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Old Jun 24, 2012, 09:44 AM
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How low should an ESC/BEC drop the Rx voltage?

I have a 4S3200mah LiPo powering a Power 32 via an E-flite 60amp ESC/BEC. I noticed my Rx voltage dipped down to 4.1v today. The Lipo went down to 13.7v. I am monitoring with my DX8 and telemetry log. Is this a normal reading?

VP
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Old Jun 24, 2012, 10:02 AM
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Since that ESC is supposed to have a switch-mode BEC, dropping that low is unusual. Do you exceed the servo load as shown in the manual?: http://www.horizonhobby.com/pdf/EFL6...CInstSheet.pdf

If not, maybe you have a binding servo?
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Old Jun 24, 2012, 10:10 AM
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Originally Posted by Wintr View Post
Since that ESC is supposed to have a switch-mode BEC, dropping that low is unusual. Do you exceed the servo load as shown in the manual?: http://www.horizonhobby.com/pdf/EFL6...CInstSheet.pdf

If not, maybe you have a binding servo?
I am not sure of the servo load, but I was doing some fancy manuevers.

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Old Jun 24, 2012, 09:53 PM
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Make sure your servos don't reach the stops and grind with full motion on the sticks, as that will really increase the current draw. Also, check to see that all the control surfaces work smoothly throughout the range by disconnecting the control rods at the servos, and move the controls as though you are the servos. If you feel any tight spots, try to figure out how to eliminate them.
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Old Jun 25, 2012, 12:42 AM
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Pete, I know you are aware of clearing the readings on your DX8 but I have forgotten a couple of times and freaked out when I checked at the end of a flight when I saw similar readings. Did it happen more than once? Just a thought.

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Old Jun 25, 2012, 04:53 AM
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Originally Posted by Wintr View Post
Make sure your servos don't reach the stops and grind with full motion on the sticks, as that will really increase the current draw. Also, check to see that all the control surfaces work smoothly throughout the range by disconnecting the control rods at the servos, and move the controls as though you are the servos. If you feel any tight spots, try to figure out how to eliminate them.
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Originally Posted by Harry H View Post
Pete, I know you are aware of clearing the readings on your DX8 but I have forgotten a couple of times and freaked out when I checked at the end of a flight when I saw similar readings. Did it happen more than once? Just a thought.

Harry
Actually this is a replacement ESC from Horizon, the one in it before seemed to be defective, I had brownouts and the Rx dropped to 3.2. Horizon never said if there was a specific problem with the ESC, they just said they would replace it. So I dont know if this is the same issue. I will check for binding.

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Old Jun 25, 2012, 06:24 AM
Jack
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"..The Lipo went down to 13.7v..."

That would be 3.45V per cell. Was that the lowest under load voltage during the entire flight and taken from a data logger? If it was the voltage at the end of the flight, the voltage was probably quite a bit lower at some point during the flight.

For best battery life (and voltage stability for the BEC and receiver) you would not want to take the cells lower than 3.7V at any point in the flight. And if you found the cells around 3.7-3.8V immediately after landing the battery would not have any useable capacity left, if would be about 90% or so depleted.

Jack
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Old Jun 25, 2012, 06:40 AM
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Originally Posted by jackerbes View Post
"..The Lipo went down to 13.7v..."

That would be 3.45V per cell. Was that the lowest under load voltage during the entire flight and taken from a data logger? If it was the voltage at the end of the flight, the voltage was probably quite a bit lower at some point during the flight.

For best battery life (and voltage stability for the BEC and receiver) you would not want to take the cells lower than 3.7V at any point in the flight. And if you found the cells around 3.7-3.8V immediately after landing the battery would not have any useable capacity left, if would be about 90% or so depleted.

Jack
Yes, 13.7 was the lowest. end of flight was 14.5. I have an alarm set for 13.7 to alert me when to end the flight. So do you think this is what caused the Rx voltage dropping?

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Old Jun 25, 2012, 09:50 AM
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How about trying a separate BEC if you have one available. Personally, I don't use the BEC that is combined with the ESC. At least if you have a ESC failure, you will still have control with a separate BEC.

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Old Jun 25, 2012, 09:50 AM
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Quote:
Originally Posted by Victory Pete View Post
Yes, 13.7 was the lowest. end of flight was 14.5. I have an alarm set for 13.7 to alert me when to end the flight. So do you think this is what caused the Rx voltage dropping?

VP
Being a voltage regulator, the BEC only needs 6.5 to 7 volts input to supply the required 5 volts out. So as long as the main battery is above 7 volts it cannot be the cause of the low voltage out of the BEC. The only reason the BEC output would be so low is that it had too high of a load. i.e., the receiver and servos simply pulled more current than the BEC was designed to supply.

Larry
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Old Jun 25, 2012, 09:51 AM
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How about trying a separate BEC if you have one available. Personally, I don't use the BEC that is combined with the ESC. At least if you have a ESC failure, you will still have control with a separate BEC.

Harry
I dont have one, but that would be an interesting experiment.

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Old Jun 25, 2012, 09:56 AM
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Originally Posted by Lnagel View Post
Being a voltage regulator, the BEC only needs 6.5 to 7 volts input to supply the required 5 volts out. So as long as the main battery is above 7 volts it cannot be the cause of the low voltage out of the BEC. The only reason the BEC output would be so low is that it had too high of a load. i.e., the receiver and servos simply pulled more current than the BEC was designed to supply.

Larry
Yes, thanks. The original ESC dipped the Rx v to 3.2 and I would lose motor controll for a few seconds while the Rx went into failsafe. I just wish I knew if Horizon found an actual problem with it or not. I did fly a few weekends with the new one without a low Rx voltage reading. It was just this last flight that I got the low reading and I was doing nonstop aerobatics so it seems it may be a servo load issue.

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Old Jun 25, 2012, 10:08 AM
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Pete, is this the ESC you have ?
http://www.e-fliterc.com/Products/De...rodID=EFLA1060


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Old Jun 25, 2012, 10:11 AM
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Pete, is this the ESC you have ?
http://www.e-fliterc.com/Products/De...rodID=EFLA1060


Harry
Yes.

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Old Jun 25, 2012, 10:25 AM
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I read the specs on that one, they say you can run 6 standard digital servos on 2.5 amps?? That sounds really optimistic. I have had a few conversations with a tech at Castle about the 10 amp BEC I was using with standard digital servos. He was very clear that using the 10 amp (5 amp continuous / 10 amp max) with anything over 4 servos (in his opinion) was borderline. I have switched to the 20amp pro in all my A/C and set it at 6v. Never see it drop down below 5.9 unless I forget to clear the DX8. Don't know if this applies to your setup.

Harry
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