john(at)ballofshame.com
Guest
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 Posted: Thu Jan 25, 2007 10:53 am Post subject: IR alternators in airplanes (JUST say NO to OV relays) |
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External OV protection with an external regulator is solid state. When
the crowbar trips, the field is grounded, thus driving the alternator
output to 0. The fact that the field circuit breaker pops some time later
is beside the point. If you wanted to you could wire the the field with a
massive bus bar and leave the circuit breaker out completely. The field
wire will be at 0 potential going into the regulator because it's
grounded. Of course, doing this would destroy your battery in short
order.
Putting OV protection on internal regulators requires the relay to work
and is much kludgier. Though the module might be the same, they function
COMPLETELY differently and shouldn't be confused.
-John
www.ballofshame.com
| Quote: | >From: "Robert L. Nuckolls, III"
>>Can I use the LR3C from B&C to prevent OV
>>problems? Or, does someone else sell such a
>>device?
>>
>>Thanks David Weber
>Internally regulated alternators are a what-you-
>see-is-what-you-get. If it is your desire to have
>these marvelous-but-not-perfect devices operated
>within the design goals we've been using for
>externally regulated alternators then some form of
>external adaptation is necessary necessary.
What does that mean?
Yea see-is-what-you-get inside of an internal
regulator:
http://img103.imageshack.us/my.php?image=slide2jo1.jpg
Here is a typical external or LR3C regulator
http://img62.imageshack.us/my.php?image=slide7bj9.jpg
or
http://img269.imageshack.us/my.php?image=slide6it5.jpg
OV protection is for externally regulated
alternators, NOT internally regulated. WHY?
Because internally regulated alternators are not
designed for external protection. External
regulators are old fashioned, even the LR3C needs
over voltage protection because they have
no protection at all (unless you use a modern
external voltage regulator, like a V120 below).
If you want OV protection for an Externally
regulated alternator use this regulator,
http://195.125.241.148/cgi-win/product.exe?V1200
OR if you are worried about your I-VR alternator,
buy a plane power alternator from Plane power,
which Vans Aircraft sells.
http://www.plane-power.com/
or
http://www.vansaircraft.com/cgi-bin/catalog.cgi?ident=1169746824-338-558&browse=engines&product=alternator-kit
The level of fear of OV is not justified by the facts
and its based on ignorance, urban legend and folklore.
Very few I-VR's have OV events and when they do
they are mild and easily controlled with RPM or
adding extra electrical load (say landing lights) or
its just not an issue.
If you want to add an OV monster relay on your
plane's I-VR ND alternator, please consider NOT
and doing the above.
The choice is about 10% technical, 40% preference
and 50% emotional, but OV relays are old time news.
The emotional part is what some vendors like B&C
use as a sales pitch with dark and stormy night
stories. If you are VFR and have modern avionics
that can handle 10-32 volts and 60 volts surge, as
most can, than considered NOT using an OV relay.
When you hear another OV happened with an I-VR,
ask really, what happened? The reality is not as
bad as the imagination might lead.
(*Call your manufacture to confirm. If operational
voltage is listed as 10-32 volts in the owners manual,
chance is the electronics has filtered protected power
supply.)
Just say NO to BIG, FAT, Heavy over voltage
relays. This is antiquated technology based on the
old days of externally regulated alternators that had
OV events and BAD ones at that. Modern OV
alternators are less likely to have over voltage
with their ON BOARD sophisticated regulators
that monitor things like temperature, which
external regulators could not ever dream of.
JUST SAY NO TO OV RELAYS, WELCOME
TO THE 21st CENTRY, I-VR ALTERNATORS
OR SOLID STATE OV PROTECTED EXTERNAL
VOLTAGE REGULATORS.
No offense to Bob, but OV relays are a step backwards.
Cheers, George
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