OK Guys, this one has me stumped.

I'm installing the systems on my new model, a Savex L-39, and to keep things simple, I decided to go with just one battery (2900mAh Li-Ion), to power the radio, ECU and e-retracts/ brakes. No air on this one.

Power splits off 3 ways from the battery. One line to a Jeti MAX BEC (5A continuous/ 10A peak) to power the Rx/ servos, and one each going directly from the battery to both the ECU (Xicoy / Wren 44) and Xicoy e-retract/ brake controller.

The BEC also has a safety switch to switch it on/off, which should act as the master power switch for everything. ECU and gear/ brake controller will draw minimal power if Rx is off. Also one main battery disconnect to isolate the battery at the end of the day for storage and to allow for charging.

What is happening is that if either of the Xicoy boxes are connected to the Rx and the battery, something is happening to cause the BEC to turn on, even if the BEC switch is off.

If the BEC is switched off but operating, disconnecting the Rx from the ECU also causes the BEC to switch off.

If I use a separate battery to power the ECU, this does not happen, it is only when I use the 3-way power feed.

Pictures attached.

1. An overall view of the main board.
2. BEC Switched Off. ECU Not Connected - BEC Off
3. BEC Switched Off. ECU Connected - BEC On

I can't work out why this is happening or how to stop it.

Ideas???




Thanks

Paul

Sounds like some sort of ground loop. Something is hooked to more than one ground reference that are at different potentials (voltages).

EDIT just a guess

Disconnect the red wire between the ECU and RX, and see what happens.

...

Just my 2 cents. I would get rid of the BEC and add a Life Battery (or two) to power the Rx and Servos. A BEC or voltage regulator is a weak link in a system. When they get overloaded they shut down. Use your existing battery for the Retracts and Turbine. Just sayin, in the interest of making it simple you added some complexity. Just my opinion.

Agree ditch the BEC (Bang Everything Cooked - its something a fellow modeller told me!)

marcs

Paul

Nice to see someone thinking about keeping things light for better flying.

If you use 2 2 cell A123 battery packs of 1100 may that will weigh the same as your single battery. I have these batteries in one of my small turbine planes and can fly up to 4 flights per charge, though you would need to confirm. You would save the weight of the BEC as it is not needed. Further weight savings could include doing away with the UAT and replacing it with a pleated paper clunk in the tank, which is all I do on all my jets. You could save a little more weight by ditching the Gyro and you could cut your equipment board down in size.

If you have time to look though the huge thread you would find that Paul Gray had the lightest installation with no equipment board, just the various components velcroed on the fuselage sides. He managed a dry weight of 8 lbs though I never managed to get mine as low as this! You unfortunately have to install brakes which adds weight due to your regulations. I would do some tests and see what the current consumption is, I would guess it is very low and you could possibly use the ecu battery with a Y lead to power the retracts. These little cells are amazing with the high C rating. I have even used them in 3 cell packs for Kero starting.

John

Matt,

You were correct. Removing the neutral wire from both the Rx/ ECU and Rx/ Retract controller harnesses fixed the problem. Still don't understand how that affected the BEC switch though.

I've now put a hard switch between the battery and the BEC to isolate it further and set the BEC switch to on and covered it in heat-shrink to keep it on.

Paul