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rv10(at)sinkrate.com
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 Posted: Wed May 07, 2008 7:25 pm Post subject: PMA-6000 intercom 28V install |
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PS Engineering’s PMA-6000 intercom has the following note:
“To reduce the amount of heat dissipated in the audio selector panel, when used in a 28
Volt aircraft, it is required that the 15-Ohm, 15-Watt dropping resistor (p/n 701-015-1501) be in-
stalled in series with the power input.”
The install manual goes on to say “failure to do so will generate unnecessary heat inside the unit and may void PS Engineering’s warranty”. Does anyone have experience installing one of these units in a 28V environment? Is the dropping resistor really required? The only reason I ask is the local radio shops don’t seem to know much about it which makes me wonder if they ever used them. They all say they can order one but nobody has one in stock.
-Ben Westfall
[quote][b]
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hooverra(at)verizon.net
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| Posted: Thu May 08, 2008 3:02 am Post subject: PMA-6000 intercom 28V install |
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Ben,
Sounds like about 12 w or so of extra heat localized near the regulator (probably not a switcher with this note) I would follow PS Engineering’s recommendation. Because some have ignored the advice and not installed the resistor and it worked doesn’t mitigate the long term effects of additional heat. Most things electronic work better and last longer if kept cool.
Ralph Hoover
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Ben Westfall
Sent: Wednesday, May 07, 2008 11:24 PM
To: aeroelectric-list(at)matronics.com
Subject: AeroElectric-List: PMA-6000 intercom 28V install
PS Engineering’s PMA-6000 intercom has the following note:
“To reduce the amount of heat dissipated in the audio selector panel, when used in a 28
Volt aircraft, it is required that the 15-Ohm, 15-Watt dropping resistor (p/n 701-015-1501) be in-
stalled in series with the power input.”
The install manual goes on to say “failure to do so will generate unnecessary heat inside the unit and may void PS Engineering’s warranty”. Does anyone have experience installing one of these units in a 28V environment? Is the dropping resistor really required? The only reason I ask is the local radio shops don’t seem to know much about it which makes me wonder if they ever used them. They all say they can order one but nobody has one in stock.
-Ben Westfall
| Quote: | | http://www.matronics.com/Navigator?AeroElectric-List |
0123456789
[quote][b]
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etienne.phillips(at)gmail
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| Posted: Thu May 08, 2008 11:03 pm Post subject: PMA-6000 intercom 28V install |
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Here's my suggestion... (Hello for the first time everybody, by the way):
What about using a DC-DC converter? Using a resistor, the extra energy provided by the 28V is simply dissipated as heat... Using a DC-DC converter, the voltage is usually dropped using a tiny switching-type power supply.
Doing the Maths:
Worst case is that the 15W resistor is being driven to the limit of 15W
Using P=I^2 * R
yields a current draw by the intercom of 1A
There is a fair variety of 14V switching voltage regulators (or DC-DC converters), eg: PT78ST114 from Texas Instruments (spec sheet: http://www.ti.com/lit/gpn/pt78st114 ) this one has a 90%+ efficiency, and is a single component with 3 legs: In, Out and Ground... In connects to 28V, Out connects to the intercom power in, and the intercom's ground, the voltage regulator's ground and panel ground connect together. It's also advised to put a smoothing cap on either side, so I guess the total component count is actually 3 parts.
No heat, no power wastage, and ripple- and spike-free power for the intercom...
Disadvantage: black box between power and intercom that could fail.
Risk: Highly unlikely, these things have all sorts of built in protection against heat, short-circuit, open circuit, over-current draw, etc...
Anyway, it's just an intercom 
What do you guys think?
Etienne
On 08 May 2008, at 12:59 PM, RALPH HOOVER wrote:
[quote]Ben,
Sounds like about 12 w or so of extra heat localized near the regulator (probably not a switcher with this note) I would follow PS Engineering’s recommendation. Because some have ignored the advice and not installed the resistor and it worked doesn’t mitigate the long term effects of additional heat. Most things electronic work better and last longer if kept cool.
Ralph Hoover
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Ben Westfall
Sent: Wednesday, May 07, 2008 11:24 PM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: PMA-6000 intercom 28V install
PS Engineering’s PMA-6000 intercom has the following note:
“To reduce the amount of heat dissipated in the audio selector panel, when used in a 28
Volt aircraft, it is required that the 15-Ohm, 15-Watt dropping resistor (p/n 701-015-1501) be in-
stalled in series with the power input.”
The install manual goes on to say “failure to do so will generate unnecessary heat inside the unit and may void PS Engineering’s warranty”. Does anyone have experience installing one of these units in a 28V environment? Is the dropping resistor really required? The only reason I ask is the local radio shops don’t seem to know much about it which makes me wonder if they ever used them. They all say they can order one but nobody has one in stock.
-Ben Westfall
0
1[b]
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hooverra(at)verizon.net
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| Posted: Fri May 09, 2008 3:08 am Post subject: PMA-6000 intercom 28V install |
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Etienne,
I suspect that PS engineering is using an analog regulator for noise concerns (cost can figure in as well). Use care inserting a switcher without properly considering the noise concern. A switcher would certainly allow for a wide input voltage range without a lot of heat. Not a show stopper but a design challenge to address.
This is just my take I have no knowledge of PS Engineering’s design or the process and decisions they have taken to arrive at their design. I have used a switcher for my ANR power supply I’ll soon find out if I have any issues!
Ralph & Laura Hoover
RV7A N527LR
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Etienne Phillips
Sent: Friday, May 09, 2008 2:58 AM
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: PMA-6000 intercom 28V install
Here's my suggestion... (Hello for the first time everybody, by the way):
What about using a DC-DC converter? Using a resistor, the extra energy provided by the 28V is simply dissipated as heat... Using a DC-DC converter, the voltage is usually dropped using a tiny switching-type power supply.
Doing the Maths:
Worst case is that the 15W resistor is being driven to the limit of 15W
Using P=I^2 * R
yields a current draw by the intercom of 1A
There is a fair variety of 14V switching voltage regulators (or DC-DC converters), eg: PT78ST114 from Texas Instruments (spec sheet: http://www.ti.com/lit/gpn/pt78st114 ) this one has a 90%+ efficiency, and is a single component with 3 legs: In, Out and Ground... In connects to 28V, Out connects to the intercom power in, and the intercom's ground, the voltage regulator's ground and panel ground connect together. It's also advised to put a smoothing cap on either side, so I guess the total component count is actually 3 parts.
No heat, no power wastage, and ripple- and spike-free power for the intercom...
Disadvantage: black box between power and intercom that could fail.
Risk: Highly unlikely, these things have all sorts of built in protection against heat, short-circuit, open circuit, over-current draw, etc...
Anyway, it's just an intercom
What do you guys think?
Etienne
On 08 May 2008, at 12:59 PM, RALPH HOOVER wrote:
Ben,
Sounds like about 12 w or so of extra heat localized near the regulator (probably not a switcher with this note) I would follow PS Engineering’s recommendation. Because some have ignored the advice and not installed the resistor and it worked doesn’t mitigate the long term effects of additional heat. Most things electronic work better and last longer if kept cool.
Ralph Hoover
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Ben Westfall
Sent: Wednesday, May 07, 2008 11:24 PM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: PMA-6000 intercom 28V install
PS Engineering’s PMA-6000 intercom has the following note:
“To reduce the amount of heat dissipated in the audio selector panel, when used in a 28
Volt aircraft, it is required that the 15-Ohm, 15-Watt dropping resistor (p/n 701-015-1501) be in-
stalled in series with the power input.”
The install manual goes on to say “failure to do so will generate unnecessary heat inside the unit and may void PS Engineering’s warranty”. Does anyone have experience installing one of these units in a 28V environment? Is the dropping resistor really required? The only reason I ask is the local radio shops don’t seem to know much about it which makes me wonder if they ever used them. They all say they can order one but nobody has one in stock.
-Ben Westfall
| Quote: | | http://www.matronics.com/contribution |
[quote][b]
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sam.marlow
Joined: 25 Feb 2006
Posts: 99
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| Posted: Fri May 09, 2008 5:15 am Post subject: PMA-6000 intercom 28V install |
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Hi Etienne,
I'm not installing an intercom,but I do have the need to reduce bus voltage to a stable 4.8 to 5.0 volts for instrumentation at times. But I was wondering why you chose the PT78ST114S,isn't that 13.9 volt max out? Wouldn't the PT78ST05S work for 5.0v out? Or am I reading the chart incorrectly?
Thanks,
Sam Marlow
---- Etienne Phillips <etienne.phillips(at)gmail.com> wrote:
=============
Here's my suggestion... (Hello for the first time everybody, by the
way):
What about using a DC-DC converter? Using a resistor, the extra
energy provided by the 28V is simply dissipated as heat... Using a DC-
DC converter, the voltage is usually dropped using a tiny switching-
type power supply.
Doing the Maths:
Worst case is that the 15W resistor is being driven to the limit of 15W
Using P=I^2 * R
yields a current draw by the intercom of 1A
There is a fair variety of 14V switching voltage regulators (or DC-DC
converters), eg: PT78ST114 from Texas Instruments (spec sheet: http://
www.ti.com/lit/gpn/pt78st114 ) this one has a 90%+ efficiency, and is
a single component with 3 legs: In, Out and Ground... In connects to
28V, Out connects to the intercom power in, and the intercom's
ground, the voltage regulator's ground and panel ground connect
together. It's also advised to put a smoothing cap on either side, so
I guess the total component count is actually 3 parts.
No heat, no power wastage, and ripple- and spike-free power for the
intercom...
Disadvantage: black box between power and intercom that could fail.
Risk: Highly unlikely, these things have all sorts of built in
protection against heat, short-circuit, open circuit, over-current
draw, etc...
Anyway, it's just an intercom
What do you guys think?
Etienne
On 08 May 2008, at 12:59 PM, RALPH HOOVER wrote:
| Quote: | Ben,
Sounds like about 12 w or so of extra heat localized near the
regulator (probably not a switcher with this note) I would follow
PS Engineering’s recommendation. Because some have ignored the
advice and not installed the resistor and it worked doesn’t
mitigate the long term effects of additional heat. Most things
electronic work better and last longer if kept cool.
Ralph Hoover
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-
aeroelectric-list-server(at)matronics.com] On Behalf Of Ben Westfall
Sent: Wednesday, May 07, 2008 11:24 PM
To: aeroelectric-list(at)matronics.com
Subject: PMA-6000 intercom 28V install
PS Engineering’s PMA-6000 intercom has the following note:
“To reduce the amount of heat dissipated in the audio selector
panel, when used in a 28
Volt aircraft, it is required that the 15-Ohm, 15-Watt dropping
resistor (p/n 701-015-1501) be in-
stalled in series with the power input.”
The install manual goes on to say “failure to do so will generate
unnecessary heat inside the unit and may void PS Engineering’s
warranty”. Does anyone have experience installing one of these
units in a 28V environment? Is the dropping resistor really
required? The only reason I ask is the local radio shops don’t
seem to know much about it which makes me wonder if they ever used
them. They all say they can order one but nobody has one in stock.
-Ben Westfall
http://www.matronics.com/contribution
|
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etienne.phillips(at)gmail
Guest
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| Posted: Wed May 14, 2008 1:25 am Post subject: PMA-6000 intercom 28V install |
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|
You're quite right Ralph, there is a noise concern. I doubt that the noise would be of a value that would cause damage, so my suggestion would be to try it, and if it doesn't work then replace it with a resistor...
An alternative would be to use a switcher to get from 28V to 14V, then use an analogue voltage regulator to go to 12V. Something like a 7812 chip (connection details are identical to that of the switcher) would work quite nicely, and would only dissipate 2W at 1A, which is still somewhat better than 15W!
You could also smooth the noise by putting a few (around 5) 100uF capacitors in parallel, upstream and downstream of the switching regulator. I suggest this rather than a two 500uF caps, as it will handle a much wider range of noise frequencies, as well as offer a degree of redundancy. They could even be wired into the loom at regular intervals between the bus, switcher and intercom
I'm of a mindset that anything that gets hot will eventually cause problems somewhere... Also in case of an alternator failure, the last thing you want is for some minor component to start wasting precious energy by converting it to heat!
I hope that this helps 
Etienne
On 09 May 2008, at 1:04 PM, RALPH HOOVER wrote:
[quote]Etienne,
I suspect that PS engineering is using an analog regulator for noise concerns (cost can figure in as well). Use care inserting a switcher without properly considering the noise concern. A switcher would certainly allow for a wide input voltage range without a lot of heat. Not a show stopper but a design challenge to address.
This is just my take I have no knowledge of PS Engineering’s design or the process and decisions they have taken to arrive at their design. I have used a switcher for my ANR power supply I’ll soon find out if I have any issues!
Ralph & Laura Hoover
RV7A N527LR
[b]
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nuckolls.bob(at)cox.net
Guest
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| Posted: Wed May 14, 2008 7:38 am Post subject: PMA-6000 intercom 28V install |
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At 08:23 PM 5/7/2008 -0700, you wrote:
| Quote: | PS Engineering s PMA-6000 intercom has the following note:
To reduce the amount of heat dissipated in the audio selector panel, when
used in a 28
Volt aircraft, it is required that the 15-Ohm, 15-Watt dropping resistor
(p/n 701-015-1501) be in-
stalled in series with the power input.
The install manual goes on to say failure to do so will generate
unnecessary heat inside the unit and may void PS Engineering s warranty
. Does anyone have experience installing one of these units in a 28V
environment? Is the dropping resistor really required? The only reason I
ask is the local radio shops don t seem to know much about it which makes
me wonder if they ever used them. They all say they can order one but
nobody has one in stock.
|
It is risky to disregard the words of the manufacturer's
installation manuals. It's also disappointing that the
manufacturers of this device did not craft a user-friendly
design.
The simplest thing to do is comply with the instructions.
The simplest way to do this is acquire a component like
this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=FVTS10-15-ND
Note that it can be mounted to some handy, out of the
way surface on a long screw. The data sheet at:
http://www.heiresistors.com/PDF/FVT_FST20%20spec.pdf
tells us the hole through the middle of this device is
0.19" in diameter . . .
The drill versus threaded sizes chart at:
http://www.phy.mtu.edu/~suits/tapsizes.html
says this is too small for a 10-32 screw but will
be just fine for an 8-32. The resistor data sheet suggests
we need one with 2" or so of over-all length. You'll
be cranking a hard force down against a ceramic tube.
Put a soft washer (some kind of rubber, plastic or even
two layers of paper from the box that comes with a tube
of toothpaste) between the end of the resistor and the
mounting surface. Tighten the screw down to finger
tight + 1 turn and spot the threads with some runny
super-glue to keep it from drifting off that pressure setting.
If your resistor comes with wires, clip them off.
Attach lead wires for intercom power to the resistor's
solder-tabs. Put double layer of heat-shrink over these
joints for vibration support.
This process has been used thousands of designs in
various vehicular products including airplanes. Simple,
lean, works as the manufacturer wishes and lasts a long
time.
BTW . . . the 15W rating is super conservative. The
intercom may draw 1A peak current but the AVERAGE
current will be much lower unless you're particularly
fond of playing Wagner at 100dB in the headphones.
Now, if you're REALLY wanting to make this more
complicated, you can purchase one of B&C's DIM3-28
dimmers at:
http://www.bandc.biz/cgi-bin/ez-catalog/cat_display.cgi?10X358218#dim3-28
and instead of installing the dimmer potentiometer,
you put the appropriate resistor between pins 1 and 3
to achieve a constant 14-volt output from the "dimmer".
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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nuckolls.bob(at)cox.net
Guest
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| Posted: Wed May 14, 2008 5:42 pm Post subject: PMA-6000 intercom 28V install |
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|
At 08:23 PM 5/7/2008 -0700, you wrote:
| Quote: | PS Engineering s PMA-6000 intercom has the following note:
To reduce the amount of heat dissipated in the audio selector panel, when
used in a 28
Volt aircraft, it is required that the 15-Ohm, 15-Watt dropping resistor
(p/n 701-015-1501) be in-
stalled in series with the power input.
The install manual goes on to say failure to do so will generate
unnecessary heat inside the unit and may void PS Engineering s warranty
. Does anyone have experience installing one of these units in a 28V
environment? Is the dropping resistor really required? The only reason I
ask is the local radio shops don t seem to know much about it which makes
me wonder if they ever used them. They all say they can order one but
nobody has one in stock.
|
It is risky to disregard the words of the manufacturer's
installation manuals. It's also disappointing that the
manufacturers of this device did not craft a user-friendly
design.
The simplest thing to do is comply with the instructions.
The simplest way to do this is acquire a component like
this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=FVTS10-15-ND
Note that it can be mounted to some handy, out of the
way surface on a long screw. The data sheet at:
http://www.heiresistors.com/PDF/FVT_FST20%20spec.pdf
tells us the hole through the middle of this device is
0.19" in diameter . . .
The drill versus threaded sizes chart at:
http://www.phy.mtu.edu/~suits/tapsizes.html
says this is too small for a 10-32 screw but will
be just fine for an 8-32. The resistor data sheet suggests
we need one with 2" or so of over-all length. You'll
be cranking a hard force down against a ceramic tube.
Put a soft washer (some kind of rubber, plastic or even
two layers of paper from the box that comes with a tube
of toothpaste) between the end of the resistor and the
mounting surface. Tighten the screw down to finger
tight + 1 turn and spot the threads with some runny
super-glue to keep it from drifting off that pressure setting.
If your resistor comes with wires, clip them off.
Attach lead wires for intercom power to the resistor's
solder-tabs. Put double layer of heat-shrink over these
joints for vibration support.
This process has been used thousands of designs in
various vehicular products including airplanes. Simple,
lean, works as the manufacturer wishes and lasts a long
time.
BTW . . . the 15W rating is super conservative. The
intercom may draw 1A peak current but the AVERAGE
current will be much lower unless you're particularly
fond of playing Wagner at 100dB in the headphones.
Now, if you're REALLY wanting to make this more
complicated, you can purchase one of B&C's DIM3-28
dimmers at:
http://www.bandc.biz/cgi-bin/ez-catalog/cat_display.cgi?10X358218#dim3-28
and instead of installing the dimmer potentiometer,
you put the appropriate resistor between pins 1 and 3
to achieve a constant 14-volt output from the "dimmer".
Bob . . .
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Thu May 15, 2008 12:55 pm Post subject: Re: PMA-6000 intercom 28V install |
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|
To be clear, a switching power brick (aka DC-DC converter) turns DC
into AC then processes it and reconverts to DC. This process makes
audio and potentially RF noise. Noise injected into your intercom
will be a much worse problem than an old resistor hung on your firewall.
A resistor should also be about 1/10 the cost of a power brick. I
would guess available of amps to squander in a voltage dropping resistor
would not be an issue in your RV-10.
Cheers,
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nuckolls.bob(at)cox.net
Guest
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| Posted: Fri May 16, 2008 5:48 am Post subject: PMA-6000 intercom 28V install |
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|
At 01:55 PM 5/15/2008 -0700, you wrote:
| Quote: |
To be clear, a switching power brick (aka DC-DC converter) turns DC
into AC then processes it and reconverts to DC. This process makes
audio and potentially RF noise. Noise injected into your intercom
will be a much worse problem than an old resistor hung on your firewall.
|
DC to DC converters come in all flavors. Modern devices have
internal operating frequencies in the hundreds of kilohertz
and generally do not present a noise issue to audio systems.
They have been BIG issues to low frequency nav aids like
VLF Omega and LORAN but few folks use these technologies.
The next most vulnerable system would be an AM radio . . .
generally used for listening to ball games while airborne.
They have packaging issues. I'm aware of no bolt-in-and-wire-
it-up product suited to this task. DC to DC converters come
packaged as components for a larger assembly. Here's an
exemplar device:
http://www.lambdapower.com/ftp/Manuals/pxe_single_ins.pdf
So after you've selected a device with the right power
ratings, now you have to put it in a package of some kind
with screw terminals, push on tabs or perhaps a connector
of some kind. Of course this also offers an opportunity to
add whatever filtering is necessary to live responsibly with
the DO-160 rules of engagement.
| Quote: | A resistor should also be about 1/10 the cost of a power brick. I
would guess available of amps to squander in a voltage dropping resistor
would not be an issue in your RV-10.
|
Dropping resistors are, as a rule, to be avoided if there
are more elegant solutions at hand. Back when 12v cars were
coming into the marketplace, one could purchase a "Glo-Bar"
resistor designed to drop 12v down to 6v for the purpose of
installing a legacy 6v radio in a new 12v car. These ran
rather warm (30 watts or so) and the "squandering" of energy
was significant but not overtaxing to the system that produced
300+ watts.
In this case, we're considering a system that draws perhaps
100 mA in a quiescent state (1.5 volts dropped across the
15-ohm resistor and tossing off 150 MILLIwatts) and averages
perhaps 300 mA while listening to some music (4.5v drop and
1.3 watts). Peak currents pushing 1A would run the PEAK
dissipation in the dropping resistor up to 10-15 watts or
so . . . but this is exceedingly transient . . . in a system
that produces over 1000 watts of useable power makes this
decision electrically trivial.
The BIG driver in these deliberations is the hassle and
expense of $time$ that it would take to put a DC to DC
converter in a system that probably should have been fitted
with such capabilities from the factory.
Bob . . .
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echristley(at)nc.rr.com
Guest
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| Posted: Fri May 16, 2008 1:51 pm Post subject: PMA-6000 intercom 28V install |
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Robert L. Nuckolls, III wrote:
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They have packaging issues. I'm aware of no bolt-in-and-wire-
it-up product suited to this task. DC to DC converters come
packaged as components for a larger assembly. Here's an
exemplar device:
check mpja.com
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part number 14335-PS
They have a number of other DC-to-DC converters available, but if it was
just one low power device, I would use a 4-legged bridge rectifier or
eight, lined up on a circuit board. The negative output of one feeding
the positive input of the next. No noise. Compact. Useful for several
amps.
--
http://www.ronpaultimeline.com
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