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CNEJR

Well Known Member
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.
 
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 ????

CNEJR said:
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.
Click to expand...

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
 
Should be better than that..

jclark said:
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.
Click to expand...

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 ...

lucky333 said:
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
Click to expand...

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.
 
Odyssey makes a small 8AH version of their AGM batteries, the PC310 (http://www.odysseybatteries.com/battery/pc310.htm). It weighs nearly 6 lbs, however. Keeping it fully charged might be accomplished with a DC-DC converter.

Of course all this might add up to be a complicated Rube Goldberg contraption too, but I'm a gear and wirehead so I like these kind of things and would consider it for my own plane.
 
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Neal - not sure why you feel the need for a DC-DC convertor to charge the PC310. Am I missing something here? This battery has seen a fair amount of successful use being charged straight from the buss, provided the buss is well regulated. Several local folks are using the PC680 as primary cranking battery, again, connected straight to the DC buss. So far they seem to be holding up well, despite seeing heavy thermal cycling with some pretty brutal winter weather.
 
Panasonic Battery Weight

I'm also thinking about using a dual screen GRT panel, and was wondering if anyone knows how much the Panasonic 7.2 AH sealed lead-acid battery weighs. It was mentioned on the first page of this post. The model number is LC-R127R2P.

Thanks,
 
We recommend the use of small sealed lead acid batteries for our systems (Enigma, Odyssey, Voyager, Explorer...).

The reason is experience with various types of batteries over many years. New type Lithium Polymer batteries are quite good and are not that volatile anymore but still require carefully matched, intelligent chargers and are not simple "fit and forget" solutions.

Our profile is based on intermittened use with short charging intervals (at perhaps less than ideal charge voltage) followed by long periods of inactivity. Also, very important, the battery may be exposed to heat and extreme cold while just sitting there doing nothing.

Once you take all factors into account (and that includes price), sealed lead acid, despite the age of the basic battery design, wins - it's hardly even a contest.

We favour external backup batteries for our instruments as this provides flexibility. You can choose desired capacity for your particular needs and also locate the battery where it can be of advantage (weight distribution) - we use a lot of our instruments in motor gliders...

Rainier
CEO MGL Avionics
 
Canadian_JOY said:
Neal - not sure why you feel the need for a DC-DC convertor to charge the PC310. Am I missing something here? This battery has seen a fair amount of successful use being charged straight from the buss, provided the buss is well regulated. Several local folks are using the PC680 as primary cranking battery, again, connected straight to the DC buss. So far they seem to be holding up well, despite seeing heavy thermal cycling with some pretty brutal winter weather.
Click to expand...

Apologies for the late response here, but since the original purpose of the additional smaller battery was to provide a robust source of backup power for the EFIS/EMS, isolated from the ship's main bus, the classical way of keeping such a backup battery charged has historically been via using a simple diode to prevent anything else in the ship from drawing juice out of that battery in the event of total failure of the main battery and charging system. A diode in series with the line that charges the backup battery from the main bus will give a forward voltage drop and the backup battery may never reach a full charge, which will give you greatly reduced runtime and possibly even shorten the useful service life of certain batteries. A DC-DC converter with a regulated output can be employed in the charging circuit for the backup battery to keep it charged at a constant full recommended float charge voltage level, even when the main bus voltage sags too much.

Expensive solution? Yup.
Complicated? Yup.
Necessary? Hmmmmm, probably not, but personally if I was going thru the ordeal of adding a separate backup battery for my avionics and since I'm an electronics geek, I would be inclined to try to conjure up some kind of solution to keep the backup battery fully charged instead of "mostly charged".

A Schottky diode will give less of a forward voltage drop than a regular silicon diode.

Battery isolators like these: http://www.hellroaring.com/nodiode.php are also an interesting possibility.
 
Neal@F14 said:
A Schottky diode will give less of a forward voltage drop than a regular silicon diode.

Battery isolators like these: http://www.hellroaring.com/nodiode.php are also an interesting possibility.
Click to expand...

Yes, you are correct, a Shottky diode is what you should use. This gets peak charge voltage to around 0.3V less than bus voltage (the current is very small when the battery reaches this level of charge, so the normal ~0.5V drop goes down somewhat).
This has very little effect on reaching a state of charge that is as near 100% as is possible with a typical gel cell.
Our built in chargers draw from incomming bus and decouple via two Shottkies in parallel (to inclease current capability also at low drop out voltage). This is then fed to a zero drop current limit switch mode supply which limits maximum charge current but also limits maximum battery charge voltage to around 14V (13.8 volt float) in case bus voltage is higher - a frequent occurance in many aircraft supply systems which tend to be regulated somewhat "rough".

Have a look at the data sheets when you buy a Shottly diode - they come in different drop out voltage vs current ratings. Some of them are not much better than your average silicon diode but others are quite impressive.

Rainier
 
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