Mamba Max internal BEC limit?

what is the voltage limit of the internal BEC in the mamba maxx ESC? Is it 3S lipo, or will it be fine on 4s?

[BrianG]

Really, you'd get best performance by using an external BEC for anything over 2s. 3s is pushing it IMO, but some people use it. Some of it depends on how strong and how many servos you have. 4s is definitely a no-no.

I'd use an external bec no matter what with the MM. I was having what appeared to be glitching issues with my radio. When I went to the external bec, all issues stopped.

[BrianG]

Well, I'd normally say yes, but it kinda depends on the drop-out value of the specific regulator you use. If running on 2s, the nominal value is 7.4v. Many regulators can have a drop-out value as high as 1.5v, which would put you under the 6v mark. And near the LVC point, the output could dip down below 5v. If running a 5v UBEC, that should be fine though. But running switching regulators so close to the drop out value might make them a little more unstable (noisier output).

[crazyjr]

I have run a MM with 3s and 12 cells and 3s no problem, but on 12 cells it would go on and off repeatedly. From my experience 3s is not a problem except it adds heat to the heat sink, but 4s (or 12 cells) is not a good idea

Brian, are you saying that there are situations where going with a linear bec is better? I have both, but my understanding was that the switching gets to be a better choice the farther you move up from 6V on your battery pack.

[BrianG]

Crazyjr: The bad part about running the BEC that hard is the it sin't even attached to the heatsink. It's hard to tell, but it looks like the regulator for the MM is actually on the other side of the board. So, the heat is being leeched away using the PCB traces and into the FETs, and then into the heatsink. Not exactly a direct connection and that heat is just making the FETs not run as well since FET current capability gets derated with higher heat.

AAngel: Sort of. The difference in efficiency between linear and switching regulators becomes very close when the supply voltage is closer to the output voltage. It almost becomes a wash. As a matter of fact, if the input voltage is very close to the output voltage, a linear regulator usually has a lower DO (drop out) voltage and can become more efficient. Weird eh... :) I'm sure switching regulators could be built with lower DO voltages, but designers realize these will mostly be used with higher pack votlages, so why bother? Linear regulators work just fine for low voltages.

To get an idea using real numbers, play around with the calculator at the bottom of this page. The switching BEC in the calculations assumes an efficiency of 85%, but that's usually at a decent current draw and higher voltage. When the input votlage is close to the output voltage, and current draw is either quite low or quite high (near the UBEC's limit), the efficiency drops to about 75%.

[crazyjr]

Originally Posted by BrianG

Crazyjr: The bad part about running the BEC that hard is the it sin't even attached to the heatsink. It's hard to tell, but it looks like the regulator for the MM is actually on the other side of the board. So, the heat is being leeched away using the PCB traces and into the FETs, and then into the heatsink. Not exactly a direct connection and that heat is just making the FETs not run as well since FET current capability gets derated with higher heat.

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I didn't know it wasn't connected, I stand corrected. I have run on a 5700 T4 and 3s for over 30 minutes and it never thermaled. The 12 cell one was a 9XL in my G2R and it would be kind of jumpy after about 30 seconds, I assumed it was the bec cutting off and on and quit mediately till i got my koolpower ubec

I've been fine running the internal BEC at 3S.... I'll have to pick up a UBEC for my 4S pack then :)

I was just thinking that it might be hard to generalize something like the topic being discussed here. It's obvious that some are having problems where some others aren't. Perhaps the acceptable range within which these controllers must perform to pass QC is kind of wide.

I have five MM controllers. On a couple, I've had problems with the bec giving me headaches with my radio. I don't know that all would have given me problems. I just went to external becs so that I wouldn't have to worry about it.

Of the controllers that I have, three will run on 5S and two won't do anything when I put more than 4S on them. I don't know.

[BrianG]

The fact that some will run on 5s and some won't suggests to me that they are running VERY close to their maximum ratings. Even the ones that are currently running are probably being pushed and will shorten their lifespan.

And yes, 3s will work using the built in BEC - but only if there is a fairly low current drain. At a moderate servo load of 1A, 3s will produce over 6 watts of heat on the BEC ((11.1v - 5v) * 1A). Doesn't sound like a lot, but it is on such a small device. Just like anything else; you might be able to get away with it, but is a $140 ESC worth risking when a UBEC can be had for as low as $10-$15? That's up to the individual I guess.

[crazyjr]

My T4 has a hitec 56 or 5925 so the amps are not bad

Hobby shop has to order my external BEC. In the meantime is it safe to run a typical 5 or 6 cell reciever pack into the?

After spending $300 on a battery and balancer I'm excited to see this thing haul ass :)

[BrianG]

6 cell is OK, but 5 would be too low IMO. 5 cells is ~6v, but the BEC has a minumum it needs to get the full 5v out. This is down as the drop-out voltage. This 1v difference is OK, but when the battery pack starts to dump, the BEC output might drop into the 4v range...

[crazyjr]

Originally Posted by BrianG

6 cell is OK, but 5 would be too low IMO. 5 cells is ~6v, but the BEC has a minumum it needs to get the full 5v out. This is down as the drop-out voltage. This 1v difference is OK, but when the battery pack starts to dump, the BEC output might drop into the 4v range...

If you mean the BEC in recievers, not sure about all, but the JR rs300's have a 5.3v bec in the battery slot, but whatever the batter is charged to in ch 3. The rs310 has no internal bec so you get all the battery has, Nomadio is the same as the rs310, my Ubec gives 6v+ on reciever power on Nomadio screen