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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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 Posted: Fri Jul 20, 2007 5:30 am Post subject: Perihelion Power Protector Proposal |
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I talk to many builders who are particularly concerned about frying their expensive avionics and glass panels. These parts are typically 1/3 of the airplane cost.
Planning the wiring of a small aircraft involves installing systems to safeguard the buses against failure of the alternator. Either an internally regulated alternator or its more adaptable brother with an external regulator still has the potential problem of a runaway condition, as well as a short circuit of the main battery to alternator B-lead, and frequent load dump OV conditions.
A solution is herein proposed—
Linear Technology has introduced a clever device, the LT4356-1 Overvoltage Protection Regulator and Inrush Limiter to address all these worries. Not only that…they list “Automotive/Avionic Surge Protection” is one of its chief applications.
The LTC approach takes the high voltage from a load dump or failed alternator and REGULATES it while the situation is being tamed. The IC package is 3mm X 4mm and drives a big N-MOSFET that does the heavy work of regulating the voltage.
So what happens? Normally the alternator current is carried by the fully on N-MOSFET. Assume the current is 50A, and the Rds(on) is 0.012 ohms. The dissipation would be only 30W. This is easy to handle with a reasonable heat sink.
Assume the alternator and/or the regulator goes cuckoo. This could happen if the alternator field winding shorts to the B-lead output or the sense lead in the regulator opens, or other untoward goings-on. The alternator output goes into an upward voltage spiral. This voltage is not unlimited, especially if there is a load on it, but could be 80 VDC.
Now the LT4356-1 REGULATES the output via the big N-MOSFET on a heat sink. The aircraft buses never sees more than 14.5 Volts (or whatever is desired). This is true for the short time (500 mS) load dumps, and it will regulate a runaway alternator for a time determined by whatever the N-MOSFET and heat sink can dissipate.
The LT4356-1 has a timer circuit to protect the N-MOSFET. If the time expires and the stress continues, the fault warning signals an impending power-down and the N-MOSFET shuts off the B-line.
Additionally, some models of the LT4356-1 have a spare amplifier/comparator that can be used for any purpose (not shown here). It operates from 4 to 80 VDC, and withstands –30V and up to 100V. A series low voltage P-MOSFET or a Schottky diode can be added to protect against a shorted alternator that would draw reverse current. The device has built-in protection again high current shorts of the B-Line to the battery.
The drawing shows a basic form. A few additional parts are necessary. However, consider the parts that WOULDN’T be necessary:
The B-Line contactor,
The OV monitor,
The load dump preventer,
The B-Line fuse,
The alternator switch.
No crow bar or linear over voltage switch.
I don’t have current plans to market this but will build one for myself.
Discussion is invited.
See attachment for a pdf version of this note with drawing.
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Download |
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Power Protector rev A.pdf |
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24.36 KB |
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465 Time(s) |
_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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mprather(at)spro.net
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| Posted: Fri Jul 20, 2007 7:39 am Post subject: Perihelion Power Protector Proposal |
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Interesting..
Kind of a regulator on a regulator..
Do you see that the addition of this circuitry will meaningfully
negatively impact the stability of the existing regulator? Existing
alternator systems are filtered by a low impedance connection to the
battery. It seems that it might be good to design the set point of this
regulator quite a bit higher than the primary - as a means of limiting
interaction between the systems.
Regards,
Matt-
| Quote: |
<emjones(at)charter.net>
I talk to many builders who are particularly concerned about frying their
expensive avionics and glass panels. These parts are typically 1/3 of the
airplane cost.
Planning the wiring of a small aircraft involves installing systems to
safeguard the buses against failure of the alternator. Either an
internally regulated alternator or its more adaptable brother with an
external regulator still has the potential problem of a runaway condition,
as well as a short circuit of the main battery to alternator B-lead, and
frequent load dump OV conditions.
A solution is herein proposed—
Linear Technology has introduced a clever device, the LT4356-1 Overvoltage
Protection Regulator and Inrush Limiter to address all these worries. Not
only that…they list “Automotive/Avionic Surge Protection” is one of
its chief applications.
The LTC approach takes the high voltage from a load dump or failed
alternator and REGULATES it while the situation is being tamed. The IC
package is 3mm X 4mm and drives a big N-MOSFET that does the heavy work of
regulating the voltage.
So what happens? Normally the alternator current is carried by the fully
on N-MOSFET. Assume the current is 50A, and the Rds(on) is 0.012 ohms. The
dissipation would be only 30W. This is easy to handle with a reasonable
heat sink.
Assume the alternator and/or the regulator goes cuckoo. This could happen
if the alternator field winding shorts to the B-lead output or the sense
lead in the regulator opens, or other untoward goings-on. The alternator
output goes into an upward voltage spiral. This voltage is not unlimited,
especially if there is a load on it, but could be 80 VDC.
Now the LT4356-1 REGULATES the output via the big N-MOSFET on a heat sink.
The aircraft buses never sees more than 14.5 Volts (or whatever is
desired). This is true for the short time (500 mS) load dumps, and it will
regulate a runaway alternator for a time determined by whatever the
N-MOSFET and heat sink can dissipate.
The LT4356-1 has a timer circuit to protect the N-MOSFET. If the time
expires and the stress continues, the fault warning signals an impending
power-down and the N-MOSFET shuts off the B-line.
Additionally, some models of the LT4356-1 have a spare
amplifier/comparator that can be used for any purpose (not shown here). It
operates from 4 to 80 VDC, and withstands –30V and up to 100V. A series
low voltage P-MOSFET or a Schottky diode can be added to protect against a
shorted alternator that would draw reverse current. The device has
built-in protection again high current shorts of the B-Line to the
battery.
The drawing shows a basic form. A few additional parts are necessary.
However, consider the parts that WOULDN’T be necessary:
The B-Line contactor,
The OV monitor,
The load dump preventer,
The B-Line fuse,
The alternator switch.
No crow bar or linear over voltage switch.
I don’t have current plans to market this but will build one for myself.
Discussion is invited.
See attachment for a pdf version of this note with drawing.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=124938#124938
Attachments:
http://forums.matronics.com//files/power_protector_rev_a_851.pdf
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echristley(at)nc.rr.com
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| Posted: Fri Jul 20, 2007 8:50 am Post subject: Perihelion Power Protector Proposal |
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Eric M. Jones wrote:
| Quote: |
I talk to many builders who are particularly concerned about frying their expensive avionics and glass panels. These parts are typically 1/3 of the airplane cost.
Planning the wiring of a small aircraft involves installing systems to safeguard the buses against failure of the alternator. Either an internally regulated alternator or its more adaptable brother with an external regulator still has the potential problem of a runaway condition, as well as a short circuit of the main battery to alternator B-lead, and frequent load dump OV conditions.
A solution is herein proposed—
<snip>
|
| Quote: | Now the LT4356-1 REGULATES the output via the big N-MOSFET on a heat sink. The aircraft buses never sees more than 14.5 Volts (or whatever is desired). This is true for the short time (500 mS) load dumps, and it will regulate a runaway alternator for a time determined by whatever the N-MOSFET and heat sink can dissipate.
The LT4356-1 has a timer circuit to protect the N-MOSFET. If the time expires and the stress continues, the fault warning signals an impending power-down and the N-MOSFET shuts off the B-line.
I'm confused by this part. It'll regulate indefinitely (if the load is
|
low enough), but it has a timer to turn off the N-MOSFET.
1) Is the timer based on power? For example, it will run indefinitely
with a 20A load, ten minutes with a 30A load, but one thirty seconds
with a 40A load? Could it be set to drive multiple N-MOSFET for
increased power handling.
2) Is the timer configurable, so that I could provide active cooling and
set it to run indefinitely regardless of the load?
3) Does it reset /is it resettable after a cool-off period? Yeah, the
alternator is on the fritz, but this device will let it run for short
periods to insure the plane make it all the way to the crash site.
4) Assuming appropriate answers to the above, what would be the
impediment to using this device as the primary regulator? It looks like
an extremely simple, compact solution, with the absolute simplest
interface possible.
It looks like a very promising solution at first glance.
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echristley(at)nc.rr.com
Guest
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| Posted: Fri Jul 20, 2007 9:03 am Post subject: Perihelion Power Protector Proposal |
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Eric M. Jones wrote:
| Quote: |
I talk to many builders who are particularly concerned about frying their expensive avionics and glass panels. These parts are typically 1/3 of the airplane cost.
Planning the wiring of a small aircraft involves installing systems to safeguard the buses against failure of the alternator. Either an internally regulated alternator or its more adaptable brother with an external regulator still has the potential problem of a runaway condition, as well as a short circuit of the main battery to alternator B-lead, and frequent load dump OV conditions.
A solution is herein proposed—
Linear Technology has introduced a clever device, the LT4356-1 Overvoltage Protection Regulator and Inrush Limiter to address all these worries. Not only that…they list “Automotive/Avionic Surge Protection” is one of its chief applications.
After my previous email, I found the data sheet.
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http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1006,C1065,P38400#simulateSection
The timer is configurable. They have way to order samples, and an
LTSpice setup to run simulations with.
Dang-it!! Another project! 8*)
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gmcjetpilot
Joined: 04 Nov 2006
Posts: 170
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| Posted: Sun Jul 22, 2007 4:56 pm Post subject: Perihelion Power Protector Proposal |
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| Quote: | From: "Eric M. Jones" <emjones(at)charter.net>\ ([email]emjones(at)charter.net>\[/email])
Planning the wiring of a small aircraft involves installing systems
to safeguard the buses against failure of the alternator.
|
Nice I like it. Here are a couple of things may be to incorporate?
How about 100% isolation/protection 100% of the time?
The idea is an "A" system and a full time isolated "B" system.
I was thinking about a DC-DC battery charger & second battery.
This would make an independent "B" system from the "A" main bat
and alternator system. The "B" battery charger/battery whould give
continuous protection, as long as the charger did not go crazy or the
"B" battery did not explode, which is unlikely. If the charger failed the
battery should still be there.
http://www.powerstream.com/DCC.htm
No mater what happens with the alternator the battery charger will
isolate. Down side is 3.3 lbs, cost, plus 2nd battery weight.
You should install a manual relay to by-pass the charger and
bring the "protected" "B" system on-line with the main "A" system
as a back up.
Jets use battery chargers for similar reasons and also because
the main "A" system or systems are AC not DC. However battery
chargers do isolate the DC system.
** The SECOND jewel I came across: "BatteyLink" ACR (tm) **
http://bluesea.com/category/2/products/7600
Before you all poo-poo it, it's NOT a parallel battery bank diode.
It is a smart/logic controlled auto charge relay (ACR), and it
isolates and protect for low and high voltage.
Voltage is user settable. Click on the tabs & the hyper links
(the hyper text is monochrome and not obviously hyper links
at least on my screen, so hunt around the link about).
This would be instead of a battery DC-DC charger.
Here's the instructions:
http://bluesea.com/files/resources/instructions/6330.pdf
With optional switch you can override. It's not made to parallel
for starting, but it can in a pinch up to 60amps. There's many
ways you can incorporate this ACR into a protected essential
"B" system in your wiring hierarchy.
Just thoughts, Cheers George
[quote][b]
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