homemade EFIS system and EMI

jcpearce wrote:

Thanks for the input.
Perhaps going with a linear power supply would be the way to go, I did
not as there are already three switching DC-DC power supplies on the
MB, the power efficiency is less than 50% for linear and I would have
to deal with the heat issues. I could just string a bunch of LM78xx and
LM79xx to get the required positive and negative voltages.

I've created a seperate smaller case for the PSU as creating a new
single case would have taken longer and I don't know about what level
of cooling issues I will have. I've noticed the PSU manufacturer (not
surprisingly) has reducd the MTBF when it is in hotter conditions. (but
hey perhaps I could use the heat to warm my cold toes in the Long Ez)
If the weather clears tomorrow I will go flying and measure how much of
a problem I have with it operating.

Thanks for the continuing input.
The LM79XX's will do you no good unless you have a source of negative
voltage to feed them. This generally will mean a dc to dc converter which
generally means switching regulators. Try putting your current powersupply
in a case and attach it directly to the MB's case and use feedthrough
capacitors in the common case bulkheads to feed the dc voltage in. Put
fedtrough caps and ferite beads on the dc in to the powersuppply case.
Cheep and will get you a good start to eliminating the noise.
John

John wrote:

jcpearce wrote:

Thanks for the input.
Perhaps going with a linear power supply would be the way to go, I did
not as there are already three switching DC-DC power supplies on the
MB, the power efficiency is less than 50% for linear and I would have
to deal with the heat issues. I could just string a bunch of LM78xx and
LM79xx to get the required positive and negative voltages.

I've created a seperate smaller case for the PSU as creating a new
single case would have taken longer and I don't know about what level
of cooling issues I will have. I've noticed the PSU manufacturer (not
surprisingly) has reducd the MTBF when it is in hotter conditions. (but
hey perhaps I could use the heat to warm my cold toes in the Long Ez)
If the weather clears tomorrow I will go flying and measure how much of
a problem I have with it operating.

Thanks for the continuing input.
The LM79XX's will do you no good unless you have a source of negative
voltage to feed them. This generally will mean a dc to dc converter which
generally means switching regulators. Try putting your current powersupply
in a case and attach it directly to the MB's case and use feedthrough
capacitors in the common case bulkheads to feed the dc voltage in. Put
fedtrough caps and ferite beads on the dc in to the powersuppply case.
Cheep and will get you a good start to eliminating the noise.
John

About $1.00 a piece from a couple sources I checked. So about $7.00 for the
PS voltages plus the dc input. (although some are sold only in 10 lots) if
you have multiple projects to use them up in you can order 100 quantity for
about $.50 each.
John

John wrote:

Thanks for the continuing input.
The LM79XX's will do you no good unless you have a source of negative
voltage to feed them. This generally will mean a dc to dc converter which
generally means switching regulators. Try putting your current
powersupply in a case and attach it directly to the MB's case and use
feedthrough capacitors in the common case bulkheads to feed the dc
voltage in. Put fedtrough caps and ferite beads on the dc in to the
powersuppply case. Cheep and will get you a good start to eliminating the
noise. John

About $1.00 a piece from a couple sources I checked. So about $7.00 for
the PS voltages plus the dc input. (although some are sold only in 10
lots) if you have multiple projects to use them up in you can order 100
quantity for about $.50 each.
John


Just checked Newark Catalog They have an interesting item:
A feed through teminal block with built-in filter capacitors
part # 95F895X
where x = number of terminals from 2 to 6.

Just something interesting to look into.
They have a lot of ideas for cap/ferite/filter ideas.
John

isn't there a step down treansformer taking 110vAC down to 12vAC then
rectified to 12vDC????


Steve
A&P and Computer Guru (and very interested in your Idea)

John wrote:
John wrote:

Thanks for the continuing input.
The LM79XX's will do you no good unless you have a source of
negative
voltage to feed them. This generally will mean a dc to dc
converter which
generally means switching regulators. Try putting your current
powersupply in a case and attach it directly to the MB's case and
use
feedthrough capacitors in the common case bulkheads to feed the dc
voltage in. Put fedtrough caps and ferite beads on the dc in to
the
powersuppply case. Cheep and will get you a good start to
eliminating the
noise. John

About $1.00 a piece from a couple sources I checked. So about $7.00
for
the PS voltages plus the dc input. (although some are sold only in
10
lots) if you have multiple projects to use them up in you can order
100
quantity for about $.50 each.
John


Just checked Newark Catalog They have an interesting item:
A feed through teminal block with built-in filter capacitors
part # 95F895X
where x = number of terminals from 2 to 6.

Just something interesting to look into.
They have a lot of ideas for cap/ferite/filter ideas.
John

wrote:

isn't there a step down treansformer taking 110vAC down to 12vAC then
rectified to 12vDC????


Steve
A&P and Computer Guru (and very interested in your Idea)

All kinds unfortunately this is for aircraft use, he's starting with 12v DC
(transformers don't work with DC) and needs to get +-12v +5 and +3.3v all
DC.
John

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John wrote:
wrote:


isn't there a step down treansformer taking 110vAC down to 12vAC then
rectified to 12vDC????


Steve
A&P and Computer Guru (and very interested in your Idea)


All kinds unfortunately this is for aircraft use, he's starting with 12v DC
(transformers don't work with DC) and needs to get +-12v +5 and +3.3v all
DC.
John

John,

I think you'll find that the -12V is used only in "legacy" PC design for
ISA busses, or serial ports (which he probably isn't using).

Evan
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All kinds unfortunately this is for aircraft use, he's starting with 12v
DC (transformers don't work with DC) and needs to get +-12v +5 and +3.3v
all DC.
John

John,

I think you'll find that the -12V is used only in "legacy" PC design for
ISA busses, or serial ports (which he probably isn't using).

Evan


Yes I did a little research on it and the only thing the negative is needed
for is the rs232 serial ports. for this you can get a $1.50 ic to convert
+12 to -12 V low current.
That said, what I'd do is get a 1.5 amp 5v TO-3 regulator and a 1 amp TO-220
regulator along with one of the TO-220 adjustable 1 amp regulators for the
3.3 v and run it all off the 12V (highly filtered) input. That said,
(again) you might have problems with th 12V regulator if the input drops
below 13.8V! So you might need to use a separate battery for it and diode
isolate it from the aircrafts electrical systm and have it charged when it
exceeds the 13.8 volt figure.
John

"Evan Carew" wrote in message ...
John,

I think you'll find that the -12V is used only in "legacy" PC design for ISA busses, or serial ports (which he
probably isn't using).

Evan


What is the +12 vdc for?