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Auxiliary / backup battery

Would it be possible to install a sort of a backup battery for essential instruments on the cockpit?

Following some issues I have with my EDM-930 primary engine monitor, the producer (JPI) replied:

On 14v systems the EDM-930 may reset on engine start. Voltage drops too low. Can install aux battery power on J5 pin #13 – Rev D board

Is there any authorized (for N registered airplanes) auxiliary battery that can be installed on my Socata TB20? Or any GA aircraft? It should be very easy to have a small LiFePo battery that always charges from the main battery and can power for a limited time a PFD, or HSI, or engine monitor.

LRIA, Romania

A Garmin GAD27 would deal with the specific problem during start – it’s used for the same purpose with the G3X. You could probably instal it as an FAA Minor Alteration on a logbook entry if you have a helpful A&P.

Avionics geek.
Somewhere remote in Devon, UK.

On the Garmin website there’s only one experimental model, listed as GAD27 experimental. And it seems it works as a simple voltage regulator, with no internal battery cells.

An auxiliary independent battery would provide a real redundancy and a peace of mind, knowing that your most critical indicators can stay alive in case of failure of the primary battery bus…

LRIA, Romania

The GAD27 is also used in the certified G3X. It has some short-term storage – not designed for use as a back-battery. From the install manual:

Voltage Stabilizer for Consistent Power

For light aircraft that may not have a redundant power source, the GAD 27 adapter can be used as a voltage stabilizer to maintain a consistent power bus output of 12 V, preventing high-draw situations such as engine startup from dropping your avionics off-line. Your G3X Touch display stays lit, your engine monitoring reference stays powered up, and you’re ab

Avionics geek.
Somewhere remote in Devon, UK.

This product from TCW Technolgies is what you are describing. They are widely used for experimental aircraft but there is also a version that has FAA TSO-C179.

Top Farm, Cambridgeshire, United Kingdom

I like the price increment for the certified version. I don’t think they needed a calculator to work this out

Does the EDM930 charge the battery, via that backup battery terminal, or do you have to arrange something? The latter is not trivial if it is to be done safely. You need 1 diode, 1 fuse, but I would worry about blowing that fuse if the aircraft is powered up with the backup battery totally flat. It really needs some electronics implementing a constant current charge.

Shoreham EGKA, United Kingdom

The TCW product includes the diode and battery charging circuit. Here is a diagram from the manual:

There are two power feeds to the unit. One simply passes through to the connected equipment when ships power is available and the other charges the battery.

Top Farm, Cambridgeshire, United Kingdom

It seems to do exactly what I need, and some more! It will power the EDM930 directly or using the AUX Power input on the EDM, both methods providing protection during startup and backup in case the alternator fails.

As a bonus, I can also connect one of the radios and the audio panel so I can explain the passengers a sudden urge for popcorn and the following landing in the cornfield.

It’s strange how the price jumps up for the 24V version, with a 3 amps hour option only. Fortunately, I need a 12V version.

LRIA, Romania

Probably the 24V version internally has two batteries in series, actually. The battery has a nominal voltage of 12.8V. Also, remember that 3Ah@24V = 6Ah@12V

Last Edited by lionel at 06 Mar 16:55
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