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Brownout, revisited

 
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Ceengland



Joined: 11 Oct 2020
Posts: 391
Location: MS

PostPosted: Fri Oct 23, 2020 11:49 am    Post subject: Brownout, revisited Reply with quote

I thought I'd share my experience with curing 'brownout' in my specific application; a followup to discussions about brownout step up converters during the last week of Sept. 
I've recently added a used (but fairly new tech) GRT Mini GA (intended for certified a/c). and an older tech GRT Horizon HX to my panel. While the Mini seems immune to voltage sag during starting, the HX is quite prone to either rebooting, or more often, simply hanging up, after the start sequence. I don't want a separate avionics switch, and the HX is fairly slow to finish its boot process even without provocation. I looked at Bob's circuit and wondered if I could simplify a bit for my limited needs. 
The HX has three separate, diode-isolated inputs. It consumes an amp or two in normal operation.
I used a 4A boost converter, bought via Amazon. I spliced the supply wire that feeds the HX, so that it also feeds the boost converter. the converter's output is adjusted to around 11.5V (enough to keep the HX alive), and is fed into one of the spare power inputs on the HX. In four or five flights since installation, I've had no issues with the HX rebooting or locking up during engine start. The booster is technically always in the circuit, but when the alternator is on line, its output 'floats' at alternator voltage, so it's not really supplying power to the HX. IIRC, its parasitic draw is under 1/2A.
End result: No relay, no extra feed circuit, and one extra feed into the HX subD connector.  Remember, the booster is feeding a single component in the panel.
So far, I'm happy with the results.
Charlie


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Charlie
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user9253



Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

PostPosted: Fri Oct 23, 2020 2:23 pm    Post subject: Re: Brownout, revisited Reply with quote

Good work Charlie.
Those DC - DC converters are so inexpensive that one could be installed for
each load that needs brownout protection. For loads that do not have built in
separate diode isolated inputs, a dual diode such as 863-MBRF20L45CTG can
be used. It is $0.83 at Mouser.


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Joe Gores
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