Toshiba TV29C90 problem; Image fades to black...

[William Sommerwerck]

That is a fault with your charger more than a fault of the batteries.
I can charge LSD NiMH batteries in a few hours in my Maha charger.

Like, wow, man. Trippy.

 

[William Sommerwerck]

Another factor is something that I understand is true about
NiMH cells in general (not just the low-self-discharge type):
charge acceptance is quite poor at low charge rates.

I've heard this as well. Specifically, at "low" charge rates (which which
would actually be on the "high" side for nicads), NiMH cells are less likely
to enter the negative delta-V region that indicates end of charge.

Having grown up with nicads, I'm reluctant to charge faster than 0.1C, but
it appears that 0.3C and even 0.5C is acceptable with good-quality NiMH
cells.

 

[William Sommerwerck]

That depends upon what power level you run the radio. I found that
out in the mid 1990's with the Ray-O-Vac rechargable alkelines.
Everything I had, except flashlights, only worked for one or two charges
before they could not put out enough current to be of any use.

In general, alkalines seem to be a poor choice for high-discharge
applications. Digicam owners have discovered this independently...
most digital cameras will "kill" alkalines quite quickly. I believe
I've read that the rechargeable alkalines were even worse in this
regard... their ESR rose significantly after a few charge/discharge
cycles. So, I don't find your experience at all surprising.

Alkalines were traditionally well-suited for high-drain applications. But
the Ray-O-Vac rechargeables had significantly higher internal resistance and
didn't handle high drain very well.

 

[William Sommerwerck]

"UCLAN" <nomail@thanks.org> wrote in message
news:7bYsk.15238$Rs1.1306@newsfe08.iad...

William Sommerwerck wrote:

I don't understand this business about "low self-discharge" NiMH
batteries,
as I'ven never noticed any particular problem with them.

There *is* no problem with them. I use several brands, including Sanyo
Eneloop. Low self-discharge NiMH batteries have made regular NiMH
batteries
obsolete, IMO. [Except for in heavily used high current applications, only
because the capacity of low-discharge NiMH batteries is not yet as high as
regular NiMH batteries.

No, I meant regular NiMH cells.

I have a big pile of them, and recharge them as needed.

 

[William Sommerwerck]

I don't understand this business about "low self-discharge" NiMH
batteries,
as I'ven never noticed any particular problem with them.

You've been lucky. I deal with a lot of 2-way radio handhelds that sit
idle for months at a time. The early NiMH batteries would self-drain to
unuseability in less that a month. At work, we replaced them all (at
least the ones we could find) after a year with newer technology NiMH
batteries like the Eneloops and such.

But why would you expect _any_ rechargeable battery (regardless of
chemistry) to keep its charge for several months?

 

[Dave Platt]

Another factor is something that I understand is true about
NiMH cells in general (not just the low-self-discharge type):
charge acceptance is quite poor at low charge rates.

I've heard this as well. Specifically, at "low" charge rates (which which
would actually be on the "high" side for nicads), NiMH cells are less likely
to enter the negative delta-V region that indicates end of charge.

I think there are two effects here - how much of the energy going into
the battery is being lost as heat, and how much of an effect the heat
change has on the voltage. NiMH cells differ from NiCd in both
respects.

Having grown up with nicads, I'm reluctant to charge faster than 0.1C, but
it appears that 0.3C and even 0.5C is acceptable with good-quality NiMH
cells.

That does seem to be the case. It appears that there are a couple of
ways to charge NiMH cells fairly safely:

[1] At a nice, slow rate - .1C or even a bit lower. At this low rate,
the cells don't heat up very much at all, and thus don't exhibit the
zero-delta-V or negative-delta-V full-charge signature. For that
reason, neither a voltage- or temperature-sensing approach can be
used reliably, and a timed charge shutoff is the only alternative.

[3] Use a relatively fast charge rate - no less than .3C, with .5C or
even 1C being common. The cells do warm up significantly during
the fast-charging, and then their temperature starts to rise
sharply (and the voltage reaches zero-delta-V and starts down into
negative-delta-V) at full charge. Today's fast chargers seem to
use either T or delta-T as the primary shutoff indicator, with
delta-V as a secondary, and a timed shutoff as the final failsafe.

Early versions of the Maha/Powerex MH-9000 had a reputation for
occasional shutoff failure - they would not detect full charge
reliably, and the batteries would become quite hot as they cooked
away. Powerex revised the charger - I think they tweaked the firmware
logic having to do with the shutoff detection - and I understand that
they *raised* the minimum recommended fast-charge rate from 0.3C to
0.5C. Presumably this results in a more rapid temperature rise at
full-charge, and makes it easier to detect.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[William Sommerwerck]

Early versions of the Maha/Powerex MH-9000 had a reputation for
occasional shutoff failure - they would not detect full charge
reliably, and the batteries would become quite hot as they cooked
away. Powerex revised the charger - I think they tweaked the firmware
logic having to do with the shutoff detection - and I understand that
they *raised* the minimum recommended fast-charge rate from 0.3C to
0.5C. Presumably this results in a more rapid temperature rise at
full-charge, and makes it easier to detect.

MAHA told me they've never revised the firmware (which I doubt). I've had no
termination-failure problems, even at 0.1C.

 

[Dave Platt]

In article <me6dnavU_PJOBinVnZ2dnUVZ_gCdnZ2d@comcast.com>,
William Sommerwerck <grizzledgeezer@comcast.net> wrote:

You've been lucky. I deal with a lot of 2-way radio handhelds that sit
idle for months at a time. The early NiMH batteries would self-drain to
unuseability in less that a month. At work, we replaced them all (at
least the ones we could find) after a year with newer technology NiMH
batteries like the Eneloops and such.

But why would you expect _any_ rechargeable battery (regardless of
chemistry) to keep its charge for several months?

Ummm... because [1] that's what I need that particular set of
batteries to do, in order to do my job, and [2] because that's what
the manufacturers are able to make them do, and advertise them to do?

Certainly, rechargeables are not likely to have the charge storage
lifetime of primary cells. However, NiCd batteries did/do have a
storage lifetime which makes it reasonable to use them for many
standby applications, and they have been used that way.
First-generation NiMH batteries were markedly worse than NiCd and
weren't suitable... but today's ultra-low-self-discharge NiMH actually
do the job quite nicely.

They also seem much less prone than alkalines to leak, if left in the
device while it's in storage. My experience is that new (unused)
alkalines seem to be quite stable in storage, but once you've used
more than a small fraction of their charge you've "started the clock
ticking" and they'll self-destruct after a couple of years of storage.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Arfa Daily]

"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news:udi8b459keje6uc4feudp4o8uga8tc4pvu@4ax.com...

On Tue, 26 Aug 2008 11:14:05 +0100, "Arfa Daily"
arfa.daily@ntlworld.com> wrote:

Bear in mind also, that the 'measured' power consumption on a
consumer-type
power meter, may not be accurate with a switch mode power supply,
particularly if it's operating in a burst standby mode at the time, where
it
might draw the full amount from the line, but only for brief periods, to
keep the standby supply resevoir cap charged.

That's obviously not the case with the DTV DVR. It doesn't need to
burn 22 watts just to keep a cazapitor charged.

However, I have a TV that I suspect uses that method because I can
barely hear the power supply whine when it's running. Seems to be
about a 5 second duty cycle. I just plugged in the Kill-A-Watt meter
and found that the display was constantly changing between zero and
about 10 watts. Thanks for the warning. I never thought about that.
I would have expected the Kill-A-Watt meter to have some manner of
averaging integrator, to better simulate the utility electric power
meter, but I guess not. My guess(tm) is about 1-2 second average but
no longer.

Some of these meters, which
are designed to give Joe Public a 'comfort factor' reading on steady draw
devices such as lamps and fridges and so on, have some difficulty doing
complex 'area under the curve' calculations for asymmetric and burst draws
by switchers, to come up with an equivalent steady draw figure that has
some
real meaning in what it is costing you.

Yep.

That said, my Sky+ box, which is also an HDD based sat rx and recorder,
and
which also has the capability of rewinding live TV to the start of the
programme, claims (again from memory) only around 10 watts or so in
standby

Ummm... the hard disk probably burns more than 10 watts. Something is
wrong here. Maybe they spin down the HD after a while of non-use?

I did a quick check with Google of what others have reported for
DirecTV DVR standby currents. Most people didn't bother supplying the
model numbers, so we have the usual muddle. Numbers vary from 10
watts to 45 watts. Sigh. Buy a Kill-A-Watt meter and measure it.
Incidentally, there are two models of the Kill-A-Watt. The later has
battery backup. I ordered one last week but it hasn't arrived.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Yes indeedy, it's a complex subject. I suspect that some of the cheap
consumer power meters, have a sort of 'peak hold' type readout to stabilize
against erratic draws, but this serves to give a false impression when a
power supply is operating in a burst standby mode. Your TV with short draws
of 10 watts, is a classic example of what might upset some meters. 5 seconds
is actually quite slow, and gives the meter time to show 10 - 0 - 10 - 0 and
so on. If it was doing it quicker, as many do, you may well get a reading
which appears to be a lot higher than the true figure, when the pulsed draw
is properly integrated.

You've got me thinking now about my Sky+ box. The HDD definitely does not
run all the time. You can clearly hear it when it is running. However, live
TV pause and rewind is always available. I wonder how that could be, unless
the disc is run at a much slower speed that you can't hear, for the purposes
of real time writing. If you are feeding it with a steady compressed data
stream, I guess it doesn't need to be rotating at full speed does it ? Do
HDDs have more than one speed ? Come to think of it, I can't recall the
drives in this machine ever sounding like they ramp down to any different
speed, unlike the DVD writer, which of course does. I'll have to see what I
can find on the 'net about these boxes.

Arfa

 

[isw]

In article
<bb99c2cf-8566-4e58-ad54-aaf1bbf6dc0a@q5g2000prf.googlegroups.com>,
"dersh.z" <dersh.z@gmail.com> wrote:

Hi Everyone, first time post... Mr. Goldwasser suggested I run this
question by this group...

I work at a small college with a bottom electromagnet driven pendulum.

The electromagnet consists of a large coil (.75H) with an iron core
and a 10uf capacitor in series with the hot leg (110vac). The pendulum
is an 8lb. iron shotput. Works great 24/7 except...

The caps, I've been using (GE 10uf @ 370VAC motor cap), last about 4
months before the circuit becomes "un-tuned" (measured capacitance
decreases - pendulum swing gradually increases then will eventually
stop and get stuck to the magnet).

I get the best swing using these params... l=.75H, C= 9.7uf, f= 59Hz.
(most of the 10uf caps have measured 9.6 - 9.8uf)

My question... can you recommend a higher reliability capacitor, one
that might last a few years instead of a few months?

Thank you for your time.

Something like 600V film caps should last nearly forever. You'll
probably have to parallel a few to get the capacitance you want, though.

Isaac

 

[Arfa Daily]

"Jerry G." <jerryg50@hotmail.com> wrote in message
news:6e2349b4-047b-474b-8bbc-76a73a9e1ae7@e53g2000hsa.googlegroups.com...
As the CRT monitors are burning out or failing, they will have to be
replaced. The only replacement is with an LCD monitor. More people
globaly are buying more computers.

The LCD monitor and LCD TV set are one of the greatest innovations in
display technology ever achieved!

Jerry G.


You *are* 'aving a larf, aren't you ... ? d;~)

Arfa

 

[Arfa Daily]

"Jerry G." <jerryg50@hotmail.com> wrote in message
news:950cbe8c-5c99-441b-bc92-834665949e6a@25g2000hsx.googlegroups.com...

--

On Aug 25, 10:38 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

troxel...@yahoo.com wrote:
I just bought a flyback tester and have a drawer full of flybacks that
I want to test. How do I know what pins to connect it to? The
directions say to simple hook it up to the primary windings, but which
pins are these?

Thanks
"Jerry G." <jerry...@hotmail.com> wrote in message

news:6d6f4f61-0db1-43a3-b809-a92e095c3ab8@t54g2000hsg.googlegroups.com...

To know this you will really need the schematics from the
manufactures.

Remember that your tester is only doing a basic reactance test of the
device ...

snip

That may not be strictly true. If it's a Bob Parker design flyback tester
(now reworked and rebranded by another company), then it actually 'rings'
the tranny, a test that shows up most common defects such as shorted turns
on the primary, and short or leaky diodes in the HV stack.

Arfa

With any of these flyback checkers they will not show high voltage
breakdown, or critical problems with the flyback. This is only a
simple test! I have been through this!

Jerry G.

Oh, I don't dispute that a BP will not pick up problems such as HV
breakdown, Jerry, but that is usually - or at least mostly - self evident in
that you can see the miniature lightning flying out of the pin hole, or
smell the ozone being generated, or see the effects on the screen as
brushing, or hear the effects on the audio, or even just hear it physically
hissing. The only point that I was making is that the BP unit is not a
'simple' reactance tester, but does a test which better simulates the
conditions that such a tranny operates in, when doing its normal job. Almost
any deviation from its correctly servicable parameters, will alter the way
in which the tranny rings, which will be picked up by the tester. Of course,
the results are open to a degree of experience and interpretation, in much
the same way as those from an ESR meter are, and a new, or at least 'known
good' tranny is useful to compare by, but never-the-less, the BP is a useful
tool even on its own, for picking up "most common defects", which is all I
was actually saying ...

Arfa

 

[Mark D. Zacharias]

<g3misa@gmail.com> wrote in message
news:0cba8e33-9d42-4a64-9891-4a6429d7c366@u33g2000pro.googlegroups.com...

Hi I have a Sony Super Beta SL-HFT7 Betamax which was playing fine
when suddenly the picture disappeared. The audio remained fine. I
was using the RCA line out cables when this happened. Then I tried
using the RF Coaxial out, everything worked fine (video and audio).
I looked at the circuit board where the RCA inputs are located and
everything looked fine. Does anybody have a clue what happened? I
prefer using the Line Outs rather than Coaxial.

Thanks.

I've seen a similar model with a shorted capacitor in the area near the
jack - I think it maybe was 1000uF. It's been a long time though...

Mark Z.

 

[William Sommerwerck]

"Dave Platt" <dplatt@radagast.org> wrote in message
news:00keo5-tot.ln1@radagast.org...

But why would you expect _any_ rechargeable battery (regardless
of chemistry) to keep its charge for several months?

, and [2] because that's what the manufacturers are able to make
them do, and advertise them to do?

I was talking in general terms. Until the Eneloop, I've never heard _any_
manufacturer claim their rechargeable cells would hold a charge for a "long"
perioud of time.

 

[Gareth Magennis]

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:ekrbb4h6besm52b5pmuu03eal9u01l1t2m@4ax.com...

On Tue, 26 Aug 2008 12:14:47 -0400, Meat Plow <meat@petitmorte.net
put finger to keyboard and composed:

What does it do exactly?

Timer? Protection circuit of some kind?

Maybe all of the above. A uP could also vary the heating time based on
the initial temperature of the toaster element.

This toaster actually sniffs the toast:
http://www.magneticdesign.co.uk/news.html
http://www.defra.gov.uk/environment/radioactivity/Government/legislation/pdf/safetytoaster-justification.pdf

Auto-lowering intelligent toaster:
http://www.breville.com.au/products_detail.asp?prod=373

Intelligent toaster brands toast with your custom logo:
http://www.farfromboring.com/Promotional-Product/Home-and-Housewares/Kitchen-Items/CUSTOM-LOGO-TOASTER-PL-8223-107201.html

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Blimey, just touch a button and the toast automatically lowers. Wow.


"Crumpet Control" was my favourite.


Gareth.

 

[Arfa Daily]

"Doug Smith W9WI" <w9wi@invalid.nospam> wrote in message
newsan.2008.08.28.14.42.22.849512@invalid.nospam...

On Thu, 28 Aug 2008 02:30:13 -0700, 151 wrote:
I just bought a new gadget (a cheap IP camera) the plug/psu of which
makes a faint high pitched whining noise when connected to the wall
socket - UNTIL I connect the other end to the camera (camera works
fine by the way). Then the noise stops.

When I plugged it in at the socket, the wall the socket was already
switched "on" and there was a little bit of a spark I think... I have
seen this occasionally before (I have no idea if the psu was totally
silent before this or if its a factor)

Also I noted that the "top" prong of the plug (UK plug) was plastic?
I.e. no earth. Could this cause the small spark I saw?

What might this noise be and should I worry?

Is this PSU relatively light in weight? (I'll bet it is)

I'm betting this is a "switchmode" PSU. There's a high-frequency
oscillator in there which, you could say, steps up the 50Hz mains
frequency to several thousand (/tens of thousands) Hz. This allows the
use of a smaller & lighter transformer to step the voltage down from 240V
to whatever the camera wants.

The actual frequency the mains are stepped up to is not well regulated.
(and doesn't need to be) I would not be surprised if it changes radically
with load - if it's much lower when the camera isn't connected and drawing
power. With no load it might be dropping to a frequency low enough to
hear, while with the camera connected it may be above the range of your
hearing.

Or, it may be reaching the mechanical resonant frequency of some part of
the PSU, allowing that part to amplify the vibrations, and the sound.

Should you worry? Good question. I think the noise would probably bother
me to the point where I wouldn't operate it with the camera disconnected
for that reason alone.

I know little or nothing about the way the UK power mains are wired so
can't really comment on the lack of an earth. Here in the States, these
plug/PSUs almost never have an earth pin at all, plastic or metal. It
would seem unnecessary if any part you can touch is isolated from the
mains by the transformer.

One of the reasons that the plastic earth pin is included, is that the line
and neutral connectors in the wall socket are always shuttered. Sometimes,
the shutter has shaped faces a bit like those on a security screw, such that
when the plug pins are inserted, the shutter 'twists' out of the way,
allowing the pins to pass by it. Many other sockets, however, have the
shutter mechanically linked to the earth pin hole, so that as the (longer)
earth pin goes into the hole, the shutter is pushed out of the way for the
other two pins to follow into their holes. Hence the dummy plastic 'earth'
pin is needed to work the mechanics, where no 'real' earth connection is
needed.

Arfa

 

[Charles]

I guess the charter for this group has changed.

 

[isw]

In article <jcmdb4h16i7qef87f8mvm30qp6p8ovisr5@4ax.com>,
greenpjs <greenpjs@neo.rr.com> wrote:

On Thu, 28 Aug 2008 02:25:13 GMT, Ross Herbert
rherber1@bigpond.net.au> wrote:

On Wed, 27 Aug 2008 08:17:39 -0700 (PDT), "dersh.z" <dersh.z@gmail.com
wrote:

:> On Tue, 26 Aug 2008 08:54:50 -0700 (PDT), "dersh.z" <ders...@gmail.com
wrote:
:
:> :Hi Everyone, first time post... Mr. Goldwasser suggested I run this
:> :question by this group...
:> :
:On Aug 27, 8:45 am, Ross Herbert <rherb...@bigpond.net.au> wrote:
: Assuming there is very little series resistance (other than the dc
:resistance of
:> the inductor) you are left with a series resonant circuit which is
:> resonant
at
:> approx 58Hz for the values given (L = 0.75H and C = 10uF). I calculate
:> the
:> current through the circuit at more than 6A so it might be dissipating a
:> fair
:> amount of heat depending upon duty cycle. The pulsed nature of the drive
voltage
:> might also contribute to premature failure.
:
:> Normally, a motor run capacitor is connected across both legs of the ac
supply
:> in series with an auxiliary winding in an electric motor in a similar
:> fashion
to
:> your circuit but I would hazard a guess that the current through the
:> motor
:> winding would be much less than in your arrangement with 0.75H.
:
:> Does the capacitor get hot?
:
:Thanks Ross, et.al,
:
:The capacitor does get warm but not hot, the coil does get quite hot
:tho without a cooling fan.
:
:Your calculations are what I get as well, I found this thing swings
:quite nicely when tuned to aprox. 58-59Hz. The old setup (1960's
:design) swung about 3ft max @220VAC, I can now get 8ft+ @115VAC...
:but, I' m having the cap failures at a much higher rate than the old
:setup. I might have changed the original caps every 10years or so.
:
:Both setups had the cap in series with the coil, the only major change
:in my setup is the coil - the old coil lost it's smoke, couldn't get
:it back in... so I had a new coil made. The old coil was hand wound
:with a solid steel core, this new coil was machine wound (epoxied,
:etc...) and I used 1/16" (no flux) welding rods tightly bundled into
:an aprox. 1.25" core diameter (I also have a few brass tubes creating
:air gaps in the core for forced air cooling from below - will cook
:without the forced air cooling tubes).
:
:I have been thinking Ceramic but am unsure as to which I should use in
:this sort of an application. I generally don't do the "industrial"
:stuff, I'm more of a component level tech - these motor caps are not
:something I normally deal with.
:
:Thanks to all for the repies, very much appreciated.


Stick to polypropylene filmcaps instead of ceramic. I would suggest a better
capacitor to use is one made by American Capacitor. The VW2M106K (1000V)
which
has rated RMS current of 19A and a peak of 2910A with high dV/dT.
http://www.americancapacitor.com/PDF/VData.pdf

You will have to contact them to get details of purchasing.
http://www.americancapacitor.com/index.htm

Hi all,
I am afraid I can't help the original poster, but I find this thread
very interesting. There is a pendulum at a local museum and I always
wondered how it worked. I assume that an electromagnet is used to
replace the small amount of energy lost during each swing of the
pendulum, but how is it actually connected and where is the
electromagnet? What does having an resonant circuit tuned to
slightly below the power line frequency have to do it? I guess I'm
asking for someone to explain the theory. I don't suppose there's a
"how stuff works" article on the subject, but I'll go check that out
now.

As the OP said, the circuit is tuned "off resonance" when the pendulum
is not close. Then when it approaches, its proximity alters the
resonance in such a way that there is more attraction while it is
approaching, and slightly less while it is receding. The net result is a
transfer of momentum to the pendulum. Sort of like the way a "slingshot"
orbit works.

Isaac

 

[isw]

In article
<9f830021-fb94-4d10-a008-6f41f410d43b@c65g2000hsa.googlegroups.com>,
Ancient_Hacker <grg2@comcast.net> wrote:

You might try using capacitors with a definite current rating.
Perhaps several of them in parallel to distribute the current. And
a sturdy varistor to clamp the peak voltage across the capacitor.

For example the Panasonic ECWF series of 1.0uF caps can take 5 amps.
Put nine of them in parallel to handle the bulk of the current and you
should be set up nicely, with a safety factor of five or so. Add a
few 0.1uF caps of the same type to fine-tune the resonance.

As for clipping the voltage peaks, I'd put a few sturdy varistors
across the coil and the capacitor.

That would probably spoil the high "Q" that makes the circuit work.

Isaac

 

[isw]

In article <jm0gb4l8scr9pdrt9uis34o6rjf35scqea@4ax.com>,
greenpjs <greenpjs@neo.rr.com> wrote:

On Thu, 28 Aug 2008 20:43:45 -0700, isw <isw@witzend.com> wrote:

snip

Hi all,
I am afraid I can't help the original poster, but I find this thread
very interesting. There is a pendulum at a local museum and I always
wondered how it worked. I assume that an electromagnet is used to
replace the small amount of energy lost during each swing of the
pendulum, but how is it actually connected and where is the
electromagnet? What does having an resonant circuit tuned to
slightly below the power line frequency have to do it? I guess I'm
asking for someone to explain the theory. I don't suppose there's a
"how stuff works" article on the subject, but I'll go check that out
now.

As the OP said, the circuit is tuned "off resonance" when the pendulum
is not close. Then when it approaches, its proximity alters the
resonance in such a way that there is more attraction while it is
approaching, and slightly less while it is receding. The net result is a
transfer of momentum to the pendulum. Sort of like the way a "slingshot"
orbit works.

Isaac

Isaac,
We're getting close. What I'm having trouble picturing is how the
attraction can be slightly less while it is receding. I can
understand the pendulum itself affecting the resonance of the circuit,
but why wouldn't it do so symmetrically? In other words, I would
think that whatever momentum is gained on the way in would be lost on
the way out. Clearly I'm wrong, but would like to understand why. By
the way, I have always wondered the same thing about slingshot orbits.
So, if you can explain it, that will kill two birds with one stone.

The two are similar in that both effect a transfer of momentum, but not
quite in the same way.

For the pendulum, the L-C circuit should have a high "Q", which means
that it will be slow to respond to changes. As the pendulum approaches,
the proximity of that large piece of iron alters the tuning, and
therefore the current through the coil (and amp-turns is what determines
the force that accelerates the pendulum). If you get it right, the
delayed response (due to the high Q; think of it as a phase shift) will
cause the peak of attraction to come just before the pendulum crosses
dead center (if not for the slow response due to the narrow bandwidth,
the peak of attraction would be at dead center and would fall off
equally whether the pendulum were approaching or receding).
Interestingly, the process tends to be self-limiting, too; if the
pendulum is moving faster (because of a larger swing), the attraction
will not be as great because there's not as much time for it to build
up, and vice-versa.

I'm an electroniker, not an orbital scientist; I was just using the
"slingshot" as another case of momentum transfer. I don't feel
comfortable addressing it at the level of explaining how it works in
detail. Very roughly, though, the spacecraft has to approach a planet
going the opposite way to the planet's motion around the sun, and leave
the planet going the same way. Properly done, the maneuver will add
twice the planet's velocity to the spacecraft's while very slightly
slowing down the planet.

Isaac