S

shiney

Well Known Member
I'm currently wiring the GRT H1 (dual screen). There are four power wires from one unit and three from the other. Is it right to splice these into one connection or should I leave them on individual fuses, or indeed any other suggestions?
 
What I did...

Hi Shiney -

There is a +14V wire from each unit which should be connected directly to a permanent supply (your main battery if you only have one). These wires provide power to the permanent memory (clocks and engine time etc.) and use minimal current drain.

There are three other +14V supply lines which can be connected to one source or alternative sources. The H1's will intuitively select the highest voltage from any of the sources available that these wires are connected to to maintain max voltage supply.

On my HX units I have connected two supply wires from each unit to my main switched Avionics supply. They are spliced in effect and I have also connected the AHRS (which have alternative supply wires as well) respectively. In my case I have dual AHRS so I connected HX1/AHRS1 and HX2/AHRS2 to separate circuit breakers on the same switched avionics bus.

I spliced the third supply wires for both the HX1/AHRS1 combination and the HX2/AHRS2 combination together and linked them through an isolator swicth directly to my Back-up battery (7AmpHr). The battery can be isolated during start-up.

On this basis I can switch on the EFIS/AHRS prior to start up with the Back-up battery isolated allowing the units to boot up while I am getting the cockpit organised. The engine can the subsequently be started without any risk of voltage/current spike on the basis that the Back-up Battery is isolated. Following engine start the Back-up Battery is reconnected via the isolator switch and the EFIS will return to drawing power from the best supply available.

Hope this makes sense?

Regards

JON
 
Thanks John,

So I can wire one +14v to my Battery Bus. I have single AHRS so I will connect HX1/AHRS1 to one breaker and HX2 to another. I don't intende having a back up battery (weight) so I will isolate these leads.

Your start up procedure makes sense so with regards to battery, I'd like your view on weight and position, it's something I decided not to do but if you have a light weight unit I'd like to know more about it.

Thanks


Martin
 
Hummmm

One wire is for the "CKA" clock keep alive circuit

One wire is for the primary input

One wire is for the secondary or backup supply

and.....

One wire is for the third power input...?? go figure..??

I for one would not tie then all together. You might want to get a backup 12vdc 7ah small battery as a backup
 
Sticky has got the terminology right however according to GRT (in terms of the way the units source power) all three of the leads are "equal" in priority.

In other words you can connect any one of the three or all three and the units will work. In a nutshell it allows more redundancy in terms of power source. If you have all three spliced and connected to the same circuit the redundancy is then lost.

In my opinion only, connecting three seperate circuits is basically overkill but two is worthwhile. Separating the AHRS power source from the H1 units is also unnecessary in my opinion however obviously if you only have one AHRS is should be connected on the primary display circuit or alternatively on its own circuit.

I have installed a Gell Cell 7Ah Back-up battery . It gets topped up when connected to the Alternator output. I chose to set up as described in my post above due to a number of comments on the forums in relation to the start-up and alignment times for the GRT units. I have a tip-up canopy and the back-up battery is located between the main panel and the sub-panel. A light weight alternative is to use a Lithium 12V rechargeable battery pack (as used in R/C Cars etc) however you need a special 12V charging unit separately connected and switched to the battery pack (it must be capable of reverting to trickle charge when the battery reaches full charge) or the main alternator feed will fry it.

My set-up simply gives me the flexibility to boot-up prior to switching on the Avionics or Master when required and the ability to direct +14V direct from the Back-up battery when (if) the main battery fails.

Hope this makes sense....
 
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Jon,

What you say makes sense....

Why a 3rd power input is beyond my imanigation?..

I have 2 batteries and 2 avionics busses. Primary to one, Secondary to the other, both the efis and the ahrs.


If that all fails I have a Dynon and steam guages.....yummy:eek:
 
One for the Main bus

One for the Essential bus

and One to the Aux battery

...at least that's how I do it.....this way, you never have to switch anything - if you have power somewhere on an aircraft bus, the EFIS has power. That's how a certain aerospace vehicle power's it's computers (more or less). ;)

Paul
 
Paul

How do you keep the aux battery charged - is it possibly as simple as running a wire from one of the busses to the aux battery with a diode in between to stop the juice from flowing out of the aux battery during start up?

thanks

erich
 
erich weaver said:
Paul

How do you keep the aux battery charged - is it possibly as simple as running a wire from one of the busses to the aux battery with a diode in between to stop the juice from flowing out of the aux battery during start up?
Click to expand...

In principal, yes. In practice, the Aux battery dioded of the main battery bus with a resistor in line to keep the curent down to a reasonable level. You also want a diode with as low a forward drop as possible. This arrangement keeps the Aux battery charged trickle charged (not perfectly, but good enough) when the aircraft sits, and tops it off when the Alternator is up.

Paul
 
Just as an aside, the three power leads into the GRT stuff are diode isolated inside the unit, so no worry about a hot wire bleeding over to other feeds or sources of power. We frequently have used 2 of the three, but after hundreds of the GRT screens I think I can count on one hand the number of times we've used all three.

As the famous guy say: "Make is just as complicated as it needs to be, no more".

Cheers,
Stein
 
And another famous one from Ed Heinemann (IIRC) - "Simplicate and add lightness"

:)
 
Ironflight said:
In principal, yes. In practice, the Aux battery dioded of the main battery bus with a resistor in line to keep the curent down to a reasonable level. You also want a diode with as low a forward drop as possible. This arrangement keeps the Aux battery charged trickle charged (not perfectly, but good enough) when the aircraft sits, and tops it off when the Alternator is up.

Paul
Click to expand...


Does anyone remember the part number for a suitable diode with a low forward drop? For the resistor value do you take the alternator output voltage and subtract the battery voltage and subtract the diode drop and then divide by the desired charging current (from battery spec sheet)? I guess I could fall back on my old engineering principle - "every hole a slot and every resistor a pot." :)
 
Backup battery circuit

Paul Dye posted a schematic to the GRT group on Yahoo a couple years ago. It used an NTE585 diode and a 15 ohm 10 watt resister. I have used this circuit in my RV7a for the last two years and it works. I used a Panasonic battery, part number LC-R127R2P, 7.2 Ah. Mousers carries these products.

Good luck.
 
Any local alarm company will have the battery........

Finally fired up my GRT 8.4 HX......almost better than sex!!:eek:
 
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