Why Does A Tall Power Thing Hum ?

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Offline neilep

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Why Does A Tall Power Thing Hum ?
« on: 01/09/2009 15:32:33 »
Dearest Peeps Of Extraordinary IQ Heights,

As a sheepy I of course luff to humm...humming is my all time favourite sound that one makes as a droany kind of moany mouth closed sound.

But *shock horror*..I is not the only thing that hums !..no no no !!

Near my field is one of these things.


[attachment=9714]
A Humming Thing

I'm convinced that it's a climbing frame for birdies but I've been told that it's holds some magical power and stuff !...woooo !!...

I notice that it also hums !...even more of a wooo !!...why does this power thingy hum ?

As a firm believer in empirical study I snuk into my neighbours house at 3am this morning. Having seen him buy some batteries and knowing that he has hummed a few times...I figure he simply must know about the hummy power thing.So, with a skip and a hop he gleefully put up no resistance as he allowed me to chloroform him again. I luff my neighbour he's great like that, and with him chloroformed up like that he also began to hum and dribble ! So, with his permission to use his car , I backed out of  his garage  and we drove to the power hummy thing. I always wondered how to open his garage doors, it only took three  attempts to reverse through them. So, there we are at 3:30am in the middle of a field ...I tried to wake him but he was so at peace and humming his lullaby that even drenching him in water failed to stir him. I figured, with the help of a winch, If I could just get him to the top of the hummy power thing that the hum would be in concert with his own humming so he could then deliver me the answer. So, I tried one more time to splash him awake and though drenched, I pulled him up to the top till some arcing stuff happened, LOL,,that woke him and I could tell he was happy because he was dancing and iridescent....The foaming at the mouth was a nice touch too..he must have been so enlightened !....though, it made his answer quite unintelligible.....I think he was speaking 'in tongues' !.........so..no luck there !..I left him to these nice people who were jumping over a fire and had something called an altar or something that they were going to make some kind of offering. I told them my neighbour would help as he is always kind like that.

So, can ewe tell me why those power hummy things hum ?...what makes them hum ?


Hugs & Shmishes


mwah mwah mwah !




Neil
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« Last Edit: 01/09/2009 15:34:33 by neilep »
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Offline RD

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Why Does A Tall Power Thing Hum ?
« Reply #1 on: 01/09/2009 16:24:07 »
Magnetostriction causes steel power lines to hum.
The high alternating current they carry creates an strong alternating magnetic field, which squishes the cable 50/60 times a second, which creates the vibration in the cable which causes the hum, (and its harmonics). 
« Last Edit: 01/09/2009 16:28:20 by RD »

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Offline LeeE

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« Reply #2 on: 01/09/2009 16:41:44 »
I thought they hummed because they were in a good mood and feeling happy.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Nizzle

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« Reply #3 on: 02/09/2009 07:44:39 »
So if someone would mess a bit with the switches in the Central distribution, and modulate the AC current through these lines, they could be playing the biggest musical instrument ever?
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Offline LeeE

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Why Does A Tall Power Thing Hum ?
« Reply #4 on: 02/09/2009 14:35:29 »
That idea really appeals to me  [:D]
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline neilep

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« Reply #5 on: 02/09/2009 15:11:11 »
Magnetostriction causes steel power lines to hum.
The high alternating current they carry creates an strong alternating magnetic field, which squishes the cable 50/60 times a second, which creates the vibration in the cable which causes the hum, (and its harmonics). 

Thank ewe very much RD for the info and links....so it literally is the cable itself vibrating !..woo !!
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Offline neilep

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« Reply #6 on: 02/09/2009 15:12:29 »
I thought they hummed because they were in a good mood and feeling happy.

Hi LeeE, yes, I am sure they are happy powery hummy things too !...I think if I was one I'd be a happy pylon too !  [:)]
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Offline Don_1

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Why Does A Tall Power Thing Hum ?
« Reply #7 on: 02/09/2009 15:13:13 »
Geeze, a vibrator made out of a big Meccano set
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Offline neilep

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« Reply #8 on: 02/09/2009 15:15:12 »
So if someone would mess a bit with the switches in the Central distribution, and modulate the AC current through these lines, they could be playing the biggest musical instrument ever?

Now That's a great idea Nizzle...Muzak literally could make the world go round ! [;)]
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Offline neilep

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« Reply #9 on: 02/09/2009 15:16:02 »
Geeze, a vibrator made out of a big Meccano set

Lol...trust ewe to think of such a thing !......ewe'd need a lot of KY !
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Offline Don_1

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« Reply #10 on: 02/09/2009 15:16:45 »
Jelly Jolly good.
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Offline neilep

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« Reply #11 on: 02/09/2009 15:54:27 »
Jelly Jolly good.

That's OKY
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Offline RD

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« Reply #12 on: 02/09/2009 16:23:36 »
..so it literally is the cable itself vibrating

I think the hum is more audible at the foot of a pylon because sound travels better through solid (metal) than through gas (air).

 (The tin can telephone is an example of this phenomenon). 

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lyner

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« Reply #13 on: 02/09/2009 18:23:12 »
I wondered about the magnetic forces between the conductors so I did a fag-packet calculation. With 1000A flowing and a 4m separation (reasonable figures, I think) you get about 0.05N of force per metre for two parallel conductors. (I've ignored the 3 phase thing which could cause all three conductors to do a nice little dance with each other, I guess)
0.05N of force on a 1m length of cable (probably about 5kg(?) would not be expected to produce a lot of oscillation. 10-2m/s/s of average acceleration. However, the whole length (and area) of cable would be moving in phase so, perhaps a low level of sound could be produced that way.
How does that compare, I wonder, with the change in diameter of the conductor produced by Magnetostriction. (Can't be sure of how to do that sum.)

I did wonder, also about the effect of the three phases of currents flowing in the three conductors Would that not tend to reduce the sound level (partial cancellation)? Could the higher level of sound near the towers be something to do with this?

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« Reply #14 on: 02/09/2009 19:03:40 »
There's also the voltage modulated corona discharge.
If the lines were DC they would hiss- that hiss is modulated at (in the UK) 50 Hz.
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Offline syhprum

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Why Does A Tall Power Thing Hum ?
« Reply #15 on: 05/09/2009 17:12:19 »
I have often contemplated erecting an antenna wire say 100m long and 2m high beneath 400Kv power lines to see how much power I could siphon off but I have not been brave enough.
It should be quite easy to calculate the power available by anyone skilled in maths, I fear it would be small and the source would be rather high impedance.

PS
1000A at 400KV *6 sounds like an awful lot of power, would not eletrostatic attraction between cables be a larger source of hum (at 50Hz and 150Hz).
« Last Edit: 05/09/2009 17:24:10 by syhprum »
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Offline Geezer

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« Reply #16 on: 05/09/2009 17:26:46 »
tell me why those power hummy things hum ?...


Obviously, because they don't know the words. Sheesh...
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lyner

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« Reply #17 on: 05/09/2009 17:34:46 »
I have often contemplated erecting an antenna wire say 100m long and 2m high beneath 400Kv power lines to see how much power I could siphon off but I have not been brave enough.
It should be quite easy to calculate the power available by anyone skilled in maths, I fear it would be small and the source would be rather high impedance..

I have a feeling that a lot of iron and a big coil may do better.

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Offline RD

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« Reply #18 on: 05/09/2009 18:08:26 »
I have often contemplated erecting an antenna wire say 100m long and 2m high beneath 400Kv power lines to see how much power I could siphon off...

[attachment=8360]

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« Last Edit: 05/09/2009 18:14:38 by RD »

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Offline that mad man

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« Reply #19 on: 05/09/2009 19:37:20 »
"I've ignored the 3 phase thing which could cause all three conductors to do a nice little dance with each other, I guess"

You often see (and hear) that dance on the 3 phase cables in lift shafts.

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Offline Geezer

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« Reply #20 on: 05/09/2009 19:59:13 »
I have often contemplated erecting an antenna wire say 100m long and 2m high beneath 400Kv power lines to see how much power I could siphon off but I have not been brave enough.
It should be quite easy to calculate the power available by anyone skilled in maths, I fear it would be small and the source would be rather high impedance.

Not too much (power) I suspect. The coupling is not going to be very efficient, but, perhaps more importantly, because your antenna is approximately the same distance from each phase conductor, the magnetic fields will cancel each other out. (This does assume the phase currents are all equal of course, but the power companies do go to a lot of trouble to keep them that way.)

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Offline syhprum

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« Reply #21 on: 05/09/2009 20:45:38 »
I was rellying on capacitive coupling between the antenna and the power line, the capacitance between the antenna and the power line and that between the antenna and ground would form a capacitive potential divider with say a division ratio of 10 to 1 giving a voltage on the antenna of 40KV while the output impedance would be 1/2πfc If I knew how to calculate the capacitance of the antenna to ground I could calculate the available power.
With the British system where the 6 conductors are arranged in a ring radiation is reduced it would work better with the continental scheme that has a 2 up and 4 down arrangement and the antenna should be slightly offset.
Due to the long wavelength I think only capacitive effects apply
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lyner

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« Reply #22 on: 05/09/2009 23:25:39 »
I was rellying on capacitive coupling between the antenna and the power line, the capacitance between the antenna and the power line and that between the antenna and ground would form a capacitive potential divider with say a division ratio of 10 to 1 giving a voltage on the antenna of 40KV while the output impedance would be 1/2πfc If I knew how to calculate the capacitance of the antenna to ground I could calculate the available power.
With the British system where the 6 conductors are arranged in a ring radiation is reduced it would work better with the continental scheme that has a 2 up and 4 down arrangement and the antenna should be slightly offset.
Due to the long wavelength I think only capacitive effects apply
Unless you were to use an enormous length of cable, the capacitance to earth would be tiny ( not many pF per m) so the source impedance would be very high and, to tune it out (at 50Hz), I think you would need a filthy great inductor. I think that magnetic coupling might be better; it would be easier to get the power out of the circuit. A long, multi-turn coil with its plane vertical and parallel with the conductors with as much iron as you could get could couple better. I'm sure. I estimate about a volt from a 10m high, 100 m loop of wire if there's 1000A flowing but that would be for a single phase system. However - the source impedance would be low enough to allow a lot of amps to flow. Solar heating might be cheaper to instal!
There is the tale of the guy who heated his greenhouses by nicking power from the nearby overhead railway lines. Could be a myth, though.

Is your comment about length and capacity based on antenna theory? That doesn't apply in this case because the source cable  is effectively infinite as the current is uniform over the length and it's not a monopole / dipole. Afaik, the situation is that you effectively have a capacitative potential divider but that you then need to match the power out of it.

Your comment about the  problem with the three  / six cables is certainly right.
« Last Edit: 05/09/2009 23:27:54 by sophiecentaur »

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Offline Geezer

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Why Does A Tall Power Thing Hum ?
« Reply #23 on: 06/09/2009 01:07:51 »
There is the tale of the guy who heated his greenhouses by nicking power from the nearby overhead railway lines. Could be a myth, though.

That might be a better way to go. Perhaps you could run a long insulated cable close to one of the rails and couple into the return current without going anywhere near the 25kV. Mind you, the current only flows when there is a train in the right relationship, and trains tend to do a lot of coasting, so power might be a bit intermittent.

Course, if you are in the South of England, you could always just tap into the live DC rail directly! (Do not try this at home!)
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Offline syhprum

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« Reply #24 on: 06/09/2009 09:45:21 »
750V DC would be a lot safer to tap than 25KV AC, wellington boots and rubber gloves should suffice although switching in a domestic environment might be a bit of a problem due to arcing.
For lighting you could use three lamps in series although you had better hurry up and buy some as filament lamps are to be banned. 
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Offline Geezer

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« Reply #25 on: 06/09/2009 23:51:44 »
You could also get about 50 car batteries (old submarine batteries might work too) connect them in series and also include a current limiting resistor, attach the whole thing to a couple of long cables with big croc clips on the ends, and nip out after dark and hook up for a quick recharge. Then, attach the batteries to a large inverter that produces 240 V, 50 Hz. to power your home. What could be simpler?

Be sure to connect the red wire to the positive rail and not the other way around, although, in the US that might be the black wire. Anyway, I'm sure you'll figure it out. (Is the third rail positive or negative? I've no idea.)
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Offline syhprum

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« Reply #26 on: 07/09/2009 07:47:09 »
I would expect it to be positive as a negative rail would be more prone to corrosion.

PS Lead acid batteries work best when charged from a constant voltage source of 2.35 volts per cell so use the appropriate number.
« Last Edit: 07/09/2009 07:50:21 by syhprum »
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« Reply #27 on: 07/09/2009 08:57:34 »
50 car batteries would cost you quite a lot. Still, you could always sell them to pay your fine when you're caught!
I can't help feeling that track maintainance would spot your cable or other evidence of your connection.

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Offline Geezer

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« Reply #28 on: 07/09/2009 19:11:24 »
SC - I think you missed my point about the big croc clips. You only sneak out at night and hook them up for a couple of hours so the track crew never see them. Mind you, that does increase the risk of being flattened by a train somewhat and humans do seem to have a very hard time judging the speed of oncoming trains, but nothing ventured.

Syphrum - Re. charging voltage, I don't think you can count on the track voltage being very constant. I would imagine there are some fairly significant voltage drops in the rails when trains are accelerating, and the voltage may exceed 750 V at certain times, so if you match the number of cells to 750 V exactly, you may get no charge at all, or far too much, which can cause very nasty problems. Other factors can affect the cell voltage too, so you really need some sort of regulator to accommodate these variables. A resistor is all it would take. Something a little more sophisticated might take a little more time to design, but while you are "in the nick" you will have plenty of time to work it out for the MK2 version  [;D]
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Offline LeeE

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« Reply #29 on: 07/09/2009 21:53:18 »
Quote
A resistor is all it would take

A bit of an understatement methinks: it would have to be a mucking hefty resitstor.  [;D]
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Geezer

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« Reply #30 on: 07/09/2009 22:51:20 »
Quote
A resistor is all it would take

A bit of an understatement methinks: it would have to be a mucking hefty resitstor.  [;D]

Not all that hefty really  [:)]

With 50 car batteries, a 3Ω resistor would limit the current to about 42A and it would "only" dissipate 5.2kW. It ought to be possible to rig up something appropriate with a network of 1kW radiant heater elements. And, the heat produced would be quite nice while hanging around outside in the middle of the night while the batteries were charging.
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Offline LeeE

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« Reply #31 on: 07/09/2009 23:06:16 »
Hmm... I believe that the typical max continuous current draw for railway traction motors is around 1800A, and this figure may be exceeded by quite a large margin (as much as 2x) for short periods, but even if you do only draw 42A, and only have to dissipate 5.2kW, that's still quite a mucking hefty resistor  [;)]
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Geezer

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« Reply #32 on: 07/09/2009 23:18:50 »
We could do all kinds of fancy stuff to eliminate the resistor, and probably increase the number of batteries also. For example, we might use a switching regulator to limit the current instead. That would reduce the amount of power dissipated considerably. But, as it's not our power, why would we care?

Thanks for the data on the current drawn by the traction motors. At those levels they are hardly likely to notice a mere 40A "leakage". (Crap, I hope nobody is taking any of this seriously.)
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Offline syhprum

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« Reply #33 on: 08/09/2009 12:00:56 »
Lead acid batteries do not like being charged from a constant current source i.e from an over voltage source via a resistor.
They bubble off Hydrogen gas which depletes the acid solution and can explode, batteries last much longer on modern cars because they are charged from a well controlled constant voltage source (2.35v per cell)
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Offline Geezer

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« Reply #34 on: 08/09/2009 17:51:42 »
Lead acid batteries do not like being charged from a constant current source i.e from an over voltage source via a resistor.
They bubble off Hydrogen gas which depletes the acid solution and can explode, batteries last much longer on modern cars because they are charged from a well controlled constant voltage source (2.35v per cell)
Agreed. With a simple resistor, we would have to disconnect the croc clips when the batteries were sufficiently charged to prevent gassing.

Supppose we connect a partially discharged 12V battery which is at, say 12.6V, to a charger at 14.1V which has almost unlimited current capacity (as the third rail supply does). The charging current will only be limited by the internal Resistance of the cells. I suspect we will easily exceed the maximum charge rate and cause the battery to vent, or possibly explode.

To prevent this, we still need something to limit the current. A current limiting circuit possibly, or perhaps a resistor. If we are using a very low resistance current source, the charger should not operate on voltage alone. Battery chargers and car alternators have some internal resistance which limits the current they can supply. The third rail system would be able to supply far more current than the batteries could safely consume.
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Offline syhprum

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« Reply #35 on: 09/09/2009 13:12:55 »
Car generators have well designed electronic current limitation, if you wanted your installation to last it would be just as well to use a proper charging regular and not just a simple resistor.
The 723 chip schematic would be a good place to look for inspiration.
« Last Edit: 11/09/2009 20:36:26 by syhprum »
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Offline Geezer

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« Reply #36 on: 09/09/2009 15:58:38 »
Would it work at 750 volts?
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Offline syhprum

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« Reply #37 on: 09/09/2009 17:45:03 »
There are of course more complex chips that work in a chopped mode fashion and are suitable for a 750V system but I showed the 723 as an example of a regulator that has voltage and current sensing.
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« Reply #38 on: 09/09/2009 18:37:01 »
BTW, the 723 regulator requires resistor R5 in series with the load to create a voltage drop so that the 723 can measure the current supplied to the load. Resistors are hard to avoid  [;D]
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« Reply #39 on: 09/09/2009 19:20:23 »
"Resistors are hard to avoid"
Ask the Borg or the Vogon guard.
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« Reply #40 on: 09/09/2009 19:30:41 »
Rats! We are discovered. Quick! Hit the probability drive.
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Offline Waldo Pepper

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« Reply #41 on: 16/10/2009 19:05:46 »
Lead acid batteries do not like being charged from a constant current source i.e from an over voltage source via a resistor.
They bubble off Hydrogen gas which depletes the acid solution and can explode, batteries last much longer on modern cars because they are charged from a well controlled constant voltage source (2.35v per cell)

Lead acid cells are fine being charged from a current limited supply as long as the voltage behind the limited current is set at 2.35v/cell. That is how domestic chargers work, albeit not a very well regulated end voltage.

The current a 200Ah+ truck battery would take when flatish being charged at constant voltage would blow your house electrics.

Exactly the same with Li-Ion cells. Charge at constant (or limited) current to the datasheet recommended rate (normally C/5) then let them take what they need until fully charged from a constant voltage 4.2V supply.

Just came across this site. Awesome! So much for me wanting to cut down on Internet usage and do something else :)

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Offline Waldo Pepper

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Why Does A Tall Power Thing Hum ?
« Reply #42 on: 16/10/2009 19:10:57 »
Would it work at 750 volts?

Yes if you dropped the supply to the device and used some high voltage transistors. BU208 ones used to be used in the EHT circuits in CRT Tellies (now old technology). High voltage regulator designs are complex and require a good knowledge base and some scary procedures unless you want to end up dead.