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donjohnston
Joined: 13 Dec 2009
Posts: 231
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 Posted: Wed Dec 03, 2014 2:00 pm Post subject: Always on supply |
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The GPS manufacturer suggests connecting a second, always on, supply (they call it "clock power") which will improve GPS position acquisition time.
What is the preferred way of providing this power? Run a fused line (they recommend a .1a fuse) directly from a battery terminal (or battery side of the master solenoid) to the GPS?
IIRC, the EFIS would like one of these always on supplies also.
So maybe run a fused wire from the battery to the panel and create an "always on" bus with fused branches off of that?
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user9253
Joined: 28 Mar 2008
Posts: 1935
Location: Riley TWP Michigan
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| Posted: Thu Dec 04, 2014 8:12 am Post subject: Re: Always on supply |
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Is GPS position acquisition time a concern? I never noticed a delay problem with my Garmin GPS 496. If an always hot supply is really needed, then a 5 amp (or less) ATC inline fuse can be connected directly to the battery or battery side of the master contactor. Smaller fuses located in the instrument panel could be tapped off from the always-hot 5 amp circuit, but I do not think that the extra fuses are necessary. Maybe others can offer their opinion.
Joe
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Joe Gores |
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tim2542(at)sbcglobal.net
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| Posted: Thu Dec 04, 2014 8:39 am Post subject: Always on supply |
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Assuming a very low current for a "keep alive circuit", you could also just use a 10k ohm resistor installed at the source end of the wire instead of a fuse.
Tim
| Quote: | On Dec 4, 2014, at 8:12 AM, user9253 <fransew(at)gmail.com> wrote:
Is GPS position acquisition time a concern? I never noticed a delay problem with my Garmin GPS 496. If an always hot supply is really needed, then a 5 amp (or less) ATC inline fuse can be connected directly to the battery or battery side of the master contactor. Smaller fuses located in the instrument panel could be tapped off from the always-hot 5 amp circuit, but I do not think that the extra fuses are necessary. Maybe others can offer their opinion.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=435321#435321
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Mauledriver(at)nc.rr.com
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| Posted: Thu Dec 04, 2014 11:04 am Post subject: Always on supply |
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| Quote: |
Is GPS position acquisition time a concern? I never noticed a delay problem with my Garmin GPS 496. If an always hot supply is really needed, then a 5 amp (or less) ATC inline fuse can be connected directly to the battery or battery side of the master contactor. Smaller fuses located in the instrument panel could be tapped off from the always-hot 5 amp circuit, but I do not think that the extra fuses are necessary. Maybe others can offer their opinion.
Joe
I'd guess not. While it may be for a device that's constantly being
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powered on and off for ad hoc use, it would seem to me that GPS
acquisition time matches up favorably with normal aircraft 'run up
time'. That is, the GPS can find itself quite easily long before you
are ready to depart.
Conversely, an always on clock power circuit for the GPS or EFIS does
not match up well with common aircraft cycle times. That is, many
aircraft sit unused for extended periods. I'm sure someone can explain
that the typical clock power drain is so minimal that extended down
times aren't be an issue (?). It certainly gave me fits on my (3) GRT
HX installation.
Ironically I think they decided to pick-up the time from the GPS if
that's possible.
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tim2542(at)sbcglobal.net
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| Posted: Thu Dec 04, 2014 1:06 pm Post subject: Always on supply |
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If a GPS has been off more than 30 minutes it needs to download a second data table from the satellites before it can get a fix, that takes longer then to get a position.
GRT made a software change a while back to pick up current time from the gps, so you can D/C the keep alive circuit if you have current software and not worry about the parasitic drain on the battery. Haven't tried it yet myself, but that's what I've been told.
Tim
| Quote: | On Dec 4, 2014, at 11:03 AM, Bill Watson <Mauledriver(at)nc.rr.com> wrote:
>
>
> Is GPS position acquisition time a concern? I never noticed a delay problem with my Garmin GPS 496. If an always hot supply is really needed, then a 5 amp (or less) ATC inline fuse can be connected directly to the battery or battery side of the master contactor. Smaller fuses located in the instrument panel could be tapped off from the always-hot 5 amp circuit, but I do not think that the extra fuses are necessary. Maybe others can offer their opinion.
> Joe
I'd guess not. While it may be for a device that's constantly being powered on and off for ad hoc use, it would seem to me that GPS acquisition time matches up favorably with normal aircraft 'run up time'. That is, the GPS can find itself quite easily long before you are ready to depart.
Conversely, an always on clock power circuit for the GPS or EFIS does not match up well with common aircraft cycle times. That is, many aircraft sit unused for extended periods. I'm sure someone can explain that the typical clock power drain is so minimal that extended down times aren't be an issue (?). It certainly gave me fits on my (3) GRT HX installation.
Ironically I think they decided to pick-up the time from the GPS if that's possible.
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deej(at)deej.net
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| Posted: Fri Dec 05, 2014 6:53 am Post subject: Always on supply |
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On 12/04/2014 04:04 PM, Tim Andres wrote:
| Quote: | GRT made a software change a while back to pick up current time from the gps, so you can D/C the keep alive circuit if you have current software and not worry about the parasitic drain on the battery. Haven't tried it yet myself, but that's what I've been told.
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That's the way mine (HX and Mini-X) are setup (no keep alive circuit for
either), and it works well. Picks up the time shortly after powerup.
No issues so far that I've noticed.
-Dj
--
Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
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Mauledriver(at)nc.rr.com
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| Posted: Fri Dec 05, 2014 12:20 pm Post subject: Always on supply |
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On 12/5/2014 9:52 AM, Dj Merrill wrote:
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On 12/04/2014 04:04 PM, Tim Andres wrote:
> GRT made a software change a while back to pick up current time from the gps, so you can D/C the keep alive circuit if you have current software and not worry about the parasitic drain on the battery. Haven't tried it yet myself, but that's what I've been told.
That's the way mine (HX and Mini-X) are setup (no keep alive circuit for
either), and it works well. Picks up the time shortly after powerup.
No issues so far that I've noticed.
-Dj
Same here. When they made the change I disco'd the stay alive circuits,
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the HXs pick up the time before I go looking for it and a nagging
battery problem went away.
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donjohnston
Joined: 13 Dec 2009
Posts: 231
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