MMP Problem

[fastbaja5b]

Hey guys, after all sorts of issues with MMM's blowing, I decided to try the MMP in my SCRT10. I am using the Castle Shortcourse motor from the Sidewinder SCT kit (as stated previously had issues with that ESC getting hot), using a Savox SC1267MG Servo and a Furaba R603GF receiver through a Futaba 4pl.

As we usually bash at night, I run LED's on the front of my Corr trucks, the Slash I have has the basic VXL esc, 4 * LED's up front and has been a rock, running fine in and out. LED's are simply part # TRA5689 from the Traxxas Summit.

This MMP will not run the lights. With or without the Servo plugged in.

I have reset the firmware with the latest settings, made sure my BEC is at 6.0V and multimeter reads 6.19v at the receiver plug. Servo reacts ok, running a Cap makes no difference either.

However they work fine when I run an external BEC. Nothing fancy, and the specs are identical to the "built in BEC"" on the MMP. Set at 6.0V, 3 Amps

http://www.hobbycity.com/hobbyking/s...idProduct=3735

With this the Cap isn't needed, the LED"s shine bright as day and the cooling fan on the motor runs notably quicker. This BEC measured 6.17v at the receiver plug.

So what's up? Is my MMP a lemon? I'm hesitant to go through an extended warranty procedure of mailing it in (2 weeks freight), waiting for turnaround, then waiting for freight back (2 weeks again) when it works ok with this $6.95 Chinese BEC.

Any ideas?

[Arct1k]

Its well documented that the MMP bec is actually only good for 2amps (Well Briang said so its gosple) and that you may need to use an external BEC.

Thx

[fastbaja5b]

True but even when I am not powering the servo, ie ESC plugged into the receiver with led's only, they still won't light up. I know my LED's and the fan don't draw 2 amps.

[BrianG]

Originally Posted by Arct1k

Its well documented that the MMP bec is actually only good for 2amps (Well Briang said so its gosple) and that you may need to use an external BEC.

lol, "gospel" eh? Not sure about "gospel", it was just measurements from the few MMPros I happen to have.

Originally Posted by fastbaja5b

True but even when I am not powering the servo, ie ESC plugged into the receiver with led's only, they still won't light up. I know my LED's and the fan don't draw 2 amps.

That doesn't make any sense at all. Unless you have the LEDs wired in such a way that they consume more than ~2A, they should light up no problem. I assume you have the proper current limiting resistor for those LEDs? Because if you don't, they can draw a lot of current (and usually blow in the process).

Make sure the LEDs use the proper resistor(s), make sure you have the LED ansodes going to + and the cathodes going to -, make sure the servo plug is inserted the proper way in the receiver, and then measure the voltage (AC too to make sure you aren't getting a ton of ripple, which means a bad BEC) at the LEDs.

[fastbaja5b]

I tried the LED's off the VXL esc in the Slash by plugging them into the 3rd channel as I do with the SCRT10

No problems there, they work fine.

Only does it on this ESC.

[fastbaja5b]

Tried it again by putting the MMP in a TT-01 which only has a Futaba S3003 and a Tamiya LED light kit. Wouldn't power up those lights either.

What should I do? Disappointed that everyone seems to love Castle products but I've got yet another faulty one, and no response from Castle in this thread either.

[Pdelcast]

Well, I don't think that makes any sense at all. If it will run an RX and servo it shouldn't have any trouble running LEDs, unless something is wired wrong.

LEDs typically only draw about 20-100 milliamps.

I hadn't responded 'cause I figured it was something wrong in the wiring and you would probably figure it out.

I also wouldn't call that a faulty unit -- if it works with an RX and servo, there's nothing wrong with the BEC. We don't warranty or guarantee that the ESC will drive anything else besides receivers and servos.

And besides -- If you are reading the correct voltage, and the servo and RX work OK, bur the LEDs don't light, I can't see how it has anything to do with the MMP.

[What's_nitro?]

Just to be clear- Even with the LEDs plugged in and not working, everything else works fine?

I doubt it's an overcurrent issue. Like BG said if the LEDs were seeing too much voltage they would just pop.

Are you using the same model Rx in both trucks? It would be silly, but maybe the SCRT10 doesn't have power internally supplied to it's 3rd channel plug... Have you checked for proper voltage at this location?

[fastbaja5b]

When the LED's are plugged in and not working, Servo and RX is fine (when I run a cap), Castle cooling fan spins notably slower compared to any other ESC.

I have tried different rx's (Futaba R603GF, Spektrum SR300), different ESC;s (VXL, Xerun 60A) and all other ESC's power lights on and with both receivers. No LED's work with the MMP, that's with any receiver, and with/without servos and with/without a Cap.

Using the same 3rd channel plug from the receiver to the lights, and running an external BEC, the lights are fine.

I have tried a mates MMP and that powers the LED's fine. The Sidewinder SCT ESC also did (although it ran hot)

I have no doubt it's an ESC issue but am hesitant to send it in given down time, freight costs etc.

[Pdelcast]

Originally Posted by fastbaja5b

When the LED's are plugged in and not working, Servo and RX is fine (when I run a cap), Castle cooling fan spins notably slower compared to any other ESC.

I have tried different rx's (Futaba R603GF, Spektrum SR300), different ESC;s (VXL, Xerun 60A) and all other ESC's power lights on and with both receivers. No LED's work with the MMP, that's with any receiver, and with/without servos and with/without a Cap.

Using the same 3rd channel plug from the receiver to the lights, and running an external BEC, the lights are fine.

I have tried a mates MMP and that powers the LED's fine. The Sidewinder SCT ESC also did (although it ran hot)

I have no doubt it's an ESC issue but am hesitant to send it in given down time, freight costs etc.

OK -- Well the Xerun and VXL both use linear regulators. The MMP uses a switching regulator. The LEDs might be tripping an over-current sense in the switching regulator for some reason.

What's the measured voltage on the RX cable with the LEDS, servo and RX all plugged in?

Is there a resistor in series with the LEDs? (This is critical!)

[What's_nitro?]

The TRA5689 LEDs are wired in a 2s2p arrangement. The 2s would lead me to believe there is no resistor included (probably intended for 5v operation). I can't see one in any picture of the product online unless they put it in the JST plug somehow...

[fastbaja5b]

I will double check, but I was under the belief that only 3mm LED's needed a resistor for 6V, 5mm LED's run at this voltage fine.

[What's_nitro?]

All LEDs need resistors, as they are basically a short circuit otherwise (Light Emitting Diode). The voltage drop of an LED is pretty large- ~2.5 volts is pretty common, so at 5v you could get away without a resistor. Each string should have a 200-300 ohm resistor in it's series to limit current to 20-30 mA. This is more to protect the LEDs from popping than it is to prevent overdrawing the BEC circuit in an ESC. Patrick would know better than anyone if the lack of a resistor could cause a problem, and why.

[BrianG]

You NEED a resistor in all cases. If you were to run, say, 2s lipo with LEDs with a Vf value of 3.2v each, the resistors are critical because the current would be 7.4v-(3.2v * 2)/0 ohms, which is mathematically infinite current.

If the LEDs are rated for 3.2v each, a string of 2 LEDs in series will require 6.4v. Running off 6v would technically be "ok" (sorta but not really), but relies on the fact that the voltage is not high enough to fully drive the LEDs and turn them into burnt silicon.

[Pdelcast]

Originally Posted by What's_nitro?

All LEDs need resistors, as they are basically a short circuit otherwise (Light Emitting Diode). The voltage drop of an LED is pretty large- ~2.5 volts is pretty common, so at 5v you could get away without a resistor. Each string should have a 200-300 ohm resistor in it's series to limit current to 20-30 mA. This is more to protect the LEDs from popping than it is to prevent overdrawing the BEC circuit in an ESC. Patrick would know better than anyone if the lack of a resistor could cause a problem, and why.

200-300 ohms might be a bit much -- but I'm thinking the LEDs might be somehow triggering the overcurrent sense on the BEC. Not sure what mechanism (maybe a negative resistance slope on the LEDs, as they turn on, is the cause??)

I'd try 100 ohms in series with the LEDs to see if that fixes the problem. I'd be happy to try to reproduce the issue in the lab, and see if I can find an easy fix.

Thanx!

Patrick