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Zoea
16-04-2017, 07:54 PM
Hi there

I bought a high voltage servo for my new 1/8 ebuggy and the ESC only outputs 6v.

Today I had a bit of a disaster when I tried to get the servo running at 2s volts. What I tried (do NOT do this) is use a servo extension, cut the red and black wires from the extension socket, extend the ESC signal wire to channel 2 of the ESC, and use the extension plug black and red wires to wire to the ESC positive and the bridge (jumper to make the batteries series) of the 2s lipos negative/positive.

This quickly caused smoke and a melted negative receiver extension wire. I think the circuit was trying to charge each lipo with 4s volts via the receiver - I'm not sure I've figured out what actually happened, it's complicated and I'm not :):yawn:

Is it possible to run a 8.4v servo/receiver from 2 2s packs and still get the throttle signal from the ESC? I do not want to spend £25 on a BEC for this, rather swap the servo. I am learning now that these HV servos are really designed to run in nitro 1/8 from the 2s receiver battery.

I was thinking, if I tap the balance ports of each lipo, wire that up to the power of the extension wire for the receiver, and ignore the ESC bec, would that do it? Bear in mind to run the 4s car on 2 2s lipo I have them connected in series. So the balance ports would be either 2 cells one from each lipo, or the other two cells and any load from running the car (?). :eh?:

I'm not sure that's much different than what I tried before though, just moving the circuit a little bit on the battery end. It's also not ideal from a wiring point of view, with every port of both 2s batteries used.

I've read on an aviation forum that's it's not possible to get 8.4v from 2*2s packs easily. Others use balance ports etc. with success I think, probably with a real 4s battery.

Opinions welcome. :woot:

(off)roadrunner
17-04-2017, 08:06 AM
Just trying to simplify what your attempting to do.

You want to power the reciever and servo without using the standard BEC from the speedo? To allow you to run the servo at 8.4v due to it being a HV servo.

Easy enough to seperate the the speedo signal by just connecting that wire the receiver on its own.

Easiest and most reliable way to get a steady 8.4v from your 2x 2s is going to be an external BEC. Which will regulate the output to 8.4v

First thing to check. Can the receiver handle 8.4v?

If yes use the external BEC to power the reciever through a spare port. This will power the servo through the reciever.
Only issue with this setup is can your transponder take the 8.4v being supplied through the reciever?

Another option...

Use the BEC from the speedo to power your receiver and transponder.

Use an external BEC purely to power your servo by seperating the signal wire and power wires. Signal wire plugged into receiver. Red and black to an external BEC.

This way your only giving the 8.4v to the servo and does not risk over voltage to other sensitive components.

Zoea
17-04-2017, 09:24 PM
Thanks, looks like a BEC / SBEC / UBEC is a requirement to properly use this servo. I think I'll try to swap it out first.

Best wishes
Zoea