Today's Message Index:
----------------------
1. 06:36 AM - Re: BNC Connector (LarryRobertHelming)
2. 06:36 AM - MOSFET potting/off topic (David A. Leonard)
3. 11:18 AM - MOSFET Off Topic (Eric M. Jones)
4. 03:18 PM - MOSFET OFF TOPIC (Eric M. Jones)
5. 05:56 PM - Re: Unstable charging system . . . (Robert L. Nuckolls, III)
6. 07:18 PM - Re: Sky-Tec starters and solenoids (Robert L. Nuckolls, III)
7. 08:59 PM - Wire runs/clamps. (Dean Psiropoulos)
Message 1
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| Subject: | Re: BNC Connector |
--> AeroElectric-List message posted by: "LarryRobertHelming" <lhelming@sigecom.net>
Thanks for the good advice. I appreciate it.
Indiana Larry, RV7 Tip-up TMX-O-360 ACS2002 Dynon CNS430 Digitrak
On Finish Kit
----- Original Message -----
From: <PeterHunt1@aol.com>
Subject: AeroElectric-List: BNC Connector
> --> AeroElectric-List message posted by: PeterHunt1@aol.com
>
> Larry,
>
> If you are installing a Garmin 430 I suggest getting top of the line
antenna
> lead-in and connectors. I just installed the antenna on my Garmin GNS
530. I
> purchased Coaxial cable (part number RG-142 Coax) and Amphenol RFX BNC
> connectors (part number 31-2-RFX) from Gulf Coast Avionics. 800-474-9714
or
> www.gulf-coast-avionics.com.
>
> This BNC connector is a male connector which fits the Garmin as well as
Van's
> antennas. The feature which I like is that it requires no crimping (no
need
> for a questionable crimping tool). A tiny male tip gets soldered to the
> internal wire. Then you just assemble the parts and screw the connector
together.
> If the instructions on the Amphenol package are not clear, just let me
know.
> The antenna cable I am suggesting is a little costly at $4.00 a foot. I
just
> don't think it is wise to install an expensive Garmin 430 and then try to
> save $10 on cheap antenna lead-in and connectors. IMHO.
>
> Pete
> RV-6, panel
> N216PH reserved
>
>
Message 2
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| Subject: | MOSFET potting/off topic |
--> AeroElectric-List message posted by: "David A. Leonard" <dleonar1@maine.rr.com>
This is an off topic question, but once again the members of this list are
the most knowlegeable
people I know in the spark chasing department.
My Old BMW 88 735..250k miles..car uses a large resistance heat sink,
called a Sword, by those that know what I'm referring to, to regulate the
fan blower speed for the HVAC. Here is a photo as my verbal explanation
leaves a little to the imagination .
http://www.bmwe34.net/E34main/Maintenance/Electrical/Sword.htm
It is about 12" long, and the main heat sink is a piece of 1/8" x 4" x 12"
aluminum plate that hangs out there in the breeze of the HVAC main
duct. On it is mounted an equally long PCB, and every 4" is a BUZ71a
Mosfet. They are rumored to be the failure mode ( and the sword seems
die regularly to the tune of $200 for the complete assembly, which has
gotten old after the third one died) and the blower will only run one speed
or not at all. The Mosfets bases ground to the plate, and feed from the
PCB. The bases are riveted to the aluminum plate. They are heavily potted
in some type of glue(epoxy?).
I have been able to remove the potting from them with a heat gun, and
remove the Mosfets, and order more ($10.00 for twice as many as I need, I
have an old core I'm working on as well as the latest failed one)
My question: both sides of the mosfet are heavily gunked with this potting,
all around the device, and also on the back of the pcb where the leads
solder in.
What does the potting do..the devices are also riveted in so it isn't
structural. Is it a moisture concern? I think they must get hot, hence the
mounting to the air cooled plate, but the heat gun will soften the potting,
so I assume they don't get real hot.
Can I use Marine tex, or structural Urethane, or 5 minute epoxy to repair
this? Hot Melt Glue? Is there a real product I should buy? Is it
important to totally encapsulate the mosfet and leads? That seems to be
the case with the original. The repair procedure seems to ignore repotting.
Thanks for the help, and I realize that I'm off topic..but I do drive it to
the airport a lot to fly the Viking, and the BMW symbol is a spinning
propeller on a blue background....
Dave Leonard, a man with a lot of old electronic junk...
Message 3
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| Subject: | MOSFET Off Topic |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
Dave,
It depends on how much re-engineering you want to do.
The BUZ71a is a good part for its time. There are better ones available, but
it will do.
Can you get a schematic of the thing? This would help a lot.
>both sides of the mosfet are heavily gunked with this potting,
>all around the device, and also on the back of the pcb where the leads
>solder in.
>What does the potting do..the devices are also riveted in so it isn't
>structural. Is it a moisture concern? I think they must get hot, hence the
>mounting to the air cooled plate, but the heat gun will soften the potting,
>so I assume they don't get real hot.
Answer to the potting question--The potting keeps people from fixing it, but
also keeps out moisture. The MOSFET is very prone to moisture problems
because of the very sensitive gate lead. There are silicones that are pretty
easy to remove. Just make sure they are thoroughly dry before first using
the device. Any potting will do.
Now for the problem. These things should not fail. Some hints and tips---
The blower motor at 250k miles is probably worn out. The motor current may
have
gone way up (check this). Of course you could put in a bigger MOSFET but you
might want to service or replace the motor.
The BUZ71a tab should be common to the center pin on the TO220. This is the
drain pin and it must be positive. This make me think the heatsink must be
V+. Is this true? Then be careful that it must remain insulated.
The MOSFET gate gets a positive voltage (<20V) from the switch to turn it
on. The gate voltage CAN'T go higher, not even for a microsecond!
MOSFETs are prone to failure from both high voltages and electrostatics
and arcing (from old switch contacts maybe?). A simple input filter to the
gate will prevent that. This filter could consist of a couple of 10V zeners
one to + and one to ground, or even a ceramic cap to ground.
The MOSFET is probably a "high-side" switch. This means that there is some
Voltage boosting circuitry driving the gate. This is always suspect
circuitry. Capacitors degrade, parts change values...
If there is some errant voltage spike from source to drain (again possible
in an old BMW) a zener diode (20 V) across the drain to source will help.
The MOSFET itself actually has one of these in it maybe it could use some
help.
You could replace the MOSFET with a MUCH beefier device and cross your
fingers that nothing downstream will fail instead. The values to look for
are:
Vdss > 60V
Rdson<0.010 Ohms
N-channel
TO-220
There is reason to suspect this may be the best way to go. My experience
both with MOSFETs and German engineers is that they don't leave any margins.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in
- - Leonard Cohen
Message 4
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| Subject: | MOSFET OFF TOPIC |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
David,
Buy these on eBay cheap:
12) IRF3710Z Power MOSFETS 100 Volts, 59 Amps Item number: 2553456836
They will do the trick.
Eric
Message 5
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| Subject: | Re: Unstable charging system . . . |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
I subscribed to the aeroelectric section and RV6 information
on Matromics. My problem with my charging system is that while
it is charging my Amp gauge rapidly deflects to the "charge" side,
and the volt meter roams around from 14.2 to 15.0 constantly.
The battery is six months old and checks out good, the voltage
regulator (ford type) checks good, and the alternator (Japanese
type) just had new bearing and brushes installed and the diodes
were good. I checked the wiring, and everything looks and tests
good. The Amp gauge is a two terminal type and one suggestion
was to get rid of that type.
Ammeters don't "go bad" and cause this. If the system
worked before, something else is going on.
. . . . The system has 648hrs. on it now
and started this several months ago, or at least the Bouncing
Amp meter. Any ideas?
Any time the ammeter and/or voltmeter jumps around even
though major components of the system checks good suggests
a wiring and/or grounding problem. Regulators can
become unstable if there is too much wiring and component
resistance between the regulator and the bus . . . and
we're talking about MILLIOHMS . . .
Try hooking your regulator right up to the back of the
alternator with lead wires of 12" or so. Ground case
of regulator to case of alternator, connect the "S" and
"A" terminals together and wire them to the alternator's
fat terminal (b-lead). Connect regulator "F" terminal
of regulator to field of alternator.
Fire up engine and see what happens. I'll bet your
voltage settles out between 14.0 and 14.4 volts and
the ammeter will stop thrashing around.
Are you using a single point ground system? How long
and what size wires are used to connect "A" and "S"
of regulator to the bus. How are you protecting the
system for OV conditions?
Bob . . .
Message 6
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| Subject: | Re: Sky-Tec starters and solenoids |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
Rich,
Denis Walsh sent me 4 solenoids which were removed
from service on his Sky-Tec starter. I've not had
time to examine them closely but the solenoid core
of one was detached such that it could be removed.
The bore in which these cores operate seem to be
lined with brass sleeves. The sleeve is fabricated
from sheet material. I peeled a corner away from
the bore wall and measured a thickness of 0.015"
Pushing the cores in by hand while applying pressure
and bending moments. I was unable to sense any
tendency to hang up.
I understood your earlier post to the AeroElectric-List
to describe vibration induced damage pattern to a plastic
wall which would occasionally prevent full travel
of the solenoid core.
Perhaps my mental image of what you described is
in error. Can you help me out here?
Bob . . .
--------------------------------------------
( Knowing about a thing is different than )
( understanding it. One can know a lot )
( and still understand nothing. )
( C.F. Kettering )
--------------------------------------------
Message 7
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| Subject: | Wire runs/clamps. |
--> AeroElectric-List message posted by: "Dean Psiropoulos" <deanpsir@easystreet.com>
A couple quick questions:
I'm looking (finally) at running some wire out to the back end of my RV-6
before I rivet the aft top skins on. I drilled some holes in the bulkheads
and Van's supplies lots of grommets which I installed. The dilemma I have
now is how to secure that wire. For the tefzel wire we use, what should I
use to secure it, adel clamps, zip ties or what? How would I fasten those
clamps along the floor of the airplane, don't want to drill a hole in the
skin, double sided tape likely won't stick to the primer or at least stay on
so.. any suggestions? Also how often should I secure the wire, every 3
inches every 6 inches, every foot, what? Thanks.
Dean Psiropoulos
RV-6A finish kit.
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