29s2p A123 booster pack

[Lowell]

Anyone have good results buying multiple Dewalt drill packs off Ebay? A 96v parallel booster pack of A123 cells would mean that cheap 18650 cells could be used for the primary battery without melting them down.

http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1643

56 cents per Wh... 25s12p pack of 18650s = 2442Wh for $1377.
6 Dewalt drill packs off Ebay = 440Wh for around $600.
2882Wh for around 2 grand, some assembly required. Now how to balance the discharge, or limit current from the 18650 pack to say 25 amps, and let the A123 cells take up the rest?

 

[Toorbough ULL-Zeveigh]

Hey girfriend, talk to the Bob (McRee). He's doing exactly this right now!! for his cruzebike project.


http://endless-sphere.com/forums/viewtopic.php?t=575
i have been lusting after A123 cells for months now, and their developer packs are a total ripoff at $120/6 cells. I have tried to buy 100 cells from them but they are not interested in little guys. I did not want to fool around buying a pack at a time at different prices on ebay, so i waited til now, and there are finally enough packs around that ebay prices have stabilized at about $115 for the 10 cell DeWalt packs.

I just bought 7 packs and I will be making a 10 lb 53V 9.2 Ah pack for one of my bikes. Total cost with shipping for the 7 will total about $900 compared with about $1400 from A123 just for the cells in developer packs.

 

[Lowell]

490Wh will barely get me anywhere though. I want to use A123 cells as high current boosters, not the primary power source.

 

[xyster]

490Wh will barely get me anywhere though. I want to use A123 cells as high current boosters, not the primary power source.

I'm planning to do this too. Either 22s1p A123's in parallel with my 20s15p main pack, or 20s1p of emoli's in parallel. I'm thinking, especially with the a123's, charging directly will not be necessary. The voltage from the main pack should keep the boost pack sufficiently charged. I'll know when the parallel back is almost drained because the voltmeter will show the significant increase in sag. At 22s, the A123's will be at their max voltage when my main pack is at 79.2 V (just under 4 volts per cell) recharging the main pack to 83-84 volts should equilibrate (balance) each of the a123's because like nickel and lead the a123's can accept an overcharge (up to 4.2 volts per cell).

 

[Lowell]

That's more or less what I was thinking! Then add A123 cells as the price drops and they become more widely available.

 

[Matt Gruber]

a123 can accept 4.2v on a rare occasion, not every day.

 

[Mathurin]

10 lb 53V 9.2 Ah

Now that would make for a good backpack pack

 

[D-Man]

cancelled

 

[xyster]

a123 can accept 4.2v on a rare occasion, not every day.

Perhaps so. But if I put a 22s string in parallel with my 20s main pack, the most any a123 will ever see is 3.8V (84 volts / 22). I'm hoping this will be sufficient to bring each A123 up to full charge, without risk of long-term damage (FWIW, B.S. recommends charging their Li-Fe-Po4 cells to 3.8v).
In effect, my 20 regular lithium chargers will charge the A123's at home, and the main pack will keep them charged out on the road between periods of heavy current usage.
Sounds like Lowell is thinking along the same lines, but at a higher voltage.
We'd need not buy separate charging apparatus if it works.

 

[Lowell]

http://cgi.ebay.com/DeWalt-DC9360-Heavy-Duty-lithium-ion-36V-Battery-Pack_W0QQitemZ150111388920QQihZ005QQcategoryZ20794QQrdZ1QQcmdZViewItem

Seems like the winning bids are pretty consistant, but the shipping pushes the price up a bunch. I'd like to buy 12 packs for around $1000 all at once with no hassles. A 29s4p 96v x 9.2Ah pack would make a nice short range setup.