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Showing Alternator Total Load?

Bill_H

Bill_H

Well Known Member
I am an aircraft electrical system newbie. I read the Nuckolls and Bingalis books long ago.

It seems that my E-LSA Skyview ammeter hookup is similar to the old automobile-type where the needle is normally centered between the "+" (amps going into the battery charging it) and "-" (discharge amps coming from the battery, potentially indicating a failed alternator.)

Is this correct? Most of the time I am showing 1 amp or less on that indicator in flight.

It is my understanding that there are different ways to wire this sensor circuit. Has anyone wired it to show the total load on the rotax generator (-alternator/dynamo/magnetohydrodynamic generator - whatever that thing is!)? That would be a very useful thing to know for those of us considering a second screen. Is it possible to have indications of both parameters?

One reason for my confusion is that the pre-Skyview wiring had the "cigarette lighter" plug coming directly from the battery and fused. Obviously such a connection would not show in any overall amp usage load - except maybe indirectly through a charging current change. Then when the Skyview mods came out, that power outlet connection was moved and the info from the Vans presentation about the mods was that "The power outlet consumption is now indicated by the amp meter." Hence some of my confusion!

Please correct any misunderstanding I am (embarrassingly) showing in this post!
 
This is a normal way the ammeter should show and does on most planes.

The drop resistor is indeed wired to show the differential between the actual load and generator current. If it reads + 1 amp it means the voltage regulator is doing its job and balances the load.
If you just have used the started motor it will show more charge current to compensate the consumed starter energy.

I wish mine works like that.
My skyview for some reason only shows discharge (7-9 A in flight)
I checked with an amp meter in the pos lead of the battery and it does charge.
The wiring is ok but i do not know whats inside the mystery box.
I asked VANs and Dynon about this and they both say its ok as it is, which i can hardly believe.
Its annoying i cannot see if the alternator works. I check if the voltage rises which is also a way to tell if it charges.
 
Bill,
Page 7-38 of the SkyView System Installation Guide, shows 3 possible locations for the current shunt. They a labeled A, B, and C.
You are correct that in location A, the ammeter will show battery discharge due to a failed alternator. However, this is redundant information because the voltmeter will show low voltage when the alternator quits working.
You could buy a shunt and insert it in series with the alternator output. A very small voltage is dropped across the shunt as current flows through it. Two small additional wires connect the shunt to the SkyView pins 24 & 25. The SkyView measures the millivolt signal and displays it as amps. If one of those small wires (that are connected to the shunt) shorts to ground, it will burn open. Therefore the small wires should be protected with fusible links as shown on Bob Nuckolls' drawings and in the SkyView installation manual.
Yes it is possible to install 2 or more shunts and connect them to the SkyView with a selector switch. However, doing so will add weight and complexity with more chance of something going wrong.
The SkyView installation manual also describes using a Hall Effect Current Sensor which has some advantages compared to a shunt.
Joe Gores
 
Joe

Can you confirm the standard wiring upgrade version only shows battery discharge and not the alternator current like mine.

I don't understand why it does that whilst the shunt is in position A
 
Jack,
I have the D-180 and not the SkyView. Thus, I can not confirm how the SkyView current shunt is wired.
As long as the battery is being charged and everything works OK, then there is nothing to worry about.
With the shunt in position "A", and if the SkyView ammeter shows a discharge when, in fact, the battery is being charged, then I suspect the wires have been switched going to the SkyView pins 24 & 25.
With the engine shut off and everything electrical turned on, what does the ammeter indicate?
Joe Gores
 
I suppose it is what you have become accustomed to for expectations of an amp meter, but for my Skyview installation, the shunt will go in the position A, the other two seem to not provide the information I would be looking for.
 
The ampmeter reads between -7 and - 10 depending on the equipment on line.
The reading is the same when the engine runs and thats my problem.

I like to see if the alternator works, which i now can only see by the voltage reading slowly increasing.
 
Jack,
What is the voltage when at cruise RPM? If it is 13.6 or more, then the alternator is definitely working no matter what the ammeter says. According to the copy of Van's schematic that I have, the ammeter shunt is in position "A" and will show battery charging or discharging current.
Confirm that the ammeter always shows a negative number and never changes polarity whether the engine is running or not.
Joe Gores
 
Alternator whine in Skyview installations?

I apologize in advance for this bit of thread drift. A question for those of you with the Skywiew installed. Do you have any alternator whine in your headsets? The whine in my airplane with the D-180 is annoying, and so far eludes my attempts to get rid of it.
 
Yes it is in A on my diagram, so it should read differential but it does not.
When have just started the engine the Efis reads 12 volt and amp meter - 9 Ams
After 45 min flight it reads 12.9 so i conclude it must charge.
The 9 amp never changes unless i engage another load

I guess i will fit another shunt in the battery lead and see what happens there.
I am not sure if the efis volts reading is accurate.
 
Jack,
12.9 volts is too low. Use a handheld voltmeter to verify the voltage. If the voltage really is too low, then I suspect the voltage regulator is bad.
Check all of the connections to the voltage regulator to make sure that they are tight. Also make sure that the regulator is bolted tightly to the firewall shelf and that there is no paint on the shelf under the regulator.
Read Mike Miller's post: http://www.vansairforce.com/community/showthread.php?t=80487
Consider adding Van's cooling kit to the regulator if you have not already done so. Heat will destroy the regulator.
Joe Gores
 
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Checked all the wiring and connections already. Grounding is ok and the modification kit is installed as well.


Will continue the detailed search on monday , but need to run the engine whilst measuring which is more difficult and dangerous.

Will share the results when i hve them
 
Jack, I would guess the two white, 12 gauge wires in the power plug are reversed at the fuse panel. It?s not possible to reverse the wires under the cowl, one wire is two short.

You can confirm this by;
1) with the engine OFF (see warning below)
2) removing the 30 Amp fuse
3) see if any electrical device works

If nothing works the power plug is mis-wired.

Warning: do not start or run the engine with the 30 Amp fuse removed, if the Power Plug is reversed, the 22,000uf cap is not in the circuit and you WILL damage the regulator and most of your avionics.

On the up side, you have an answer to Bill H?s question, 7-10 Amps for a Skyview RV-12 with your installed options.

Mike
 
Good going Mike Miller. Your hypothesis explains the always negative amp reading that varies with the load.
The low voltage could be due to instrument error.
Joe Gores
 
Thank you Joe, actually low voltage on the Dynon display fits the theory. With reversed power plug wires, the Dynon voltage sense input is after the shunt. The displayed voltage will be offset by the IR drop across the shunt. So, as the alternator output (Amps) goes up, the IR drop across the shunt goes up, and the displayed voltage goes down by that amount.

Mike
 
Mike,
The shunt will account for part of the low voltage. Most shunts are designed to drop less than 0.1 volt. 50mv is common. But I do not know what voltage the RV-12 shunt drops.
According to Dynon forums, the shunt should drop 1mV per amp. 10amps through the shunt should drop 0.010 volts.
Joe Gores
 
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It took a long time but i found the problem*!!!

The yellow enable wire of the voltage regulator was intermittend 12 and 0 volts with the master switch on.*

It appears to be a bad master switch. This has two contacts : one for control of the master relay and the other for enabling 12 volts to the voltage regulator.*
I jumpered the enable contact and everything works fine. Engine off -7 amps at 12 volt; engine running + 2 or 3 amps and voltage increasing to 13.8 v which seems normal.*

I removed the switch from the panel and one of the two contacts fails 4 out of 5 times.*

I asked Van's send me a new master panel switch

I also verified the accuracy of the voltage and amp readings with an handheld Fluke and shunt in the battery lead. Both are quite accurate.

Quite a relief.

Thanks for your support and ideas
 
Good going Jack,
Intermittent problems can be hard to troubleshoot because test measurements are based on constantly changing conditions that the technician is unaware of.
Joe Gores
 
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