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'[EE] AC power through capacitors'
2010\01\05@174931 by ivp

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I'm going to make up a low-voltage AC supply. 0 - 35V, 1A
and variable frequency, 0 - ?. It'll be made up of circuits I've built
and used before, designed to be run from 12VDC

http://home.clear.net.nz/pages/joecolquitt/variable_ac.gif

The power amp would normally have a large DC-blocking cap
to protect the speaker

I could leave it out, but if it's in, how would that affect the I vs V
phase ?  Is that related to Power Factor wastage ?

wbr

2010\01\05@181326 by Bob Blick

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On Wed, 06 Jan 2010 11:49:10 +1300, "ivp" <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz>
said:
> I'm going to make up a low-voltage AC supply. 0 - 35V, 1A
> and variable frequency, 0 - ?. It'll be made up of circuits I've built
> and used before, designed to be run from 12VDC
>
> home.clear.net.nz/pages/joecolquitt/variable_ac.gif
>
> The power amp would normally have a large DC-blocking cap
> to protect the speaker
>
> I could leave it out, but if it's in, how would that affect the I vs V
> phase ?  Is that related to Power Factor wastage ?

Hi Jinx,

It looks like you are running two amps into your load, one inverted, so
there will be no net DC to the load and you have no need for the
capacitor. If you did have the capacitor it would affect the phase but
less at higher frequencies.

Cheerful regards,

Bob

--
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2010\01\05@183542 by ivp

face picon face

> It looks like you are running two amps into your load, one inverted,

That's correct, as a bridge configuration

> so there will be no net DC to the load

Yes. With no signal, each output would be at mid-rail. Using audio amps
is often suggested as a current booster for AC signals. If you were to
use a home stereo then it's likely there would be blocking caps in case
of a an output fault eg the speaker line could go to a rail if a transistor
failed

> and you have no need for the capacitor. If you did have the capacitor
> it would affect the phase but less at higher frequencies

Okey-doke. The sinewave generator can go down to < 1Hz (with the
appropriate capacitor) although I doubt I would ever use that. Most
probably just 50Hz and 60Hz and multiples for testing various circuits
and mechanisms. And I guess you could put a PIC in there as a DAC
to crudely synthesise arbitrary waveforms

wbr

2010\01\05@185314 by Bob Blick

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On Wed, 06 Jan 2010 12:35:11 +1300, "ivp" <.....joecolquittKILLspamspam@spam@clear.net.nz>
said:

> Okey-doke. The sinewave generator can go down to < 1Hz

Yes, you wouldn't want to use a coupling capacitor at 1 Hz, it would
need to be way big to pass 1A.

BTW, most home stereo amps are direct coupled. They use + and - power
supplies. But there will be some limit to the lower frequency since they
will have at least a capacitor in the input even if you went straight to
the power amp.

Cheers,

Bob

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2010\01\05@205355 by Barry Gershenfeld

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I have an amp like that from long ago, which is darned near a servo
controller.  There are relays that yank the speaker connection if anything
goes wrong.  And the relays double as an audible notification system.  With
many problems in the past I got used to hearing those relays.

For phase effects or whatever else, without getting into much math, figure
the reactance of the capacitor with X=1/(2 * pi * f * C) and compare that to
the impedance of the speaker/amp/wiring.  If it's much lower, then no
worries.  You'll be able to figure out at what frequency you want to start
caring.

Generally speaking, the wastage in Power Factor isn't about "lost" energy,
rather, it's about having to build a bigger amp than you might need
otherwise.

2010\01\05@211425 by ivp

face picon face
> BTW, most home stereo amps are direct coupled. They use + and
> - power supplies

That's the sort I'm more familiar with, and they'll have a cut-out relay (as
Barry mentioned) or perhaps an SCR crowbar to protect the speaker. I
could do a split rail but it seems unnecessary for this application. The
bridge could drive a transformer too, leading to all sorts of VA output
combinations and tapping

> But there will be some limit to the lower frequency since they will have
> at least a capacitor in the input even if you went straight to the power
> amp

I'd expect less than 10Hz would be well in the attenuation range of many
power amps intended for home stereo use (not forgetting sub-woofers)

2010\01\05@211516 by ivp

face picon face

> For phase effects or whatever else, without getting into much math, figure
> the reactance of the capacitor with X=1/(2 * pi * f * C)
> .....
> Generally speaking, the wastage in Power Factor isn't about "lost" energy,
> rather, it's about having to build a bigger amp than you might need
> otherwise.

Thanks

2010\01\05@223808 by enkitec

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ivp wrote:
> I'm going to make up a low-voltage AC supply. 0 - 35V, 1A
> and variable frequency, 0 - ?. It'll be made up of circuits I've built
> and used before, designed to be run from 12VDC
>
> home.clear.net.nz/pages/joecolquitt/variable_ac.gif
>  

   Any reason for not using an audio amplifier IC?

   BTW, those two 33 Ohm resistors can be substituted for one 68 Ohm.

   Mark Jordan

2010\01\05@234610 by ivp

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>> home.clear.net.nz/pages/joecolquitt/variable_ac.gif
>>  
>
>    Any reason for not using an audio amplifier IC?

No, not really. Although I do have all the parts to make a discrete
pair and can't be bothered going shopping (tried conveniently locally
but the bins were empty. Big surprise). I've found that many of the
SIL and TO220-5 types need quite a few extra components anyway
so it's hardly any more work, plus I get to save going out across town
in the stinking hot sun. There are the larger modules, up to 200W I
think, which need just a PSU (more $$$) but a bit over-blown for
what I'm wanting. Did consider them at one stage

> hose two 33 Ohm resistors can be substituted for one 68 Ohm

I've always made that amp (low power guitar and other audio) as is
and it seems to work OK that way. Have you mis-read the circuit ?

2010\01\06@041453 by Alan B. Pearce

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>plus I get to save going out across town
>in the stinking hot sun.

Lucky you, I cannot get to work today for 11cm of snow, it is going to be
hard enough to get to the shop for a newspaper and bottle of milk ;))))

2010\01\06@075056 by enkitec

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ivp wrote:
>> Those two 33 Ohm resistors can be substituted for one 68 Ohm
>>    
>
> I've always made that amp (low power guitar and other audio) as is
> and it seems to work OK that way. Have you mis-read the circuit ?
>  


   Please note I wrote "can be substituted".
   There is no need for two 33 Ohm resistors there. Just one 68 Ohm
does the job.
   There are several amplifiers using just one resistor there,
connected between
the two output transistor bases, without connection to the central line.
 
   Here is some info about it:

   http://users.ece.gatech.edu/mleach/lowtim/output.html

   Mark Jordan

2010\01\06@092548 by Carl Denk

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If my calculator is right, that's 4.33" of snow. We can get that in a
couple of hours, or wind whip an inch into 24" (61 cm.) drifts in 20
minutes. an hour's drive East along Lake Erie, the lake effect can dump
60 cm. in 12 hours. Life keeps going here in Northern Ohio. We have 30
cm. on the ground and got some freezing rain. People here stock up, if
it gets really bad, they have food and stuff for a week. :)

Alan B. Pearce wrote:
>> plus I get to save going out across town
>> in the stinking hot sun.
>>    
>
> Lucky you, I cannot get to work today for 11cm of snow, it is going to be
> hard enough to get to the shop for a newspaper and bottle of milk ;))))
>
>  

2010\01\06@115328 by Alan B. Pearce

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>If my calculator is right, that's 4.33" of snow.

About right.

>We can get that in a couple of hours, or wind whip an inch
>into 24" (61 cm.) drifts in 20 minutes. an hour's drive East
>along Lake Erie, the lake effect can dump 60 cm. in 12 hours.
>Life keeps going here in Northern Ohio. We have 30 cm. on
>the ground and got some freezing rain. People here stock up,
>if it gets really bad, they have food and stuff for a week. :)

Yeah, but this is the UK, an inch of snow is enough to stop the country ...
;)))

This lot is the worst they have had in something like 30 years.
http://news.bbc.co.uk/1/hi/uk/8442739.stm


2010\01\06@163344 by ivp

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>    http://users.ece.gatech.edu/mleach/lowtim/output.html

Thanks, I'll be reading that and

http://users.ece.gatech.edu/mleach/lowtim/

2010\01\06@195148 by enkitec

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ivp wrote:
>  
>  
>>    users.ece.gatech.edu/mleach/lowtim/output.html
>>    
>
> Thanks, I'll be reading that and
>
> http://users.ece.gatech.edu/mleach/lowtim/
>  

   I recommend building that amplifier.
   For sure the best audio power amplifier I ever build.

   Mark Jordan


2010\01\08@171945 by Eoin Ross

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part 1 1429 bytes content-type:text/plain; charset=US-ASCII (decoded quoted-printable)

I heard on the radio that they were debating/questioning road issues with the snow in the UK (House of Lords or Commons I don't know)
Anywho... it came out that they apparently has 500 snow ploughs... for the COUNTRY??!!

Ohio would have that in a couple of counties.

--
Eoin Ross
Industrial computer support and design

CHEMSTATION INTERNATIONAL
http://www.chemstation.com

3400 Encrete Lane Ph 937 294 8265 Ext 1109
Dayton Fax 937 534 0368
Ohio
45439

>>> On 06 Jan 10 at 09:25:32, in message <4B449D5C.2060607spamKILLspamwindstream.net>, Carl
Denk <.....cdenkKILLspamspam.....windstream.net> wrote:
> If my calculator is right, that's 4.33" of snow. We can get that in a > couple of hours, or wind whip an inch into 24" (61 cm.) drifts in 20 > minutes. an hour's drive East along Lake Erie, the lake effect can dump > 60 cm. in 12 hours. Life keeps going here in Northern Ohio. We have 30 > cm. on the ground and got some freezing rain. People here stock up, if > it gets really bad, they have food and stuff for a week. :)
> > Alan B. Pearce wrote:
>>> plus I get to save going out across town
>>> in the stinking hot sun.
>>>     >>
>> Lucky you, I cannot get to work today for 11cm of snow, it is going to be >> hard enough to get to the shop for a newspaper and bottle of milk ;)))) >>
>>  


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part 3 35 bytes content-type:text/plain; charset="us-ascii"
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2010\01\08@174820 by Carl Denk

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It's not unusual for the TV news to report a city, or local Ohio State
Highway garage (maybe 30 or 40 in the state) to have 50 - 100 of each on
the road at one time. Our little township with 83 miles of side roads
(the county and State highways are maintained by those dept.) runs 2
good sized plows, doing our street 3 times a day if needed.

But then again, a few years back a 18 wheeler (Over the road semi truck)
with a freight box trailer got stranded on a back highway, winds drifted
the snow to 20 feet. They went looking for him with snowmobiles. 3 days
later his son spotted 1 CB antenna sticking out of the snow, the other
antenna was broken previously. The drive was good shape, resting
comfortably.

I have more than a few times hit 5' drifts with a Ford Bronco full size
SUV 4WD at 50 mph, snow flying all over the place, end up with 2' of
snow in front of the windshield on the hood (bonnet). Just remember to
have the drives side window down, to watch the edge of the road. :)

Eoin Ross wrote:
> I heard on the radio that they were debating/questioning road issues with the snow in the UK (House of Lords or Commons I don't know)
> Anywho... it came out that they apparently has 500 snow ploughs... for the COUNTRY??!!
>
> Ohio would have that in a couple of counties.
>
>  

2010\01\08@180810 by ivp

face picon face
Nice hi-res picture of the UK under snow (3400 x 4400 3MB)

http://earthobservatory.nasa.gov/images/imagerecords/42000/42237/gbritain_tmo_2010007_lrg.jpg

A friend in Gosport (opposite Isle Of Wight) said half the
neighbourhood's cars were buried in a drift in the car park
and it took all morning to find individual cars and get them
out. Much worse than any winter for a long long time

2010\01\09@140211 by Marechiare

picon face
enkitec wrote:
> ivp wrote:
>>> Those two 33 Ohm resistors can be substituted for
>>> one 68 Ohm
>>
>> I've always made that amp (low power guitar and other
>> audio) as is and it seems to work OK that way. Have
>> you mis-read the circuit ?
>
>    Please note I wrote "can be substituted".
>    There is no need for two 33 Ohm resistors there. Just
> one 68 Ohm does the job.

It does not. Two 33 Ohm resistors provide _local_ negative feedback.
One 68 Ohm does not. If you wanted to state that the local negative
feedback is never needed, just do so. Where is Olin, by the way?

2010\01\09@150935 by Picbits Sales

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----- Original Message -----
>From: "Marechiare"
>I Where is Olin, by the way?

Glad its not just me who's noticed he's not been about.

2010\01\09@172448 by Dario Greggio

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Picbits Sales ha scritto:

>> I Where is Olin, by the way?
>
> Glad its not just me who's noticed he's not been about.


I did wonder the same some 2 days ago

--

Ciao, Dario
--
Cyberdyne

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