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Relay Question: Adding control relay to SD-8 circuit

 
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ceengland7(at)gmail.com
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PostPosted: Sun Feb 04, 2018 1:35 pm    Post subject: Relay Question: Adding control relay to SD-8 circuit Reply with quote

On 2/4/2018 1:45 PM, Airdog77 wrote:
Quote:


Joe,
> If you describe the intended load and under what conditions it should be turned on or off

It's a 2.5A charging lead for a backup battery system that I don't want to draw off the E-Bus in a scenario where my main alternator goes down and I'm on SD-8/E-Bus only power. The condition is simply if the SD-8 is turned on for use as the primary alternator --again, in a scenario where the main alternator is taken offline-- then I would like this to be an automatic ancillary function of the SD-8 being brought online (the opposite holds true as well: SD-8 OFF, then the charging circuit is reestablished).

In my attempt to integrate this after all the cables are run through bulkheads, etc. my optimal access to this charging lead is in the nose, with my SD-8 in the aft section of the aircraft (Long-EZ/pusher).

Much thanks!

Regards,
Wade

--------
Airdog
Wade Parton
Building Long-EZ N916WP
www.longezpush.com
What's it going to power? If it powers the same stuff as the main

battery, simply upsizing the main battery might make more sense.

On the other hand, if it's in good condition it will be almost totally
topped off (fully charged) within minutes after engine start, so it
won't be sucking on the backup alternator at all.

If you're holding it in reserve in case of SD-8 failure *and* main
battery failure, why not use a fat Schottky diode to isolate it from
discharge? Schottky diodes are now cheap & widely available. (But double
failures in one flight might be less of a concern than airframe
structural failure...)

Charlie

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Airdog77



Joined: 24 Nov 2013
Posts: 78
Location: Northern Virginia

PostPosted: Sun Feb 04, 2018 2:47 pm    Post subject: Re: Relay Question: Adding control relay to SD-8 circuit Reply with quote

Charlie,

Quote:
On the other hand, if it's in good condition it will be almost totally
topped off (fully charged) within minutes after engine start, so it
won't be sucking on the backup alternator at all.


Yes, this is correct.

Quote:
If you're holding it in reserve in case of SD-8 failure *and* main
battery failure, why not use a fat Schottky diode to isolate it from
discharge? Schottky diodes are now cheap & widely available. (But double
failures in one flight might be less of a concern than airframe
structural failure...)


It's not really about a totally battery failure. Yes, I do have panel items with power inputs on the battery backup system as a tertiary backup in case of the total doomsday scenario... then I have about 45 min worth of use on those components. But my bigger concern is in the event of JUST a main alternator failure, and I go to SD-8 alternator power only. I simply want to ensure that at no time does the backup battery system decide it wants to starting charging at 2.5 amps sucking up on/about 25-50% of my SD-8 output (depending on my engine RPM).

I understand the likelihood of this event is low, but if it's simple and doable enough I'd like to add in this circuit now (i.e. while the weather is COLD) before I move on to more pressing aircraft build matters.

I'll definitely look at using a Schottky as well. Thanks!

Regards,
Wade


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Airdog
Wade Parton
Building Long-EZ N916WP
www.longezpush.com
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