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Alt Light Flickers

 
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h&jeuropa



Joined: 07 Nov 2006
Posts: 634

PostPosted: Fri Apr 27, 2018 8:01 am    Post subject: Alt Light Flickers Reply with quote

The alt light (it’s a LED, not incandescent) on my Rotax 914 (over 900 hours) has started to flicker even when at cruise (5000 rpm). It has often flickered when at low rpm and it always turns full on when the engine is not running. I have two Hall amp sensors but I can only display one at a time. At cruise, the amps being delivered by the Rotax system are about 8 to 10 which I what I expect given the loads turned on. At cruise the amps measured at the battery are roughly 0, the indication will vary a little from +1 or 2 to – 1 or 2 which I take to be instrument error. The bus voltage is around 13.3 prior to engine start. After start it slowly climbs to about 14.4 after 20-30 minutes of cruise.

The aircraft is wired in accordance with AeroElectric Z-16. The battery is an EarthX ETX680 and its monitoring circuit does not show any problem. I switched from lead acid to EarthX ETX36 in 2014 and in March 2017 changed to ETX 680C. I’ve only had this problem recently. Everything was normal at first after installing the ETX680C.

In 2014 I added external diodes to supplement the original Ducatti (PN 343620) regulator/rectifier and a few months later I replaced that Ducatti R/R as the alt light was illuminating while operation seemed normal. The replacement was the later model Ducatti (PN 362001) but I left the diodes in place.

I discovered (I think during 2017) that the Rotax system was not delivering a high enough voltage to keep the EarthX fully charged. I added a diode in series in the C lead to boost the voltage. While troubleshooting the charging problem I changed back to the original Ducatti which has operated fine until the recent flickering issue.

I can’t decide if I have a battery problem or a Rotax/Ducatti problem.

Jim Butcher
Europa XS


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gregoryf.flyboy(at)comcas
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PostPosted: Fri Apr 27, 2018 11:27 am    Post subject: Alt Light Flickers Reply with quote

Hello Jim,

I too, am using an LED in substitution of an incandascent light. I don't ever remember it flickering while the engine is running.
I assume that your hall sensor reading the batt current will have a significant reading right after starting the aircraft(while its chargine), before it settles down to zero in cruise? ...just to verify its working somewhat..
According to a description in a regulator manual I have,
'The light should come on only when the system is not charging or is discharging the battery'.

The battery charging voltage in cruise is 14.4, so it appears to be at a healthy charging voltage. In other words, its not discharging.

Since the alternator/Ducati are producing power for your accessories, I'll take that to mean the system is 'charging' to use the term in the first sentence.

Unless there is a short-term voltage dropout caused by a shorted coil or magnet broken loose (could be found by a scope) or a wiring/connection issue, it seems the regulator has a higher chance of being the culprit, IMO.

Just out of curiosity...it seems your original Ducati had the same issues, and that is why you replaced it, before re-installing it later. Could it be that the original Ducati's twerking is coming back around to roost? Maybe throw the newer regulator back on and see what happens?

Greg

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gregoryf.flyboy(at)comcas
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PostPosted: Sat Apr 28, 2018 7:58 am    Post subject: Alt Light Flickers Reply with quote

Here's a Lockwood article that has some info about the regulator light
operation and hookups..


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h&jeuropa



Joined: 07 Nov 2006
Posts: 634

PostPosted: Sun Apr 29, 2018 6:50 am    Post subject: Re: Alt Light Flickers Reply with quote

Greg,

Thanks for the article. It contains about the only description of the operation of the ALT light I've seen.

I think my Ducatti is operating correctly given the voltage and amps perform as expected which leads me to think the problem is using a LED instead of a incandescent lamp. The light circuit uses a MOSFET acting as a switch. I don't know much about MOSFETs, but if it allows (leaks) even a little current to flow, the LED may try to illuminate. Rotax and Lockwood specify a 3 watt 12 volt lamp. That will require substantial current (.25 amp) to illuminate.

I found an article on Aero Electric and a drawing from Perihelion Design that address using a LED as a replacement for a incandescent lamp. Both advocate adding a 100 to 150 ohm resister in parallel with the LED. That will "drain" any "leakage" from the MOSFET.

I hope to install such a resistor in the next few days and will report the results.

Thanks for the help.

Jim


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h&jeuropa



Joined: 07 Nov 2006
Posts: 634

PostPosted: Sun Apr 29, 2018 7:04 am    Post subject: Re: Alt Light Flickers Reply with quote

Greg,

Thanks for the article. It contains about the only description of the operation of the ALT light I've seen.

I think my Ducatti is operating correctly given the voltage and amps perform as expected which leads me to think the problem is using a LED instead of a incandescent lamp. The light circuit uses a MOSFET acting as a switch. I don't know much about MOSFETs, but if it allows (leaks) even a little current to flow, the LED may try to illuminate. Rotax and Lockwood specify a 3 watt 12 volt lamp. That will require substantial current (.25 amp) to illuminate.

I found an article on Aero Electric and a drawing from Perihelion Design that address using a LED as a replacement for a incandescent lamp. Both advocate adding a 100 to 150 ohm resister in parallel with the LED. That will "drain" any "leakage" from the MOSFET.

I hope to install such a resistor in the next few days and will report the results.

Thanks for the help.

Jim


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h&jeuropa



Joined: 07 Nov 2006
Posts: 634

PostPosted: Sat Jun 02, 2018 11:49 am    Post subject: Re: Alt Light Flickers Reply with quote

The problem has been solved by replacing the LED with a 1 1/2 watt incandescent lamp. The install manual calls for 3 watt but that’s not available in the size / style I need.

I tried the resistor idea and the LED was on all the time.

Jim Butcher


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