DIY back-up avionics battery

[Paul K]

I've searched the forums for the last hour and have still not found the answers to how to make my own back-up battery connection for my GRT's. I am using the third power input for this function and have found a 5.8 AH gel battery that will power the essential GRT units for about an hour if all else fails. Also want to use this back-up to power the units during engine start per the GRT installation guide.

So, I need to be educated on how to charge this small battery when not in use and anything else I am not thinking about. Anybody?

[humptybump]

Hi Paul K,

Paul D posted a very good write-up of the electrical system in their RV-3. I think you will find some useful information about backup battery configuration for "run" and "charge".

http://www.vansairforce.com/communit...t=power+system

It's definitely a good place to start.

[Wayne Gillispie]

Paul,

I have one alt, 925L main and 680 aux. I power up all avionics first using 16AH aux bat, then start engine with main. I then close a crossfeed contactor to recharge aux.

I could also charge aux bat by powering ebus through cbs and b&c diode from main bus. Diode prevents aux battery/ebus from powering up main bus which would blow my 30a fuse at aux battery. If aux bat requires excessive charge current it might trip my main to ebus cbs hence the reason I close the xfd contactor after engine start. You are using smaller battery but same principle.

[Paul K]

Thanks Glen. That was exactly what I was looking for!

I'll get with Stein to see if they can help me with the resistor and diode.

[tommylewis]

I used the circuit that Paul Dye uses with a Panasonc battery LC R127R2P1, a 7.2 Ah battery. The resister is a 15ohm 10w. The diode is a NTE 585. These parts are availabe from Mouser Electronics. I used this circuit for the backup battery in both my rvs. It has worked well in my RV7a for 900 hours and 5 years.

[BillFear]

I need to replace the Yuasa 7.4AH back-up battery in the 7a. Sounds like this and the panasonic have been popular choices for the essential bus back-ups. My battery weighs 5lbs, just wondering if anyone has found a reasonable substitute that is lighter and will fit in the same mounting system. The yuasa is roughly 6" x 2.6" x 3.7".

Thanks for any ideas

[BillFear]

Something like this looks to have the capacity, the size and only weighs 1lb or less. Any thoughts or experiences? I think these are the same as the aerovoltz products. Looks like you can get them online for $50 or so.

http://www.ballisticparts.com/produc...ries/4cell.php