MGL Avionics User Forum

If I install more than the Ibox and two screens the voltage on the Avioguard drops to 9.8 V. Obviously this is unacceptable.

After checking the avioguard again today with a input of 14V the output is now 3.86 volts. Obviously this piece of equipment has no place in a airplane and will be removed as a total loss.

I wasn't impressed with my Avioguard either. Sitting on the shelf.

Thanks, I know it's not just me. I'm installing a avionics fuse bus. I noticed that the Avioguard seems to not be available for sale, Michigan doesn't list it anymore. It would have been nice if we got a heads up from the manufacturer....

Your avioguard is likely going into shutdown mode.

The avioguard is capable of producing around 10 amps (even though we rate it less).
However it is FAST - when it starts up it ramps up the output voltage rapidly and if the current exceeds the limit at this point it does what it is designed to do - it switches off. It then restarts within milliseconds and tries again. This cycle repeats itself if it is never able to reach operating voltage without going exceeding the current limit.
What causes the high current ? Capacitors charging up. At power application they are a short circuit. The more equipment you add the worse this gets. With two panels and an iBOX you are already close to 7000uF capacitance.

Something like a 0.5ohm resistor in the feed to high input capacitance users fixes the issue by limiting the current to sane levels.

When the avioguard starts up like this and you measure the voltage using a voltmeter you see the AVERAGE voltage between shotdown and startup attempts. If you connect an oscilloscope it looks like a sawtooth wave.

The current at it's output must never exceed 10A (or 12A for newer models). Not even for a millisecond. It will trip if that happens. It moves the Earth to protect itself.

Thanks Rainier but if it cannot protect my EFIS system which I bought it for of what use is it? Two screens and a Ibox is not a lot to ask of a protection system.

Just read what I wrote above - just make provision so startup does not look like a short circuit.
The Avioguard is not specifically designed for a purpose - it's a universal "power recreator".

Place a 0.5 ohm resistor (2 Watts is fine) into the supply line to every user you have connected. This will prevent the need to supply as much as 30-50 amps of initial current to the system.

Without the avioguard - similar happens and you can easily see the effect if you connect an oscilloscope to the EFIS supply input and switch on - the voltage dips quite a bit as the effect of your combined wiring resistance and battery internal resistance takes the hit - it acts like a resistor and this limits the startup current. With the avioguard you need to emulate this in many cases as the avioguard's effective output resistance is zero.

Also be aware that there is a potential secondary problem - the avioguard will switch off (similar to an overcurrent at the output) if your input voltage falls below 9V - even briefly. As you switch on - the output current can be very high (but below the limits) but your input voltage supply can't cope and there is a voltage dip - the overall effect is exactly the same as an output overload. The combined resistance of your input wiring (resistance of wires (including ground), circuit breakers and power source resistance (battery) all are in series and add up. This means you need to pay attention to these things.

Thanks Rainier, it's nice that you're active on this site. I'll give the Avioguard another try when I'm up to crawling under my panel again.

I also have a question regarding use of the Avioguard.
What is the way to monitor aircraft voltage when all avionics is connected via Avioguard?

I am using iEFIS Challenger with ibox and RDAC XF.