> > Why not use isolation transformers between the measured voltage and > > the meters? > > Then his wall wart will still power all the meters, the meters are not > > at some eelvate4d voltage to ground.
> Yeah! (Smacks forehead)
> That'd work if you could locate transformers that had an exact 1:1 match > (primary to secondary) at ~230 VAC and you terminated the output of the > transformers with 'matching' resistors.
> With a resistive voltage divider, you could use a cheap transformer that > output a few volts higher than it's input voltage. Calibrate at time > of manufacture.
> For extra credit, add a secondary and a few cents of electronics to power > each meter, eliminating the wall warts.
> Dayum nutz, you are smart!
> --Winston
> -- > The good news is that you have a new lawn mower. > The bad news is it's rated in 'Sears horsepower' and the > warranty is in 'AT&T months'.
Why would you need any exact numbers anyway? a 24 volt transformer is fine. He just wants to see the relative voltages. Something cheap somewhere.
> Why would you need any exact numbers anyway? a 24 volt transformer is > fine. > He just wants to see the relative voltages. > Something cheap somewhere.
Maybe I misread PV but I got the impression that he would prefer that the readings be as close to reality as possible. Perhaps I'm projecting.
> >> The battery contacts are within a few volts of the RPC outputs. > >> If PV should decide to change multimeter batteries with the RPC still > >> running and connected, he stands a good chance of receiving an > >> impromptu fibrillation. Something about this just doesn't sound safe.
> > Why in hell would someone do that? Why would you build the damn > > thing so that you could even try?
> It's worth the effort to design stuff that doesn't require the user > to have an EE degree in order to use it safely.
Sigh. Why would you need a degree for any type of engineering to read some meters? or to install a proper safety interlock in the covers?
> Half-nutz's idea of using isolation transformers on the input side > is a winner, I think. Adding a secondary to power each meter eliminates > batteries *and wall warts*.
> (...)
> > I've seen piles of those surplus for $20 each. I didn't buy any of > > them.
> Can you forward the address of your meter source to PV?
They were at several surplus stores in the Orlando area, and a half dozen hamfests. You just have to keep your eyes open. I've even seen them at regular flea markets where someone bought a batch at an industrial auction. There are several meters on E-bay that are powered by a low voltage AC or DC source and are isolated. I posted a link in this thread. They are in the $20 dollar range.
> > Why would you need any exact numbers anyway? a 24 volt transformer is > > fine. > > He just wants to see the relative voltages. > > Something cheap somewhere.
> Maybe I misread PV but I got the impression that he would prefer > that the readings be as close to reality as possible. > Perhaps I'm projecting.
Use 10-1 stepdown transformers and move the decimal point on the displays.
> Sigh. Why would you need a degree for any type of engineering to > read some meters? or to install a proper safety interlock in the covers?
We've become specialized enough that we sometimes assume that our 'knowledge set' is shared by nearly everybody. Ain't necessarily so.
(...)
>> Can you forward the address of your meter source to PV?
> They were at several surplus stores in the Orlando area, and a half > dozen hamfests. You just have to keep your eyes open. I've even seen > them at regular flea markets where someone bought a batch at an > industrial auction. There are several meters on E-bay that are powered > by a low voltage AC or DC source and are isolated. I posted a link in > this thread. They are in the $20 dollar range.
Kewl!
--Winston
-- The good news is that you have a new lawn mower. The bad news is it's rated in 'Sears horsepower' and the warranty is in 'AT&T months'.
> > Sigh. Why would you need a degree for any type of engineering to > > read some meters? or to install a proper safety interlock in the covers?
> We've become specialized enough that we sometimes assume that our > 'knowledge set' is shared by nearly everybody. Ain't necessarily so.
Like they say, 'You can't fix stupid' Some people will rip out any protection designed into any tool, just because they can. Like I always say, 'Common sense wouldn't have a name if it was really common. :)
> >> Can you forward the address of your meter source to PV?
> > They were at several surplus stores in the Orlando area, and a half > > dozen hamfests. You just have to keep your eyes open. I've even seen > > them at regular flea markets where someone bought a batch at an > > industrial auction. There are several meters on E-bay that are powered > > by a low voltage AC or DC source and are isolated. I posted a link in > > this thread. They are in the $20 dollar range.
> Kewl!
> --Winston
> -- > The good news is that you have a new lawn mower. > The bad news is it's rated in 'Sears horsepower' and the > warranty is in 'AT&T months'.
>> We've become specialized enough that we sometimes assume that our >> 'knowledge set' is shared by nearly everybody. Ain't necessarily so.
> Like they say, 'You can't fix stupid' Some people will rip out any >protection designed into any tool, just because they can. Like I >always say, 'Common sense wouldn't have a name if it was really common.
I bought a very nice worm drive Skillsaw...with the guard wired back..from a fellow who had a moment of forgetfulness and now needed the money because he was no longer able to work in the carpentry business due to some serious leg problems.
I pondered on the bloodstains for a few moments..then he lowered the price down to "very low"..and I paid him, while listening to his story about how he really fucked up wiring that guard open.
Shrug
Gunner
"IMHO, some people here give Jeff far more attention than he deserves, but obviously craves. The most appropriate response, and perhaps the cruelest, IMO, is to simply killfile and ignore him. An alternative, if you must, would be to post the same standard reply to his every post, listing the manifold reasons why he ought to be ignored. Just my $0.02 worth."
Michael A. Terrell wrote: > Winston wrote: >> Half-nutz wrote:
>> (...)
>>> Why would you need any exact numbers anyway? a 24 volt transformer is >>> fine. >>> He just wants to see the relative voltages. >>> Something cheap somewhere. >> Maybe I misread PV but I got the impression that he would prefer >> that the readings be as close to reality as possible. >> Perhaps I'm projecting.
> Use 10-1 stepdown transformers and move the decimal point on the > displays.
That's up to PV. The 10:1 reduction in resolution might be a show-stopper.
--Winston
-- The good news is that you have a new lawn mower. The bad news is it's rated in 'Sears horsepower' and the warranty is in 'AT&T months'.
> Michael A. Terrell wrote: > > Winston wrote: > >> Half-nutz wrote:
> >> (...)
> >>> Why would you need any exact numbers anyway? a 24 volt transformer is > >>> fine. > >>> He just wants to see the relative voltages. > >>> Something cheap somewhere. > >> Maybe I misread PV but I got the impression that he would prefer > >> that the readings be as close to reality as possible. > >> Perhaps I'm projecting.
> > Use 10-1 stepdown transformers and move the decimal point on the > > displays.
> That's up to PV. > The 10:1 reduction in resolution might be a show-stopper.
> --Winston
> -- > The good news is that you have a new lawn mower. > The bad news is it's rated in 'Sears horsepower' and the > warranty is in 'AT&T months'.
No reduction in resolution, if you have a 24 volt voltmeter. That is why they have a range.
> No reduction in resolution, if you have a 24 volt voltmeter. That is > why they have a range.
Right you are. You get +-100 mV resolution with a typical panel meter, either way. (Accuracy numbers can swamp that quickly. One Red Lion part has +- 430 mV accuracy in our application.)
Each transformer could drive 1/3 of a 3 phase rectifier that in turn would drive a power supply circuit for the meters. If each meter drew 6 W, it's clear that each transformer would want to be say, 12 W or larger to minimize data coloration imposed by the meter itself.
If you used little multimeters, you would need a tiny fraction of that power; could get away with much smaller transformers.
--Winston
-- The good news is that you have a new lawn mower. The bad news is it's rated in 'Sears horsepower' and the warranty is in 'AT&T months'.
> On Mon, 02 Nov 2009 20:01:19 -0500, "Michael A. Terrell" > <mike.terr...@earthlink.net> wrote:
> >> We've become specialized enough that we sometimes assume that our > >> 'knowledge set' is shared by nearly everybody. Ain't necessarily so.
> > Like they say, 'You can't fix stupid' Some people will rip out any > >protection designed into any tool, just because they can. Like I > >always say, 'Common sense wouldn't have a name if it was really common.
> I bought a very nice worm drive Skillsaw...with the guard wired > back..from a fellow who had a moment of forgetfulness and now needed the > money because he was no longer able to work in the carpentry business > due to some serious leg problems.
> I pondered on the bloodstains for a few moments..then he lowered the > price down to "very low"..and I paid him, while listening to his story > about how he really fucked up wiring that guard open.
He should be thankful he didn't win a 'Darwin Award'.
> Michael A. Terrell wrote: > > Winston wrote: > >> Half-nutz wrote:
> >> (...)
> >>> Why would you need any exact numbers anyway? a 24 volt transformer is > >>> fine. > >>> He just wants to see the relative voltages. > >>> Something cheap somewhere. > >> Maybe I misread PV but I got the impression that he would prefer > >> that the readings be as close to reality as possible. > >> Perhaps I'm projecting.
> > Use 10-1 stepdown transformers and move the decimal point on the > > displays.
> That's up to PV. > The 10:1 reduction in resolution might be a show-stopper.
There is no change in resolution. You still have a 3.5 or 4.5 digit meter. Some allow the decimal point to be hard wired and the display will be exactly the same.
> > No reduction in resolution, if you have a 24 volt voltmeter. That is > > why they have a range.
> Right you are. You get +-100 mV resolution with a typical panel meter, > either way. > (Accuracy numbers can swamp that quickly. One Red Lion part has > +- 430 mV accuracy in our application.)
> Each transformer could drive 1/3 of a 3 phase rectifier that in turn > would drive a power supply circuit for the meters. If each meter drew > 6 W, it's clear that each transformer would want to be say, 12 W or > larger to minimize data coloration imposed by the meter itself.
> If you used little multimeters, you would need a tiny fraction of that > power; could get away with much smaller transformers.
Use AC voltmeters. The load impedance will be quite migh, and the current well under a mil per phase. Most of the meter modules are 10 Mohm input impedance.
Michael A. Terrell wrote: > Winston wrote: >> Half-nutz wrote:
>> (...)
>>> No reduction in resolution, if you have a 24 volt voltmeter. That is >>> why they have a range. >> Right you are. You get +-100 mV resolution with a typical panel meter, >> either way. >> (Accuracy numbers can swamp that quickly. One Red Lion part has >> +- 430 mV accuracy in our application.)
>> Each transformer could drive 1/3 of a 3 phase rectifier that in turn >> would drive a power supply circuit for the meters. If each meter drew >> 6 W, it's clear that each transformer would want to be say, 12 W or >> larger to minimize data coloration imposed by the meter itself.
I caught a boo-boo. Under these circs, each transformer would want to be capable of say, 24 W (not 12 W) so that any one phase could power the entire meter circuit (posited to require 18 W). Clearly using the cheap multimeters instead of the sexeee large digital panel meters would save significant cash in transformers. (Three 1 W isolation transformers would probably be less than half the cost of three 24 W transformers.)
>> If you used little multimeters, you would need a tiny fraction of that >> power; could get away with much smaller transformers.
> Use AC voltmeters. The load impedance will be quite migh, and the > current well under a mil per phase. Most of the meter modules are 10 > Mohm input impedance.
We are in violent agreement.
The burden imposed by the *signal input* of the meter itself is inconsequential in relation to the amount of current necessary to power the meter electronics. If we choose to go 'batteryless', that power has to come from somewhere. Ideally, we could power the meter electronics from the output of the same isolation transformer that we are metering, as per Half-nutz's idea.
Obviously we are talking about digital, not analog meters here.
--Winston
-- The good news is that you have a new lawn mower. The bad news is it's rated in 'Sears horsepower' and the warranty is in 'AT&T months'.
> Michael A. Terrell wrote: > > Winston wrote: > >> Half-nutz wrote:
> >> (...)
> >>> No reduction in resolution, if you have a 24 volt voltmeter. That is > >>> why they have a range. > >> Right you are. You get +-100 mV resolution with a typical panel meter, > >> either way. > >> (Accuracy numbers can swamp that quickly. One Red Lion part has > >> +- 430 mV accuracy in our application.)
> >> Each transformer could drive 1/3 of a 3 phase rectifier that in turn > >> would drive a power supply circuit for the meters. If each meter drew > >> 6 W, it's clear that each transformer would want to be say, 12 W or > >> larger to minimize data coloration imposed by the meter itself.
> I caught a boo-boo. Under these circs, each transformer would want to be > capable of say, 24 W (not 12 W) so that any one phase could power the entire > meter circuit (posited to require 18 W). Clearly using the cheap multimeters > instead of the sexeee large digital panel meters would save significant > cash in transformers. (Three 1 W isolation transformers would probably be > less than half the cost of three 24 W transformers.)
> >> If you used little multimeters, you would need a tiny fraction of that > >> power; could get away with much smaller transformers.
> > Use AC voltmeters. The load impedance will be quite migh, and the > > current well under a mil per phase. Most of the meter modules are 10 > > Mohm input impedance.
> We are in violent agreement.
> The burden imposed by the *signal input* of the meter itself is inconsequential > in relation to the amount of current necessary to power the meter electronics. > If we choose to go 'batteryless', that power has to come from somewhere. > Ideally, we could power the meter electronics from the output of the same > isolation transformer that we are metering, as per Half-nutz's idea.
> Obviously we are talking about digital, not analog meters here.
You want to power each meter separately. I only see the need for one power transformer for all three meters, and use small 10:1 transformers for isolating the inputs. Its much safer, that way and the losses in the stepdown transformers are a lot higher than the load from the meters. One side of all three secondaries can be grounded.
The power required for the meters depends on the display. LCD is minimal. LED is a LOT higher, and large LED displays are the worst. The LCD meters need less than a Watt.
>> Michael A. Terrell wrote: >> > Wild_Bill wrote: >> >> Adding AC powered instrumentation to utility-source line voltage equipment >> >> is somewhat complicated, and a little more complicated for 3-phase circuits, >> >> where one needs to be aware of peak voltages.
>> >> Winston offered a practical and safe solution. Stormin's suggestion would >> >> also work if you utilize 3 separate battery holders, one for each meter. >> >> Holders for 6 C or D cells are fairly common (6x1.5V = 9V).
>> >> FWIW, many small AC adapters and DC chargers aren't designed for line >> >> voltage isolation.
>> > Then they aren't safe for any application.
>> But what is 'totally safe'? Even KANO kills thousands a year.
>> PV was operating three digital mulimeters, each one floating hundreds >> of volts above ground, and he lived to tell about it.
> What is the lost voltage rating you've seen for magnet wire? For the >nylon bobbins? Even the old waxed paper separators were good for 600 >volts. Any reputable manufacturer Hi-pot tests at 500 volts.
I think you meant "lowest" voltage rating.
I don't know where the FWIF came from but I don't know of ANY walwarts, AC adapters or DC chargers which do not isolate the low voltage output from the line voltage. In the UK at least any such a device would be illegal.
Twice working voltage plus 1000V is a pretty common acceptance standard and this is well below normal device capability. Out of interest I tried but was unable to breakdown a Motorola cell phone walwart even at 2,850V (the highest available voltage) for half an hour.
>> The burden imposed by the *signal input* of the meter itself is inconsequential >> in relation to the amount of current necessary to power the meter electronics. >> If we choose to go 'batteryless', that power has to come from somewhere. >> Ideally, we could power the meter electronics from the output of the same >> isolation transformer that we are metering, as per Half-nutz's idea.
>> Obviously we are talking about digital, not analog meters here.
> You want to power each meter separately. I only see the need for one > power transformer for all three meters, and use small 10:1 transformers > for isolating the inputs. Its much safer, that way and the losses in > the stepdown transformers are a lot higher than the load from the > meters. One side of all three secondaries can be grounded.
Not powered separately. Each phase would provide 1/3 the power to drive all three meters under normal circs. That would balance the metering power burden among phases. (A tiny amount of power when using the little multimeters but still a 'style thing'.) Any one phase would power all three meters in the event that the RPC was only providing a single phase. This makes the design easy to install because it's 'self-powering' and does not require a separate wall wart or the need for any batteries.
> The power required for the meters depends on the display. LCD is > minimal. LED is a LOT higher, and large LED displays are the worst. > The LCD meters need less than a Watt.
Yup! In the case of the little DMMs, we are talking about milliwatts.
--Winston
-- The good news is that you have a new lawn mower. The bad news is it's rated in 'Sears horsepower' and the warranty is in 'AT&T months'.
pentag...@yahoo.com wrote: > On Sun, 01 Nov 2009 15:53:30 -0500, "Michael A. Terrell" > <mike.terr...@earthlink.net> wrote:
>> Winston wrote: >>> Michael A. Terrell wrote: >>>> Wild_Bill wrote: >>>>> Adding AC powered instrumentation to utility-source line voltage equipment >>>>> is somewhat complicated, and a little more complicated for 3-phase circuits, >>>>> where one needs to be aware of peak voltages.
>>>>> Winston offered a practical and safe solution. Stormin's suggestion would >>>>> also work if you utilize 3 separate battery holders, one for each meter. >>>>> Holders for 6 C or D cells are fairly common (6x1.5V = 9V).
>>>>> FWIW, many small AC adapters and DC chargers aren't designed for line >>>>> voltage isolation.
>>>> Then they aren't safe for any application. >>> But what is 'totally safe'? Even KANO kills thousands a year.
>>> PV was operating three digital mulimeters, each one floating hundreds >>> of volts above ground, and he lived to tell about it.
>> What is the lost voltage rating you've seen for magnet wire? For the >> nylon bobbins? Even the old waxed paper separators were good for 600 >> volts. Any reputable manufacturer Hi-pot tests at 500 volts.
> I think you meant "lowest" voltage rating.
> I don't know where the FWIF came from but I don't know of > ANY walwarts, AC adapters or DC chargers which do not isolate > the low voltage output from the line voltage. In the UK at least > any such a device would be illegal.
On several notebook computer power supplies I tested, the negative D.C. output was bonded to A.C. ground which as you know has a low impedance connection to A.C. neutral. In the intended application, this is safe and moral and legal *and* proper. To power instruments (that are also connected directly to alternating current), not so much.
> Twice working voltage plus 1000V is a pretty common > acceptance standard and this is well below normal device > capability. Out of interest I tried but was unable to breakdown > a Motorola cell phone walwart even at 2,850V (the highest > available voltage) for half an hour.
"I tested 'Z' so you can safely use 'A' 'B' or 'C' in your application."
Hmmm. :)
--Winston
-- The good news is that you have a new lawn mower. The bad news is it's rated in 'Sears horsepower' and the warranty is in 'AT&T months'.
Winston writes: > On several notebook computer power supplies I tested, the negative > D.C. output was bonded to A.C. ground which as you know has a low > impedance connection to A.C. neutral.
Really? I've never seen a notebook power supply that had a grounded plug.
>> On several notebook computer power supplies I tested, the negative >> D.C. output was bonded to A.C. ground which as you know has a low >> impedance connection to A.C. neutral.
>Really? I've never seen a notebook power supply that had a grounded plug.
>> On several notebook computer power supplies I tested, the negative >> D.C. output was bonded to A.C. ground which as you know has a low >> impedance connection to A.C. neutral.
> Really? I've never seen a notebook power supply that had a grounded plug.
> >> The burden imposed by the *signal input* of the meter itself is inconsequential > >> in relation to the amount of current necessary to power the meter electronics. > >> If we choose to go 'batteryless', that power has to come from somewhere. > >> Ideally, we could power the meter electronics from the output of the same > >> isolation transformer that we are metering, as per Half-nutz's idea.
> >> Obviously we are talking about digital, not analog meters here.
> > You want to power each meter separately. I only see the need for one > > power transformer for all three meters, and use small 10:1 transformers > > for isolating the inputs. Its much safer, that way and the losses in > > the stepdown transformers are a lot higher than the load from the > > meters. One side of all three secondaries can be grounded.
> Not powered separately. Each phase would provide 1/3 the power to drive > all three meters under normal circs. That would balance the metering power > burden among phases. (A tiny amount of power when using the little > multimeters but still a 'style thing'.) Any one phase would power all > three meters in the event that the RPC was only providing a single phase. > This makes the design easy to install because it's 'self-powering' and > does not require a separate wall wart or the need for any batteries.
I wouldn't use a wall wart, I would use a filament transformer or other low power uncased transformer and mount it in the RPC cabinet. That way the meters could be used to meter other parts of the system, even if the RPC isn't running. Add three CTs and you could switch from voltage to current monitoring on the fly.
> > The power required for the meters depends on the display. LCD is > > minimal. LED is a LOT higher, and large LED displays are the worst. > > The LCD meters need less than a Watt.
> Yup! In the case of the little DMMs, we are talking about milliwatts.
> I wouldn't use a wall wart, I would use a filament transformer or > other low power uncased transformer and mount it in the RPC cabinet. > That way the meters could be used to meter other parts of the system, > even if the RPC isn't running. Add three CTs and you could switch from > voltage to current monitoring on the fly.
We are starting to violate KISS here, yes?
A natural extension would be to eliminate the multimeters in preference for a data acquisition system. If it were fast enough, you could present the user with realtime displays of voltage, current, frequency, power factor and THD on all three phases. Add logging software and an Ethernet port and you could check up on your drill press from anywhere in the world!
But I digress.
--Winston
-- The good news is that you have a new lawn mower. The bad news is it's rated in 'Sears horsepower' and the warranty is in 'AT&T months'.
>> I wouldn't use a wall wart, I would use a filament transformer or >> other low power uncased transformer and mount it in the RPC cabinet. That >> way the meters could be used to meter other parts of the system, >> even if the RPC isn't running. Add three CTs and you could switch from >> voltage to current monitoring on the fly.
> We are starting to violate KISS here, yes?
> A natural extension would be to eliminate the multimeters in preference > for a data acquisition system. If it were fast enough, you could present > the user with realtime displays of voltage, current, frequency, power > factor > and THD on all three phases. Add logging software and an Ethernet port > and you could check up on your drill press from anywhere in the world!
> But I digress.
> --Winston
Hey, add CNC and a web portal and you can have your designs altered from anywhere in the world too.
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