Alternatives to GRT's Back-up Battery?

I just ordered a GRT Horizon HXR EFIS and was surprised to learn that it doesn't come with any sort of battery back-up.

GRT will be glad to sell me one for "only" $140 extra, but they "recommend" the $275 version.

Given that I could buy another Concorde battery and wire in an entirely separate and redundant battery system for the entire plane for less, I have hesitated and did not order their battery.

Has anyone found an acceptable alternative?

Search, but Odyssey PC680 is my plan. Everyone was so giddy about a $95 shipped deal around Christmas that I jumped on the bandwagon, and have one sitting on the shelf waiting for some sort of install. There are, like, diodes and stuff you need to put in, apparently, but, hey, man, I'm slingin' mad volume and fat stackin' benjis, you know what I'm sayin'? I can't be all about, like, diodes and stuff.

You can use just about any smaller 12v battery for a backup to your efis especially since it really needs a power switch anyway.
I used a $20 computer battery that is easy to replace at any electronics or auto parts store. I think it is an 8 amp hr battery which I mounted under the floor boards of my rv8.
To make it work you need a diode such as the ebus diode sold by B&C for about $7
To install:
Disconnect the efis power wire from the efis
From the efis power wire, install diode to let current flow towards the efis
Run a wire from the diode to a toggle switch
From that same switch pole, run a wire to the back up battery
Don't forget to ground the bu battery neg pole to the airframe
From the other pole on the toggle, run a wire to the main power of the efis as normal

With this set up, you can power up the efis from the BU battery, with the master off, for programming, boot up, etc. by turning on the new toggle
When you turn on the master and start the engine, the ship main system takes over powering the efis and even charges the back up battery
It has worked well for me for many years now
You can use the same battery to power up additional stuff like a second efis, etc
Just put a diode between each separate device and the main bus
Good luck

I have one of these as a backup-up on my GRT.

http://www.tcwtech.com/IBBS.htm

It's simple and seems reliable but it was dead after sitting for 3 months the other day. I didn't wire it so it charged the back-up from the main battery when the master is off.

Since the GRT EFIS has multiple power inputs, it is easy to wire in a backup battery. I did mine before the TWC option was available and used a method similar to the one Steve described.

I used a 7.5 Ahr alarm system battery and a 3 position toggle switch (OFF-ON-ON). In the 1st ON position, power is applied to +12V input "A" on the EFIS from the B/U battery. In the 2nd ON position, "A" is still on and +12V input "B" power is applied from the Avionics.

The B/U battery is mounted on the firewall. A +12 line off the main power fuse block (with an in-line diode) is used to charge the battery when the Master is ON.

I power up one EFIS (1st ON position) prior to engine start to let the AHRS initialize. After engine start, I place both EFIS switches in the 2nd ON position.

jjhoneck said:

I just ordered a GRT Horizon HXR EFIS and was surprised to learn that it doesn't come with any sort of battery back-up.

Click to expand...

Isn't your mission VFR, and if so, do you really need that redundancy?

Brownout

I think a lot of of us GRT folks have installed a small 7ah aux battery for brown out and back up. But it's easy to do both at the same time with one battery and provide anything else that needs it at the same time, like a 430 for example. Let's you enter a flight plan and not lose it when you crank. As has been said a lot of equipment has multiple diode isolated inputs so it's easy to wire.
A Schottky diode, perhaps a resistor to limit charge current and you have it.
Search the forum there are several threads on it.
Tim

This is what we have

Something like this. Works fine, but it is really heavy by todays standards. I would try to use something lighter if doing it over. it is very nice to have as a 2nd battery to run cockpit lights or update a database without worrying about the starter battery.

http://www.amazon.com/APC-Back-UPS-...7&sr=8-5&keywords=apc+ups+battery+replacement

FWIW, my GRT-sourced backup battery is still working great 3.5 years after installation. At the last annual (Nov) I let it support the EFIS about two hours, and there was no significant voltage drop.

Also, FWIW, long term support for your new EFIS requires a vendor profit. Yeah, maybe the battery is a high-margin add-on sell, like the drink selection at a fast food restaurant. Consider it like leaving a good tip for excellent future service at your favorite restaurant.

Steve,

How about a quick sketch of what you wired up? It would be a great timesaver for all, including me!

Thanks in advance.

Wiring Diagram

If I could figure out how to post a pdf image on here I would show you how you can wire it. If anybody wants to see it, just drop me a email address in a PM and I will forward you my wiring diagram. Having re-done 4 RV electrical systems because of poor quality and almost no diagrams it is very helpful to have something available when you need to troubleshoot.

Wiring Diagram for back up battery

Hey Steve,

Appreciate your offer of the wiring diagram for the circuit you described in the forum.

Sent you a PM.

pdf of circuit sent email

Copy sent email to Vince and Carl.
If anyone else wants a .pdf copy, let me know.
[email protected]

Thanks, Steve, here's a copy for everyone:

I needed to create both the charging circuit *and* the dual source circuit (since my EMS did not support dual power sources. Since the GRT has two power inputs, you don't need the right most diode in my design. So, in the diagram here, just remove the shottky diode on the right and you are left with a "main" input and a charge output at "backup".

Not to nit-pick too much, but those fuses have to carry the charging current which could be fairly large if the battery has sat for a while (?); but they also protect the wire to the EFIS which typically is only #20 or 22, so they can't be too large, either.

As others noted, you can make the charging circuit do nothing but charge, and feed the GRT thru a second power input (they are isolated internally).

DanH said:

FWIW, my GRT-sourced backup battery is still working great 3.5 years after installation. At the last annual (Nov) I let it support the EFIS about two hours, and there was no significant voltage drop.

Also, FWIW, long term support for your new EFIS requires a vendor profit. Yeah, maybe the battery is a high-margin add-on sell, like the drink selection at a fast food restaurant. Consider it like leaving a good tip for excellent future service at your favorite restaurant.

Click to expand...

I'm certain that it is top quality piece of kit. At $275, however, it's too rich for my blood. This entire upgrade has come in about 10% over budget (thanks to my stupidly sitting in a plane with both an 8" and a 10" screen, and seeing the real difference!), so I've got to cut corners where I can.

Polarity reversed

catmandu said:

Thanks, Steve, here's a copy for everyone:

Click to expand...

I know this is an old thread, but isn't the back-up battery in backwards? Positive terminal is shown connected directly to ground.

backing up the power

An old thread comes to life. Makes me wonder if the GRT price on a backup battery came down.
Yes, the schematic technically shows the battery reversed... but the author clearly said + 12 V in the right place. Just those pesky short lines and long lines....
I did LIKE Dan Horton's thought about keeping good companies like GRT going strong. From other avionics news, we can hope the penetration into some old Cessna trainers etc. bypassing TSO costs at small companies is going to be good for all.