"ABC hits harder than XYZ set at the same voltage..."

[AttyPops]

I was with ya zoiDman until that last post. MORE JOKES, less water boiling.

Don't make me get my paper cup and start boiling stuff......it's too late at night for me.

 

[Rocketman]

For a 50% duty cycle, 700hz waveform, and a loaded max of 7.4 volts, the RMS voltage applied to a load is 5.23 volts.
The average voltage for this 50% Duty Cycle waveform (what a cheap metering circuit will indicate) is 3.7 volts.
For an indicated 3.7 volts, it's hitting like 5.23 volts because it IS 5.23 volts.

For a Duty Cycle of 30%, the RMS voltage applied to the load would be 4.68 volts and the indicated/set voltage of an average indicating meter circuit would be 2.96 volts.

AVERAGE to RMS voltage errors will increase as duty cycle is decrease
(7.4v @ 10% duty cycle is 2.34vRMS and 0.74 average volts)
At a high duty cycle the Average voltage approaches the true RMS value
(7.4v @ 95% duty cycle is 7.21vRMS and 7.03 average volts)

With cycle times of 1 to 16 milliseconds (1KHz to 60Hz) power integration of a heater is fairly uniform. (Turn your stove top ON and OFF 1000 times a second )

If a PWM device "Hits Harder" than a DC device, at the SAME volts,

The VOLTS AIN'T THE SAME

RMS voltage is used to calculate heater circuit from central heating units in your home to temperature controlled precision measuring instruments. PWM is NOT NEW SCIENCE.

 

[zoiDman]

Best... post... ever...

And if I was drinking, I would have liked it even more.


I'm not saying I agree or disagree, but that's neither here nor there.
And although I was a physics minor in college, I thought Maxwell was a ..........

And differential equations? Yikes!!
I got a solid B grade in that class, and I never knew what the hell I was doing.

Yeah, I understand that Maxwell wasn't much Fun at Parties. But he Did Unify Electricity and Magnetism. And he did it in Only Four Very Simple Equations. I guess if you figured up out How ANYTHING Electro-Magnetic and the Equations can be written on a T-Shirt, you're not All Bad.

And Trust me, Nobody Like Dif-Eq. Especially those who have to teach it every Now and Again.

 

[AttyPops]

So... RMS is usually used for AC applications, no? Otherwise, AC would "average" out to near zero. I looked up RMS earlier but the forum I looked at said something about "%duty X Vin = RMS reading for DC" so I ignored the whole RMS thing.

How did you calc that?

 

[AttyPops]

Yeah, I understand that Maxwell wasn't much Fun at Parties. But he Did Unify Electricity and Magnetism. And he did it in Only Four Very Simple Equations. I guess if you figured up out How ANYTHING Electro-Magnetic and the Equations can be written on a T-Shirt, you're not All Bad.

And Trust me, Nobody Like Dif-Eq. Especially those who have to teach it every Now and Again.

Jokes. That's better....way to contradict yourself!

 

[Wishdog]

OK, the off topic police can repremand me. Two lame jokes:

An engineer, a mathematician, and a physicist are each presented with a beautiful woman and the stipulation that at each time interval, they may move half of the remaining distance towards her.

The mathematician concludes that after N iterations there will be 8 divided by 2^N feet remaining which will never equal zero so he gives up on the spot.

The physicist opines that if each iteration requires a finite amount of energy then the energy expended in the approach will be inversely proportional to the distance remaining and gives up on the spot.

The engineer says "8 feet, 4 feet, 2 feet, 1 foot, 6 inches, good enough for practical purposes".

An engineer, a mathematician, and a physicist are testing the theory that all odd numbers are prime.

Physicist: "1 is prime, 3 is prime, 5 is prime, 7 is prime, 9 - must be experimental error, 11 is prime, 13 is prime. That's enough data points; the theory is true."

Mathematician: "By convention, 1 is not prime, but 3 is prime, 5 is prime, and 7 is prime. Using mathematical induction, we can infer that all odd numbers are prime."

Engineer: "1 is prime, 3 is prime, 5 is prime, 7 is prime, 9 is prime, 11 is prime, 13 is prime, 15 is prime, 17 is prime, 19 is prime... Hmmm, theory appears to be true."

Edited to add (cause I always have to edit to add stuff): http://www.farmdale.com/emp-jokes.shtml

 

[thinkingaboutit]

Same setup exactly on different pv's? And different vapes? This is the intangible that most engineers deny. Must be the gods. Seriously, though, what is it?

I think it's really easy to explain. One of them was not actually putting out 4.5 volts. Maybe both of them weren't. I have no idea the duty cycle of either. I really don't care as long as I don't pick up a cig because they keep me happy.

 

[Rocketman]

How many remember the same discussions about the old eGo?
How many called it a 3.2 volt device.
It ain't. 3.2 volts don't vape. Or, hardly don't vape
Now we have stacked battery PWM devices and the confusion starts all over again.
I've even seen 9 volts Peak to Peak claimed as the reason ABC hits harder.
(the 9 volts Peak to Peak is poor application of the measuring instrument).

With a good set of cells the first few hits might be 8 volts (4 volts per cell, loaded).
Unloaded test have no purpose in evaluating how a device hits.

 

[DC2]

Yeah, I understand that Maxwell wasn't much Fun at Parties. But he Did Unify Electricity and Magnetism. And he did it in Only Four Very Simple Equations. I guess if you figured up out How ANYTHING Electro-Magnetic and the Equations can be written on a T-Shirt, you're not All Bad.

And Trust me, Nobody Like Dif-Eq. Especially those who have to teach it every Now and Again.

Most of the cool kids in physics did things in ONE equation.


Reminds me of the time I had a physics professor (waves and light) who said we could bring to the final a cheat sheet with three equations.
I brought a cheat sheet with only one equation.

It went something like this...

(E - MC2) + (g - 9.8 m/s2) + (F - MA) + (V - IR)................................................... = 0

Anyway, you get the picture.

I showed it to the teacher before class, because it was a full page, and I didn't want to get busted.
He said I could use it, and I think he was very impressed.

 

[zoiDman]

OK, the off topic police can repremand me. Two lame jokes:





Edited to add (cause I always have to edit to add stuff): Mike Schuh's collection of engineer-mathematician-physicist jokes

I consider myself duly put is his Place. No more Boil Water Sa-nair-re-o’s.

 

[Stosh]

The way I understand the difference (and it could be way off base) it PWM switches the duty cycle between the battery max voltage and 0 volts to produce an average. Switched regulation, when you push the button will go up to the set voltage, say 4.2V, when it gets to 4.22V it switches off until it drops to 4.18, switches on.....etc.

This gives the switched voltage a stable voltage at a set level, like producing 5V logic power for IC / computer type supplies where a very steady voltage is required, minimum ripple.

The PWM is more like sticking one hand in ice water and the other in boiling water, it averages out to nice warm water...

 

[zoiDman]

...
The PWM is more like sticking one hand in ice water and the other in boiling water, it averages out to nice warm water...

Did I hear Water? Boiling Water?

 

[AttyPops]

Rocket is ignoring me. Not the 1st time.

So for DC voltage..... RMS voltage <> %duty x Vin? Guess the forum was wrong.

Did I hear Water? Boiling Water?

Wow. Humor AND boiling water in the same post.
Score one for zoiDman

 

[Rocketman]

I think one of the reasons people find RMS hard to grasp is the AC volts applications.
With your household 60HZ AC the voltage changes direction but a dumb device like a heater or incandescent bulb don't know it. To the heater it's just a really rounded 120 Hz PWM waveform. When you do pretty much the same thing with a squared off waveform, duty cycle comes into play.


and Stosh, pretty good explanation of a switching regulator.

 

[Rocketman]

Rocket is ignoring me. Not the 1st time.

So for DC voltage..... RMS voltage <> %duty x Vin? Guess the forum was wrong.



Wow. Humor AND boiling water in the same post.
Score one for zoiDman

Sorry, didn't mean to

Square root of Duty Cycle (like 0.1, or 0.3, or 0.9) times max volts.



This button

 

[Stosh]

Thanks Rocketman although I think zoiDman like the PWM better.....

You were right on with the old eGo discussions, it's like the bumblebee, all the equations, measurements, studies prove it can't fly....but nobody told the bumblebee.

 

[Wishdog]

The PWM is more like sticking one hand in ice water and the other in boiling water, it averages out to nice warm water...

A physicist, an engineer, and a statistician were out game hunting. The engineer spied a bear in the distance, so they got a little closer. "Let me take the first shot!" said the engineer, who missed the bear by three metres to the left. "You're incompetent! Let me try" insisted the physicist, who then proceeded to miss by three metres to the right. "Ooh, we got him!!" said the statistician.

 

[AttyPops]

I'm tell'n ya... I looked it up. See? Equivalent DC voltage of a PWM signal

Guess they are physicists... and accept 2 sigma answers.
They didn't even use the

button.

 

[zoiDman]

Thanks Rocketman although I think zoiDman like the PWM better.....

...

Heck, I'm still trying to figure out why My Square Root button Doesn't work with Negitive Numbers?

 

[AttyPops]

Imagine........