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How many amps can a servo draw
Had an interesting failure today. On Flight number 20, an 8611 developed an internal short. I use the Powerflite adjustable voltage regulators, which are rated at 7.5 amps continuous and 10 amp surge. The bad servo maxed out the regulator and knocked the voltage on that circuit down to 1 volt. Thank goodness I use isolated circuits or that would have been the end of the flight.......and the plane.
Being curious, I removed the bad servo and hooked it up directly to a 5 cell nicad pack with an ampmeter. The result? 15 amps draw! Of course the thing started hissing and smoking. I had no idea that those little servo wires could handle that kind of amperage.....granted, it was just long enough to put a plane in the dirt. 15 amp draw is enough to take out any pair of regulators I have yet seen in RC planes! Anyway, I thought some of you would be interested to know just how much a servo can draw in certain failures. The Powerflite regulator was outstanding with its built in overload protection. After removing the short, the abused regulator almost immediately returned to normal operation. CJ |
RE: How many amps can a servo draw
Hmm. Maybe servos like these should include a 5 amp fuse on the servo lead? I would think a properly operating servo should never draw more than 1-2 amps.
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RE: How many amps can a servo draw
JR says that their standard plug is only good for 3 amps max. Interesting that you are seeing such a higher draw. The plug should have gone well before you saw that load. 5 times the rated capacity is impressive.
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RE: How many amps can a servo draw
Just shows to go ya......you can't believe everything that's advertised. By the way, it all went up in smoke at the same time - servo, wire, plug.......sssssmmmokin!
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RE: How many amps can a servo draw
The latest test in 3dflyer shows with 278 oz. the 8611 drew 1.9A. In the test they listed (mA) which I believe was a miss-print, all other servos showed (A).
BNG-I Think you exceeded that.:D |
RE: How many amps can a servo draw
RTK I have the magazine too. the misprint was for the Futaba. The 8611 was 1.8 amps @ 260 ozs on 6 volts.
Kelly |
RE: How many amps can a servo draw
OOPS, guess I should have looked a little closer. Maybe its time for glasses:)
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RE: How many amps can a servo draw
ORIGINAL: Blow n Go Had an interesting failure today. On Flight number 20, an 8611 developed an internal short. I use the Powerflite adjustable voltage regulators, which are rated at 7.5 amps continuous and 10 amp surge. The bad servo maxed out the regulator and knocked the voltage on that circuit down to 1 volt. Thank goodness I use isolated circuits or that would have been the end of the flight.......and the plane. Being curious, I removed the bad servo and hooked it up directly to a 5 cell nicad pack with an ampmeter. The result? 15 amps draw! Of course the thing started hissing and smoking. I had no idea that those little servo wires could handle that kind of amperage.....granted, it was just long enough to put a plane in the dirt. 15 amp draw is enough to take out any pair of regulators I have yet seen in RC planes! Anyway, I thought some of you would be interested to know just how much a servo can draw in certain failures. The Powerflite regulator was outstanding with its built in overload protection. After removing the short, the abused regulator almost immediately returned to normal operation. CJ I'm installing a power distribution system where each servo has its own regulator and a short will just shut down that servo and won't affect the rest of the system. No wires will burn either because the regulator shuts that circuit down if it sees a short so it will take very little out of the battery. Another question is would a second servo on an aileron for example be able to back drive the shorted servo? I assume it would but perhaps it was mechanically jammed up. Was that the reason for the short? It would be bad news if a stalled servo failed in a manner that would create a short. Someone needs to do some destructive tests to see what happens. This is a very interesting problem. Jim |
RE: How many amps can a servo draw
You're right, the regulator was maxed out, so there were not 15 amps available to draw in the plane. I assume the short drew over 7.5 amps until the regulator overheated. The Powerflight regulator automatically reduces it's output during an overload to reduce the heat generation. So once it built up enough heat, it was only producing about 2 amps as tried to protect itself.
The point I was making is that the average plane is set-up with two batteries (most with 2 regulators!?!). These would provide about 15 amps continuous current. If this failure happened on an average plane, it would have been a race to see which destructed first.........the regs or the servo lead. In any event, you would have no usable power for the plane until the servo lead finished frying. Mechanically the failed servo was fine. The three other servos on the circuit were dead, but they free streamed with the airflow. Could be that the matchbox was set wrong, but we'll never know now that it's fried. |
RE: How many amps can a servo draw
ORIGINAL: Blow n Go You're right, the regulator was maxed out, so there were not 15 amps available to draw in the plane. I assume the short drew over 7.5 amps until the regulator overheated. The Powerflight regulator automatically reduces it's output during an overload to reduce the heat generation. So once it built up enough heat, it was only producing about 2 amps as tried to protect itself. The point I was making is that the average plane is set-up with two batteries (most with 2 regulators!?!). These would provide about 15 amps continuous current. If this failure happened on an average plane, it would have been a race to see which destructed first.........the regs or the servo lead. In any event, you would have no usable power for the plane until the servo lead finished frying. Mechanically the failed servo was fine. The three other servos on the circuit were dead, but they free streamed with the airflow. Could be that the matchbox was set wrong, but we'll never know now that it's fried. It sounds like the shorted servo also free streamed. That is good. Regards, Jim O |
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