What Battery to use?
 

I am using the GRT Horizon 1 system in my 6, I have been trying to figure out what battery to use as a backup. I think a 12v 4.5 amh battery would be okay. I thought about lithium ion, lithium polymer, but these seem to be high maintenance and have their risk (fairly volitile, fire, etc.) How about NMH? what is everyone using? Any advice would be appreciated.

My BMA EFIS1 required a 12v 2.9 AH battery like this one. It would run the system for 2 hours. It was charged by wiring it the master switch with a diode to prevent discharge.

http://www.apexbattery.com/universal...l-battery.html

backup battery
 

Chuck, I picked a Panasonic LC-R127R2P valve regulated lead acid battery. It is a 7.2 AH sealed battery sold by Mouser and others. In my opinion, check out the spec sheet for the "duration of discharge vs discharge current" curves. Decide you much current you want for how long from a backup battery and pick the AH battery to match. I found the Panasonic batteries from multiple sources so decided to go with them. I believe Mouser had the spec sheets for download.

I have three GRT H1 screens on a backup battery.

How long do you want it to run ????
 

Using a 7.5 AH battery from Batteries Plus, driving dual Horizon screens plus AHRS. Was charged to about 12.5 volts. Down to about 9.0-9.5 in 30 minutes. At about 9.0, one of the displays (one with GPS) went south.

Your mileage may vary.

James

Hummmmm
 

$24.00 for a $6.00 battery......hummmmm

Should be better than that..
 

Jim,
Are you sure your battery is being fully charged? These guys want about 13.5-13.8 volts for a float-type charge. If you are only getting to 12.5V, the battery won't charge to full capacity. Given GRT's spec of 3.25A for 2 screens + AHRS and the spec sheet for the LR.. battery above, you should be getting a bit over an hour's useful time. Yours should be similar. Of course, that time is affected by charge quality, battery age, number and type of cycles, temperature etc etc. but it seems like you're being short-changed.

FWIW, we change all of the batteries in our computer backup power supplies, alarms etc. every 2 years as a preventative measure (same type of battery). With infrequent use, we find that they age and cannot be relied upon when needed.

Properly used and maintained, these batteries should be a good choice for backups. YMMV

John

Just a comment for the OP- you aren't going to be able to use anything besides a lead acid without a lot of work. NiMH, LiIon, NiCad, and others all require a smarter charger than the basic aircraft power system. If you just hook them up to the aircraft bus like you would with a LA battery, they have a great chance of catching fire.

To use anything besides LA, your EFIS really needs to support it directly, and know how to manage it intelligently.

Good catch ...
 

The battery is **NOT** getting the full charge. I plan to supply it from a different place (where the voltage is higher), rather than from the convenient place (will take a lot more work ... later).

For now it is not very useful other than I know it works (just not very long). The charge is not up to 12.5 now (I measured 12.5 shortly after install but after some discharges I find it is not being supplied with a high enough voltage (my fault ... convenience).

BUT ... back to the original questions. With a dual screen, with GPS and powering the AHRS, I still think the 7.5 AH is the way to go to be assured of at least 30 minutes. The other reason for this is to be able to use it to supply the EFIS without draining the main battery when one is learning or "planning".

James

I finally just had my guys at my hobby shop make me up a 4ah NMH battery out of ten Sanyo Cells. I think it will hold up the EFIS for at least 30 minutes.
I mounted it on a flip down bracket behind the panel so I could remove it for charging easily. The dimensions were 7.5 L x 2.5 W x 5/8", weighs just a little over a pound. I plan on testing it of course after everything is installed.

It came out to be a very neat, small installation. I like the idea of keeping this circuit completely separate from the rest of the electrical system. I am using a small 6 fuse holder from B&C and one main toggle switch to activate power. Just trying to keep it simple. I wanted it where I could remove the battery for charging & cycling. (I do not like to charge batteries externally when mounted in the airplane).

The problem with NiMH is the self-discharge rate. They discharge up to 10% on the first day after charge, and can be down 75% after a month. In general, the bigger the cell, the faster the self-discharge.

NiMH is great for a lot of things, but sitting around as an emergency standby is not one if the strengths of this chemistry. If you stay with this and really want to use it, you should charge the battery every two weeks.

If you truly want something just for a manual backup, normal Alkaline D-cells would do great. They'll last at least one year without any maintenance.