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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Fri 09, 2019 8:55 pm 
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Yes, Mike. A marketing "someone". Can't upset those people expecting a launch now, can we. IMHO, and I believe backed up by subsequent investigation, the decision was made based at least in part due to the cost of scrubbing and rescheduling the launch. So avoidable. :(:

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Fri 09, 2019 10:07 pm 
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You should always consider film caps for this sort of application. More costly than electrolytics, but still just a few $$.

https://www.mouser.com/ProductDetail/EP ... aQOQ%3D%3D

4uF 650VDC 7ARMS 0.023 ohm 100,000 hour 30mm dia X 65mm H $5.55 for one.

Ted


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Fri 09, 2019 10:48 pm 
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Management ignored people who knew what they were talking about. A common problem.

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Fri 09, 2019 10:52 pm 
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Thanks Ted. I didn't know you can use a non polarized in place of an aluminum ELECTROLYTICS filter caps .
I've never heard of that.


Unless the polypropylene cap is a polarized
capacitor
Mike


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Fri 09, 2019 11:00 pm 
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Ted, tell me more about these poly caps used in place of a common aluminum electrolytics

Mike


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Fri 09, 2019 11:06 pm 
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Location: Sunbury, Ohio 43074
For some applications, possibly even most, a cap is a cap... .basically a 10uf Electrolytic for instance can generally be replaced by a 10uF Mylar. There are exceptions of course, and the reverse is not always true.

It's a fairly recent thing, since in the past, a 10uF Mylar capacitor would cost as much as a small speedboat. Not anymore. The issue may be the RIPPLE handling capability of the Mylar... there is more than just uF that has to be considered. For a power supply filter, electrolytics are generally capable of handling much higher ripple than their non polarized replacements.

That's it in a nutshell. THere's plenty of reading material out there if you use Google.... I've been typing all day.... lol.

Maybe someone else will post a dissertation here, but it's not a secret. Just requires a basic knowledge of circuits, and an above basic knowledge of capacitors.

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Fri 09, 2019 11:46 pm 
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Ted , I just read an article by TDK on replacing electrolytic caps with MLCC s multi level ceramic chip capacitors. I think they said its possible but may introduce oscillation because of the ultra low esr. In some circuits. I think the mousers link was the epcos/tdk AC Capacitor. Are you advocating using an ac capacitor to replace a dc capacitor?

Mike

Maybe someone else could weigh in on this


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sat 10, 2019 8:26 pm 
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I think the MLCC electrolytic replacements are mostly for low voltage.

Usually the current rating for film caps is much higher than it is for electrolytics of the same value and voltage. The losses are much smaller, so there is less heat generated. See the part linked above.

However, there are film caps with relatively poor current ratings, so you should check before you buy.

An AC rated cap will generally operate happily with the full rated AC voltage across it. Usually at 60 or 50 Hz. In a DC filter application, the AC voltage seen by the capacitor will be a fraction of the voltage rating.

Capacitors sold for motor run and lamp ballast service make robust DC filter caps. That's just where the market volume is today, so the manufacturer mentions those applications. AC rated film capacitors are not made differently, the different ratings are marketing driven. Most name-brand caps have both AC and DC ratings.

You usually can't go the other way. You don't want to try to use an electrolytic cap in place of a film cap in an AC circuit.

It is often possible to replace the paper filter caps in very old AC radios with electrolytics. This can be the cheapest way to get the radio to play. Not generally the best thing to do.

The film caps are most useful in older tube type power supplies, where paper or early, low uF electrolytics, were original.

There should be no problems with oscillation or other instability due to using film caps in place of electrolytics in equipment using an 80, or a 5U4, with a big choke or two. If your circuit involves an LDO negative voltage regulator IC, you need to be careful.

Polypropylene seems to be the favored dielectric for these caps. Mylar is OK, though.

Ted


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 12:45 am 
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Ted, that's great news that i can use a motor run capacitor " like an ac start cap from a fan motor" in place of the original paper filter capacitor. Or use a non polarized poly cap replacement?

Am I understanding you correctly?

Mike


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 2:59 am 
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mdm54 wrote:
Ted, that's great news that i can use a motor run capacitor " like an ac start cap from a fan motor" in place of the original paper filter capacitor.

No! A motor run capacitor, not a motor start capacitor.

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 3:56 am 
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Most fan motors are not capacitor start, since the load is so light at low RPMS.

A motor starting capacitor is only working for a few seconds, until the motor gets up to speed. They are usually non-polar electrolytics. One of these might work in a pinch as a DC filter cap, but cannot be recommended for that application.

Motor run caps, on the other hand, have to function for untold hours with a large AC voltage across them. That's the sort you might use for your DC filter cap.

Ted


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 5:48 am 
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Ok Ted, it sounds like the ac caps in my central ac outdoor
Compressor. That's the type the would work
Right ?


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 12:35 pm 
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A motor start capacitor? Most have considerably more leakage on DC than electronic grade capacitors. It doesn't matter when starting a motor, but it certainly would to your rectifier tube.

Film capacitors might be used to replace electrolytics in some cases, but you really have to be careful about ripple current. It isn't even rated for many types of film caps, which means "not designed for that or we'd spec it." On the other hand, a can electrolytic in an analog power supply might handle hundreds of milliamps, perhaps amps of ripple current. If you want to avoid premature failure, a good rule of thumb is to use a ripple current rating about three times the DC load current.

It's a fact of life, but as the voltage ratings of electrolytics are made higher, their ESR becomes higher too. This is because the dielectric layer has to be made thicker to withstand the higher voltage. Also, most electrolytics rated for more than 450 VDC consist of two or more extremely well matched "cells" connected in series inside the package. Obviously two (or more) capacitors in series will have more ESR than one. This is one of several reasons circuit designers avoid putting higher voltage electrolytics in circuits than necessary.

As for the amount of ESR, in most competently designed equipment it is considered carefully. Low ESR equates to low energy dissipation in the capacitor and low noise on the power supply rails, but it is also part of what determines the peak forward currents on the rectifier and power transformer. It plays into the impedance of the power supply rails at various frequencies, which is critical for stability of any circuit which involves amplification. Putting a low ESR cap into a circuit that didn't have one originally will not necessarily improve it.

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 2:15 pm 
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Excellent info Ted ! That explains why the aluminum. Electrolytics are still the component of choice for most power supplies. The best engineered power supply always use polarized electrolytes. The old days was paper but today aluminum Electrolytic.

So low esr is not always best for power filter supplies.
Now that's a new one ! So in the design of a power supply
, the esr is an important factor. So what the designer choose for that that circuit "esr" is an important consideration for the "forward current to the rectifier tube. " Cost not being a factor.

When I choose a replacement capacitor for a filter cap I always choose a " low esr one" over one that has high esr.

What you're saying is that may not be the best choice?
And I should consider the ripple current data as much as the esr ?


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 2:48 pm 
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This is getting pretty convoluted......

Here's a simple rule for design: The right design is one that meets all the requirements within the available resources (eg money and time) There is almost never only one solution that works.

A good designer is normally not going to start with a part that has the best spec on some parameter. The typical process is to start with an assumed configuration, plug in some typical part values, and perform an analysis. This shows where things need to be tweaked.
Once the analysis shows that all the requirements are being met, then a breadboard is built and testing begins.
Test results are then used to further tweak the design.

As part of this process, the designer will normally start with part types that are intended for the application. This means that the starting point for a DC power supply is not likely to include a capacitor intended for a "motor run" application. It's also not likely to include 20 or 30uF film capacitors for the filters.

My point??
Studying the nuances of different part types is useful, but a large percentage of new designs start with understanding why similar designs are what they are.

My 1970s Tek scope is running on the original filter caps (aluminum electrolytic, I assume). Did they consider using film caps, AC-rated motor caps, or some other option?----maybe, but I doubt it.

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 3:33 pm 
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The oldest AC operated radios and amplifiers used big paper capacitors (0.5 mfd and up) and large value chokes in the power supply. The wet electrolytic capacitors were available, but didn't become widely used until around 1931; maybe there were patent issues.

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 3:34 pm 
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Tim Tress wrote:
The oldest AC operated radios and amplifiers used big paper capacitors (0.5 mfd and up) and large value chokes in the power supply. The wet electrolytic capacitors were available, but didn't become widely used until around 1931; maybe there were patent issues.

And tuned chokes.....
The design was driven by the available parts.

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 4:12 pm 
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These are my objectives when replacing an old electrolytic.

Low esr = better
High temp rating "105c"= better
Higher voltage rating= better
Longer life hrs = better

I'm only talking about the typical old tube power supply filter capacitor.

Why would anyone dispute that?

Mike


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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 4:46 pm 
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mdm54 wrote:
Why would anyone dispute that?

None of those matter if the cap can't handle the ripple current.

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 Post subject: Re: High esr miec electrolytic aluminum capacitors
PostPosted: Aug Sun 11, 2019 5:28 pm 
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Location: San Manuel AZ
Steve, assuming the ripple current is within specs. I should have added that! Thanks


By the way Steve nice website!

Mike


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