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Understanding generator / alternator disconnect requirement

 
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kenryan



Joined: 20 Oct 2009
Posts: 426
PostPosted: Thu Nov 13, 2014 12:44 pm    Post subject: Understanding generator / alternator disconnect requirement Reply with quote
Thanks Jim, definitely helpful. Do you have any experience with the hall effect current sensor available from GRT? Are they accurate? I will be monitoring bus voltages but that's not going to allow me to monitor both alternators and am thinking the hall effect sensors might be best bet.

Agree about rotax-owner.com being superb. I am a paid subscriber.
Ken


On Thu, Nov 13, 2014 at 10:31 AM, h&amp;jeuropa <butcher43(at)att.net (butcher43(at)att.net)> wrote:
[quote]--> RotaxEngines-List message posted by: "h&amp;jeuropa" <butcher43(at)att.net (butcher43(at)att.net)>

Hi Ken

Welcome to the Rotax forum.  The other really good places to get Rotax information are Rotax-Owner.com (Rob is very knowledgeable on 914) and of course the factory website, Rotax-aircraft-engines.com.

I'll try to help you with your questions.

Relay 58 is not included with the engine.  You can get suitable relays from B&C Specialty or Stein Avionics or many other places.

The external alternator is a conventional automotive style alternator and really doesn't need to disconnected.  However, circuit breakers 43 and 45  will disconnect it and many prefer to start their engine with the alternator off line.

Indicator lights 36 illuminate when their respective alternator is not operating.  Funny I hadn't noticed they both have the same number 36!

In an experimental aircraft you can do whatever you like.  Probably you have other means of indicating the operation of the alternators such as voltmeters and or ammeters.  But the lights don't add weight and do give you indication of what is happening.

Yes, you can use LEDs.  Be sure they have current limiting resistors.  In both cases, the L lead is where the negative lead of the LED connects.  I have a LED on my 914 (no external alternator).

Others should answer about the external alternator, but I believe it is internally regulated which means the IG wire is used to sense system voltage which in turn is used by the regulator to control the alternator.  I could be mistaken in this so check with others.

The regulator 13 has proven to be temperature sensitive.  Be sure you provide cooling air to it, mount it on a metal surface if possible and put a temperature indicating strip on it to be sure it stays below 80C.  You should have the same strips on the ignition modules. I also drilled a small hole in the fin and connected the ground wire there rather than using one of the mounting bolts to get a more secure physical connection.

Using LED lighting for position and strobes, you may not need the external alternator.  In my Europa I have 914, two screen EFIS, GNS430 nav-com-gps, transponder, audio panel , xm weather and AeroLED lights.  In cruise the built in alternator puts out less than 10 amps.

AeroElectric Connection has a pretty good electrical system design, Z-16 for a Rotax.

Hope this is helpful.

Jim Butcher




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h&jeuropa



Joined: 07 Nov 2006
Posts: 645
PostPosted: Thu Nov 13, 2014 1:25 pm    Post subject: Re: Understanding generator / alternator disconnect require Reply with quote
Ken,

Yes Hall Effect current sensors are accurate and easy to install. I actually have two, one on the output of the alternator and one on the positive lead of the battery to monitor system performance. I use a switch to select which one is the input to my EIS.

You can use the 50 amp sensor and run the wire thru twice to make it a 25 amp sensor.

Also be aware that the bus voltage may not be what it says. If you have a GRT EIS, the voltage the EIS measures is it's input and is accurate. If it is being fed from a E Buss, there probably is a diode in the circuit which drops the voltage. Just compare what EIS reports and a voltmeter on your battery to see the difference. If you have a multiple input EFIS, there are probably diodes in it too. Again, compare to a voltmeter. Mine drop about .4 volts.

BTW, just click "reply to post" to keep all the posts in one thread. Makes it easier when you look for this again in 5 years!!

Jim Butcher

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kenryan



Joined: 20 Oct 2009
Posts: 426
PostPosted: Thu Nov 13, 2014 2:27 pm    Post subject: Understanding generator / alternator disconnect requirement Reply with quote
You completely lost me when you say to run the wire twice through the 50 amp to make it a 25 amp.

Also, I do not see any link that says "Reply to Post" so I guess I'll just have to use the "Reply" button.
Ken


On Thu, Nov 13, 2014 at 12:25 PM, h&amp;jeuropa <butcher43(at)att.net (butcher43(at)att.net)> wrote:
[quote]--> RotaxEngines-List message posted by: "h&amp;jeuropa" <butcher43(at)att.net (butcher43(at)att.net)>

Ken,

Yes Hall Effect current sensors are accurate and easy to install.  I actually have two, one on the output of the alternator and one on the positive lead of the battery to monitor system performance.  I use a switch to select which one is the input to my EIS.

You can use the 50 amp sensor and run the wire thru twice to make it a 25 amp sensor.

Also be aware that the bus voltage may not be what it says.  If you have a GRT EIS, the voltage the EIS measures is it's input and is accurate.  If it is being fed from a E Buss, there probably is a diode in the circuit which drops the voltage.  Just compare what EIS reports and a voltmeter on your battery to see the difference.  If you  have a multiple input EFIS, there are probably diodes in it too.  Again, compare to a voltmeter.  Mine drop about .4 volts.

BTW, just click "reply to post" to keep all the posts in one thread.  Makes it easier when you look for this again in 5 years!!

Jim Butcher




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h&jeuropa



Joined: 07 Nov 2006
Posts: 645
PostPosted: Thu Nov 13, 2014 3:17 pm    Post subject: Re: Understanding generator / alternator disconnect require Reply with quote
Ken,

As you did this time, just hit Post Reply.

A Hall Effect sensor measures the magnetic field generated when current passes thru a wire. More current, stronger field. Notice that the sensor looks like a doughnut. It is the amount or strength of the magnetic field within the doughnut that is measured and is proportional to the current in the wire.

The sensor outputs a voltage proportional to the amps. The amp rating of the sensor is how many amps are required for the sensor to output it's maximum voltage. If you put 75 amps thru a 50 amp sensor, it wont be damaged but it will not output a voltage that corresponds to 75 amps.

So if you run the wire thru the doughnut twice, there is twice the field inside. The sensor says there is X amps. But since X is generated by the wire thru twice, the wire is actually carrying X\2 amps.

So a 50 amp sensor can be a 25 / 16.6 / 12.5 etc sensor. You might want to do this to get better resolution. Say you have a 50 amp sensor. That means it will output it's max voltage (5 volts for ones like the GRT) when there is 50 amps. But your alternator only is capable of 25 amps. So when the alternator is at 25 amps the sensor will output 2.5 volts. And 5 amps would be .5 volts. If you double the wire, those become 5 and 1 volts so you can see small changes easier.

This help?

Jim

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kenryan



Joined: 20 Oct 2009
Posts: 426
PostPosted: Thu Nov 13, 2014 4:17 pm    Post subject: Understanding generator / alternator disconnect requirement Reply with quote
Yes I think I follow
Thanks. On Nov 13, 2014 2:33 PM, "h&amp;jeuropa" <butcher43(at)att.net (butcher43(at)att.net)> wrote:[quote]--> RotaxEngines-List message posted by: "h&amp;jeuropa" <butcher43(at)att.net (butcher43(at)att.net)>

Ken,

As you did this time, just hit Post Reply.

A Hall Effect sensor measures the magnetic field generated when current passes thru a wire.  More current, stronger field.  Notice that the sensor looks like a doughnut.  It is the amount or strength of the magnetic field within the doughnut that is measured and is proportional to the current in the wire.

The sensor outputs a voltage proportional to the amps.  The amp rating of the sensor is how many amps are required for the sensor to output it's maximum voltage.  If you put 75 amps thru a 50 amp sensor, it wont be damaged but it will not output a voltage that corresponds to 75 amps.

So if you run the wire thru the doughnut twice, there is twice the field inside.  The sensor says there is X amps.  But since X is generated by the wire thru twice, the wire is actually carrying X2 amps.

 So a 50 amp sensor can be a 25 / 16.6 / 12.5 etc sensor.  You might want to do this to get better resolution.  Say you have a 50 amp sensor.  That means it will output it's max voltage (5 volts for ones like the GRT) when there is 50 amps.  But your alternator only is capable of 25 amps.  So when the alternator is at 25 amps the sensor will output 2.5 volts.  And 5 amps would be .5 volts.  If you double the wire, those become 5 and 1 volts so you can see small changes easier.

This help?

Jim




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http://forums.matronics.com/viewtopic.php?p=433632#433632







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p.com" target="_blank">www.homebuilthelp.com
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BARRY CHECK 6



Joined: 15 Mar 2011
Posts: 738
PostPosted: Sat Nov 15, 2014 4:27 am    Post subject: Understanding generator / alternator disconnect requirement Reply with quote
ROTAX....
Yea, one thread, you got that right... 
"You can use the 50 amp sensor and run the wire thru twice to make it a 25 amp sensor."  Isn't that the other way around? 
On Thu, Nov 13, 2014 at 4:25 PM, h&amp;jeuropa <butcher43(at)att.net (butcher43(at)att.net)> wrote:
[quote]--> RotaxEngines-List message posted by: "h&amp;jeuropa" <butcher43(at)att.net (butcher43(at)att.net)>

Ken,

Yes Hall Effect current sensors are accurate and easy to install.  I actually have two, one on the output of the alternator and one on the positive lead of the battery to monitor system performance.  I use a switch to select which one is the input to my EIS.

You can use the 50 amp sensor and run the wire thru twice to make it a 25 amp sensor.

Also be aware that the bus voltage may not be what it says.  If you have a GRT EIS, the voltage the EIS measures is it's input and is accurate.  If it is being fed from a E Buss, there probably is a diode in the circuit which drops the voltage.  Just compare what EIS reports and a voltmeter on your battery to see the difference.  If you  have a multiple input EFIS, there are probably diodes in it too.  Again, compare to a voltmeter.  Mine drop about .4 volts.

BTW, just click "reply to post" to keep all the posts in one thread.  Makes it easier when you look for this again in 5 years!!

Jim Butcher




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=433623#433623







===========
et="_blank">www.aeroelectric.com
sbooks.com" target="_blank">www.buildersbooks.com
rget="_blank">www.homebuilthelp.com
rget="_blank">www.mypilotstore.com
="_blank">www.mrrace.com
="_blank">http://www.matronics.com/contribution
le, List Admin.
===========
es-List" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List
===========
">http://forums.matronics.com
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