snipped-for-privacy@downunder.com used his keyboard to write :
Did you not read what I asked? Power means usable power. Measured value is DATA or SIGNAL. Semafore flags will get you galvanic isolation for data!!
Is there any useful galvanic isolation for USEFUL Power other than a transformer???? :-?
motor-generator piezoelectric
I've seen switched capacitor proposed.
snipped-for-privacy@my-deja.com Inscribed thus:
If you look at the photo you can see the double insulation ! Anyway you need a megger to check that there is no leakage between the prongs on the plug and any accessible metal parts.
"Bob Boblaw"
** Could be either.With a class 2 transformer: apply the worst case overload and if the windings do not reach a high enough temp to damage the insulation materials used - then there is no problem.
With most class 2 transformers, this normally means using a thermal cut out embedded in the primary winding.
With a " universal " motor, it may well be that the self inductance is high enough to limit the stall current to a safe number.
This would be entirely consistent with the " AC ONLY " marking on the name plate of the Sears drill.
... Phil
"Baron"
** To have any idea of the drill is safe, the owner needs to stall the motor at full setting and see what happens.He has never done this and is basing his conclusions on PURE ASSUMPTION !
BTW:
Any ( genuine) class 2 transformer will pass a similar test with no possibility of the core, frame or secondary windings becoming live at supply voltages.
This is fairly easily achieved and incorporated in HUNDREDS of MILLIONS of units.
.... Phil
On a sunny day (Sun, 12 Aug 2012 20:31:18 +1000) it happened John G wrote in :
How much is useful?, for one it is uW, for the other GW.
Light source -> photocells is a low energy alternative to a transformer. A motor driving a generator is a very high energy alternative to a transformer. All come in various sizes and efficiencies.
Use brain, if present.
Sorry to nit pick (I made the same mistake myself). Class 2 appears to refer to some US regional NEC specific issues (e.g. limiting power levels to 100 VA) etc.
If I understand correctly, we are discussing about IEC 60950 Class II double isolated issues.
According to my understanding, the electronics sitting at the HV potential (100-500 kV) requires less than 1 W of power.
You might need a 100-1000 W input power laser at ground potential, in order to get 1 W of photo cell output power at the line potential.
Depends how you define USEFULL. If it works, why fix it ?
snipped-for-privacy@downunder.com wrote in news: snipped-for-privacy@4ax.com:
why would they go to that complexity? they could just power their measuring device and optical transmitter from the HV line,just a few turns of well-insulated wire around the HV conductor ought to do it.. or a solar panel and secondary battery....
No such requirement, the sum of the breaker ratings can, and often is, greater than the main
Mostly
Major appliance ratings can be a lot higher than 25A
32A on a single
The whole circuit is at HV potential (hundreds of kV). Batteries tend to be unreliable and will all die very quickly in terms of power transmission line lifetime, and in some cases there may not be any light available.
The laser power method is a reasonable solution. The power laser will be on the ground and easily replaced if they die.
Efficiency is pretty tolerable, if you only need hundreds of milliwatts transmitted over hundreds of meters. There are standard products on the market.
Best regards, Spehro Pefhany
Oops. I stand corrected:
Adding up the breakers on my 200A panel, I get 250amps. Argh.
True. My electric stove and small water heater are on 25A breakers. If I had electric heating, a heat pump, or an air conditioner, it might require a larger breaker.
This little bit of the thread has deteriorated into the usual inapprarite impractical waffle. :-@
Plain old analog CTs are insulated for their operating voltage. And they are usually mounted to some structure.
There are digital CT assemblies (and other instrumentation) that use power over fiber as well as fiber data return. These are used in substations where the potential rise across long instrumentation circuits could be problematic in the event of a close-in primary fault.
Some hanging CTs are line current powered and either record line parameters for download after removal or can be interrogated over an RF link. Some hanging CTs are simple fault current detectors. They are line powered and just flash LEDs if fault current passes through.
Mmmmmm! Waffles!
-- Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
------------------------------------------------------------------ Just say 'No' to Windows. -- Department of Defenestration.
So maybe its 25% efficient. No good for a wall wart. But if you need the electrical isolation (at any cost) it works.
Even 10% wouldn't be too bad. JDS seem to be a bit cagey about the actual efficiency of their products.
Best regards, Spehro Pefhany
That's one of those accursed moulded plugs that seem to be compulsory on newly-purchased equipment here in the UK. As it is not possible to dismantle them to find out how well (or not) they are made, the best thing to do is cut the damn thing off and fit a quality 3-pin plug.
Trouble is, even with low-current equipment most people replace a blown fuse with a 13 amp one. Well, a blown fuse is so inconvenient, isn't it? The problem is compounded because if you purchase a new plug, it invariably comes with a 13 amp fuse prefitted. It really would be a lot better if we referred to them as "3-pin mains plugs", rather than "13 amp plugs", as the latter suggest that they should have a 13 amp fuse. Sometimes, just to confuse things, the descriptions seem to be mixed...
Yep. See second bullet point under "Indications of a substandard electrical installation" here:
Quick summary here:
The "Buzz Bar" amused me.
-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Have something to add? Share your thoughts — no account required.
Ask the community — no account required