MMP max bec output on 2s - RC-Monster Forums

bdebde · **MMP max bec output on 2s -** 11.25.2010, 05:46 PM

What is the max bec output that can be used when running the MMP on 2s? Will setting it at 7.4 cause problems when voltage drops below that? I have a high voltage servo I would like to try, but not ready to wire direct to battery as I am not sure if I will keep this servo in this car.

BrianG · 11.25.2010, 06:06 PM

For a stable output voltage, the BEC should be set to at least 1.5v lower than the lowest supply voltage. Setting the BEC for 7.4v on 2s will cause the actual BEC voltage to be around 1v lower than the battery voltage and it will fluctuate as battery voltage dips and rises with the load. The servo may be able to handle this ok, but the receiver may have problems with the fluctuating voltage.

I would set it for 6v max for best results.

kingdomracer · 11.27.2010, 09:23 PM

I'm running a 7950TH on a 2s setup with MMP and have the BEC set at 7v which I believe is the highest you can set it at and have had no probs.

fastbaja5b · 11.28.2010, 09:07 AM

I have the MMP in my SCRT10 and it ran my Savox 1267MG Servo ok set at 6V but the castle blower on my motor was laboured (slow) and my LED's wouldn't light up at all. I have since changed it to an external bec and everything is spot on now, servo is happy, Fan spins quick and LED's are bright!

01.08.2011, 03:12 PM

running a savox in mine and it doesnt wanna run at all well... very jittery... is that due to the bec voltage being to low or the fact its not supplying enough amps?

01.08.2011, 11:16 PM

Quote:

Originally Posted by Bazzokajoe

running a savox in mine and it doesnt wanna run at all well... very jittery... is that due to the bec voltage being to low or the fact its not supplying enough amps?

Im in the same boat, just got a Savox 1256tg and it glitches when I rotate back and forth real fast, the servo just stalls, then returns slowly back to center.
Hooked it up to my MMM and no problems.

Edit: The problem was on a MMP with the BEC at 6v

fastbaja5b · 01.09.2011, 08:30 AM

...so is the problem something to do with the ESC or Savox Servos I wonder?

Either Way, my $7 chinese BEC is having no dramas doing the job

01.09.2011, 09:01 AM

I think it has to do with the BEC in the MMP

simplechamp · 01.09.2011, 11:00 AM

Yes it does, this is a fairly common issue, I've dealt with it on my MMP also.. The BEC doesn't hold voltage very well when loaded up by amp-hungry servos and causes brown outs to the RX. You can use a capacitor on a spare RX channel and that should help, but really an external BEC is a true fix.

Can you even set the internal MMP BEC to 7.4V? I thought it was only 7V max?

bdebde · 01.09.2011, 03:53 PM

Quote:

Originally Posted by simplechamp

Yes it does, this is a fairly common issue, I've dealt with it on my MMP also.. The BEC doesn't hold voltage very well when loaded up by amp-hungry servos and causes brown outs to the RX. You can use a capacitor on a spare RX channel and that should help, but really an external BEC is a true fix.

Can you even set the internal MMP BEC to 7.4V? I thought it was only 7V max?

Yep, the capacitor may make it run fine; my 7940th would just stutter without it. A BEC would eliminate any issues.

01.09.2011, 04:20 PM

so... capacitor will sort me out... may get a bec as well...

Exact setup is:

MMP (well, qbase ;) ), savox sc1257tg, 3s 40c 5000mah lipos, hkgt2 radio gear....

hmmm...

capacitor time...

BrianG · 01.09.2011, 05:22 PM

A cap MAY sort you out. Generally, a cap will help with a noisy BEC, or helps provide a little extra current for bursts. But a cap will not help the BEC cope with a high overall load. For that you simply need a BEC with a higher current output.

01.09.2011, 05:37 PM

ah right, thanks for the clarification,

what bec would you reccomend, the castle one?

what difference will it make of both bec's are set to 6v (servo max as far as i know) ?

why does the mmp voltage fluctuate under load so much as well?

BrianG · 01.09.2011, 05:42 PM

The Castle one is fine. DimensionEngineering and WesternRobotics both make decent BECs as well.

I wouldn't run both BECs, disable the ESC BEC and use the external one solely.

I really don't know why the MMPro BEC has trouble. IIRC, Castle said the design is the same as the MMM. But, out of the 3 MMPros I have, all 3 have trouble at anything above ~2A load.

DrKnow65 · 01.09.2011, 09:02 PM

I'm starting to lean twards the Savox. My MMM wouldn't power the ultra speed Savox I was using in my Hyper 7. I fixed it by running the CC BEC I had laying around, worked well for a few runs (2 or 2-1/2 hours total) then I was having the car shut down when I steered. Thought my CC died, but after some investigation found that the Savox is dead... Have not opened it up yet to find out if I can determine the cause of failure...