Need Dewalt pack gurus!!

[Whiplash]

OK, I got my kit ordered and I am now ready to decide on the batteries, I am not 100% yet, because for now I need to run 48 volts and the controller is setup with the low cutoff for 48 volts. What would be the best way to achieve the correct array of batteries to make sure the low volt cutoff works properly? Will the cycle analyst work with any controller to cut the power if you go below the low volts? I know it does this but I want to be sure it will work with this cheapo controller for now until I get some more money together for the good 72 volt controller...

I found some good deals on batteries on fleabay for (8) 18.5 volt 4AH LIPOs for $349.00 shipped! but I am not sure this will work because it will not add up to the 48 volts I need.

SOOOO, what I am considering doing, is getting the Dewalt packs I found ($300 for 6 packs brand new) and trying to cut them up and build (3) 24 volt packs and then wire two packs in series to get 48 volts and then add the third when I am ready to go to 72 volts...Does this make sense? This is the last piece of the puzzle I have yet to figure out for sure, I REALLY like the idea of doing the Dewalts, because I know it will fit my bike and make GREAT power, I am just not sure how to balance/charge them... Can I get some help on this from someone who actually has used them??

 

[katou]

What you are asking is not related to the Dewalt cells specifically, this is a normal pack building question.

Which packs did you buy? These are the ones you want.
http://www.toolking.com/dewalt-dc9280-28-volt-lithium-ion-nano-battery

I will assume that these are the packs you bought.

Each dewalt pack has about 10 cells in each (I think, someone back me up here).

Each A123 M1 26650 cell is 3.3 v nominal, and 2.3 ah

You need to do the math to figure out how to arrange the pack. How many amp*hours do you want your pack to be?

I will assume that you will have 50 cells from the packs for the example. This could be arranged in many ways.

25 in series, 2 parallel, 5 series, 10 parallel, 50s 1p, whatever you want.

To find out how many cells you need in series, and you want 48v, then divide 48v by 3.3v/cell

To find out how many cells you need in parallel, assuming a 10ah pack, then divide 10ah by 2.3ah/cell

Multiply these #'s together to make sure you have enough cells.

Let's do an example:

48v 10ah pack will require:
48v/3.3v per cell = 14.5s
10ah/2.3ah per cell = 4.3p

Now clearly we can't use half-cells, so we round down to 14s and 4p.

Quick check to see if we have enough cells:
14s x 4p = 56 cells !!

That's no good. How about 14s and 3p?
14s x 3p = 42 cells, this works.

But how many amp*hours do we have now?
3 cells in parallel x 2.3 ah per cell = 6.9 ah

Hmm, that's a little low, I think I might rather go the other way and get 6 more cells to meet the original design goal of a 10 ah pack.

HTH, that's about as clear as I can make it. I wish someone had laid it out for me like this. Good luck with your project.

Katou

 

[Whiplash]

I actually am looking to buy, but they are the 36 volt packs not the 28. they are 2.4 mAh supposedly....Really me question is for the balancing and charging, I think I understand the assembly of the cells themselves, I just don't know how to wire the BMS or if I even need one in this situation??? I have heard these don't really need them is this true? And what charger do I use for these once they are built into 24V 10AH packs?? I want the option to either run two for 48 volts or three for 72 volts or use 48 volts and add the AH from the third pack.....I can buy more packs I understand that six packs wont get this all done yet..

 

[katou]

I see. You will have a lot of reading here on the sphere to do if you want to build your own pack, set up a charging solution and build a BMS.

The first thing to do is ask yourself if you want to invest the time in learning all you will need. If you have the money, you can just buy a solution that is every bit as good as homemade. I'd probably look at getting Hobbyking lipo and lipo chargers if I had the cash.

If you are dedicated, and don't have much money, then the first thing to do is figure out what voltage you will have. It won't be 24v because there is no multiple of 3.3v that hits 24v right on.

8 x 3.3 does not equal 24v. After you figure out the voltages, you can start looking for a charging solution.

After that, start work on the BMS.

It's not a short road, but to my mind, it is worthwhile.

Katou

 

[Whiplash]

Ah, I see OK well I am not flush with cash and i want the best possible, most powerful setup for my bike, and of course at the best possible price. I am not afraid of this I just don't want to waste money burning things up. do you have any links to step by step build ups of these A123 style packs? Also, if I wanted to control this whole pack of say, 72ish volts 10-15AH How would I setup a BMS to run it so it was a simple plug and play re-charge/balance system? Any links to a BMS that is capable of this? I really like the A123 style because they are relatively small and package easily into odd shapes like this chassis I am building...

 

[MitchJi]

Hi,

You should start here (good review for Katou also :wink: ) for excellent info on the Dewalt/A123 Cells):
http://endless-sphere.com/forums/viewtopic.php?f=14&t=2498

Here is an excellent thread on pack building:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=17912

If toolking ever gets them in stock again for the same price the 28v packs (8 cells) were a better deal than most 36v packs (10 cells):
http://www.toolking.com/dewalt-dc9280-28-volt-lithium-ion-nano-battery

Availability: Out of stock
$49.99

When they finish their v4 one of these BMS's with a cheap power supply for charging will be a good affordable combo:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=5416

 

[katou]

Mitch is the board memory, he can find threads on any topic. I am consistently amazed at the speed with which he does this. Dude, how do you do that?

I've read all those threads myself, many, many times. Well, with the exception of the BMS thread. No way am I wading through that. I just pop in at the end every once in a while to see if they're ready yet.

Those threads are excellent introductions, and I would second the suggestion to read them carefully.

If you want to build with A123 from toolpacks, nobody's got info better than the Care and Feeding thread.

It looks like you're going down the road of the Stealth Bomber, which is a very nice looking bike. Anything is possible, but get ready to learn a bunch before building. Pretty much any ebike costs around $1000 until you know some ways to cut some deals. That's for a hub motor kit. Making a radical design will cost more.

Just my experience so far. My bike parts have cost so far about 600 and I have about 300 more to buy in controller, battery, etc.

Katou

 

[Whiplash]

Thanks soo much guys, I know what I will be reading this weekend!