New warning insert in MMM box: "DO THE MATH!"
 

My friend got his replacement MMM back from CC last week and told me that there was a new piece of paper inside the box. I have attached it for you here.

http://i143.photobucket.com/albums/r...po_Warning.jpg

Essentially, CC is now saying "We aren't going to name names, but don't use cheap lipos or bad things can be expected to happen!". Which is something we have known all along. My question is about their minimum recommendation of 4000mah 20C cells. If they are stating that the MMM can sometimes demand 100 amps in peaks and that you should always stay at 80A Continuous or LOWER, why is it that everyone seems to always recommend 25-30C packs? If I'm supposed to try and stay at 80 or lower, then my 5000mah 25C Flightpower packs are overpowered according to this graph right?
5A x 25C =125 x 80% = 100. I guess I'm just confused.

It makes me wonder if they think the reason so many MMM's are failing are because of cheap batteries or overpowered batteries? All I know, is that once I get my MMM back, which should be soon, and get my Neu either fixed or replaced, I'm going to continue running 6s, but I'm gearing way down. I'll probably pickup a couple 2s packs and run them as 4s too.

There are tons of people out there running the MMM system with no problems. The ones that have, it's hard to say just why it happened I guess.

What this means it that now any users of MaxAmps packs will be more confused than ever! Since MaxAmps only specifies a surge rating now, users will have no logical way to do the math on the Castle insert.

How can anyone know how much current they're pulling?

I am with CC though. I do not see how it makes sense to go with the surge rating. I would also think if using cheaper cells that giving yourself a buffer would be a given as well.

They aren't saying to stay at 80 amps or lower they are saying that you need batteries that are capable of more than 80amps. there really is no such thing as an overpowered battery, as long as it's less than 6s for the monster. If you could fit 6s 6000mah 40C that's great, capable of 240amps! 6000mah 10C = not good at only 60amps

Eagle tree!

I guess I'm still not getting it. If they are saying you need batteries that are capable of more than 80 amps, why did they print "We suggest you never run the system at more than 80% of the max continuous rating."???

And their formula for the 5000mah 20C cells is right at 80%. Then they go on to say (as if you can't read! HA!), that they suggest a minimum of 4000mah 20C packs.

So, they say "never run at MORE than 80% of the max continuous rating" and suggest that the MMM can hit 100 amp peaks. Right? So if my Flightpower 5000 25C cells which according to their formula put out 100 amps max continuous, and they say "don't run the system at more than 80%", how can higher be better?

I mean, this is what I've assumed all along.. that the more on tap the better, but it seems to contradict what they are saying. It's almost like that thing they wrote up is written incorrectly. No?

of your batts, not the controller... to account for bs lipo claims I'm sure

The system will draw what the system is setup to draw, regardless of what battery you use. If you are geared to draw 100amps, that is what you will draw. Now if the battery cannot handle 100 amps you will have battery and esc issues, and alot of heat before something craps out. Their recommendation of 4000 20c lipo is way too low, but the rest of the info is good and should be listened to.

The 80% rule should also be applied to DOD (depth of discharge) as well. If you want your lipos to last as long as possible, only removing 80% of the total capacity (mah) from them is a good idea. Plane guys do this, but they usually time their flights in order to do this. You could probably do the same thing with a few test runs and a stop watch. Not sure if setting the lvc higher will gaurantee good result with trying to stay under 80% DOD.

Well yea, but you can't expect everyone with a MMM to buy a data logger. In any case, we all know to buy good quality batteries :yes:

My thoughts exactly!

Maxamps is trying to rate batteries in surge watts according to the rating of a motor?

Here we have a reputable President of a ESC/Motor company saying "Don't do it!"

:whistle: Hmmm.........whoever shall we listen to? :whistle:

I vote CASTLE!!! :yes:

i still think its a joke that the MMM will die if you use cheap cells, how come the MM never had that problem?

^^ oh cummon! it's exctly like trying to run a big block V8 sprint car on standard octane fuel!!
yeah sure, it runs..but really bady!!

The mm didn't have these problems cause it couldn't handle this kind of power period. How many people ran 5s on a mm? Not many cause it worked for some and smoked for others. The mst you could reliablly get on a mm was 4s and the heaviest you could really go was a light e-maxx geared conservativelly, or a 1/8 buggy geared for a track. I can almost gaurantee that 90% of the failures from poor batteries have been in heavy vehicles with high gearing that will stress even the best batteries.

Not too many people would run a 1515 sized motor with a MM either. The MMM just deals with more power.

It's like Briggs & Stratton using "gross torque" on their engines instead of HP because THEY think it is a better way to rate the engine...... No other company uses that method... :grrrrrr: So it makes it much harder for consumers to compare different brands.

Well I run IB 5000mah 40C packs, 40C being the stated constant rating, so 200 Amps, my eagletree has shown a max amp spike of 121 amps from the Savage Flux so I have a 40% buffer.

I can live with that :)

maxamps 60c? what a lie

only us crazy mofos do it :lol:




im really enjoying these turn of events the last few days:intello:

I havent been into the calculators in a while, so is there a way to have it also calculate maximum amp draw based on motor and gearing? It might already be there....just havent looked.

Believe me, there are a lot of people trying to run 15C 3200mah packs... /sigh

No such thing yet. Even with specifying gearing and such, there are simply too many variables to consider to be anywhere near accurate. The best you can do is estimate average current draw by your runtime and battery capacity figures, and then estimate burst current by multiplying the average current by 6-8.

On the next version of your ESCs, incorporate a mechanical fist that comes out and punches the user if they try to use such packs. :smile:

Seems if you want to spec a minimum capable battery for an esc, there should be some standard to defining a batteries performance. Anyone can write anything they want on the side of a lipo and have people buy it these days. Sure makes it hard for the consumers to wade thru the muck when the ESC manufacturers are saying minimum rating of a battery needs to be one thing, except for some brands that arent good no matter how they are rated, and the leading lipo pack builder has stopped using those rating standards all together.


Wait a minute.... What did I just say? :neutral:


I don't get it anymore. I liked the days of figure it out yourself, burn a few things up and eventually you learn what actually works.

Is that why you haven't included this on your calc sheets?http://www.rc-monster.com/forum/show...motor+amp+draw

:diablo: Just figures.....sometimes looking at all these electrical numbers gives that feeling of doom I had 20 years ago in my EE and EEET classes in college. If it weren't for HP calculators, I would never had made it through those classes.:sleep:

Well, there are a couple reasons I didn't add that (yet):

- I forgot about it :smile:
- No feedback.

I still have my trusty old HP48gx, with a whopping 512k RAM card. lol.

no, they do it to hide the fact that they can't make power...:lol:

I like this latest development, its a kick in the teeth for noobs and those who mislead noobs. If your lipo puffs, then you know the manufacturer mislead you on its ratings/capabilities. If it doesnt puff, then its all gravy.

I think the 80amps minimum thing applies to mild setups though, rather than extreme setups (same reason for having mild gearing with nimhs and nicads).

People need to start thinking about the power systems as just that "SYSTEMS". The ESC, Motor ,Battery & gearing are the system. The components of the SYSTEM are individual peices that need to be suitable for use with each other.

You would not go down to tire rack & get a set of subcompact car tires and expect them to work on a Boeing 747-400. Yes I know the 747 uses tires, but not ones ment for a corrola.

So yes, we all need to do the math.

Your right, the Boeing 747 tires cost as much as a corolla.

More, much more....

Theres still too many problems with the way manufactures rate lipos. 3200mah 15C batteries should be good for 48 amps continuous. To me, That means you should be able to pull 48 amps continuously during the run, sometimes more, sometimes less but an average of 48 amps. Thats a lot of amps and I can guarantee that most runs wont even come close. Even though I agree that they wont work, the math says it does and I think its the lipo manufactures are the ones at fault for improperly rating their lipos. I have learned , not thru math but trial and error, to always buy more battery than I need, but I still dont understand why we have to. It wasnt until I bought a wattmeter that I finally understood that 15C really means 5C to most manufactures.

It's not current that's the problem but the voltage spikes that kill the esc. Even though a 48 amp battery can supply the needed current, it's voltage spikes will be a lot more violent, compared to those from an 80 amp rated battery. C rating mostly decided on being able to hold a voltage, which makes higher amp capable packs better. You'd be amazed at how high voltage spikes can get during braking, easily twice the pack nominal voltage with bad packs. Since the the MMM and MM both have 30 volt fets this was not an issue with the MM as 3s was the rated limit.

Ya thats a great point. So really then we should be telling everyone to buy a battery that has a continuous rating of what we expect the surges to be. There is also a huge range on C rating. My 11.1V, 10C 5000mah truerc battery can hold 40-50A with good voltage with bursts of over 120A according to their website. My ebay 11.1V, 10C 5000mah battery can hold 10A at around 9.6V and weighs about half as much. I dont use either of these on my MMM though, but I bet the truerc battery would work fine.

I dont know if this matters, but my velineon ESC weeds out the bad batteries by the use of LVC. Its set very sensetive from the factory and on cheap batteries I get approx 10 seconds runtime from a full charge on a 10C cheap 5000mah battery before it shuts down. When the ESC pulls too much current and the voltage drops it shuts down. Shouldnt the same thing be happening on the MMM? If not maybe setting this feature from the factory so its more sensitive might help to prevent failures due to bad batteries?

There is a TVS on the MMM which limits these spikes to something around 26-28v.

This is a double-edged sword. If you make the LVC too sensitive, it false trips all the time. If you make the LVC less sensitive to spikes, battery or ESC damage could occur. So, the LVC probably looks at the voltage over a set time and if it falls consistently below a certain value, it trips.

LOL, I still have my HP38G calc. I recently took a chem class after 10 years of graduating college (now applying to med school). It was great, when I took a test, the calc checkers had no idea to look for stored notes in my HP. They were like whatever and gave it back to me. That calc had a great solver function. Sorry OT :whistle:

Naaahhh. Just make a version with HUGE caps so that you get a giant spark...

while maintaining the current dimensions:tongue:

And this is why on 4s the failure rate for the MMM is far lower than on 6s, greater difference between the pack voltage and fet rating... right?

Exactly. I think there was also some flaw in the early software that prevented the MMM esc from being able to detect those spikes properly, which lead to the V1 and V2 failures. But of course even with the TVS working properly, the more the esc has to depend on it, the more likely damage will occur (I can only guess).