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About my capacitor failure (etc.) issue:

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Ray Albers-2

About my capacitor failure (etc.) issue:

Many to all who posted/responded to my recent post about an electrolytic
capacitor failure in my power supply. Lots of very interesting reading
about peoples' industry experiences - thank you!

Several have pointed out that using a 20A supply with my K3/100 is pushing
close to (or over!) the limit. Even though I am measuring just 16A at the
power level I'm running (and not running anything but the K3 on this
supply) I agree that I'm skirting the edges. So even though I've been
getting away with it for a long time, this morning I ordered a 35A supply.
I'll probably sleep better.

73
Ray K2HYD

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Christopher Hoover

Re: About my capacitor failure (etc.) issue:

You might want to replace the bridge rectifier in that new 35A power supply.

Yep, right out of the box.

At some point, Astron started shipping RS-35A's with a 25A bridge
rectifier. They paralleled two out of four of the 25A diodes twice over
to make, supposedly, a pair of 50A diodes for center-tapped full-wave
rectification. That's not good engineering practice as the diodes in each
pair will not share current equally because of differences in Vf and
tempco. Once one blow, the other will blow shortly after.

After I fixed my own RS-35A with this problem, I've helped several other
hams fix this same problem in theirs. Not a random sample, as this is just
folks on my local machine and in local clubs.

You can get a 50A bridge in the same package for under $3.

Perhaps Astron has fixed the problem since ....

73 de AI6KG -ch

On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]> wrote:

> Many to all who posted/responded to my recent post about an electrolytic
> capacitor failure in my power supply. Lots of very interesting reading
> about peoples' industry experiences - thank you!
>
> Several have pointed out that using a 20A supply with my K3/100 is pushing
> close to (or over!) the limit. Even though I am measuring just 16A at the
> power level I'm running (and not running anything but the K3 on this
> supply) I agree that I'm skirting the edges. So even though I've been
> getting away with it for a long time, this morning I ordered a 35A supply.
> I'll probably sleep better.
>
> 73
> Ray K2HYD
>
> <
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Adrian-3

Re: About my capacitor failure (etc.) issue:

When you say 'blow' are you saying it short circuits internally or open
circuits internally due to the event ?

Adrian Fewster

On 20/4/20 8:07 am, Christopher Hoover wrote:

> You might want to replace the bridge rectifier in that new 35A power supply.
>
> Yep, right out of the box.
>
> At some point, Astron started shipping RS-35A's with a 25A bridge
> rectifier. They paralleled two out of four of the 25A diodes twice over
> to make, supposedly, a pair of 50A diodes for center-tapped full-wave
> rectification. That's not good engineering practice as the diodes in each
> pair will not share current equally because of differences in Vf and
> tempco. Once one blow, the other will blow shortly after.
>
> After I fixed my own RS-35A with this problem, I've helped several other
> hams fix this same problem in theirs. Not a random sample, as this is just
> folks on my local machine and in local clubs.
>
> You can get a 50A bridge in the same package for under $3.
>
> Perhaps Astron has fixed the problem since ....
>
> 73 de AI6KG -ch
>
>
>
>
> On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]> wrote:
>
>> Many to all who posted/responded to my recent post about an electrolytic
>> capacitor failure in my power supply. Lots of very interesting reading
>> about peoples' industry experiences - thank you!
>>
>> Several have pointed out that using a 20A supply with my K3/100 is pushing
>> close to (or over!) the limit. Even though I am measuring just 16A at the
>> power level I'm running (and not running anything but the K3 on this
>> supply) I agree that I'm skirting the edges. So even though I've been
>> getting away with it for a long time, this morning I ordered a 35A supply.
>> I'll probably sleep better.
>>
>> 73
>> Ray K2HYD
>>
>> <
>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
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Don Wilhelm

Re: About my capacitor failure (etc.) issue:

If the diode shorts, it Will cause excessive ripple from the half wave
rectification.
I suspect that the failure mode is an open causing the remaining diode
to carry the full current, which will cause its eventual failure.

In any case, paralleling two diodes without some form of resistance in
series will be a prescription for failure.

73,
Don W3FPR

On 4/19/2020 7:24 PM, Adrian wrote:
> When you say 'blow' are you saying it short circuits internally or open
> circuits internally due to the event ?
>
>
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Christopher Hoover

Re: About my capacitor failure (etc.) issue:

In reply to this post by Adrian-3

opens in my limited experience.

On Sun, Apr 19, 2020 at 4:26 PM Adrian <[hidden email]> wrote:

> When you say 'blow' are you saying it short circuits internally or open
> circuits internally due to the event ?
>
>
> Adrian Fewster
>
> On 20/4/20 8:07 am, Christopher Hoover wrote:
> > You might want to replace the bridge rectifier in that new 35A power
> supply.
> >
> > Yep, right out of the box.
> >
> > At some point, Astron started shipping RS-35A's with a 25A bridge
> > rectifier. They paralleled two out of four of the 25A diodes twice over
> > to make, supposedly, a pair of 50A diodes for center-tapped full-wave
> > rectification. That's not good engineering practice as the diodes in
> each
> > pair will not share current equally because of differences in Vf and
> > tempco. Once one blow, the other will blow shortly after.
> >
> > After I fixed my own RS-35A with this problem, I've helped several other
> > hams fix this same problem in theirs. Not a random sample, as this is
> just
> > folks on my local machine and in local clubs.
> >
> > You can get a 50A bridge in the same package for under $3.
> >
> > Perhaps Astron has fixed the problem since ....
> >
> > 73 de AI6KG -ch
> >
> >
> >
> >
> > On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]> wrote:
> >
> >> Many to all who posted/responded to my recent post about an electrolytic
> >> capacitor failure in my power supply. Lots of very interesting reading
> >> about peoples' industry experiences - thank you!
> >>
> >> Several have pointed out that using a 20A supply with my K3/100 is
> pushing
> >> close to (or over!) the limit. Even though I am measuring just 16A at
> the
> >> power level I'm running (and not running anything but the K3 on this
> >> supply) I agree that I'm skirting the edges. So even though I've been
> >> getting away with it for a long time, this morning I ordered a 35A
> supply.
> >> I'll probably sleep better.
> >>
> >> 73
> >> Ray K2HYD
> >>
> >> <
> >>
> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
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> >> ______________________________________________________________
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> >>
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Jim Rhodes-2

Re: About my capacitor failure (etc.) issue:

Or sometimes, just to get your attention, they will short out then
explosively go open with a bang. The is usually no doubt figuring out which
component is bad.

On Sun, Apr 19, 2020, 19:56 Christopher Hoover <[hidden email]> wrote:

> opens in my limited experience.
>
> On Sun, Apr 19, 2020 at 4:26 PM Adrian <[hidden email]> wrote:
>
> > When you say 'blow' are you saying it short circuits internally or open
> > circuits internally due to the event ?
> >
> >
> > Adrian Fewster
> >
> > On 20/4/20 8:07 am, Christopher Hoover wrote:
> > > You might want to replace the bridge rectifier in that new 35A power
> > supply.
> > >
> > > Yep, right out of the box.
> > >
> > > At some point, Astron started shipping RS-35A's with a 25A bridge
> > > rectifier. They paralleled two out of four of the 25A diodes twice
> over
> > > to make, supposedly, a pair of 50A diodes for center-tapped full-wave
> > > rectification. That's not good engineering practice as the diodes in
> > each
> > > pair will not share current equally because of differences in Vf and
> > > tempco. Once one blow, the other will blow shortly after.
> > >
> > > After I fixed my own RS-35A with this problem, I've helped several
> other
> > > hams fix this same problem in theirs. Not a random sample, as this is
> > just
> > > folks on my local machine and in local clubs.
> > >
> > > You can get a 50A bridge in the same package for under $3.
> > >
> > > Perhaps Astron has fixed the problem since ....
> > >
> > > 73 de AI6KG -ch
> > >
> > >
> > >
> > >
> > > On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]>
> wrote:
> > >
> > >> Many to all who posted/responded to my recent post about an
> electrolytic
> > >> capacitor failure in my power supply. Lots of very interesting
> reading
> > >> about peoples' industry experiences - thank you!
> > >>
> > >> Several have pointed out that using a 20A supply with my K3/100 is
> > pushing
> > >> close to (or over!) the limit. Even though I am measuring just 16A at
> > the
> > >> power level I'm running (and not running anything but the K3 on this
> > >> supply) I agree that I'm skirting the edges. So even though I've been
> > >> getting away with it for a long time, this morning I ordered a 35A
> > supply.
> > >> I'll probably sleep better.
> > >>
> > >> 73
> > >> Ray K2HYD
> > >>
> > >> <
> > >>
> >
> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
> > >> Virus-free.
> > >> www.avast.com
> > >> <
> > >>
> >
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> > >> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
> > >> ______________________________________________________________
> > >> Elecraft mailing list
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> > >> Help: http://mailman.qth.net/mmfaq.htm
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> > >>
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> > >>
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Bob McGraw - K4TAX

Re: About my capacitor failure (etc.) issue:

I had a ham mention to me that this power supply blew up. He was somewhat annoyed when I ask if anyone was injured in the explosion.

Folks, for us trying to assist with technical issues, please give complete and accurate descriptions. You will get better answers.

Bob, K4TAX

Sent from my iPhone

> On Apr 19, 2020, at 10:33 PM, Jim Rhodes <[hidden email]> wrote:
>
> Or sometimes, just to get your attention, they will short out then
> explosively go open with a bang. The is usually no doubt figuring out which
> component is bad.
>
>> On Sun, Apr 19, 2020, 19:56 Christopher Hoover <[hidden email]> wrote:
>>
>> opens in my limited experience.
>>
>>> On Sun, Apr 19, 2020 at 4:26 PM Adrian <[hidden email]> wrote:
>>>
>>> When you say 'blow' are you saying it short circuits internally or open
>>> circuits internally due to the event ?
>>>
>>>
>>> Adrian Fewster
>>>
>>> On 20/4/20 8:07 am, Christopher Hoover wrote:
>>>> You might want to replace the bridge rectifier in that new 35A power
>>> supply.
>>>>
>>>> Yep, right out of the box.
>>>>
>>>> At some point, Astron started shipping RS-35A's with a 25A bridge
>>>> rectifier. They paralleled two out of four of the 25A diodes twice
>> over
>>>> to make, supposedly, a pair of 50A diodes for center-tapped full-wave
>>>> rectification. That's not good engineering practice as the diodes in
>>> each
>>>> pair will not share current equally because of differences in Vf and
>>>> tempco. Once one blow, the other will blow shortly after.
>>>>
>>>> After I fixed my own RS-35A with this problem, I've helped several
>> other
>>>> hams fix this same problem in theirs. Not a random sample, as this is
>>> just
>>>> folks on my local machine and in local clubs.
>>>>
>>>> You can get a 50A bridge in the same package for under $3.
>>>>
>>>> Perhaps Astron has fixed the problem since ....
>>>>
>>>> 73 de AI6KG -ch
>>>>
>>>>
>>>>
>>>>
>>>> On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]>
>> wrote:
>>>>
>>>>> Many to all who posted/responded to my recent post about an
>> electrolytic
>>>>> capacitor failure in my power supply. Lots of very interesting
>> reading
>>>>> about peoples' industry experiences - thank you!
>>>>>
>>>>> Several have pointed out that using a 20A supply with my K3/100 is
>>> pushing
>>>>> close to (or over!) the limit. Even though I am measuring just 16A at
>>> the
>>>>> power level I'm running (and not running anything but the K3 on this
>>>>> supply) I agree that I'm skirting the edges. So even though I've been
>>>>> getting away with it for a long time, this morning I ordered a 35A
>>> supply.
>>>>> I'll probably sleep better.
>>>>>
>>>>> 73
>>>>> Ray K2HYD
>>>>>
>>>>> <
>>>>>
>>>
>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
>>>>> Virus-free.
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>>>>>
>>>
>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link
>>>>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>>>> ______________________________________________________________
>>>>> Elecraft mailing list
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>>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>>> Message delivered to [hidden email]
>>>>>
>>>> ______________________________________________________________
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>>>>
>>> ______________________________________________________________
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Ray Albers-2

Re: About my capacitor failure (etc.) issue:

In reply to this post by Christopher Hoover

This thread started as my description of the failure of my Astron RS-20A
power supply, caused by a bad electrolytic capacitor on the regulator
circuit board. Several hams posted advice that a 20Amp supply was really
too small for a K3/100, especially if running full power. This led me to
order an Astron RS-35 supply.

Chris Hoover, AI6KG, posted the below advice, warning about possible under-
engineered rectifier diode arrangement in the RS-35A.

Today the big brown truck delivered my RS-35M-AP (the M and AP signify it
has meters and Anderson Power Poles on the front panel). Chris speculated
that Astron may have made changes more recently. So the first thing I did
was to open the case to check out the rectifier arrangement. Here's what I
found:

My unit bears Serial Number 2019110051. I am speculating that the leading
digits 2019 signifies 2019 manufacture. Interestingly, the schematic that
shipped with the unit says Rev.1, April 2020. The schematic shows two
bridge rectifiers, DB3501. Two diodes are used from each bridge, and sure
enough the diodes are paralleled. The DB3501 is spec'd at 35A, so that
seems to be an improvement from the 25A diodes Chris mentioned. That's
what's in the schematic. Inside the power supply, there are indeed two
rectifier packages bolted to the floor, with heavy (maybe 14ga) solid wires
connecting terminals in parallel. I'm unable to confirm what the rating of
these diode packages is. They are not labeled DB3501. Instead, they say
"Astron 5001," and one of them also bears some Chinese characters. So
custom made for Astron?

Well, I have ordered a 50Amp rated diode package, but am undecided if I
will replace the diodes in the supply. 35 Amp rated diode bridges is an
upgrade from the 25 diode bridges that Chris mentioned finding. It does
puzzle me why, with 50A (and better) diodes being so cheap, would Astron do
it this way? I can only think of two reasons: 1) We think having two
packages bolted to the case will make for better heat dissipation of the
total heat generated at max current and 2), the ever present, "because
we've always done it this way!"

Finally, I'll mention that, like my old RS-20A, I found the negative
terminal bonded to the case. I consider this bad practice so I removed that
bond.

73 to all
Ray K2HYD

On Sun, Apr 19, 2020 at 6:07 PM Christopher Hoover <[hidden email]>
wrote:

> You might want to replace the bridge rectifier in that new 35A power
> supply.
>
> Yep, right out of the box.
>
> At some point, Astron started shipping RS-35A's with a 25A bridge
> rectifier. They paralleled two out of four of the 25A diodes twice over
> to make, supposedly, a pair of 50A diodes for center-tapped full-wave
> rectification. That's not good engineering practice as the diodes in each
> pair will not share current equally because of differences in Vf and
> tempco. Once one blow, the other will blow shortly after.
>
> After I fixed my own RS-35A with this problem, I've helped several other
> hams fix this same problem in theirs. Not a random sample, as this is just
> folks on my local machine and in local clubs.
>
> You can get a 50A bridge in the same package for under $3.
>
> Perhaps Astron has fixed the problem since ....
>
> 73 de AI6KG -ch
>
>
>
>
> On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]> wrote:
>
>> Many to all who posted/responded to my recent post about an electrolytic
>> capacitor failure in my power supply. Lots of very interesting reading
>> about peoples' industry experiences - thank you!
>>
>> Several have pointed out that using a 20A supply with my K3/100 is pushing
>> close to (or over!) the limit. Even though I am measuring just 16A at the
>> power level I'm running (and not running anything but the K3 on this
>> supply) I agree that I'm skirting the edges. So even though I've been
>> getting away with it for a long time, this morning I ordered a 35A supply.
>> I'll probably sleep better.
>>
>> 73
>> Ray K2HYD
>>
>> <
>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
>> >
>> Virus-free.
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Rick Bates, NK7I

Re: About my capacitor failure (etc.) issue:

No! That is the CORRECT thing to do; all grounds should equal ground.
You should reconnect that to the chassis ground, it is not a design flaw.

Rick NK7I

On 4/24/2020 12:11 PM, Ray Albers wrote:
> Finally, I'll mention that, like my old RS-20A, I found the negative
> terminal bonded to the case. I consider this bad practice so I removed that
> bond.
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Jim Brown-10

Re: About my capacitor failure (etc.) issue:

Ray is correct. A study of the schematics for Astron linear supplies
makes it clear that nothing in the circuitry is referenced to the
chassis.The vast majority of PSUs are built so that V- can be bonded or
not. V- is NOT ground, it is V-. And in our systems, it should NOT be
bonded in the PSU. See my previously posted link for a discussion of WHY
V- should not be bonded.

73, Jim K9YC

On 4/24/2020 12:20 PM, Rick Bates, NK7I wrote:

> No! That is the CORRECT thing to do; all grounds should equal ground.
> You should reconnect that to the chassis ground, it is not a design flaw.
>
> Rick NK7I
>
> On 4/24/2020 12:11 PM, Ray Albers wrote:
>> Finally, I'll mention that, like my old RS-20A, I found the negative
>> terminal bonded to the case. I consider this bad practice so I removed
>> that
>> bond.

Elecraft mailing list

Re: About my capacitor failure (etc.) issue:

In reply to this post by Ray Albers-2

Another possibility is that is what they had on hand

Sent from my iPhone

> On Apr 24, 2020, at 3:13 PM, Ray Albers <[hidden email]> wrote:
>
> This thread started as my description of the failure of my Astron RS-20A
> power supply, caused by a bad electrolytic capacitor on the regulator
> circuit board. Several hams posted advice that a 20Amp supply was really
> too small for a K3/100, especially if running full power. This led me to
> order an Astron RS-35 supply.
>
> Chris Hoover, AI6KG, posted the below advice, warning about possible under-
> engineered rectifier diode arrangement in the RS-35A.
>
> Today the big brown truck delivered my RS-35M-AP (the M and AP signify it
> has meters and Anderson Power Poles on the front panel). Chris speculated
> that Astron may have made changes more recently. So the first thing I did
> was to open the case to check out the rectifier arrangement. Here's what I
> found:
>
> My unit bears Serial Number 2019110051. I am speculating that the leading
> digits 2019 signifies 2019 manufacture. Interestingly, the schematic that
> shipped with the unit says Rev.1, April 2020. The schematic shows two
> bridge rectifiers, DB3501. Two diodes are used from each bridge, and sure
> enough the diodes are paralleled. The DB3501 is spec'd at 35A, so that
> seems to be an improvement from the 25A diodes Chris mentioned. That's
> what's in the schematic. Inside the power supply, there are indeed two
> rectifier packages bolted to the floor, with heavy (maybe 14ga) solid wires
> connecting terminals in parallel. I'm unable to confirm what the rating of
> these diode packages is. They are not labeled DB3501. Instead, they say
> "Astron 5001," and one of them also bears some Chinese characters. So
> custom made for Astron?
>
> Well, I have ordered a 50Amp rated diode package, but am undecided if I
> will replace the diodes in the supply. 35 Amp rated diode bridges is an
> upgrade from the 25 diode bridges that Chris mentioned finding. It does
> puzzle me why, with 50A (and better) diodes being so cheap, would Astron do
> it this way? I can only think of two reasons: 1) We think having two
> packages bolted to the case will make for better heat dissipation of the
> total heat generated at max current and 2), the ever present, "because
> we've always done it this way!"
>
> Finally, I'll mention that, like my old RS-20A, I found the negative
> terminal bonded to the case. I consider this bad practice so I removed that
> bond.
>
> 73 to all
> Ray K2HYD
>
>
>> On Sun, Apr 19, 2020 at 6:07 PM Christopher Hoover <[hidden email]>
>> wrote:
>>
>> You might want to replace the bridge rectifier in that new 35A power
>> supply.
>>
>> Yep, right out of the box.
>>
>> At some point, Astron started shipping RS-35A's with a 25A bridge
>> rectifier. They paralleled two out of four of the 25A diodes twice over
>> to make, supposedly, a pair of 50A diodes for center-tapped full-wave
>> rectification. That's not good engineering practice as the diodes in each
>> pair will not share current equally because of differences in Vf and
>> tempco. Once one blow, the other will blow shortly after.
>>
>> After I fixed my own RS-35A with this problem, I've helped several other
>> hams fix this same problem in theirs. Not a random sample, as this is just
>> folks on my local machine and in local clubs.
>>
>> You can get a 50A bridge in the same package for under $3.
>>
>> Perhaps Astron has fixed the problem since ....
>>
>> 73 de AI6KG -ch
>>
>>
>>
>>
>>> On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]> wrote:
>>>
>>> Many to all who posted/responded to my recent post about an electrolytic
>>> capacitor failure in my power supply. Lots of very interesting reading
>>> about peoples' industry experiences - thank you!
>>>
>>> Several have pointed out that using a 20A supply with my K3/100 is pushing
>>> close to (or over!) the limit. Even though I am measuring just 16A at the
>>> power level I'm running (and not running anything but the K3 on this
>>> supply) I agree that I'm skirting the edges. So even though I've been
>>> getting away with it for a long time, this morning I ordered a 35A supply.
>>> I'll probably sleep better.
>>>
>>> 73
>>> Ray K2HYD
>>>
>>> <
>>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
>>>>
>>> Virus-free.
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>>> <
>>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link
>>>>
>>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>> ______________________________________________________________
>>> 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]
>>>
>>
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Martin Sole-3

Re: About my capacitor failure (etc.) issue:

In reply to this post by Ray Albers-2

I can add perhaps another data point on the rectifier matter. Years back
my employer, one of the largest ground to air radio manufacturers was
having failures with their mainstay transmitter, a 50w carrier AM unit.
It had a large toroidal transformer and a packaged rectifier. The
rectifier was bolted to the steel sub chassis and all was fine in
regular intermittent service but in ATIS service the transmitter runs
essentially continuous, so about 160-180 PEP, and rectifiers were failing.

Investigation showed that the steel chassis was not 100% flat and the
contact surface of the rectifier was compromised. The fix was to insert
a (really) flat aluminium bar under the rectifier and bolt that to the
chassis. The bar did much of the heat sinking and had many more contact
patches with the steel sub chassis. Even paint ridges can be a source of
reduced contact leading to overheating of the rectifier package and
those things really do need to shift some heat. A good way to think of
it is like you would a PA transistor in a 100 watt amplifier, we
appreciate how well they need to be bolted to a heat sink and your
rectifier package wants very similar assessment.

It's not so much the current that causes failure rather the heat is not
being dissipated properly from the smaller package.

Martin, HS0ZED

On 25/04/2020 02:11, Ray Albers wrote:

> This thread started as my description of the failure of my Astron RS-20A
> power supply, caused by a bad electrolytic capacitor on the regulator
> circuit board. Several hams posted advice that a 20Amp supply was really
> too small for a K3/100, especially if running full power. This led me to
> order an Astron RS-35 supply.
>
> Chris Hoover, AI6KG, posted the below advice, warning about possible under-
> engineered rectifier diode arrangement in the RS-35A.
>
> Today the big brown truck delivered my RS-35M-AP (the M and AP signify it
> has meters and Anderson Power Poles on the front panel). Chris speculated
> that Astron may have made changes more recently. So the first thing I did
> was to open the case to check out the rectifier arrangement. Here's what I
> found:
>
> My unit bears Serial Number 2019110051. I am speculating that the leading
> digits 2019 signifies 2019 manufacture. Interestingly, the schematic that
> shipped with the unit says Rev.1, April 2020. The schematic shows two
> bridge rectifiers, DB3501. Two diodes are used from each bridge, and sure
> enough the diodes are paralleled. The DB3501 is spec'd at 35A, so that
> seems to be an improvement from the 25A diodes Chris mentioned. That's
> what's in the schematic. Inside the power supply, there are indeed two
> rectifier packages bolted to the floor, with heavy (maybe 14ga) solid wires
> connecting terminals in parallel. I'm unable to confirm what the rating of
> these diode packages is. They are not labeled DB3501. Instead, they say
> "Astron 5001," and one of them also bears some Chinese characters. So
> custom made for Astron?
>
> Well, I have ordered a 50Amp rated diode package, but am undecided if I
> will replace the diodes in the supply. 35 Amp rated diode bridges is an
> upgrade from the 25 diode bridges that Chris mentioned finding. It does
> puzzle me why, with 50A (and better) diodes being so cheap, would Astron do
> it this way? I can only think of two reasons: 1) We think having two
> packages bolted to the case will make for better heat dissipation of the
> total heat generated at max current and 2), the ever present, "because
> we've always done it this way!"
>
> Finally, I'll mention that, like my old RS-20A, I found the negative
> terminal bonded to the case. I consider this bad practice so I removed that
> bond.
>
> 73 to all
> Ray K2HYD
>
>
> On Sun, Apr 19, 2020 at 6:07 PM Christopher Hoover <[hidden email]>
> wrote:
>
>> You might want to replace the bridge rectifier in that new 35A power
>> supply.
>>
>> Yep, right out of the box.
>>
>> At some point, Astron started shipping RS-35A's with a 25A bridge
>> rectifier. They paralleled two out of four of the 25A diodes twice over
>> to make, supposedly, a pair of 50A diodes for center-tapped full-wave
>> rectification. That's not good engineering practice as the diodes in each
>> pair will not share current equally because of differences in Vf and
>> tempco. Once one blow, the other will blow shortly after.
>>
>> After I fixed my own RS-35A with this problem, I've helped several other
>> hams fix this same problem in theirs. Not a random sample, as this is just
>> folks on my local machine and in local clubs.
>>
>> You can get a 50A bridge in the same package for under $3.
>>
>> Perhaps Astron has fixed the problem since ....
>>
>> 73 de AI6KG -ch
>>
>>
>>
>>
>> On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]> wrote:
>>
>>> Many to all who posted/responded to my recent post about an electrolytic
>>> capacitor failure in my power supply. Lots of very interesting reading
>>> about peoples' industry experiences - thank you!
>>>
>>> Several have pointed out that using a 20A supply with my K3/100 is pushing
>>> close to (or over!) the limit. Even though I am measuring just 16A at the
>>> power level I'm running (and not running anything but the K3 on this
>>> supply) I agree that I'm skirting the edges. So even though I've been
>>> getting away with it for a long time, this morning I ordered a 35A supply.
>>> I'll probably sleep better.
>>>
>>> 73
>>> Ray K2HYD
>>>
>>> <
>>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
>>> Virus-free.
>>> www.avast.com
>>> <
>>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link
>>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>> ______________________________________________________________
>>> 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]
>>>
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> ______________________________________________________________
> 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]

Bob McGraw - K4TAX

Re: About my capacitor failure (etc.) issue:

I've always put a bit of heat sink compound on the rectifier unit before
mounting it to the bottom plate.    I've found several power supplies
where the bridge rectifier assembly failed and upon removal, there was
no heat sink compound.   Add a new bridge assembly and some heat sink
compound resolved the issues.   Never had one come back.

73

Bob, K4TAX

On 4/24/2020 10:50 PM, Martin Sole wrote:

> I can add perhaps another data point on the rectifier matter. Years
> back my employer, one of the largest ground to air radio manufacturers
> was having failures with their mainstay transmitter, a 50w carrier AM
> unit. It had a large toroidal transformer and a packaged rectifier.
> The rectifier was bolted to the steel sub chassis and all was fine in
> regular intermittent service but in ATIS service the transmitter runs
> essentially continuous, so about 160-180 PEP, and rectifiers were
> failing.
>
> Investigation showed that the steel chassis was not 100% flat and the
> contact surface of the rectifier was compromised. The fix was to
> insert a (really) flat aluminium bar under the rectifier and bolt that
> to the chassis. The bar did much of the heat sinking and had many more
> contact patches with the steel sub chassis. Even paint ridges can be a
> source of reduced contact leading to overheating of the rectifier
> package and those things really do need to shift some heat. A good way
> to think of it is like you would a PA transistor in a 100 watt
> amplifier, we appreciate how well they need to be bolted to a heat
> sink and your rectifier package wants very similar assessment.
>
> It's not so much the current that causes failure rather the heat is
> not being dissipated properly from the smaller package.
>
> Martin, HS0ZED
>

Christopher Hoover

Re: About my capacitor failure (etc.) issue:

In reply to this post by Ray Albers-2

If they are paralleling two 35A diodes in the new builds, they may have
repeated the same mistake.

Does this give a 50% derating (a typical factor) for full load forward
current?

I dunno. One can do the math [1] and figure it out.

A 50 A bridge (no need to parallel) is OK by design. That's just a smidge
under 50% derating.

I used a 75A bridge, IIRC.

73 de AI6KG

[1]
https://www.st.com/resource/en/application_note/dm00098381-current-sharing-in-parallel-diodes-stmicroelectronics.pdf

On Fri, Apr 24, 2020 at 12:11 PM Ray Albers <[hidden email]> wrote:

> This thread started as my description of the failure of my Astron RS-20A
> power supply, caused by a bad electrolytic capacitor on the regulator
> circuit board. Several hams posted advice that a 20Amp supply was really
> too small for a K3/100, especially if running full power. This led me to
> order an Astron RS-35 supply.
>
> Chris Hoover, AI6KG, posted the below advice, warning about possible
> under- engineered rectifier diode arrangement in the RS-35A.
>
> Today the big brown truck delivered my RS-35M-AP (the M and AP signify it
> has meters and Anderson Power Poles on the front panel). Chris speculated
> that Astron may have made changes more recently. So the first thing I did
> was to open the case to check out the rectifier arrangement. Here's what I
> found:
>
> My unit bears Serial Number 2019110051. I am speculating that the leading
> digits 2019 signifies 2019 manufacture. Interestingly, the schematic that
> shipped with the unit says Rev.1, April 2020. The schematic shows two
> bridge rectifiers, DB3501. Two diodes are used from each bridge, and sure
> enough the diodes are paralleled. The DB3501 is spec'd at 35A, so that
> seems to be an improvement from the 25A diodes Chris mentioned. That's
> what's in the schematic. Inside the power supply, there are indeed two
> rectifier packages bolted to the floor, with heavy (maybe 14ga) solid wires
> connecting terminals in parallel. I'm unable to confirm what the rating of
> these diode packages is. They are not labeled DB3501. Instead, they say
> "Astron 5001," and one of them also bears some Chinese characters. So
> custom made for Astron?
>
> Well, I have ordered a 50Amp rated diode package, but am undecided if I
> will replace the diodes in the supply. 35 Amp rated diode bridges is an
> upgrade from the 25 diode bridges that Chris mentioned finding. It does
> puzzle me why, with 50A (and better) diodes being so cheap, would Astron do
> it this way? I can only think of two reasons: 1) We think having two
> packages bolted to the case will make for better heat dissipation of the
> total heat generated at max current and 2), the ever present, "because
> we've always done it this way!"
>
> Finally, I'll mention that, like my old RS-20A, I found the negative
> terminal bonded to the case. I consider this bad practice so I removed that
> bond.
>
> 73 to all
> Ray K2HYD
>
>
> On Sun, Apr 19, 2020 at 6:07 PM Christopher Hoover <[hidden email]>
> wrote:
>
>> You might want to replace the bridge rectifier in that new 35A power
>> supply.
>>
>> Yep, right out of the box.
>>
>> At some point, Astron started shipping RS-35A's with a 25A bridge
>> rectifier. They paralleled two out of four of the 25A diodes twice over
>> to make, supposedly, a pair of 50A diodes for center-tapped full-wave
>> rectification. That's not good engineering practice as the diodes in each
>> pair will not share current equally because of differences in Vf and
>> tempco. Once one blow, the other will blow shortly after.
>>
>> After I fixed my own RS-35A with this problem, I've helped several other
>> hams fix this same problem in theirs. Not a random sample, as this is just
>> folks on my local machine and in local clubs.
>>
>> You can get a 50A bridge in the same package for under $3.
>>
>> Perhaps Astron has fixed the problem since ....
>>
>> 73 de AI6KG -ch
>>
>>
>>
>>
>> On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]> wrote:
>>
>>> Many to all who posted/responded to my recent post about an electrolytic
>>> capacitor failure in my power supply. Lots of very interesting reading
>>> about peoples' industry experiences - thank you!
>>>
>>> Several have pointed out that using a 20A supply with my K3/100 is
>>> pushing
>>> close to (or over!) the limit. Even though I am measuring just 16A at
>>> the
>>> power level I'm running (and not running anything but the K3 on this
>>> supply) I agree that I'm skirting the edges. So even though I've been
>>> getting away with it for a long time, this morning I ordered a 35A
>>> supply.
>>> I'll probably sleep better.
>>>
>>> 73
>>> Ray K2HYD
>>>
>>> <
>>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
>>> >
>>> Virus-free.
>>> www.avast.com
>>> <
>>> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link
>>> >
>>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>> ______________________________________________________________
>>> 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]
>>>
>>
>
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon> Virus-free.
> www.avast.com
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> <#m_-4856506079513387734_m_-8205502227484171307_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>

Christopher Hoover

Re: About my capacitor failure (etc.) issue:

In reply to this post by Martin Sole-3

We're getting far off the topic of Elecraft radios ...
>
>
> Investigation showed that the steel chassis was not 100% flat and the
> contact surface of the rectifier was compromised.

Good lesson. Contact resistances need to be accounted for in the thermal
model and analysis.. They are never zero like they are in the textbook.
Nothing is ever flat (P-V). TIMs (thermal interface material) can help
but need to go into the model.

73 de AI6KG

On Fri, Apr 24, 2020 at 8:52 PM Martin Sole <[hidden email]> wrote:

> I can add perhaps another data point on the rectifier matter. Years back
> my employer, one of the largest ground to air radio manufacturers was
> having failures with their mainstay transmitter, a 50w carrier AM unit.
> It had a large toroidal transformer and a packaged rectifier. The
> rectifier was bolted to the steel sub chassis and all was fine in
> regular intermittent service but in ATIS service the transmitter runs
> essentially continuous, so about 160-180 PEP, and rectifiers were failing.
>
> Investigation showed that the steel chassis was not 100% flat and the
> contact surface of the rectifier was compromised. The fix was to insert
> a (really) flat aluminium bar under the rectifier and bolt that to the
> chassis. The bar did much of the heat sinking and had many more contact
> patches with the steel sub chassis. Even paint ridges can be a source of
> reduced contact leading to overheating of the rectifier package and
> those things really do need to shift some heat. A good way to think of
> it is like you would a PA transistor in a 100 watt amplifier, we
> appreciate how well they need to be bolted to a heat sink and your
> rectifier package wants very similar assessment.
>
> It's not so much the current that causes failure rather the heat is not
> being dissipated properly from the smaller package.
>
> Martin, HS0ZED
>
>
> On 25/04/2020 02:11, Ray Albers wrote:
> > This thread started as my description of the failure of my Astron RS-20A
> > power supply, caused by a bad electrolytic capacitor on the regulator
> > circuit board. Several hams posted advice that a 20Amp supply was really
> > too small for a K3/100, especially if running full power. This led me to
> > order an Astron RS-35 supply.
> >
> > Chris Hoover, AI6KG, posted the below advice, warning about possible
> under-
> > engineered rectifier diode arrangement in the RS-35A.
> >
> > Today the big brown truck delivered my RS-35M-AP (the M and AP signify
> it
> > has meters and Anderson Power Poles on the front panel). Chris
> speculated
> > that Astron may have made changes more recently. So the first thing I did
> > was to open the case to check out the rectifier arrangement. Here's
> what I
> > found:
> >
> > My unit bears Serial Number 2019110051. I am speculating that the
> leading
> > digits 2019 signifies 2019 manufacture. Interestingly, the schematic
> that
> > shipped with the unit says Rev.1, April 2020. The schematic shows two
> > bridge rectifiers, DB3501. Two diodes are used from each bridge, and sure
> > enough the diodes are paralleled. The DB3501 is spec'd at 35A, so that
> > seems to be an improvement from the 25A diodes Chris mentioned. That's
> > what's in the schematic. Inside the power supply, there are indeed two
> > rectifier packages bolted to the floor, with heavy (maybe 14ga) solid
> wires
> > connecting terminals in parallel. I'm unable to confirm what the rating
> of
> > these diode packages is. They are not labeled DB3501. Instead, they say
> > "Astron 5001," and one of them also bears some Chinese characters. So
> > custom made for Astron?
> >
> > Well, I have ordered a 50Amp rated diode package, but am undecided if I
> > will replace the diodes in the supply. 35 Amp rated diode bridges is an
> > upgrade from the 25 diode bridges that Chris mentioned finding. It does
> > puzzle me why, with 50A (and better) diodes being so cheap, would Astron
> do
> > it this way? I can only think of two reasons: 1) We think having two
> > packages bolted to the case will make for better heat dissipation of the
> > total heat generated at max current and 2), the ever present, "because
> > we've always done it this way!"
> >
> > Finally, I'll mention that, like my old RS-20A, I found the negative
> > terminal bonded to the case. I consider this bad practice so I removed
> that
> > bond.
> >
> > 73 to all
> > Ray K2HYD
> >
> >
> > On Sun, Apr 19, 2020 at 6:07 PM Christopher Hoover <[hidden email]>
> > wrote:
> >
> >> You might want to replace the bridge rectifier in that new 35A power
> >> supply.
> >>
> >> Yep, right out of the box.
> >>
> >> At some point, Astron started shipping RS-35A's with a 25A bridge
> >> rectifier. They paralleled two out of four of the 25A diodes twice
> over
> >> to make, supposedly, a pair of 50A diodes for center-tapped full-wave
> >> rectification. That's not good engineering practice as the diodes in
> each
> >> pair will not share current equally because of differences in Vf and
> >> tempco. Once one blow, the other will blow shortly after.
> >>
> >> After I fixed my own RS-35A with this problem, I've helped several other
> >> hams fix this same problem in theirs. Not a random sample, as this is
> just
> >> folks on my local machine and in local clubs.
> >>
> >> You can get a 50A bridge in the same package for under $3.
> >>
> >> Perhaps Astron has fixed the problem since ....
> >>
> >> 73 de AI6KG -ch
> >>
> >>
> >>
> >>
> >> On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[hidden email]>
> wrote:
> >>
> >>> Many to all who posted/responded to my recent post about an
> electrolytic
> >>> capacitor failure in my power supply. Lots of very interesting reading
> >>> about peoples' industry experiences - thank you!
> >>>
> >>> Several have pointed out that using a 20A supply with my K3/100 is
> pushing
> >>> close to (or over!) the limit. Even though I am measuring just 16A at
> the
> >>> power level I'm running (and not running anything but the K3 on this
> >>> supply) I agree that I'm skirting the edges. So even though I've been
> >>> getting away with it for a long time, this morning I ordered a 35A
> supply.
> >>> I'll probably sleep better.
> >>>
> >>> 73
> >>> Ray K2HYD
> >>>
> >>> <
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