* * * Group Battery Purchase * * *

[Deepkimchi]

Basically for Lunar New year here S Korea all the construction sites are shutting down from Wednesday thru Friday. Not much will move until next Monday.

DK

 

[safe]

We do have ThunderSky in hand, and these are only $2/Ah, instead of the of $3/Ah for the 40138. These are the 40 and 90 Ah cells - they are rated 3C...

Yeah I like those cells. They are still $100 each for the 40 Ah right?

So to go to 24 volt I'm looking at:

3.3v * 8 = 26.4v ... $800.

And in order to use that I'd need a decent 24 volt motor like the PMG 080. Hmmmmm....

Sounds like I'll still be thinking about all this for a while. I was hoping to get a deeper price cut somehow on the 40138's but it looks like you are firm on the $30, so the ThunderSky cells are a better deal. I like the form factor too... square is easier to build with than round.

 

[recumbent]

... square is easier to build with than round

:? Not for me it isn't, I need the flatter rectangle to fit my rear panniers.

 

[Patrick]

The ThunderSky (LFP40AHA) are $80, not $100 ($2/Ah). Also, they are nominal 3.2 volts, rather than 3.3.

The BMS being built for the TS is for fairly large systems. There is an individual board that mounts on each cell, and does the LVC and charge balance. They all communicate over CANbus with a central controller, so all the voltages etc. are programmable. Don't have a cost on this system yet, but it should be middle-tier.

Square vs. round is very vehicle dependent. I have seen 4 TS cells in a pannier, but it's pretty chunky. I think it could be done nicely, but it would be a lot easier with the 40138s. Also much easier to get higher voltages when your basic cell is only 10 Ah instead of 40.

 

[safe]

The ThunderSky (LFP40AHA) are $80, not $100 ($2/Ah). Also, they are nominal 3.2 volts, rather than 3.3.

Wow, that's a good price and for a whopping 40 ah

Let's see...

3.2v * 12 = 38.4 volts... 12 * $80 = $960

3.2v * 15 = 48 volts... 15 * $80 = $1200

Hmmmm... that's getting pretty good.

No hurry on these right?

(no volume issues to worry about?)

 

[Patrick]

No, no hurry on these unless they get used or sold. No volume issues either.

How many cells you use is somewhat dependent on your electronics and charging system/methodology. I would use 4 cells for each 12 volts of nominal load, and charge to somewhere under 4 volts/cell - this should match lead applications pretty closely in terms of max voltage, voltage under load, LVC, etc. Ideally you will tune this with a programmable BMS and charger.

 

[safe]

Ideally you will tune this with a programmable BMS and charger.

Well the thinking right now is to use 12 Thundersky cells (38.4v 1536Wh $960) and then use a small bicycle (legal) motor in the 750 watt range. The range would be about 80 miles at full power. Then add an individual cell voltage meter of some sort on the bike to be able to monitor each cell and watch for low voltage situations. I'd prefer this because I like to know what's going on verses using some automated method of monitoring. (if a cell is going into decline I want to know about it early) When it comes to charging I'd also charge at an individual level to make sure things are optimized.

I'd probably have to design the frame around the pack because this would represent about 2.5 times the pack I was originally thinking about. However, the idea of having a range that is up around 80 miles is really nice. With that kind of range I'd only ride once a day and then recharge, so slow charging is also more acceptable. My bike would have a maximum discharge of 1C... which is almost an insult to LiFePO4. :lol:

But give me some time, I'm still figuring things out.

The amazing thing is that at this price ($80) it's actually as good of a deal as is SubC NiMh which was the cheapest thing I could find before. I would be buying a lot more than I need, but I'm pretty sure that calender life will kill the cells before my motors strain will...

 

[Deepkimchi]

Thundersky 40 ah is 1.7 $ per ah if you buy more than a hundred.

http://www.thunder-sky.com/order_en.asp

Still have shipping though..

 

[safe]

Thundersky 40 ah is 1.7 $ per ah if you buy more than a hundred.

http://www.thunder-sky.com/order_en.asp

Still have shipping though..

Patrick is quoting the same price for less than 100 ($2/Ah) but he hasn't said anything about shipping costs. Maybe he has enough business with them that it's a small addon.

I like the idea of getting enough people together to exceed 100 cells of these so that we could get it down to $1.7/Ah... but that means we need to find about 8-9 people who are interested in spending $816 each to build a 36V pack of 1536 Wh for themselves. That's a lot for your dollar, but it's going to take some effort to find that many people who might be interested.

That would be a great deal... 1536 Wh for $816

Update: This was for the LMP's... the wrong product.

 

[flip_normal]

Thundersky 40 ah is 1.7 $ per ah if you buy more than a hundred.

http://www.thunder-sky.com/order_en.asp

That's not what I'm reading.

LFP = Lithium Iron Phosphate ≤ 100Ah ≤10000Ah = USD 2.50/Ah (column 1, row 1)

So if you buy 100 x 40Ah = 4000Ah it'll cost USD 2.50/Ah.

The only ones I can see for USD 1.70/Ah are the LMP(?) ones but you'll need to buy >10,000Ah to get that price.

ie. 251 40AH cells!

 

[safe]

http://electricmotorsport.com/store/ems_ev_parts_batteries_thunder_sky.php

Thunder Sky is one of the largest manufacturer of lithium batteries in the world. The chemistry of these cells is Lithium Iron Phosphate (LiFePO4) or LFP. The main advantage of LFP batteries is that they do not have the volatile thermal issues that Li-ion batteries have, making LFP batteries much safer then Li-ion. The other advantage is that they have very high cycle life of up to 2000 cycles compared with Sealed Lead Acid (SLA) batteries that have a cycle life of about 400 cycles. This means that the LFP cells can last 5 times as long as the SLA batteries. The price of lithium batteries keeps coming down and the price of lead batteries keeps going up. Hopefully lithium batteries will eventually become equal in price or even cheaper then SLA batteries. If you factor in the cycle life of LFP batteries it can be argued that LFP batteries are already cheaper per use then SLA batteries.

We have been experimenting with these cells for the past year in several real life EV applications such as Electric motorcycles, Electric quads and Electric scooters. The capacity and discharge characteristics have met our expectations. The jury is still out on the manufactures claim of a battery life of 2000 cycles.

These cells are currently for sale to developers only.

So Patrick being able to sell them at $2/Ah seems to mean he is selling off old inventory. Which can't be all that old since they are pretty new cells. (they just got them) My guess is that their company has made some decision that pointed their efforts in another direction so they might be no longer interested in making a business with these.

Patrick... if you are listening... could you comment on this. Is your company planning to make these Thundersky cells central to future efforts or are you looking past them already?

I actually don't mind the idea of getting brand new cells at a discount simply because company plans have changed.

Their "management decision" might mean our savings.

 

[safe]

LCP - 50Ah

The LCP's are just a little different. Their low voltage cuttoff is only 3 volts and the charging rate is half to a third of the Ah so they must use a different chemistry. For electric bicycle applications 150 amps of peak current is so far beyond what you need that discharge rates are not a problem. I'm planning on using one type of these cells at only about 40 amps peak, so I would actually be running at under 1C.

These are actually more expensive...

 

[safe]

LFP - 40 Ah

The LFP's don't seem half bad. The high and low for charging and discharging are 4.25v and 2.5v. The charging rate is an "insane" 3C so you could in theory charge these suckers at a truly "sick" 120 amps. Laugh.... ha... ha... oh that's just a crackup.... 120 amps per cell charging. :lol:

Continious discharge of 120 amps is also way beyond the needs of most electric bicycles as well.

You wouldn't be going wrong with the LFP's...

 

[safe]

LMP - 40 Ah

There's a reason that the LMP's are so cheap. Their lifecycles are simply terrible. No way would you want to only get 300 cycles for this kind of money.

Apparently "LMP" is an acronym for "Limping" as in:

"I was riding my bike when the cells cut out and I had to limp home."

 

[lawsonuw]

http://www.thunder-sky.com/technical_en.asp?id=399&typeid=99&orderby=40

please look carefully at the serial numbers Thunder-sky uses. They don't just make LiFePO4 chemistry cells. LF -> LiFePO4, LM -> LiNiMnO2, and LC -> LiCoO2

Marty

 

[safe]

They don't just make LiFePO4 chemistry cells.

Good observation. I had assumed they were all LiFePO4's and they definitely are not.

 

[Deepkimchi]

OOps - sorry. Thought it would be per piece > 101...

 

[safe]

OOps - sorry. Thought it would be per piece > 101...

That's for the LMP's.

Patrick's price of $80 per LFP cell is still very good. At $2.00/Ah it's below their stated price of $2.50/Ah. I'd still like to know what kind of plans Patrick's company has as far as what cells they see as being central to their future. It might be a secret that they don't want to reveal for a variety of reasons.

 

[Deepkimchi]

Too bad we can't just solidify on the 40138s and just get them ordered. This back and forth on whether LFP 40ah or 40138s is probably driving Patrick nuts. :|

 

[safe]

The Thundersky 40 ah cells are a little large for most ebike applications. If you look at my bike the volume is exactly equal, in fact, for me I could simply substitute my SLA's with these using four per original cell. (the sizes are the same)

But I wouldn't do that and would prefer to build a new bike for them...

The 40138's are smaller and probably make more sense for ebikes, but they are more expensive relative to their energy capacity.

Patrick has said that no volume discounts are possible, so $80 per cell is the final offer. This means that compared to my original SLA price ($128 total) I would be spending 7.5 times the price for 2.5 times the energy and one third the weight.

 

[eP]

The Thundersky 40 ah cells are a little large for most ebike applications.
The 40138's are smaller and probably make more sense for ebikes, but they are more expensive relative to their energy capacity.

40 Ah cells are more dedicated to 12-24V geared motors.
600-1200W (@50A load) is still a lot of power. Most hubs if not all can't work efficiently at such low voltages (at that kind power level).

My point is - lets start similar threads for motors and gearboxes. That way more guys will want spend theirs money for that batteries too. As smaller packs would be much more affordable for much wider audience. And the risk of spending money for bad quality cells would be smaller too.

That way the same cells would be used for gass bike conversions as well as for moderate e-bikes or assisted e-bikes. That way would be possible to use the same batteries packs for second or third electric vehicle instead of using dedicated small cells packs for each vehicle.

Isn't it the fine way for great savings ?
Especially if we keep on mind large cycle life LiFePO4 batteries.

 

[magudaman]

Just a heads up to avoid future confusion, lifepo4's nominal voltage is 3.3v. So anytime you see 4.2v or 3.7 then your already too high and most likely in an old lithium chem = low cycles and high volatility.

 

[Deepkimchi]

So Patrick, how's it going with the 40138s?

DK

 

[safe]

So Patrick, how's it going with the 40138s?

I don't think Patrick is involved in anything 40138 related. This thread is a place to post great offers for a potential group purchase... if ANYONE knows of a great deal then by all means post it here and let's see if anything can be put together.

As of right now the deal with Patrick is a "firm" $80 per cell of the 40ah Thundersky cells. No volume advantages exist.

 

[TylerDurden]

So Patrick, how's it going with the 40138s?

I don't think Patrick is involved in anything 40138 related.

Read the first post. :lol: