Voltage Losses in Wiring Systems

Jan 1, 2012   //   by admin   //   Tech Info  //  No Comments
  • Voltage Losses : A Salutary Tale

 A re-print of a previous article submitted by Brian Smith

Essential wiring system safety checks: Especially at the start of the flying season

 I always charge my plane up prior to flying, using the normal transmitter and receiver charger as supplied with the set. On arriving at the flying site, I checked the receiver battery with a meter and noticed that the battery was not fully charged. I then fully charged the battery with a “Pro-Peak” 12 volt charger and obtained a reading of 90% voltage.

I then flew the model.  After two flights, I noticed that the battery voltage seemed to be going down quickly. I naturally thought that as the battery was two to three years old, that this was the problem and it needed replacement.

Further investigations revealed that this was not the problem. Taking the battery out of the ‘plane and checking the battery voltage directly on the terminals, revealed that it was still indicating 90% voltage capacity. However, taking a voltage reading through the normal charging lead on the “off” side of the on/off switch, showed a reading of only 60% battery voltage. I then disconnected the battery feed wire to the receiver, switched the switch to “on” and connected the battery to the receiver feed wire directly to my meter. This caused the current to flow through the switch harness. In this mode, I only managed a reaing of 40% battery voltage.

 I guessed that I either had “ Black Wire Corrosion” or that the switch was worn out. This was a JR switch that had been used a lot since 2001.  I replaced the entire switch harness, after which I immediately achieved a battery voltage reading of 90% of full voltage. Incindently, I have taken voltage drop readings along a two foot servo extension lead which gave me only 60% of the battery voltage.

Can anyone confirm that this is a normal voltage drop to expect ?  I also checked a “Y” lead, which indicated a 15% voltage drop. So I tried a different make of “Y” lead. This was equipped with a double socket and this gave me only a 10% voltage drop. 

The moral of this, is that from now on , I shall be testing all my wiring leads before installing them in my plane. 

Brian Smith.

In models with long extension leads, you will need to fit a 6 volt battery pack to compensate for the voltage drop. Also, as you note. It is possible to buy thicker leads made up from more strands of wire.  Which, although more expensive,  are well worth the money.

Nigel Rollason

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