Film capacitor as power-supply filter

Is there any reason not to use a 20-uF 900-volt film capacitor as a power supply filter?

I'm updating a vintage Heathkit capacitor checker that I use regularly for re-forming electrolytics, and its power supply filter is currently two 40-uF 450-V in series, without balancing resistors; applied voltage is nominally 600 V DC.

This hasn't given any trouble, but I'm uneasy about its future. Now that film capacitors are available with suitable ratings, is there any good reason not to use one?

(P.S. This may be one of the few instruments in active use that have both a tuning eye tube and an LED. It's already an anachronism.)

 

[whit3rd]

On Sunday, October 6, 2019 at 9:19:57 PM UTC-7, m...@uga.edu wrote:

Is there any reason not to use a 20-uF 900-volt film capacitor as a power supply filter?

I'm updating a vintage Heathkit capacitor checker that I use regularly for re-forming electrolytics, and its power supply filter is currently two 40-uF 450-V in series, without balancing resistors; applied voltage is nominally 600 V DC.

This hasn't given any trouble, but I'm uneasy about its future. Now that film capacitors are available with suitable ratings, is there any good reason not to use one?

Sounds like a good idea, to me. If there's no limit resistor, it might help to put ten ohms
in series (old electrolytics weren't low-ESR, and you don't want to find out that the inrush to
a good capacitor blows your rectifier).

 

Thanks. The rectifier is a vacuum tube. If I change it to a diode, I'll add resistance.

 

On Sun, 6 Oct 2019 21:19:52 -0700 (PDT), mc@uga.edu wrote:

Is there any reason not to use a 20-uF 900-volt film capacitor as a power supply filter?

I'm updating a vintage Heathkit capacitor checker that I use regularly for re-forming electrolytics, and its power supply filter is currently two 40-uF 450-V in series, without balancing resistors; applied voltage is nominally 600 V DC.

This hasn't given any trouble, but I'm uneasy about its future. Now that film capacitors are available with suitable ratings, is there any good reason not to use one?

(P.S. This may be one of the few instruments in active use that have both a tuning eye tube and an LED. It's already an anachronism.)

The film cap should be fine.

I don't think that electrolytic caps in series need balancing
resistors. They take care of themselves. If you need a bleeder, you
may as well split it in two, but otherwise don't bother.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

This, maybe?
https://www.mouser.com/ProductDetail/EPCOS-TDK/B32776Z0206K000?qs=sGAEpiMZZMsh%252B1woXyUXj1%2FT6OBaNpJ8kU%2Fi46kWMVw%3D

Reading the spec sheet, I see that it is self-healing, which sounds great...

That would not be the only anachronism in this vintage instrument. It also has a power-on LED that I added a few years ago.

 

On Monday, October 7, 2019 at 11:47:58 AM UTC-4, Winfield Hill wrote:

mc@uga.edu wrote...

20-uF 900-volt film capacitor ...

Did you have a specific part in mind?

This, maybe?
https://www.mouser.com/ProductDetail/EPCOS-TDK/B32776Z0206K000?qs=sGAEpiMZZMsh%252B1woXyUXj1%2FT6OBaNpJ8kU%2Fi46kWMVw%3D

 

[Winfield Hill]

mc@uga.edu wrote...

20-uF 900-volt film capacitor ...

Did you have a specific part in mind?


--
Thanks,
- Win

 

[Winfield Hill]

mc@uga.edu wrote...

On October 7, 2019Winfield Hill wrote:
mc@uga.edu wrote...

20-uF 900-volt film capacitor ...

Did you have a specific part in mind?

This, maybe?
https://www.mouser.com/ProductDetail/EPCOS-TDK/B32776Z0206K000?qs=sGAEpiMZZMsh%252B1woXyUXj1%2FT6OBaNpJ8kU%2Fi46kWMVw%3D

That's a good one.


--
Thanks,
- Win

 

[Phil Allison]

jla...@highlandsniptechnology.com wrote:

----------------------------------------

The film cap should be fine.

I don't think that electrolytic caps in series need balancing
resistors. They take care of themselves. If you need a bleeder, you
may as well split it in two, but otherwise don't bother.


** It's highly amusing that while electros generally self protect when used in series, film caps do not.

It is a near certainty that poly caps in series will fail from overvoltage if no balancing Rs are used.

Direct opposite of what so many assume.


.... Phil

 

On Monday, October 7, 2019 at 12:19:57 AM UTC-4, m...@uga.edu wrote:

Is there any reason not to use a 20-uF 900-volt film capacitor as a power supply filter?

I'm updating a vintage Heathkit capacitor checker that I use regularly for re-forming electrolytics, and its power supply filter is currently two 40-uF 450-V in series, without balancing resistors; applied voltage is nominally 600 V DC.

This hasn't given any trouble, but I'm uneasy about its future. Now that film capacitors are available with suitable ratings, is there any good reason not to use one?

(P.S. This may be one of the few instruments in active use that have both a tuning eye tube and an LED. It's already an anachronism.)

Look at the ripple voltage and verify that your film can take the ripple current. Films don't last long when you run them up to rated. Then there is the turn-on time of the circuit. Does this Heath Kit have a lot of tubes in it, or what kind of electronic does it have. The old tube circuit DC supplies would overshoot at turn-on until the tube filaments warmed up and the tubes started conducting, drawing down the rail voltage. Until then, the applied DC voltage rail would be way high, like 150% nominal. And this could last for tens of seconds. The electrolytics are designed to handle this temporary overvoltage, usually spec'd for 30 seconds, the film definitely are not.

 

[Phil Allison]

Winfield Hill wrote:

-----------------

Phil Allison wrote...

jla...@highlandsniptechnology.com wrote:

I don't think that electrolytic caps in series need balancing
resistors. They take care of themselves. If you need a bleeder, you
may as well split it in two, but otherwise don't bother.


** It's highly amusing that while electros generally self
protect when used in series, film caps do not.

It is a near certainty that poly caps in series will fail
from overvoltage if no balancing Rs are used.

Direct opposite of what so many assume.


I'm not comfortable with self-balancing for any type.

** Win's alleged discomfort is his problem.

Electrolytic leakage currents must create small carbon
pathways, that's not good.

** Paranoid nonsense.

Leakage current with high voltage electros is normal, adding " balancing " Rs to a series pair only increase it by forcing one cap to a higher voltage.

BTW Win :

Got any more silly crap to post about noise in BJTs used or mic-pres?

Or about pretending Toyota Hybrids and full EVs are the same ?

Or the loopy notion that what you chose to do and believe is normal ?



...... Phil

Thanks,
- Win

 

[Winfield Hill]

Phil Allison wrote...

jla...@highlandsniptechnology.com wrote:

I don't think that electrolytic caps in series need balancing
resistors. They take care of themselves. If you need a bleeder, you
may as well split it in two, but otherwise don't bother.


** It's highly amusing that while electros generally self
protect when used in series, film caps do not.

It is a near certainty that poly caps in series will fail
from overvoltage if no balancing Rs are used.

Direct opposite of what so many assume.

I'm not comfortable with self-balancing for any type.
Electrolytic leakage currents must create small carbon
pathways, that's not good.


--
Thanks,
- Win

 

[Steve Wilson]

On Monday, October 7, 2019 at 5:51:00 PM UTC-4, Winfield Hill wrote:

I'm not comfortable with self-balancing for any type.
Electrolytic leakage currents must create small carbon
pathways, that's not good.

Thanks,
- Win

Capacitor forming in electrolytic capacitors causes a thin dielectric layer to form on the anode. This is simple electrolysis and the film is aluminum oxide, Al2O3, which is non-conductive. The leakage current is through the dielectric. There are no carbon paths.

When the capacitor is left with no supplied voltage, the film tends to dissociate and become thinner. Applying a voltage to the cap restores the film.

An excellent description is given in

"Leakage current properties of modern electrolytic capacitors"

https://tadiranbatteries.de/pdf/applications/leakage-current-properties-of-modern-electrolytic-capacitors.pdf

 

[John Larkin]

On Mon, 7 Oct 2019 14:10:32 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

jla...@highlandsniptechnology.com wrote:

----------------------------------------



The film cap should be fine.

I don't think that electrolytic caps in series need balancing
resistors. They take care of themselves. If you need a bleeder, you
may as well split it in two, but otherwise don't bother.


** It's highly amusing that while electros generally self protect when used in series, film caps do not.

Neither some polymer aluminum caps. Some have upward-curving leakage
which seems to auto-balance and does no harm, but I have seen some
that behave like film caps, linear ohmic up to some point of instant
failure.

 

[Phil Allison]

bloggs.fre...@gmail.com wrote:

-------------------------------

Look at the ripple voltage and verify that your film can take the
ripple current.

** Absurd advice.

Then there is the turn-on time of the circuit. Does this Heath Kit have a lot of tubes in it, or what kind of electronic does it have. The old tube circuit DC supplies would overshoot at turn-on until the tube filaments warmed up and the tubes started conducting, drawing down the rail voltage.

** Funny how rectifier tubes have long warm up times too.

Until then, the applied DC voltage rail would be way high, like 150% nominal.

** Whata pile of fucking crap !!!

Even with silicon diodes in the PSU, the voltage excess is never more than 15% - something electros ARE rated for FFS.


And this could last for tens of seconds.

** No it wouldn't.

> The electrolytics are designed to handle this temporary overvoltage, usually spec'd for 30 seconds, the film definitely are not.

** More complete bullshit .

Film caps have plenty of overvoltage capacity, most do not break down until double or triple DC voltage is applied.

Go away you alarmist IDIOT !!!


..... Phil

 

[Phil Allison]

m...@uga.edu wrote:

---------------------

The film capacitor is rated for many amperes of ripple current
(vs about 1 A for the competing electrolytic);

** Of course, polyesters can tolerate ripple voltages with the same p-p as the DC rating at hundreds or thousands of Hz. Polypropylenes are even better.

Electros can do nothing of the kind.

1 kV working voltage;
150% overvoltage for 10 seconds; and it's going to be carrying a
nominal 600 volts. So I think it's OK.

** Course it will be.

Good HV electros are expensive, so your single poly cap is probably more affordable too.


..... Phil

 

On Monday, October 7, 2019 at 6:34:30 PM UTC-4, bloggs.fre...@gmail.com wrote:

On Monday, October 7, 2019 at 12:19:57 AM UTC-4, m...@uga.edu wrote:
Is there any reason not to use a 20-uF 900-volt film capacitor as a power supply filter?

I'm updating a vintage Heathkit capacitor checker that I use regularly for re-forming electrolytics, and its power supply filter is currently two 40-uF 450-V in series, without balancing resistors; applied voltage is nominally 600 V DC.

This hasn't given any trouble, but I'm uneasy about its future. Now that film capacitors are available with suitable ratings, is there any good reason not to use one?

(P.S. This may be one of the few instruments in active use that have both a tuning eye tube and an LED. It's already an anachronism.)

Look at the ripple voltage and verify that your film can take the ripple current. Films don't last long when you run them up to rated. Then there is the turn-on time of the circuit. Does this Heath Kit have a lot of tubes in it, or what kind of electronic does it have. The old tube circuit DC supplies would overshoot at turn-on until the tube filaments warmed up and the tubes started conducting, drawing down the rail voltage. Until then, the applied DC voltage rail would be way high, like 150% nominal. And this could last for tens of seconds. The electrolytics are designed to handle this temporary overvoltage, usually spec'd for 30 seconds, the film definitely are not.

The film capacitor is rated for many amperes of ripple current (vs about 1 A for the competing electrolytic); 1 kV working voltage; 150% overvoltage for 10 seconds; and it's going to be carrying a nominal 600 volts. So I think it's OK.

 

[Phil Allison]

Winfield Hill Posts another Fuckwit OT reply :

--------------------------------------------

Leakage current with high voltage electros is normal,
adding " balancing " Rs to a series pair only increase
it by forcing one cap to a higher voltage.


Excuse me! Where do you think those currents through
an insulator are coming from? Any forming processes
aside, high-voltage leakage,** over-voltage, or over
anodization, which we're talking about, involves series
current pathways, carbon formation, corrosion, oxygen
loss, and eventually, failure. The currents increase
exponentially with modest over-voltage. Proper usage
is spelled out in the Guideline for use of aluminium
electrolytic capacitors, DIN 45811, and elsewhere.

** Low-voltage applications don't use series capacitors.

** Is this meant to be a reply to MY post ?

There was another poster who disputed Win's hypothesis re "carbon pathways".

Hmmmmm.....

Might be another one of those AKW / CO2 paranoid, fear mongering stories.

Greta would be amused.



...... Phil

 

On October 7, 2019Winfield Hill wrote:
mc@uga.edu wrote...

20-uF 900-volt film capacitor ...

Did you have a specific part in mind?

This, maybe?
https://www.mouser.com/ProductDetail/EPCOS-TDK/B32776Z0206K000?qs=sGAEpiMZZMsh%252B1woXyUXj1%2FT6OBaNpJ8kU%2Fi46kWMVw%3D

That's a good one.

Thank you! I have ordered it.

 

[Winfield Hill]

Phil Allison wrote...

Winfield Hill wrote:

Electrolytic leakage currents must create
small carbon pathways, that's not good.

Leakage current with high voltage electros is normal,
adding " balancing " Rs to a series pair only increase
it by forcing one cap to a higher voltage.

Excuse me! Where do you think those currents through
an insulator are coming from? Any forming processes
aside, high-voltage leakage,** over-voltage, or over
anodization, which we're talking about, involves series
current pathways, carbon formation, corrosion, oxygen
loss, and eventually, failure. The currents increase
exponentially with modest over-voltage. Proper usage
is spelled out in the Guideline for use of aluminium
electrolytic capacitors, DIN 45811, and elsewhere.

** Low-voltage applications don't use series capacitors.


--
Thanks,
- Win