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Simple EFIS backup battery wiring

 
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mrcc1234(at)sbcglobal.net
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PostPosted: Sun Nov 12, 2017 7:00 am    Post subject: Simple EFIS backup battery wiring Reply with quote

I need to install a small battery on my MGS Extreme so that it can be kept up and running during engine start for my VFR 601XL. I would like to keep the wiring as simple as possible, but also allow the 1.2 AH battery to be maintained by the alternator. MGL has an example that uses a diode and switch to power the backup pin on another system, but the Extreme does not include this.
How has everyone else handled this?
Thanks,
Matt Stecher
Skydive Houston Airpark


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donjohnston



Joined: 13 Dec 2009
Posts: 203

PostPosted: Sun Nov 12, 2017 1:26 pm    Post subject: Re: Simple EFIS backup battery wiring Reply with quote

I have a GRT EFIS and here's how I did mine. (The diode is a 10A/60V MBR1060G)

FYI, I have mine setup so I can power up the Primary EFIS prior to engine start so I don't have to wait for it to boot when I'm ready to start the engine.


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user9253



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PostPosted: Sun Nov 12, 2017 3:48 pm    Post subject: Re: Simple EFIS backup battery wiring Reply with quote

Here is a circuit similar to the above. A battery fuse and switch could be added if desired.

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Joe Gores
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PostPosted: Sun Nov 12, 2017 4:04 pm    Post subject: Simple EFIS backup battery wiring Reply with quote

And if you want max voltage available in a simple circuit like that,
Schottky diodes are pretty cheap now. Just search ebay for lots of
options. Somewhat lower forward voltage drop than silicon.

On 11/12/2017 5:48 PM, user9253 wrote:
Quote:


Here is a circuit similar to the above. A battery fuse and switch could be added if desired.

--------
Joe Gores


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Eric Page



Joined: 15 Feb 2017
Posts: 109

PostPosted: Wed Nov 15, 2017 9:44 pm    Post subject: Re: Simple EFIS backup battery wiring Reply with quote

mrcc1234(at)sbcglobal.net wrote:
I need to install a small battery on my MGS Extreme so that it can be kept up and running during engine start for my VFR 601XL. I would like to keep the wiring as simple as possible, but also allow the 1.2 AH battery to be maintained by the alternator. MGL has an example that uses a diode and switch to power the backup pin on another system, but the Extreme does not include this.
How has everyone else handled this?


First, let me say: full credit to Eric Jones. What follows is thanks to his design and prototyping work.

About four years ago when this topic came up...

...on the second page here: http://forums.matronics.com/viewtopic.php?t=98976

...then continued here: http://forums.matronics.com/viewtopic.php?t=99301

...and here: http://forums.matronics.com/viewtopic.php?t=99555

...Eric Jones designed a "De-Slumpifier" or “voltage slump eliminator” circuit using supercapacitors (see his schematic at the second link above, and mine attached below). Another forum member (Joe, "user9253") successfully tested Eric's prototype in his RV-12, but Eric decided that additional capacitance was needed.

I've adapted Eric's design to increase capacitance from 0.25F to 0.55F and to match the balance resistors to the new capacitors' leakage current specification. Otherwise, the design is largely unchanged. I've also prepared a circuit board layout, so that the device can be easily duplicated by anyone who needs it.

If you're trying to prevent EFIS/EMS brownout/reboot during engine start, this will do the trick. Note, however, that this device is not an endurance supply and it won't support a load in the event of bus failure or shutdown. The device would cost about $40 to build, and it would eliminate the periodic testing and replacement associated with a battery installation. It's designed to fit a 2" x 2-3/4" box, and it will weigh just a few ounces.

Operation is simple: apply bus power and ground to the input, and route output power and ground to the EFIS/EMS. Assuming a fully charged battery at ~12.7V, the bus will charge the capacitors to ~12.3V within 20 seconds once power is applied. During engine cranking, the capacitors will power the EFIS/EMS at >8V (minimum for the MGL Xtreme units) for ~13 seconds, assuming a 2.8W load. [The MGL Xtreme manuals specify power draw of 130mA at 13.8V for the EMS and 200mA at 13.8V for the EFIS; the latter equals 2.8W.] Assuming a healthy battery and an engine that starts within a few seconds, your EFIS/EMS won't brownout/reboot.

You can order the parts and assemble it yourself, or I'd be happy to do it for you for the cost of parts and postage. Here's a link for a .ZIP file on my Google Drive that contains my DipTrace CAD files, as well the RS-274X Gerber files needed to order the printed circuit board: https://preview.tinyurl.com/yajod9m6

If you'd like some guidance on ordering the boards and components --or-- if you'd like me to assemble one and send it to you, just let me know. It would take 2-3 weeks, so you'd have it within a month or so.

If anyone else wants one, just chime in. Up to ten copies will not increase the cost of PCB production, so I can make several for just the incremental cost of components.

Eric

P.S. A few items to note if you assemble this yourself:

1. Diode D1 is a bidirectional transient voltage suppressor. It can be installed in either direction, regardless of its markings.

2. Diodes D2-D4 are installed standing on end, with the cathode (white band) facing up, away from the board. Fold the cathode lead over the diode's body, so it goes through the pad hole next to the body.

3. If it were my airplane, I would use the bottom of the box as a mounting base and install the device without the top of the box attached. The large resistor briefly dissipates substantial energy as heat when the supercapacitors are charging, and the capacitors will live longer, happier lives if that heat isn't dumped inside an enclosed space.

4. A blob of *neutral cure* RTV silicone or Shoe Goo around the base of the large TO-220 resistor will promote long-term durability. Its leads support both the resistor body and the heatsink, so in an environment subject to g-loads and vibration, added mechanical support will relieve stress from the leads. [Do *not* use standard "kitchen and bath" silicone on electronics; the vinegar smell while it cures is acetic acid, a corrosive.]


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Last edited by Eric Page on Wed Dec 06, 2017 10:20 am; edited 2 times in total
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user9253



Joined: 28 Mar 2008
Posts: 1325
Location: Riley TWP Michigan

PostPosted: Thu Nov 16, 2017 2:11 pm    Post subject: Re: Simple EFIS backup battery wiring Reply with quote

Good job Eric Page. Some aircraft owners and/or builders will appreciate your work.

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