Troubleshooting RFI from switch-mode PS

[laga...@gmail.com]

I have a Samlex 120VAC-13.5VDC at 35A switch mode power supply for my amateur radio equipment. Working great for last 7 years. Recently it's now producing "swooshing" noise in my radio receiver, especially on frequencies from 1.8-10MHz. Took it apart and noticed blown tops on the 3 output filter electrolytics, so I replaced those. But that did not help.

I could replace the 2 larger input filter electrolytics but they "look" OK and I wonder if maybe I should be thinking of also replacing the switcher MOSFET - I don't know where else the noise could be coming from?

Any ideas greatly appreciated.

[Charles]

wrote in message
news:0f362b7e-4756-4027...@googlegroups.com...

If the supply is normal in all other ways, it could be that your replacement
caps are not suitable. Filtering switcher hash requires very low esr caps.

[ohg...@gmail.com]

I've never seen a power mosfet do anything but work normally or become zero ohm jumpers.

Are you sure it's the supply? Put a scope to the output and see what's going on. As far as the capacitors "looking" OK, remember that electrolytics need not be vented or bulged to be bad. Either put an ESR meter to *all* of them in the supply (including the primary) or scope them (preferred method).

[whit3rd]

On Sunday, November 20, 2016 at 11:49:41 AM UTC-8, laga...@gmail.com wrote:
> I have a Samlex 120VAC-13.5VDC at 35A switch mode power supply for my amateur radio equipment. Working great for last 7 years. Recently it's now producing "swooshing" noise in my radio receiver, especially on frequencies from 1.8-10MHz. Took it apart and noticed blown tops on the 3 output filter electrolytics, so I replaced those. But that did not help.
>

> I could replace the 2 larger input filter electrolytics but they "look" OK and...

The fast rectifiers on the low voltage side can fail/become leaky, and when they
do, they can take out capacitors. Check those.

[Jeff Liebermann]

I can't tell from here where the noise is coming from. Usually, I put
a small loop antenna on my spectrum analyzer and save it around the
power supply while under load. That usually locates the general area.

Much more interesting is why three capacitors would decide to bulge.
Bulging is usually caused by excessive ripple current through the
filter capacitors. High ripple could be coming from the diodes, or
simply from undersized capacitors that can't hold a charge between
switching cycles and therefore draw more current than normal.

I suggest you put a scope on the output while under load and see if
there's any ripple present. Compare the value with the manufactures
specs. Also, use an IR thermometer to measure the case temperature of
the capacitors. If they are getting warm, then there's ripple current
going through them.

--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[pf...@aol.com]

On Sunday, November 20, 2016 at 2:49:41 PM UTC-5, laga...@gmail.com wrote:

a) Replace all the caps. Unless you have both X-ray eyes and an ESR meter, you have no effective way of discerning whether they are good or not.
b) If it works otherwise - that is, produces the correct voltage - unlikely that the MOSFet is bad.
c) It becomes a close-run thing whether the cost/time involved in repairs exceeds the value of the device if it is more than just the caps.

Peter Wieck
Melrose Park, PA

[Jeff Liebermann]

On Sun, 20 Nov 2016 22:29:35 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

>I can't tell from here where the noise is coming from. Usually, I put
>a small loop antenna on my spectrum analyzer and save it around the
>power supply while under load. That usually locates the general area.

Is this the one or is there some reason you didn't bother disclosing
the model number? Notice that the SEC-1235 is a 12V 30A device and
current limits at 35A. How many amps are you drawing?
<http://www.samlexamerica.com/products/ProductDetail.aspx?pid=66>

See page 10 for RFI information:
<http://www.samlexamerica.com/documents/manuals/11001-SEC-1235-1235M-1114.pdf>

[ohg...@gmail.com]

On Monday, November 21, 2016 at 1:29:40 AM UTC-5, Jeff Liebermann wrote:

> Much more interesting is why three capacitors would decide to bulge.

>

> --
> Jeff Liebermann je...@cruzio.com
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 http://802.11junk.com
> Skype: JeffLiebermann AE6KS 831-336-2558

In the last 15 years, I've changed literally thousands of bulged electrolytics in consumer electronics for no other reason except they were just crappy parts at the end of their limited lifetimes. Most of those that bulge or vent are higher value types, say those beyond 330uf or so. Smaller electros fail at the same rate of their big brothers but don't generally visually vent. In the old days, capacitors didn't bulge unless they were tortured. Today it's mediocre chemistry that causes this, not circuit issues.

If you were to take apart 10 working flat screen TVs made in the last few years, half of them would show some sign of bulged or top vented capacitors despite running normally.

[Jeff Liebermann]

On Mon, 21 Nov 2016 08:46:43 -0800 (PST), ohg...@gmail.com wrote:

>In the last 15 years, I've changed literally thousands of
>bulged electrolytics in consumer electronics for no other
>reason except they were just crappy parts at the end of
>their limited lifetimes. Most of those that bulge or vent
>are higher value types, say those beyond 330uf or so.
>Smaller electros fail at the same rate of their big
>brothers but don't generally visually vent.

I know the feeling:
<http://802.11junk.com/jeffl/pics/repair/slides/bad-caps.html>
That's about a 5 month collection, mostly from motherboards, power
supplies, and LCD monitors. I've cut back on the component level
repairs in the last year, so this years collection is about 1/3 the
size. I have 4 different ESR testers and use them often.

>In the old days, capacitors didn't bulge unless they were
>tortured. Today it's mediocre chemistry that causes this,
>not circuit issues.

In the bad old daze, the electrolytics were running at 60Hz, not
60KHz. The power (heat) dissipated in the electrolytics is a function
of frequency.

>If you were to take apart 10 working flat screen TVs made
>in the last few years, half of them would show some sign of
>bulged or top vented capacitors despite running normally.

Ok, time to vent...

I blame CAD (computer aided design) for the problem. CAD has allowed
designers to accurately predict the life of some components including
electrolytics. If the operating parameters are known (voltage, temp,
ripple current, starting ESR, etc), the lifetime can be calculated.
Having a component last longer than the warranty period is considered
wasteful by many manufacturers. Therefore, they select the cheapest
possible part that will work up to when the warranty expires but no
longer. The result is a product where every component blows up at the
same time, just after the warranty expires. The 10 flat screens in
your example will not show one bad component. Instead, there will be
dozens, all different brands and values. This is not due to crappy
manufacturing, but rather due to careful selection for the MINIMUM
lifetime of the component.

[pf...@aol.com]

On Monday, November 21, 2016 at 1:07:20 PM UTC-5, Jeff Liebermann wrote:
>> SNIPPAGE<<

> Ok, time to vent...
>
> I blame CAD (computer aided design) for the problem. CAD has allowed
> designers to accurately predict the life of some components including
> electrolytics. If the operating parameters are known (voltage, temp,
> ripple current, starting ESR, etc), the lifetime can be calculated.
> Having a component last longer than the warranty period is considered
> wasteful by many manufacturers. Therefore, they select the cheapest
> possible part that will work up to when the warranty expires but no
> longer. The result is a product where every component blows up at the
> same time, just after the warranty expires. The 10 flat screens in
> your example will not show one bad component. Instead, there will be
> dozens, all different brands and values. This is not due to crappy
> manufacturing, but rather due to careful selection for the MINIMUM
> lifetime of the component.

I would refine this somewhat. When this happens, the average consumer will change brands as most (well, not the typical Trump supporter) recognize that something failing just after the warranty period is the manufacturer wanting to maintain the demand stream. I have found that such electronics - based on average hours used and other factors - tent to last about 25% beyond the warranty period - that is, if they last the first six weeks. Just long enough for the consumer to forget the warranty period.

There are exceptions: We have a Sony CRT-type TV purchased in Saudi in 2002 that has probably 13,000 hours on it that has survived two moves, two ocean voyages, kids, cats, dogs and such without a hitch. The Panasonic Plasma with about 6,000 hours on it is doing fine (so far) as well. Frigidaire refrigerators have about 5 years + one month before they crap out. GE units of US origin (in our experience) are pretty bullet proof. Bosch appliances, also, are pretty bullet-proof. It's all according to a mix of decent manufacture and pure blind luck.

[Dave Platt]

In article <l3d63c93jobjuht7h...@4ax.com>,

Jeff Liebermann <je...@cruzio.com> wrote:

>Having a component last longer than the warranty period is considered
>wasteful by many manufacturers. Therefore, they select the cheapest
>possible part that will work up to when the warranty expires but no
>longer. The result is a product where every component blows up at the
>same time, just after the warranty expires. The 10 flat screens in
>your example will not show one bad component. Instead, there will be
>dozens, all different brands and values. This is not due to crappy
>manufacturing, but rather due to careful selection for the MINIMUM
>lifetime of the component.

That's an "honorable" American tradition that dates back at least a
century. The story goes that Henry Ford has his engineers buy and
disassemble scrapped Ford cars, to see which parts had failed and
which ones were still in good shape. He pointed out that the company
could often save money by redesigning (more cheaply) parts which
rarely failed... so the new versions would wear out and fail at about
the same time as everything else.

I remember one of the Lord Darcy stories by Randall Garrett, which
involved a (magic-based) process somewhat like this for the human
body. The spells would draw upon the health of long-lived parts of
the body, to support those which were more prone to obvious aging.

The recipient of this treatment might have the apparent health and
vigor of one in his thirties, and sustain this for several decades
(e.g. up until the age of 60 or so). At that point, all of the body
systems would collapse simultaneously, and the patient would die of
old age in the space of an hour or two.

[pf...@aol.com]

Live fast.
Die young.
Leave a good looking corpse.

[Phil Allison]

Jeff Liebermann wrote:

>
>
> In the bad old daze, the electrolytics were running at 60Hz, not
> 60KHz. The power (heat) dissipated in the electrolytics is a function
> of frequency.
>

** The heat loss in an electro is related to ripple current and ESR at the frequency in use. ESR is much HIGHER at 60Hz or 120Hz than it is at 60kHz - so losses are LOWER at high frequencies.

Also, ESR goes down with increasing temperature - by up 5 times at the max rated temp of the cap.

Running in a hot environment is the main cause of short lifetimes, eg with nearby heatsinks and no fan.




..... Phil

[ohg...@gmail.com]

On Monday, November 21, 2016 at 1:07:20 PM UTC-5, Jeff Liebermann wrote:

> In the bad old daze, the electrolytics were running at 60Hz, not
> 60KHz. The power (heat) dissipated in the electrolytics is a function
> of frequency.

They've been using high frequency smps since the late 70s (Sony was the first that I can recall (and boy were they *squirrely*). And while we replaced capacitors on the wholesale level even back then, they didn't bulge. The vented cap syndrome (VCS?) has really only been an issue since about 2004 or so. Around 2008 was the real big explosion of top bulged caps, when we'd see TVs in warranty with bulged/vented caps. There's been a big slowdown in bulged caps in recent years.

[Dave Platt]

In article <9234021a-116c-431f...@googlegroups.com>,

<ohg...@gmail.com> wrote:

> The vented cap syndrome
>(VCS?) has really only been an issue since about 2004 or so. Around 2008 was the
>real big explosion of top bulged caps, when we'd see TVs in warranty with
>bulged/vented caps. There's been a big slowdown in bulged caps in recent years.

Sounds like this might be the "capacitor plague" problem? Bad
water-based electrolyte?

https://en.wikipedia.org/wiki/Capacitor_plague

[Phil Allison]

Jeff Liebermann wrote:


>
> Notice that the SEC-1235 is a 12V 30A device and
> current limits at 35A. How many amps are you drawing?
>
>

** Transceivers tend to draw a LOT LESS current while in receive mode - which is the only time PSU generated RF noise might be a problem.

SMPSs often send a fair amount of RFI back up the AC power cable, even when running at low power outputs which makes them troublesome when used with radio receivers - especially in the lower part of the HF band.

The OP's supply may have deteriorated components ( plastic film caps most likely ) in the filter fitted to the incoming AC line. Only way to know for sure is to get another, similar supply and try it.

If the OP has a linear 12V supply that can run the transceiver in receive mode, he should try that too.



..... Phil

[laga...@gmail.com]

I will respond to some of the posts above, without discussing the side topic of poorly manufactured capacitors etc.

1) the PS is rated at 35A, but I rarely draw more than 18A - and that is not a continuous draw.
2) I run the PS in a cool room, and also as a result of point 1 above the cooling fan has never come one (but has been tested to work). In other words the PS runs very cool
3) nothing has changed for 7 years until recently so this is definitely recent noise coming from the PS as I can switch to a deep cycle battery instantly and the RX noise disappears.

I have ordered the two 1000uF, 200V input caps and should replace them in about 3 days and will let you all know the results.

[Jeff Liebermann]

On Mon, 21 Nov 2016 19:20:43 -0800 (PST), laga...@gmail.com wrote:

>I will respond to some of the posts above, without discussing
>the side topic of poorly manufactured capacitors etc.

Sorry for the topic drift, but my intuition tells me that the noise is
somehow related to the bulging caps.

>1) the PS is rated at 35A, but I rarely draw more than 18A -
>and that is not a continuous draw.

That's nice. Now, for the 2nd time, will you kindly disclose the
model number of the power supply. Is it this one?
<http://www.samlexamerica.com/products/ProductDetail.aspx?pid=66>

>2) I run the PS in a cool room, and also as a result of point
>1 above the cooling fan has never come one (but has been tested
>to work). In other words the PS runs very cool

I didn't suggest that the power supply was overheating. I suggested
that the capacitors might be overheating from too much ripple current.
I also suggested that you use an IR thermometer to measure the case
temperature of the capacitors.

>3) nothing has changed for 7 years until recently so this is
>definitely recent noise coming from the PS as I can switch to a
>deep cycle battery instantly and the RX noise disappears.

Nothing has changed is what all my customers say. Nothing means
nothing that is obvious to them. In most cases, that's a polite way
for them to suggest that I not pry too deeply into what the customer
has been doing with the device. If I do pry, I often find
questionable practices. I had one like that 2 days ago. Nothing had
changed in years before the computer crapped out. Too bad the fan and
most of the insiders were packed with cat hair.

>I have ordered the two 1000uF, 200V input caps and should replace
>them in about 3 days and will let you all know the results.

I rarely have any problems with the input caps. It's the lower
voltage caps that blow.

[ohg...@gmail.com]

On Tuesday, November 22, 2016 at 12:15:58 AM UTC-5, Jeff Liebermann wrote:

>
> I rarely have any problems with the input caps. It's the lower
> voltage caps that blow.
>

Not common, but not unheard of. I've replaced a bunch of 450V PFC capacitors in smps that don't show signs of venting, but they're dead and when removed, feel like half the weight of what they should be. They also "rattle" inside as the assy inside has shrunk.

[laga...@gmail.com]

On Monday, 21 November 2016 21:15:58 UTC-8, Jeff Liebermann wrote:

>
> That's nice. Now, for the 2nd time, will you kindly disclose the
> model number of the power supply. Is it this one?
> <http://www.samlexamerica.com/products/ProductDetail.aspx?pid=66>

Yes, that's the one. Does that make a difference to your assessment?

> I didn't suggest that the power supply was overheating. I suggested
> that the capacitors might be overheating from too much ripple current.

OK, I understand, and I wonder whether the output caps which I've replaced have
blown because the input caps are not as effective at removing ripple?

> ... If I do pry, I often find

> questionable practices. I had one like that 2 days ago. Nothing had
> changed in years before the computer crapped out. Too bad the fan and
> most of the insiders were packed with cat hair.

How is that relevant to my post and my situation?

> I rarely have any problems with the input caps. It's the lower
> voltage caps that blow.

See my suggestion above....

[Tim R]

On Monday, November 21, 2016 at 3:12:13 PM UTC-5, Dave Platt wrote:
> In article <l3d63c93jobjuht7h...@4ax.com>,
> Jeff Liebermann <je...@cruzio.com> wrote:
>
> >Having a component last longer than the warranty period is considered
> >wasteful by many manufacturers. Therefore, they select the cheapest
> >possible part that will work up to when the warranty expires but no
> >longer. The result is a product where every component blows up at the
> >same time, just after the warranty expires. The 10 flat screens in
> >your example will not show one bad component. Instead, there will be
> >dozens, all different brands and values. This is not due to crappy
> >manufacturing, but rather due to careful selection for the MINIMUM
> >lifetime of the component.
>
> That's an "honorable" American tradition that dates back at least a
> century. The story goes that Henry Ford has his engineers buy and
> disassemble scrapped Ford cars, to see which parts had failed and
> which ones were still in good shape. He pointed out that the company
> could often save money by redesigning (more cheaply) parts which
> rarely failed... so the new versions would wear out and fail at about
> the same time as everything else.

Much further back than that:

by Oliver Wendell Holmes (1809-1894)
Have you heard of the wonderful one-hoss shay,
That was built in such a logical way
It ran a hundred years to a day,
And then, of a sudden, it — ah, but stay,
I’ll tell you what happened without delay,
Scaring the parson into fits,
Frightening people out of their wits, —
Have you ever heard of that, I say?

Seventeen hundred and fifty-five.
Georgius Secundus was then alive, —
Snuffy old drone from the German hive.
That was the year when Lisbon-town
Saw the earth open and gulp her down,
And Braddock’s army was done so brown,
Left without a scalp to its crown.
It was on the terrible Earthquake-day
That the Deacon finished the one-hoss shay.

Now in building of chaises, I tell you what,
There is always somewhere a weakest spot, —
In hub, tire, felloe, in spring or thill,
In panel, or crossbar, or floor, or sill,
In screw, bolt, thoroughbrace, — lurking still,
Find it somewhere you must and will, —
Above or below, or within or without, —
And that’s the reason, beyond a doubt,
A chaise breaks down, but doesn’t wear out.

But the Deacon swore (as Deacons do,
With an “I dew vum,” or an “I tell yeou”)
He would build one shay to beat the taown
’N’ the keounty ’n’ all the kentry raoun’;
It should be so built that it couldn’ break daown:
“Fur,” said the Deacon, “’tis mighty plain
Thut the weakes’ place mus’ stan’ the strain;
’N’ the way t’ fix it, uz I maintain,
Is only jest
T’ make that place uz strong uz the rest.”

So the Deacon inquired of the village folk
Where he could find the strongest oak,
That couldn’t be split nor bent nor broke, —
That was for spokes and floor and sills;
He sent for lancewood to make the thills;
The crossbars were ash, from the straightest trees,
The panels of white-wood, that cuts like cheese,
But lasts like iron for things like these;
The hubs of logs from the “Settler’s ellum,” —
Last of its timber, — they couldn’t sell ’em,
Never an axe had seen their chips,
And the wedges flew from between their lips,
Their blunt ends frizzled like celery-tips;
Step and prop-iron, bolt and screw,
Spring, tire, axle, and linchpin too,
Steel of the finest, bright and blue;
Thoroughbrace bison-skin, thick and wide;
Boot, top, dasher, from tough old hide
Found in the pit when the tanner died.
That was the way he “put her through.”
“There!” said the Deacon, “naow she’ll dew!”

Do! I tell you, I rather guess
She was a wonder, and nothing less!
Colts grew horses, beards turned gray,
Deacon and deaconess dropped away,
Children and grandchildren — where were they?
But there stood the stout old one-hoss shay
As fresh as on Lisbon-earthquake-day!

EIGHTEEN HUNDRED; — it came and found
The Deacon’s masterpiece strong and sound.
Eighteen hundred increased by ten; —
“Hahnsum kerridge” they called it then.
Eighteen hundred and twenty came; —
Running as usual; much the same.
Thirty and forty at last arrive,
And then come fifty, and FIFTY-FIVE.

Little of all we value here
Wakes on the morn of its hundreth year
Without both feeling and looking queer.
In fact, there’s nothing that keeps its youth,
So far as I know, but a tree and truth.
(This is a moral that runs at large;
Take it. — You’re welcome. — No extra charge.)

FIRST OF NOVEMBER, — the Earthquake-day, —
There are traces of age in the one-hoss shay,
A general flavor of mild decay,
But nothing local, as one may say.
There couldn’t be, — for the Deacon’s art
Had made it so like in every part
That there wasn’t a chance for one to start.
For the wheels were just as strong as the thills,
And the floor was just as strong as the sills,
And the panels just as strong as the floor,
And the whipple-tree neither less nor more,
And the back crossbar as strong as the fore,
And spring and axle and hub encore.
And yet, as a whole, it is past a doubt
In another hour it will be worn out!

First of November, ’Fifty-five!
This morning the parson takes a drive.
Now, small boys, get out of the way!
Here comes the wonderful one-hoss shay,
Drawn by a rat-tailed, ewe-necked bay.
“Huddup!” said the parson. — Off went they.
The parson was working his Sunday’s text, —
Had got to fifthly, and stopped perplexed
At what the — Moses — was coming next.
All at once the horse stood still,
Close by the meet’n’-house on the hill.
First a shiver, and then a thrill,
Then something decidedly like a spill, —
And the parson was sitting upon a rock,
At half past nine by the meet’n-house clock, —
Just the hour of the Earthquake shock!
What do you think the parson found,
When he got up and stared around?
The poor old chaise in a heap or mound,
As if it had been to the mill and ground!
You see, of course, if you’re not a dunce,
How it went to pieces all at once, —
All at once, and nothing first, —
Just as bubbles do when they burst.

End of the wonderful one-hoss shay.
Logic is logic. That’s all I say.

[whit3rd]

On Monday, November 21, 2016 at 7:20:48 PM UTC-8, laga...@gmail.com wrote:

> 1) the PS is ...

> 3) nothing has changed for 7 years until recently so this is definitely recent noise coming from the PS as I can switch to a deep cycle battery instantly and the RX noise disappears.
>
> I have ordered the two 1000uF, 200V input caps and should replace them in about 3 days and will let you all know the results.

The input filter capacitors serve no RF function, so won't solve anything related to RF noise.

[Phil Allison]

whit3rd wrote:

>
> > I have ordered the two 1000uF, 200V input caps and should replace them
> > in about 3 days and will let you all know the results.
>
>
> The input filter capacitors serve no RF function, so won't solve anything
> related to RF noise.
>

** The OP is clutching at straws, big fat & expensive ones at that.

He ought to very carefully check the AC supply connection from his PSU to ground - any resistance there due to tarnished pins would send EMI way up.

BTW:

a portable AM-SW radio can be used to "sniff" for the source of the EMI.


.... Phil

[laga...@gmail.com]

Phil: thanks for your comments. Yes, I am grasping at straws - I fully realize that, and as I somewhat expected, replacing the input caps did nothing to alleviate the noise.

I have checked the AC connection to ground and that is all OK.

And I have also attempted some time ago to use your trick of a small SW receiver to attempt to find the noise but cannot pin down any one component as the culprit as the noise seems to emanate from all over the output section.

I am loath to start replacing any more caps until I really determine where it is coming from...

[Phil Allison]

laga...@gmail.com wrote:
>
> Phil: thanks for your comments. Yes, I am grasping at straws - I
> fully realize that, and as I somewhat expected, replacing the input
> caps did nothing to alleviate the noise.
>
> I have checked the AC connection to ground and that is all OK.
>
> And I have also attempted some time ago to use your trick of a small
> SW receiver to attempt to find the noise but cannot pin down any
> one component as the culprit as the noise seems to emanate from all over the > output section.
>

** I did not intend that meaning - the small AM-SW radio should tell you if the EMI is being radiated by the AC lead entering the PSU plus cabling in the premises.

With the covers on, the PSU itself ought not to be radiating any distance at all - at least with low power drain during receive mode.

Does the PSU have an inlet filter ?

http://www.westek.com.au/wp-content/uploads/2012/08/IEC-Inlet-Filter.jpeg

This would be the first suspect.


.... Phil

[legg]

On Mon, 21 Nov 2016 19:20:43 -0800 (PST), laga...@gmail.com wrote:

If the output inductor of the filter fails, the unit may continue to
run with excessive ripple current in the output filter and excessive
switching noise, due to increased peak currents.

The filter caps will eventually fail too, bulging or otherwise, due to
increasing ESR.

You would see abnormal output ripple voltage, even with good caps, if
the output choke has failed.

I've seen this twice in KW rated single-output supplies, but below 12V
output in both cases. Due to age, it meant rewinding the choke, rather
than replacing it (and replacing previously overstressed caps...).

Output ripple was evident (>10x normal) even though there was a two
stage filter.

RL