[PStechPaul]

I went today to the www.hobbyking.com website and put together a shopping cart for several LiPo batteries as well as other items, as follows:

Quantity Stock Product description Price Weight
OK T50004S-20HC - Turnigy 5000mAh 4S1P 14.8v 20C hardcase .. $22.59 598
OK 601Ax5 - Male XT60 connectors (5pcs/bag) GENUINE $2.16 29
OK T1000.1S.20 - Turnigy 1000mAh 1S 20C Lipoly (Single Ce.. $4.84 140
OK 9331000001 - Hobbyking DC-4S Balance Charger & Cell C.. $8.99 113
OK T5000.1S.40 - Turnigy 5000mAh 1S 40C Lipoly (Single Ce.. $11.60 165
OK LPGUARD25x33 - Lithium Polymer Charge Pack 25x33cm JUMB.. $2.73 260
OK 070000017 - In-Line Voltage and Amperage Meter $4.99 28
OK TR-Wattmeter - Turnigy 130A Watt Meter and Power Analyz.. $23.95 129

The shipping charge seemed to be about $16 via USPS but at checkout the only option was UPS which was $44. Apparently it was because of the LiPo batteries. I understand that they are considered hazardous.

So I changed the order and the four non-LiPo items is being shipped via USPS for $5. But I do want to get some LiPo or other LiIon batteries to work with. One application will be a low-resistance ohmmeter which drives high current of 1, 10, or 100A through a shunt or other low resistance device and reads the voltage for a resistance reading. It can also be used to check the quality of connections. I have a tentative design that uses a 6V 4 A-Hr Lead-acid battery and some supercapacitors to provide a high current low voltage pulse, but the high discharge LiPo cells sounded much better. But even one of these costs $35 to ship!
http://www.hobbyking.com/hobbyking/s...gle_Cell_.html

I found a LiIon cell 2600 mA-Hr battery for $10:
http://www.jameco.com/webapp/wcs/sto...001_2140349_-1
And I don't think there is a shipping surcharge, but this is a protected cell and I think the output is limited to 2C into a short. So I don't think that will work for me.

They also have a 10 Ah LiFePO4 Prismatic cell for $35:
http://www.jameco.com/webapp/wcs/sto...atalogId=10001

That's a bit steep for 32 Wh, but about $1/Wh is not too far above the lowest I found elsewhere, about $0.65/Wh. Like this:
http://www.hobbyking.com/hobbyking/s...ePo4_Pack.html

That's 4200 mAh 6.4V 2S2P, 28 watts for $21 or $0.75/Wh, and it can be shipped International Airmail for $10. I don't know if it's the safer chemistry or less restriction on the air mail. But that sounds like a good deal, and it is good for 30C and up to 40C burst, so it will more than meet my ultimate goal of 100A.

I'd rather have just the single cells, however. Can a pack like this be taken apart safely? Well, maybe I shouldn't even worry about it for an industrial meter that will sell for over $1000!

Maybe I should get 4 of them for 24 volts for my voltage booster. They'd be a lot easier to work with than a couple of lead-acid batteries. And They should easily supply 100 watts which is enough to run a 2 HP VFD and 3-phase motor for testing. And it would even let me run my little tractor which takes about 400 watts, for maybe 10-15 minutes of testing. Sounds like a plan!

[PStechPaul]

OK, I just placed the order with HobbyKing:

4x #Z42002S-30-2P/14065 ZIPPY Flightmax 4200mAh 2S2P 30C LiFePo4 Pack = $77.68
1x #LPGUARD18x22/4134 Lithium Polymer Charge Pack 18x22cm Sack = $1.99
1x #LPGUARD25x33/4364 Lithium Polymer Charge Pack 25x33cm JUMBO Sack = $2.73
2x #T5000.1S.40/18562 Turnigy 5000mAh 1S 40C Lipoly (Single Cell) = $23.20

VISA / MASTERCARD (No Paypal) + $1.50
UPS Express 3 Day (USA) 2kg $44.69
Taxes: $0.00
-------------------
Total: $151.79

I accidentally clicked on the "No Paypal" option at checkout so the $1.50 will be credited back to me as "points" toward future purchases. If I had re-ordered, I would have lost the special discount on the batteries which are normally $20.53 and I got them for $19.42. So I spent close to an hour with customer support chat to save $4. Well, while I was waiting on chat, I checked eBay for any better deals and the best I could find was this:
http://www.ebay.com/itm/DIY-KIT-24V-...item2c670e8287

It's 240 Wh for $203 and includes a 7A charger with BMS. If you knock off $20 for the charger it's still $0.76/Wh. And the shipping is $85 and a warranty is $35 so that's $303. My deal is about 1/3 that for 105 Wh. Maybe the Jameco Prismatic cells are the better deal at about $1/Wh if there is no shipping penalty. Bottom lines are tricky.

So if I got 48 of these I'd have 307V and 1.351 kWh for about $1400 with shipping. For a really good EV at 200 Wh/mile it would go a little over 6 miles. I'd really need full size cells and packs if I did that. So, what's the going rate for LiFePO4? $1.50/Ah or $0.50/Wh? Alittle better. I'll see how this little pack works on my tractor. Maybe I'll get 10 minutes running at 400 watts which is 4C? What's Peukert's number for LiFePO4? If I use the maximum of 30C that will give me about 3000 watts or 4HP for a few seconds. Maybe enough to get a little feeling of the potential power.

I think I'll still use lead-acid for the tractor. $250 for 3600 W-Hr seems pretty good. I'll usually be running at about 0.1C so I should get an honest ten hours of run time! Even doing work at 2HP would be about 0.5C so at least 1/2 hour and maybe 1 hour?