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Why spektrum rx batt has 3 wires?

Old 10-09-2007, 07:35 PM
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allanflowers
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Default Why spektrum rx batt has 3 wires?

My new Spektrum DX7 has a flat nicad rx battery pack with THREE wires coming from it. It doesn't fit in my plane's battery box and I am thinking of getting a SQUARE pack, which would fit. Most square packs just have two wires though....
What is different about the Spektrum system that might need three wires?
Old 10-09-2007, 07:58 PM
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GaGeeBees
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Default RE: Why spektrum rx batt has 3 wires?

Mine has only two wires.
Old 10-09-2007, 08:18 PM
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bruce88123
 
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Default RE: Why spektrum rx batt has 3 wires?

A lot of battery packs have 3 wires but not really needed for our applications. It center-taps between the second and third cells in a 4 cell pack. Don't worry about if it is there or not.
Old 10-09-2007, 08:26 PM
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Redback
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Default RE: Why spektrum rx batt has 3 wires?

You don't need a 3 wire lead to the battery pack, but you do need a 3 wire SWITCH HARNESS with the Spektrum. This is because the bind plug needs to be able to ground the signal lead on the battery input.

Spektrum sets come with a 3 wire switch, however if you don't have one (eg changing out a plane to a Spektrum Rx) one solution is to plug a Y harness into the Rx battery input. Connect one leg of the Y to the 2 wire switch lead and use the second leg to insert the bind plug.

Regards

Terry
Old 10-10-2007, 09:34 AM
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Default RE: Why spektrum rx batt has 3 wires?

The third wire, if present on a receiver battery pack for RC use is not connected and under no circumstance would be connected as a center tap connection, as that would put voltage on the signal output of the receiver (if you have a three wire harness) when the receiver shares the last channel with the designated battery input (very common).
Three wire switch harnesses are also used for the DSC function (direct servo control), all of my switch harnesses are three wire (MPI heavy duty).
I think that it probably is cheaper from a manufacturing point of view to use a standard three wire servo plug on a battery, as these are produced in larger numbers than ones produced for use on batteries.
Pete
Old 10-10-2007, 10:04 AM
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Rafael23cc
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Default RE: Why spektrum rx batt has 3 wires?

Why spektrum rx batt has 3 wires?
Simply because is cheaper to use the wire that they have on hand than to purchase additional wire to make just the battery packs. There are only two wires utilized on the 3 wire set-up on a battery pack. The switch is another story as explained above.

Rafael
Old 10-10-2007, 10:35 AM
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allanflowers
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Default RE: Why spektrum rx batt has 3 wires?

Thanks guys,
This group is a great resource for anyone like me with a question.
Old 10-10-2007, 02:14 PM
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rmh
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Default RE: Why spektrum rx batt has 3 wires?


ORIGINAL: pilotpete2

The third wire, if present on a receiver battery pack for RC use is not connected and under no circumstance would be connected as a center tap connection, as that would put voltage on the signal output of the receiver (if you have a three wire harness) when the receiver shares the last channel with the designated battery input (very common).
Three wire switch harnesses are also used for the DSC function (direct servo control), all of my switch harnesses are three wire (MPI heavy duty).
I think that it probably is cheaper from a manufacturing point of view to use a standard three wire servo plug on a battery, as these are produced in larger numbers than ones produced for use on batteries.
Pete
I have used and flown a number of times ,a three wire -right into the Spektrum RX-- from a A123 battery - no problem - but I did not want to tempt fate so I clipped the signal lead -from the switch.
My A123 cell pack (two cells ), has a center tap which allows the charger to monitor and charge each cell for purposes of balancing.
Yeh-- I was surprised when I found the 3.5 volts from the center tap showed no effect. It was a brain far t initially and when I realized I had been flying it in that setup (on two different models ) I was mortified. But again - no effect.

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