prices for transistors just doesnt make sense

[tooki]

I suppose so. But like the load banks and track resistors, that is an application well afield of electronics. Even calling those “power electronics” is a stretch.

[tooki]

you combine resistors with transistors and it makes them work better.   if u need to invert a transistor, u need a resistor, if you need to delay, u need a cap,  this is ordinary stuff.  i do alot wierder things with them.

Kinda sorta. “Work better” is certainly not how I’d word it.


Nonetheless, do you understand that, say, if you were making a power supply capable of supplying a megawatt, that this doesn’t mean you’d be using megawatt resistors to build it??

Do you understand the example I have with the MOSFETs? Yes or no, simple question.

[rstofer]

A car can be moved with under a hundred Watts, albeit very slowly.

The DC motor in the Chevy Bolt is 149 kW or 200 HP.  The thing is, the lag between throttle off and full power is nearly instantaneous.  The gasoline engine doesn't come up to full horsepower until the RPM is near max.  The Bolt can be quite sporty!

[rstofer]

I suppose so. But like the load banks and track resistors, that is an application well afield of electronics. Even calling those “power electronics” is a stretch.

My fuel rod example above was phase angle fired IGBTs in a tightly controlled PID loop.  There were actually 2 parallel locomotive drives controlled by the test platform.  Mostly electrical but definitely electronic control.

[Capernicus]

you combine resistors with transistors and it makes them work better.   if u need to invert a transistor, u need a resistor, if you need to delay, u need a cap,  this is ordinary stuff.  i do alot wierder things with them.

Kinda sorta. “Work better” is certainly not how I’d word it.


Nonetheless, do you understand that, say, if you were making a power supply capable of supplying a megawatt, that this doesn’t mean you’d be using megawatt resistors to build it??

Do you understand the example I have with the MOSFETs? Yes or no, simple question.

I dont know exactly,   so I'm down a few points there.    But I know that low resistances heat up more than high resistances with the same wattage, and not all your power is going down the whole thing,  Alot of the time I end up with 1 fried resistor and the rest are ok.

But I think I'm missing a piece of knowledge here to answer your question properly.

[TimFox]

At my previous employer, we bought a custom precision linear power supply from Danfysik (in Denmark) to supply 250 A into a 1 ohm electromagnet load (250 V) for 62.5 kW output power.  (They used one of their DCCTs to achieve better than 1 ppm stabilization.). The pass transistor used maybe 100 2N3772 TO-3 NPNs on a water-cooled plate.  The pre-regulator was a servo-controlled variac ahead of the rectifier to keep the V_CE at a few volts.  Each transistor had a fuse in the emitter, and an interlock to allow operation with less than 10% of the transistors failed.
It was expensive.

[TimFox]

you combine resistors with transistors and it makes them work better.   if u need to invert a transistor, u need a resistor, if you need to delay, u need a cap,  this is ordinary stuff.  i do alot wierder things with them.

Kinda sorta. “Work better” is certainly not how I’d word it.


Nonetheless, do you understand that, say, if you were making a power supply capable of supplying a megawatt, that this doesn’t mean you’d be using megawatt resistors to build it??

Do you understand the example I have with the MOSFETs? Yes or no, simple question.

I dont know exactly,   so I'm down a few points there.    But I know that low resistances heat up more than high resistances with the same wattage, and not all your power is going down the whole thing,  Alot of the time I end up with 1 fried resistor and the rest are ok.

But I think I'm missing a piece of knowledge here to answer your question properly.

Why do you say that low resistance resistors heat up more than high restances at the same power?  That is true (all other things equal) at the same voltage , not power.

[dmills]

The pass transistor used maybe 100 2N3772 TO-3 NPNs on a water-cooled plate.  The pre-regulator was a servo-controlled variac ahead of the rectifier to keep the V_CE at a few volts.  Each transistor had a fuse in the emitter,

Distinct shades of old school ion laser power supplies, dozens of '3055s on a water cooled plate.
Trouble with those was always that the electronics was installed on a board below the cold plate, so when you shut down and the chilled water drove the cold plate below the dew point...

Yea made some decent bank back in the day rebuilding those things.

[tooki]

I dont know exactly,   so I'm down a few points there.    But I know that low resistances heat up more than high resistances with the same wattage, and not all your power is going down the whole thing,  Alot of the time I end up with 1 fried resistor and the rest are ok.

But I think I'm missing a piece of knowledge here to answer your question properly.

Thank you, now we’re getting somewhere. Remember, nobody here is trying to embarrass you or anything. But you did need to stop acting as if you understand everything, and coming in making grand claims about things you don’t actually understand.

Every single one of us here was a total beginner at some point, and gained knowledge over time. You will too and people here will help!


Your observations about resistors are partly correct. The wattage of a resistor is simply how much heat it can tolerate before it burns up. That’s independent of the value as such.

You sorta correct that, with voltage (not power!) held equal, a resistor of lower resistance will heat up more than one with a higher resistance. This is Ohm’s Law at work: as the voltage “pushes” current through the resistor, the lower resistance allows more current to flow, but also means a larger voltage drop. The larger current, according to the formula I gave earlier (P_loss=I²R)*, means more heat.

A higher value (resistance) resistor will heat up just as much, it just takes a higher voltage to do it. For example, 1A through a 10 ohm resistor, or 0.1A through a 1000 ohm resistor, both dissipate 10W. Within a product line, both of those resistors would be the same size and appearance, though their internal construction would differ. (And the voltages would differ: the voltage across the 10 ohm resistor would be 10V, while it’d be 100V across the 1000 ohm resistor.)

In a voltage divider, the voltage gets divided up proportionally among the resistors, as you know. The current, however, may not be the same across the branches of the divider. Since current is what causes the heating, the differing amounts of current through different branches is how you’ve ended up with some resistors fried and others fine.

That’s a great observation. The key now is to understand why and how it happens.


*this is known as Ohm’s power law. P_loss=I²R is basically shorthand for P_loss=V*I, referring not to the supply voltage, but to the voltage drop across the resistor. But to calculate the voltage drop is I*R, so we just substitute that into the formula, giving I*R*I, or I²R.

[Capernicus]

There is no voltage drop across a resistor, otherwise capacitors wouldnt even charge with a resistor in front of them.  how the hell would it ever equalize with the power supply if that was true.

But the high value resistor seems to die at a lower amount of amps than the low value resistor,  and thats what I initially thought would happen, because the low value resistor affects the value less, so it wont heat up as much.

BUT!

Nonintuitability strikes again,  and its the LOW VALUE resistor that takes the heat,  not the high value.

So I guess you guys are experts at making toaster ovens.  And that can help a great deal for more fancier technology as well, like nuclear reactors for example.

What about constant current circuits,  the amount of current is now the OPPOSITE of what the resistance is with a raw connection,  the lower the resistor the less current is there, and the more resistance the more current.  thats going to trick people when they read your circuit!  youll have to apologize for everything being backwards because it just had end being that way when everything ended up working.

But, I have a gift for u dudes,  perhaps something you do not know yet, as I thank you for bringing me up to speed on the wattage heat issue,  and its the fact that a resistor will not oppose any current until enough current has tried to force its way through it,  otherwise it will go through unaffected by the tighter pipe.

[rstofer]

But, I have a gift for u dudes,  perhaps something you do not know yet, as I thank you for bringing me up to speed on the wattage heat issue,  and its the fact that a resistor will not oppose any current until enough current has tried to force its way through it,  otherwise it will go through unaffected by the tighter pipe.

That claim contradicts Ohm's Law and it is a LAW; you can't treat it like a speed limit.

E = I * R
I = E / R
R = E / I

These 3 equalities hold.

P = I * E
P = I² * R
P = E² / R

These Power equalities also hold.

E in Volts
I in Amps
R in Ohms
P in Watts

[Capernicus]

But what if your supplying less current via PWM.

Im talking about loadless resistance, a lack of amps.


Another way Ohms Law doesnt hold is when the battery is out of omph, like during a short,  and it hasnt enough energy in it to fill the entire circuit,   least resistance gets it all. high resistance misses out.

Ohms law only holds for an ideal infinite power source.

Increasing the volts,   without increasing the amps,  the same thing.

[Manul]

Sadly, I think it's a case of a CPU core running under induced brownout.

[TimFox]

A resistor (a block with two leads) doesn’t know what the external circuit is:  it only knows the current through it and the voltage across it.  The ratio is the resistance (Ohm’s Law) and the product is the power dissipated in it.  “Voltage drop” is another term for the voltage across the resistor, which is the voltage between the two leads (whether wires, surface-mount terminations, or other terminals).

[Capernicus]

I don't trust the voltmetre. I think it reads lies,  I'm always careful when I look at that thing suspiciously and watch out for the electric shocks at the same time.

[rstofer]

Another way Ohms Law doesnt hold is when the battery is out of omph, like during a short,  and it hasnt enough energy in it to fill the entire circuit,   least resistance gets it all. high resistance misses out.

Ohms law only holds for an ideal infinite power source.

Increasing the volts,   without increasing the amps,  the same thing.

Norton's Theorem and Thevenin's Theorem explain all we need to know about internal resistance.
When we say E = I * R, we include ALL of the R in the circuit including the source output resistance.

The current goes down all of the branches in proportion to their resistance.  It you have 10 Ohms in parallel with 100 Ohms, you can expect the current through the 10 Ohm resistor to be 10 times the current through the 100 Ohm resistor.  That's because the same voltage is across each resistor.

E = I * R
E = 1V <= identical arbitrary voltage across each resistor
1V = 0.1A * 10 Ohms  <= the current through the 10 Ohm resistor (0.1 Amps)
1V = 0.01A * 100 Ohms <= the current through the 100 Ohm resistor (0.01 Amps)

You seriously need to take a DC Circuits class.

[rstofer]

But what if your supplying less current via PWM.

So what?  You do an RMS calculation on the PWM duty cycle and use that value for E.  You will get I_RMS for whatever resistance you use in E=I*R

Im talking about loadless resistance, a lack of amps.

In which case you are talking about 0 Volts.  Ohm's Law does hold, you just need to include all the resistance.

Another way Ohms Law doesnt hold is when the battery is out of omph, like during a short,  and it hasnt enough energy in it to fill the entire circuit,   least resistance gets it all. high resistance misses out.

Ohms law only holds for an ideal infinite power source.

Increasing the volts,   without increasing the amps,  the same thing.

For a given resistance, you can't increase the volts without increasing the amps.  Ohm's Law ALWAYS holds!  That's why it is a LAW, not a suggestion.

[Capernicus]

So.  let me draw a picture.
               
..................................-(neg)
......................................
.....................................|
.....................................|
.....................................|
..+(pos) -/switch  --100r-----100r---  +(pos)

ok so heres  a couple of 100r's with a switch on the left side.

I'm guessing that you guys think that when that switch closes, the absolute resistance drops given the two lines and more is asked of the battery to fill those lines.
And the battery will always have this power.

This is the flaw.

Sometimes, the battery hasnt got the PEAK OUTPUT required to fill both the lines. or if its a capacitor, it simply runs out.  and then something happens,  the resistance becomes relative.

Now,   youll get two lines with half the current each,  and it will use the ratio of the two resistances.

If it so happened to be this->


..................................-(neg)
......................................
.....................................|
.....................................|
.....................................|
..+(pos) -/switch  --1r---------100r---  +(pos)

now there is alot less resistance on the switch.

When this baby closes theres not enough power on jupiter to even run that line alone,   and the line with the resistor actually gets NILL current completely.


The smaller the battery you use,  the less absolute resistance is obeyed by the system,    and the resistors are now seen in a relative speed to each other,  who gobbles up the current first gets it all.


If you deliver a 1% PWM ratio to a circuit, with a big long gap,    this short pulse of energy  (Which can actually be any amount of amps, if its a very sharp loud pulse.)
Will be eaten up by the least resistance first,   and the higher resistance lines are so slow, they miss out on it completely.

The less amps given to the circuit,  the more relative the resistance becomes.


The extreme end of this,   is a 1 ohm resistor can actually pass equal current to a 10k resistor, if there isnt much supplied.   yes, the 1ohm resistor gets it alot quicker, but it just shoots through it like lightning with nothing after,  the 10k resistor, being slow as it is,  if its still able to contain that amount of current till the next pulse,  will the pass the same amount of amps as the 1ohm, but it goes through smoothly continuously over time.


Amazin' eh?

How the circuit is powered, is just as important as what the circuit is.



You can increase the volts without increasing the amps,  its what transformers do.

[TimFox]

"Ohms law only holds for an ideal infinite power source."

No.

[rstofer]

I hope a noob never sees this thread!   It will set them back decades in their understanding of circuits.

[tooki]

There is no voltage drop across a resistor, otherwise capacitors wouldnt even charge with a resistor in front of them.  how the hell would it ever equalize with the power supply if that was true.

But the high value resistor seems to die at a lower amount of amps than the low value resistor,  and thats what I initially thought would happen, because the low value resistor affects the value less, so it wont heat up as much.

BUT!

Nonintuitability strikes again,  and its the LOW VALUE resistor that takes the heat,  not the high value.

So I guess you guys are experts at making toaster ovens.  And that can help a great deal for more fancier technology as well, like nuclear reactors for example.

What about constant current circuits,  the amount of current is now the OPPOSITE of what the resistance is with a raw connection,  the lower the resistor the less current is there, and the more resistance the more current.  thats going to trick people when they read your circuit!  youll have to apologize for everything being backwards because it just had end being that way when everything ended up working.

But, I have a gift for u dudes,  perhaps something you do not know yet, as I thank you for bringing me up to speed on the wattage heat issue,  and its the fact that a resistor will not oppose any current until enough current has tried to force its way through it,  otherwise it will go through unaffected by the tighter pipe.

Oh, honey… you need to shush before you make yourself look silly!

Voltage drop is real, and easily measured. It’s how voltage dividers work. And of course a cap can charge via a resistor (and remember, since everything has parasitic resistance, every cap does charge and discharge through a resistance). Look up RC time constants…

I understand where you’re coming from regarding resistance vs heating; as a kid, I intuitively expected the same. But once I learned more, I learned how the opposite is the case. Heating is the result of current and resistance, and a lower resistance allows more current to flow. It’s that simple. I’ve explained it to you twice.

You have no idea what a constant current circuit is.

I’m coming to realize that I don’t think you actually understand what current is.

Your “gift” is random electrical words put near each other. They don’t make any sense as a whole.

But what if your supplying less current via PWM.

Im talking about loadless resistance, a lack of amps.


Another way Ohms Law doesnt hold is when the battery is out of omph, like during a short,  and it hasnt enough energy in it to fill the entire circuit,   least resistance gets it all. high resistance misses out.

Ohms law only holds for an ideal infinite power source.

Increasing the volts,   without increasing the amps,  the same thing.

Complete and utter nonsense.

So.  let me draw a picture.
               
..................................-(neg)
......................................
.....................................|
.....................................|
.....................................|
..+(pos) -/switch  --100r-----100r---  +(pos)

ok so heres  a couple of 100r's with a switch on the left side.

I'm guessing that you guys think that when that switch closes, the absolute resistance drops given the two lines and more is asked of the battery to fill those lines.
And the battery will always have this power.

This is the flaw.

Sometimes, the battery hasnt got the PEAK OUTPUT required to fill both the lines. or if its a capacitor, it simply runs out.  and then something happens,  the resistance becomes relative.

Now,   youll get two lines with half the current each,  and it will use the ratio of the two resistances.

If it so happened to be this->


..................................-(neg)
......................................
.....................................|
.....................................|
.....................................|
..+(pos) -/switch  --1r---------100r---  +(pos)

now there is alot less resistance on the switch.

When this baby closes theres not enough power on jupiter to even run that line alone,   and the line with the resistor actually gets NILL current completely.


The smaller the battery you use,  the less absolute resistance is obeyed by the system,    and the resistors are now seen in a relative speed to each other,  who gobbles up the current first gets it all.


If you deliver a 1% PWM ratio to a circuit, with a big long gap,    this short pulse of energy  (Which can actually be any amount of amps, if its a very sharp loud pulse.)
Will be eaten up by the least resistance first,   and the higher resistance lines are so slow, they miss out on it completely.

The less amps given to the circuit,  the more relative the resistance becomes.


The extreme end of this,   is a 1 ohm resistor can actually pass equal current to a 10k resistor, if there isnt much supplied.   yes, the 1ohm resistor gets it alot quicker, but it just shoots through it like lightning with nothing after,  the 10k resistor, being slow as it is,  if its still able to contain that amount of current till the next pulse,  will the pass the same amount of amps as the 1ohm, but it goes through smoothly continuously over time.


Amazin' eh?

How the circuit is powered, is just as important as what the circuit is.



You can increase the volts without increasing the amps,  its what transformers do.

More complete and utter nonsense.

[Capernicus]

If you count the off periods of the PWM as infinite resistance maybe it holds true to ohms law,  I haven't thought about it yet.

It's funny that you guys dont believe in me,  But boy do I believe in myself!!!

I've been a little slow, and its actually been about 5 years, and I haven't finished an oscillator yet, but when I get it, I'm not going to be average and just leave it there as a set of christmas lights, I'm going all the way to a full pipelined asic.   Its going to be great.

Its actually not that hard,   a ttl pipelined asic is doable by anyone, especially with fpga experience.     you can get the whole machine plotted tiny little and gates, im sure you can fit 10,000 on a pcb one sided,  but I dont want to buy parts for my stuff.

I'm going to do all my design in open-scad, circuit, bodywork, everything,  my favorite CAD software,  because I've been coding for a good 17 or so years now,   and I am going to fire into hardware, frizzly resistorz.   And script modelling is good for people that have been pretty much typing more lines ever since being an insubbordinate student in primary school.

https://openscad.org/   <-decent program.


And im going to undercut china single handed.    But sillyness aside, I think china or anyone else dont really care,  theyve got all their own technology as well...   but I'm gonna kickass for the OZZIES.

[tooki]

If you count the off periods of the PWM as infinite resistance maybe it holds true to ohms law,  I haven't thought about it yet.

Clearly. I’m skeptical about the “yet” part, as that implies it might happen later.

It's funny that you guys dont believe in me,

I can’t imagine why…

But boy do I believe in myself!!!

That much is evident. The unfounded confidence is… impressive!

[Simon]

So how much does someone actually pay for a 30k watt transistor?   

and how much power is that exactly?   I'm pretty sure you could move a car with that much power?

Sounds like you don't really know what you are talking about. what was the purpose of this thread again? Yea right now stuff is expensive, it's called supply and demand. As already pointed out 2 parts sold on ebay with free shipping is no comparison to a mainstream distributor, guess where the ebay seller get's them from. I did it too once, made a nice bit on the side!