Re: International standards (2023 Update)

As in subject line I want to convert from 110v to 240v

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for DC current and good isolation we used a Shut going through a torrid, the small windings around the toride get a heavy change effects in its inductance as the current in the field causes it to collapse. thus a DC current trough a torride can cause the inductance to change. use this as part of a Freq to Voltage converter circuit.. we also use a small mini circuit using a shunt bar where both sides are input to the + and - side via resistors to an op-amp using a dual supply., this supply is fully ground isolated via a transformer type on the secondary side so that the op-amp components do not come in contact with any other electrical which could potentially over voltage the op amp./ in this case the op-amp output drives an OP-coupler with transistor output. if you really want to get crude, you can use a low voltage incandescent lamp accrossed the shunt in a mini tube with a photo detector on the other end of the tube.

Daniel Rudy wrote:

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To convert from 110V to 240V get an appropriaty transformer. If you want a more detailed answer you'll have to provide more info about the mixer. Another problem you may run into is the 50/60Hz difference. Once more knowledge of properties or specs of the mixer is necessary.

petrus bitbyter

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No, but keep them cool and dry, in the meat bin of the fridge maybe.

John

That amp is out of gain-bandwidth. Flat out, with no feedback at all, its gain at 35K is only about 30. You need an amp with a lot more gain-bandwidth product, or you can cascade two or three stages of lower gain/stage.

A single gain stage, even with a hotter amplifier, will suffer from parasitic capacitance across such a big feedback resistor. The several-stage thing is a cleaner way to get a lot of gain.

John

Hello Everyone!

I've ran into a situation where I need to sense a very large flow of current (100A) at 24VDC or so. This is for a motor supply feed. The problem that I'm running into is isolation because there is a microcontroller that is part of the control circuit that electrically needs to stay away from this line as its powered from a different source. So far, there are two ways that I'm aware of to do this:

1. Use a very low value resistor (I would need a few in parallel), sense and amplify the voltage across that. Then feed that into a voltage to frequency converter so it can be sent across an opto-isolator and then on to a timer on the microcontroller.

1. Wind a couple of turns of the main feed wire onto a torridal core form. The torrid has a gap cut into it. Inside that gap is a hall effect device that is epoxied into place. This inherently provides the galvanic isolation that is required. After signal conditioning, the analog voltage can be sent directly to a ADC input on the controller.

I would prefer to use #2 as that would be easier to implement, and it seems to have a lower parts count. Accuracy in the area of 1 amp resolution or better, if possible, would be good. Any advise, links, etc. is appreciated. Thanks.

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If you want to construct a simple etched printed circuit board, check out . But if you don't expect to be doing much more electronic construction, it might be simpler to just use a piece of perfboard. You bend the leads and stick them through the holes just as in protoboard, only you push each component all the way flush with the surface. Then you hold it tight to the surface while you wrap the protruding lead around another protruding lead, or wrap with a separate piece of hookup wire to make the connection. Solder each joint after it is mechanically sound, then clip off the excess leads. You usually want to insert only a few components at a time and wire them up before adding more components, or the back side will look like a porcupine and be hard to work on. After you push a component down to the surface, spread the leads on the back side a little to hold it there while you insert the next one.

Hope this helps!

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

You posed the question. I just answered it. I never made any claims as to the worldly importance of my comments.

There are ways of offering protection to the microcontroller input that are much simpler and cheaper than full isolation. Usually the ADC input will have a protection diode built in so that just adding a resistor in series between the input and the test circuit will be sufficient (see the microcontroller datasheet). Zener diodes or a wide range of filtering circuits can also be used to protect the input. It would seem unlikely that full isolation should be necessary for a 24vdc system, but more details would be required to say that for sure.

I have 500+ small button cells. I was wondering how can I store them so as to not drain them ? Do I have to store them independently ?

Marcel

"Daniel Rudy"

Has hall device ICs that are good for

100A. I just received some samples, but have not yet designed with them. They look promising, high isolation and 0-5V output.

see the thread in sci.electronics from April of this year.

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John Popelish

Good morning, Dan. If you need isolated sensing of AC current, you would use a current transformer. For DC current, the best way might be to use a hall effect sensor. Several manufacturers make hall effect sensors built onto a zero ohm shunt with integrated electronics. The current is then sensed by the electrically isolated circuit, which gives you an analog output voltage proportional to the DC current.

Allegro makes integrated current sensors which are good to up to 100 amps, available off the shelf. One product you might want to look at is the ACS750SCA-100, which operates on your microcontroller 5V supply. These are available from stock at newark.com and other sources.

Good luck Chris

You have two problems. The first is that the LM358 has a gain bandwidth product of about 500,000. Divide that by 35,000 and you get a gain of about 14 or so. Include negative feedback, and you get less. You could use several stages with gain of less than 10, each, and arrive at a total gain of 500, but then the second problem shows up. 500 gain would turn 5 millivolts into 2.5 volts, but assuming these are peak to peak values much less than RMS) this implies an output rate of change of about .35 volts per microsecond, max. The LM358 slews at no more than .5 volts per microsecond, so you are very close to having the last opamp not being able to swing its output fast enough to keep up with the signal. If the 5 millivolt input is an RMS value, you are in big trouble.

To achieve this 500 gain with a single opamp, it should have a gain bandwidth product about 10*500*35,000=175MHz. Such a beast can be quite difficult to get working correctly without a good layout and some experience or luck.

I would probably go with a dual opamp that had a gain bandwidth product of about 7 to 10 MHz, each. Each amplifier would have a gain of about 22. This is based on needing the square root of 500 gain in each stage for a GBP of 10*sqrt(500)*35000=7.8MHz. An LM6132, perhaps. Its slew rate of about 8 volts per microsecond is also much more capable of keeping up with the demands of the 2.5 volt output signal.

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John Popelish

Jack,

Check the ELM339 - Infrared Remote Control from Elm. It will control 3 devices:

Otherwise I see a lot of tossed out VCRs and remotes in the garbage and for a few bucks at garage sales. You could hack the remote board directly or take the IR sensor out of the VCR and use the remote to transmit digital words to a PIC you programmed. Which I usually avoid. a lot of IR info at:

Good luck

Richard

I think that you can buy these sensors ready-made from people like LEME who use them in their DC clamp meters.

We had a similar problem with some data loggers, but were able to use an RS 232 Galvanic Isolator between the loggers and the PC. The loggers were battery powered. We had problems with currents flowing down the RS232 cable between the PC ground and the equipment ground.

Peter

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You more than likely won't be able to do anything about making it run off

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Got names mixed up there, it was HEME (that was subsequently bought by LEM)

Peter

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And somewhere around the time of 08/01/2004 08:11, the world stopped and listened as scada contributed the following to humanity:

I went looking and found the ACS750ECA-100. Arrow has 6 peices available for $8.43 each.

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Daniel Rudy

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