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Fwd: KX3 Relay Control For Desktop Amplifiers

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Jimk8mr

Fwd: KX3 Relay Control For Desktop Amplifiers

I blew the switching FET with about 50 ma of current (12 volts) from a
DownEast Microwave transverter. Elecraft says it should have handled it, but
anyway, FWIW.

The FET has been replaced, and an intermediate switching transistor
installed in the switchbox for the several transverters. Now switching 1 or 2 ma,
hope that holds!

73 - Jim K8MR

____________________________________
From: [hidden email]
To: [hidden email]
Sent: 3/12/2013 12:07:26 P.M. Eastern Daylight Time
Subj: [Elecraft] KX3 Relay Control For Desktop Amplifiers

Most common desktop amps have a relay circuit that requires a transceiver
to short 12 VDC at 100 ma to key the amplifier on.
In the KX3 specs, the maximum amp relay current is stated to be 100 ma.
Has anyone keyed a desktop amp directly with a KX3 or is it recommended to
use an intermediate external relay circuit?

Thanks,

W9DBR

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Bill Clarke

Re: Fwd: KX3 Relay Control For Desktop Amplifiers

A very simple device I use for amp switching is a reed relay from Radio
Shack (part # 275-233) that I power with a 9 volt battery. I have been
using this device for years on may rigs and it works fine.

Of course there are no solid state devices used on a well designed
circuit board, nor a micro-processor with buggy software - so the
solution may not be acceptable to all.

Bill W2BLC
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Rich Heineck

Re: Fwd: KX3 Relay Control For Desktop Amplifiers

In reply to this post by Jimk8mr

Jim,

The FET shouldn't have had any problem with 50 mA. It's a 2N7002 and is
rated for 115 mA continuous and 800 mA pulsed, with 60V max voltage when
off. One possibility is that the load being switched was inductive
(like a relay), and the FET's voltage rating was exceeded when the relay
was released due to inductive kickback. The simplest solution to snub
the kickback spike is to put a reverse diode, like a 1N4002, across the
relay coil (cathode side to the relay's '+' supply).

It's also possible the FET was defective or damaged to begin with, which
led to an early failure.

73,
Rich AC7MA

On 03/12/2013 01:28 PM, [hidden email] wrote:

> I blew the switching FET with about 50 ma of current (12 volts) from a
> DownEast Microwave transverter. Elecraft says it should have handled it, but
> anyway, FWIW.
>
> The FET has been replaced, and an intermediate switching transistor
> installed in the switchbox for the several transverters. Now switching 1 or 2 ma,
> hope that holds!
>
>
> 73 - Jim K8MR
>
>
>
> ____________________________________
> From: [hidden email]
> To: [hidden email]
> Sent: 3/12/2013 12:07:26 P.M. Eastern Daylight Time
> Subj: [Elecraft] KX3 Relay Control For Desktop Amplifiers
>
>
> Most common desktop amps have a relay circuit that requires a transceiver
> to short 12 VDC at 100 ma to key the amplifier on.
> In the KX3 specs, the maximum amp relay current is stated to be 100 ma.
> Has anyone keyed a desktop amp directly with a KX3 or is it recommended to
> use an intermediate external relay circuit?
>
> Thanks,
>
> W9DBR
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

ke9uw

Re: Fwd: KX3 Relay Control For Desktop Amplifiers

The 2N7002 has an internal diode for any inductive collapse.

Sent from my iPad
Chuck, KE9UW
(Jack for BMW motorcycles)

On Mar 12, 2013, at 6:58 PM, "Rich Heineck" <[hidden email]> wrote:

> Jim,
>
> The FET shouldn't have had any problem with 50 mA. It's a 2N7002 and is rated for 115 mA continuous and 800 mA pulsed, with 60V max voltage when off. One possibility is that the load being switched was inductive (like a relay), and the FET's voltage rating was exceeded when the relay was released due to inductive kickback. The simplest solution to snub the kickback spike is to put a reverse diode, like a 1N4002, across the relay coil (cathode side to the relay's '+' supply).
>
> It's also possible the FET was defective or damaged to begin with, which led to an early failure.
>
> 73,
> Rich AC7MA
>
>
> On 03/12/2013 01:28 PM, [hidden email] wrote:
>> I blew the switching FET with about 50 ma of current (12 volts) from a
>> DownEast Microwave transverter. Elecraft says it should have handled it, but
>> anyway, FWIW.
>> The FET has been replaced, and an intermediate switching transistor
>> installed in the switchbox for the several transverters. Now switching 1 or 2 ma,
>> hope that holds!
>> 73 - Jim K8MR
>> ____________________________________
>> From: [hidden email]
>> To: [hidden email]
>> Sent: 3/12/2013 12:07:26 P.M. Eastern Daylight Time
>> Subj: [Elecraft] KX3 Relay Control For Desktop Amplifiers
>>
>>
>> Most common desktop amps have a relay circuit that requires a transceiver
>> to short 12 VDC at 100 ma to key the amplifier on.
>> In the KX3 specs, the maximum amp relay current is stated to be 100 ma.
>> Has anyone keyed a desktop amp directly with a KX3 or is it recommended to
>> use an intermediate external relay circuit?
>>
>> Thanks,
>>
>> W9DBR
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html

Chuck, KE9UW

Jack Smith-6

Re: Fwd: KX3 Relay Control For Desktop Amplifiers

Isn't the 2N7002's internal diode arranged to conduct if the drain is
negative with respect to the source, but the inductive spike from low
side switching will be positive with respect to the drain?

What you really want for this situation where the relay is presumably
inaccessible and hence cannot be fitted with a clamping diode or RC
snubber is an avalanche rated FET, and the 2N7002 is not avalanche
rated. It may well be that the 2N7002 will handle some number of
breakdown events but the breakdowns degrade the device and will cause
failure sooner or later. Unless a particular device is explicitly rated
for avalanche operation, it must be assumed it is not to be used in
breakdown mode.

I like the Vishay/Siliconix SI2328DS-T1-E3 for FET switching of relays
where you cannot be assured access to the relay coil. It's rated at
100V, 1.5A and is avalanche capable to 6A. It's an SOT-23 surface mount
package.

Or, if an avalanche rated device is not to be used, a zener with a
breakdown voltage less than the maximum rated drain voltage of the FET
can be used from the drain to ground. It also has the advantage of being
more easily replaced in the future as bog standard parts are involved.

Jack K8ZOA

On 3/12/2013 8:01 PM, hawley, charles j jr wrote:

> The 2N7002 has an internal diode for any inductive collapse.
>
> Sent from my iPad
> Chuck, KE9UW
> (Jack for BMW motorcycles)
>
> On Mar 12, 2013, at 6:58 PM, "Rich Heineck"<[hidden email]> wrote:
>
>> Jim,
>>
>> The FET shouldn't have had any problem with 50 mA. It's a 2N7002 and is rated for 115 mA continuous and 800 mA pulsed, with 60V max voltage when off. One possibility is that the load being switched was inductive (like a relay), and the FET's voltage rating was exceeded when the relay was released due to inductive kickback. The simplest solution to snub the kickback spike is to put a reverse diode, like a 1N4002, across the relay coil (cathode side to the relay's '+' supply).
>>
>> It's also possible the FET was defective or damaged to begin with, which led to an early failure.
>>
>> 73,
>> Rich AC7MA
>>
>>
>> On 03/12/2013 01:28 PM,[hidden email] wrote:
>>> I blew the switching FET with about 50 ma of current (12 volts) from a
>>> DownEast Microwave transverter. Elecraft says it should have handled it, but
>>> anyway, FWIW.
>>> The FET has been replaced, and an intermediate switching transistor
>>> installed in the switchbox for the several transverters. Now switching 1 or 2 ma,
>>> hope that holds!
>>> 73 - Jim K8MR
>>> ____________________________________
>>> From:[hidden email]
>>> To:[hidden email]
>>> Sent: 3/12/2013 12:07:26 P.M. Eastern Daylight Time
>>> Subj: [Elecraft] KX3 Relay Control For Desktop Amplifiers
>>>
>>>
>>> Most common desktop amps have a relay circuit that requires a transceiver
>>> to short 12 VDC at 100 ma to key the amplifier on.
>>> In the KX3 specs, the maximum amp relay current is stated to be 100 ma.
>>> Has anyone keyed a desktop amp directly with a KX3 or is it recommended to
>>> use an intermediate external relay circuit?
>>>
>>> Thanks,
>>>
>>> W9DBR
>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home:http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help:http://mailman.qth.net/mmfaq.htm
>>> Post:mailto:[hidden email]
>>>
>>> This list hosted by:http://www.qsl.net
>>> Please help support this email list:http://www.qsl.net/donate.html
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home:http://mailman.qth.net/mailman/listinfo/elecraft
>> Help:http://mailman.qth.net/mmfaq.htm
>> Post:mailto:[hidden email]
>>
>> This list hosted by:http://www.qsl.net
>> Please help support this email list:http://www.qsl.net/donate.html
> ______________________________________________________________
> Elecraft mailing list
> Home:http://mailman.qth.net/mailman/listinfo/elecraft
> Help:http://mailman.qth.net/mmfaq.htm
> Post:mailto:[hidden email]
>
> This list hosted by:http://www.qsl.net
> Please help support this email list:http://www.qsl.net/donate.html
>

Rich Heineck

Re: Fwd: KX3 Relay Control For Desktop Amplifiers

In reply to this post by ke9uw

There's a drain-source diode, but it doesn't protect the 2N7002 in this
configuration. Typical sink-to-ground relay driver circuits put a diode
across the coil so it keeps the switched side of the relay from going
way above the supply voltage when the relay is turned off.

Rich AC7MA

On 03/12/2013 05:01 PM, hawley, charles j jr wrote:

> The 2N7002 has an internal diode for any inductive collapse.
>
> Sent from my iPad
> Chuck, KE9UW
> (Jack for BMW motorcycles)
>
> On Mar 12, 2013, at 6:58 PM, "Rich Heineck" <[hidden email]> wrote:
>
>> Jim,
>>
>> The FET shouldn't have had any problem with 50 mA. It's a 2N7002 and is rated for 115 mA continuous and 800 mA pulsed, with 60V max voltage when off. One possibility is that the load being switched was inductive (like a relay), and the FET's voltage rating was exceeded when the relay was released due to inductive kickback. The simplest solution to snub the kickback spike is to put a reverse diode, like a 1N4002, across the relay coil (cathode side to the relay's '+' supply).
>>
>> It's also possible the FET was defective or damaged to begin with, which led to an early failure.
>>
>> 73,
>> Rich AC7MA
>>
>>
>> On 03/12/2013 01:28 PM, [hidden email] wrote:
>>> I blew the switching FET with about 50 ma of current (12 volts) from a
>>> DownEast Microwave transverter. Elecraft says it should have handled it, but
>>> anyway, FWIW.
>>> The FET has been replaced, and an intermediate switching transistor
>>> installed in the switchbox for the several transverters. Now switching 1 or 2 ma,
>>> hope that holds!
>>> 73 - Jim K8MR
>>> ____________________________________
>>> From: [hidden email]
>>> To: [hidden email]
>>> Sent: 3/12/2013 12:07:26 P.M. Eastern Daylight Time
>>> Subj: [Elecraft] KX3 Relay Control For Desktop Amplifiers
>>>
>>>
>>> Most common desktop amps have a relay circuit that requires a transceiver
>>> to short 12 VDC at 100 ma to key the amplifier on.
>>> In the KX3 specs, the maximum amp relay current is stated to be 100 ma.
>>> Has anyone keyed a desktop amp directly with a KX3 or is it recommended to
>>> use an intermediate external relay circuit?
>>>
>>> Thanks,
>>>
>>> W9DBR
>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html

Jimk8mr

Re: Fwd: KX3 Relay Control For Desktop Amplifiers

In reply to this post by Jimk8mr

The DEM transverters also have the diode snubber.

So things remain a mystery, hopefully never to repeat.

73 - Jim K8MR

In a message dated 3/12/2013 8:02:08 P.M. Eastern Daylight Time,
[hidden email] writes:

The 2N7002 has an internal diode for any inductive collapse.

Sent from my iPad
Chuck, KE9UW
(Jack for BMW motorcycles)

On Mar 12, 2013, at 6:58 PM, "Rich Heineck" <[hidden email]> wrote:

> Jim,
>
> The FET shouldn't have had any problem with 50 mA. It's a 2N7002 and is
rated for 115 mA continuous and 800 mA pulsed, with 60V max voltage when
off. One possibility is that the load being switched was inductive (like a
relay), and the FET's voltage rating was exceeded when the relay was
released due to inductive kickback. The simplest solution to snub the kickback
spike is to put a reverse diode, like a 1N4002, across the relay coil
(cathode side to the relay's '+' supply).
>
> It's also possible the FET was defective or damaged to begin with, which
led to an early failure.
>
> 73,
> Rich AC7MA
>
>
> On 03/12/2013 01:28 PM, [hidden email] wrote:
>> I blew the switching FET with about 50 ma of current (12 volts) from a
>> DownEast Microwave transverter. Elecraft says it should have handled
it, but
>> anyway, FWIW.
>> The FET has been replaced, and an intermediate switching transistor
>> installed in the switchbox for the several transverters. Now switching
1 or 2 ma,

>> hope that holds!
>> 73 - Jim K8MR
>> ____________________________________
>> From: [hidden email]
>> To: [hidden email]
>> Sent: 3/12/2013 12:07:26 P.M. Eastern Daylight Time
>> Subj: [Elecraft] KX3 Relay Control For Desktop Amplifiers
>>
>>
>> Most common desktop amps have a relay circuit that requires a

transceiver
>> to short 12 VDC at 100 ma to key the amplifier on.
>> In the KX3 specs, the maximum amp relay current is stated to be 100 ma.
>> Has anyone keyed a desktop amp directly with a KX3 or is it
recommended to

>> use an intermediate external relay circuit?
>>
>> Thanks,
>>
>> W9DBR
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
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Post: mailto:[hidden email]

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Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
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Jimk8mr

Re: Fwd: KX3 Relay Control For Desktop Amplifiers

In reply to this post by Jimk8mr

In my case the FET failed somewhat gradually. I made several QSOs by
momentarily turning off the transverter power. When I turned it back on, it came
up in receive mode. Then I'd transmit, power cycle the transverter to
return to receive, and repeat.

After several such QSOs power cycling would not get the relay to drop out.

73 - Jim K8MR

In a message dated 3/12/2013 8:53:12 P.M. Eastern Daylight Time,
[hidden email] writes:

Isn't the 2N7002's internal diode arranged to conduct if the drain is
negative with respect to the source, but the inductive spike from low
side switching will be positive with respect to the drain?

What you really want for this situation where the relay is presumably
inaccessible and hence cannot be fitted with a clamping diode or RC
snubber is an avalanche rated FET, and the 2N7002 is not avalanche
rated. It may well be that the 2N7002 will handle some number of
breakdown events but the breakdowns degrade the device and will cause
failure sooner or later. Unless a particular device is explicitly rated
for avalanche operation, it must be assumed it is not to be used in
breakdown mode.

I like the Vishay/Siliconix SI2328DS-T1-E3 for FET switching of relays
where you cannot be assured access to the relay coil. It's rated at
100V, 1.5A and is avalanche capable to 6A. It's an SOT-23 surface mount
package.

Or, if an avalanche rated device is not to be used, a zener with a
breakdown voltage less than the maximum rated drain voltage of the FET
can be used from the drain to ground. It also has the advantage of being
more easily replaced in the future as bog standard parts are involved.

Jack K8ZOA

On 3/12/2013 8:01 PM, hawley, charles j jr wrote:

is rated for 115 mA continuous and 800 mA pulsed, with 60V max voltage when
off. One possibility is that the load being switched was inductive (like a
relay), and the FET's voltage rating was exceeded when the relay was
released due to inductive kickback. The simplest solution to snub the kickback
spike is to put a reverse diode, like a 1N4002, across the relay coil
(cathode side to the relay's '+' supply).
>>
>> It's also possible the FET was defective or damaged to begin with,
which led to an early failure.
>>
>> 73,
>> Rich AC7MA
>>
>>
>> On 03/12/2013 01:28 PM,[hidden email] wrote:
>>> I blew the switching FET with about 50 ma of current (12 volts) from a
>>> DownEast Microwave transverter. Elecraft says it should have handled
it, but
>>> anyway, FWIW.
>>> The FET has been replaced, and an intermediate switching transistor
>>> installed in the switchbox for the several transverters. Now switching
1 or 2 ma,

>>> hope that holds!
>>> 73 - Jim K8MR
>>> ____________________________________
>>> From:[hidden email]
>>> To:[hidden email]
>>> Sent: 3/12/2013 12:07:26 P.M. Eastern Daylight Time
>>> Subj: [Elecraft] KX3 Relay Control For Desktop Amplifiers
>>>
>>>
>>> Most common desktop amps have a relay circuit that requires a

transceiver
>>> to short 12 VDC at 100 ma to key the amplifier on.
>>> In the KX3 specs, the maximum amp relay current is stated to be 100
ma.
>>> Has anyone keyed a desktop amp directly with a KX3 or is it
recommended to

>>> use an intermediate external relay circuit?
>>>
>>> Thanks,
>>>
>>> W9DBR
>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home:http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help:http://mailman.qth.net/mmfaq.htm
>>> Post:mailto:[hidden email]
>>>
>>> This list hosted by:http://www.qsl.net
>>> Please help support this email list:http://www.qsl.net/donate.html
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home:http://mailman.qth.net/mailman/listinfo/elecraft
>> Help:http://mailman.qth.net/mmfaq.htm
>> Post:mailto:[hidden email]
>>
>> This list hosted by:http://www.qsl.net
>> Please help support this email list:http://www.qsl.net/donate.html
> ______________________________________________________________
> Elecraft mailing list
> Home:http://mailman.qth.net/mailman/listinfo/elecraft
> Help:http://mailman.qth.net/mmfaq.htm
> Post:mailto:[hidden email]
>
> This list hosted by:http://www.qsl.net
> Please help support this email list:http://www.qsl.net/donate.html
>