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capacitance related to amperage...

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Russlk said:
Ron: I liked your previous picture much better!
Thanks, Russ! Do you mean Mars face (which I had up for a couple of days), or the Tonto picture? That was actually my son, who is a full-blooded gringo. Before Tonto, there was a picture of me in my gold-prospecting getup, and before that, the Mars face again.
I'm having an identity crisis!:eek:
 
whiz115 said:
guys i have downloaded the LTspice...please help me to setup a simulation! :)
Copy this code and paste it into Notepad, then save it in the SwCADIII directory as fullwave rectifier.asc.
Then start up LTspice and run this file. After it runs, a window will pop up with choices of node voltages and branch currents to probe. Probe v(out) to start.
Then you can experiment with component values, etc.
Code:
Version 4
SHEET 1 880 680
WIRE 128 0 128 -48
WIRE 128 192 128 80
WIRE 224 80 224 64
WIRE 272 -48 128 -48
WIRE 272 -16 272 -48
WIRE 272 64 224 64
WIRE 272 64 272 48
WIRE 272 96 272 64
WIRE 272 192 128 192
WIRE 272 192 272 160
WIRE 384 -48 272 -48
WIRE 384 -16 384 -48
WIRE 384 64 384 48
WIRE 384 96 384 64
WIRE 384 192 272 192
WIRE 384 192 384 160
WIRE 544 64 384 64
WIRE 544 96 544 64
WIRE 544 192 544 160
WIRE 592 64 544 64
WIRE 672 64 592 64
WIRE 672 96 672 64
WIRE 672 192 672 176
FLAG 224 80 0
FLAG 544 192 0
FLAG 672 192 0
FLAG 592 64 out
SYMBOL voltage 128 -16 R0
WINDOW 3 -177 101 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(0 17 50)
SYMATTR InstName V1
SYMBOL diode 368 -16 R0
SYMATTR InstName D1
SYMATTR Value 1N4001
SYMBOL diode 256 96 R0
WINDOW 3 133 65 Left 0
SYMATTR InstName D2
SYMATTR Value 1N4001
SYMBOL diode 288 48 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D3
SYMATTR Value 1N4001
SYMBOL diode 400 160 R180
WINDOW 0 24 72 Left 0
WINDOW 3 136 -2 Left 0
SYMATTR InstName D4
SYMATTR Value 1N4001
SYMBOL cap 528 96 R0
SYMATTR InstName C1
SYMATTR Value 4000µ
SYMBOL res 656 80 R0
SYMATTR InstName R1
SYMATTR Value 15
TEXT 202 242 Left 0 !.tran 50m
 
Ron H said:
Copy this code and paste it into Notepad

thank you Ron H! you're great guy! :D

while i was waiting your reply i tried to play with LTspice and i almost
did the simulation by myself! it looks very close to what you did...with
some mistakes ofcourse! check it if you want! it's my first time working
this program... and i think it's very cool :) i'm very new and i don't know...are there any better than this? :rolleyes:

to the subject...
experimenting with the code you just gave me i realized that too much
capacitance it doesn't solve the problem with ripple noise, there is a limit
and after that it's pointless! am i correct?

please tell me what is V(n001) V(n002)?

I(C1) probably it's the current in the capacitor, but why i see spikes
every 10ms? :confused: (sorry...probably it's very stupid question...
but i can't understand what i see there)

how accurate is this program?

here's my code! :p :)

Code:
Version 4
SHEET 1 880 680
WIRE 432 32 32 32
WIRE 592 32 432 32
WIRE 240 64 -304 64
WIRE 32 128 32 32
WIRE 96 128 32 128
WIRE 240 128 240 64
WIRE 240 128 160 128
WIRE 592 160 592 32
WIRE -304 176 -304 64
WIRE 432 176 432 32
WIRE 32 192 32 128
WIRE 240 192 240 128
WIRE 32 208 32 192
WIRE 432 240 432 224
WIRE 32 320 32 256
WIRE 96 320 32 320
WIRE 240 320 240 256
WIRE 240 320 160 320
WIRE 432 320 432 240
WIRE 432 320 240 320
WIRE 592 320 592 224
WIRE 592 320 432 320
WIRE -304 384 -304 256
WIRE -80 384 -304 384
WIRE 32 384 32 320
WIRE 32 384 -80 384
WIRE -80 480 -80 384
FLAG -80 480 0
SYMBOL voltage -304 160 R0
WINDOW 123 24 132 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value2 AC 12
SYMATTR InstName V1
SYMATTR Value SINE(0 12 60)
SYMBOL schottky 96 144 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D1
SYMATTR Value MBRS1100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky 96 304 M90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D2
SYMATTR Value MBRS1100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky 48 192 M0
SYMATTR InstName D3
SYMATTR Value MBRS1100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky 256 192 M0
SYMATTR InstName D4
SYMATTR Value MBRS1100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL polcap 416 176 R0
WINDOW 3 24 64 Left 0
SYMATTR Value 4700µ
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=50 Irms=2 Rser=0.041 MTBF=2000 Lser=0 ppPkg=1
SYMBOL res2 576 160 R0
SYMATTR InstName R1
SYMATTR Value 30
SYMATTR SpiceLine tol=1 pwr=5
TEXT -208 504 Left 0 !.tran 1
 
whiz115 said:
thank you Ron H! you're great guy! :D

while i was waiting your reply i tried to play with LTspice and i almost
did the simulation by myself! it looks very close to what you did...with
some mistakes ofcourse! check it if you want! it's my first time working
this program... and i think it's very cool :) i'm very new and i don't know...are there any better than this? :rolleyes:
Your code gives me an "unknown schematic syntax" error, but the "retry" option worked. Don't know what that's all about.
You should move your ground symbol to the bottom end of the cap/resistor if you want to simulate a transformer driving a bridge rectifier.

to the subject...
experimenting with the code you just gave me i realized that too much
capacitance it doesn't solve the problem with ripple noise, there is a limit
and after that it's pointless! am i correct?
Not sure what you mean. More cap gives less ripple. Caveat: Huge capacitors can cause very high peak currents (see below). These can damage the diodes and/or the capacitor, and can cause EMI (electromagnetic interference).

please tell me what is V(n001) V(n002)?
They are the voltages at the terminals of the voltage source. Have you discovered how to probe with the mouse?

I(C1) probably it's the current in the capacitor, but why i see spikes
every 10ms? :confused: (sorry...probably it's very stupid question...
but i can't understand what i see there)
In order for the cap to recharge every half cycle, high-current spikes must flow through the rectifiers and into the capacitor. Probe the diode currents to see what I mean.

how accurate is this program?
Only as accurate as the models of the components. For simple circuits like this, it's pretty good, although the high peak currents involved can cause problems in a real circuit if you don't build it to handle them.
 
Ron H said:
Only as accurate as the models of the components. For simple circuits like this, it's pretty good, although the high peak currents involved can cause problems in a real circuit if you don't build it to handle them.
PLEASE take a look at the RMS current in the capacitor! Most caps your voltage formulas etc are going to have you choosing will burn themselves up!

D.
 
Ron H said:
Not sure what you mean. More cap gives less ripple. Caveat: Huge capacitors can cause very high peak currents (see below). These can damage the diodes and/or the capacitor, and can cause EMI (electromagnetic interference).

i saw that huge capacitance does not improve ripple rejection... :rolleyes:
also i have never thought that huge capacitors can damage the power supply! so... if i want to charge very big capacitors, my transformer and my rectification bridge must support it or else i'll burn them...right?
LTspice is not capable to report an error in this case?

Ron H said:
They are the voltages at the terminals of the voltage source. Have you discovered how to probe with the mouse?

YES! and it's very cool function! :)

Ron H said:
In order for the cap to recharge every half cycle, high-current spikes must flow through the rectifiers and into the capacitor. Probe the diode currents to see what I mean.

how much current a capacitor will draw and then be able to supply it
it depends on the voltage...so at 12V if we use 1uF=3,5mA someone told that before and he was right! what i knew (1uF=1mA) is totally wrong!

Ron H said:
Only as accurate as the models of the components. For simple circuits like this, it's pretty good, although the high peak currents involved can cause problems in a real circuit if you don't build it to handle them.

well...i tried to change source voltage at 12V and after rectification i had again almost 12V! the only thing i have changed are the diodes with schottky 45V/7,5A because i had the same problem you had when you tried to open my code.
 
Last edited:
whiz, I think you need to go back to basics and learn how capacitors work because there is no relation between capacitance and current like you're suggesting. A 1uF capacitor can provide pulses of current limited only by it's series resistance (which can be very low)
For example a 1u capacitor charged to 12 volts and then discharged through a 1 ohm load will provide 12amps of current exponentially decaying the voltage and current to about 1 volt in about 2.5 micro seconds. The same capacitor discharged through a 100 ohm load will take 250 micro seconds to discharge, because the current is lower so it lasts longer. When a capacitor discharges it's voltage, and hence current decay exponentially.
 
whiz115 said:
:confused: :confused:

why? i think it's irrelevant if i use regulator or what is the input voltage,
i think a capacitor can charge to any voltage within it's limits,
as i said before, someone told me that 1uF=1mA...if we have 1uF capacitor
it can keep charge of 1mA and i just want to ask if this is the actual ratio...

if you need to know voltage...ok let's say 12V but i don't understand what's
the point... :)
1uF=1ma is a common rule of thumb, nothing more.

Capacitors have internal resistance losses that precipitate a max RMS current rating which varies with operating temperature beyond which internal heating degrades the capacitor.

The simulations being suggested by others are concentrating on ripple voltage and it's effect on output regulation, if you do not want it to self destruct, you need to look at the ripple current rating. All the other suggestions here are tending toward smaller unreliable solutions.

Did you ever wonder why the caps are so big? It is not for the ripple voltage, it is to reduce the ESR to the point that the things won't burn up.

D.
 
LTspice helps me much! :) although i have downloaded TINA (which i haven't used it yet.) i didn't knew about SPICE programs up to now!!!
this program can help me shorten my knowledge gaps alot!!

unfortunately it has poor library...and i don't know how to add more components...Yesterday playing with Ron H's code...i was very disappointed when i was trying to find a suitable diode for my simulation and i couldn't find one! :eek:

a second problem that i noticed is when i ran Ron H's code, the voltage before and after rectification was almost the same.... and not something like that:
12*1,41= 16,92V :eek:

and something which i noticed today...is that even if i lower "resistor Wattage"
it doesn't affect the circuit. I have used a load resistor wattage for my experiment which in reality should be blown!!! and in the simulation nothing happend! :eek:
 
This is a classic example of how simulators get people into trouble. If you don't understand electronics, simulators will only confuse you. As I said before, garbage in=garbage out.
Whiz, simulators will allow you to run sims (and they will seem to work just fine) that, if built in hardware, would go up in smoke. They are not a substitute for education and common sense.
I'm not sure why SwCAD III includes wattage in the resistor definition box. As far as I know, it has no relevance to the simulation.
Cadstarsucks has good advice about ESR and the possibility of destroying your capacitors. BTW, Cadstarsucks, in my own defense, I DID say
Caveat: Huge capacitors can cause very high peak currents (see below). These can damage the diodes and/or the capacitor, and can cause EMI (electromagnetic interference).
 
whiz115 said:
a second problem that i noticed is when i ran Ron H's code, the voltage before and after rectification was almost the same.... and not something like that:
12*1,41= 16,92V :eek:

Almost the same?? :eek: Where did you put the probe? and what do you see?

Try this: place two labels (a and b) at the pins of the generator. Run the simulation and click on "Add Trace". Write V(b)-V(a) in the edit box. You'll see a 12 Vrms sine wave.
 
Ron H said:
I'm not sure why SwCAD III includes wattage in the resistor definition box. As far as I know, it has no relevance to the simulation.
I also think that it has no relevance.
But you can plot the power dissipation. Have you tried to hold down the Alt key and move the mouse over a resistor? :)
 
Ron H said:
This is a classic example of how simulators get people into trouble. If you don't understand electronics, simulators will only confuse you. As I said before, garbage in=garbage out.
Whiz, simulators will allow you to run sims (and they will seem to work just fine) that, if built in hardware, would go up in smoke. They are not a substitute for education and common sense.
I'm not sure why SwCAD III includes wattage in the resistor definition box. As far as I know, it has no relevance to the simulation.
Cadstarsucks has good advice about ESR and the possibility of destroying your capacitors. BTW, Cadstarsucks, in my own defense, I DID say
Not a problem. I was not accusing you of anything, just trying to make sure there were no surprise fireworks ;)

I had, however, missed the capacitor phrase in your warning about emi and blowing diodes.

It is interesting to note that diodes tend to be more robust that the capacitors and do not tend to be effected by RMS current but average. It has a lot to do with the p=i2r in the cap as opposed to the p=ei in the diode. That little 2 can be a real nuisance! :)

D.
 
yes.. and since power is proportional to i^2, what about splitting the input capacitor into two capacitors in parallel to achieve the same value? The ripple current would be shared between the two caps.
 
Simulators don't get people into trouble, people get people into trouble. You should NEVER implicitly trust a circuit that works in a simulator without first considering the real world component, environment, and parasitics, all that fun stuff the same goes for any circuit provided by another person or website. Spend enough time working with basic circuits in a simulator and building them on a breadboard and comparing performance and why they differ is a great learning experience though.
 
Last edited:
eng1 said:
yes.. and since power is proportional to i^2, what about splitting the input capacitor into two capacitors in parallel to achieve the same value? The ripple current would be shared between the two caps.
That is indeed common practice. In production supplies it is often a balancing act between ratings and prices...as better parts come down in price the older ones get switched out.

D.
 
eng1 said:
Almost the same?? :eek: Where did you put the probe? and what do you see?

Try this: place two labels (a and b) at the pins of the generator. Run the simulation and click on "Add Trace". Write V(b)-V(a) in the edit box. You'll see a 12 Vrms sine wave.

input is the same as the output...12V at the source, 12V after rectification.
i haven't found the "Add trace" where is it?
btw eng1 i found the thermometer! :) now the "resistor power rating" is useful
but it should show an error or an alarm in cases that the rating is not appropriate...

Discovering the thermometer makes me believe that the program has many hidden parameters! for example if you right click on the capacitor you can see a list of them...i can even add ESR value and many others so i believe i can see exactly what's happening with the circuit and check many of the aspects you're talking about... i might be wrong with that too...as i was with some others things before! but don't forget that i'm trying hard to learn some things and i think you could help more than a book or website to boost my try! because here i have the opportunity to ask questions! :)

btw i'm computer science student and not electronics...many things i'm sourcing from my school and from fellow students or friends...but i just can't ask all the time teachers or friends. :rolleyes:

can you help me add more components to the library?
 
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