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Help needed with Compro Controller and 22.2v

Old 08-25-2004, 01:34 PM
Randy Smith
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Default Help needed with Compro Controller and 22.2v

I am in need of help with running two large LiPoly packs in series with my controller.
I am confused about the connection of the receiver signal lead from my controller to the throttle port of my receiver.

I have heard that when using more than 12 cells (14.4V) that I must remove the red wire from the receiver signal lead connector coming out of the speed controller so that I will not damage my receiver with over voltage. Is this true?

I am running two ThunderPower 3S-2P 2100mah packs in series. So I have 22.2 volts and 4200mah. I am using a MGM Compro TMM 5024-3s speed controller. I have disconnected the red lead from the controller plug going into the throttle port of my Hitec 555 receiver and when trying to start the motor I get a repetitive "BEEP" from the controller with the green LED flashing.

The instructions with the controller state that this error code might indicate no signal from the receiver. I am hesitant to reconnect the red lead of the throttle wire from the controller into the receiver for fear of destroying the receiver. Can anyone help ? The sun is finally shining and I want to fly my new Shoestring sport scale model. []


Jim Smith, Saskatoon, Saskatchewan, Canada
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Old 08-25-2004, 02:13 PM
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Default RE: Help needed with Compro Controller and 22.2v

When you disconnect the red lead, you no longer have any power going to the RX. Hook a standard RX battery to the RX and it will (or ought to..) work.

EDIT: When I typed that reply, I was not aware that this controller might be an OPTO coupled controller. I saw a reply from another poster regarding this and they were pretty sure it was. I have no experience with OPTO contollers, the reply I gave was based on plain ol' ESC/BEC combinations where if you disable the BEC via disconnecting the red BEC wire, you must supply another source of power to the RX.

And I don't think overvoltage to the RX is why you can't run the BEC on 22V, it's that the BEC delivers less power as voltage increases, so at 22V there is just not enough power from the BEC to run anything..
Old 08-26-2004, 07:05 AM
Matt Kirsch
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Default RE: Help needed with Compro Controller and 22.2v

The best thing is to take what you HEAR with a grain of salt, and RTFM (read the fine manual). People tend to speak in sweeping generalizations, and that can sometimes get you into trouble.

Read the instructions for your particular ESC, and determine if it has a BEC in the first place (it won't if it's an OPTO, or "optocoupled," meaning there is an optical filter between the receiver and ESC to eliminate electrical noise). If it doesn't have a BEC, removing the red wire won't achieve anything.

If the ESC has a BEC, the instructions will tell you when it needs to be disabled. Generally speaking, but not necessarily in all cases, the limit is 10 cells, or a 3S LiPoly. Any more than that, and the BEC can't handle the heat, so to speak. Again, refer to the instructions to be absolutely sure. There may also be a more elegant way to disable the BEC than just disconnecting the red wire. You can sometimes disable the BEC through programming or a switch.

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