### Author Topic: Things derped engineers say.  (Read 35539 times)

0 Members and 1 Guest are viewing this topic.

#### tom66

• Super Contributor
• Posts: 3642
• Country:
• Electron Fiddler, FPGA Hacker, Embedded Systems EE
##### Re: Things derped engineers say.
« Reply #75 on: May 06, 2013, 01:10:11 am »
I have two 12V, 98A power supply for server use. A 20cm length of AWG26 was melted on the output and the voltage didn't drop by more than 0.1V. The wire glowed white hot before failing and now my room smells of melted rubber.

#### c4757p

• Super Contributor
• Posts: 7805
• Country:
##### Re: Things derped engineers say.
« Reply #76 on: May 06, 2013, 01:15:14 am »
The voltage output will never go above the set voltage in a decent power supply, but it will go below to restrict the current.

Sorry if I may seem like a dunce, but I was always under the impression that the voltage and the resistance determine the current, but from what I understand from your text its the current that determines the voltage.

Basic algebra. Any equation can be reversed. If 2V gives you 2A, then 2A gives you 2V.
No longer active here - try the IRC channel if you just can't be without me

#### Jimbz

• Contributor
• Posts: 27
##### Re: Things derped engineers say.
« Reply #77 on: May 06, 2013, 01:51:30 am »
The voltage output will never go above the set voltage in a decent power supply, but it will go below to restrict the current.

Sorry if I may seem like a dunce, but I was always under the impression that the voltage and the resistance determine the current, but from what I understand from your text its the current that determines the voltage.

Basic algebra. Any equation can be reversed. If 2V gives you 2A, then 2A gives you 2V.

Yes I realize that, but this does not really have anything to do with the matter at hand. Also in your previos post, what does the maximum of the current and the maximum voltage have anything to do with limiting said parameters ? If my power supply can go upto 50 volts and 10 amps, then why do these matter at all when i limit the votlage and current at lesser values. In constant voltage mode, it will draw its own current, but not above the maximum 10A, in constant current mode it will draw its own voltage, but not above the maximum 50 volts. I can limit the voltage and current in lesser values as I please, all dependant on the load.

Main argument was that "constant current" and "current limit" are not the same... In my eyes, they arent the same, how can they be, in one mode you will always have a constant current and voltage at the same time, depending on the load. In the other, you will have your current maximum value set to a point, you can fiddle around with the voltage, but it will never go over your set limit, only under ?

I do not have a bench power supply myself, but this is as much as I have gathered from the videos and tutorials over the internet

#### c4757p

• Super Contributor
• Posts: 7805
• Country:
##### Re: Things derped engineers say.
« Reply #78 on: May 06, 2013, 01:59:26 am »
Yes I realize that, but this does not really have anything to do with the matter at hand. Also in your previos post, what does the maximum of the current and the maximum voltage have anything to do with limiting said parameters ? If my power supply can go upto 50 volts and 10 amps, then why do these matter at all when i limit the votlage and current at lesser values.

When did I say that?

Quote
Main argument was that "constant current" and "current limit" are not the same... In my eyes, they arent the same, how can they be, in one mode you will always have a constant current and voltage at the same time, depending on the load. In the other, you will have your current maximum value set to a point, you can fiddle around with the voltage, but it will never go over your set limit, only under ?

A constant current and voltage at the same time? What if I set a constant 1V, 1A and connect a 2 ohm resistor across the output? The only way it can get 1A is to output 2V and the only way to get 1V is to output 0.5A.

They are the same thing being used in different ways. A "current limited" supply is typically being used under its set current, and a "constant current" supply is typically being used at its set current.
No longer active here - try the IRC channel if you just can't be without me

#### Jimbz

• Contributor
• Posts: 27
##### Re: Things derped engineers say.
« Reply #79 on: May 06, 2013, 02:15:24 am »
Yes I realize that, but this does not really have anything to do with the matter at hand. Also in your previos post, what does the maximum of the current and the maximum voltage have anything to do with limiting said parameters ? If my power supply can go upto 50 volts and 10 amps, then why do these matter at all when i limit the votlage and current at lesser values.

When did I say that?

Quote
Main argument was that "constant current" and "current limit" are not the same... In my eyes, they arent the same, how can they be, in one mode you will always have a constant current and voltage at the same time, depending on the load. In the other, you will have your current maximum value set to a point, you can fiddle around with the voltage, but it will never go over your set limit, only under ?

A constant current and voltage at the same time? What if I set a constant 1V, 1A and connect a 2 ohm resistor across the output? The only way it can get 1A is to output 2V and the only way to get 1V is to output 0.5A.

They are the same thing being used in different ways. A "current limited" supply is typically being used under its set current, and a "constant current" supply is typically being used at its set current.

When did you say that ? Well... you didnt, got the guys forumgoers mixed up in page 5 xD I just looked at the flag, not the username, and hastily responded...

Dunno about you, but I have never in my life seen a power supply that allows you to have CC and CV on at the same time. You enable one and the other disables, also come to think of it, I think this post was not ment for you, lolz

#### c4757p

• Super Contributor
• Posts: 7805
• Country:
##### Re: Things derped engineers say.
« Reply #80 on: May 06, 2013, 02:36:00 am »
Understood.

Dunno about you, but I have never in my life seen a power supply that allows you to have CC and CV on at the same time. You enable one and the other disables

I have yet to see one where you enable one. Typically there is a set voltage and a set current, and it just tries to deliver the maximum of both without exceeding either.
No longer active here - try the IRC channel if you just can't be without me

#### lemmegraphdat

• Frequent Contributor
• Posts: 273
• Country:
##### Re: Things derped engineers say.
« Reply #81 on: May 06, 2013, 03:37:46 am »
The voltage output will never go above the set voltage in a decent power supply, but it will go below to restrict the current.

Sorry if I may seem like a dunce, but I was always under the impression that the voltage and the resistance determine the current, but from what I understand from your text its the current that determines the voltage.

Basic algebra. Any equation can be reversed. If 2V gives you 2A, then 2A gives you 2V.
Yes, because on the right side of the equation it is saying that a resistance changes a current into a voltage. On the left side is it better to say that a conductance gives a current?
Start right now.

#### c4757p

• Super Contributor
• Posts: 7805
• Country:
##### Re: Things derped engineers say.
« Reply #82 on: May 06, 2013, 03:51:59 am »
If you like to think of it that way, I'd say so. Additional resistance requires additional voltage to push current (V = IR), and additional conductance permits additional current when given voltage (I = VG). (G is conductance.)

However - I do think conductance is a good thing to understand for your own personal electrical intuition (I tend to picture resistors as restricted conductors, for instance), but using two different names for what is essentially the same thing adds confusion to most discussions. I think it's to be avoided when giving explanations, even if it's personally useful to you.
No longer active here - try the IRC channel if you just can't be without me

#### lemmegraphdat

• Frequent Contributor
• Posts: 273
• Country:
##### Re: Things derped engineers say.
« Reply #83 on: May 06, 2013, 03:52:46 am »
I wonder how it is with bacon. Gonna try that. I'll let you know.

Well, it can't possibly get any worse...
99% was sold out. Tried bacon with 85%. Flavors cancelled out. Just a greasy texture.
Start right now.

#### lemmegraphdat

• Frequent Contributor
• Posts: 273
• Country:
##### Re: Things derped engineers say.
« Reply #84 on: May 06, 2013, 04:05:11 am »
If you like to think of it that way, I'd say so. Additional resistance requires additional voltage to push current (V = IR), and additional conductance permits additional current when given voltage (I = VG). (G is conductance.)

However - I do think conductance is a good thing to understand for your own personal electrical intuition (I tend to picture resistors as restricted conductors, for instance), but using two different names for what is essentially the same thing adds confusion to most discussions. I think it's to be avoided when giving explanations, even if it's personally useful to you.
When I get confused I get pissed off and that's how I know I'm learning something new or a different way to look at something old. And then it is fun to combine things, like the above. Especially when I'm half asleep, like now. I'll have cool dreams somrtimes
Start right now.

#### IanB

• Super Contributor
• Posts: 9681
• Country:
##### Re: Things derped engineers say.
« Reply #85 on: May 06, 2013, 04:28:11 am »
Now if you help me clarify one thing I may have learned something today.

Let us say we want to have "constant current" of 100mA on a random load, and it will set its voltage to 25V, the voltage will not drop or go above it, all it wants is to maintain its 100mA. And now let us set a "current limit" to 100mA, am i to understand correctly, that it will not go above 25V on the same load ? Regardless what it says on the display screen ? Also am I correct to understand that you can fiddle with the voltage as much as you want, you can always go below in "current limit" but never above with voltage with the same load ? If you go below 25V you drop your 100mA to a lesser value, does this not differentiate "constant current" and "current limit" ? In where one you have set voltage and set current on a load, but in the other you can play around with the voltage as much as you want, but the voltage will never go above the current limit of 25V ?

Let's make this concrete with an actual example. Let our "random load" be a 10 ohm resistor.

We have set our power supply to have a current limit of 100 mA and a voltage limit of 25 V. What's going to happen?

Well the power supply is going to vary the output voltage until a current of 100 mA is flowing through the load resistor. When this happens the output voltage will settle at 1 V (10 ohms x 0.1 A = 1 V). Since 1 V is lower than the voltage limit of 25 V the power supply can do this and all is good.

Now suppose we replace the load with a 1000 ohm resistor. The same thing will happen; the power supply will vary the output voltage until the current through the resistor is 100 mA. With our 1000 ohm resistor the required voltage will be 100 V. The power supply will keep increasing the voltage towards 100 V, but before it gets there it will hit the voltage limit of 25 V. When this happens the voltage may not go any higher, so the supply will switch to voltage regulating mode and try to keep the voltage at 25 V instead. The system will settle with a voltage of 25 V and a current through the load of 25/1000 = 0.025 A or 25 mA.

As you can see, the power supply is not "constant current", because the current varied between 100 mA and 25 mA in the two cases. Also the power supply is not "constant voltage" because the output voltage varied between 1 V and 25 V in the two cases.

Quote
Also could you please clarify for me why would the voltage increase in a short circuit ? I was always under the impression the only the current will increase ?

I don't see where I said that, but I have edited my original post for increased clarity.
« Last Edit: May 06, 2013, 05:24:37 am by IanB »
I'm not an EE--what am I doing here?

#### blasto9000

• Contributor
• Posts: 18
• Country:
• Electromechanical
##### Re: Things derped engineers say.
« Reply #86 on: May 06, 2013, 09:30:29 pm »
You should try 99% chocolate sometime, It's crazy strong.

Almost impossible to chew without being overcome with bitterness. You have to let it dissolve on your tongue.

Actually, I rather enjoy the "strong" Lindt chocolate so long as there's enough peanut butter handy.

(BTW, I've been to many countries and everyone I've ever mentioned that to thought it was disgusting.  So ifyou're gagging right now at the thought of chocolate + peanut butter, I won't take it personally.)

#### c4757p

• Super Contributor
• Posts: 7805
• Country:
##### Re: Things derped engineers say.
« Reply #87 on: May 06, 2013, 09:44:38 pm »
(BTW, I've been to many countries and everyone I've ever mentioned that to thought it was disgusting.  So ifyou're gagging right now at the thought of chocolate + peanut butter, I won't take it personally.)

Really? It never occurred to me that people would think that's a weird combination.
No longer active here - try the IRC channel if you just can't be without me

#### IanB

• Super Contributor
• Posts: 9681
• Country:
##### Re: Things derped engineers say.
« Reply #88 on: May 06, 2013, 09:49:02 pm »
Really? It never occurred to me that people would think that's a weird combination.

Yeah, peanut butter and chocolate is pretty much an American cultural phenomenon, one heavily promoted by Reese's.
I'm not an EE--what am I doing here?

#### ddavidebor

• Super Contributor
• Posts: 1167
• Country:
##### Things derped engineers say.
« Reply #89 on: May 06, 2013, 09:50:40 pm »
Yeeah every places has it.

In italy we have nutella!
Davide Bortolami,
Fermium LTD

#### c4757p

• Super Contributor
• Posts: 7805
• Country:
##### Re: Things derped engineers say.
« Reply #90 on: May 06, 2013, 09:51:31 pm »
But they're so good together!!

In italy we have nutella!

That stuff is motherf-ing delicious too.
No longer active here - try the IRC channel if you just can't be without me

#### ivan747

• Super Contributor
• Posts: 2020
• Country:
##### Re: Things derped engineers say.
« Reply #91 on: May 06, 2013, 11:32:17 pm »
This is going to be nominated for EEVBlog's derailed topics 2013

Back in derailed topics 2012 the thread got itself derailed...
https://www.eevblog.com/forum/chat/best-hijack-of-an-eevblog-topic-for-2012/

And by the way, I haven't got a chance to try nutella.
« Last Edit: May 07, 2013, 01:43:03 am by ivan747 »

#### lemmegraphdat

• Frequent Contributor
• Posts: 273
• Country:
##### Re: Things derped engineers say.
« Reply #92 on: May 07, 2013, 01:56:23 am »
Yeeah every places has it.

In italy we have nutella!
You also have cannoli. I love cannoli. We got a real italian makes it good. And the pizza, oh man.
Start right now.

#### smashedProton

• Frequent Contributor
• Posts: 644
• Country:
##### Re: Things derped engineers say.
« Reply #93 on: May 07, 2013, 02:00:55 am »
Today my chemistry teacher completely  butchered electronics when teaching the electrochemistry unit.
In one 40 min period, he: neglected to mention ohms law, declared the mains to be dc, ridiculed electricians as being dumb asses when posting "danger high voltage" signs, and claimed that a car battery can kill.  A real nutjob...
http://www.garrettbaldwin.com/

Invention, my dear friends, is 93% perspiration, 6% electricity, 4% evaporation, and 2% butterscotch ripple.

#### c4757p

• Super Contributor
• Posts: 7805
• Country:
##### Re: Things derped engineers say.
« Reply #94 on: May 07, 2013, 02:01:13 am »
This is going to be nominated for EEVBlog's derailed topics 2013

No, it's only slightly changed. We've gone from talking about things said by derpy engineers to being engineers saying derpy things. I for one say that's on topic.
No longer active here - try the IRC channel if you just can't be without me

#### c4757p

• Super Contributor
• Posts: 7805
• Country:
##### Re: Things derped engineers say.
« Reply #95 on: May 07, 2013, 02:02:14 am »
Today my chemistry teacher completely  butchered electronics when teaching the electrochemistry unit.
In one 40 min period, he: neglected to mention ohms law, declared the mains to be dc, ridiculed electricians as being dumb asses when posting "danger high voltage" signs, and claimed that a car battery can kill.  A real nutjob...

Dude, shut up about our schools! You'll make them all think we're stupid...
No longer active here - try the IRC channel if you just can't be without me

#### N2IXK

• Frequent Contributor
• Posts: 701
• Country:
##### Re: Things derped engineers say.
« Reply #96 on: May 07, 2013, 02:09:36 am »
A car battery could certainly kill you. Just have one blow up in your face, or drop onto your head from a sufficient height...
"My favorite programming language is...SOLDER!"--Robert A. Pease

#### digsys

• Supporter
• Posts: 2179
• Country:
##### Re: Things derped engineers say.
« Reply #97 on: May 07, 2013, 04:21:22 am »
... speaking of which, does anyone know how to sew silk onto denim? Would I need a cross-stitch?
Hello <tap> <tap> .. is this thing on?

#### smashedProton

• Frequent Contributor
• Posts: 644
• Country:
##### Re: Things derped engineers say.
« Reply #98 on: May 07, 2013, 05:05:17 am »
Today my chemistry teacher completely  butchered electronics when teaching the electrochemistry unit.
In one 40 min period, he: neglected to mention ohms law, declared the mains to be dc, ridiculed electricians as being dumb asses when posting "danger high voltage" signs, and claimed that a car battery can kill.  A real nutjob...

Dude, shut up about our schools! You'll make them all think we're stupid...

I just realized that it has been a common topic for me to dislike my school...  Thank you.   I shot him an email; he didnt realize that he implied that.

It just aggravates me when professional teachers (payed 80 grand a year in this case) don't bother to fact check.
http://www.garrettbaldwin.com/

Invention, my dear friends, is 93% perspiration, 6% electricity, 4% evaporation, and 2% butterscotch ripple.

• Super Contributor
• Posts: 1425
• Country:
##### Re: Things derped engineers say.
« Reply #99 on: May 07, 2013, 07:06:08 am »
It just aggravates me when professional teachers (payed 80 grand a year in this case) don't bother to fact check.
I used to think, rather used to want to believe, that "professional teachers" would deliberately feed students misinformation with the intent to "get caught" to see if anybody was paying attention and would call them out on it.
Ya, not so much...
For the most part, they believe what they want to believe, and nobody can change that, sometimes even after presented with hard evidence to the contrary.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.

Smf