8cell A123 on MMM?
 

Would the MMM speed controller handle the extra voltage? I've been running my E-Revo on 6s lipo for awhile now with no problems.(MMM & Neu 1521/1Y_1577kv). I would really like to go with the A123 cells but I run in too a voltage dilemma. I can either go with lower voltage packs and take a voltage hit, or go with huge 6s packs which are not only pricey, but also very hard to fit. So this got me thinking. What if i just bought 2 4cell packs and ran the truck at 26 volts. You guys think the MMM could handle it?

I've been threw just about every brand of ESC and have no desire to go with any other controller, so lets not go down that road. Also if you are wondering how I will be fitting A123 cells in my E-Revo its because I have the Kershaw-Designs chassis http://home.ptd.net/~kershawd/Kersha...vo-Chassis.htm

So what do you guys think? Should I do it, or would I just be sending my MMM to certain death?

You'd let the smoke out. The most the MMM can do is 7S A123, and that's due to the voltage rating on the components.

you'd want a 2p setup anyway

Not necessarly. 7s1p shall work too: 1400-1750 Watt peak ... more then enough. Runtime will be reduced though and depending on your gearing you will work them hard with your big motor. Even if you deplete those A123 in 5 minutes, they will take the "abuse" and still provide a few hundred cycles.

Here are a 2 videos of an E-Revo with centerdiff (needs thicker diff oil) with 8s1p A123 (they fit in the battery trays 2x 4s1p), Neu 1515/2Y (1100kv), MGM 14035. Spur 40 / pinion 18. Runtime between 7-9 Minutes. Recharge time 15 minutes.

Run on Grass: http://www.braintrust.at/2007/ds/rc/revo_wiese.wmv
Run on a track: http://www.braintrust.at/2007/ds/rc/revo_track.wmv

...not to mention the voltage of a fully charged pack vs. nominal voltage. I know u said not to do this, but have u tried the luntach 10s ESC??

you mean the esc the size of texas?:lol:

Come on now. Aren't we exaggerating a little? Everyone knows those ESCs are only the size of a small state. :smile:

Anyway, I would not run the MMM with any voltage past 6s. Patrick has stated that there is a components that will fry if over 26v IIRC. So, I would stick to 6s lipo (25.2v peak @ 4.2v/cell), 7s A123 (25.2v peak at 3.6v/cell), or 18 NiXX cells (25.2v peak @ 1.4v/cell).

Don't the "good" NiMh cells peak at 1.55+? That would be too much, I think, depending on how fast you got them from the charger and into the truck. My Tenergy 3500 cells have gone to that level on all of my last 5 cycles.

Actually it's the size of Jamaica :lol: and you don't need a fan either:whistle:

I'm testing the 120A esc(size of a McDonald's Bigmac) of Lutach and that little suckers takes 7s A123 like a champ, running the 1512 2y.

Good NiMh packs have a higher resistance and thus will actually peak at a lower voltage than cheaper/crappier packs. If my memory serves me correctly, 1.4x V is about where they peak at.

And even if they do peak a bit higher, just let them sit for about 10 minutes and that voltage will drop a bit.

Hmm.... That's weird. All of the "factory team" manufacturers always brag that their cells are higher voltage. How much higher resistance can they be and still support the 10C current draw?

The higher voltage they brag about is their loaded voltage. I know 2+ years ago they would use a 30 or 35amp load and provide numbers based on that.

I see. Thanks for the info. I think they still use those numbers.

Wow, 30-35 amp load.... We would have to run nimhs in 2p to even get close to lipo. Can you imagine the weight...

A123 cells have their benefits, but will have a very hard time matching a good lipo. If you want a low weight/long runtime lipo is the way to go.

In all honesty, A123 have to do fast recharge, if they didn't no one would be interested. The only benefit they have in my eyes is that they are less sesitive to abuse. But a properly made tray can protect a lipo just as well. And lipo packages better for our uses.

>In all honesty, A123 have to do fast recharge, if they didn't no one would be interested

Don't want to start a debate, but there are a few more advantages worth mentioning
. No need for an LVC or balancer
. Shorter Constant Voltage phase while recharging
. Will last a few hundred cycles longer
. Easier to reconfigure/assembling
. More secure: No fires, explosions, puffing ...
. I'm not worried when i subject A123 cells to water/snow
and so on ... simply fool proof

Of course lipos will remain unmatched when it comes to performance/wheight ratio.

what r the best places to find a123 cells?? any1 have experience with hobbycity cells?

If it says A123 on the label thats all that matters- stay away from more generic looking versions that just say li-ion or lifepo4 without the A123 badge.

Best bet for genuine A123s is tanicpacks.com, though hobbycity do cell individual cells too yeah:

clicky

The prices have gone up quite steadily for a while, I remember when they were more like $10 about a year ago, it was just the high shipping costs that was annoying back then...

And now, the disadvantages:

- Relatively heavy, especially in 2P mode.

- Resulting pack can be large and difficult to fit into typical battery trays, depending on vehicle.

- Really needs to be in 2P mode for decent runtime and constant current output. You could get by with 1P if in a light vehicle and/or run HV instead to reduce current.

Very true. For some setups/intended uses the a123 cells just fit the bill perfectly. For others lipo works better.

Lifespan is not something I usually think of, but for someone who only has 1 rc and plays with it alot it can be a big deal. I have never worn out a lipo... Usually change the setup and sell it or take it apart to make a different pack.

I am usually trying to get the weight down, and jsut find that lipo packages easier... But that is just my personal feelings. I think that the a123 tech will be the gateway to better electric storage for homes and full size cars. They just need to scale up the packs to car battery size. Imagine what a 50 pound a123 pack would be capable of.

sry to be thread jacking here but can any1 tell me the dimensions of these cells?? thnx

The traditional 2300mAh cells are 26mm x 65mm. The smaller ones (1100mAh) are 18mm x 65mm.

thnku sir