New warning insert in MMM box: "DO THE MATH!" - Page 2 - RC-Monster Forums

Metallover · 08.02.2009, 06:59 PM

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

08.02.2009, 09:00 PM

Quote:

Originally Posted by Metallover

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

only us crazy mofos do it

im really enjoying these turn of events the last few days

JThiessen · 08.02.2009, 09:15 PM

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.

Pdelcast · 08.02.2009, 11:44 PM

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

BrianG · 08.03.2009, 12:05 AM

Quote:

Originally Posted by JThiessen

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.

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.

Quote:

Originally Posted by Pdelcast

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

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.

jhautz · 12:14 AM

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?

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.

hemiblas · 12:41 AM

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.

fastbaja5b · 08.02.2009, 08:54 PM

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 :)

emaxxnitro · 08.02.2009, 08:55 PM

maxamps 60c? what a lie

suicideneil · 08.03.2009, 04:25 PM

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).

TexasSP · 08.03.2009, 07:09 PM

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

JThiessen · 08.03.2009, 08:00 PM

Quote:

Originally Posted by TexasSP

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

More, much more....

SpEEdyBL · 08.04.2009, 02:06 AM

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.

fastbaja5b · 08.05.2009, 01:26 AM

Quote:

Originally Posted by SpEEdyBL

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.

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?

NIX · 04:06 PM

Quote:

Originally Posted by fastbaja5b

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?

MGM compro did testing on voltage: http://mgm-compro.com/pdf/en-motor-braking-050409-g.pdf It is quite interesting to see what the effect is of using breaks over the ESC. It is quite some info but the same voltage problems when braking can occur in all on the market available ESC's. Principles are the same. It can cause quite some troubles/failures in setups but with this knowledge one can prevent problems to occur.

If you want to run your ESC's bullit proof a few conclusions I took myself after discussed this with Grisa of MGM is:
1. Use a ESC that is rated for 2s higher than you are running. So a 6s when running a 4s setup, 8s when running a 6 setup etc..
2. Rating of ESC's max A draw is given for certain temperatures. A lot of setups (bad ones..) give higher temperatures and by that inner resistance will go up and max amp draw capable to handle will be lower (much lower). For that take a margin of 30 - 50%.
3. Use a good akku. Rating continuous should be 50% higher than the continuous rating needed for the motor you use. Especially with when you use packs that are branded with just 'marketing/making sales' in mind. Maxamps isn't the only one who is 'confusing'......
4. A BEC gives extra temperature in an ESC. Using a ubec makes a big diffference!! The castle creations UBEC is lightweight and can make real difference in temperatures you are measering. The temperature loss on a BEC (switching and linear are both very big, so it are small heaters on should get rit of in the system).
More on cooling /temperatures of ESC's:http://mgm-compro.com/pdf/controller...n-models-h.pdf

A well balanced setup can run cool without fan's etc. If a setup needs to be run with a fan for cooling down the elements it is a no good setup. A MMM can do a good job to without its fan if one plans it setup.

I think that a lot of the new 4s ESC's coming on the market (LRP etc) will give a lot people headaches.... Also marketing specifications....

MGM compro will come out on a short time with 'controlled breaking resistors' break device that will prevent problems caused as described. So no problems anymore with 6s esc's run on 6s.
They also have introduced a ESC that is completely waterresistant (you can even run under water).... For US buyers these might be quite expensive but on the european market the price difference is at the same level as the there to highly priced MMM v3.