Hello Peter, you wrote….
“For example, certain airframe serial numbers of my aircraft type (not mine though) could be charged via the external power connector – the same one you would start the aircraft with. On mine, you have to apply power to the 3rd (small) pin on the connector for a relay to energise.
But I think a battery charging / conditioning connector can just be permanently connected…..!
Would it be possible to manufacture a connector (where to get?) that can be wired / plugged to a CTEK MX4 like you mentioned in one of your former threads? Which kind of plug would I need for a TB 20 power connectir to apply power to the 3rd small connector-pin? I my opinion this could be a fine solution without keeping the baggage door open battery clamped and for any additional wiring that anybody curious of the flying club gets entangled by any additional wire. 
There are numerous military spec connectors which would be suitable. I would get one which can take a screw-on or twist-on cap, to seal it when the charger is not being connected. The caps normally have a chain to stop them getting lost but that would get chucked around in the airflow so best removed.
If you search Ebay for e.g.
circular milspec connector 2 pin
you get the idea. I would buy a pair together, because digging out the right P/Ns for the plug and socket can be a right job.
You can expect to pay several tens of € for this, but all connectors of good quality cost that much.
For example, certain airframe serial numbers of my aircraft type (not mine though) could be charged via the external power connector – the same one you would start the aircraft with. On mine, you have to apply power to the 3rd (small) pin on the connector for a relay to energise.
This 3 pin connector, often reffered to as “Cessna style” plug is in my opinion the best plug available for external power. The relay ensures it is safe, as it will not power when connections are reversed, and the sockets only gets connected to the battery after the plug has been fully inserted. As soon as the plug is removed their is no more voltage available at the socket, so no risk of shorting. This connection is not really suited for charging. It uses a big relay which draws quite some current.
On some (could be all TB-20 not sure from memory) with this three pin Cessna style socket you couldn’t charge anyway as the external power will power the aircraft instead of the battery, so there is no connection to the battery.
On other point of attention is that intelligent chargers, such as the CTEK models need to “see” the battery. As the Cessna style connectors are potential free with no power on the smaller pin, this system wouldn’t work, unless you would use a seperate power supply to engage the relay. These interlligent chargers determine their charging strategy based on the battery voltage by measuring the battery voltage every now and then.
The CTEK chargers come with connectors which are up to the job. They just lack fuses, which I can not understand with such a high quality product. As absolute minium you would need to use a fuse at the battery side.
Having a big 2 pin Piper Style connector which can be used for starting, directly connected to the battery is unsafe as well. As it wouldn’t be possible to use a proper fuse, due too start current requirements, while one could short the socket with the plug itself, or a screwdriver etc. In my opinion this 2 pin adapter is unsuitable for safe operation.
Having a big 2 pin Piper Style connector which can be used for starting, directly connected to the battery is unsafe as well. As it wouldn’t be possible to use a proper fuse, due too start current requirements, while one could short the socket with the plug itself, or a screwdriver etc. In my opinion this 2 pin adapter is unsuitable for safe operation.
Huh? The PA28 I fly – with a 2 pin connector – has an external power relay. You could short the socket and nothing would happen.
Huh? The PA28 I fly – with a 2 pin connector – has an external power relay. You could short the socket and nothing would happen.
True, IF you haven’t used the external power connector, or used the proper procedure.
The external power relay is powered by the center pin of the plug (positive) while the negative side is controlled by the master switch. So for external power you need to plug in external power AND then turn on the master switch. This will engage the external power relay. When you “just” unplug the external power, the socket is still live. The relais is keeping itself alive. The proper shutdown procedure would switch the master switch off (this would make the external power relay go off, remove the external power connector, and switch back on the master switch.
This double switching will prevent the connector parts from arcing, and will prevent the external power socket from staying live.
The external power relay is powered by the center pin of the plug (positive) while the negative side is controlled by the master switch. So for external power you need to plug in external power AND then turn on the master switch. This will engage the external power relay. When you “just” unplug the external power, the socket is still live. The relais is keeping itself alive.
Yes, of course…
The proper shutdown procedure would switch the master switch off (this would make the external power relay go off, remove the external power connector, and switch back on the master switch.
The POH procedure for starting the engine with external power is to have the master switch OFF during the whole procedure until the engine has started and the external power has been unplugged, then the master switch is turned on.
I guess this is so no external power is “wasted” charging the batteri during engine start. To prevent the connector from being live it would suffice to cycle the master switch after external power has been removed.
That sort of procedure can be heavily aircraft dependent and e.g. on the TB20 there have been several variations since c. 1982. Also the Master switch needs to be OFF anytime the external power (starting) cable is being connected or disconnected, otherwise there is a fuse (~1A) which will blow.
This is getting well off topic but the TB20 external power starting procedure is
Battery Master Off
Connect external plug and switch on the external power
Start Engine
Disconnect external plug
Battery Master On
That sort of procedure can be heavily aircraft dependent and e.g. on the TB20 there have been several variations since c. 1982.
Correct. The same with the PA28. The PA28 we have in maintenance require the master switch to be ON (else the external power relay isn’t activated). Wonder if Airborne Agains’s is much younger, I suspect so, as it sure is safer.
Most electronic systems, and protection systems are improved over the years (Cessna worthless LOW voltage, HIGH voltage light for example) while the restart series have a decend system.
On topic: In general a 3 pin will always be safer then a 2 pin. None of these are really suiteable to keep the battery charged, and will often rule out smart charges. Using the a good charger (CTEK for example) with it’s own included connectors, adding fuses, will give you save and good charging system.
Correct. The same with the PA28. The PA28 we have in maintenance require the master switch to be ON (else the external power relay isn’t activated). Wonder if Airborne Agains’s is much younger, I suspect so, as it sure is safer.
It’s manufactured in 1979.
We have a 3 pin NATO connector on our aeroplane, so when she is parked in the hangar we plug the CTEK charger in to keep the battery in good condition, especially in the winter.
If you get one of the high current CTEKs (25A?) you can run the avionics off the external power, which is quite useful sometimes….We also carry the cable in the plane so if we get marooned somewhere it is easy enough to get a jump start.
