MM on 6s A123 and Kb 45 questions
 

I am new to A123 and any help will be much appreciated!

First, what kind or voltage drop do the A123 cells exhibit? I know they are 3.3v nominal, but what kind of discharge can they handle while keeping the voltage ,say, over 3v?

Also, what do you guys think the mm will think of 6s A123? Anyone tried this?

My current setup that I would like to try the A123 packs in is a Ultra GTP with either a kb 45 8l (2300kv) or a kb45 10l (1800kv). Current gearing on 4s lipo puts the 8l in the high 40mph range, and the 10l closer to 40mph.

With the 8l the MM is getting quite hot, so I may add a fan over it. Not much airflow where it is, and cutting the body will not do much either. Motors are getting warm too, but not bad. My trakpowers are keeping up, but I think the 8l is drawing near the max of the MM and the lipos.

So I would like to try 5s a123, in a 2p configuration as I have enough cells to do that. Battery space is not an issue, as I have the entire side open for batts.

Will I notice a performance difference from the 4s lipo going to 5s a123? The trakpowers are good for at least 100 amps with decent voltage, and does not hit the lvc until the end of the run. The 8l is pulling the voltage down, that is for sure. I would also like to try 6s a123 with the 8l motor, but it will be spinning near 45k rpm, and getting near 70mph too. Not sure if the MM will handle that load! Or the motor! I am kind of stuck with the 20/51 gearing, as it the largest pinion I have with a 6mm bore. I cold have the shaft turned down to 5mm, then I could go up to a 24t pinion that I have. That with 5s a123 and the 8l should be fast enough for me.

Here is a pic of the car, sorry about the dust!

http://i206.photobucket.com/albums/b...p/DSCF1927.jpg

Any thoughts, or ideas are more than welcome!

I found my 6S2P A123 to be nearly identical in performace to my True RC 5S 5000 mah pack. My A123s were right around 3 volts under load.

I use 6s A123 on my mamba, which is at 20 something volts at rest. Someone had posted 110A at 2.25Volts per cell, which I have found to be true.

Thanks for the info, I will have to give it a try!

Is that voltage drop in a 1p config, or 2p? What kind of load do you have with the 6s a123? Is the vehicle heavy, 4wd?

That is with a 1p config and at burst. The ride is the FLM Rustler dragster with a 3100xl basic lehner. The 8L hacker took a bit less. But once the batteries warm up a bit, you gain some voltage under load.

Ok, makes sense. So do you think that I can expect 3v per cell with a 5s2p A123 configuration with 100amp loads? Or is that asking too much? I guess that I will have to try it out! Not like I can damage the cells!

You'll see a bit lower of a voltage at 100A in 2p mode(2.8V). But at that draw the batteries will just laugh at you.

I think I posted this before: 3s2p and look at the 100A draw line

http://i189.photobucket.com/albums/z...ustler3s2p.jpg

I run 5s2p on my mm/9xl Revo & MM/1515-2.5d LSP and it is fine. I haven't put the ET on it yet but can.

I tried 6s2p briefly in the basement and it ran ok but I figured pushing it too much so never took it outside on 6s.

It is really a testiment to how good the MM is/was when you consider the MMM will only do 7s...

For you guys that use the dewalt packs, how many cells come in them. I am assuming 11, is this correct. I am considering using A123, but like linc, I am trying to learn a little first.

I really need to find time and get with some of you hamdrl guys snellemin. I am sure I could learn a lot..........

Anyway, linc, sorry for the thread hijack.

10 cells - They peak at 3.6v hence 36v

I bought three packs and stripped them down partially - I used all the existing tabs... Layout of the cells isn't perfect but made life easier.

I've read that the 36v Dewalt pack is no longer using a123 cells but some lower volt/capacity chinese version. Have not seen anyone detail how or if you can tell them apart or even a good date when the change was made. I wouldn't want to pay what these are getting on ebay righ now and wind up with the chinese cells.

One more question, on the A123's, you don't need an LVC, correct?

Probably would be a good idea. However you deffinately know when they are out of juice. Your RC will pretty much come to a stop in the middle of the yard / track.

If you unplug the minute they dump then you will probably be OK.

I don't bother with one....

If I was to set the lvc, 2v per cell correct? Also just got a used hypersonic charger, and wanted to know if anyone knows how to wire the balancer cable? A stock hitec servo plug will fit, just need to know where the balnce wire goes. I see that the 2s packs only have 1 balance wire, and the 3s packs have 2. But the input has 3 pins on the charger. Any ideas?

No drawings on site but think you can tell from these pics...

White at 3.3v

http://a123racing.com/a123popups/popup_2s1p.html

Guess on 3s but would guess white 3.3, red 6.6

http://a123racing.com/a123popups/popup_3s1p.html

The middle pin is used for 2s packs, with the balance wire connected between the first and second pack.

The outer pins are used for 3s packs. The 1st pin is connected between the first and second battery, and the 3rd pin is connected between the second and third battery. If you connect it backwards, it won't charge. Nothing will blow.

http://i189.photobucket.com/albums/z...111_Page_2.jpg

Ok, so on a 2s pack, the wire goes in the middle of the plug, and on a 3s pack the wires go on the outside pins. Which way do the 3s wires go? Would the balance wire between the 1st and 2nd cell go on the left side (fuse side) or the right side(led side)?

Many thanks, as I have a 2s pack charging at the moment!

It would go to the fuse side.

Thanks Romano, I appreciate it! Got all of the batteries charged, now just have to wait on the diff parts I exploded to try the a123 cells out!

The DeWalt 28V packs have 8 a123 cells also. Just buy three of them to get the 24 cells you'll need for 2 x 6s2p.

I heard DW aren't using A123 cells anymore... anyone confirmed this yet?

JohnRobHolmes confirmed that the newest DeWalt packs will no longer have a123 cells. There isn't any immediate way to know which packs are "new" and which are "old".

that just sucks big time... I was about to get some more... so what will they be using?...

So they buy cheaper cells and sell the packs at the same price.......nice! :no:

:slap:

Here's the thread with the details.

Start at post #15.

I personally probably wouldn't recommend someone go and by 3 packs to get a123 cells then without mentioning that :)

Yeah, good call. I guess the first line should have read, "Some of the DeWalt 28V packs ..." or something like that.

Brain fart on my part. Apologies.

So is a cut off voltage of 2v per cell fine for A123?

Yes, but I don't bother with the cutoff.

Ya no need to use a cutoff with A123. Youre truck will get really really slow and you will want to charge it up. No harm to the batteries. The last run of the day I make sure that I pop them on the zip charger for a least 1 min so that I bump them up to spec before I put them away.

The difference between when the cutoff would kick in a a empty battery could be as short as 20 seconds.

Highflier

I just got 2 packs and they contained A123 cells. Maybe the grape vine twisted the reality. A123 cells are not made in a different factory. But they still are A123 cells :)

Highflier

One thing I have found from when I first got some M1 cells directly from A123 website 2 years ago and the cells you buy now from dewalt packs is the quality control. The original cells are absolutely identical... whereas the cells from these dewalt packs are all different, especially when you first use them.

Linc, A123 cells are good to a solid 70 amps, when I say solid I mean 'useful' power in a r/c application, although, I have had burst up to 120 amps (over 50C) on a 7s1p pack, which was 1800 watts. Any more and you should add a cell, and gear down, try it out, etc.

That's good to hear, I don't know if this is just a rumor or something thats going to eventually happen. It was announced on this board and others I frequent. Last time I looked on rcgroups, other than your thread, I don't see anything.

Maybe you're right - overhyped rumor. One thing for sure, days of buying a Dewalt pac for $69 are long gone.