power up

[Flybyjim]

Is there a proper way to power up the glass panels, as power them up before engine start (to see oil pressure or other items) or is it best to start the engine then power up the avionics. I have read about a power drop to the screens during engine start. What are the thoughts out there?

[DesertFox4]

<——————- TCW has Intelligent Power that protects valuable delicate electronics on start up and shutdon. Cheap insurance.

[PapuaPilot]

You want to have your avionics powered up so you can see the oil pressure. You need to provide a way so that the voltage doesn't go too low, causing the screen to reboot.

There are several ways to do this.
- The TCW product can do it.
- I installed a second battery to power my essential bus during the start. My E-bus powers everything needed to run my screen / engine sensors / electronic ignition, and is separated from the main bus by a power diode. My starter is on the main bus, so when the main bus voltage drops lower than the E-bus the second battery takes over and keeps the screen alive.

Initially I used a 4 AH sealed lead acid battery (mounted in my tail), which weighed about 5 pounds with wiring. I removed it last year and replaced it with a LiPo battery & charger/maintainer circuit board that I assemble from parts I found online. The entire unit weighs less than 1 pound so I shaved off 4 pounds.

If anybody is interested in building their own backup battery I can give you the information. It uses 3 LiPo batteries and a charger/maintainer circuit board. I also added a relay that turns it on with the master switch. I spent about $45 for all the parts and build an equivalent to the TCW part. I used Tenergy batteries and circuit board, not inexpensive Chinese stuff.

The one I made can power my E-Bus for 15-20 minutes, but it really only needs to work for a few seconds during the start.

[David47]

Phil, I’m interested. I’ll try and pm you.

[PaulSS]

Hi Phil,

The UK LAA allows certain electronic instruments to be used as backup sources of info e.g. airspeed and altitude but they must have their own backup power source. Some manufacturers have instruments with the facility but the likes of the MGL Vega ASV-1 do not and need to have a backup battery. I've been trying to figure out such a system, so I'd be very interested to hear how you did it on a larger scale and then, maybe, I could shrink it to fit. The ASV-1 only draws 73mA even at maximum backlight so the battery does not need a huge Ah. I was trying to see how I could do it, avoiding 'backup' switches i.e. an automatic change over and think I've got that figured out but I am a bit concerned about the means of charging a small battery and think I need to add something else to my system :)

With the diagram in the attachment, with 12V the relay closes, wigglies flow to the backup battery and ASV-1 and everybody is happy (I think). I don't know at this stage if the B/U battery would get charged or if it needs something else there to (a)charge it and (b)stop it over-charging. When the 12V stops flowing from the main aircraft system the relay opens and the ASV-1 is automatically powered by the B/U battery.

I have no doubts that I have something wrong my theory and would welcome advice on (a) and (b) above :confused:

Edited to add: I've just realised that unless the ASV-1 has an on/off switch then this system would mean the instrument would carry on being powered even when the battery master is off and the aircraft is tucked up in bed. Not ideal. Sorry, I also noticed I missed the obvious diode needed after the relay to stop the B/U battery trying to 'back power' the aircraft system.

[Flybyjim]

I see there is a choice of 4 or 8 amp for the TCW unit, what have you used?

[PaulSS]

I've got the 4A. I'm running all my MGL gear off that (RDAC CAN, Status Monitor, iEFIS, Extender Module and Magnetometer). All up that 975mA, so 4A is more than enough :)

[jiott]

The Dynon/AFS EFIS has no problem being ON during engine start. Maybe its because I have their EFIS backup battery.

[PapuaPilot]

I posted information about my homemade backup battery in the "Electrical" section.