I hope I've come to the right forum about this...

I'm planning on building an e-bike using RC components, except I'm not going to use a transmitter and receiver. Instead, I'll use a Servo Tester to control the speed of my brush-less DC motor. The motor is driven by an ESC (Electronic Speed Controller) which in turn is controlled by the Servo Tester.

I'm planing on using LiPo 6s(22.2V) battery.

Ive researched for several days now and came found that I need a BEC (Battery Eliminator Circuit) to lower the 22.2V to 5V so the servo tester doesn't get damaged.

Now Im just wondering about the current.

Ive seen some people have a separate battery for the servo tester which seems to be the simplest solution but I want to be effcient and use my main battery for that.

Im thinking of splitting the cables to go to both ESC and BEC -> ServoTester.

I know that the setup is going to draw a lot of current maybe up to 50A or more (not continuously) so then I'm wondering if that current is going to go through the BEC and then into the servo tester and fry it. Or will most of the current choose to go through the ESC and only what is needed goes through the BEC?

PS. Im not an electrician x)

This is how Im planning to connect everything Please dont laugh:

enter image description here

Will this setup work or should I stop trying before I get hurt? :)


The components specs and explanation:

  • Motor: Brushless 190 rpm/V 90A max Resitsance is unknown Motor link
  • ESC(Electronic Speed Controller) this decides in which coils in the motor the current will go through making it spin. 120-180A 18.5-44.4V ESC link
  • BEC(BatteryEliminatorCircuit) lowers output voltage to 5V BEC Link
  • \$\begingroup\$ For the people not familiar with models etc, can you tell us what an ESC is? Also, we will need to know the specs of all your modules/motors etc; or at the least, the model/part number, so we can tell you what will/won't fry \$\endgroup\$ – CL22 May 5 '15 at 12:16
  • \$\begingroup\$ Yes of course I will do that right away ;) \$\endgroup\$ – Arbitur May 5 '15 at 12:17
  • \$\begingroup\$ Does your ESC really have no 5V output? They usually provide at least a minimal "BEC" to power the receiver. \$\endgroup\$ – Dzarda May 5 '15 at 12:19
  • \$\begingroup\$ @Dzarda The ESC Im planning on buying has no BEC: hobbyking.com/hobbyking/store/… \$\endgroup\$ – Arbitur May 5 '15 at 12:27
  • \$\begingroup\$ @Jodes I have updated the question tell me if you need more info ;) \$\endgroup\$ – Arbitur May 5 '15 at 12:27

This setup should not pose any problems so long as the servo tester, ESC, and BEC are made for the voltage you are giving it.

With most devices, you just have to worry about supplying the correct voltage because the device has an internal resistance which will cause it to draw a specified amount of current. This is okay because the manufacturers designed it that way.

A good example is with a lightbulb. If you directly connect 110V from an electrical outlet, it will only draw a very small amount of current. It has the capability of drawing thousands of amps, but it only draws couple hundred milliamps. This is because there is an internal resistance in the bulb, such as many other devices out there, that cause it to draw only so much.

  • \$\begingroup\$ Yes every component shoul be compatible with the voltage with the exception for the servo tester which only handles 5V which is the reason fot the BEC. \$\endgroup\$ – Arbitur May 5 '15 at 12:59

What you have drawn is perfectly fine. Just one remark: You'd better be sure, that your ESC doesn't provide 5V on it's servo cable. I say this, because you've drawn three wires going from the ESC to the Servo Tester.

What I think is the reason you ask this question, is the common misconception, that current is fed. Instead, voltage sources (a battery), serve voltage and the load draws as much current as it wants. We see this thinking all the time.

If you wanna know more, see Ohm's law.

  • \$\begingroup\$ I thought the current went from the tester to the esc :O \$\endgroup\$ – Arbitur May 5 '15 at 12:55
  • \$\begingroup\$ Yes thats what I remember from electric class a couple of years ago that it only draws as much amps it needs. \$\endgroup\$ – Arbitur May 5 '15 at 12:56

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