Few Questions

1. What makes an AC current rating different from a DC current rating? I was taught that AC crating were always given in Root Mean Square (RMS), and that RMS is the DC equivalent.

2. Why are technicians taught electron flow, but engineers are taught conventional?

3. I've seen some schematics here that have diodes with the arrow facing away from an IC output. In electron flow, they teach that current flows in the direction opposite the arrow. Meaning the current is flowing into the IC output.... why would that be desirable? I just learned the term sinking... is that what is happening?

4. How can a device operate on 26VAC OR 26VDC when the supply is the same terminal for both. Or in other words i can plug 26Vac into the same terminal as I can plug 26VDC into. Can a bridge rectifier pass DC without any other modifications? This question is in regard to LED lighting systems.

1. What makes an AC current rating different from a DC current rating? I was taught that AC crating were always given in Root Mean Square (RMS), and that RMS is the DC equivalent.

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RMS and DC are not equivalent.

DC are average values, sum of the samples / # of samples.
DC = (V1 + V2 + V3...+Vn) / n

RMS are the root of the mean(average) of the squares of the samples
RMS = sqrt( (V1^2 + V2^2 + V3^2 ...+ Vn^2) / n)

AC are often expressed in RMS because the DC value of any pure sinusoidal signal is always 0.

2. Why are technicians taught electron flow, but engineers are taught conventional?

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I'm not aware of this thing, I thought most technicians know the conventional . One reason why engineers are taught conventional might be because formula works on conventional flow

3. I've seen some schematics here that have diodes with the arrow facing away from an IC output. In electron flow, they teach that current flows in the direction opposite the arrow. Meaning the current is flowing into the IC output.... why would that be desirable? I just learned the term sinking... is that what is happening?

Click to expand...

In conventional flow we call it sourcing. sometimes we want to allow current to flow on one direction(look for ORing diode configuration) that's why we use a diode to do the job.

4. How can a device operate on 26VAC OR 26VDC when the supply is the same terminal for both. Or in other words i can plug 26Vac into the same terminal as I can plug 26VDC into. Can a bridge rectifier pass DC without any other modifications? This question is in regard to LED lighting systems.

Click to expand...

Yes bridge rectifier can pass DC. If you can recall, a bridge rectifier converts AC to DC and it has no problem if DC is supplied on its input.

ClickKlick said:

1. What makes an AC current rating different from a DC current rating? I was taught that AC crating were always given in Root Mean Square (RMS), and that RMS is the DC equivalent.

Click to expand...

They are equivalent from a power viewpoint. The RMS voltage or current value of an AC waveform generates the same power into a resistive load as the same value DC voltage or current.

ClickKlick said:

1. What makes an AC current rating different from a DC current rating? I was taught that AC crating were always given in Root Mean Square (RMS), and that RMS is the DC equivalent.

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Depends on what the device.
Switches for example have AC and DC ratings which are usually very different.
This is to do with the current breaking capacity of the switch.
When breaking a current, an arc will be drawn, if the current flow is AC the current will drop to zero every half cycle and the arc will extinguish very easily. If the current is DC however, the arc will be maintained until the switch contacts are a large distance apart, and the arc will burn the contacts.

ClickKlick said:

2. Why are technicians taught electron flow, but engineers are taught conventional?

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I did not know that they were.
Conventional current is a convenient way of referring to the current flow and flows from +ve to -ve in a circuit. (Probably because the early electrical pioneers had not sussed out electron flow yet.
Electron flow on the other hand is essential to understanding the operation of devices like valves and transistors.

ClickKlick said:

3. I've seen some schematics here that have diodes with the arrow facing away from an IC output. In electron flow, they teach that current flows in the direction opposite the arrow. Meaning the current is flowing into the IC output.... why would that be desirable? I just learned the term sinking... is that what is happening?

Click to expand...

No idea, show an example.

ClickKlick said:

4. How can a device operate on 26VAC OR 26VDC when the supply is the same terminal for both. Or in other words i can plug 26Vac into the same terminal as I can plug 26VDC into. Can a bridge rectifier pass DC without any other modifications? This question is in regard to LED lighting systems.

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If a device requires 26vac, it will almost certainly operate from 26vdc, (assuming that there is no transformer on the input).
If the device requires 26vdc, it is almost certain that it will not operate from 26vac.
You must study the circuit to be sure.

JimB

Electrical Engineering and Physics also disagree regarding how to represent current flow. The Physics people will tell you EE's are still wet behind the ears ,and Physics is a much older discipline, which just happened to give birth to Electrical Engineering.

We were taught that the RMS value of a waveform would produce the same heating effect as its equivalent DC value.

ericgibbs said:

We were taught that the RMS value of a waveform would produce the same heating effect as its equivalent DC value.

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Which is probably the best explanation, we were taught that too.

Ok that helps. Thanks

I finished my AAS degree in Electronics Technology so I could be a Technician and I learned everything in electron flow.

One more question.

Using a True RMS Power Analyzer, bench meter, to take V, A, and W measurements between a metal halide ballast and the lamp. The VA reading and the W reading are always different. For example, a 39W metal halide ballst is powering a 39W lamp. The VA reading is 39, but the W reading is 80. Shouldn't the VA and W reading be the same?

ClickKlick said:

4. How can a device operate on 26VAC OR 26VDC when the supply is the same terminal for both. Or in other words i can plug 26Vac into the same terminal as I can plug 26VDC into. Can a bridge rectifier pass DC without any other modifications? This question is in regard to LED lighting systems.

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ONLY if it is talked in terms of RMS value of AC and not peak value.

In military electronics schools, vo-tech schools .... schools that are producing technicians .... electron flow theory is taught. It's easier to explain some things.

In college as an EE major, conventional flow was taught. Solid state device symbols were designed so that the arrows "work right" with conventional flow. Sourcing and sinking are conventional terms. And along with conventional theory, we were taught that the electron flow was in the opposite direction of current flow.

I think you can argue either method and come to a draw. The bottom line is, do you understand the electronics and can you work in your chosen system successfully?

AC current rating vs. DC current rating for CONTACTS of switches, relays, etc. definitely are different!

Dean