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Power supply V drop - was poor CW on K3S

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Chuck Chandler

Power supply V drop - was poor CW on K3S

Here's an update.

I replaced the power cable running from the powerstrip with a 3-foot length
with glass fuse holders in each leg. I also adjusted the power supply to
14.50V at rest. The K3S now shows 14.2V at rest. At 100W TX the K3S shows
13.2V, so a 1 volt drop. Way too much.

The power supply voltage measured at the terminals drops from 14.50 to
14.44 for full power TX. This seems too much, I had read the drop should
be no more than 0.01V and this is 0.06V.

So, suspecting the in line fuse holders I made up another cable with dual
blade-fuse holders, which was worse. TX voltage on the K3S display dropped
to 12.9V.

I'm suspecting my power supply is to blame - it's a TenTec 963, a
re-branded Astron SS-30. Alternatively, I have another commercial power
cable with fuse holders I can cut down and try.

Many thanks for all the help both here on the reflector and the direct
emails from several fellows, and to Rich VE3KI for the on-air tests this
morning!

73 de Chuck, WS1L

--

===================
Chuck Chandler
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===================
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rcbenedict1545

Re: Power supply V drop - was poor CW on K3S

If it’s a regulated power supply with crowbar And the radio has a fuse why are you using inline fuses?

Sent from my iPhone

> On Apr 25, 2020, at 10:04, Chuck Chandler <[hidden email]> wrote:
>
> Here's an update.
>
> I replaced the power cable running from the powerstrip with a 3-foot length
> with glass fuse holders in each leg. I also adjusted the power supply to
> 14.50V at rest. The K3S now shows 14.2V at rest. At 100W TX the K3S shows
> 13.2V, so a 1 volt drop. Way too much.
>
> The power supply voltage measured at the terminals drops from 14.50 to
> 14.44 for full power TX. This seems too much, I had read the drop should
> be no more than 0.01V and this is 0.06V.
>
> So, suspecting the in line fuse holders I made up another cable with dual
> blade-fuse holders, which was worse. TX voltage on the K3S display dropped
> to 12.9V.
>
> I'm suspecting my power supply is to blame - it's a TenTec 963, a
> re-branded Astron SS-30. Alternatively, I have another commercial power
> cable with fuse holders I can cut down and try.
>
> Many thanks for all the help both here on the reflector and the direct
> emails from several fellows, and to Rich VE3KI for the on-air tests this
> morning!
>
> 73 de Chuck, WS1L
>
> --
>
>
> ===================
> Chuck Chandler
> [hidden email]
> ===================
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

k6dgw

Re: Power supply V drop - was poor CW on K3S

In reply to this post by Chuck Chandler

"glass fuses"? You want to avoid the in-line cylindrical cartridge
fuses, the holders almost always have too much resistance. Blade-type
automotive fuses are much better ... much more contact surface, much
more contact pressure, and a wiping action as you insert the fuse. A
drop of DeOxit on the blades as you insert the fuse will also help. If
this is a fixed installation and your power supply has some form of
overcurrent protection [e.g. crowbar], there may be no need for any
fuses in the power cable.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 4/25/2020 9:01 AM, Chuck Chandler wrote:

> Here's an update.
>
> I replaced the power cable running from the powerstrip with a 3-foot length
> with glass fuse holders in each leg. I also adjusted the power supply to
> 14.50V at rest. The K3S now shows 14.2V at rest. At 100W TX the K3S shows
> 13.2V, so a 1 volt drop. Way too much.
>
> The power supply voltage measured at the terminals drops from 14.50 to
> 14.44 for full power TX. This seems too much, I had read the drop should
> be no more than 0.01V and this is 0.06V.
>
> So, suspecting the in line fuse holders I made up another cable with dual
> blade-fuse holders, which was worse. TX voltage on the K3S display dropped
> to 12.9V.
>
> I'm suspecting my power supply is to blame - it's a TenTec 963, a
> re-branded Astron SS-30. Alternatively, I have another commercial power
> cable with fuse holders I can cut down and try.
>
> Many thanks for all the help both here on the reflector and the direct
> emails from several fellows, and to Rich VE3KI for the on-air tests this
> morning!
>
> 73 de Chuck, WS1L
>

Augie "Gus" Hansen

Re: Power supply V drop - was poor CW on K3S

On 4/25/2020 12:19 PM, Fred Jensen wrote:
> ... If this is a fixed installation and your power supply has some
> form of overcurrent protection [e.g. crowbar], there may be no need
> for any fuses in the power cable.

A crowbar circuit will short the output of the PS to prevent an
over-voltage event from damaging the equipment being powered. A fuse or
fast acting breaker is used to guard against over-current events.

Gus Hansen
KB0YH

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Charlie T, K3ICH

Re: Power supply V drop - was poor CW on K3S

In reply to this post by k6dgw

Well, if you simply "must" have a fuse, use the type that those monster car blasters use, an AGU (5AG) type. They are 1½" long and 13/32" in diameter with usually gold plated endcaps.

The holders are up to the task as well, with low resistance gold plated pressure fit caps, and are typically water proof. They have hex key set screws for the (BEEEG) wire connection.
Perfect for under hood or home use with fuses available from 100 mA up to 200 Amp ratings at 32VDC.

I don't think you can find a more efficient fuse & holder for low voltage drop.

73, Charlie k3ICH

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of Fred Jensen
Sent: Saturday, April 25, 2020 2:20 PM
To: [hidden email]
Subject: Re: [Elecraft] Power supply V drop - was poor CW on K3S

"glass fuses"? You want to avoid the in-line cylindrical cartridge fuses, the holders almost always have too much resistance. Blade-type automotive fuses are much better ... much more contact surface, much more contact pressure, and a wiping action as you insert the fuse. A drop of DeOxit on the blades as you insert the fuse will also help. If this is a fixed installation and your power supply has some form of overcurrent protection [e.g. crowbar], there may be no need for any fuses in the power cable.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 4/25/2020 9:01 AM, Chuck Chandler wrote:

> Here's an update.
>
> I replaced the power cable running from the powerstrip with a 3-foot
> length with glass fuse holders in each leg. I also adjusted the power
> supply to 14.50V at rest. The K3S now shows 14.2V at rest. At 100W
> TX the K3S shows 13.2V, so a 1 volt drop. Way too much.
>
> The power supply voltage measured at the terminals drops from 14.50 to
> 14.44 for full power TX. This seems too much, I had read the drop
> should be no more than 0.01V and this is 0.06V.
>
> So, suspecting the in line fuse holders I made up another cable with
> dual blade-fuse holders, which was worse. TX voltage on the K3S
> display dropped to 12.9V.
>
> I'm suspecting my power supply is to blame - it's a TenTec 963, a
> re-branded Astron SS-30. Alternatively, I have another commercial
> power cable with fuse holders I can cut down and try.
>
> Many thanks for all the help both here on the reflector and the direct
> emails from several fellows, and to Rich VE3KI for the on-air tests
> this morning!
>
> 73 de Chuck, WS1L
>

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K8TE

Re: Power supply V drop - was poor CW on K3S

In reply to this post by rcbenedict1545

This is a huge misperception that is very dangerous! If the power supply
(PSU) doesn't have an in-line fuse on the 12VDC, then you're taking a grave
chance should a short occur in the cable between the PSU and radio. Ask
folks who have set their cars on fire.

Like a battery, there should be a fuse at the PSU to open should the 12VDC
supply lead short. Some will whine about Voltage drop, but safety is far
more important to me. The K3 internal meter will indicate the Voltage at
the rear APP.

73, Bill, K8TE

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