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12-31-2009, 08:27 AM
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Join Date: Dec 2006
Location: Oakland CA
Posts: 771
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GRT starting voltage sag
Hi All
I have my plane wired up with 2 PC680 batteries. I start the engine on both batteries. Problem is, my GRT Horizon 1 dual screens come on with the master but the starting voltage sag causes them to reboot. Is this bad for them...do I need to install a switch or switches and keep them off until after starting? I didn't think with 2 batteries the starting current draw would still reboot the systems, but...
Jeremy
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12-31-2009, 12:34 PM
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Join Date: Mar 2005
Location: Northern California, USA
Posts: 537
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Does this happen with other EFISs?
Does the reboot-on-engine-start also happen on
Garmin G3X?
Aspen PFD?
Dynon?
I am building a similar electrical system (two batteries that can be -- but need not be -- paralleled for starting) and am wondering if I need to plan on a little battery to keep the EFIS alive.
I fly a Diamond DA42 at work that has a G1000 and it never reboots during start...I wonder what the differences are?
Thanks,
Martin
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Martin Gomez
Redwood City, CA
"My RV-7 is a composite airplane: it's made of aluminum, blood, sweat, and money"
RV-7 Slider QB
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12-31-2009, 12:55 PM
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Join Date: Dec 2006
Location: UK
Posts: 368
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Jeremy,
My plan (not flying yet) is two batteries (one PC680 plus a 9Ah aux SLA battery) but starting the engine only off the PC680. My AFS EFIS/EMS will be isolated from the PC680 and connected only to the aux battery until after engine start.
Lots of people say that an avionics buss is nolonger necessary but I just feel happier protecting all the high value electronic items from the electrical vaguaries of the start process.
Happy New Year!
__________________
Steve Hutt
West Sussex, UK
RV-7 G-HUTY (not flying yet)
( Tip-UP / TMX-IO-360-M1B / Hartzell 7497-2 / 1x LSE PLASMA III / Dual AF4500's / AF-Pilot AP / 695 )
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12-31-2009, 01:03 PM
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Join Date: Jun 2005
Posts: 693
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Most avionics are designed to operate down to 10 volts. So when you start a 12v system, most of the time the voltage drops down below 10v. The DA42 is a 24v system, so there is more "headroom" during start. There may a small aux battery tied into the G1000 as well - don't know for sure.
The GRT/AFS/Dynon/MGL all have small aux batteries that can be purchased separately, and we generally recommend that both for starting and for backup power in flight.
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Marc Ausman
RV-7 980 hours, IO-390, VP-X (sold)
RV-8 (flying a friend's)
Thinking about low and slow backcountry build.
VAF Advertiser - Aircraft Wiring Guide
Book to help with experimental aircraft wiring.
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12-31-2009, 05:27 PM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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Hi JJ,
One neat thing about the GRT's (and I believe some of th others), is that they have three power feeds, all dioded inside the boxes, so you can feed them from three different sources. Yes, the voltage sag of engine start will reboot them every time -unless one of the power feeds is connected to a little Aux battery. The boxes draw from whatever source has a higher voltage, and they never mis a beat this way. I always boot my systems prior to start (so that I am ready to taxi when oil pressure stabilizes), and never have a problem - unless I forget to flip on the Aux battery before hitting the start switch...
Paul
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Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
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12-31-2009, 06:25 PM
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Join Date: Jun 2005
Location: Woodinville, WA
Posts: 1,499
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Since someone asked about Dynon, the Dynon stuff has a few options, such as an internal battery that keeps it on when the voltage sags. If you have an internal battery, it just works, no need to wire something funny up to keep it on. AFS offers this as well. GRT does not. MGL can do stuff with an external battery.
At Dynon, we also design our stuff to run way below 10V. In fact SkyView can run as low as 3V. Our current EMS systems run down to 5V, since EMS is what people really need right after start. Even with a reboot, the EFIS-D100 only takes about 6 seconds to boot so it's not much of an issue.
Most 12V planes sag to about 8V when starting, and permanent magnet starters can be much worse. If your stuff only stays on to 10V, you do need something to keep it on during start.
We 100% suggest you have our stuff on during crank. I know it's contrary to what you may expect from older electronics, but we design for that. It's actually much less sensitive than older stuff. We've sold over 8,000 units and I don't believe I've ever heard someone say "It was on, but it died when I cranked the engine."
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12-31-2009, 06:30 PM
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Join Date: Jan 2006
Posts: 934
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With GRT, if you also have the EIS installed where you can see the display, it will not re-boot on start, so you'll have RPM and Oil pressure during start if it's on. I don't run an aux battery, but start with EIS on, and EFIS off until after start and it seems to work just fine.
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12-31-2009, 06:34 PM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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I would recommend to move the HX off your master and have it start with the avionics switch. I asked GRT specifically about this and the Horizon is no protected like the EIS. I have only my EIS on the master and reason for that is that I want to know about my oil pressure right away.
As for the HX rebooting, it might be because it draws the most power right at the beginning for its screen. I can't remember the exact amount of draw but I know for sure as mine was once rebooting when I had run the battery some what down. But if it booted, then it would run OK even with low voltage on the battery.
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Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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12-31-2009, 07:05 PM
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Join Date: Dec 2006
Location: Oakland CA
Posts: 771
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yup, EIS stays on...
but it looks like I need to install either a switch or an aux battery. I'm leaning away from yet another battery...Coin flip or is there something a bit more meaningful to base the decision on  ?
Just for discussion purposes, I have 2 identical pc680 batteries and 2 masters. Procedure is to turn both on for start, taxi and runup, then turn one off for the duration of the flight. Next flight, fly and charge the other battery. The thinking is that I will always have a known good battery in my back pocket if needed.
Jeremy
Last edited by jjconstant : 12-31-2009 at 07:09 PM.
Reason: more info
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12-31-2009, 08:18 PM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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Quote:
Originally Posted by jjconstant
Just for discussion purposes, I have 2 identical pc680 batteries and 2 masters. Procedure is to turn both on for start, taxi and runup, then turn one off for the duration of the flight. Next flight, fly and charge the other battery. The thinking is that I will always have a known good battery in my back pocket if needed.
Jeremy
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You could do a fairly simple re-wire that allows you to power the EFIS from one battery when the other is isolated for the start. That is where the mupliple power feeds are useful. But then again, if you don't mind waiting for EFIS boot after start, the EIS is plenty enough to monitor oil pressure - as is a simple oil pressure switch.
Paul
__________________
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
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