.2V but it will not sustain that kind of load for more than a few seconds before it starts to sag further.

 

[liveforphysics]

Yep, that's about how this cell performed before shorting it a number of times, overheating it, bending it, etc. It has been a learning process to get this all figured out, and the poor cell got the snot shorted and beat out of it in the process.

I'm hopefully going to have the test setup done this morning Then once I prove it performs correctly with no surprise shorting or failures, I will make some vids with the virgin cells.

 

[cell_man]

Yep, that's about how this cell performed before shorting it a number of times, overheating it, bending it, etc. It has been a learning process to get this all figured out, and the poor cell got the snot shorted and beat out of it in the process.

I'm hopefully going to have the test setup done this morning Then once I prove it performs correctly with no surprise shorting or failures, I will make some vids with the virgin cells.

I hope so. You said before shorting the test cell etc, don't you mean after? Anyone that looked at the values on those videos would rightly believe that the cells are nothing more than fairly reasonable but not particularly special cells.

All my tests were done using off the shelf test equipment. It might not be the best available equipment but the accuracy is within a small error margin and the discharge rates I have seen with every cell that I have tried are very similar to what I have shown above and in my other posts on the matter.

 

[liveforphysics]

Sorry to make myself unclear! I meant, the voltage vs current numbers in your photos is roughly how this cell performed BEFORE I damaged it.


I just stepped on my soldering iron with my barefoot about 10mins ago... Didn't hurt badly at the time, now it's starting to build up into something that gets my attention. lol Don't worry, I'm not letting it slow down the cell test setup.

 

[Momentous]

ouch !
If these cells are used for my electric bike, do I need to use such big wire for a 500watt 36volt rig ?

 

[swbluto]

ouch !
If these cells are used for my electric bike, do I need to use such big wire for a 500watt 36volt rig ?

Not if you set your controller's current limit appropriately.

 

[liveforphysics]

Nope! The only reason you would need wire this big is if you're going to be pulling 450-600amps at 3v, and you need to minimize voltage drop in the wires to get resistance low enough at the loadbank.

For a 36v pack on a 500-1000w bike, little 10-12awg wires would do just fine. A 500w 36v setup would only be pulling 14amps.

 

[Ypedal]

I'm actually very interested in the abuse tolerance and effects, that cell is a great guineapig !

 

[liveforphysics]

I'm actually very interested in the abuse tolerance and effects, that cell is a great guineapig !

Yep, I'm going to cut it open and photograph the construction inside once I'm done using it to get my test rig dialed-in.

Right now, I'm happily drawing 400amps at 100hz, and the FETs are just mildly warm. The FET driver gets extremely hot though, and I have to stop after 20 seconds or so. I'm using 8x100ohm gate resistors, so it doesn't seem like it could be pulling more than a half-amp or so, and it's rated to 7amps, so I'm a little confused with what is happening there. I used 10x10ohm resistors last time with the same model of driver, and it never got more than warm. Any ideas?

BigMoose mentioned the system inductance. I felt evidence of this in inductive kickback. When manually operating the FET gates I happened to have my hand touching both of the FET array buss bars, and when I lifted the gate wire, I felt a jolt! I can barely feel a tickle when working with 48v, and this was a pretty defined jolt. Is this going to kill my FETs if it's above 100v? Do I need any special precautions to clamp this? I've got a decent selection of zeners I could throw across there, would that be a good solution, or should I not worry about it?

PS: Don't step on soldering irons barefoot, it makes you lame in more than one way.

 

[swbluto]

PS: Don't step on soldering irons barefoot, it makes you lame in more than one way.

I imagine not much good could from that. Hope you get better.

P.S. Soldering stands have a raison d'etre.

 

[liveforphysics]

I imagine not much good could from that. Hope you get better.

P.S. Soldering stands have a raison d'etre.

Thank you for the kind words. I really should use my soldering stand more than I do, I know I'm going to burn the damn house down one of these days, or step on it again... Shoes would be a pretty good idea to wear in my project room as well, being as the floor is covered in copper, stainless, aluminum, fiberglass, and carbon fiber shavings and shards. My cleaning chick right now is the type who just throws away everything small on the floor that she doesn't recognize, so I've been having her not clean my project room. I miss my favorite cleaning chick who would painstakingly go through and sort everything she found on the floors. :'(

 

[cell_man]

I'm actually very interested in the abuse tolerance and effects, that cell is a great guineapig !

I've just made a video that I'm currently trying to upload that shows a cell with over 400A initially and then sustained until the cell is virtually discharged. Initial voltage with over 400A is over 2.5V. As the cell discharges it drops to just under 2.20V and then rises again as it gets some heat into the cell. There is no cooling and the temperature gets up to 67deg C and after the test was finished it reached 69deg C. This cell has already been abused before and performs just like any other cell I pull out of the stack. Is that enough abuse?

All cells need to be treated with some respect and dead shorts or physical damage cannot be classed as reasonable abuse IMO. Also until I know otherwise I will be ensuring all cells are kept under some pressure whilst being discharged and any assembled pack I supply will be built in this way. Once I have time I will determine at what kind of current cooling panels are required and will be offering packs with cooling panels included where necessary or requested.

 

[thomas]

For 3000$ you can probably get a cba 3 and 4 amplifiers for 2000W testing.

 

[liveforphysics]

I made a copper heat-sink for the FET driver that was getting hot, insulated the bottom side of it, then ran it again, and this time it made a little crackle noise and let the magic smoke out... :x

WTF would cause this??

This is the spec sheet or the part:

http://focus.ti.com/lit/ds/slus324/slus324.pdf

Here is a picture of how it's wired up:

Any ideas?

 

[cell_man]

For 3000$ you can probably get a cba 3 and 4 amplifiers for 2000W testing.

That's my plan but I've already spent thousands on test kit, tools, other products I'm gonna be selling, not to mention the last 6 months I've been living in China with no income and last but not least enough of these cells to be able to offer them for the price I am and still make a small profit. The money tree is getting a little light at the moment

 

[GGoodrum]

FWIW, I've got some regular a123 cells that have been abused to the point that they they will sag below 2V under similar loads. One thing I've noticed with these is that after charging, they won't hold a surface charge, and the voltage quickly "burns off" to about 3.35-3.40V, instead of staying up around 3.55-3.60V.

-- Gary

 

[Doctorbass]

Maybe you could ask John from Camlight for the CC-400 he is building!!

Probably that for 3000$ he could assemble enough modular unit to carry more than 2000W

I think it’s somewhere around 500 and 550$ for 500W so probably that for 6 unit for 3000$ you could get 3000W

These 500W units are very high quality and nice desing... and half size than the CBA amplifier for the same power.


http://www.rcgroups.com/forums/showthread.php?t=938266

BTW.. I think that everyone here that are interested to better understand the LFP cells must watch the Thundersky test video of Jack Richard at EVTV.ME
I dont necessarely agree with all his claims.. almost for the balance at the bottom principle.. but for the rest I think everything else make sence to me. That video where he explain how LiFePO4 cell work is very instructing correlate with the Battery univercity references and will give you many answers about voltage sag and surrounding effects

Gary, I've noticed that effect too on my some of my abused A123 cells

Doc

 

[swbluto]

If you're willing to DIY, you can do it A LOT CHEAPER.

It seems to me, cell_man, that the most expensive part of these systems are the load. For single cell testing, galvanized fencing cut to *just* the right size submerged in water can take a whole lot of watts due to the high surface area and the resistance can be just suitable for a single cell. Look for the tightly meshed type with a lot of criss-crossing tiny wires. For frequency testing, I have no idea if it's appropriate due to inductance, but for a constant DC load, it seems far more than adequate and doesn't cost more than $10.