Multisim 8 Glitch? Or Me? File Included

[adamthole]

I'm working on simulating a power supply in multisim. Currently all I have is the 120V source ran through a transformer, through a bridge diode, through a filter capacitor, and to the load (just a resistor). It works fine, until I add the capacitor. When I add the capacitor I get 0V on my oscilloscope readings, instead of a filtered FW signal. I have had this problem countless times and wanted to see if it was me or multisim. The file is included. Notice the GND of the oscope is connected to the circuit, the image just cut it off.

Thanks

Notice, change .txt to .ms8

 

[adamthole]

Okay, I have figured out one problem. My transformer is blowing. When I run the simulation the transformer smokes and blows. Pretty neat...except I never knew what it was doing. Now that I know though, it is cool.

The problem, why is it blowing?

Possibly because when it charges the capacitor the capacitor is at first acting as a short (like capacitors do). But shouldnt the resistance through the diodes be enough to not blow it? Any suggestions?

 

[evandude]

depends on whether multisim is treating the components as ideal.

sure, real components all have some resistance so there's never infinite current, but you might have to add a small value series resistor after the bridge rectifier to limit the current in your simulation... basically modeling the resistance of "real" components

 

[audioguru]

Maybe Multisim thinks the transformer is made in China. Can't you tell it that the transformer is good and strong and made in the USA?

Did you fail to tell Multisim that the transformer is UL approved?

Doesn't Multisim know that the cap charges very quickly and there isn't enough time for the transformer to even get warm? Maybe Multisim gets stuck and ignores that the cap is charging.

Doesn't Multisim know that you soldered to the transformer terminals really well, and didn't use those darn "quick-connectors" that are always loose?

Dumb sims!

Can you post a video of the transformer blowing up? I don't have the sim program so just a "screen capture" will be fine. :lol:

 

[adamthole]

LOL at audioguru

I would post the transformer blowing up, but it is too fast to get captured with a screen capture and I dont have any software that does video screen captures. It goes so fast it just looks like a glitch, which I originally thought it was.

I added a series resistor of 5K, and it still blew. Ridiculous. When I got ridiculously high it didnt blow...but became worthless. I've gotten around the problem by just using the voltage source at my 22 RMS and not messing with the transformer at all.

 

[evandude]

hey, you shouldn't complain, at least you got multisim to simulate something without crashing... that's something pretty rare in my experience :lol:

 

[adamthole]

No kidding

You use anything else that you like better? I just downloaded SwitcherCad III today, and it seems pretty good, but I havent got real in depth with it yet...or figured out how to import spice models, which is pretty important.

 

[Nigel Goodwin]

Just to add my thoughts again! - there are a great many posts on these forums about problems with simulators, and suggestions of how to modify the circuit to make the simulation work.

This seems to make simulators worse than useless - if the simulation isn't EXACTLY the same as the real world there doesn't seem much point to it?.

Why not do the experiment for real! - then you KNOW the result is correct, and that's the only time you do know.

 

[instruite]

Just curious can you see what happens if you use a normal transformer (rather than the centred tapped which you have used now).
I dont have multisim here so can simulate it myself if you have time just let me know what is the response

 

[adamthole]

Nigel, I'm not a fan of simulators either. However a working simulation is required, as this is for an ECET class. BTW, how many keyboards have you broken the "!" key on so far?

I'll try it with a non CT some time, see if it helps.

 

[Nigel Goodwin]

Nigel, I'm not a fan of simulators either.

The circuit you have posted is fine, if the simulator won't run it then the simulator is useless.

However a working simulation is required, as this is for an ECET class.

I don't know what ECET is?, but if the simulator supplied won't run an incredibly basic circuit like that I would suggest they find a better one?.

BTW is this an 'Electronics' course, or a 'computer games' course :lol:

BTW, how many keyboards have you broken the "!" key on so far?

At the present time this is the third computer using this keyboard, which actually is an old AT one, and I use it with a 5 pin DIN to PS2 adaptor lead :lol:

I'll try it with a non CT some time, see if it helps.

It's not even connected?.

 

[evandude]

Well nigel, if you're looking for reasons for using a simulator instead of solely real-world testing... for those of us who don't have enough test equipment to do much real test work, a simulator can come in extremely handy. also, when designing things like filters and amplifiers, running a simulation is a much faster way to test out component values than swapping them out in a breadboard.

sure, a simulation is to be taken for what it is, and not assumed to entirely represent real-world behavior... but it gets you in the ballpark, and gives you a good starting point for testing a real circuit... which is good, if you're like me and have to carry all your parts and tools down to the school's engineering building to do any real testing.

with that said, i share your opinion of multisim, sometimes I can't believe they even got that program to market considering how grossly inaccurate and extremely unstable it is... but there are several others which are pretty decent, like switchercad or micro-cap.

 

[Roff]

Well nigel, if you're looking for reasons for using a simulator instead of solely real-world testing... for those of us who don't have enough test equipment to do much real test work, a simulator can come in extremely handy. also, when designing things like filters and amplifiers, running a simulation is a much faster way to test out component values than swapping them out in a breadboard.

sure, a simulation is to be taken for what it is, and not assumed to entirely represent real-world behavior... but it gets you in the ballpark, and gives you a good starting point for testing a real circuit... which is good, if you're like me and have to carry all your parts and tools down to the school's engineering building to do any real testing.

with that said, i share your opinion of multisim, sometimes I can't believe they even got that program to market considering how grossly inaccurate and extremely unstable it is... but there are several others which are pretty decent, like switchercad or micro-cap.

And of course, integrated circuits of today's complexity would be impossible without simulators. Of course, this has very little relation to the use of simulators by hobbyists. I use them at work, where they are an absolute necessity, and also for fun. The user needs enough experience to know when he's getting garbage out (often a result of garbage in).