Topics

Polarity Protection


Bob Lunsford
 

Here is a simple circuit for polarity protection. The LED can be substituted with a Sonalert or a Sonalert can also be used to warn that the applied voltage polarity is wrong. Also, if the relay is double pole, merely wiring the two polls in parallel can provide more current if needed. Good thing is that the circuit does not draw current unless the polarity is reversed. Got it from an old CQ magazine with some modification. I'm sure a lot of us in this forum have some left-over relays.

Bob — KK5R

Inline image


John Baines
 

If reverse polarity is applied, then it is connected to the circuit until the relay operates. Only milli/microseconds but…

73
John
M0JBA

On 9 Aug 2020, at 23:58, Bob Lunsford via groups.io <nocrud222@...> wrote:

Here is a simple circuit for polarity protection. The LED can be substituted with a Sonalert or a Sonalert can also be used to warn that the applied voltage polarity is wrong. Also, if the relay is double pole, merely wiring the two polls in parallel can provide more current if needed. Good thing is that the circuit does not draw current unless the polarity is reversed. Got it from an old CQ magazine with some modification. I'm sure a lot of us in this forum have some left-over relays.

Bob — KK5R

<1597013689601blob.jpg>

<1597013689601blob.jpg>


Evan Hand
 

John is correct.  A better solution is to reverse the diode and connect the power to the rig to the NO side of the relay.  The relay will pull in to energize the rig.  The disadvantage is that the relay will draw power all the time that the rig is on.  Not good for battery operation.  It would be better just to use the diode in series with the power for battery power operation where power draw is a concern.

73
Evan
AC9TU


Evan Hand
 

One other option is to use a fuse with a reverse diode to blow the fuse.  Since the diode is across the supply, the forward voltage would be the most that the rig would see.


Bob Lunsford
 

It takes a few milliseconds for the operating voltage to be applied and during that time, the board/components are not affected. But if it makes you feel better, here is the "fix."



On Sunday, August 9, 2020, 7:26:39 PM EDT, John Baines via groups.io <jbaines@...> wrote:


If reverse polarity is applied, then it is connected to the circuit until the relay operates. Only milli/microseconds but…

73
John
M0JBA

On 9 Aug 2020, at 23:58, Bob Lunsford via groups.io <nocrud222@...> wrote:

Here is a simple circuit for polarity protection. The LED can be substituted with a Sonalert or a Sonalert can also be used to warn that the applied voltage polarity is wrong. Also, if the relay is double pole, merely wiring the two polls in parallel can provide more current if needed. Good thing is that the circuit does not draw current unless the polarity is reversed. Got it from an old CQ magazine with some modification. I'm sure a lot of us in this forum have some left-over relays.

Bob — KK5R


<1597013689601blob.jpg>

<1597013689601blob.jpg>


Bob Lunsford
 

Inline image


On Sunday, August 9, 2020, 8:08:08 PM EDT, Bob Lunsford via groups.io <nocrud222@...> wrote:


It takes a few milliseconds for the operating voltage to be applied and during that time, the board/components are not affected. But if it makes you feel better, here is the "fix."



On Sunday, August 9, 2020, 7:26:39 PM EDT, John Baines via groups.io <jbaines@...> wrote:


If reverse polarity is applied, then it is connected to the circuit until the relay operates. Only milli/microseconds but…

73
John
M0JBA

On 9 Aug 2020, at 23:58, Bob Lunsford via groups.io <nocrud222@...> wrote:

Here is a simple circuit for polarity protection. The LED can be substituted with a Sonalert or a Sonalert can also be used to warn that the applied voltage polarity is wrong. Also, if the relay is double pole, merely wiring the two polls in parallel can provide more current if needed. Good thing is that the circuit does not draw current unless the polarity is reversed. Got it from an old CQ magazine with some modification. I'm sure a lot of us in this forum have some left-over relays.

Bob — KK5R


<1597013689601blob.jpg>

<1597013689601blob.jpg>


Dale Parfitt
 

For one more diode voltage drop you can simply use a bridge rectifier arrangement. Regardless of which way  you connect the power supply- the proper polarity is always delivered to the load. No relay. The only downside is 2 forward voltage drops. That can be  minimized by using Schottky diodes.

 

Dale W4OP

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Bob Lunsford via groups.io
Sent: Sunday, August 9, 2020 8:12 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Polarity Protection

 

Inline image

 

On Sunday, August 9, 2020, 8:08:08 PM EDT, Bob Lunsford via groups.io <nocrud222@...> wrote:

 

 

It takes a few milliseconds for the operating voltage to be applied and during that time, the board/components are not affected. But if it makes you feel better, here is the "fix."

 

Error! Filename not specified.

 

On Sunday, August 9, 2020, 7:26:39 PM EDT, John Baines via groups.io <jbaines@...> wrote:

 

 

If reverse polarity is applied, then it is connected to the circuit until the relay operates. Only milli/microseconds but…

 

73

John

M0JBA



On 9 Aug 2020, at 23:58, Bob Lunsford via groups.io <nocrud222@...> wrote:

 

Here is a simple circuit for polarity protection. The LED can be substituted with a Sonalert or a Sonalert can also be used to warn that the applied voltage polarity is wrong. Also, if the relay is double pole, merely wiring the two polls in parallel can provide more current if needed. Good thing is that the circuit does not draw current unless the polarity is reversed. Got it from an old CQ magazine with some modification. I'm sure a lot of us in this forum have some left-over relays.

 

Bob — KK5R

 

 

<1597013689601blob.jpg>

 

<1597013689601blob.jpg>

 


Bob Lunsford
 

The relay circuit tells you there is a polarity problem. A diode shunt with a fuse wastes fuses. The 0.6V drop across the diode is a minimal factor if it protects the radio. Simply putting in a series diode does the trick but there is no warning about reverse polarity. A series diode also must be able to carry the load current. I have a few 5A diodes I got at Radio Shack back whenever so that is what I'd use. But the only incident of reverse polarity I've experienced was putting a batter charger on my car, much to the sadness of the charger.

I saw that circuit when reading a CQ magazine that is about 22 years old and though it might be of interest to some users here. At least it causes people to be reminded of being polarity conscious which may not be a bad thing. Troubleshooting a smoked board just cannot be much fun.

Bob — KK5R

On Sunday, August 9, 2020, 8:39:55 PM EDT, Dale Parfitt <parinc1@...> wrote:


For one more diode voltage drop you can simply use a bridge rectifier arrangement. Regardless of which way  you connect the power supply- the proper polarity is always delivered to the load. No relay. The only downside is 2 forward voltage drops. That can be  minimized by using Schottky diodes.

 

Dale W4OP

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Bob Lunsford via groups.io
Sent: Sunday, August 9, 2020 8:12 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Polarity Protection

 

Inline image

 

On Sunday, August 9, 2020, 8:08:08 PM EDT, Bob Lunsford via groups.io <nocrud222@...> wrote:

 

 

It takes a few milliseconds for the operating voltage to be applied and during that time, the board/components are not affected. But if it makes you feel better, here is the "fix."

 

Error! Filename not specified.

 

On Sunday, August 9, 2020, 7:26:39 PM EDT, John Baines via groups.io <jbaines@...> wrote:

 

 

If reverse polarity is applied, then it is connected to the circuit until the relay operates. Only milli/microseconds but…

 

73

John

M0JBA



On 9 Aug 2020, at 23:58, Bob Lunsford via groups.io <nocrud222@...> wrote:

 

Here is a simple circuit for polarity protection. The LED can be substituted with a Sonalert or a Sonalert can also be used to warn that the applied voltage polarity is wrong. Also, if the relay is double pole, merely wiring the two polls in parallel can provide more current if needed. Good thing is that the circuit does not draw current unless the polarity is reversed. Got it from an old CQ magazine with some modification. I'm sure a lot of us in this forum have some left-over relays.

 

Bob — KK5R

 

 

<1597013689601blob.jpg>

 

<1597013689601blob.jpg>

 


MadRadioModder
 

This one is better:




MRM

 


On Aug 9, 2020, at 6:46 PM, Evan Hand <elhandjr@...> wrote:

One other option is to use a fuse with a reverse diode to blow the fuse.  Since the diode is across the supply, the forward voltage would be the most that the rig would see.

--

…_. _._


Gordon Gibby
 

As long as you don't smoke the radio, I'm not sure arguing over which is better is worth it;  however, I'm surprised no one has mentioned the very slick p-channel enhancement mode MOSFET solutions.   

On Mon, Aug 10, 2020 at 12:56 AM MadRadioModder <madradiomodder@...> wrote:
This one is better:




MRM

 


On Aug 9, 2020, at 6:46 PM, Evan Hand <elhandjr@...> wrote:

One other option is to use a fuse with a reverse diode to blow the fuse.  Since the diode is across the supply, the forward voltage would be the most that the rig would see.

--

…_. _._


Dean Souleles
 

This EDN article covers the topic thoroughly.

For my less than a dollar, an in line fuse and a reverse diode across VCC to ground is the ticket. I can live with blowing the occasional fuse.

Speaking from direct personal experience, this works. :-)

Pick your poison, but protect your circuits.

Dean





Evan Hand
 

I would agree with Dean, also from personal experience :-)

73
Evan
AC9TU


Vince Vielhaber
 

A diode shunt doesn't waste fuses, the person who keeps replacing the fuse and continues to connect the radio backwards is wasting fuses.

Vince - K8ZW.

On 08/09/2020 08:59 PM, Bob Lunsford via groups.io wrote:
The relay circuit tells you there is a polarity problem. A diode shunt
with a fuse wastes fuses. The 0.6V drop across the diode is a minimal
factor if it protects the radio. Simply putting in a series diode does
the trick but there is no warning about reverse polarity. A series diode
also must be able to carry the load current. I have a few 5A diodes I
got at Radio Shack back whenever so that is what I'd use. But the only
incident of reverse polarity I've experienced was putting a batter
charger on my car, much to the sadness of the charger.

I saw that circuit when reading a CQ magazine that is about 22 years old
and though it might be of interest to some users here. At least it
causes people to be reminded of being polarity conscious which may not
be a bad thing. Troubleshooting a smoked board just cannot be much fun.

Bob — KK5R

On Sunday, August 9, 2020, 8:39:55 PM EDT, Dale Parfitt
<parinc1@...> wrote:


For one more diode voltage drop you can simply use a bridge rectifier
arrangement. Regardless of which way you connect the power supply- the
proper polarity is always delivered to the load. No relay. The only
downside is 2 forward voltage drops. That can be minimized by using
Schottky diodes.



Dale W4OP



*From:*BITX20@groups.io [mailto:BITX20@groups.io] *On Behalf Of *Bob
Lunsford via groups.io
*Sent:* Sunday, August 9, 2020 8:12 PM
*To:* BITX20@groups.io
*Subject:* Re: [BITX20] Polarity Protection



Inline image



On Sunday, August 9, 2020, 8:08:08 PM EDT, Bob Lunsford via groups.io
<nocrud222=yahoo.com@groups.io> wrote:





It takes a few milliseconds for the operating voltage to be applied and
during that time, the board/components are not affected. But if it makes
you feel better, here is the "fix."



*Error! Filename not specified.*



On Sunday, August 9, 2020, 7:26:39 PM EDT, John Baines via groups.io
<jbaines=mac.com@groups.io> wrote:





If reverse polarity is applied, then it is connected to the circuit
until the relay operates. Only milli/microseconds but…



73

John

M0JBA



On 9 Aug 2020, at 23:58, Bob Lunsford via groups.io <http://groups.io>
<nocrud222=yahoo.com@groups.io <mailto:nocrud222=yahoo.com@groups.io>>
wrote:



Here is a simple circuit for polarity protection. The LED can be
substituted with a Sonalert or a Sonalert can also be used to warn that
the applied voltage polarity is wrong. Also, if the relay is double
pole, merely wiring the two polls in parallel can provide more current
if needed. Good thing is that the circuit does not draw current unless
the polarity is reversed. Got it from an old CQ magazine with some
modification. I'm sure a lot of us in this forum have some left-over relays.



Bob — KK5R





<1597013689601blob.jpg>



<1597013689601blob.jpg>




Bob Lunsford
 

It does not work. Check it out.

On Monday, August 10, 2020, 12:56:21 AM EDT, MadRadioModder <madradiomodder@...> wrote:


This one is better:




MRM

 


On Aug 9, 2020, at 6:46 PM, Evan Hand <elhandjr@...> wrote:

One other option is to use a fuse with a reverse diode to blow the fuse.  Since the diode is across the supply, the forward voltage would be the most that the rig would see.

--

…_. _._


Bob Lunsford
 

The relay draws current constantly. A simple series diode works, is simpler and is foolproof. But Groucho Marx would send us a fool to try it. Ha

On Monday, August 10, 2020, 1:26:21 AM EDT, Gordon Gibby <docvacuumtubes@...> wrote:


As long as you don't smoke the radio, I'm not sure arguing over which is better is worth it;  however, I'm surprised no one has mentioned the very slick p-channel enhancement mode MOSFET solutions.   

On Mon, Aug 10, 2020 at 12:56 AM MadRadioModder <madradiomodder@...> wrote:
This one is better:




MRM

 


On Aug 9, 2020, at 6:46 PM, Evan Hand <elhandjr@...> wrote:

One other option is to use a fuse with a reverse diode to blow the fuse.  Since the diode is across the supply, the forward voltage would be the most that the rig would see.

--

…_. _._


Bob Lunsford
 

The diode does not need to be a high current diode. A 1A will do it.

On Monday, August 10, 2020, 7:54:00 AM EDT, Dean Souleles <dsouleles@...> wrote:


This EDN article covers the topic thoroughly.

For my less than a dollar, an in line fuse and a reverse diode across VCC to ground is the ticket. I can live with blowing the occasional fuse.

Speaking from direct personal experience, this works. :-)

Pick your poison, but protect your circuits.

Dean