[18650battery]

Hi all
after reading about Tesla and the Tzero using these ubiquitous cells to make large battery packs, I want to do the same for a 25kwh (approx) pack.
The reasons are 3 fold: saving weight, volume and cost when compared to large format (100ahr + Li cells)
I have made a smaller (0.72kwh) pack for my Ebike and the soldering was pretty tedious. however it was a success - the most important thing.

Basically i am planning to spot weld about 60 3ahr cells in parallel to make a 3.7V 180Ahr cell and then series connect these to make a 120V pack with a BMS for each 180Ahr unit.

The total ahr and voltage are flexible but 25kwh is a good target.
any ideas? anyone done anything similar and can give me any good tips?
looking forward to some helpful responses...

[lumberjack_jeff]

I have thought about doing the same thing, but using my cnc router to do the capacitive spot welding.

Carve a wooden cell locating template, populate it with cells, then replace the router with a spot welder.

How would the cost compare to prismatic lifepo4?

[ev-converter]

Originally Posted by lumberjack_jeff

I have thought about doing the same thing, but using my cnc router to do the capacitive spot welding.

Carve a wooden cell locating template, populate it with cells, then replace the router with a spot welder.

How would the cost compare to prismatic lifepo4?

I built a 32kw battery system using 18650 Sanyo cells in 2005 and powered the first Li-ion street car in the US if not in the world. Tesla was still working on their battery design at that time. You can use these cells, but the important design has got to be a BMS. I didnt have a BMS in 2005, so it was very difficult to charge and discharge without damaging the cells. Cells are still going strong today after a couple of re-designs and configurations. Go for it, its fun and rewarding.

[SandRailEV]

I don't know where you get your cells from, but for the online pricing I am finding, 18650s seem to cost way more than large prismatic cells for the same capacity...

[ev-converter]

Originally Posted by SandRailEV

I don't know where you get your cells from, but for the online pricing I am finding, 18650s seem to cost way more than large prismatic cells for the same capacity...

If you read my posting you would have noticed I did it in 2005. There was no other Li-ion cells available anywhere, except to laptop manufacturers. Today you can buy 18650 for about 75 cents per ah. CALB cells are $1.25 per ah and the voltage range is limited compared to the 18650 cells of 2.5-4.5vdc. Why do you think Tesla has been so successful using the 18650 cells?

[lumberjack_jeff]

Where are you finding $.75/ah?

I see $3.50+ per ah for 18650's.

[SandRailEV]

Originally Posted by ev-converter

If you read my posting you would have noticed I did it in 2005. There was no other Li-ion cells available anywhere, except to laptop manufacturers. Today you can buy 18650 for about 75 cents per ah. CALB cells are $1.25 per ah and the voltage range is limited compared to the 18650 cells of 2.5-4.5vdc. Why do you think Tesla has been so successful using the 18650 cells?

Of course I read your post. You Said, "The reasons are 3 fold: saving weight, volume and cost when compared to large format...."

So, I simply questioned the cost aspect of your statement. I have not seen any lithium cells of any size cheaper per watt/hour than prismatic. If you have a source or a reference, please provide it (unless it's secret)...

[Elithion]

Originally Posted by 18650battery

i am planning to spot weld about 60 3ahr cells in parallel to make a 3.7V 180Ahr cell and then series connect these to make a 120V pack with a BMS for each 180Ahr unit.
anyone done anything similar and can give me any good tips?

Been there, done that.

We used 26650 A123 M1 cells to make PHEV packs to convert Prius from HEV to PHEV.

Helpful tips?

The mechanical design is what will come back to bite you.
- Be prepared to pay $ 8 K to $ 25 K and 3 months of labor just for the set-up (not including cells). I am not exaggerating!
- Put a lot of thought in the design of the battery block and the complete battery
- Use a hexagonal pattern
- You'll need a fixture shaped just right to squeeze the cells together
- Glue the cells together with Elmers Glue or the like, into a block
- Make yourself a mask, to physically prevent you from unintentionally shorting across cells where you don't mean to
- Get an honest to goodness cell welder (no soldering)
- Build a table for the welder. Use rollers to help you shift the battery block in place
- Get nickel sheets (5 to 10 mils) and cut them to shape, to create your electrodes
- Have an expert set the welding profile for your cells and your nickel plate
- Practice, practice practice welding cells before you start on a real block
- Design an enclosure for the battery blocks: isolated, yet sturdy
- Use flexible connection between battery blocks (for example, braid strap)
- Add fuses rated for the full pack voltage, to blow in case you short across a block or misconnect blocks during battery pack assembly.



The BMS is easy:
BMS selector

• Option 1: lots of wires: use a non-distributed BMS, such as the Orion BMS, outside the battery
• Option 2: lots of ell boards: use a distributed BMS, such as the Lithiumate, inside the battery. These cell boards are exactly the right size for 18650 cells, and fit in the nook between 2 adjacent cells, so they take no extra space.

[PStechPaul]

I found 2400 A-Hr cells for $6 each ($2.50/A-Hr or $1.00/W-Hr). http://www.batteryjunction.com/ultra...lue-18650.html

A 14.8V 10 A-Hr pack is about $150 (also about $1.00/W-Hr)
http://www.batteryjunction.com/tenergy-31357.html

The same company has 16pcs of 10 A-Hr NiMH D-cells for $113. Of course they are about 1/2 the voltage of LiPo. So $0.47/W-Hr.
http://www.batteryjunction.com/16dni10reba.html

And a 24V 10 A-Hr NiMHpack is about $150 ($0.62/W-Hr)
http://www.batteryjunction.com/24vpk.html

I found a 60 W-Hr LiPo pack for $33 ($0.55/W-Hr)
http://www.usbphoneworld.com/dell-17...LAID=916836065

That's $671 for 20 pieces, 1200 W-Hr, 222V 4.8 A-Hr. That would make a nice pack for my 1-2 HP tractor. I'd probably use 30 pieces for 333 volts, just right for a 220 VAC VF drive and 1800 W-Hr, for about $1000.

For a 25kW-Hr pack you'd need 400 pieces. The price might drop at that quantity, so maybe $10,000. You should be able to get 50-70 miles range if the 330 W-Hr/mile figure applies and you can use close to full capacity.

[adeyo]

Are these similar to the Sanyo cells in the Ford escape hybrid? ...which is somewhere around 325 volts (250 cells, 1.3 volt, 5.5 ah). With this logic, could one save a lot of time and money and simply wire these in parallel? (they are readily available at my local salvage yard anyway).