This has got me wondering… what is actually wrong with charging the battery via the normal external power connector?
If there was a safety issue with it, one could have a little current limiting circuit which limits the current to say 1A and then you could trickle charge the battery that way.
I suppose the big problem with using the standard connector for routine charging is that getting the plug in and out of the socket is an absolute bastard.
Perhaps the reason for not doing it is that the power drain, especially with a flat battery, would reduce the current available for starting the engine.
This has got me wondering… what is actually wrong with charging the battery via the normal external power connector?
In my aircraft, the external power connector first powers a relay (“solenoid”) which then connects it to the electric system and the battery. It also powers up the avionics bus which means the gyros start spinning up. Definitely not the way to charge the battery. The reason is that it can be used when the battery is flat and not able to switch the relay.
The reason is that it can be used when the battery is flat and not able to switch the relay.
In mine, the battery is not needed for the external power connector to work. There is a diode which energises a relay from the incoming power but only if the power is the right way round (to prevent blowing up the whole aircraft).
One could have another diode just going straight to the battery, optionally via a suitable current limiting circuit, such that even if the battery is short-circuit, nothing goes up in smoke.
That would also be nice for stuff like aircraft exhibitions, or during servicing, where you have the external power on the whole time, and it would be nice to be trickle charging the battery. Also, if somebody turns off the external power supply by accident, the aircraft just switches over to the aircraft battery and flattens it…
I don’t see the problem?
When using the external power relay, you will waste a lot of energy from the external power relay alone. On some aircraft all equipment will turn on, wearing out gyro’s etc. Just doesn’t make sense.
Keep the power low, that is the safest way of charging.
External power input is made for powering the aircraft for start-up and/or maintenance.
BTW at least on of the Piper POH’s shows a diagram of another system, then the same manual describes. Seems Piper has changed this system a couple of times.
Interesting subject, and not trivial IMHO. First, I have seen the need for frequent charging on certain planes, especially during wintertime. I have seen several batteries been destroyed by being left discharged after failed start attempts in wintertime. The pilots were not comfortable with accessing the battery.
Then I know an electrician (not aircraft rated) who declined mounting such a cable/plug just because of risk/liability in case of a short circuit and risk of fire. I guess if the wire is taken through a panel or wall there is always some sort of risk of chafing and shortcircuiting?
I know at least three airplanes with such non-approved installations, and they have all passed several annual inspections etc without any comments.I find it useful, and sensible if done by someone knowledgeable.
You must have a fuse in the positive wire and the fuse must be near the battery terminal (an inline fuse usually) so that any short between that wire and the airframe doesn’t start a fire.
The bit of wire between the battery terminal and the fuse has to be done such it “cannot possibly ever” get damaged and touch the airframe.
There is always a fire hazard because the thick starter motor wire doesn’t have any fuse protection. I guess it should be sized to be thick enough to not catch fire itself in the event of a short, knowing the maximum current the battery can source (500A+?). That wire is quite vulnerable… it goes all around the aircraft, through some relay(s)…
Hello,
I am thinking about installing the battery minder airframe interface kit so as to keep the charger always connected.
http://www.batteryminders.com/batteryminder-model-bm-aik2-airframe-interface-kit-for-use-with-faa-certified-aircrafts/
What about paper work under EASA, would it be possible to cover it under CS-STAN? Or minor mod?
Thank you
Thomas
That is not covered in CS-STAN, thus it requires a minor change.
IMHO they did something stupid in their design. Then have chosen (or didn’t care) to take the short cap to the battery terminal. When you unscure the fuse holder, or when it goes open, it can short out. When you take the longer side, the fuse will be there to protect it, and less change to short it out.
Thank you once more Jesse!
So the thing would be to reverse the fuse holder.
I guess a minor change would cost around 10 times the price of this kit…
Thank you Peter for keeping all this merged.
Thomas
