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Overvoltage Protector

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Scott Ellington

Overvoltage Protector

Some power supplies, like the Samlex SEC 1235, have no built-in overvoltage protection. All regulated power supplies are capable of producing much more than their normal output voltage if any one of a number of things fails. Linear supplies are particularly susceptible, since the pass transistor can short.

While Elecraft assures me that the K3 can survive an overvoltage with minimal damage, I prefer to be on the safe side. So I designed a crowbar circuit, which can be used with any 12 V power supply up to 30A. If the voltage exceeds the trip point (14-16 V), it will short the power supply output and, if necessary, blow a fuse.

http://www.ssec.wisc.edu/~scotte/hr/OVP.pdf

I haven't built this one yet, but a very similar one I built in 1984 worked fine.

73,

Scott K9MA

Scott Ellington
Madison, Wisconsin
USA

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P.B. Christensen

Re: Overvoltage Protector

Scott,

Great contribution. Surprising how many switch-mode supplies do not include
OVP. AD5X created a similar circuit using a single high-peak-current
transient suppressor:

http://www.radiodan.com/ad5x/images/Articles/VcondRevA.pdf

Paul, W9AC

----- Original Message -----
From: "Scott Ellington" <[hidden email]>
To: <[hidden email]>
Sent: Friday, August 20, 2010 4:00 PM
Subject: [Elecraft] Overvoltage Protector

> Some power supplies, like the Samlex SEC 1235, have no built-in
> overvoltage protection. All regulated power supplies are capable of
> producing much more than their normal output voltage if any one of a
> number of things fails. Linear supplies are particularly susceptible,
> since the pass transistor can short.
>
> While Elecraft assures me that the K3 can survive an overvoltage with
> minimal damage, I prefer to be on the safe side. So I designed a crowbar
> circuit, which can be used with any 12 V power supply up to 30A. If the
> voltage exceeds the trip point (14-16 V), it will short the power supply
> output and, if necessary, blow a fuse.
>
>
> I haven't built this one yet, but a very similar one I built in 1984
> worked fine.
>
> 73,
>
> Scott K9MA
>
> Scott Ellington
> Madison, Wisconsin
> USA

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Joe Subich, W4TV-4

Re: Overvoltage Protector

The same/similar article from the original source:
http://www.ad5x.com/images/Articles/Vprotect.pdf

73,

... Joe, W4TV

On 8/20/2010 4:22 PM, Paul Christensen wrote:

> Scott,
>
> Great contribution. Surprising how many switch-mode supplies do not include
> OVP. AD5X created a similar circuit using a single high-peak-current
> transient suppressor:
>
> http://www.radiodan.com/ad5x/images/Articles/VcondRevA.pdf
>
> Paul, W9AC
>
> ----- Original Message -----
> From: "Scott Ellington"<[hidden email]>
> To:<[hidden email]>
> Sent: Friday, August 20, 2010 4:00 PM
> Subject: [Elecraft] Overvoltage Protector
>
>
>> Some power supplies, like the Samlex SEC 1235, have no built-in
>> overvoltage protection. All regulated power supplies are capable of
>> producing much more than their normal output voltage if any one of a
>> number of things fails. Linear supplies are particularly susceptible,
>> since the pass transistor can short.
>>
>> While Elecraft assures me that the K3 can survive an overvoltage with
>> minimal damage, I prefer to be on the safe side. So I designed a crowbar
>> circuit, which can be used with any 12 V power supply up to 30A. If the
>> voltage exceeds the trip point (14-16 V), it will short the power supply
>> output and, if necessary, blow a fuse.
>>
>>
>> I haven't built this one yet, but a very similar one I built in 1984
>> worked fine.
>>
>> 73,
>>
>> Scott K9MA
>>
>> Scott Ellington
>> Madison, Wisconsin
>> USA
>
> ______________________________________________________________
> 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
>

Scott Ellington

Re: Overvoltage Protector

In reply to this post by P.B. Christensen

The K3 actually has a couple even larger transient suppressors built-in. While they have high peak current ratings, a failed power supply could make them dissipate hundreds of watts continuously, and fail. If they failed shorted, the rest of the radio would be protected, but I'm not sure you can count on that.

Scott K9MA

On Aug 20, 2010, at 3:22 PM, Paul Christensen wrote:

> AD5X created a similar circuit using a single high-peak-current
> transient suppressor:
>
> http://www.radiodan.com/ad5x/images/Articles/VcondRevA.pdf

Scott Ellington
Madison, Wisconsin
USA

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Eric Swartz - WA6HHQ

Re: Overvoltage Protector

Administrator

In reply to this post by Scott Ellington

I'd like to clarify this a bit.

While the K3 does have some protection against over voltage on its supply, we do not garantee it will survive an overvoltage event in all cases.

73,
Eric

www.elecraft.com
_..._

On Aug 20, 2010, at 1:00 PM, Scott Ellington <[hidden email]> wrote:

> Some power supplies, like the Samlex SEC 1235, have no built-in overvoltage protection. All regulated power supplies are capable of producing much more than their normal output voltage if any one of a number of things fails. Linear supplies are particularly susceptible, since the pass transistor can short.
>
> While Elecraft assures me that the K3 can survive an overvoltage with minimal damage, I prefer to be on the safe side. So I designed a crowbar circuit, which can be used with any 12 V power supply up to 30A. If the voltage exceeds the trip point (14-16 V), it will short the power supply output and, if necessary, blow a fuse.
>
> http://www.ssec.wisc.edu/~scotte/hr/OVP.pdf
>
> I haven't built this one yet, but a very similar one I built in 1984 worked fine.
>
> 73,
>
> Scott K9MA
>
> Scott Ellington
> Madison, Wisconsin
> USA
>
>
>
> ______________________________________________________________
> 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

Scott Ellington

Overvoltage Protector Update

In reply to this post by Scott Ellington

I've updated the drawing to include construction notes and a mechanical sketch:

http://www.ssec.wisc.edu/~scotte/hr/OVP.pdf

The large heat sink, I know, will seem to some like overkill. To me, an extra 20 bucks seems like cheap insurance. See the notes.

As W8JI notes, a simpler circuit just uses a zener diode to drive the SCR. I chose the more complex version to allow the trip point to be set close to the operating voltage. The K3, for example, has a maximum rating of 15.0 V, too close to 13.8 for the simpler circuit.

At the moment, all the parts are available from Digi-Key.

Scott K9MA

On Aug 20, 2010, at 3:00 PM, Scott Ellington wrote:

Scott Ellington
Madison, Wisconsin
USA

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John Huggins, kx4o

Re: Overvoltage Protector Update

Nice circuit. Since this is meant to help protect the K3 from faulty
power supplies, this begs the question of what abuse can the K3 (or K2)
take from the power bus.

As an automotive power bus is a terrible awful place, will the K3 design
tolerate these typical values found on a vehicle power rail:

- Steady State Voltage between 12.5 to 15 Vdc,
- Upper and lower ripple of +/- 1 Vpeak riding on the Steady State values,
- Surge values between 9 and 20 Vdc for 600 ms,
- Spikes of +/- 125 Volts peaking for 70 uS falling to steady state levels
after 1 ms,

?

> I've updated the drawing to include construction notes and a mechanical
> sketch:
>
> http://www.ssec.wisc.edu/~scotte/hr/OVP.pdf
>
>
> The large heat sink, I know, will seem to some like overkill. To me, an
> extra 20 bucks seems like cheap insurance. See the notes.
>
> As W8JI notes, a simpler circuit just uses a zener diode to drive the SCR.
> I chose the more complex version to allow the trip point to be set close
> to the operating voltage. The K3, for example, has a maximum rating of
> 15.0 V, too close to 13.8 for the simpler circuit.
>
> At the moment, all the parts are available from Digi-Key.
>
> Scott K9MA
>
>
>
>
> On Aug 20, 2010, at 3:00 PM, Scott Ellington wrote:
>
>> Some power supplies, like the Samlex SEC 1235, have no built-in