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Kitfox Pilot
06-12-2021, 11:27 AM
I'm needing help on 915is charging systems and I can't seem to find answers to questions in the two pics below.
Could anyone help me answer the vertical power questions in the pics?
The first pic is the question for primary alt.
2nd pic is question for back up alt.
All I can find is the engine alt is 16a and the battery and firewall back alt is 28a. Thanks

Shadowrider
06-12-2021, 08:20 PM
Do you have control of the engine alternator? Do they both have external regulators? I thought the engine alternator is not controlled by the pilot in anyway? Seems like if I recall, as far as the vertical power is concerned, you only have one alternator? If the engine alternator fails what happens? Trying to understand the 915 logic?

Kitfox Pilot
06-13-2021, 06:46 PM
Dustin, I'm not sure my self. I can't find any real good answer to that. I found a video on vans rv channel and it showed 2 going into the fuse box but the computer controls them as far as when the engine one quits its automatic as far as switching to the other alt, you are probably right about not having any control on the engine alt for sure.
There's more than I understand about the vertical power and the 915s charging system. I was hoping someone had done this install because there isn't much info on the pair out there that I can find.

Geek
06-14-2021, 10:12 AM
Harlan - Have you downloaded the 915is Operator's Manual? I copied this out of it where it talks to how the generators work. A lot of people (Dustin is one and I am planning on doing it) add in another 'external' alternator that is above and beyond the two that are stock. The fact that if Alt 1 dies and the ECU takes Alt 2 to run the engine was enough for me to want a 'third' alternator. Here's the link for what I think is the latest manual.

https://www.rotax-owner.com/en/support-topmenu/engine-manuals#915-i-series-engines

The two generators (Generator 1 and Generator 2) are
mounted electrically isolated on one stator. Each generator is
connected with a regulator mounted on the Fusebox. The Fusebox
takes care of the energy management and allows selecting
whether the EMS is supplied by an external power source (e.g.
Battery) or one of the generators. The selection of which generator
is powering the EMS depends on the engine status and
can only be done by the Engine Control Unit (ECU).
During the engine start an external power source is needed to
power the EMS. After the engine speed is high enough to power
the EMS with the Generator 2, for running the engine the external
power source is only required in emergency situations. If a
defined engine speed threshold has been reached for a certain
time Generator 1 takes over to supply the EMS. After this, Generator
2 can be used to supply the Airframe (e.g. instrumentation).
In no operation state can Generator 1 be used to supply
the airframe.
Malfunction In case of an malfunction of Generator 1 the internal electric
supply system changes to fail-safe mode where Generator 2
again is in charge to supply the EMS. In fail-safe mode Generator
2 is not able to charge external power sources or supply the
airframe.
The EMS is not capable of supervising the power provided to
the airframe. If the EMS is powered by Generator 1 and Generator
2 fails; no indication is provided from engine side

I am not at home right now but think I have found a schematic that shows you can turn the factory alternators "off" so they don't run down the battery through the field wiring. I think part of the problem with Rotax is that they write the manuals but English isn't their primary language so some of the terminology gets confusing. If I have time here tonight I'll hunt around and see if I can find that schematic online. When I was looking at wiring for the Vertical Power I used the primary alternator to control the stock alternator system (alternators 1 and 2) and then added a line to another "external alternator" that is my third one and has its own separate external regulator. Note here that this was done while I was waiting for my kit so is all theoretical wired on paper. I haven't actually wired it in, it just looked like that was how it would work to me.

Kitfox Pilot
06-14-2021, 02:38 PM
Thanks Gary, I have that downloaded and I guess I just didn't see it cause I thought I looked through it but glad you found it for me. I would love to see how you have it laid out because wiring this plane is Greek to me and I barely speak English. Haha
I think I have most the garmin 900 page download figured out and most of the vertical power is pretty simple but the 915 part is just not clear to me. Thanks again Gary.

edit added, on the third alt your talking about adding in case the number 2 quits, I thought your battery and backup battery would keep the screen and autopilot stuff going for a while?

Geek
06-14-2021, 04:04 PM
........edit added, on the third alt your talking about adding in case the number 2 quits, I thought your battery and backup battery would keep the screen and autopilot stuff going for a while?

In theory it should. The TCW Battery Back Up says it will and the one I think Kitfox recommends is the 6amp hour so it depends on your load as to how long it keeps things going and if I remember it does have some limitations. My first cut at my loads had my system running pretty much the higher end of the 28 amp alternator if I had everything on and I am using the heated pitot tube which was a big dog in current draw (remember I haven't wired it yet and done the final system - I was and am still, working with a paper system). I don't like running electrical at the higher end of capabilities. My desire to put in the third alternator comes from my dislike of the Rotax system that can take your alternator from you on its own. Major part of my flying experience comes from flying with the Navy and my experience there was if things went South, it was at the worst time (dark and at the back end of the boat) and when you really wanted systems that the boldface checklist was telling you to shut down so my perspective is slightly biased there. I think you're right in the belief that the battery back up and battery itself will at least let you find a place to land and get a beer while you sort it all out.

I think Dustin had an issue with his electrical once but couldn't find it to reference with a quick look. Maybe he will chime in on why he too added the additional alternator. My recollection of his issue was there was a failure and he had to shut some systems down to shed the load. Again my recollection was his third alternator was his primary and the 28Amp Rotax was his backup. No big deal but with the third alternator, if the Rotax engine alternator dies and it takes the second alternator to keep that important fan working out there, I don't care other than maybe having more time to find a place with a better selection of beer.

I have most of my system drawn up. When I get home, I'll send them to you to peruse.

G

Geek
06-17-2021, 07:48 PM
.........

I have most of my system drawn up. When I get home, I'll send them to you to peruse.

G

Harlan - I got home and took a look at my 'system' again and realized that it was not quite right. I have learned stuff that I hadn't edited into the system drawings so am afraid they would mess you up more than help. I did look at the TCW Battery Back Up wiring and think that is still good so I have attached what I think I am doing. You can see the Aircraft Power 1 pins of the units are all going to the Vertical Power for control and the Aircraft Power 2 pins are where I connected the TCW. With what I have connected, the load is 4.5A. If you give the TCW credit for the advertised 6AHr rating, you'll have a little over an hour of power.

G

28274

Kitfox Pilot
06-17-2021, 08:12 PM
So I take it that the alternators don't hook to the vertical power at all in that drawing?
That will make it easier to do. I was just confused because vp asked the questions about the alternators.

Geek
06-18-2021, 05:20 AM
So I take it that the alternators don't hook to the vertical power at all in that drawing?
That will make it easier to do. I was just confused because vp asked the questions about the alternators.

Harlan I think I am making this harder for you than easier. My TCW was addressing the battery back up edit and how long you had if the Rotax alternator quit. I think Dustin was right on in that in a "normal" Rotax configuration you have no control over the alternator. Here's what it says to do in the Vertical Power guide for the Rotax (page 29 in my version of the manual).

"If you want to leave the alternator in its standard configuration where it is always on, then follow the manufacturer’s instructions. When configuring the VP-X, disable the primary alternator circuit. "

So in your pictures, it would look like this.

28275

Apologize for making it confusing. Too much electronics - to little common sense in this case.

Gary

Kitfox Pilot
06-18-2021, 05:29 AM
Ok Gary I understand now, I'm a little slow on this stuff for sure. Trying to absorb all this on a subject I don't fully understand is different for me and becomes frustrating. As I look back at several of the good builders logs, there are always lots of panel wiring questions so I guess I'm not alone. Thanks for the help.