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Servo Amp Draw and your ESC

Servo Amp Draw and your ESC

Old 10-22-2013, 08:02 PM
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Default Servo Amp Draw and your ESC

This is beginning to become an issue for RC enthusiasts. Servo manufacturers are creating higher speed/higher torque servos that are placing greater demands on the BEC's in the ESC's use.

Some servos are so amp hungry that brownouts are an issue and some users are spending excessive money on more servos, receivers, and radio systems to fix the issues.

Simple knowledge of amp draw requirements for servos would help many users make educated decisions about what servos their system can handle. I see so many people using 200 oz.-in. torque servos in 1/10th scale vehicles that just don't need that much torque. 90 to 100 oz-in is plenty for most 1/10th classes unless your doing rock-crawling 4x4 SC.

People need to realize that the BEC in their ESC has a finite current capability and it needs to be meted out carefully with that in mind. If you have a servo that can draw as much as 5 amps on a BEC that only produces 3 amps continuous (which I consider to be the industry average BEC amp output), then you add a transponder and a motor fan, you will eventually burn out the BEC and end up replacing your ESC. Ouch!

Savox posts the amp draws at peak, at idle, and in motion unloaded. I cannot find such data available on sites like Futaba, Airtronics, Hitec, or KO Propo.

Even though these amp draws are posted on the Savox site, Savox seems to be the cause of most brown-outs. Let this thread be a warning to you. A glitch buster might help for a little while, but if you have a 3 amp BEC and run a servo capable of 5 amps of draw at stall/peak your little BEC WILL fail eventually.

Its just like floating checks on a checking account, eventually one is going to bounce.

Either purchase a more expensive ESC with a BEC to handle the servo you feel you need, or buy a servo that does not exceed your BEC amp rating. It will save you a ton of money in the future and reduce the number of disgruntled customers posting hate mail on forums like this one. It sucks to buy something and assume it will work to find out a week later that your $70 servo just wrecked your $200 ESC.

Last edited by Banshee8530; 10-22-2013 at 08:33 PM.
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Old 10-22-2013, 09:27 PM
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http://www.amainhobbies.com/product_...Adjustable-BEC
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Old 10-23-2013, 03:46 AM
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There you go, problem fixed.
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Old 10-23-2013, 11:27 AM
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Yes, this is a viable solution; one which I currently employ, but the reason I started this thread was to create an opportunity to educate others who do not make informed decisions about there electronics.

There are many options out there to create a system of electronics on your RC vehicle that won't be overtaxed causing potentially dangerous situations.

1.) An external BEC can be used if you want to run a high torque/speed servo with limited internal BEC output. There are steps that must be taken to do this correctly, but we can discuss those later.

2.) Select a new ESC which has an internal BEC capable of handling the high amp requirements of stronger servos. The Novak Impulse, Tekin RS, and Viper VTX-10 series are just a few potential options that possess an internal BEC that provides 5 amps of continuous current.

3.) Purchase a servo with peak amp draw low enough that your existing internal BEC amp output will not be exceeded. This is a situation that I would like to see manufacturers remedy. They know what the peak amp draws of their products are, but very few publish that specification. I know that it can be calulated from what is typically given along with your known BEC Voltage, but the average consumer is not going to be able to perform that calculation, nor should they be expected to. Knowledge of your class and what loads the steering will typically see can help a person choose a good servo. as I said before, 1/10th 2wd classes don't require 150+ oz.-in. of torque! 90 to 100 oz.-in. is plenty for these classes.
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Old 10-23-2013, 04:13 PM
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Default BEC

I run a external bec on all my cars. No problems for me.
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