AHRS power

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eschlanser
Posts: 14
Joined: Fri Mar 15, 2013 9:26 pm

AHRS power

Post by eschlanser »

I need some help figuring out the wiring as I Install the AHRS in my HXr system.

Per the Pin Out Description, the primary AHRS power input port is Pin 23 on the connector and the input is referred to as Aircraft Power Input A.

In the Installation Manual is a note saying the Display and AHRS should be off during start up with a user supplied optional switch to control the Display power. although there is no mention of a switch for the AHRS.

The Commercial AHRS description says the power draw is 250 mA.

I can find no other GRT references to the AHRS power, power control or installation.

I have tentatively decided to connect the AHRS primary power input (pin 23) to the E bus and protect it with a 1 amp fuse. No switch to control the power to the AHRS.

Is this a reasonable wiring design?

Thank you in advance,
Eric Schlanser
W-10 12v system with HXr, single display, single AHRS.
Bobturner
Posts: 444
Joined: Mon Mar 11, 2013 6:34 pm

Re: AHRS power

Post by Bobturner »

Why not just run a #18 wire to the same switch/CB as the HXr?
eschlanser
Posts: 14
Joined: Fri Mar 15, 2013 9:26 pm

Re: AHRS power

Post by eschlanser »

Bobturner wrote:Why not just run a #18 wire to the same switch/CB as the HXr?
Bob,

Because that would be too simple and make too much sense.

I'm thinking a 22awg wire because that is what is pre-supplied by GRT for the AHRS primary power input wire.

Thank you for the answer,

Eric
eschlanser
Posts: 14
Joined: Fri Mar 15, 2013 9:26 pm

Re: AHRS power

Post by eschlanser »

eschlanser wrote:
Bobturner wrote:Why not just run a #18 wire to the same switch/CB as the HXr?
Bob,

Because that would be too simple and make too much sense.

I'm thinking a 22awg wire because that is what is pre-supplied by GRT for the AHRS primary power input wire.

Thank you for the answer,

Eric
Bob,

I called GRT and per Ben, a single EFIS/AHRS switch can supply power to both EFIS and AHRS. Each wire to each device after the switch and before the device should be have circuit protection. In my case, a 3amp fuse for the EFIS and a 2amp fuse for the AHRS. These are in addition to the 10amp fuse at the bus on the wire to the EFIS/AHRS switch.

I do not have an avionics bus. The wiring would be somewhat different in that case.

Eric
eschlanser
Posts: 14
Joined: Fri Mar 15, 2013 9:26 pm

Re: AHRS power

Post by eschlanser »

eschlanser wrote:
eschlanser wrote:
Bobturner wrote:Why not just run a #18 wire to the same switch/CB as the HXr?
Bob,

Because that would be too simple and make too much sense.

I'm thinking a 22awg wire because that is what is pre-supplied by GRT for the AHRS primary power input wire.

Thank you for the answer,

Eric
Bob,

I called GRT and per Ben, a single EFIS/AHRS switch can supply power to both EFIS and AHRS. Each wire to each device after the switch and before the device should be have circuit protection. In my case, a 3amp fuse for the EFIS and a 2amp fuse for the AHRS. These are in addition to the 10amp fuse at the bus on the wire to the EFIS/AHRS switch.

I do not have an avionics bus. The wiring would be somewhat different in that case.

Eric

For anyone following this thread,
I recognized Ben's scheme is better, so I won't lose both the AHRS and the EFIS at the same time due to some fault with one or the other that trips its own fuse. Decided Bobturner's idea was good enough for me and wired both the AHRS and EFIS power to a common fuse and switch. If either device trips the fuse, I lose both as I have a single screen/single AHRS system.
Eric
Bobturner
Posts: 444
Joined: Mon Mar 11, 2013 6:34 pm

Re: AHRS power

Post by Bobturner »

Remember the fuse protects the wires. Use large enough wires so that one won't turn into a toaster at the maximum current allowed by tbe fuse.
akskyhawk
Posts: 23
Joined: Thu Mar 14, 2013 4:41 pm

Re: AHRS power

Post by akskyhawk »

Eric
Your idea of one power feed and suppling both units if fine but,
You might want to consider to supply your EFIS and AHRS via two power inputs since you have a E bus.
Both the EFIS and AHRS has 3 power inputs.
Run one power input to each via your avionics supply controled by avionics switch off your main battery bus.
The second and more important is via the E bus through a EFIS switch. This gives you redundcy power supply and more importantly you can have your EFIS on and running during start-up (because your E bus should be able to isolate from main battery) and this is also really handy for sitting in the plane and playing with your EFIS without your master switch being on!
During flight operation iyou can always turn your EFIS switch off (if needed) which will take it off of the E bus but your EFIS will still be powered up as long as the Avionics switch is on!

Jim
eschlanser
Posts: 14
Joined: Fri Mar 15, 2013 9:26 pm

Re: AHRS power

Post by eschlanser »

Bobturner wrote:Remember the fuse protects the wires. Use large enough wires so that one won't turn into a toaster at the maximum current allowed by tbe fuse.
Dear Bobturner,

This is from the HXr Install Manual:
>The display units consume approximately 1 amp
>Power supplied to the EFIS must pass through an external fuse or circuit breaker. It should be sized to allow at least 2 amps per display unit, with a maximum rating of 5amps.
>Per Ben at GRT, the AHRS uses 0.25amps.

Since I have a single/single, my max draw should be no more than 1.5-2.5amps.
I have a 5amp fuse on a 3 foot 22awg wire.
Do you think that the wire is too small or the fuse is too big?

Eric
eschlanser
Posts: 14
Joined: Fri Mar 15, 2013 9:26 pm

Re: AHRS power

Post by eschlanser »

akskyhawk wrote:Eric
Your idea of one power feed and suppling both units if fine but,
You might want to consider to supply your EFIS and AHRS via two power inputs since you have a E bus.
Both the EFIS and AHRS has 3 power inputs.
Run one power input to each via your avionics supply controled by avionics switch off your main battery bus.
The second and more important is via the E bus through a EFIS switch. This gives you redundcy power supply and more importantly you can have your EFIS on and running during start-up (because your E bus should be able to isolate from main battery) and this is also really handy for sitting in the plane and playing with your EFIS without your master switch being on!
During flight operation iyou can always turn your EFIS switch off (if needed) which will take it off of the E bus but your EFIS will still be powered up as long as the Avionics switch is on!

Jim
Jim,
I did consider using the multiple power inputs to the EFIS/AHRS, but there's only the one main battery. No back up battery. Backup Power to the E-bus/EFIS/AHRS/etc. is an SD-8 backup alternator through the battery bus.
E-bus/EFIS can be fed from the one main battery through a diode off the master relay or by turning on the SD-8 and closing the E-bus alternate feed switch allowing power from the battery bus.

With the master relay off and the E-bus alt feed switch closed, the EFIS can be played on while on the ground powered by the one main battery.

An oil pressure sensor with an idiot light plus the EIS switched on will both monitor engine start.

If both alternators fail in flight, I can close the E-bus alt feed switch and run the EFIS on the one main battery.

Eric
Bobturner
Posts: 444
Joined: Mon Mar 11, 2013 6:34 pm

Re: AHRS power

Post by Bobturner »

5 amp fuse is okay.
My chart shows #22 will heat up about 21 degrees F above ambient at 5 amps, so that should be okay too.
At the actual current draw and just 3 feet in length the voltage drop is with #22 is also acceptable.
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