[bmentink]

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?

[JRoque]

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

[Duncan]

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!!

[bmentink]

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 .....

[Duncan]

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!

[frodus]

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.

[bmentink]

Originally Posted by frodus

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.

[bmentink]

Originally Posted by Duncan

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 ...

[Duncan]

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??