# Cheap Lithium Ion Cells ... seen these?



## bmentink (Apr 22, 2011)

Hi Guys,

In my search for the best bang-for-buck regarding Lithium Ion/Polymer cells I have come across a Chinese supplier of Lithium Ion cells and have managed to get a quote from them.

For example a 100Ah cell, they quote $15.50US for 1 off quantity, $13.50US for >100 quantity ... so this is .15c per Ah which is much less than the typical $1.20 .. $1.50 per Ah I have been seeing elsewhere.

Granted, you have to add freight to that ... but still very cheap.

So at the moment I am trying to get performance graphs from them, but from the datasheet (attached) it looks like the cells are similar to ThunderSky cells (although ThunderSky don't make a 100Ah cell, so confused ) ..

What do people think?


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## JRoque (Mar 9, 2010)

Hi. I think they might have fudged the decimal point. There's no way they can possibly sell a 100Ah cell for $15.. unless freight is $100 for each cell.

I'll side with the "too-good-to-be-true" camp.

JR

PS: here's a link to Thundersky's 100Ah cell: http://www.thunder-sky.com/pdf/201121921736.pdf


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## Duncan (Dec 8, 2008)

Hi Bmentink,

Sounds too good to be true - unfortunately - keep us posted as to what you find, I will be looking to buy cells in a few months and I'm interested in what these would cost landed here in NZ

If those prices are right I will have 100 tomorrow!!


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## bmentink (Apr 22, 2011)

Hi Guys,

Unfortunately you guys are right ... too good to be true. The young Chinese lady made a slip up with the quote ... more like $130 which doesn't make it any cheaper than anyone else.

In the meantime I have been looking at making my own packs up using 16Ah Headway cells ... I can get these from China at $1US per Ah in reasonable quantities (2000), I only need about 440 so anyone else interested? ..

The nice thing about these cells is they can handle 10C continuous discharge and 5C continuous charge. I have 5 in parallel in my pack that make for a whopping 16x10x5=800A CONTINUOUS. Since I will only be running 50..100A most of the time, that makes for huge headroom and must make for a longer life for the battery.

Maybe I should start another thread on the subject though .....


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## Duncan (Dec 8, 2008)

Hi Bmentink,

I was going to go for TS but if you can get Headways for that you can add my order - only 100 unfortunately - that gets us to 540 - only another 1460 to go!


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## frodus (Apr 12, 2008)

People out there want them, I did a group buy a couple years back and we got just over 1500 cells on our order from 34 different people in a little over 2 weeks.... and they were mostly bicycle guys. If you put something like this together, let me know, I have some tips and info.


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## bmentink (Apr 22, 2011)

Duncan said:


> Hi Bmentink,
> 
> I was going to go for TS but if you can get Headways for that you can add my order - only 100 unfortunately - that gets us to 540 - only another 1460 to go!


Putting on sales hat: Duncan, you sure you only want 100? remember you will need 5 x16Ah Headways in parallel to be the equivalent of one 100Ah TS cell, so if you where going to order 100 x 100Ah TS, then you want 500 Headways ...


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## bmentink (Apr 22, 2011)

frodus said:


> People out there want them, I did a group buy a couple years back and we got just over 1500 cells on our order from 34 different people in a little over 2 weeks.... and they were mostly bicycle guys. If you put something like this together, let me know, I have some tips and info.


Any tips and info, especially on connecting the cells, is most welcome.

My thoughts are to use PCB material as the cell support, which will also double up to add circuitry to monitor cell voltages(to warn on low voltage at the end of discharge), i.e there will be PCB tracks going to the cell sub pack (5 cells in parallel) as well as copper buses screwed into the terminals. I intend charging the pack in parallel (not series like is mostly done) to top balance the cells, I will do that by using a cheap DC-DC converter set to 3.65 volts output on each sub pack .. i.e I will need in my case 90 converters. These will be distributed around the pack(s), the cost will be similar to buying a high voltage series style charger, but I won't need any BMS  That's the plan at the moment.


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## Duncan (Dec 8, 2008)

Hi Bmentink'

Battery requirements – thinking out loud
Last two years – Driving history
Around Gore 
work/back, sometimes errands 21Km? - 500 times - 50 Kph limit so 200 whrs/mile = 125 whrs/km = 2.7 Kwhrs
Invercargill and back – 150 Km – 20 times – 100kph limit so 300 whrs/mile = 190 whrs/km = 29Kwhrs
Dunedin and Back – 300 km – 5 times – 57 Kwhrs
Christchurch – 460 km – 7 times – 87 Kwhrs

I could pack 150v of TS 200Ah cells into my little car but it would weigh 300Kg and cost ~ $18,000 and still not get me to Invercargill and back!

Two strings of 16Ah headways would give me 150v x 32Ah = 4.8Kwhrs at 80% = 3.8Kw would weigh ~ 50kg and cost ~$2,300
(use 92 – two strings of 46 and keep 8 for spares – use for auxiliary battery)

Available current,
I am building an OpenRevolt controller – maximum motor current 500 amps, - 
I estimate that if I do a drag 
Time(sec) Battery current(amps)
1 - 28
2 - 71
3 - 115
4 - 158
5 -  201
6 - 245
7 - 288
8 - 332
9 - 375
10 - 418
11 - Motor over revs and blows up

If I can use 10C on two 16Ah strings – 320Amps – only go to “burst” for two seconds

The CurrentEV web page has the Headways at 5C, - that would give me 160 Amps – so I would be on “burst” for 6 seconds 

Using the CurrentEV numbers my alternatives were 
Headway – two strings of 16Ah – 3.8Kwhrs - cost $4,300 - 160amps continuous
Headway – four strings of 16Ah – 7.6Kwhrs - cost $8,600 - 320amps continuous
TS – 60Ah – 7.2Kwhrs – cost $4,800 – 180 amps continuous – 110Kg
TS – 40Ah – 4.8Kwhrs – cost $3,230 – 120 amps continuous – 72Kg

On those numbers the TS would win – nearly twice the range and a lot easier to fit – even if heavier

Two strings of 16Ah headways would give me 150v x 32Ah = 3.8Kw would weigh ~ 50kg and cost ~$2,300 (your numbers)

Much easier to get past the "spousal financial committee"

On the Headways - do they need to be supported on the ends or can I simply pack them together in layers??


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## bmentink (Apr 22, 2011)

Duncan said:


> The CurrentEV web page has the Headways at 5C, - that would give me 160 Amps – so I would be on “burst” for 6 seconds
> 
> On the Headways - do they need to be supported on the ends or can I simply pack them together in layers??


Hi Duncan,

I think you are mistaken on several fronts:

The Headways can discharge at 10C continuous and charge at 5C continuous.
You can CONTINUOUSLY discharge at 160A, not burst. Your range is reduced though, to be expected. I have 5 cells in parallel, that means I can CONTINUOUSLY discharge at 160A x 5 = 800A!!

Using 100 headways will get you nowhere in range, for me I need 23Kw/hrs to get a reliable range over 100kms to 70% DOD. That is 440 Headway cells .. which is roughly equivalent of 80 90A/h TS.

So costs for a similar range:

TS: 80 x 90A/h cells at $130 each = $10400
Headway: 440 cells at $17 each = $7480

So for the same range Headways cost nearly $3K less ... 
The Headways are also more configurable into how you arrange the parallel and series cells to get the voltage you want. I had problems with the TS cells to get the voltage I want for the 23Kw/hrs storage I need.

Hope this is all clear to you.

It makes sense to support at the ends, as that is where you attach the busbars ..


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## Duncan (Dec 8, 2008)

Hi Bmentink

I hope you are correct about the Headways and 10C - but the CurrentEV page does say 5C discharge.

I think you probably are correct - small cylindrical cells should be capable of much higher discharge than prismatic's

You may need 23Kwhrs - but I need either 3Kwhrs for 90% of my journeys or over 30Kwhrs for a once a month journey 
So I am going for a dinky little lightweight pack - and the wife's car for the longer journeys

A 23Kwhrs pack would be useless to me! - too big and too small

If you can get the Headways at $17 I'm in for 100!


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## bmentink (Apr 22, 2011)

Duncan said:


> Hi Bmentink
> 
> I hope you are correct about the Headways and 10C - but the CurrentEV page does say 5C discharge.
> 
> I think you probably are correct - small cylindrical cells should be capable of much higher discharge than prismatic's


I got 10C discharge direct from the manufacturer in China ..


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## karlos (Jun 30, 2008)

bmentink said:


> I got 10C discharge direct from the manufacturer in China ..


From memory, the Headways are not all the same and it is only the 16amps cells that do the 10C


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## Duncan (Dec 8, 2008)

_*I got 10C discharge direct from the manufacturer in China ..*_

Sounds damn good to me!

Did you get your comment about mounting the cells by the ends from the manufacturers as well?


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## Hemon Dey (Jul 31, 2008)

I have previously tested 10AHr Headways up to 8C, but you've got to watch the electrode temperature. If it starts inching close to max battery temperature ratings (minus some tolerance) you need to ease off on the load or increase the cooling - IMHO thermal management is a big and important part of battery pack design. It doesn't take a lot of air to cool down the cells, but they do need good air flow. The 16AHr might be better in some regards enabling you to pull more current with less I2R losses, hence less heat - but monitor temps all the same at least during the test phase. 

I lost 20% capacity in a cell from what I think was overheating. I was monitoring the body of the cell (cuz I was silly), but the electrodes were far far hotter (above 90 degrees, probably higher again inside the pack)- it did highlight to me that temperature was an important factor. It took 2-3 minutes to get up to that temperature at 8C load, but it was relatively easy to cool with a fan.

Just some random thoughts, HTH.

Regards,
Hemon


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## frodus (Apr 12, 2008)

> Any tips and info, especially on connecting the cells, is most welcome.


If you want to know more about how I'm building my pack, go to www.evfr.net.




> but I won't need any BMS  That's the plan at the moment


And how do you plan on detecting low voltage cutoff on a parallel group of cells? you still need some sort of monitoring, but you don't need something that balances.

-----------


All this talk about the 10C rate is pretty funny. 10C not continuous if you want any life out of your battery. they heat up at 10C. 10C is meant to be a short duration and I have a hard time believing anyone on a roadgoing EV will be doing that for long. Design your pack around 5C continuous or less. 10C burst is just fine, but do not run that continuously out of your pack, add more cells in parallel to increase amperage.

I can't stress this enough.... *DO NOT mount cells by the ends.* The cell body should be supported, but the cell screw ends are made to interconnect only. Even the manufacturer will tell you this. The ends are not meant to support the weight of the cell.

And FYI, I've been dealing with Headway for the last 2 years and imported cells myself and worked for EV Components and Manzanita Micro selling Headway cells. I've got my own test setup in my lab and can test up to 160A on my CBA-II and CC400. I've seen what these can do (and am quite happy putting them in my motorcycle), and I've seen how people design packs (the good and the bad). In the end, same as with all battery packs, the closer to 1C (or below) continuous discharge you can get, the better off your cells will be. If you're wanting to build a pack with 96 16Ah cells in series for a 48s2p design and expect to be able to drive around at 320A all the time in a car, you'll be replacing your pack very soon due to heating and the fact that high discharge rates damage cells. 5C is continuous on the 10Ah, 12Ah and 16Ah cells. The 16Ah cells seem to handle 10C a little better, but it should be used as a PEAK. Now, I know you can go all the way to 20C, but at what cost?

If you spend time looking at discharge graphs, you'll see what i mean. The voltage drop is the important thing to look for. If someone wants to send me a 16Ah cell, I can discharge it and show you.


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## bmentink (Apr 22, 2011)

Hemon Dey said:


> I have previously tested 10AHr Headways up to 8C, but you've got to watch the electrode temperature. If it starts inching close to max battery temperature ratings (minus some tolerance) you need to ease off on the load or increase the cooling - IMHO thermal management is a big and important part of battery pack design. It doesn't take a lot of air to cool down the cells, but they do need good air flow. The 16AHr might be better in some regards enabling you to pull more current with less I2R losses, hence less heat - but monitor temps all the same at least during the test phase.
> 
> I lost 20% capacity in a cell from what I think was overheating. I was monitoring the body of the cell (cuz I was silly), but the electrodes were far far hotter (above 90 degrees, probably higher again inside the pack)- it did highlight to me that temperature was an important factor. It took 2-3 minutes to get up to that temperature at 8C load, but it was relatively easy to cool with a fan.
> 
> ...


You are right about electrode temperature. In my pack I will be connecting in parallel every 5 cells with a 8mm thick x 25mm wide busbar, this allows 300A with little temperature rise, and also the large amount of copper helps keep the electrodes cool ... there will also be a lot of ventilation around the cells as they are 5..10mm apart and they are not in an enclosed box.

Moral of the story: Use the largest thickest copper bus bars that you can afford to connect the cells ...


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## bmentink (Apr 22, 2011)

frodus said:


> And how do you plan on detecting low voltage cutoff on a parallel group of cells? you still need some sort of monitoring, but you don't need something that balances.


Well parallel cells are SELF balancing, you can treat them as a single cell. I will be monitoring each parallel group for under-voltage at end-of-discharge(as a precaution as I only intend to operate down to 20..30%)
NB: If you open a TS cell, you will see parallel cells !!

As I am automatically top-balancing with every charge (by parallel charging), I don't need a BMS as such.



frodus said:


> All this talk about the 10C rate is pretty funny. 10C not continuous if you want any life out of your battery. they heat up at 10C. 10C is meant to be a short duration and I have a hard time believing anyone on a roadgoing EV will be doing that for long. Design your pack around 5C continuous or less. 10C burst is just fine, but do not run that continuously out of your pack, add more cells in parallel to increase amperage.


I must be looking at different graphs from a different manufacturer .. my graphs show only a 7 deg themperature rise at 10C continuous, at the end of discharge, not that I would be running them like that, but it gives me confidence that the cells can handle it, at least better than TS cells.

I agree that you don't get the same capacity, and you do get voltage sag at these high rates.



frodus said:


> I can't stress this enough.... *DO NOT mount cells by the ends.* The cell body should be supported, but the cell screw ends are made to interconnect only. Even the manufacturer will tell you this. The ends are not meant to support the weight of the cell.


I agree, I would support them "towards" the ends of the cells ..


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## frodus (Apr 12, 2008)

> Well parallel cells are SELF balancing, you can treat them as a single cell. I will be monitoring each parallel group for under-voltage at end-of-discharge(as a precaution as I only intend to operate down to 20..30%)
> NB: If you open a TS cell, you will see parallel cells !!
> 
> As I am automatically top-balancing with every charge (by parallel charging), I don't need a BMS as such.


Exactly, which is why I said "you don't need something that balances." I was trying to draw the difference between balancing and monitoring. There are many type's of BMS, and I realize you're balance charging, but you didn't mention monitoring LVC. Just make sure you monitor on a cell level and you should be good. I just wanted to make sure, i've seen people say "no bms" and they wonder why their pack dies. (And BTW, I'm a proponent of individual charging, good to see you taking that route.). BTW, monitoring is still a battery management system, it just happens to be the bare minimum, but since you're monitoring AND charge balancing, you basically have a BMS system.




> I must be looking at different graphs from a different manufacturer .. my graphs show only a 7 deg themperature rise at 10C continuous, at the end of discharge, not that I would be running them like that, but it gives me confidence that the cells can handle it, at least better than TS cells.


Yes you must be. Are they for Headway cells? Temperature rise for 10C continous on a 38120S is over 20C.




> I agree, I would support them "towards" the ends of the cells


This is how I'm doing it:


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## bmentink (Apr 22, 2011)

frodus said:


> .... but since you're monitoring AND charge balancing, you basically have a BMS system.


Point taken .. 




frodus said:


> Yes you must be. Are they for Headway cells? Temperature rise for 10C continous on a 38120S is over 20C.


I am looking at the curves for the 16Ah cells, they must be a lot better perhaps ..  will check when I get home ..


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## frodus (Apr 12, 2008)

bmentink said:


> I am looking at the curves for the 16Ah cells, they must be a lot better perhaps ..  will check when I get home ..


Doubtful that it's the 10C curve, but if you have it, can you post it?

I need to get my hands on one. I can only go to 160A, so 10C is about all I can do with my discharging setup, but it's continuous and fairly accurate.


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## bmentink (Apr 22, 2011)

Still looking for the 10C curve, I have it somewhere ..

In the meantime I will post the 5A charge/discharge curve which shows the internal resistance of Headway cells ... much lower than there datasheet, which just says <8mohm. I have attached both the datasheet and the curves for your perusal ..


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## frodus (Apr 12, 2008)

Is that curve from headway? How are they testing the IR? Not sure how, but it looks like they're using only one current and watching voltage and doing V/I, but it doesn't work out, so I'm stumped. That curve is at 0.35C.

I just can't believe that at 10C the rise is less than 20degrees, I've done enough testing to know that even an A123 cell rises more than that, with a lower IR. I've tested a 16Ah cell, and less amps, and it rose more than 20 degrees.

I'll wait for the 10C curve.


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## bmentink (Apr 22, 2011)

frodus said:


> Is that curve from headway? How are they testing the IR? Not sure how, but it looks like they're using only one current and watching voltage and doing V/I, but it doesn't work out, so I'm stumped. That curve is at 0.35C.
> 
> I just can't believe that at 10C the rise is less than 20degrees, I've done enough testing to know that even an A123 cell rises more than that, with a lower IR. I've tested a 16Ah cell, and less amps, and it rose more than 20 degrees.
> 
> I'll wait for the 10C curve.


Yes, that curve is from Headway. I have also attached more curves for both the 15Ah cell and the 16Ah cell .. however, the temperature rise is only indicated on the 15Ah cell, no actual curve.

I have asked Lorainne(Headway) to re-send the temperature curves as I have misplaced them.


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## Duncan (Dec 8, 2008)

Hi bmentink,

Any more thoughts on your group buy?
I have decided to ask for 150 - if you go ahead


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## bmentink (Apr 22, 2011)

Duncan said:


> Hi bmentink,
> 
> Any more thoughts on your group buy?
> I have decided to ask for 150 - if you go ahead


Hi Duncan,

Just trying to get together some other folk ... will let you know ..


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## karlos (Jun 30, 2008)

bmentink said:


> Hi Duncan,
> 
> Just trying to get together some other folk ... will let you know ..


Did you get my PM? It's a bit earlier than I wanted but I could be serious about joining the group buy at that price.


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## bmentink (Apr 22, 2011)

karlos said:


> Did you get my PM? It's a bit earlier than I wanted but I could be serious about joining the group buy at that price.


Hi Karlos,

No, did not get your PM, actually it is a bit early for me as well, but will note you as an interested party as well. Where are you located? and how many cells?


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## frodus (Apr 12, 2008)

bmentink said:


> Yes, that curve is from Headway. I have also attached more curves for both the 15Ah cell and the 16Ah cell .. however, the temperature rise is only indicated on the 15Ah cell, no actual curve.
> 
> I have asked Lorainne(Headway) to re-send the temperature curves as I have misplaced them.


Exactly! Even though it's a 15Ah cell, (the 16Ah cell won't be much different. Same chemistry, same cell style) Those documents show a 50C (29c to 79C) rise on a 15Ah cell at 10C (150A)..... and that is way over the actual spec of 60 degrees C, by almost 20degreesC.

That is way too hot. Put them in a pack, and you compound the issue. Even if you cool them, the temperature inside the cell will be hot.

Then look at the voltage drop. 10C voltage drop is going to be right at 2.6V. You notice that the curve increases a little right? That's because of heat. the 2.6V valley is what you should go by, because you should only be doing bursts anyway, so you'll spend more time at the very initial part of the voltage curve. 

I still say build a larger pack, so your "continuous" is closer to 5C or lower.


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## karlos (Jun 30, 2008)

bmentink said:


> Hi Karlos,
> 
> No, did not get your PM, actually it is a bit early for me as well, but will note you as an interested party as well. Where are you located? and how many cells?


I'm up the other end of the country, Whangarei and at this time need 560 16amp cells. I'll PM my email address.


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## Duncan (Dec 8, 2008)

Hi bmentink,

Did you get my PM?


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## bmentink (Apr 22, 2011)

Duncan said:


> Hi bmentink,
> 
> Did you get my PM?


Yep, replied ..


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## bmentink (Apr 22, 2011)

Hi Guys,

Just to let you know I received 4 sample cells from Headway so that I can verify their charge/discharge behaviour ... I will test them in series noting any cell imbalance ..

They arrived with an identical 3.32v on all 4 cells.

I will get some graphs up, when I am done.

Cheers,
Bernie


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## frodus (Apr 12, 2008)

that doesn't mean they're charged, Charge them up all the way before you proceed.


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## bmentink (Apr 22, 2011)

frodus said:


> that doesn't mean they're charged, Charge them up all the way before you proceed.


Yep, was going to do that. I understand they supply them at roughly 50% charged.


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## frodus (Apr 12, 2008)

yeah. I didn't realize that at first, and some cells self discharged over the course of a year.....

Looking forward to seeing the results. Monitor temperature at the high discharge rates.


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## albo2 (Oct 4, 2011)

I'm looking at batteries at the moment, interested in what you chose to go for.


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## bmentink (Apr 22, 2011)

albo2 said:


> I'm looking at batteries at the moment, interested in what you chose to go for.


Hi, so far I am still looking at the headway cells (I have been busy with other parts of the conversion .. will be buying batteries at the very last moment)

I am still doing more testing .. will post here when completed.

Cheers,
Bernie


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