Who wants to know why more about DC Electronics? Ohms law part 1 and part 2

[k0ua]

No good deed goes unpunished... eh?

Something like that..I will think twice before I offer any more free education.

 

[MossRoad]

Something like that..I will think twice before I offer any more free education.

If it's any consolation, I'm reading the links as time permits. Always good to do a refresher once in a while. :thumbsup:

 

[k0ua]

If it's any consolation, I'm reading the links as time permits. Always good to do a refresher once in a while. :thumbsup:

Good deal.. I was just thinking that since there must be hundreds of "my tractor won't start (when they mean to say crank) threads on here, I thought some simple education about Ohm's law would help a few of these guys to understand the why for and how come of simple DC electrical principles. I wish these things were taught in 8th or 9th grade, but they aren't and guys just don't have much opportunity to learn these things. Also I have found that so many people cannot learn much from just reading something in print. But anyway, I guess if it helps just one person, maybe that's a good thing.

 

[lilranch2001]

James, I for one have learned, or relearned many things from your posts.
I am sure many other people have as well.
Please do not stop offering advise and knowledge.

 

[radios1]

I ws working on a DC motor drive last week on a machine that makes Tyvek suits. I thought the SCRS were bad, but they turned out to be OK. The transistor that fires them turned out to be bad. The transistor had been replaced before, and there was no information on it. Digikey got 70000 hits when inputting the number.

Schematics not anywhere to be found on this popular make of drive.

Anyway, there were only two other types of transistors on the PCB. PNPs and NPS all being the same. I guessed, the driver for the SCRS was PNP since the SCRs required a positive trigger or gate signal. But it did not work. Contacted someone on EBAY selling the same motor control and he was nice enough to provide the number of the OEM transistor. It was NPN! Put a generic one in, tht has been in my basement for thirty years and the thing worked.

I can't figure out why it was an NPN transistor.

it's an NPN because it feeds the pulse transformer. one end of the primary winding goes to the collector, and the other end of the primary goes to the + supply, either +5V or +12V. one end of the secondary of the pulse transformer goes to a diode, and then to the gate of the SCR. the other end goes to the cathode of the SCR. when the transistor switches off, a pulse forms from the collapsing field, and fires the SCR..

 

[MossRoad]

Good deal.. I was just thinking that since there must be hundreds of "my tractor won't start (when they mean to say crank) threads on here, I thought some simple education about Ohm's law would help a few of these guys to understand the why for and how come of simple DC electrical principles. I wish these things were taught in 8th or 9th grade, but they aren't and guys just don't have much opportunity to learn these things. Also I have found that so many people cannot learn much from just reading something in print. But anyway, I guess if it helps just one person, maybe that's a good thing.

That's part of the art if interrogation! :laughing:

I worked 30 years in I.T. and spent a lot of time answering "My computer doesn't work." calls. Well, what do you mean by it doesn't work?

Is there a picture on the screen?
NO
Is the monitor turned on?
YES
Is the PC turned on?
I just told you it was turned on.
No, you told me the monitor was turned on. The monitor and the PC are two different things.
WELL, I DON'T KNOW WHICH THING DOES WHAT, YOU NEED TO COME OUT HERE!.............

Those are the kind of conversations you're trying to avert here by offering education, and, well, :dance1: :laughing:

 

[k0ua]

That's part of the art if interrogation! :laughing:

I worked 30 years in I.T. and spent a lot of time answering "My computer doesn't work." calls. Well, what do you mean by it doesn't work?

Is there a picture on the screen?
NO
Is the monitor turned on?
YES
Is the PC turned on?
I just told you it was turned on.
No, you told me the monitor was turned on. The monitor and the PC are two different things.
WELL, I DON'T KNOW WHICH THING DOES WHAT, YOU NEED TO COME OUT HERE!.............

Those are the kind of conversations you're trying to avert here by offering education, and, well, :dance1: :laughing:

That reminds me of the computer (joke?) conversation that went something like the conversation above, but the person says that "everything is blank" When the tech asked them to get behind the computer and see if it is plugged into the wall outlet, they said it was too dark to see behind the computer. "why is it so dark?, flip on a light?" "well it is dark because the power is out to our building"...Ok just box it up and send it back as you are too stupid to own a computer. .

I have been helping dozens of guys get on a new ham radio digital mode that came out in June of 2017. Maybe close to 100 guys now, I had to learn it myself, and of course I read the developers manual and figured out the rest pretty quickly. But lots of guys just don't know which way to even start. Or what hardware/software will be needed let alone how to configure it to get it working. Yes there are several pieces to the puzzle. Network time control, Audio coupling to a transceiver OR preferably USB virtual audio. Then the so called CAT control (Computer Aided Transceiver). Then issues to work out like RFI getting into the computer from the antenna and dropping the connection. etc. Then getting all the levels set correctly to prevent overdriving of the software or worse yet overdriving of the transmitters input circuits causing "splatter". And on and on. I do this mainly over the telephone and with Teamviewer sessions. It can be a bit of a task, as the radios are all different, and as I cannot see and program the radios (I nearly always download their manuals to assist the callers) I have to rely on what they see and what they say they have done. Not always accurate!

The end result is I have helped a lot of people solve a problem they couldn't solve themselves. Also end result, I have gotten even better at figuring out people and they way they think!

 

[Industrial Toys]

Thanks Radios. But it didn't have a transformer. I had no schematics and traced the Gates of both of the SCRs to the defective TO92 Package Silicone transistor via a series diode.

 

[mbohuntr]

Thanks Radios. But it didn't have a transformer. I had no schematics and traced the Gates of both of the SCRs to the defective TO92 Package Silicone transistor via a series diode.

Without a schematic, I'm only guessing, but the trigger could be either always on (collector side), and grounded by a gate pulse, or on the emitter, and pulsed on. Either would use an NPN. I guess you would have to know what triggers the gate, a sink, or source IC

 

[MossRoad]

That reminds me of the computer (joke?) conversation that went something like the conversation above, but the person says that "everything is blank" When the tech asked them to get behind the computer and see if it is plugged into the wall outlet, they said it was too dark to see behind the computer. "why is it so dark?, flip on a light?" "well it is dark because the power is out to our building"...Ok just box it up and send it back as you are too stupid to own a computer. .

I have been helping dozens of guys get on a new ham radio digital mode that came out in June of 2017. Maybe close to 100 guys now, I had to learn it myself, and of course I read the developers manual and figured out the rest pretty quickly. But lots of guys just don't know which way to even start. Or what hardware/software will be needed let alone how to configure it to get it working. Yes there are several pieces to the puzzle. Network time control, Audio coupling to a transceiver OR preferably USB virtual audio. Then the so called CAT control (Computer Aided Transceiver). Then issues to work out like RFI getting into the computer from the antenna and dropping the connection. etc. Then getting all the levels set correctly to prevent overdriving of the software or worse yet overdriving of the transmitters input circuits causing "splatter". And on and on. I do this mainly over the telephone and with Teamviewer sessions. It can be a bit of a task, as the radios are all different, and as I cannot see and program the radios (I nearly always download their manuals to assist the callers) I have to rely on what they see and what they say they have done. Not always accurate!

The end result is I have helped a lot of people solve a problem they couldn't solve themselves. Also end result, I have gotten even better at figuring out people and they way they think!

Teamviewer is great! Especially for people that want to show you what is going on and cannot describe it well. I've used it several times on my kids' machines over the years while they were away at school. Unfortunately, it only works if they can turn the darn the on in the first place!!! :laughing: