Current varies a lot

[ultralight]

Dear Sirs,

We have found following problem during installation and test flight of our LSA airplane:

When engine is running constant RPMs, the current displayed on Dynon D120 display is not constant and it varies very quicky and rapidly between 1 - 5 A when use your originally supplied ammeter shunt.

When we use our external measuring gauge instead of reading from EMS D120, the measured current is more or less constant (it varies in tenths of Ampers). What can cause this problem?

Thank you.

 

[dynonsupport]

Where are you reading your current in the system? The D120 install manual shows 3 possible places to install the shunt. Are you sure you're using the multimeter in the same place?

The D120 reads current instantaneously, while many multi meters average over time. It could be that something like the transponder is drawing current in bursts and you don't see that on something that averages.

Try turning different equipment on and off and see if you can find what equipment is drawing power in bursts.

 

[ultralight]

We are following the Installation manual EMS-D120, Rev. B, 10/4/2006. Thanks for explanation how D120 reads the current. It is used the position "A" from page 2.11 - Ammeter Shunt, our measurements with the external multi-meters were done in the same position. The settings on Dynon D120, learned from page 4.12 is "Current -> Type -> -60 A to +60 A". All the instruments are off (currently, there is no even radio, transponder, GPS installed, just both D100 and D120).

• If the engine is off, the Current readings are OK.

• If the engine is on, the Current readings are oscillating, the values moves from +1 to +10 A (!). On basis of the standard known recommendation from Rotax company, we have installed the noise suppression capacitor 22000microF (25V) and it makes the readings better, but still not good. Now it oscillates from +1 to +5 A.

(For the place of installation the capacitor pls. see official Rotax 912 ULS engine installation manual)

Do you think that it can help to shield the cables as specified in D120 installation manual, page 2.11, table - PIN 24 (Amps HIGH) and PIN 25 (Amps LOW)??

We have checked almost everything, but this remains for us still mystery.

 

[dynonsupport]

Shielding probably wouldn't help. We've heard isolated reports of the generators on some Rotax engines having really noisy power, but unfortunately, we don't have any other ideas either.

 

[alan_milner]

Hi

Did you find a solution or explanation to this?  I have a Rotax 912S and am using the Dynon shunt to read current at position A.  The installation is big standard with the capacitor at the usual location off the regulator.

I get readings fluctuating up to about 10 amps over 3 seconds or so.  Only the EMS D10 is powered up.  Just incase it was a poor earth bolt off the regulator I remade this, but on remoavl it seemed tight enough still.  I plugged a laptop in and have 15 mins or so of logs if it's any use, see a small snippit below.

Alan

time	fraction/64	amps
00:01:52	00	-5
00:01:52	16	-7
00:01:52	32	-8
00:01:52	48	-7
00:01:53	00	-6
00:01:53	16	-5
00:01:53	32	-5
00:01:53	48	-5
00:01:54	00	-5
00:01:54	16	-6
00:01:54	32	-8
00:01:54	48	-6
00:01:55	00	-5
00:01:55	16	-4
00:01:55	32	-4
00:01:55	48	-4
00:01:56	00	-3
00:01:56	16	-3
00:01:56	32	-3
00:01:56	48	-4
00:01:57	00	-6
00:01:57	16	-8
00:01:57	32	-8
00:01:57	48	-9
00:01:58	00	-7
00:01:58	16	-8
00:01:58	32	-9
00:01:58	48	-10
00:01:59	00	-11
00:01:59	16	-11
00:01:59	32	-11
00:01:59	48	-9
00:02:00	00	-9
00:02:00	16	-9
00:02:00	32	-9
00:02:00	48	-9
00:02:01	00	-9
00:02:01	16	-8
00:02:01	32	-8
00:02:01	48	-7
00:02:02	00	-8
00:02:02	16	-7
00:02:02	32	-6
00:02:02	48	-6
00:02:03	00	-8
00:02:03	16	-7
00:02:03	32	-6
00:02:03	48	-5
00:02:04	00	-6
00:02:04	16	-6
00:02:04	32	-8
00:02:04	48	-7
00:02:05	00	-6
00:02:05	16	-5
00:02:05	32	-6
00:02:05	48	-9
00:02:06	00	-8
00:02:06	16	-9
00:02:06	32	-8
00:02:06	48	-7
00:02:07	00	-7
00:02:07	16	-7
00:02:07	32	-9
00:02:07	48	-10
00:02:08	00	-11
00:02:08	16	-11
00:02:08	32	-11
00:02:08	48	-11
00:02:09	00	-9
00:02:09	16	-11
00:02:09	32	-10
00:02:09	48	-10
00:02:10	00	-8
00:02:10	16	-9
00:02:10	32	-9
00:02:10	48	-8
00:02:11	00	-9
00:02:11	16	-9
00:02:11	32	-10
00:02:11	48	-10
00:02:12	00	-8
00:02:12	16	-9
00:02:12	32	-8
00:02:12	48	-9
00:02:13	00	-9
00:02:13	16	-9
00:02:13	32	-8
00:02:13	48	-7
00:02:14	00	-9
00:02:14	16	-9
00:02:14	32	-10
00:02:14	48	-9
00:02:15	00	-8
00:02:15	16	-7
00:02:15	32	-5
00:02:15	48	-7
00:02:16	00	-7
00:02:16	16	-7
00:02:16	32	-7
00:02:16	48	-5
00:02:17	00	-5
00:02:17	16	-5
00:02:17	32	-7
00:02:17	48	-6
00:02:18	00	-5
00:02:18	16	-5
00:02:18	32	-7
00:02:18	48	-6
00:02:19	00	-8
00:02:19	16	-9
00:02:19	32	-10
00:02:19	48	-9
00:02:20	00	-11
00:02:20	48	-9
00:02:21	00	-10
00:02:21	16	-11
00:02:21	32	-10
00:02:21	48	-10
00:02:22	00	-9
00:02:22	16	-8
00:02:22	32	-10
00:02:22	48	-8
00:02:23	00	-7
00:02:23	16	-6
00:02:23	32	-5
00:02:23	48	-4
00:02:24	00	-4
00:02:24	16	-4
00:02:24	32	-4
00:02:24	48	-5
00:02:25	00	-8
00:02:25	16	-8
00:02:25	32	-7
00:02:25	48	-7
00:02:26	00	-6
00:02:26	16	-5
00:02:26	32	-7
00:02:26	48	-7
00:02:27	00	-6
00:02:27	16	-5
00:02:27	32	-5
00:02:27	48	-7
00:02:28	00	-6
00:02:28	16	-7
00:02:28	32	-9
00:02:28	48	-9
00:02:29	00	-9
00:02:29	16	-7
00:02:29	32	-8
00:02:29	48	-9
00:02:30	00	-10
00:02:30	16	-8
00:02:30	32	-8
00:02:30	48	-9
00:02:31	00	-11
00:02:31	16	-9
00:02:31	32	-8
00:02:31	48	-8
00:02:32	00	-8
00:02:32	16	-7
00:02:32	32	-7
00:02:32	48	-9
00:02:33	00	-8
00:02:33	16	-10

 

[opticsguy]

I have the same problem on my CT. Current jumps everywhere and reads from 0 to -10A! even when the battery is charging. I've checked the shunt connection several times. Perhaps some sort of electric field is interfering with the D120.

My Ammeter is useless and it will be a problem if I want to sell my plane. My Flight Design dealer has had an their electrical guy down here and he can't find anything wrong either.

 

[PilotKris]

I am having the same problem with the D180 installed in my Sky Arrow (912ULS) except the current fluctuates to impossible levels (like 30 amps). The shunt is installed on the alternator output.

I am also experiencing similar fluctuations in the oil temp and CHT of about 10+- degrees.

The fluctuations stop when I turn off the alternator but do not when I pull the alternator c/b (located down-stream of the shunt).

I too put a multimeter across the shunt and got believable readings (about 8-9mv) and no excessive fluctuations.

I initially thought it might be a bad ground on the D180 but I installed a 12g wire directly from the battery to the case of the D180 and it made no difference.

I was going to beat up the A/C manufacture but, since others are having the same problem, I now think it is a problem with the Dynon.

Any sugestions?

 

[PilotKris]

Seriously!
I'm Stumped.
Any Sugestions?

 

[PilotKris]

Update.

I put an oscilloscope across the shunt last night. It was still reading in the 8-9mv range with some noise (looks like a little AC ripple) but not much. The D180 ammeter was jumping all over the place (+-10A) and the oil temp was jumping +-10 degrees as well.

When a pulled the main Alt breaker (located downstream of the shunt) the oscilloscope went to 0 (<1mv) with pretty much no noise. However, the D180 ammeter was still jumping and went as high as 90+A (an impossible level) as was the oil temp.

When I turned off the alternator, the ammeter eventually went to 0 and the oil temp stopped bouncing around.

In situations like this the first place I look is the ground. However, I believe that the engine has a good ground as the starter turns over very easily (and it's a brand new airplane). As I stated in an earlier post, I grounded the D180 case directly to the battery with a 12g wire.

I'm stumped.

Could there be something wrong with the D180?

One last diagnostic I can try is to see if the problem is coming over the D180 power. I'll pull the D180's c/b (and run on the internal battery) and see if that has any effect.

 

[dynonsupport]

The Dynon EMS systems must have at least 6V common mode voltage on the shunt to work properly. When you pull the breaker, you're probably sending the shunt to 0V, so you will get weird readings. This is expected. You really should install the shunt so that it always sees battery voltage, no matter what breakers have popped.

I'd still look at the ground. We've had plenty of new airplanes that start easily, but have 20-50 mV of drop between the engine and the EMS ground path under normal loads (10-20A). This is much more common in compositie aircraft, but we've seen it on all types. This almost always shows up as unstable oil temp since it's the most sensitive sender to voltage fluctuations. Try hooking a scope or sensitive voltmeter between the case of the engine and the case of the EMS while the alternator is putting out some current. If you're seeing more than 10mV of drop here, a better ground would help.

The ground that really matters is the case of the engine to the negative battery terminal. Make sure this ground path is of sufficiently large gauge, and is free of paint or anything else that could insulate it.