There is also an ongoing discussion regarding this issue in the visforvoltage site. As long as "usatracey" stays out of the discussion, it might remain constructive:
http://visforvoltage.org/forum/2515-any ... y-supplierAs far as my communication with Li Peng so far, he seems fairly knowledgeable The full text of my e-mail correspondence with him, so far, is included below:
MY FIRST E-MAIL:
Can you provide me more information on your 48 volt battery packs packs?
My minimum requirements are 40 amp-hours and a maximum discharge rate of
95 amps for short periods, or 50 amps continuous. I will probably
have use a combination of smaller packs in parallel to fit them in my
scooter's multiple battery box arrangement. The scooter is also
capable of running on 60 volts for more speed, so I may upgrade to a 60 volts.
Therefore, my questions are:
1. Could you provide prices and dimensions for your various capacity 12, 24, 36 and 48 volt packs?
2. What is the maximum amp discharge for each pack size?
3. Could two or more parallel-connected packs be safely connected in
series to obtain a 60 volt pack? The best setup would be a 48 volt
pack in series with a 12 volt pack so it could be returned to the
factory 48 volt arrangement, if needed. But 24 and 36 volt packs in
series are another possibility.
Thank you for time answering my my questions,
Paul Donahue
Pittsburgh Pennsylvania, USA
HIS REPLY, THE NEXT DAY:
Hi Paul,
Thanks for your mail. We can make 60 volts 40 amp-hours LiFePO4
batteries. Our battery packs can easily discharge at 2C current
continuous. To meet your requirement, we can set rated discharging
current at 50 amps and cut-off current at 100 amps. It's not our
standard product. So it will take 15 days to disign, produce and test it.
My answers to your questions are bellow,
1. These are retail prices of our standards 48v products,
48v 10ah 400 usd
48v 15ah 600 usd
48v 20ah 800 usd
Before 2008, every standard product has a 15% off discount and
customized product 10% off for Christmas, so prices will be 48v 10ah
340 usd 48v 15ah 510 usd 48v 20ah 680 usd Shipping Fee to US and
Canada 48v 10ah 65 usd 48v 15ah 85 usd 48v 20ah 105 usd
All prices after discount don't include chargers. 48v charger is
priced 20usd. [!! - PJD]
You could count prices of other products of voltage and capacity based
on the per volt per amp-hour price above. For example, 48v10ah is
priced 400usd, so 24v10ah is 200usd.
60v40ah is not a standard product of us. It's a customized product and
priced 2000usd. 1600usd after discount. The charger is also
customized, priced 50usd.
2. The max continuous discharge rate of our battery packs is 2C and
peak 3C so far, although every single cell can discharge at 5C or higher.
It's easy for a single LiFePO4 battery cell to discharge at a high rate.
However, it's difficult for a series of battery cells to discharge at
high current on condition that it still have a more than 1000 times
lifecycle. That's why we need BMS (Battery Monitor or Management
System) to smart control and balance the charge and discharge of the
whole battery pack. We are continuously developing more intelligent
control technologies for higher discharge rate.
3. 200x150x450mm is the recommended dimension of your packs. In this
shape, the total length of the wires connecting the cells is shortest,
so the resistance of wire is lowest. Of course, we can make the pack
in other shape. It's easy to connect a series of battery packs into a
bigger one, just like buiding blocks. But the difficulty is control
and balance, what a BMS is doing, as I mentioned in Answer Two.
Therefore, someday, if you want split the big pack into two small
ones, you need to change the BMS. But the BMSs are not expensive,
usually priced from 10usd to 20usd. What you have to do is to weld the
wires of splitted battery to the new BMS and buy new chargers.
Hope my answers will help you. Any further questions, please feel free
to ask me.
Best regards,
Ping Li
Shanghai, China
MY RESPONSE:
Ping,
Thanks for the prompt response.
Unfortunately, a single 200x150x450 will not fit in the battery boxes for my
motor scooter application.
I have the following spaces to fit the batteries:
Box 1 - 285mm long, 225mm wide 190mm high
Box 2 - 190 long, 180 wide, 220 high
Box 3 - 185 long, 75 wide, 165 high - probably not usable space.
Box 4 - (under-seat space) 280 long, 200 wide, 225 mm high.
But, Box 4 is useful cargo space, so I would like to minimize use of it.
So, I will probably have to use a combination of your standard smaller packs
in each of these boxes. I was hoping fit a minimum of 40 AH in these boxes,
and obtain the required maximum amperage, by parallel-connecting a
combination of smaller 48 volt packs.
So, what are the dimensions and maximum amperage of the packs whose prices
you provided?
HIS REPLY:
Hi Paul,
I have applied to my partners for 15% off special discount for you. No
matter you buy standard products or customized.
The 60v40ah pack is made of a series of smaller pack. Let's call it base
unit. For 60v40ah, the base unit [i.e cell - PJD] is 3.2v40ah. Therefore, we need to connect
20 base units together. The dimension of each base unit is 100x140x45. If
you want a 48v40ah plus a 12v40ah, box 1 must contain 16 base units. The
whole pack of 280x200x180 looks to fit the box. However, we need some space
for wires. Usually we spare 10mm for the wires. I'm not sure 285mm long can
meet the 280mm length of battery and wires. Another solution looks better,
36v40ah plus 24v40ah. Box1 fits 270x200x190 of 36v pack and box2 fits
180x140x200. Furthermore, there's enough space left for BMS.
Another issue is the location of BMS. Although we split a 60v pack into two
smaller packs physically, logically they're one system and managed by one
BMS. The BMS controls all the 20 base units. So it should be placed in one
of your boxes. The BMS is a PCB, not big. But there must be a group of wires
between the two box. You should be very careful while using the pack. The
wires between the 2 boxes have resistance. Unbalanced higher resistance of
wires between base units is harmful to lifecycle of lithium battery packs.
So you'd better make the two boxes closer.
Standard dimensions and max amperage of our 48v packs are
48v 10ah 150x105x190mm max continuous 20a, peak 40a
48v 15ah 150x100x280mm max continuous 20a, peak 40a
48v 20ah 150x100x360mm max continuous 30a, peak 60a
Regards,
Ping