multiswitches and surge suppression

Stephen wrote:
"Stephen" wrote in message
o.uk...
"Bill Wright" wrote in message
...
Stephen wrote:
Given my experience with Switch mode PSU's I can make the following
comments.if the multiswitches do use switch mode PSU's:
[snip]

Many thanks for that. All has been taken on board and will be acted upon.

Bill


Actually to come to think of it, the most stressful time for Switch Mode
PSU's is when they start up or shut down.

So the most likeliest time to fail is when they are turned on or off, i.e.
at the beginning and end of power cuts.

You might want to consider using a small UPS to power your multiswitch
through the power cut. Given their low power consumption, a small 650VA UPS
would probably last at least an hour or two

In addition they often have surge suppression built in as well as
undervoltage and over voltage protection.

The very big head-ends do run on UPSs, sometimes a dedicated one,
sometimes the one for the IT. I have wondered about extending this
downwards.

But what about small plug-in surge protectors? Do they do any good?

Bill

Stephen wrote:
For those of you interested in power supplies and want a bit more
information on switch mode, I have found the following poster very
informative:

http://focus.ti.com/lit/sg/sluw001d/sluw001d.pdf

The most common topology I see in TV/Sat gear than uses SM PSU is the
flyback topology.

[snip]

Do you repair these things commercially? I mean multiswitches and the
larger distribution amps.

Bill

This shows one that's been re-canned TWICE!

http://www.rru.com/~meo/AX84/Etc/rubycon.html

Russian doll electrolytics. Now I've seen everything!

--
Graham.

%Profound_observation%

"Stephen" wrote in message o.uk...

"Andy Burns" wrote in message o.uk...
Stephen wrote:

I've lost count of supposedly good quality electronics that use
either capacitors of questionable quality or of dodgy origin

Including selling smaller value capacitors as larger values, by
"re-canning" them ...

http://i106.photobucket.com/albums/m...eCapacitor.jpg


Well I never..... shouldn't surprise me but that pic took my breath away..... after all the capacittors I've seen, burst,
bulged, domed, dried out, you name it, I've seen them all, except for the recanned ones.

This one will be tricky to catch in the field as if the small capacitor fails, bursts, leaks, domes etc, you would not see it
visually as it would all be retained within the outer can and that would block your view of the inner capacitor.

The only way to spot these is to measure the actual capacitance and compare with the actual value staetd on the can which will
involve taking the cap out of circuit.

Another way would be to x-ray it.

Stephen

Or weigh it if you have an accurate reference.

You would have thought the photographer would have rotated the outer can
so we could see the voltage clearly. I think it's 50v

--
Graham.

%Profound_observation%

If you have a Peak or David Smith ESR meter you can check the capacitors
ESR (equivalent series resistance) while they are still fitted to the PCB. This is a huge time and labour saving device.

Here is the Peak one:
http://www.peakelec.co.uk/acatalog/jz_esr60.html

I don't seem to be able to locate info on the David Smith version. No mention of it on the Satcure page. Shame, as it's the one I
used to great effect.

Dick, not David.
http://www.flippers.com/esrktmtr.html

It's amazing how we managed without these instruments years ago.
I'm also surprised why ESR functionality isn't routinely built into
multimeters, you are more likely to get a capacitance meter but
that is useless compared to ESR.



--
Graham.

%Profound_observation%

In message on Sat, 25 Jun 2011 17:22:46 +0100
Bill Wright wrote:


The very big head-ends do run on UPSs, sometimes a dedicated one,
sometimes the one for the IT. I have wondered about extending this
downwards.

But what about small plug-in surge protectors? Do they do any good?


I wonder if the problem is the same one that affected some STBs a few years ago
- Pace, IIRC. The (internal) power supplies ran very hot and the capacitor
ratings were somewhat on the low side. All would be fine until there was a
power cut or the STB was just unplugged for a time. When power was restored,
the PSU was dead.

If this is the case, surge protection in any form is not going to help.

--

Terry

Actually to come to think of it, the most stressful time for Switch Mode
PSU's is when they start up or shut down.

So the most likeliest time to fail is when they are turned on or off, i.e.
at the beginning and end of power cuts.

You might want to consider using a small UPS to power your multiswitch
through the power cut. Given their low power consumption, a small 650VA UPS
would probably last at least an hour or two

In addition they often have surge suppression built in as well as
undervoltage and over voltage protection.

The very big head-ends do run on UPSs, sometimes a dedicated one,
sometimes the one for the IT. I have wondered about extending this
downwards.

But what about small plug-in surge protectors? Do they do any good?


Well, I use two main suppliers for surge/spike protection, there is
Bowthorpe EMP which is basically an oversize wall plug similar in size
to a lawnmower type RCD breaker plug. You remove the old plug of the
equipment you wish to protect and fit this onto the now plug less
cable. I like this approach as its much harder for the great unwashed
to remove the spike/surge protection from the equipment inadvertently
and hence it stays with the equipment. Last time I bought these it was
around 30 quid but this was a few years ago, I now use UPS'es which
have their own surge/spike protection.

http://www.keison.co.uk/bowthorpe.shtml is a good starting point.

The other type I've used is made by Belkin, called a surgemaster it
looks like a 6 way power distribution strip board, and they often have
additional spike/surge protection sockets and plugs for ADSL modems,
UHF co-ax, ethernet and telephone lines added in so you can protect
your Hi-fi or computer from spikes surges coming in via telephone or
aerial cables. They have an equipment insurance which claims to pay
out to 20 to 30K for any damaged equipment that it failed to protect.
I'm not certain that the insurance would extend to being used in a
commercial environment such as yours instead of domestic environments.

http://www.belkin.com/uk/powersolutions/products/

In your particular situation, if you're looking to protect against
surges & spikes, you also need to look at protecting your co-axial
cables as well as mains cables. How one would do that cost effectively
with 5 CT100 cables is a good question as the aerials and satellite
dishes mounted high up in the air can become highly charged, and the
static electricity can conduct down and kill the multiswitch. Having
said that this is made worse by the fact that there is a higher chance
of static sensitive IC's in multiswitch than in a bog standard
terrestrial amplifier.

As others have indicated, when a multiswitch fails, it would be a good
idea to examine it to work out where the failure happened. It might be
worth actaully taking a Multiswitch apart at initial installation and
measure the voltages between the PSU and the main board and making a
note of these (this would be at risk of losing the manufacturers
warranty though as you've opened the case).

When you have a multiswitch fail, measure these voltages again. If its
all the same as before, then its the main board that has a problem and
that would indicate a high probability of a spike or surge coming in
via the co-ax cables from the aerial or LNB. No mains spike/surge
protector is going to help in this case.

If the voltages are no longer the same, then its a PSU problem, and
that would point to bad caps or shorted chopper transistor. mains
based Surge/spike protection will not protect you against bad caps but
it may do in the case of the chopper transistor. In any case replacing
the chopper transistor with a more robust higher working voltage would
be just as good as fitting a spike/surge arrestor.

As for bad caps, as reliability is important to you and your
customers, I'd probably just whip them out and replace them with
Panasonic FM or FC series caps prior to installation.

Regards

Stephen

On Jun 25, 6:06*pm, Bill Wright wrote:
Stephen wrote:
For those of you interested in power supplies and want a bit more
information on switch mode, I have found the following poster very
informative:

http://focus.ti.com/lit/sg/sluw001d/sluw001d.pdf

The most common topology I see in TV/Sat gear than uses SM PSU is the
flyback topology.

[snip]

Do you repair these things commercially? I mean multiswitches and the
larger distribution amps.


Sadly I don't.

You will find that its about the same cost in replacing the the
multiswitch as in paying someone to repair it. You're probably better
off doing a self learning course in repairing SM PSU's and fix them
yourself, although you won't make any extra money, it should improve
the reliability and hence improve your customers satisfaction with
your company.

On Jun 25, 7:47*pm, Terry Casey wrote:
In message on Sat, 25 Jun 2011 17:22:46 +0100
*Bill Wright wrote:



The very big head-ends do run on UPSs, sometimes a dedicated one,
sometimes the one for the IT. I have wondered about extending this
downwards.

But what about small plug-in surge protectors? Do they do any good?

I wonder if the problem is the same one that affected some STBs a few years ago
- Pace, IIRC. The (internal) power supplies ran very hot and the capacitor
ratings were somewhat on the low side. All would be fine until there was a
power cut or the STB was just unplugged for a time. When power was restored,
the PSU was dead.

If this is the case, surge protection in any form is not going to help.

--

Terry

yes it was Pace, and I agree with surge protection is not going to
help with PSU's with marginally specced components.

Stephen

wrote:
Actually to come to think of it, the most stressful time for Switch Mode
PSU's is when they start up or shut down.
So the most likeliest time to fail is when they are turned on or off, i.e.

[snip]


As for bad caps, as reliability is important to you and your
customers, I'd probably just whip them out and replace them with
Panasonic FM or FC series caps prior to installation.

Regards

Stephen
Food for thought here... a lot of food for a lot of thought...

Bill