X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fmailhost04.isp.att.net ([204.127.217.104] verified) by logan.com (CommuniGate Pro SMTP 5.2.13) with ESMTP id 3556361 for flyrotary@lancaironline.net; Mon, 23 Mar 2009 11:08:20 -0400 Received-SPF: pass receiver=logan.com; client-ip=204.127.217.104; envelope-from=bbradburry@bellsouth.net Received: from laptop (adsl-146-126-109.mco.bellsouth.net[72.146.126.109]) by isp.att.net (frfwmhc04) with SMTP id <20090323150736H04009jvgie>; Mon, 23 Mar 2009 15:07:36 +0000 X-Originating-IP: [72.146.126.109] From: "Bill Bradburry" To: "'Rotary motors in aircraft'" References: Subject: RE: [FlyRotary] Re: Alternator (Off topic Date: Mon, 23 Mar 2009 11:07:41 -0400 Message-ID: <0035D1B497FF4E27BFD9F2349147C6B7@LAPTOP> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0018_01C9ABA7.966E02D0" X-Mailer: Microsoft Office Outlook 11 Thread-Index: AcmrtStCVOwy4r6iReKnEaG3SBAjDgAExPSA In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_0018_01C9ABA7.966E02D0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Gary, Here is something you can try. Take the belt off the alternator and using your hand, spin the alternator pulley, Then turn on the master and spin the pulley. Then turn on the alternator and spin the pulley. Tell us again what you think happens when that "3 amps" of field current hits that alternator. If you can turn that pulley with your hand with the alternator on, I apologize profusely! Not because I am wrong, but because you will have to be one Gorilla! Bill B _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Gary Casey Sent: Monday, March 23, 2009 8:44 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Alternator (Off topic This discussion on alternators is interesting. First, I'll have to disagree with Bill B about the alternator "load" with the engine not running. The voltage capability of the alternator is proportional to rpm and at cranking speed it will not be able to deliver battery voltage and therefore its output will be zero and therefore the power to turn it will be no more than the friction in the bearings. The field will, of course, be full on, which will result in a battery drain of about 3 amps. Compared to the starter draw of maybe 200 amps it is trivial. Some people leave the alternator off to save that current, but there isn't much incentive to do that. The only real reason to ever turn the master on without the alternator is if you don't intend to start the engine (maintenance, setting the radios, or whatever) - then there will be less draw on the battery. The second post by Tom is partly true - most voltage regulators are "switching" regulators in that the field is either turned on or off. But the battery only partially smoothes the output. The main reason this works is that the alternator field windings (in the armature) have a very high inductance and a "free-wheeling" or "clamping" diode is placed across the field. When the regulator turns off current continues to flow through the field, driven by the inductance of the field itself. This is easiest to visualize by drawing the field coil with a diode connecting the top and bottom (ground terminal). Shut off the supply and pretend that the coil is a big flywheel and the current doesn't want to stop - it will flow through the diode from the ground to the top (supply) end, which is now at a slightly negative voltage.. The alternator output will decrease gradually (well, in milliseconds) until the system voltage drops below the threshold set in the regulator, whereupon the regulator will turn full on again, bumping it back up. Imagine a bicycle wheel that you just have to hit now and then to keep it turning - or read Jim's explanation. The big advantage of this is that the regulator is either full on or full off and therefore will dissipate very little heat. The disadvantage is that electrical noise will generated by the switching, but that noise is generally not a problem for any other electrical device. There are some regulators (B&C for example) that are "linear" and they actually regulate a continuous current in the field and the manufacturers of these claim that their system is "quieter." They will, however, draw more continuous current will run hotter, requiring some sort of cooling fins or something. Are they worth the extra cost? I doubt it, but I have one that was acquired as part of the system. I believe Tom's idea of turning on all the electrical loads in a car to test the battery is that the alternator is typically incapable of supplying that load at idle speed and therefore the battery voltage will drop enough to cause the engine electronics to stop working, "killing" the engine. Problem is that all current automotive systems will continue to work down to less than 6 volts. The battery would have to be virtually gone to drop that low. Gone far enough that it probably couldn't crank the engine. Finally, Mike has a question on alternator "noise." This is generally caused by the high-frequency pulses of current produced by the alternator stator windings. All diodes have finite response time and when "hit" with a sudden pulse there will be a slight delay before they start conducting. This produces a sharp voltage spike in the windings and this will propagate throughout the electrical system of the plane. If you put a scope on the main power line you will see this characteristic if you look close enough. The voltage spikes will be small and very short - maybe one microsecond - but they are there. The repetition rate of these is such that it is in the audible frequency range and therefore can sometimes be heard in the audio system. (as I recall, a typical alternator puts out something like 14 pulses per rev and it turns at about 2.5 times engine speed, which is 583 Hz at 1,000 rpm. The best way to kill this noise is to use a "feed-thru capacitor" in the alternator output line. I'll take that back - the BEST way is to buy components that aren't sensitive to the noise, but how do you know that until you've already spent the money. Feed-thru caps with the required capacity are typically metal cylinders about an inch long with a heavy wire going into each end and a mounting tab on the side. The mouting tab is important - that's the path that conducts the noise to ground. It's best to mount the cap directly to the noise source - the alternator - and the next best is to the engine. Also, you should check all the connections in the high current path. Maybe run a ground wire from the alternator ground terminal to the engine (I know, the alternator is already bolted to the engine, but do it anyway). Gary Casey -----Inline Message Follows----- This is why you should not turn your alternator on until after the engine starts. The alternator loads will almost double the load on the starter. The voltage regulator will call for maximum output from the alternator while the starter is cranking. For a 60A alternator this is about 720 watts. Darn near 1 HP! In cars, the alternator is automatically put to sleep during starting by the ignition switch. In planes, it is up to us. Bill B The field is either on or off. The regulator would create too much heat with a linear function, so solution is just a 'switch' function in the regulator IC. Battery does the trick in smoothing the voltage. George -- simple test is with the engine idling, kick on the lights/fan... note the rpm drop. That is the load of the alternator turning on. Newer vehicles will have additional inputs to the alternator so it knows when the AC is on, or when you kick WOT (wide open throttle) as it will disconnect the alternator and A/C off for a brief amount of time. Also a simple battery test is to (in the car) kick on all loads at idle.... if the engine dies, battery reserve isn't there and time to replace 'em. Tom However, by switching the field on and off at a fairly fast rate and varying the pulse width duration of the field current, a linear approximation can be achieved with a constant voltage as the result, within the limits of the system of course. That is in essence how the voltage regulator achieves its function. Jim Slightly off topic, but does anyone have a suggestion for an off the shelf filter to kill/reduce alternator electrical noise? I have an alternator off of a Geo Metro/Chevy Sprint with internal regulator. I have a switch on the panel to energize the field. After the engine is running and I switch on the alternator I get a noticeable hum in the intercom. This is one of those nagging little issues I havent gotten around to fixing yet since first flight. Also in a previous thread someone (maybe Al G.?) mentioned an over-voltage protection device for the alternator output that would be compatible with the internally regulated alternator. I'd like to add something like that as well - suggested sources? Thanks, Mike Wills RV-4 N144MW ----- Original Message ----- From: James Maher To: Rotary motors in aircraft Sent: Sunday, March 22, 2009 7:45 AM Subject: [FlyRotary] Re: Alternator (Off topic) Tom, You are right, of coarse, about the alternator field being either on or off. I may have implied that the field current was a linear function but I was only trying to simplify the explanation. However, by switching the field on and off at a fairly fast rate and varying the pulse width duration of the field current, a linear approximation can be achieved with a constant voltage as the result, within the limits of the system of course. That is in essence how the voltage regulator achieves its function. As for your "simple test" it may not give the expected results, as most modern car engines, those that are controlled by computers, will have the idle speed determined by the computer as well. So increasing the load at idle, either mechanical or electrical, will cause the computer to sense a decrease in RPM and if it goes below a predetermined value the computer will open the throttle (or idle speed valve) to increase the RPM to the correct idle speed. Jim --- On Sun, 3/22/09, thomas walter wrote: From: thomas walter Subject: [FlyRotary] Re: Alternator (Off topic) To: "Rotary motors in aircraft" Date: Sunday, March 22, 2009, 10:03 AM Jim, The field is either on or off. The regulator would create too much heat with a linear function, so solution is just a 'switch' function in the regulator IC. Battery does the trick in smoothing the voltage. George -- simple test is with the engine idling, kick on the lights/fan... note the rpm drop. That is the load of the alternator turning on. Newer vehicles will have additional inputs to the alternator so it knows when the AC is on, or when you kick WOT (wide open throttle) as it will disconnect the alternator and A/C off for a brief amount of time. Also a simple battery test is to (in the car) kick on all loads at idle.... if the engine dies, battery reserve isn't there and time to replace 'em.. Tom 1) Re: Alternator (Off topic) by James Maher George, I'm sorry to disagree with you but you are quite mistaken in your belief about the alternator function. The alternator output is mostly a function of load because of the voltage regulator, whose function is to keep the voltage constant with changes in load and RPM. It performs this function by varying the field current in the alternator. If fact this is one of the many advantages of the alternator over a generator. The alternator's voltage output is also more or less constant regardless of engine RPM, also due to the regulator's function. You said "The alternator charges the battery - which in turn runs the accessories". This is not exactly true. If the battery voltage is below that of the alternator output then yes the alternator will function to charge the battery, however if the battery is fully charged then the alternator will not be charging the battery but will provide the necessary power to drive any other loads connected to the system. So reducing the electrical load on the system will indeed reduce the mechanical load on the engine thereby using less overall energy. Hope this clarifies your misconception. Don't feel bad, many people do not fully understand even the most simple of electrical devices and the alternator/regulator charging system is fairly complex. Jim -----Inline Message Follows----- With the fuel injected rotaries we are dependent on a good source of power to run the computer and fuel pumps. I used the information on the AeroElectric list to design my wiring. http://www.matronics.com/Navigator?AeroElectric-List They have information on what and where to get over-voltage controllers. Whey also have several wiring diagrams for "all electric" aircraft. These include ways to feed the Critical Buss through several different independent paths so one failure does not turn you into a glider. Dennis Haverlah Mike Wills wrote: Slightly off topic, but does anyone have a suggestion for an off the shelf filter to kill/reduce alternator electrical noise? I have an alternator off of a Geo Metro/Chevy Sprint with internal regulator. I have a switch on the panel to energize the field. After the engine is running and I switch on the alternator I get a noticeable hum in the intercom. This is one of those nagging little issues I havent gotten around to fixing yet since first flight. Also in a previous thread someone (maybe Al G.?) mentioned an over-voltage protection device for the alternator output that would be compatible with the internally regulated alternator. I'd like to add something like that as well - suggested sources? Thanks, Mike Wills RV-4 N144MW ----- Original Message ----- From: James Maher To: Rotary motors in aircraft Sent: Sunday, March 22, 2009 7:45 AM Subject: [FlyRotary] Re: Alternator (Off topic) Tom, You are right, of coarse, about the alternator field being either on or off. I may have implied that the field current was a linear function but I was only trying to simplify the explanation. However, by switching the field on and off at a fairly fast rate and varying the pulse width duration of the field current, a linear approximation can be achieved with a constant voltage as the result, within the limits of the system of course. That is in essence how the voltage regulator achieves its function. As for your "simple test" it may not give the expected results, as most modern car engines, those that are controlled by computers, will have the idle speed determined by the computer as well. So increasing the load at idle, either mechanical or electrical, will cause the computer to sense a decrease in RPM and if it goes below a predetermined value the computer will open the throttle (or idle speed valve) to increase the RPM to the correct idle speed. Jim --- On Sun, 3/22/09, thomas walter wrote: From: thomas walter Subject: [FlyRotary] Re: Alternator (Off topic) To: "Rotary motors in aircraft" Date: Sunday, March 22, 2009, 10:03 AM Jim, The field is either on or off. The regulator would create too much heat with a linear function, so solution is just a 'switch' function in the regulator IC. Battery does the trick in smoothing the voltage. George -- simple test is with the engine idling, kick on the lights/fan... note the rpm drop. That is the load of the alternator turning on. Newer vehicles will have additional inputs to the alternator so it knows when the AC is on, or when you kick WOT (wide open throttle) as it will disconnect the alternator and A/C off for a brief amount of time. Also a simple battery test is to (in the car) kick on all loads at idle.... if the engine dies, battery reserve isn't there and time to replace 'em. Tom 1) Re: Alternator (Off topic) by James Maher George, I'm sorry to disagree with you but you are quite mistaken in your belief about the alternator function. The alternator output is mostly a function of load because of the voltage regulator, whose function is to keep the voltage constant with changes in load and RPM. It performs this function by varying the field current in the alternator. If fact this is one of the many advantages of the alternator over a generator. The alternator's voltage output is also more or less constant regardless of engine RPM, also due to the regulator's function. You said "The alternator charges the battery - which in turn runs the accessories". This is not exactly true. If the battery voltage is below that of the alternator output then yes the alternator will function to charge the battery, however if the battery is fully charged then the alternator will not be charging the battery but will provide the necessary power to drive any other loads connected to the system. So reducing the electrical load on the system will indeed reduce the mechanical load on the engine thereby using less overall energy. Hope this clarifies your misconception. Don't feel bad, many people do not fully understand even the most simple of electrical devices and the alternator/regulator charging system is fairly complex. Jim -----Inline Message Follows----- Mike; The first thing to try is a large capacitor at the alternator between the B terminal (output) and grnd (the case). Try about 10,000 microFarad in an electrolytic type. Be aware of polarity to connect it right. The over-voltage (crowbar circuit) that I have I got from Aeroelectric Connection. I don't think he sells stuff directly anymore but maybe you can get it from B&C. Connects across the field supply circuit breaker, and fails to short above something like 17-18 volts (IIRC) - tripping the breaker. Don't know about yours; but normally automotive alternators with internal regulators feed the current to the field internally directly from the regulator. The small excitation current required to get things started comes through the 'idiot' light circuit (one of the terminals on the alt).. Over-voltage protection on that circuit won't do anything.. On my Mitsubishi alternator, I took it apart and undid the internal connection. I learned about this from an article in Contact! years ago (Issue 46, Sept 1998). Maybe you can find a circuit diagram for your alternator; or maybe it is made by Mitsubishi or Nippondenso, both of which are covered in the article. I can provide a copy if that helps. Best, Al -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mike Wills Sent: Sunday, March 22, 2009 7:37 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Alternator (Off topic) Slightly off topic, but does anyone have a suggestion for an off the shelf filter to kill/reduce alternator electrical noise? I have an alternator off of a Geo Metro/Chevy Sprint with internal regulator. I have a switch on the panel to energize the field. After the engine is running and I switch on the alternator I get a noticeable hum in the intercom. This is one of those nagging little issues I havent gotten around to fixing yet since first flight. Also in a previous thread someone (maybe Al G.?) mentioned an over-voltage protection device for the alternator output that would be compatible with the internally regulated alternator. I'd like to add something like that as well - suggested sources? Thanks, Mike Wills RV-4 N144MW ----- Original Message ----- From: James Maher To: Rotary motors in aircraft Sent: Sunday, March 22, 2009 7:45 AM Subject: [FlyRotary] Re: Alternator (Off topic) Tom, You are right, of coarse, about the alternator field being either on or off. I may have implied that the field current was a linear function but I was only trying to simplify the explanation. However, by switching the field on and off at a fairly fast rate and varying the pulse width duration of the field current, a linear approximation can be achieved with a constant voltage as the result, within the limits of the system of course. That is in essence how the voltage regulator achieves its function. As for your "simple test" it may not give the expected results, as most modern car engines, those that are controlled by computers, will have the idle speed determined by the computer as well. So increasing the load at idle, either mechanical or electrical, will cause the computer to sense a decrease in RPM and if it goes below a predetermined value the computer will open the throttle (or idle speed valve) to increase the RPM to the correct idle speed. Jim --- On Sun, 3/22/09, thomas walter wrote: From: thomas walter Subject: [FlyRotary] Re: Alternator (Off topic) To: "Rotary motors in aircraft" Date: Sunday, March 22, 2009, 10:03 AM Jim, The field is either on or off. The regulator would create too much heat with a linear function, so solution is just a 'switch' function in the regulator IC. Battery does the trick in smoothing the voltage. George -- simple test is with the engine idling, kick on the lights/fan... note the rpm drop. That is the load of the alternator turning on. Newer vehicles will have additional inputs to the alternator so it knows when the AC is on, or when you kick WOT (wide open throttle) as it will disconnect the alternator and A/C off for a brief amount of time. Also a simple battery test is to (in the car) kick on all loads at idle.... if the engine dies, battery reserve isn't there and time to replace 'em. Tom 1) Re: Alternator (Off topic) by James Maher George, I'm sorry to disagree with you but you are quite mistaken in your belief about the alternator function. The alternator output is mostly a function of load because of the voltage regulator, whose function is to keep the voltage constant with changes in load and RPM. It performs this function by varying the field current in the alternator. If fact this is one of the many advantages of the alternator over a generator. The alternator's voltage output is also more or less constant regardless of engine RPM, also due to the regulator's function. You said "The alternator charges the battery - which in turn runs the accessories". This is not exactly true. If the battery voltage is below that of the alternator output then yes the alternator will function to charge the battery, however if the battery is fully charged then the alternator will not be charging the battery but will provide the necessary power to drive any other loads connected to the system. So reducing the electrical load on the system will indeed reduce the mechanical load on the engine thereby using less overall energy. Hope this clarifies your misconception. Don't feel bad, many people do not fully understand even the most simple of electrical devices and the alternator/regulator charging system is fairly complex. Jim -----Inline Message Follows----- ------=_NextPart_000_0018_01C9ABA7.966E02D0 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

Gary,

Here is something you can = try.  Take the belt off the alternator and using your hand, spin the alternator = pulley,  Then turn on the master and spin the pulley.  Then turn on the = alternator and spin the pulley.  Tell us again what you think happens when that = “3 amps” of field current hits that alternator.

If you can turn that pulley with = your hand with the alternator on, I apologize profusely!  Not because I am = wrong, but because you will have to be one Gorilla!

 

Bill B

 

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Gary Casey
Sent: Monday, March 23, = 2009 8:44 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Alternator (Off topic

 

This discussion on alternators is interesting.  First, I'll = have to disagree with Bill B about the alternator "load" with the = engine not running.  The voltage capability of the alternator is = proportional to rpm and at cranking speed it will not be able to deliver battery voltage = and therefore its output will be zero and therefore the power to turn it = will be no more than the friction in the bearings.  The field will, of course, = be full on, which will result in a battery drain of about 3 amps. =  Compared to the starter draw of maybe 200 amps it is trivial.  Some people = leave the alternator off to save that current, but there isn't much incentive = to do that.  The only real reason to ever turn the master on without the alternator is if you don't intend to start the engine (maintenance, = setting the radios, or whatever) - then there will be less draw on the = battery.

 

The second post by Tom is partly true - most voltage regulators = are "switching" regulators in that the field is either turned on = or off.  But the battery only partially smoothes the output.  The main = reason this works is that the alternator field windings (in the armature) have = a very high inductance and a "free-wheeling" or "clamping" = diode is placed across the field.  When the regulator turns off current continues to flow through the field, driven by the inductance of the = field itself.  This is easiest to visualize by drawing the field coil with a = diode connecting the top and bottom (ground terminal).  Shut off the = supply and pretend that the coil is a big flywheel and the current doesn't want to = stop - it will flow through the diode from the ground to the top (supply) end, = which is now at a slightly negative voltage..  The alternator output will decrease gradually (well, in milliseconds) until the system voltage = drops below the threshold set in the regulator, whereupon the regulator will turn = full on again, bumping it back up.  Imagine a bicycle wheel that you just = have to hit now and then to keep it turning - or read Jim's explanation. =  The big advantage of this is that the regulator is either full on or full off = and therefore will dissipate very little heat.  The disadvantage is = that electrical noise will generated by the switching, but that noise is = generally not a problem for any other electrical device.  There are some = regulators (B&C for example) that are "linear" and they actually = regulate a continuous current in the field and the manufacturers of these claim = that their system is "quieter."  They will, however, draw more = continuous current will run hotter, requiring some sort of cooling fins or = something.  Are they worth the extra cost?  I doubt it, but I have one = that was acquired as part of the system.

 

I believe Tom's idea of turning on all the electrical loads in a = car to test the battery is that the alternator is typically incapable of = supplying that load at idle speed and therefore the battery voltage will drop = enough to cause the engine electronics to stop working, "killing" the = engine.  Problem is that all current automotive systems will continue to = work down to less than 6 volts.  The battery would have to be virtually gone = to drop that low.  Gone far enough that it probably couldn't crank the = engine.

 

Finally, Mike has a question on alternator "noise."  This is generally caused by the high-frequency pulses of current = produced by the alternator stator windings.  All diodes have finite response = time and when "hit" with a sudden pulse there will be a slight = delay before they start conducting.  This produces a sharp voltage spike = in the windings and this will propagate throughout the electrical system of the = plane.  If you put a scope on the main power line you will see this characteristic if you look close enough.  The voltage spikes will = be small and very short - maybe one microsecond - but they are there.  The repetition rate of these is such that it is in the audible frequency = range and therefore can sometimes be heard in the audio system.  (as I = recall, a typical alternator puts out something like 14 pulses per rev and it = turns at about 2.5 times engine speed, which is 583 Hz at 1,000 rpm.  The = best way to kill this noise is to use a "feed-thru capacitor" in the alternator output line.  I'll take that back - the BEST way is to = buy components that aren't sensitive to the noise, but how do you know that = until you've already spent the money.  Feed-thru caps with the required = capacity are typically metal cylinders about an inch long with a heavy wire going = into each end and a mounting tab on the side.  The mouting tab is = important - that's the path that conducts the noise to ground.  It's best to = mount the cap directly to the noise source - the alternator - and the next best is = to the engine.  Also, you should check all the connections in the high = current path.  Maybe run a ground wire from the alternator ground terminal = to the engine (I know, the alternator is already bolted to the engine, but do = it anyway).

 

Gary Casey

 


-----Inline Message Follows-----

This = is why you should not turn your alternator on until after the engine starts.  = The alternator loads will almost double the load on the starter.  The = voltage regulator will call for maximum output from the alternator while the = starter is cranking.  For a 60A alternator this is about 720 watts.  Darn = near 1 HP!  In cars, the alternator is automatically put to sleep during = starting by the ignition switch.  In planes, it is up to = us.

 

Bill = B

 

  


The field is either on or off. 

The regulator would create too much heat with a linear function, so = solution is just a 'switch' function in the regulator IC.

Battery does the trick in smoothing = the voltage.

George -- simple test is with the engine idling, kick on the = lights/fan... note the rpm drop.
That is the load of the alternator turning on. Newer vehicles will = have additional inputs to the alternator so it knows when the AC is on, or = when you kick WOT (wide open throttle) as it will disconnect the alternator = and A/C off for a brief amount of time.    Also a simple = battery test is to (in the car) kick on all loads at idle.... if the engine = dies, battery reserve isn't there and time to replace 'em.  

Tom

 

 

However, by switching the field on and off = at a fairly fast rate and varying the = pulse

width duration of the field current, a = linear approximation can be achieved with a constant voltage as the result, = within the limits of the system of course.

That is in essence how the voltage = regulator achieves its function.

 

Jim

 

Slightly off topic, but = does anyone have a suggestion for an off the shelf filter to = kill/reduce alternator electrical noise? I have an alternator off of a Geo = Metro/Chevy Sprint with internal regulator. I have a switch on the panel to = energize the field. After the engine is running and I switch on the alternator I = get a noticeable hum in the intercom. This is one of those nagging little = issues I havent gotten around to fixing yet since first = flight.

 

 Also in a previous thread someone (maybe Al = G.?) mentioned an over-voltage protection device for the alternator output = that would be compatible with the internally regulated alternator. I'd = like to add something like that as well - suggested = sources?

 

Thanks,

 

Mike Wills

RV-4 N144MW

----- Original Message ----- =

From: James Maher =

Sent: Sunday, = March 22, 2009 7:45 AM

Subject: = [FlyRotary] Re: Alternator (Off topic)

 

Tom,

You are right, of coarse, about the = alternator field being either on or off.

I may have implied that the field current = was a linear function but I was only trying = to

simplify the = explanation.

 

However, by switching the field on and off = at a fairly fast rate and varying the = pulse

width duration of the field current, a = linear approximation can be achieved with a constant voltage as the result, within the = limits of the system of course.

That is in essence how the voltage = regulator achieves its function.

 

As for your "simple test" it may = not give the expected results, as most modern car engines, those that are = controlled by computers, will have the idle speed determined by the computer as = well.

So increasing the load at idle, either = mechanical or electrical, will cause the

computer to sense a decrease in RPM and if = it goes below a predetermined value the computer will open the throttle (or = idle speed valve) to increase the RPM to the correct idle = speed.

 

Jim
--- On Sun, 3/22/09, thomas walter = <roundrocktom@yahoo.com> wrote:

From: thomas = walter <roundrocktom@yahoo.com>
Subject: [FlyRotary] Re: Alternator (Off topic)
To: "Rotary motors in = aircraft" <flyrotary@lancaironline.net>
Date: Sunday, March 22, 2009, 10:03 AM

Jim,

The field is either on or off. 

The regulator would create too much heat with a linear function, so solution is just a 'switch' function in the regulator IC.

Battery does the trick in smoothing = the voltage.

George -- simple test is with the engine idling, kick on the = lights/fan... note the rpm drop.
That is the load of the alternator turning on. Newer vehicles will = have additional inputs to the alternator so it knows when the AC is on, = or when you kick WOT (wide open throttle) as it will disconnect the = alternator and A/C off for a brief amount of time.    Also a simple = battery test is to (in the car) kick on all loads at idle.... if the engine = dies, battery reserve isn't there and time to replace 'em..   =

Tom





1) Re: Alternator (Off topic)
    by James Maher = <delta11xd@att.net>

George,

I'm sorry to disagree with you but you = are quite mistaken in your belief about the

alternator = function.

The alternator output is mostly a = function of load because of the voltage regulator,

whose function is to keep the voltage = constant with changes in load and RPM.

It performs this function by varying the = field current in the alternator.

If fact this is one of the many = advantages of the alternator over a generator.

The alternator's voltage output is also = more or less constant regardless of engine RPM, also due to the regulator's function.

You said "The alternator charges the = battery - which in turn runs the = accessories".

This is not exactly true. If the battery = voltage is below that of the alternator output

then yes the alternator will function to = charge the battery, however if the battery is fully charged then the = alternator will not be charging the battery but will provide the necessary = power to drive any other loads connected to the = system.

So reducing the electrical load on the = system will indeed reduce the mechanical load on

the engine thereby using less overall = energy.

Hope this clarifies your = misconception.

Don't feel bad, many people do not fully understand even the most simple of electrical devices and the alternator/regulator charging system is fairly = complex.

Jim

 



-----Inline Message Follows-----

With the fuel injected rotaries we are dependent on a good source of = power to run the computer and fuel pumps.  I used the information on the AeroElectric list to design my wiring.   http://www.matronics.com/Navigator?AeroElectric-List    They have information on what and where to get over-voltage = controllers.  Whey also have several wiring diagrams for "all electric" aircraft.  These include ways to feed the Critical Buss through several different independent = paths so one failure does not turn you into a glider.

Dennis Haverlah


Mike Wills wrote:

Slightly off topic, but does anyone have a suggestion = for an off the shelf filter to kill/reduce alternator electrical noise? I = have an alternator off of a Geo Metro/Chevy Sprint with internal regulator. I = have a switch on the panel to energize the field. After the engine is running = and I switch on the alternator I get a noticeable hum in the intercom. This is = one of those nagging little issues I havent gotten around to fixing yet since = first flight.

 

 Also in a previous thread someone (maybe Al = G.?) mentioned an over-voltage protection device for the alternator output = that would be compatible with the internally regulated alternator. I'd = like to add something like that as well - suggested = sources?

 

Thanks,

 

Mike Wills

RV-4 N144MW

----- Original Message ----- =

Sent: Sunday, = March 22, 2009 7:45 AM

Subject: = [FlyRotary] Re: Alternator (Off topic)

 

Tom,

You are right, of coarse, about the = alternator field being either on or off.

I may have implied that the field current = was a linear function but I was only trying = to

simplify the = explanation.

 

However, by switching the field on and off = at a fairly fast rate and varying the = pulse

width duration of the field current, a = linear approximation can be achieved with a constant voltage as the result, = within the limits of the system of course.

That is in essence how the voltage = regulator achieves its function.

 

As for your "simple test" it may = not give the expected results, as most modern car engines, those that are = controlled by computers, will have the idle speed determined by the computer as = well.

So increasing the load at idle, either = mechanical or electrical, will cause the

computer to sense a decrease in RPM and if = it goes below a predetermined value the computer will open the throttle (or = idle speed valve) to increase the RPM to the correct idle = speed.

 

Jim
--- On Sun, 3/22/09, thomas walter = <roundrocktom@yahoo.com><= /a> wrote:

From: thomas = walter <roundrocktom@yahoo.com><= /a>
Subject: [FlyRotary] Re: Alternator (Off topic)
To: "Rotary motors in = aircraft" <flyrotary@lancaironlin= e.net>
Date: Sunday, March 22, 2009, 10:03 AM

Jim,

The field is either on or off. 

The regulator would create too much heat with a linear function, so = solution is just a 'switch' function in the regulator IC.

Battery does the trick in smoothing = the voltage.

George -- simple test is with the engine idling, kick on the = lights/fan... note the rpm drop.
That is the load of the alternator turning on. Newer vehicles will = have additional inputs to the alternator so it knows when the AC is on, = or when you kick WOT (wide open throttle) as it will disconnect the = alternator and A/C off for a brief amount of time.    Also a simple = battery test is to (in the car) kick on all loads at idle.... if the engine = dies, battery reserve isn't there and time to replace 'em.   =

Tom





1) Re: Alternator (Off topic)
    by James Maher = <delta11xd@att.net>

George,

I'm sorry to disagree with you but you = are quite mistaken in your belief about the

alternator = function.

The alternator output is mostly a = function of load because of the voltage regulator,

whose function is to keep the voltage = constant with changes in load and RPM.

It performs this function by varying the = field current in the alternator.

If fact this is one of the many = advantages of the alternator over a generator.

The alternator's voltage output is also = more or less constant regardless of engine RPM, also due to the regulator's function.

You said "The alternator charges the = battery - which in turn runs the = accessories".

This is not exactly true. If the battery = voltage is below that of the alternator output

then yes the alternator will function to = charge the battery, however if the battery is fully charged then the = alternator will not be charging the battery but will provide the necessary = power to drive any other loads connected to the = system.

So reducing the electrical load on the = system will indeed reduce the mechanical load on

the engine thereby using less overall = energy.

Hope this clarifies your = misconception.

Don't feel bad, many people do not fully understand even the most simple of electrical devices and the alternator/regulator charging system is fairly = complex.

Jim

 



-----Inline Message Follows-----

Mike;

 

The first thing to try is a large capacitor at the = alternator between the B terminal (output) and grnd (the case). Try about 10,000 microFarad in an electrolytic type. Be aware of polarity to connect it = right.

 

The over-voltage (crowbar circuit) that I have I got from Aeroelectric Connection.  I don’t think he sells stuff = directly anymore but maybe you can get it from B&C.  Connects across the field = supply circuit breaker, and fails to short above something like 17-18 volts = (IIRC) – tripping the breaker.

 

Don’t know about yours; but normally automotive = alternators with internal regulators feed the current to the field internally directly = from the regulator.  The small excitation current required to get things = started comes through the ‘idiot’ light circuit (one of the = terminals on the alt)..  Over-voltage protection on that circuit won’t do = anything..  On my Mitsubishi alternator, I took it apart and undid the internal = connection.  I learned about this from an article in Contact! years ago (Issue = 46, Sept 1998). Maybe you can find a circuit diagram for your alternator; or = maybe it is made by Mitsubishi or Nippondenso, both of which are covered in = the article.  I can provide a copy if that = helps.

 

Best,

 

Al

 

 

-----Original Message-----
From: Rotary motors in aircraft = [mailto:flyrotary@lancaironline.net] On Behalf Of Mike Wills
Sent: Sunday, March 22, = 2009 7:37 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Alternator (Off topic)

 

Slightly off topic, but does anyone have a suggestion = for an off the shelf filter to kill/reduce alternator electrical noise? I = have an alternator off of a Geo Metro/Chevy Sprint with internal regulator. I = have a switch on the panel to energize the field. After the engine is running = and I switch on the alternator I get a noticeable hum in the intercom. This is one of = those nagging little issues I havent gotten around to fixing yet since first = flight.

 

 Also in a previous thread someone (maybe Al = G.?) mentioned an over-voltage protection device for the alternator output = that would be compatible with the internally regulated alternator. I'd = like to add something like that as well - suggested = sources?

 

Thanks,

 

Mike Wills

RV-4 N144MW

=

----- Original Message ----- =

From: James Maher =

Sent: Sunday, = March 22, 2009 7:45 AM

Subject: = [FlyRotary] Re: Alternator (Off topic)

 

Tom,

You = are right, of coarse, about the alternator field being either on or = off.

I = may have implied that the field current was a linear function but I was only trying to

simplify the explanation.

 

However, by switching the field on and off at a fairly fast rate and varying = the pulse

width duration of the field current, a linear approximation can be achieved with a = constant voltage as the result, within the limits of the system of = course.

That is in essence how the voltage = regulator achieves its function.

 

As = for your "simple test" it may not give the expected results, as most = modern car engines, those that are controlled by computers, will have the = idle speed determined by the computer as well.

So = increasing the load at idle, either mechanical or electrical, will cause = the

computer to sense a decrease in RPM and if it goes below a predetermined value the computer will open the throttle (or idle speed valve) to increase the = RPM to the correct idle speed.

 

Jim
--- On Sun, 3/22/09, thomas walter = <roundrocktom@yahoo.com> wrote:

From: thomas walter <roundrocktom@yahoo.com>
Subject: [FlyRotary] Re: Alternator (Off topic)
To: "Rotary motors in = aircraft" <flyrotary@lancaironline.net>
Date: Sunday, March 22, 2009, 10:03 AM

Jim,

The field is either on or off. 

The regulator would create too much heat with a linear function, so solution is just a 'switch' function in the regulator IC.

Battery does the trick in smoothing = the voltage.

George -- simple test is with the engine idling, kick on the = lights/fan... note the rpm drop.
That is the load of the alternator turning on. Newer vehicles will = have additional inputs to the alternator so it knows when the AC is on, = or when you kick WOT (wide open throttle) as it will disconnect the = alternator and A/C off for a brief amount of time.    Also a simple = battery test is to (in the car) kick on all loads at idle.... if the engine = dies, battery reserve isn't there and time to replace 'em.   =

Tom




1) Re: Alternator (Off topic)
    by James Maher = <delta11xd@att.net>

George,

I'm sorry to disagree with you but you are quite mistaken in your belief = about the

alternator function.

The alternator output is mostly a function of load because of the = voltage regulator,

whose function is to keep the voltage constant with changes in load and = RPM.

It performs this function by varying the field current in the = alternator.

If fact this is one of the many advantages of the alternator over a = generator.

The alternator's voltage output is also more or less constant regardless = of engine RPM, also due to the regulator's = function.

You said "The alternator charges the battery - which in turn runs = the accessories".

This is not exactly true. If the battery voltage is below that of the = alternator output

then yes the alternator will function to charge the battery, however if = the battery is fully charged then the alternator will not be charging = the battery but will provide the necessary power to drive any other = loads connected to the system.

So reducing the electrical load on the system will indeed reduce the mechanical load on

the engine thereby using less overall = energy.

Hope this clarifies your misconception.

Don't feel bad, many people do not fully understand even the most simple = of electrical devices and the alternator/regulator charging system is = fairly complex.

Jim

 

 



-----Inline Message Follows-----

 

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