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Old January 11th 04, 12:44 PM
Richard Hosking
 
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Default Overvoltage and reverse voltage protection

Dear all
I want to design a power supply for a low power rig with protection for
reverse and overvoltage. The requirement would be about 1A at 12-14V.
What is the best way of achieving this? I guess a diode would give
reverse voltage protection but the 0.6V drop is a problem.

Richard

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Old January 11th 04, 03:05 PM
Mike W
 
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On Sun, 11 Jan 2004 19:44:19 +0800, Richard Hosking
wrote:

Dear all
I want to design a power supply for a low power rig with protection for
reverse and overvoltage. The requirement would be about 1A at 12-14V.
What is the best way of achieving this? I guess a diode would give
reverse voltage protection but the 0.6V drop is a problem.

Richard

Rick,
one way for reverse protection is to include a bridge recifier in the
rigs power line ( internally fitted ), but this causes a drop in
available volts.

I prefer a diode into a relay coil, with the relay contacts enabling
the power when the relay coil is correctly polarised and powered (
also internally fitted ).

This enables full volts to the rig and also gives reverse protection,
however this is at the cost of further ( and some may say excessive )
drain of the power source.
Over voltage should be by fuse and a crowbar circuit. Do a search on
crowbar for details.

The diode + relay circuit should be obvious to you, I use a 9v relay
coil with a 1N4001 in the activation side and a DPDT contact,in
parallel, to switch the power. For the power you are talking about a
14pin DIL relay should be adequate.

HTH, Mike W, G8NXD qthr
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Old January 11th 04, 03:05 PM
Mike W
 
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Default

On Sun, 11 Jan 2004 19:44:19 +0800, Richard Hosking
wrote:

Dear all
I want to design a power supply for a low power rig with protection for
reverse and overvoltage. The requirement would be about 1A at 12-14V.
What is the best way of achieving this? I guess a diode would give
reverse voltage protection but the 0.6V drop is a problem.

Richard

Rick,
one way for reverse protection is to include a bridge recifier in the
rigs power line ( internally fitted ), but this causes a drop in
available volts.

I prefer a diode into a relay coil, with the relay contacts enabling
the power when the relay coil is correctly polarised and powered (
also internally fitted ).

This enables full volts to the rig and also gives reverse protection,
however this is at the cost of further ( and some may say excessive )
drain of the power source.
Over voltage should be by fuse and a crowbar circuit. Do a search on
crowbar for details.

The diode + relay circuit should be obvious to you, I use a 9v relay
coil with a 1N4001 in the activation side and a DPDT contact,in
parallel, to switch the power. For the power you are talking about a
14pin DIL relay should be adequate.

HTH, Mike W, G8NXD qthr
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Old January 11th 04, 04:34 PM
Doug Smith W9WI
 
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Default

Mike W wrote:
Over voltage should be by fuse and a crowbar circuit. Do a search on
crowbar for details.


If you already have a fuse & crowbar circuit for overvoltage, wouldn't
the easy way to handle reverse polarity be a diode hooked in the
(normally) non-conducting direction across the output?
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

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Old January 11th 04, 04:34 PM
Doug Smith W9WI
 
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Default

Mike W wrote:
Over voltage should be by fuse and a crowbar circuit. Do a search on
crowbar for details.


If you already have a fuse & crowbar circuit for overvoltage, wouldn't
the easy way to handle reverse polarity be a diode hooked in the
(normally) non-conducting direction across the output?
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com



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Old January 11th 04, 06:47 PM
Jim Weir
 
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Default


I'm not understanding something here. You want to design a power supply that
protects against reverse voltage and overvoltage. OK. Is this power supply a
battery or are you actually building a power supply that runs from the wall
outlet?

The requirements are quite different, depending on what you are trying to
achieve.

Jim



Richard Hosking
shared these priceless pearls of wisdom:

-Dear all
-I want to design a power supply for a low power rig with protection for
-reverse and overvoltage.


Jim Weir, VP Eng. RST Eng. WX6RST
A&P, CFI, and other good alphabet soup
  #7   Report Post  
Old January 11th 04, 06:47 PM
Jim Weir
 
Posts: n/a
Default


I'm not understanding something here. You want to design a power supply that
protects against reverse voltage and overvoltage. OK. Is this power supply a
battery or are you actually building a power supply that runs from the wall
outlet?

The requirements are quite different, depending on what you are trying to
achieve.

Jim



Richard Hosking
shared these priceless pearls of wisdom:

-Dear all
-I want to design a power supply for a low power rig with protection for
-reverse and overvoltage.


Jim Weir, VP Eng. RST Eng. WX6RST
A&P, CFI, and other good alphabet soup
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