Tecnam Sierra Overvoltage

[kiwiaviator]

Our club had a new Sierra delivered at the beginning of the year. It was noted that the voltmeter reads anywhere between 14 and 14.9 v and varies a lot in this range even at a constant rpm. We checked the bus voltage with two different multimeters and the voltmeter seems to be indicating correctly. It was delivered with a lithium ion battery with does have a higher max voltage. Regulator was changed out on advice from Tecnam agents. This did not fix the problem. Aircraft went back to the NZ agents to have some warranty issues sorted including this problem. The agents changed the battery to a sealed lead acid. No change. They then isolated the aircraft electrical system and ran just the alternator, regulator and battery as a separate circuit. Voltage was normal (13.8v). They then contacted Tecnam and were told that they were aware of the issue and it was happening with all new aircraft off the assembly line. Tecnam indicated that they will release a directive re the issue shortly. I just want to see if anyone else has seen this issue with new Tecnams?

 

 

[Nobody]

Have a read here. I think this has been an commonish issue with a number of 912 instalations if there is a poor connection to the regulator.

 

 

[kiwiaviator]

OK. Have an answer from Tecnam. They have added a resistor to the resistor voltage sense line to up the charge voltage due to the lithium ion batteries higher nominal voltage. So it is apparently normal although I hope it does not have downstream effects on our avionics etc

 

 

[kiwiaviator]

I meant regulator voltage sense.

 

 

[facthunter]

I would imagine that it could damage equipment that is voltage sensitive. A lead acid goes to about 14.2 and tends to damp out voltage fluctuations, when connected with heavy wires (low resistance).

 

PS In the charge circuit. Nev

 

 

[kiwiaviator]

Thanks Nev. I don't think I will leave it there. Next step will be to check voltage parameters for avionics and instruments.

 

 

[facthunter]

I'm no expert. There are devices around that limit voltage, I believe. Nev

 

 

[Downunder]

Perhaps they should have used a different regulator? (I take it, it's the standard rotax).

 

I can't see a normal rotax regulator lasting a particularly long time with a "bumped up" voltage operating outside the design limits.

 

Then again, Tecnam might have done their homework, and it's all good.

 

The standard regulator can struggle to disperse heat at times.

 

Max operating temp 80 degrees C.

 

 

[Montymagic]

I thought lithium ion batteries were not safe for aircraft use or at least not recommended. I read it in the raa magazine a while back.

 

 

[Nobody]

I thought lithium ion batteries were not safe for aircraft use or at least not recommended. I read it in the raa magazine a while back.

This topic has been discussed before here:

http://www.recreationalflying.com/threads/the-real-dangers-of-lithium-ion-batteries.125732/

 

The key issue is that not all lithium eateries are the same and some would likely be acceptable while others not.

 

 

[kiwiaviator]

Just clarifying that our battery is a lithium iron phosphate not lithium ion polymer. Apologies for the previous misinformation and thanks for all the good info/discussion on this.

 

 

[cavalon48]

Your rectifier has 2 x positives, 1 x goes to your ignition and the other to your battery. You may need to connect a 25mp capacitor to discharge the excess current generated or matter of time the rectifier will fail, it happened to me.

 

 

[kiwiaviator]

We have received a Release to Service from the Tecnam agents. Summary from the LAME below:

 

Information supplied by Tecnam Australasia. I spoke to the assembly line technicians and engineers with electro-avionics on the issue of overload voltage, referring to them the type of battery (ALIANT ultralight lithium iron battery) mounted on the Sierra in question. I replied that, in fact there is no problem for the airworthiness of the aircraft because with this type of battery, the voltage of 14.9 volts is normal for its operation(in this respect, it is considered overchanging only when the battery voltage exceeds 15 volts) It is the same case for the Astore. Therefore,the fact that the voltmeter reads that value is normal, as per design of the electrical system. The high value of voltage detected is due to the presence of a resistance in series on the point C of the regulator. This resistance has been inserted to allow the battery to fully charge during the flight and then allow the client to be able to restart the engine while the aircraft has not been operating for a long time. Nothing prevents, however, to take away the resistance bypassing it. Obviously this will lengthen the charging time of the battery. In a nutshell (considering for example a flight that lasts 1h) - With the resistance - battery charges faster - Without resistance battery will charge less, with the possibility that the battery can not ensure the necessary current for future engine ignition.

 

 

[kiwiaviator]

Your rectifier has 2 x positives, 1 x goes to your ignition and the other to your battery. You may need to connect a 25mp capacitor to discharge the excess current generated or matter of time the rectifier will fail, it happened to me.

Hoping it wasn't the ignition rectifier?

 

 

[Downunder]

Your rectifier has 2 x positives, 1 x goes to your ignition and the other to your battery. You may need to connect a 25mp capacitor to discharge the excess current generated or matter of time the rectifier will fail, it happened to me.

The regulator disperses extra capacity as heat, not the capacitor.

 

The capacitor smoothes out the voltage spikes coming from the generator to the regulator I believe, protecting the regulator.

 

A failed capacitor is much cheaper to replace than a regulator.

 

The Rotax 25v capacitor is very marginal. Most "in the know" use a 40v one as spikes from the generator can be well over 25v.

 

I have had a 25v capacitor fail and replaced this with a 40v one.

 

Thanks to those on this forum for their advice on that matter.......

 

 

[cavalon48]

The regulator disperses extra capacity as heat, not the capacitor.The capacitor smoothes out the voltage spikes coming from the generator to the regulator I believe, protecting the regulator.

A failed capacitor is much cheaper to replace than a regulator.

 

The Rotax 25v capacitor is very marginal. Most "in the know" use a 40v one as spikes from the generator can be well over 25v.

 

I have had a 25v capacitor fail and replaced this with a 40v one.

 

Thanks to those on this forum for their advice on that matter.......

The regulator/rectifier has a series of diodes and resistors (hence called a voltage converter) where does the extra current go if the capacitor does not take up the load and discharge the excess!! If you do not have a capacitor connected to second positive (lead heading to the battery) the rectifier will heat up until one day you will end up with an open circuit. If no capacitor connected to `G`positive and say you have a loose ignition connection or you inadvertently turn `C` positive which is your ignition before shutting the mags you will cook the regulator in about 2-3 attempts.

 

 

[Downunder]

[MAP][/MAP]There are people here better able to explain it than me but I believe what I've said to be correct.

 

The capacitor is a recomended option by Rotax. Some people do not fit it.

 

http://pointsforpilots.blogspot.com.au/2012/12/testing-rotax-912914-generator-and.html

 

 

[cavalon48]

[MAP][/MAP]There are people here better able to explain it than me but I believe what I've said to be correct.The capacitor is a recomended option by Rotax. Some people do not fit it.

http://pointsforpilots.blogspot.com.au/2012/12/testing-rotax-912914-generator-and.html

Here is the rectifier connection drawings i received from Bert Flood when doing my wiring, if the 22mf 25v capacitor was an option why is it on the drawing, and why was i told that it must be added.

rotax_capacitorconnection_drawing313.pdf

 

rotax_capacitorconnection_drawing313.pdf

 

rotax_capacitorconnection_drawing313.pdf