MGL Avionics User Forum

I have installed an extreme EMS in my 28v Glasair III.
The voltage indication only reads the 14v that is necessarily supplied to the RDAC. This obviously affects Volts and Amps.
Is there some way to normalize this voltage/amperage reading for a 28v system?

TIA
Jeff

Supply the RDAC with 28V as well.
It does work - the specs are a bit conservative.

Really? Matt and the installation instructions were very specific.

Can you explain why/how I can get away with deleting the voltage transformer safely? [A PM is fine.]

That would certainly be an easy fix, but I do not know enough about electronics to understand/appreciate the effects of this change, especially since it is not optioned as part of an install. What really confuses me is that 28v aircraft are not uncommon. Why didn't MGL just make that "option" standard, like almost every other product for aircraft?

Please, more info is needed and appreciated.

Jeff

Nothing to do other than connect the RDAC to 24/28V instead of 12/14V supply.

The RDAC and many of our sensors like the AHRS etc have linear voltage regulators - that means they produce the required regulated output voltage (usually 5V or 3.3V) in one or two stages by converting excess energy to heat. The RDAC first goes to 5V and from there to 3.3V using a second regulator. The first one is rated to 35V so it handles 24/28V just fine. It gets a bit hotter as it has to fry away a bit more excess power but it is not too bad if you are not using the 5V output of the RDAC (so all power required is internal only).

We specc'ed the RDAC conservatively - much like most aircraft engine manufacturers derate their engines (meaning they can actually produce more power than advertised).

Obviously, if you are running it at 12V it has a huge margin of safety in case your power supply goes wrong. If you run at 24/28V the margin gets a lot smaller. It does not mean it will blow up in your face the moment it gets more than 35V - in fact there is a third stage that kicks in the moment you get over about 34V - and that one will hold off another 100V+ on top of the 34V - but only for short duration - that's intended to protect the system against high but short voltage spikes.

Many run their RDAC at higher voltage - does not seem to be an issue.

Wow, thank you, both for the advice and explanation.

I will remove the voltage converter post haste.

Jeff