I can understand the other way round being a no-no but what is wrong with
using switch mode power suply type electrolytics for mains smoothing of high
voltage rails.?

On 23 Apr, 17:43, "N Cook" wrote:

I can understand the other way round being a no-no but what is wrong with
using switch mode power suply type electrolytics for mains smoothing of high
voltage rails.?

for mains or hv rails?

If you want to use smpsu caps on mains there are 2 problems:
1. the lytic caps aren't bipolar
2. the caps also arent X rated (for L-N connection) nor Y rated (For L-
E connection)

If you meant using them for hv dc rails, why not?


NT

On Apr 23, 9:43 am, "N Cook" wrote:
I can understand the other way round being a no-no but what is wrong with
using switch mode power suply type electrolytics for mains smoothing of high
voltage rails.?


absolutely NO PROBLEM.
Usually the only time this kind of thing becomes an issue is if the
electrolytic is expected to handle and extreem amount of ripple such
as the rather physically big 4.7 uf @ 50V electrolytics used in some
monitor deflection circuits.... if you try to substitute an equal
value 4.7uf @ 50V normal size (much smaller) electrolytic it will
OVERHEAT and burst because the "power factor" rating of the smaller
cap is not adequate.
For what you described, I have used those kinds of electrolytics in 60
Hz filtering applications many times. NO PROBLEMS.
electricitym

wrote in message
ps.com...
On 23 Apr, 17:43, "N Cook" wrote:

I can understand the other way round being a no-no but what is wrong
with
using switch mode power suply type electrolytics for mains smoothing of
high
voltage rails.?

for mains or hv rails?

If you want to use smpsu caps on mains there are 2 problems:
1. the lytic caps aren't bipolar
2. the caps also arent X rated (for L-N connection) nor Y rated (For L-
E connection)

If you meant using them for hv dc rails, why not?


NT


For more clarity, I was meaning the 300V or 400V electrolytics used after
rectifying the mains and before 40/50KHz chopping to drive a smps
transformer.
Then using those on the secondary side after rectification, of a totally
50/60Hz mains transformer, with high voltage secondary. I thought the SMPS
ones had a different formulation or something to allow for high frequency
current demand.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N Cook" wrote in message
...
I can understand the other way round being a no-no but what is wrong with
using switch mode power suply type electrolytics for mains smoothing of
high
voltage rails.?


The high voltage electrolytics in SMPSs are not specced for 40/50kHz. That
would be the low voltage ones on the secondary, after the high voltage DC
has been chopped at 50kHz, and transformed down. The high voltage one(s) are
merely the smoothers for the primary DC rail, derived from the normal line
frequency (50/60Hz) input. There is absolutely no reason at all that these
primary smoothers cannot be used for exactly the same purpose on normal line
frequency transformer-derived supplies, such as might be found in valve
amplifiers, and indeed, I have used them for such purpose on many occasions.

Arfa

Arfa Daily wrote in message
...

"N Cook" wrote in message
...
I can understand the other way round being a no-no but what is wrong with
using switch mode power suply type electrolytics for mains smoothing of
high
voltage rails.?


The high voltage electrolytics in SMPSs are not specced for 40/50kHz. That
would be the low voltage ones on the secondary, after the high voltage DC
has been chopped at 50kHz, and transformed down. The high voltage one(s)
are
merely the smoothers for the primary DC rail, derived from the normal line
frequency (50/60Hz) input. There is absolutely no reason at all that these
primary smoothers cannot be used for exactly the same purpose on normal
line
frequency transformer-derived supplies, such as might be found in valve
amplifiers, and indeed, I have used them for such purpose on many
occasions.

Arfa



I've never actually weighed or measured any but I always thought that V for
V and uF for uF that the ones from SMPS were always lighter than the the
more general application ones. Therefore implying something different about
their construction.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N Cook" wrote in message
...
Arfa Daily wrote in message
...

"N Cook" wrote in message
...
I can understand the other way round being a no-no but what is wrong
with
using switch mode power suply type electrolytics for mains smoothing of
high
voltage rails.?


The high voltage electrolytics in SMPSs are not specced for 40/50kHz.
That
would be the low voltage ones on the secondary, after the high voltage DC
has been chopped at 50kHz, and transformed down. The high voltage one(s)
are
merely the smoothers for the primary DC rail, derived from the normal
line
frequency (50/60Hz) input. There is absolutely no reason at all that
these
primary smoothers cannot be used for exactly the same purpose on normal
line
frequency transformer-derived supplies, such as might be found in valve
amplifiers, and indeed, I have used them for such purpose on many
occasions.

Arfa



I've never actually weighed or measured any but I always thought that V
for
V and uF for uF that the ones from SMPS were always lighter than the the
more general application ones. Therefore implying something different
about
their construction.


Whether or not they are made lighter ( and I suspect that in a lot of cases
it's that they are made smaller to better fit switchers and modern consumer
equipment physically ), if you think about it, they are just working at 100
/ 120Hz fundamentally, as their primary ( ha ! ) job is just to smooth the
main rail after the bridge, and the ripple from that bridge is just line
frequency x 2. Whether or not there is a transformer before the bridge, does
not have any basic effect on this. I can't immediately think of any other
differences that would cause the caps to *need* to be any different, but I
would agree that they do tend to be small compared to those found as
original in amps.

It might just be a cost thing. As these amps are not generally short of
internal space, perhaps it is more economical just to use a cheap 'big' one

Arfa

On 23 Apr, 20:44, "N Cook" wrote:
wrote in message
ps.com...
On 23 Apr, 17:43, "N Cook" wrote:

I can understand the other way round being a no-no but what is wrong
with
using switch mode power suply type electrolytics for mains smoothing of
high
voltage rails.?

for mains or hv rails?

If you want to use smpsu caps on mains there are 2 problems:
1. the lytic caps aren't bipolar
2. the caps also arent X rated (for L-N connection) nor Y rated (For L-
E connection)

If you meant using them for hv dc rails, why not?

NT

For more clarity, I was meaning the 300V or 400V electrolytics used after
rectifying the mains and before 40/50KHz chopping to drive a smps
transformer.
Then using those on the secondary side after rectification, of a totally
50/60Hz mains transformer, with high voltage secondary. I thought the SMPS
ones had a different formulation or something to allow for high frequency
current demand.

Reusing 100Hz reservoirs as 100Hz reservoirs is absolutely fine.


NT

In article , Arfa Daily wrote:

"N Cook" wrote in message
...
Arfa Daily wrote in message
...

"N Cook" wrote in message
...
I can understand the other way round being a no-no but what is wrong
with
using switch mode power suply type electrolytics for mains smoothing of
high
voltage rails.?


The high voltage electrolytics in SMPSs are not specced for 40/50kHz.
That
would be the low voltage ones on the secondary, after the high voltage DC
has been chopped at 50kHz, and transformed down. The high voltage one(s)
are
merely the smoothers for the primary DC rail, derived from the normal
line
frequency (50/60Hz) input. There is absolutely no reason at all that
these
primary smoothers cannot be used for exactly the same purpose on normal
line
frequency transformer-derived supplies, such as might be found in valve
amplifiers, and indeed, I have used them for such purpose on many
occasions.

Arfa

I've never actually weighed or measured any but I always thought that V
for
V and uF for uF that the ones from SMPS were always lighter than the the
more general application ones. Therefore implying something different
about
their construction.


Whether or not they are made lighter ( and I suspect that in a lot of cases
it's that they are made smaller to better fit switchers and modern consumer
equipment physically ), if you think about it, they are just working at 100
/ 120Hz fundamentally, as their primary ( ha ! ) job is just to smooth the
main rail after the bridge, and the ripple from that bridge is just line
frequency x 2. Whether or not there is a transformer before the bridge, does
not have any basic effect on this. I can't immediately think of any other
differences that would cause the caps to *need* to be any different, but I
would agree that they do tend to be small compared to those found as
original in amps.

I'm not sure I go along with your ripple argument here.

The ripple in a SMPS input capacitor has two components. The AC current
into it at 100/120Hz, typically rather peaky as the input bridge
conducts for a fairly small angle when the mains exceeds the
capacitor voltage. The current being taken out of it goes into the
SMPS transformer, typically a sawtooth (with gaps) at the SMPS frequency.
As current in equals current out of the capacitor (when averaged),
the ripple thus has roughly equal components at both 100/120Hz
and the SMPS 40/50kHz. Thus this capacitor does need to be
rated for SMPS frequency ripple current.

However, I agree that a SMPS rated input capacitor should still be
fine for use generally at 100/120Hz (so long as its ripple current
rating is adequate for the application).

Regards,
Mike.