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Admiral RX700T telemetry voltage reading way high

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  • Admiral RX700T telemetry voltage reading way high

    I just purchased the Admiral RX700T telemetry receiver with 130A current sensor to go with the Freewing T-33 purchased same time. Both arrived two days ago. All telemetry came right up in my Spektrum DX18 tx. All are good but flight battery voltage. This shows as being 29.4 volts but it's a 6 cell pack showing 22.4 volts. When I toss a 3 cell lipo on that is resting at 11 ish volts the telemetry shows nearly 15 volts. Both the T-33's ESC (came preinstalled) and the current sensor have EC5 ends (as supplied by Motion). The Current sensor has male one side and female on the other side so it can only be attached to the ESC's connector one way. You can't get that wrong. In the manual it shows the small two wire voltage leads coming from the current sensor to be coming from the ESC's side of the current sensor while I can see my current sensor has these small leads coming from the battery side of the sensor. Could this be causing the problem? voltage should not be above the 22.4v of my brand new battery pack as read with a reliable volt meter. It is a 6 cell pack incapable of being at 29.4 volts without bursting into flames.

  • #2
    1. Did you plug that 3-wire lead into the appropriate port on the RX? I'm looking at the manual and it shows a 3-wire lead, not a 2-wire lead. If not plugged into the proper port, it could read anything and could also damage the RX. There is also a 3-wire to 1-wire lead that is labeled Voltage only sensor and that plugs into the same port. HOWEVER, you can only plug in one or the other. If you want ONLY voltage, you plug in the 3-1 lead. The single end goes into the 6th cell hole of the battery's balance port. You DO NOT plug in BOTH. If you choose the current/voltage sensor, you plug that in to get other stuff like amps BUT don't use if amps is more than what the sensor is rated for (60A). You can get an optional 120A sensor.
    2. A fully charged 6s LiPo should be putting out 25.2V. The control circuits of your typical LiPo charge should prevent any charging over this voltage unless you have one that you can set to more (not wise).
    3. "You can't get that wrong" ........................... No, you can't connect it wrong BUT that's not all that's to it. This is the same (or similar) to the Lemon variant of this device. I've gone through a dozen of these current sensors. They have an internal circuitry that can become faulty very quickly or not work at all out of the box. I've even had a couple that cut out periodically while the plane is in the air, mimicking a momentary "brown out". When taken apart, there were wires inside that had the solder points come apart. They were so bad, that RC Castle started sending me spare ones as "gifts" when I bought something else. I've stopped using the current sensor entirely and use only the single (voltage only) lead into the balance port line for battery voltage. PS. That current/voltage sensor (the big connector) can read a strange number and can't always be relied upon.
    4. You know which one is the temp probe, right?

    Key point ................ you do NOT use both current/voltage AND voltage sensor at the same time.


    • #3
      You are correct it is a 3 wire. I did catch that you use one or the other of the voltage only or current sensor which also gives voltage. This rx comes with a 130A current sensor as a package and advertised at 130A. Sold that way so assuming all good w/ 130A.
      See from attached photos that Motion info from manual states the voltage reading 3 wires should come from the ESC side as photo suggests. The one I have shoots these wires out the battery connection side of the sensor.
      Hope these are not so unreliable. Hoped to save some $ by using this rx with current sensor included rather than Spektrum rx and buy an $80 current sensor on top of it. Can't afford to put the jet and all it's contents in jeopardy if the rx may crap out mid flight. That would be very bad.


      • #4
        With the 130A option, you're good to go for most applications. Don't worry about where the wires come out. The important thing is how they are connected internally. It's all hooked to the tiny circuit board inside. It's not relevant which side those wires come out of. It's purely for ease of packaging and assembly. As far as accuracy, I've never found that big plug to be all that accurate when it came to reading the flight pack voltage. I'm not even sure it was all that useful for amps, either. The single wire input is the one that is the most accurate. If memory serves me correctly, you must push that single pin into the red wire of the balance plug. This gives you total voltage of the battery. If you put it into any of the other holes, it gives you the voltage up to that many cells at that wire. Also, that pin is a bit too big to go easily into the hole. On all my leads, I had to squeeze the bare pin until it was thin enough to actually fit in the hole.
        In the early days of the Lemon equivalent, it was possible to calibrate/adjust all the parameters like voltage, temp with little screws hidden under the label. I don't believe this is possible with the current units. I guess people were really messing those things up when they tried to calibrate them.


        • #5
          Motion is sending a replacement in exchange. They sent a return label and I've mailed mine back. Said it was a calibration issue and easier to exchange which is fine. Current sensor/capacity sensor appeared dead accurate to a high dollar watt meter I put in line to check. After finding the voltage off I wanted to know current was accurate.