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.