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[eternal422]

As some of you may know if you have been reading my Danny Boy build log, I have had some electronics gremlins which I would really like to understand and solve.


The set up is a 12v SLA connected via DPDT switch (to allow switching between a charging socket and powering the boat) to an Action Electronics P112 power distribution card, using one of those outputs to go to an Mtroniks Viper Marine 20 ESC, using the BEC to power the receiver.


During testing I noticed sometimes when throwing the switch that I didn't get any power to the P112.  Switching off and back on everything worked ok again.  I took everything apart to examine for any bad solder connections / shorts, etc., and ensuring everything was ok then re-assembled.  The no power on switching on issue seemed to get more and more frequent.  Using a multimeter the input voltage on the P112 was dropping to around 3v when the ESC was connected.  Disconnecting the ESC made everything ok and the full 12v was available on the P112.


At one point previously trying to diagnose this fault I think that I shorted the motor wires from the ESC momentarily, however the ESC did work ok afterwards up until the point this week that the intermittent issue of no power when switching on became that everytime I switched on with the ESC connected I would get nothing.  Connecting the battery directly to the motor works and shows very little voltage drop - so I know that the battery is fine.  Then I reached the point of the ESC not working at all.


I'm fairly sure that there is a fault with the DPDT toggle switch - moving the lever side to side can cause the power to go off, so I am replacing the switch with a nice rocker switch to solve that issue.


So, my questions are :


1.  Could the momentary motor wire short (around 1 second) have caused some damage that would allow the ESC to continue to work afterwards but eventually fail?


2.  I am using a fully charged new 12v SLA battery which is showing a voltage of 13.2v - is this too high a voltage for the ESC?  Mtroniks say that these ESCs work on a fully charged 12v SLA, which would have a higher voltage so I'm thinking this should be ok?


3.  The motor is an MFA Torpedo 800, which does appear to have internal capacitors fitted, so I have not fitted any external ones to the terminals and case - is this correct?  I'm not suffering any interference of the servos, but wonder if this causing problems for the ESC?


I now have a replacement Mtroniks Viper Marine 20 ESC and with the new rocker switch I am hoping that once fitted will resolve these issues, but just a bit nervous that something is fundamentally wrong which is causing the problems?

[chas]

To try and answer your questions as best I can.
  The Viper is fine on a fully charged 12 volt lead acid, they actually say that in the blub  online.
13.2 volts is correct, I've sometimes had trouble explaining that 11 to 12 volts with a lead acid means it is flat, and won't operate equipment properly. Is that a possibility in your earlier testing?
The MFA 800 motor suppression capacitors are fine, nothing else is needed. It's worth noting that the stall current is over 20 amps, that will blow your esc if you were to get weed or similar around your prop. I'd fit a fuse, it's cheaper than a new esc.
  As to whether the short circuit has damaged your viper, only the manufacturer can give a definite answer, but it is possible. They are tough reliable units, but a direct short is rather asking for trouble. It's probably best to test it in isolation, on the bench.
I can't comment much on your wiring, like anyone else I'd need to see it, but I have one idea. I don't like to use a switch to change over to charging with a built in battery, too many chances for a mistake. I've used a make/ break socket in the past, that way the current can't go the wrong way via a faulty or forgotten switch.
  Good luck with everything, Charles.

[eternal422]

To try and answer your questions as best I can.
  The Viper is fine on a fully charged 12 volt lead acid, they actually say that in the blub  online.
13.2 volts is correct, I've sometimes had trouble explaining that 11 to 12 volts with a lead acid means it is flat, and won't operate equipment properly. Is that a possibility in your earlier testing?
The MFA 800 motor suppression capacitors are fine, nothing else is needed. It's worth noting that the stall current is over 20 amps, that will blow your esc if you were to get weed or similar around your prop. I'd fit a fuse, it's cheaper than a new esc.
  As to whether the short circuit has damaged your viper, only the manufacturer can give a definite answer, but it is possible. They are tough reliable units, but a direct short is rather asking for trouble. It's probably best to test it in isolation, on the bench.
I can't comment much on your wiring, like anyone else I'd need to see it, but I have one idea. I don't like to use a switch to change over to charging with a built in battery, too many chances for a mistake. I've used a make/ break socket in the past, that way the current can't go the wrong way via a faulty or forgotten switch.
  Good luck with everything, Charles.

Hi Charles - many thanks for the answers     I have a 15A fuse in between the motor and the ESC which will hopefully protect the ESC should the motor stall.  I'm hoping that the reason for the original ESC failing is down to damage caused by the short as aside from that everything else looks to be absolutely fine.  I guess time will tell, especially when I reach the stage of sailing the boat !

[malcolmfrary]

When picking an ESC, the normal consideration, apart from operating voltage, is its current rating.  Normal rule of thumb is "whatever I think the motor will draw, double that, pick the next value up".  This gives a safe margin for error.
Most ESCs have a limited amount of over current protection - the FETs they use tend to be self restricting - they start to shut down as they heat up due to abuse.  If driving a single motor, a fuse between ESC and motor only serves to provide a test point/fault liability.  Multiple motors, they become useful.
The place for a fuse is between ESC and battery to protect both the battery and the rest of the boat from excess current being drawn by a broken ESC or faulty wiring.
Any BEC, either discrete or built in to an ESC, if abused, will go into one of its fail modes.  This includes a reduced output voltage.  Cooking one gives many possible fail modes, including dropping its output voltage because whatever it is driving is demanding too much current.  If the ESC that it is sealed into has been damaged, that might include the BEC.  The damage might also cause the internal circuit of the ESC to draw more current than it should.
Look out for ground line wiring.  If the main -ve power path from battery to ESC is not good, and an alternative exists via the radio, when there is a full current demand from the ESC, strange things start to happen.  Over time, the metal in the black wire in the ESC-radio lead vaporises.  Odd things happen, getting worse until everything stops.
When checking voltages, it is good practice to not just stick to using battery -ve as the reference for the meter.  Looking down from +ve can be quite illuminating in the event of a faulty -ve line.