AMPs

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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Sling 2 Pilot
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AMPs

Postby Sling 2 Pilot » Sun Sep 23, 2018 6:15 pm

I’m running a Rotax 912 ULS in my Sling. At 52-5300 RPM, what should my ammeter show? I have dual G3X Touch screens, autopilot, single com and remote transponder. Nav, landing, taxi and strobes are All LED. I rarely use landing, taxi or Nav Lites, only strobes. Voltage is at 14. What should amperage be under power?

roger lee
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Re: AMPs

Postby roger lee » Sun Sep 23, 2018 6:44 pm

Amperage can vary. It may swing from -3 to + 6. I most likely won't be steady and that's okay. So long as it doesn't go way plus or way minus and stay there then all is good. Most are in the fluctuations of -2 to +4.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)

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Re: AMPs

Postby Sling 2 Pilot » Mon Sep 24, 2018 7:23 am

roger lee wrote:Amperage can vary. It may swing from -3 to + 6. I most likely won't be steady and that's okay. So long as it doesn't go way plus or way minus and stay there then all is good. Most are in the fluctuations of -2 to +4.


Thanks Roger, I watch my voltage and never really payed attention to AMPs. Saw +1 and thought it might be low. Thanks again.

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drseti
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Re: AMPs

Postby drseti » Mon Sep 24, 2018 11:30 pm

The 912ULS internal alternator is rated at only 15 amps. That's probably not enough current to power the dual glass panels, GPS, transponder, intercom and autopilot, so your plane probably has the 20 amp auxiliary generator installed as well.

In most installations the ammeter measures the current being supplied by the generator(s) to recharge the battery, not the total current being supplied to the avionics. So, for example, if the avionics current draw is 25 amps peak, and you have both the main and aux generators capable of putting out up to 35 amps, that leaves you 10 amps remaining to charge the battery.

Of course, depending on its state of charge, the battery wouldn't necessarily draw that much. In fact, when it's fully charged, it will draw zero current, and your ammeter will indicate that. It doesn't mean that the avionics isn't drawing any current, merely that the current required is all being supplied by the generator(s), and the battery doesn't have to supply any.

In the rare case of your aircraft being lit up like a Christmas tree (all avionics and lights running) the required current might exceed the total output of the generator(s), and the system will also be drawing off the battery in flight. In this case, the ammeter will read negative. This is OK for a little while, but if you keep it up long enough to deplete the battery, next flight you may find there's not enough juice to turn the engine over fast enough to start it. ;( if this happens too often, you may have to consider using a battery tender in the hangar (or turning off stuff when you fly).
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

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Re: AMPs

Postby Sling 2 Pilot » Tue Sep 25, 2018 7:11 am

Paul, when I spec’d out my Sling, I asked if I needed the Aux generator and was told that I didn’t. They, TAF, could have easily sold it to me at the time I ordered my plane. When we dropped the steam altimeter and airspeed gauges for the G5, it was brought up again. Again, I was told no problem. Worst case, I can always add it. I flew it back from CA with out issue.

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drseti
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Re: AMPs

Postby drseti » Tue Sep 25, 2018 8:48 am

Well, I'm glad you're not having an issue, though surprised that 15 amps is enough to power dual glass plus an autopilot. Mechanically, the aux gen add-on is easy, if you end up needing it. Don't know how difficult the extra wiring would be on your plane.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

roger lee
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Re: AMPs

Postby roger lee » Wed Sep 26, 2018 8:25 am

"The 912ULS internal alternator is rated at only 15 amps. That's probably not enough current to power the dual glass panels, GPS, transponder, intercom and autopilot, so your plane probably has the 20 amp auxiliary generator installed as well."

Hi Paul,
The internal generator is rated at 20 amp DC max. It's real peak is actually 18 and its constant amps can be 16. You can easily run a full dual glass panel, gps, intercom, AP, radio and transponder on this. Flight Design has been doing it since 2006 and so has a few others. Instrumentation is more efficient now days vs yesteryear.
The info is in the Rotax Operators manual section 1.6 page 1-10.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)

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drseti
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Re: AMPs

Postby drseti » Wed Sep 26, 2018 10:11 am

Thanks, Roger. I stand corrected - I've been telling my students 15 amps continuous. That extra amp will certainly make a difference. ;)
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

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dstclair
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Re: AMPs

Postby dstclair » Wed Sep 26, 2018 1:00 pm

Did a little digging on current draw of my panel:

* D100 - 1.5A
* D120 - 1.0A
* Garmin 327 - 1.5A
* Garmin SL-40 - 0.6A
* Garmin 795 - 0.4A
* GDL-39 - 0.3A
* GDL-82 - 0.5A
* Dynon AP - 1.3 x 2

So around 9A continuous for my core panel. My lights are LED so I can light up like a Christmas tree and still have headroom with the stock alternator. Other things will add a bit (charger for my phone running iFly, encoded, Dynon remote compass and backup instruments) but I'm not overly concerned given when I put the battery on a tender after flight it jumps to full charge in a minute or two.
dave


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