MMM Explodes into FLAMES!

[hemiblas]

I have been running my MMM on 4S and 5S for a while now with no issues with all types of batteries, motors and configurations. I do a lot of hard starting and stopping and havent had any issues, mostly bashing. I decided to try some 6S setups conservatively geared just to test and have now gone thru 2 controllers in 3 weeks. The same controllers that were operating perfectly at 4S and 5S did not work on 6S for to long. In both cases the controllers failed while the truck was coming to a stop. The second failure took out one of my lipos. I will be sending the second one in this week, but I am pretty sure that if you are using the MMM on 6S and using the ESC for braking, I think the probability of failure goes up quite a bit. Maybe I am just unlucky twice this month, but it just seems like to much coincidence that this would happen. My solder connections were solid in both cases, no binding on the truck, I really have no other explanation as to why this could happen. AFter reading Brians post above it makes sense. On the second controller I could see puffs of smoke coming out as it came to a stop at my feet. I was braking hard as always with the 40 percent brake setting so the truck doesnt flip over going forward.

[jpoprock]

Originally Posted by hemiblas

but I am pretty sure that if you are using the MMM on 6S and using the ESC for braking, I think the probability of failure goes up quite a bit. Maybe I am just unlucky twice this month, but it just seems like to much coincidence that this would happen.

Pardon my ignorance... but is there ANOTHER way you can brake without relying on the ESC?

[BrianG]

Originally Posted by jpoprock

Pardon my ignorance... but is there ANOTHER way you can brake without relying on the ESC?

Mechanical brakes like the nitros use...

[Unsullied_Spy]

I managed to kill mine in my Muggy under really hard braking. 80mm Medusa, 16/46 gearing with 40 series wheels/tires, 4s lipo, and it took repeated hard braking for it to finally stop working. No drama, it just stopped working right as if I had burned out a phase. Got my replacement and it's still going strong ~4 months later.

[hemiblas]

When I get my controllers back, I will be going back to 4S and 5S setups, but I agree, Castle should maybe look into this to see if there is anything to your theory. It may help to explain why they get some of their controllers back for warranty work. After my experiences this week, I think you are on to something too. So basically this would also apply to heavy vehicles on 4 and 5S setups.

[suicideneil]

5s lipo or 6s2p A123 ftw

ON another note, yeah, I hope there were two of those Zippies in parallel, as 3500mah x 30c = 105amps at best, and as much as I like the Zippies, I prefer lipos that can do 120amps plus, hence why I use a pair of 5s 25-35c 4000mah zippy-Hs in parallel to get me 200amps continuous for my hefty setup (lots of hard braking and violent acceleration and no dead esc yet).

[jpoprock]

Also, I think I might go ahead and buy a couple Flightmax 2s packs that are 30C or higher and go down to 4s rather than 6s just to be safe.

UNLESS you feel that if I gear down considerably on 6s, that would be just as safe. I'm just wondering... what gearing? 68/18?

[jpoprock]

Wow, that is unbelievable. I didn't realize such a mod could be done on a BL machine like the Revo!

[BrianG]

Well, vehicles converted from nitro to electric will be easier because it was designed for mechanical brakes (has the discs, pads, linkages, etc), but electric-specific models like the E-Revo may require some fancy modding since they are not initially set up to have mech brakes. But it can be done.

Just be aware that if you go to mechanical brakes, you won't have reverse unless you use CH3 to activate the brake...

[jpoprock]

Sounds like a nightmare. A better solution would be to just watch your gearing and lipo combination and you would ASSUME one would be just fine.

However, on something like an LST2 conversion, it sounds like a possible good idea and much easier! Which btw... and LST2 conversion is in my future anyway!

[BrianG]

It can be. Personally, I would only use mechanical brakes in heavy vehicles and/or setups that use high voltage (6s+) because back-EMF generated during braking becomes considerable at higher voltages...

[shaunjohnson]

CC HV-200 @ 90v FTW!!!!
hmm....barbie jeep anyone.
shaun

[jpoprock]

I'm starting to buy into the theory that running the MMM V3 with 6s is possible, but it comes with "use extreme caution".

Maybe it's just me, but that sorta goes against CC's marketing for this controller. They make it sound like 6s is the only way to go. But i'm starting to wonder if maybe 4s is the sweet spot, and 6s is for occasional use only. I dunno though.

That being said, I might pickup a set of 2s Lipos and run them together as one 4s. My only question though, is do they make 2s packs with a discharge rate of 30c? Or do only 3s and beyond supply that? The reason I'm asking, is because I'm thinking of buying some Zippy Flightmax Lipos. I seem to recall hearing that if you're going to buy "cheaper" Lipos to run w/ the MMM, you need to make sure they are at least 30c

Is that accurate?

[hemiblas]

You should really just post some links on what you are considering. You can get 30C 2S packs just like you get them in 3S packs, just depending on how you want them built. I dont think they offer the 30C is 2S for the flightmax lipos. Just the C rating is not going to help. 2200 30C lipos wont work, but some 8000mah 20C lipos will. Are you looking at the 5000mah lipos at 20 and 30C?
You really want to look at the continuous current rating of the battery. I think someone posted 120A or over is a good number and I think I agree. So some 25C 5000mah packs should do nicely.

[Bondonutz]

http://www.hobbycity.com/hobbycity/s...cing_Lipo_Pack