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Charging system & Dynon questions


John Vance

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I'd like to make sure that I'm correctly interpreting the electrical current reading / warnings on the Dynon EMS in my CT.

 

1) From the electrical schematic, it looks like the Dynon is wired to indicate a negative current when the battery is being charged (the battery side of the shunt is wired to the high side of the D120 ammeter). Is that correct?

2) What is a normal value for electrical current? The indication I get during cruising flight when starting with a fully charged battery (using CTEK charger) bounces between (roughy) -4 and -11 amps with all the equipment running. That seems high to me, and is mostly in "yelllow" territory on the screen.

3) Could the following scenario have been caused by low battery charge state?: A couple of weeks ago, I got a "low current" warning on the D120, during climb-out for what was supposed to be a longish cross-country flight. Ground idle time before takeoff was prolonged due to other traffic. After takeoff, the current flirted with the low limit for awhile, then pegged out at -31 amps and stayed there. It took about 15 minutes to return to the airport, and during that time, the D120 showed the voltage at 13.1. After landing, with engine at idle, voltage dropped to 12.1. I have not, until yesterday, used a battery charger, so the battery was not fully charged before this flight.

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I have been having the same problem for about 6 months. First thing Dynon said to do was install a larger capacitor. That seemed to help for a while but then more alarms. The latest thing they said to do was tighten all the grounds. That took care of the problem for less than a week and they are back again. I will be calling Dynon again for further instructions.

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I am assuming a carb version for this post.

 

Positive is being charged. Negative is being discharged. That's standard in aviation and includes CTs, if done properly.

 

If yours is backwards, flip the two connections at the ammeter shunt mounted on the inside of the firewall. It looks like a copper bar.

 

If you have the little capacitor that FD shipped their airplanes with, your ammeter is absolutely useless. The electrical noise that is output by the generator screws with it. Don't even look at it before changing the capacitor.

 

If you do have a larger cap: 4-11 amps in flight sounds more like your system is wired into the regulator output, rather into the battery loop. Does flipping on and off different systems change that?

 

These aircraft do not have very powerful magneto-generators. Around 2500-3000 RPM is when they reach full output. Idle barely generates anything. If you have a prolonged wait, shut down power hungry systems or it will drain your battery.

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Thanks, Corey. It's a 2010 LS, carbureted. I did find the shunt but can't find the capacitor. Is 22,000 mkF the correct size, or something larger? At next opportunity, I'll see if I can verify that the shunt is wired between the battery and the gen breaker, as the schematic shows. The ammeter bounces like crazy so maybe the cap is the problem.

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I have been having the same problem for about 6 months. First thing Dynon said to do was install a larger capacitor. That seemed to help for a while but then more alarms. The latest thing they said to do was tighten all the grounds. That took care of the problem for less than a week and they are back again. I will be calling Dynon again for further instructions.

Definitely interested if anything comes out of your call to Dynon.

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The capacitor is in the engine compartment on the battery side. Up high right behind the upper square engine mount. It is held on by wire ties. Be careful moving it around as you can easily break the contacts off the capacitor. 22,000 mkf is the correct minimum size. Rotax only designates this as minimum, and larger  would be better, but this is adequate. the new 912iS engine has two 33,000.

 

p.s.

If you disconnect it remember when you hook it back up it is polarity sensitive. The straipped line down one side is negative.

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Thanks Tom & Roger. I'm pretty ignorant about electrical things but thought I might test the capacitor to see if it's shorted internally. Will I fry my multimeter if I try to test resistance across the contacts? Also if you have suggestions for replacement parts and sources, that would be very helpful.

 

Thanks

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Flew a 2-hour round trip to a BBQ restaurant in SC today starting with fully charged battery, and had no problems. Voltage stayed around 13.5 or so, and current bounced but was in the green for the most part. Not sure what's going on but maybe I just need to start with a charged batt.

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Yes, Pik-n-Pig is one of our go-to places for a nice flight, good food, and airplane watching. We went to Stanton's because my wife had not been there yet, plus ther's that grass runway! We may be up for BBQ again by the 21st. Will let you know if we decide to go that day.

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If you install the 100k capacitor that chanik on this forum installed on his, it will reduce that ammeter bounce to almost nothing and also nearly eliminate all electrical noise in a properly functioning system.

 

Kemet ALS40A104KF025

 

Mouser: http://www.mouser.com/ProductDetail/Kemet/ALS40A104KF025/?qs=Ces2wY188b349PJKsEMT0w%3D%3D

 

This thing is like a small soda can.

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Then something else in your system is still wrong. I've done it to 4 aircraft and they work beautifully, and dynon makes it part of their protocol now to recommend it to people because of how well it has worked for their tech support as well.

 

That's why I said in a properly functioning system!

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A voltmeter across a working capacitor with DC applied will show system bus once charged. When a capacitor is charged, it acts like an open in the circuit, and therefore, in a CT, will be the same as placing the leads across the battery terminals.

 

An internally shorted capacitor on the other hand, will likely be popped long before you get to it. If it's not already popped, your system bus will show a low voltage and heavy amp load anyways.

 

The purpose of the capacitor is to supplement the battery in smoothing out the rectified voltage from the magneto generator. The generator does not output a smooth flat line; it is quite irregular. NO rotating electrical generation device outputs a flat line. So what the capacitor does, is take a rapidly swinging voltage and averages it out (the battery does most of it, but the electronics are sensitive enough that we need supplemental). The bigger the cap, the flatter the bus excitation fluctuations.

 

The purpose of this test is to make sure that the capacitor is receiving power at the terminals. There is one more test we can do to roughly verify the capacitor is functioning, but it requires disconnecting it, and I want to verify you are getting power there in the first place. It's likely not the capacitor that is the problem since you said you replaced it and the issue came back a week later, but probably something just upstream of it.

 

That said, you probably wouldn't have any harm in disconnecting grounds, cleaning the terminals up real well, coating them in a quality dielectric grease, and clamping them back down. The purpose of the dielectric is to protect against corrosion without running the risk of shorting. Dow Corning 4 is my preferred grease because its jelly like but extremely fluid, it moves out of the way with ease, something that you want when clamping contacts back down so they get metal to metal.

 

Do NOT use dielectric on electronic communication lines, especially those related to radios and transponders, as these are highly sensitive to capacitance. It WILL alter the signals, sometimes significantly. Dielectric changes the capacitance of the connection. Only use it on POWER connections, where the tiny capacitance changes don't matter in the grand scheme of things.

 

Doug: It's AC that won't show a potential on a cap (if the cap is big enough and the period fast enough), because the average of the sine wave is 0 (no potential). Badly shorted caps will also show no voltage, but by the time you get to one, it will have popped, or there will be other symptoms.

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  • 4 months later...

I have also been having the Hi Currant Alarm on 2006 CTSW. I Installed 100,000 mkf. Capacitor, New Battery and checked all connectors to no avail. So here is the low down, the problem also occurred with Engine off and Avionics On. I tapped the screen with finger and Amps returned to correct readings with various connected loads, verified with AmpMeter. This I replicated many times. I removed the D120, cleaned rear connector blocks. This tells me the problem lies in the D120 itself. I started doing the Annual inspection and will post flight results next week. I will be specific with my report in order that it may be helpful to my fellow Pilots

Thanks 

Oliver

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  • 4 weeks later...

I found three 1 amp fuses behind EFIS on the electric Shunt. One had a cracked glass. Replaced and Rewired big new Capacitor.

I then went flying and bingo no Alarms. So now ATC does not see my Altitude. I guess that will be a visit to the Avionics Shop.

Regards

keep the blue side up

 

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