 |
Search Sci.Electronics.Basics |
|
|
|
|
|
|
 |
|
|
Sci.Electronics.Basics -> Power Supply Rectification and Smoothing
There are 94 messages in this thread.
You are currently looking at messages 80 to 94.
|
Author: NobodyDate: 19:10 16-10-07
|
|
On Tue, 16 Oct 2007 08:09:17 +0900, spamfree wrote:
>>Yes, you can use the itty bitty caps. Verify their current ratings if
>>you can -- some of what makes the spendy caps spendy is the AC ripple
>>current they can deliver without overheating.
>
> I'm confused. This ripple current is surely what I want the caps to
> absorb, not to deliver, or am I on the wrong tack as usual? :)
When you attach capacitors across rectified AC, they store charge in short
bursts at the peak of the waveform then release it the rest of the time.
When dealing with large currents, don't add more capacitance than you
need. Or, to put it another way, don't make the ripple voltage any lower
than it needs to be.
The lower the ripple voltage, the smaller the conduction angle
(the portion of the cycle where the smoothing capacitor is being charged
throught the rectifier). The average current is determined by the load, so
a smaller conduction angle results in higher peak currents.
As power dissipation in resistive loads (e.g. the transformer windings,
the capacitor's ESR, etc) is proportional to the square of the current,
twice the current for half the time means twice the power dissipation.
If your current draw consists of short, tall spikes, the RMS current will
be substantially higher than the mean continuous current. Component
ratings are based upon RMS current; if you choose components based upon
the mean current and the RMS current is substantially higher, your PSU may
become a single-use smoke generator ;)
|
|
|
|
|
|
On Wed, 17 Oct 2007 00:10:56 +0100, Nobody <nobody@nowhere.com> wrote:
>On Tue, 16 Oct 2007 08:09:17 +0900, spamfree wrote:
>
>>>Yes, you can use the itty bitty caps. Verify their current ratings if
>>>you can -- some of what makes the spendy caps spendy is the AC ripple
>>>current they can deliver without overheating.
>>
>> I'm confused. This ripple current is surely what I want the caps to
>> absorb, not to deliver, or am I on the wrong tack as usual? :)
>
>When you attach capacitors across rectified AC, they store charge in short
>bursts at the peak of the waveform then release it the rest of the time.
>
>When dealing with large currents, don't add more capacitance than you
>need. Or, to put it another way, don't make the ripple voltage any lower
>than it needs to be.
>
>The lower the ripple voltage, the smaller the conduction angle
>(the portion of the cycle where the smoothing capacitor is being charged
>throught the rectifier). The average current is determined by the load, so
>a smaller conduction angle results in higher peak currents.
>
>As power dissipation in resistive loads (e.g. the transformer windings,
>the capacitor's ESR, etc) is proportional to the square of the current,
>twice the current for half the time means twice the power dissipation.
>
>If your current draw consists of short, tall spikes, the RMS current will
>be substantially higher than the mean continuous current. Component
>ratings are based upon RMS current; if you choose components based upon
>the mean current and the RMS current is substantially higher, your PSU may
>become a single-use smoke generator ;)
Now that's very helpful. Thanks, jack
|
|
|
|
|
|
On Tue, 16 Oct 2007 12:35:36 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>
>
>spamfree@spam.heaven wrote:
>
>> Eeyore wrote:
>>
>> >Such transients won't
>> >appreciably affect the voltage on the reservoir caps, there isn't enough
energy in
>> >them to do so.
>>
>> Surely that depends on how much energy is in the mains transients.
>> With a rated surge tolerance of less than twice the nominal working
>> voltage.... Careful Laddie, ye'll get a bullet! :)
>
>I suggest you take a look at the voltage on some reservoir caps with a scope and
look
>for these alleged transients that over-volt them. You'll be looking a long time.
OK, I will one day. But can you see my dilemma? I see you use
intemperate language and assert errors, so how can I take notice of
what you say here? YOU may know what you know, and what the status is
of what you say, but I'm afraid that I can't tell. jack
ps My problem with your advice is that it seems so black-and-white
and adamant. From my reading of the EvoxRifa article, it seems that
capacitor life is the key factor. The electrolytics in some of my
catalogues are rated at ~2000 hours. Evox Rifa seem to be saying that
spikes and transients (yes, from the mains) can shorten cap life. If
you are saying that this is not significant in the case I'm citing
here, then that's fine, but to scream that anyone who states the
principle, or who disagrees with your proclamations is a grade one
IDIOT, or should be SHOT shows your advice is flaky at best.
|
|
|
|
|
|
On Tue, 16 Oct 2007 12:33:46 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>spamfree@spam.heaven wrote:
>
>> Eeyore wrote:
>> >spamfree@spam.heaven wrote:
>> >> Eeyore wrote:
>> >> >spamfree@spam.heaven wrote:
>> >> >
>> >> >> I'm confused. This ripple current is surely what I want the
caps to
>> >> >> absorb, not to deliver, or am I on the wrong tack as usual?
:)
>> >> >
>> >> >The caps do both. They 'absorb' the current as the cap is
recharged at the peak
>> >> >of the input voltage from the transformer/rectifier and then
deliver it to the
>> >> >load when that input is providing no more charge. You see the
>> >> >transformer/rectifier deleivers the input power in 'blips' every
10ms and the
>> >> >caps job ios to smooth it out.
>> >>
>> >> Yes, I understand the buffering effect, but had not thought of the
>> >> caps as producing their own ripple.
>> >
>> >Absolutely not. They are entirely passive components. They get charged up
every 10ms
>> >and then they release some of their charge during the rest of the mains
half cycle.
>> >That's where the ripple comes from, from the regular charge and discharge
of the
>> >caps.
>>
>> Must be my misunderstanding of the word "deliver". I get the sense of
>> "manufacture and then pass on", but my dictionary states otherwise,
>> and that is to merely "pass along". All's clear now, thanks for your
>> persistence, jack
>
>The caps do no manufacturing,
Do you not understand what I wrote, Graham?
That's what I was querying when I thought someone else was claiming
that the caps "manufactured" or "produced" a ripple - due to my
misunderstanding of the word "deliver". It usually means merely pass
on, which is in complete accord with my understanding of the actual
process happening with these buffer caps.
jack
|
|
|
|
|
|
On Tue, 16 Oct 2007 12:30:06 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>spamfree@spam.heaven wrote:
>
>> Eeyore wrote:
>> >spamfree@spam.heaven wrote:
>> >> Eeyore wrote:
>> >> >spamfree@spam.heaven wrote:
>> >> >> Eeyore wrote:
>> >> >>
>> >> >> >If it says '500W' I'd expect it to mean 500W input power.
>> >> >>
>> >> >> Well you would disagree with NEMA. jack
>> >> >
>> >> >Can you explain what you mean by that ? NEMA has no real relevance
in this matter.
>> >>
>> >> NEMA are in charge of electric motor labelling standards, I thought.
>> >
>> >You thought WRONG.
>> >
>> >NEMA is merely a US trade assocation and it's 'standards' or recomendations
have no authority
>> >worldwide. Look for *** IEC ** standards instead.
>> >
>> >IEC = International Electrotechnical Commission and all your Oz electrical
standards are based
>> >on IEC ones, not some stupid US trade association like NEMA.
>> >
>> >> Surely that's entirely relevant. jack
>> >
>> >No it's not.
>>
>> So you don't like NEMA?
>
>It's not a case of whether I like it or not. It has no authority or relevance
outside the borders
>of the USA.
Sorry to disagree, but my old man used to sell electric motors to
mining concerns, and NEMA was relevant to him.
NEMA is very important to all users of American motors. And I think
you wil find there is quiite a lot in the rest of the world.
>> I thought it was fairly relevant to US
>> electric motor manufacturers and suppliers. Is it significantly
>> different from IEC recommendations?
>
>Most US regs have typically been rather different to International ones, although UL
is now
>harmonising somewhat with IEC.
Sounds like bullshit to me :)
>> So could you please quote me where IEC advocate that an XkW motor is
>> a motor that needs an input of XkW and is not a motor that supplies X
>> kW of mechanical power for the task required? jack
>You'd have to look for yourself but I do know that wherever the IEC rates power in
all the
>standards I know it rates by INPUT power.
But you can't quote anything? How do you know this then?
Perhaps you should read
http://www.pdhonline.org/courses/e156/e156content.pdf
and especially the bottom of page 20.
Seems you know less than you think you know :)
>It wouldn't be a bad thing to know what the input power is for sure.
Of course not, as it would'nt the voltage, the weight, the fixing
dimensions, the rpm, and so on, but a 1kW motor puts out one kilowatt.
It's so that mechanical engineers can specify that they want a 50kW
motor here and a 35kW motor there to drive things that need that
amount of power. What good is a figure that is only useful to the
installation sparkies so they can install the right size starters and
breakers.
I guess you have been sucked in by the great American advertising
machine which will always choose the biggest number available to flog
their merchandise. "Truth? What in tarnation do you mean, Boy?"
jack
|
|
|
|
|
|
On Tue, 16 Oct 2007 12:18:26 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>spamfree@spam.heaven wrote:
>
>> Eeyore wrote:
>> >
>> >Where do you get 10,800 uF from ?
>>
>> From the formula on page 9 of the Evox Rifa article.
>>
>> "Needed capacitance to manage a certain level of
>> ripple voltage is
>>
>> Cmin= 2P/ [(Umax2 - Umin2) x f rectifier]
>>
>> P is the power load in watts.
>> Remember that this is the minimum required capacitance."
>
>Yes, a cookbook formula. I prefer working with the raw data.
Apparently Evox Rifa find their simplified formula to be useful. The
problem up to now has been that you have chosen your satisfactory
ripple, and others have chosen different ripples.
My preference is strawberry...
So different capacitance requirements will be calculated.
Not IDIOTS but just different folk calculating different things.
>> >If you actually paid atention to the equation I used you can determine what
you
>> >need for yourself. Let me tell you, 'cookbook' equations don't substitute
for
>> >calculating from first priciples which is what I did.
>>
>> And tell me, what percentage of ripple suppression were you aiming at
>> with your first principles calculation? Perhaps we are comparing
>> apples with cockroaches? jack
>
>I wasn't working with any 'percentage' that's not a particularly useful measure.
Surely it is as good as any? A ten percent residual ripple is
apparently what is specified for some uses. Can't remember what the
application was, but the first 56,000uF calculation was for a 10%
residual ripple.
You went on to calculate for a 14% residual ripple, and claimed
everyone else was an IDIOT!
> I was
>targeting a practical ripple voltage.
What do you mean by "practical"?
Anything to do with DC brushed motor, speed controllers?
>Your 56,000 uF gave a very low value of 2V pk-pk
>so I sugegsted a more practical (and cheaper) capacitor size. 22,000 uF should give
you
>5V pk-pk ripple at 15A load.
>
>Honestly, a bit of ripple won't hurt you.
You say this not knowing a thing about the motor controller I intend
using. You seem to insist they are as robust as motors. I have good
anecdotal evidence that they are extremely sensitive to slight
overvoltage. Motors are extremely insensitive to overvoltage, so long
as they can stay together mechanically from the increased speed.
Many users will replace their 24V motor + controllers for a 48 volt
controller and use the same motor at the now double voltage. Some are
even more extreme. They push it until the smoke escapes.
Unfortunately, no-one I've read has tried a power source with any
ripple.
How can I reasonably accept your often intemperately stated assurances
that I have nothing to worry about? Maybe I don't, but I would prefer
to take the advice of someone with at least a passing knowledge of
these controllers. No offense intended, Graham, rgds, jack
|
|
|
|
Author: meDate: 00:27 17-10-07
|
|
spamfree@spam.heaven wrote in
news:o0lah35ih18kie8pdc0l52fgjr9bjhe9iu@4ax.com:
>On Tue, 16 Oct 2007 12:18:26 +0100, Eeyore
><rabbitsfriendsandrelations@hotmail.com> wrote:
>
>>spamfree@spam.heaven wrote:
>>
>>> Eeyore wrote:
>>> >
>>> >Where do you get 10,800 uF from ?
>>>
>>> From the formula on page 9 of the Evox Rifa article.
>>>
>>> "Needed capacitance to manage a certain level of
>>> ripple voltage is
>>>
>>> Cmin= 2P/ [(Umax2 - Umin2) x f rectifier]
>>>
>>> P is the power load in watts.
>>> Remember that this is the minimum required capacitance."
>>
>>Yes, a cookbook formula. I prefer working with the raw data.
>
>Apparently Evox Rifa find their simplified formula to be useful. The
>problem up to now has been that you have chosen your satisfactory
>ripple, and others have chosen different ripples.
>My preference is strawberry...
>So different capacitance requirements will be calculated.
>Not IDIOTS but just different folk calculating different things.
>
>>> >If you actually paid atention to the equation I used you can
>>> >determine what you need for yourself. Let me tell you, 'cookbook'
>>> >equations don't substitute for calculating from first priciples
>>> >which is what I did.
>>>
>>> And tell me, what percentage of ripple suppression were you aiming
>>> at with your first principles calculation? Perhaps we are comparing
>>> apples with cockroaches? jack
>>
>>I wasn't working with any 'percentage' that's not a particularly
>>useful measure.
>
>Surely it is as good as any? A ten percent residual ripple is
>apparently what is specified for some uses. Can't remember what the
>application was, but the first 56,000uF calculation was for a 10%
>residual ripple.
>You went on to calculate for a 14% residual ripple, and claimed
>everyone else was an IDIOT!
>
>> I was
>>targeting a practical ripple voltage.
>
>What do you mean by "practical"?
>Anything to do with DC brushed motor, speed controllers?
>
>>Your 56,000 uF gave a very low value of 2V pk-pk
>>so I sugegsted a more practical (and cheaper) capacitor size. 22,000
>>uF should give you 5V pk-pk ripple at 15A load.
>>
>>Honestly, a bit of ripple won't hurt you.
>
>You say this not knowing a thing about the motor controller I intend
>using. You seem to insist they are as robust as motors. I have good
>anecdotal evidence that they are extremely sensitive to slight
>overvoltage. Motors are extremely insensitive to overvoltage, so long
>as they can stay together mechanically from the increased speed.
>
>Many users will replace their 24V motor + controllers for a 48 volt
>controller and use the same motor at the now double voltage. Some are
>even more extreme. They push it until the smoke escapes.
>Unfortunately, no-one I've read has tried a power source with any
>ripple.
>
>How can I reasonably accept your often intemperately stated assurances
>that I have nothing to worry about? Maybe I don't, but I would prefer
>to take the advice of someone with at least a passing knowledge of
>these controllers. No offense intended, Graham, rgds, jack
>
You have been given good advice, if you don't like it then don't use it.
Asking for advice and then complaining about it is pretty dumb. You can
fix your confusion over the differing information by breaking down and
reading some actual books on motors, controls, capacitance and
electronics. You can find such books in most college book stores in the
electrical engineering section.
----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
|
|
|
|
Author: Ross HerbertDate: 03:56 17-10-07
|
|
On Wed, 17 Oct 2007 09:11:41 +0900, spamfree@spam.heaven wrote:
>On Tue, 16 Oct 2007 12:35:36 +0100, Eeyore
><rabbitsfriendsandrelations@hotmail.com> wrote:
>
>>
>>
>>spamfree@spam.heaven wrote:
>>
>>> Eeyore wrote:
>>>
>>> >Such transients won't
>>> >appreciably affect the voltage on the reservoir caps, there isn't
enough energy in
>>> >them to do so.
>>>
>>> Surely that depends on how much energy is in the mains transients.
>>> With a rated surge tolerance of less than twice the nominal
working
>>> voltage.... Careful Laddie, ye'll get a bullet! :)
>>
>>I suggest you take a look at the voltage on some reservoir caps with
a scope and look
>>for these alleged transients that over-volt them. You'll be looking
a long time.
>
>OK, I will one day. But can you see my dilemma? I see you use
>intemperate language and assert errors, so how can I take notice of
>what you say here? YOU may know what you know, and what the status is
>of what you say, but I'm afraid that I can't tell. jack
>
>ps My problem with your advice is that it seems so black-and-white
>and adamant. From my reading of the EvoxRifa article, it seems that
>capacitor life is the key factor. The electrolytics in some of my
>catalogues are rated at ~2000 hours. Evox Rifa seem to be saying that
>spikes and transients (yes, from the mains) can shorten cap life. If
>you are saying that this is not significant in the case I'm citing
>here, then that's fine, but to scream that anyone who states the
>principle, or who disagrees with your proclamations is a grade one
>IDIOT, or should be SHOT shows your advice is flaky at best.
What you don't seem to understand is that the amplitude of a mains
spike will be reduced by the turns ratio of the transformer at the
secondary. In your case about 6.5 times reduction.
Next thing, the impedance of your capacitor smoothed DC supply will be
so low that any transient spike induced in the secondary will not
appear across the output capacitor since it looks like a short circuit
to the transient. The impedance of the secondary winding will be far
greater than that of the capacitor filter itself and thus the
transient voltage spike will be dissipated in the winding via leakage
capacitance etc.
|
|
|
|
|
|
On Wed, 17 Oct 2007 07:56:41 GMT, Ross Herbert
<rherber1@bigpond.net.au> wrote:
>What you don't seem to understand is that the amplitude of a mains
>spike will be reduced by the turns ratio of the transformer at the
>secondary. In your case about 6.5 times reduction.
But let's see, its energy content will remain about the same, and
according to most experts in this area that I've read, electrolytic
cap life is reduced by spikes, especially when the rated voltage is so
close to the actual working voltage. (50V caps for a 36V supply) Now,
I don't know how much effect mains spikes will have on the lifespan of
caps in my application, but I have had variable advice, and am merely
trying to clarify this.
>Next thing, the impedance of your capacitor smoothed DC supply will be
>so low that any transient spike induced in the secondary will not
>appear across the output capacitor since it looks like a short circuit
>to the transient.
Of course, but adding spike energy to the cap - my concern at this
point.
>The impedance of the secondary winding will be far
>greater than that of the capacitor filter itself and thus the
>transient voltage spike will be dissipated in the winding via leakage
>capacitance etc.
That's interesting, thanks. So a lot of the spike energy is dissipated
in heating up the secondary winding of the transformer (not that there
is likely to be that much energy there) and of course, my secondary
windings are way more robust than delicate electrolytic caps as I'm
using 41 0.32 30A rated flex.
My main problem of ignorance (I've plenty of these :) now is how
smooth a current these motor speed controllers demand. I really don't
want to suck it and see. I once knew of an EE who has built many, and
modified the Chinese and other controllers. He's not on the group he
used to be but I think I have his website somewhere. I'll try to find
him and ask. He's usually terribly helpful.
I've also got a couple of good quality brushless 24V 400W motors with
built in brushless controllers. He rebuilds these to reverse the
rotation. I will ask him about these too. Cheers, jack
|
|
|
|
Author: EeyoreDate: 06:19 17-10-07
|
|
spamfree@spam.heaven wrote:
> Eeyore wrote:
> >spamfree@spam.heaven wrote:
> >> Eeyore wrote:
> >>
> >> >Such transients won't appreciably affect the voltage on the reservoir
caps, there
> isn't enough energy in
> >> >them to do so.
> >>
> >> Surely that depends on how much energy is in the mains transients.
> >> With a rated surge tolerance of less than twice the nominal working
> >> voltage.... Careful Laddie, ye'll get a bullet! :)
> >
> >I suggest you take a look at the voltage on some reservoir caps with a scope
and look
> >for these alleged transients that over-volt them. You'll be looking a long
time.
>
> OK, I will one day. But can you see my dilemma? I see you use
> intemperate language and assert errors, so how can I take notice of
> what you say here?
I have given a worked (mathematical) example of the effect of a transient.
Science beats voodoo, myth and rumour (and cookbook equations) in my book.
> YOU may know what you know, and what the status is
> of what you say, but I'm afraid that I can't tell. jack
I can though. I've just about had my fill of IDIOTS and trust me they're everywhere
these
days, screwing things up wherever they go.
Many even rise to quite high levels of management where they can cause untold damage.
http://en.wikipedia.org/wiki/Peter_Principle
> ps My problem with your advice is that it seems so black-and-white
> and adamant. From my reading of the EvoxRifa article, it seems that
> capacitor life is the key factor. The electrolytics in some of my
> catalogues are rated at ~2000 hours.
2000 hours AT THE RATED AMBIENT TEMPERATURE and the RATED RIPPLE CURRENT. Voltage
incidentally is the one thing that appears to have NO influence on lifetime provided
it's
within the rated value.
Life doubles typically for every 10C below that figure. Operate '2000 hour' 85C rated
electrolytics at 45C ambient and they'll be good for 32,000 hours.
You need to read that Evox article in more detail perhaps and/or place it in the context
of other information it doesn't provide before drawing conclusions like those you have.
> Evox Rifa seem to be saying that
> spikes and transients (yes, from the mains) can shorten cap life.
If those transients EXCEED the voltage rating. Which they won't in this case.
> If you are saying that this is not significant in the case
No, I'm saying that those transients will have minimal effect on the voltage on the
reservoir caps. A more detailed explanation of this has been supplied by Ross Herbert.
> I'm citing here, then that's fine, but to scream that anyone who states the
> principle, or who disagrees with your proclamations is a grade one
> IDIOT, or should be SHOT shows your advice is flaky at best.
My advice is first class actually. Of course if you were to do some serious study, you'd
understand that. The thing about the IDIOTS is that they can sound plausible too to the
newbie or non-expert. And there's no shortage of them. The only way to remove the
influence of their stupidity is to reveal them for what they are.
Graham
|
|
|
|
Author: EeyoreDate: 06:38 17-10-07
|
|
spamfree@spam.heaven wrote:
> On Wed, 17 Oct 2007 07:56:41 GMT, Ross Herbert
> <rherber1@bigpond.net.au> wrote:
>
> >What you don't seem to understand is that the amplitude of a mains
> >spike will be reduced by the turns ratio of the transformer at the
> >secondary. In your case about 6.5 times reduction.
>
> But let's see, its energy content will remain about the same,
Well actually NO. Ross explained how the transformer will tend to attenuate and
filter it.
> and according to most experts in this area that I've read, electrolytic
> cap life is reduced by spikes, especially when the rated voltage is so
> close to the actual working voltage. (50V caps for a 36V supply)
That's NOT close. Those 50V caps have a 63V 'surge' rating and you're not
remotely near either of those ratings. Why do you think a surge rating is
specified ?
Graham
|
|
|
|
Author: EeyoreDate: 06:39 17-10-07
|
|
spamfree@spam.heaven wrote:
> my secondary windings are way more robust than delicate electrolytic caps
Large power supply electrolytics are NOT 'delicate'.
Graham
|
|
|
|
Author: EeyoreDate: 06:43 17-10-07
|
|
spamfree@spam.heaven wrote:
> My main problem of ignorance (I've plenty of these :) now is how
> smooth a current these motor speed controllers demand.
The controllers won't 'demand' ANYTHING. They'll just pass the voltage/current.
You did say they were PWM types, yes ? All they do is switch the circuit on and
off at a high speed. They simply 'don't care' about the voltage you supply as
long as it's not above their specified rating.
The only think that might happen IME is that your motor might hum audibly very
slightly due to supply ripple.
Graham
|
|
|
|
|
|
On Wed, 17 Oct 2007 11:19:13 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:
>spamfree@spam.heaven wrote:
>
>> Eeyore wrote:
>> >spamfree@spam.heaven wrote:
>> >> Eeyore wrote:
>> >>
>> >> >Such transients won't appreciably affect the voltage on the
reservoir caps, there
>> isn't enough energy in
>> >> >them to do so.
>> >>
>> >> Surely that depends on how much energy is in the mains transients.
>> >> With a rated surge tolerance of less than twice the nominal working
>> >> voltage.... Careful Laddie, ye'll get a bullet! :)
>> >
>> >I suggest you take a look at the voltage on some reservoir caps with a
scope and look
>> >for these alleged transients that over-volt them. You'll be looking a long
time.
>>
>> OK, I will one day. But can you see my dilemma? I see you use
>> intemperate language and assert errors, so how can I take notice of
>> what you say here?
>
>I have given a worked (mathematical) example of the effect of a transient.
I asked if this was based on the max spike I would likely suffer.
And then I want to know what effect on lifespan these spikes might
have on 50V cap in a 36V PS. If <5% OK, otherwise...
>Science beats voodoo, myth and rumour (and cookbook equations) in my book.
Of course, but you give that label to everything but your opinion, and
your opinions include several glaring errors so far.
Your opinion of the ripple tolerance of DC brushed motor speed
controllers is worth nothing to me, sorry, and that is the main query
I have posed here
>> YOU may know what you know, and what the status is
>> of what you say, but I'm afraid that I can't tell. jack
>
>I can though. I've just about had my fill of IDIOTS and trust me they're everywhere
these
>days, screwing things up wherever they go.
And even you, the self-proclaimed expert of experts have shown
yourself to be an IDIOT here.
>Many even rise to quite high levels of management where they can cause untold
damage.
>http://en.wikipedia.org/wiki/Peter_Principle
Only the very gullible are in danger on usenet.
And gullible I ain't.
I've a very sensitive bullshit detector hated buy not a few on usenet
over the years :)
>> ps My problem with your advice is that it seems so black-and-white
>> and adamant. From my reading of the EvoxRifa article, it seems that
>> capacitor life is the key factor. The electrolytics in some of my
>> catalogues are rated at ~2000 hours.
>
>2000 hours AT THE RATED AMBIENT TEMPERATURE and the RATED RIPPLE CURRENT.
I've never seen ambient temp rated. Perhaps I need to get out more.
I've only seen max temp rated.
>Voltage
>incidentally is the one thing that appears to have NO influence on lifetime provided
it's
>within the rated value.
Could well be true. But as the person telling me has lost his
credibility...
So a 37V rated cap would last as long as a 100V rated cap, so long as
36V was never exceeded? What is the margin of error here?
20% +/- on capacitance, usually.
>Life doubles typically for every 10C below that figure. Operate '2000 hour' 85C
rated
>electrolytics at 45C ambient and they'll be good for 32,000 hours.
Sorry, I don't follow. Where I live, 45C is the record high ambient
outside on a hot Summer day. Where do they have 85C ambient temps?
>You need to read that Evox article in more detail perhaps and/or place it in the
context
>of other information it doesn't provide before drawing conclusions like those you
have.
Not sure of what conclusions you are referring to. I've asked
questions, and quoted it, but...
>> Evox Rifa seem to be saying that
>> spikes and transients (yes, from the mains) can shorten cap life.
>
>If those transients EXCEED the voltage rating. Which they won't in this case.
Taken on board, thankyou.
>> If you are saying that this is not significant in the case
>
>No, I'm saying that those transients will have minimal effect on the voltage on the
>reservoir caps. A more detailed explanation of this has been supplied by Ross
Herbert.
But my interest here is in cap lifespan. If this is not affected, I
don't care what the transients do.
>> I'm citing here, then that's fine, but to scream that anyone who states the
>> principle, or who disagrees with your proclamations is a grade one
>> IDIOT, or should be SHOT shows your advice is flaky at best.
>
>My advice is first class actually.
In the light of your clangers listed elsewhere? I don't theenk so!
>Of course if you were to do some serious study, you'd
>understand that.
Well, I studied what the IEC said on motor power and found you were
dead wrong, I studied many anecdotes of motor and controller failure,
and found you were wrong...
>The thing about the IDIOTS is that they can sound plausible too to the
>newbie or non-expert. And there's no shortage of them. The only way to remove the
>influence of their stupidity is to reveal them for what they are.
How apt. jack
|
|
|
|
|
|
|
|
|
Contact | Electronic Portal
|
|
|
