Are you guys using a switch between the TCU battery and the TCU? Is the Futaba heavy duty switch ok for this?

Mitchell

I have switches on my PST Turbines. They come that way from the factory. It's a Toggle switch like you could buy at Radio Shack.

I don't use switches on the TCU at all, I plug in with Deans Ultra plugs....R

I thought all turbines came with switches til I heard the story of the guy whose jet and trailer caught on fire cuz he left the rx switch on...

I believe it is a good idea to have one. I make up a harness with a deans plug at each end, and a heavy duty toggle switch in the middle, and put it in between the battery and the ecu..

I make a habbit of just disconnecting the battery whaen I am done flying for the day, I use deans connectors in the battery line.

mark

here it is right from 'the horses mouth' so to speak.....JetCat says no to the switch theory being a good idea....Deans Ultra plugs are my choice...

Ron

http://www.rcuniverse.com/forum/m_2822092/tm.htm

..other manufacturers have different recommendations, though......

I dug this summary out of the Superman fire thread from last year...

With the JetCat system, even if the TCU is left plugged in, once the Rx has been shut off there is no current draw to the TCU whatsoever.....there had been some discussion on this before so I measured it with my trusty meter and found it to be zero. Therefore, as long as the RX is shut off, technically the TCU could be left plugged in with no 'bad stuff' happening. The buzzing of the servos as well as the onboard LCD voltmeter pretty well assure that the RX is shut off after every flight. I do of course, unplug the TCU at the end of the day as well but not between flights.

I don't trust switches in general except for some of the 'fail safe' switches on the market and most if not all of those are unable to handle the amperages required for autostart (especially now with kero start options). If I were inclined to use a switch on the TCU it would be a heavy duty toggle switch like Nony suggests where amperage load would be a non issue....and 'failsafe' switches on the RX and optical isolators.....Ron

Just to clarify... The switches used in PST turbines (and others using GB Hobby ECU's as I understand it) are a dual pole type, where both circuits are used to conduct the positive lead to the battery. The use of the dual pole switch in this manner acts to give the system redundancy. The Ground is always connected to the battery so long as the Deans Ultra connectors are together. The reasoning for using a switch at all likely relates to the fact that the majority (if not all) of the circuitry in the ECU is powered by the ECU pack, and not the RX pack.

Kelly

Kelly...I agree that the majority of the TCU is powered by the TCU pack but as it was explained to me (in simple terms so I can understand it) it is the RX power that actually 'turns the TCU on' so to speak. If this is in fact the case, even with the TCU battery plugged in the TCU will still not see or draw any current. This is just for the sake of discussion, to each his own of course....Ron (I didn't use the switches when I was running Gb's)

Hey Ron,

I'm obviously not the ECU designer, but here's my interpretation. This particular version of the GB ECU has a CPU that's powered by the ECU pack and not the RX pack. The RX lead does connect the receiver's ground and +ve leads, but I don't think they're responsible for much of the functionality.

When switching on the ECU, the bootup screen appears, it tells you what the software versions are, the diagnostic LED on the side of the ECU lights up based on the shaft position, the RPM sensor functions, etc. It will display a no R/C error until the receiver is turned on and connected properly. When uploading ECU software for a particular engine type, only the ECU pack is required to power the CPU; no connection to the R/C system is necessary. On the flip side, when the R/C system is powered up alone, I don't believe anything functions in the ECU. Essentially nothing happens... I can't verify that the RPM sensor doesn't work without an oscilloscope but I'd bet its powered by the ECU pack since a sensitivity adjustment POT is on the 2nd board. The start gas valve is definitely driven by the ECU pack, since its driven by a voltage higher than that of the RC system. My take on the RX connection is that it may or may not share the ground with the ECU pack, but the +ve lead may only be used as a baseline in a comparator circuit where the ECU needs to know a sample voltage with which to compare the pulse width signal maximum. Obviously the bottom of the pulse width curve would be ground, and the upper bound would likely be near that of the +ve lead.

I know for a fact that if the switch is left on and a pack is plugged in, it will drain it. I ran a NiCad dry once or twice before I trained myself to switch it off or unplug it when it's out of action, which is even more important now that I'm running Duralites! Now I make sure to unplug the pack after the day's done, but I just switch it off when its dormant in the pits between flights. I should find some time run a current measurement on the lines in the RX lead, but I doubt it will be much.

The point I was trying make earlier was that a switch does have some value when the ECU is powered primarily by the ECU pack. The earlier FADEC's, for example, are powered by the RX battery but I believe the newer version is ECU pack driven from posts I've read. In the GB Hobby / TEMS case, it makes sense to have a switch, but the downside is adding another component to the system with the potential for failure. They mitigate that concern by designing the system with redundancy.

Kelly

Kelly, I see now where you are coming from, in short, you can turn on the GB TCU without the RX being turned on, with JetCat if the Rx is not on, the TCU is not on even if the power to the TCU is connected.....I can leave my TCU plugged in for a week (although I wouldn't do that of course) and it will not draw any power as long as the RX is turned off.

Ron

Hi Ron, Kelly,
You are both right...except you are not discussing the same circuit. Ron is referencing the JetCat ECU, and Kelly is referencing the PST TEMS (GB Hobby) TCU. These are two vastly different circuits that do essentially the same thing, control a turbine. The ECU will remain off without Rx power applied, while the TCU will drain its battery if the switch is left closed. The switch as it is wired is a DPDT and does give the redundance of using both poles to switch only the positive line. JetCat has decreed that using a switch in the system is not allowed, while the GB system makes very good use of a switch. Personally I removed the switch as a another potential failure eliminated, but I made sure to disconnect the battery post operation. Hope this clears it up a bit...

I thought about doing that on my PST (600R) but thought better of it, thinking it would invalidate the warranty. Thoughts?

Mike

thanks Len, I knew if we put enough bait on the hook we would see you rise to it and clarify all this for us!.....Ron