 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
chaskuss(at)yahoo.com
Guest
|
 Posted: Sat Feb 15, 2020 4:38 am Post subject: Alternator, battery and bus question |
 |
|
Excessive output can either immediately or slowly over time, damage or destroy one or more of the diodes in the alternators rectifier. The rectifier converts the AC current into the DC current that your aircraft needs. Most alternators have six diodes in them. Normal failure mode is for a diode to fail open circuit. So for each diode that fails you will lose one sixth of the alternators output. More Insidious, is if a diode fails shorted. In that case there will be no drop-off in the alternators output and an ammeter test will not show the failure. The failure will cause AC current to bleed into the system. Batteries hate AC current. AC current will destroy a brand new battery in a few months.
Charlie
Sent from Yahoo Mail on Android
| Quote: | On Fri, Feb 14, 2020 at 10:08 PM, Krea Ellis
<krea.ellis(at)gmail.com> wrote:
--> AeroElectric-List message posted by: Krea Ellis <krea.ellis(at)gmail.com (krea.ellis(at)gmail.com)>
What happens if an alternator is temporarily overloaded (let’s say it’s rated at 40 amps) and you draw 45 amps. Assume the battery is well maintained and fully charged. A current limiter (ANL/AML) is installed as well.
You intend to load shed, but don’t do so immediately. What are the consequences?
My assumption is the voltage will drop and the battery will supplement the alternator for some period of time until you can load shed and then the alternator will carry the entire load? I assume the current limiter will not blow with a short duration small overload.
Thanks in advance for educating me.
http://www.matronics.com/cont= Thank you for your generous support!
_p; -Matt Drasp; - The AeroElectric-List Email Forum -
http://www.matronics.com/Navigator?AeroElectric-Listhttp://forums.matronics.comhttp://www.matronics.com/contribution====================
|
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
 |
chaskuss(at)yahoo.com
Guest
|
| Posted: Sat Feb 15, 2020 4:44 am Post subject: Alternator, battery and bus question |
|
|
The situation described in my last post is not likely to happen on an aircraft that has a fully charged battery. The most common way that rectifier diodes get damaged is by jump starting a vehicle that has a dead battery. The alternator is then forced to generate current at maximum output for an extended length of time to refill the battery. That could cause the diodes to overheat and fail. So the lesson is if you have a dead battery don't just jump start it. Recharge the battery before you start the engine.
Charlie
Sent from Yahoo Mail on Android
| Quote: | On Fri, Feb 14, 2020 at 10:08 PM, Krea Ellis
<krea.ellis(at)gmail.com> wrote:
--> AeroElectric-List message posted by: Krea Ellis <krea.ellis(at)gmail.com (krea.ellis(at)gmail.com)>
What happens if an alternator is temporarily overloaded (let’s say it’s rated at 40 amps) and you draw 45 amps. Assume the battery is well maintained and fully charged. A current limiter (ANL/AML) is installed as well.
You intend to load shed, but don’t do so immediately. What are the consequences?
My assumption is the voltage will drop and the battery will supplement the alternator for some period of time until you can load shed and then the alternator will carry the entire load? I assume the current limiter will not blow with a short duration small overload.
Thanks in advance for educating me.
Krea Ellis
; -Matt Dralle, List Admin.
http://www.matronics.=================
http://wiki.matronics.com<====================
http://w======
|
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
nuckollsr
Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS
|
| Posted: Sat Feb 15, 2020 3:01 pm Post subject: Re: Alternator, battery and bus question |
|
|
| Quote: | | What happens if an alternator is temporarily overloaded (let’s say it’s rated at 40 amps) and you draw 45 amps. Assume the battery is well maintained and fully charged. A current limiter (ANL/AML) is installed as well. |
An alternator is inherently overload-proof. The magnetics
prevent output at more than a few percent above nameplate
rating. This is temperature dependent. We have discussed
instances here on the list where a cold alternator attempting
to stuff electrons into a badly discharged batter will trip the
b-lead breaker on some single engine aircraft. This is rare
but not unheard-off . . . happened to me once and the ensuing
load-dump killed the regulator. Flew the whole drip in the
dark-panel mode.
A current limiter is exceedingly robust . . . they will carry
50 to 100 percent of rating indefinitely. This is why they
are used as DISTRIBUTION protection and have replaced the
legacy 60A breaker that was common on most single engine
aircraft with 60A alternators.
Assuming one has installed PROPER b-lead protection in
the way of a current limiter, then all is well on the alternator
side of the equation. An alternator cannot open it's own
properly designed b-lead protection except in the case of
BADLY damaged (shorted) rectifiers. Haven't seen a case
of that since . . . oh . . . about 1975 on some Chrysler products.
| Quote: | | You intend to load shed, but don’t do so immediately. What are the consequences? |
The alternator will put out it's rated current indefinitely with no
potential for hazard to any equipment in the airplane. It essentially
becomes a constant current/constant voltage power supply
operating in the constant current mode until demands are
reduced whereupon bus voltage will rise to the regulation
set-point and normal operations resume.
| Quote: |
My assumption is the voltage will drop and the battery will supplement the alternator for some period of time until you can load shed and then the alternator will carry the entire load? I assume the current limiter will not blow with a short duration small overload. |
Correct.
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
nuckollsr
Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS
|
| Posted: Sat Feb 15, 2020 3:19 pm Post subject: Re: Alternator, battery and bus question |
|
|
[quote]The situation described in my last post is not likely to happen on an aircraft that has a fully charged battery. The most common way that rectifier diodes get damaged is by jump starting a vehicle that has a dead battery. The alternator is then forced to generate current at maximum output for an extended length of time to refill the battery. That could cause the diodes to overheat and fail. So the lesson is if you have a dead battery don't just jump start it. Recharge the battery before you start the engine. [quote]
The legacy prohibition for doing a ground power start on a aircraft
with a dead battery has more to do with risks to the battery than
to the alternators/generators.
Suppose you've got a PC680 or smaller battery on an airplane fitted
with a 60A or larger alternator. That little hunk of plastic enclosed lead
will quite willingly accept what ever the alternator offers. If bus loads are
low, then you're going to be pounding the little feller pretty hard.
Similarly, biz-jets might have a 40 a.h. battery charged by a PAIR of
300 or 400 amp starter generators. Same problem in spades.
There is little risk for jump starting most light aircraft 'cause you can't
get full output from the alternator at taxi rpms . . . so by the time you're
out at the runway ready to take off, recharge current has dropped off
substantially . . . but the risks are not zero. If you've got instrumentation
to manage battery recharge rates it's no big deal. But try to add 3 or 4
paragraphs on this topic to the pilot's handbook on a TC GA aircraft and
you'll have the sales wienies all over you.
We used to have some nice fat loads (landing lights and pitot heaters)
that would help manage recharge rates on SE aircraft. Those assets
are going away. Know what needs to be done and make sure you
CAN do it.
Solution is a placard: "Charging a dead battery with ships generators
is not recommended (or prohibited)." Risk goes away along with any
need to further educate a pilot. Best thing to do is recharge the battery
before spooling up for departure but there are alternatives for the astute
owner/operator.
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
