Need trouble shooting help (pics)

[billbyrd1945]

When everything is connected, the 12v motor runs only on the 5v. A YouTube video demonstrated the project as a way of understanding BJT transistors. I copied it as faithfully as possible, but can't get it to work. Any help will be appreciated.

[Richard Crowley]

When you connect the motor directly to the 12V power supply, does it operate properly?
That means with no other part of the circuit connected to the motor.

Do you have a DMM?  Can you measure the amount of current that the motor draws at 12V?

According to this data sheet:  http://www.futurlec.com/Transistors/C9014.shtml
The C9014 transistor is only rated for 0.15 A of current. 
It seems quite possible that your motor takes more than that.
You may have destroyed the transistor.
If you don't alreday have one, it would be good to have one of those $10 component testers.
Then you could at least check whether the transistor is good.

You didn't indicate the polarity of your 5V power source?

[fourtytwo42]

Hello, well as Richard says you need a larger transistor BUT you have another problem and that is the circuit is an emitter follower, VBE of the transistor is about 600mV and can never be negative, so the emitter will not rise more than 600mV below the base, in this case around 4.4V.  To allow the emitter to rise further you need a higher base voltage, in your circuit you could dispense with the 5V supply and instead connect the base resistor to your 12V supply.

[rstofer]

Using that common collector configuration, the motor voltage will never be higher than the base voltage minus about 0.6V.  So, about 4.4V, give or take.

That's a horrible circuit, junk it!

With only the 12V supply:  Connect the emitter to PS (-) which we will call ground.  Connect the motor between the PS (+) and the collector.  Put the diode across the motor with the cathode (bar end) pointing back to the PS (+) (reverse biased).

Use the 4.7k (keep reading) resistor from the +12V (collector) and the base.

There will be limitiations.  The maximum base current is (12-0.6) / 4700 or about 2 mA.  If the transistor current gain is 100 then the maximum collector current is 200 mA.  It's pretty obvious this isn't going to work.  Try 1k...  Then the maximum base current is (12-0.6)/1000 or 11 mA and if the gain is 100, the maximum collector current is 1.1 Amps.

All assuming of course that the transistor can handle 1.1 Amp of collector current while maintaining a current gain of 100.

For the 2N3055 (big power transistor), the gain at 1 Amps is about 90.  So, maybe we have to kick the base current up a bit.  Perhaps the resistor should be 470 Ohms.

Now, when it comes time to shut the transistor, we need to pull the base and the 470 Ohm resistor down to 0V.  Well, that takes a current of 12V / 470 Ohm = 26 mA.  We might use another transistor to do that.  Perhaps a 2N3904.  We would connect the emitter to ground, the collector to the base of the 2N3055 and then when we apply base voltage through a 1K resistor, a high voltage will turn the 2N3904 ON and this will turn the 2N3055 OFF.  When we pull the base of the 2N3904 to 0V, the transistor is off and the 470 Ohm resistor turns the 2N3055 ON.

Something like that!

The base current issue (high base current for big power transistors) is one of the reasons we use MOSFETs.

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF
https://www.onsemi.com/pub/Collateral/2N3903-D.PDF

[Richard Crowley]

If we knew which YouTube video you got your information from, we could either:

a) Help you understand what the video was trying to say
        or
b) Identify what was wrong with the information on the video(?)

If they really showed using a C9014 transistor then they must have been using a much smaller motor.
We wouldn't typically expect a small plastic TO-92 transistor to be able to control such a large motor.
Transistors have maximum voltage ratings, and maximum current ratings.  Above those limits they self-destruct.

[Richard Crowley]

I have drawn some of the different diagrams here in the "conventional" way, highest voltage rail at the top and going down to lowest voltage (ground = 0 or even negative) at the bottom.  And with the "signal flow" from left to right.

1. Here is the original circuit as you showed in your first post.  (Redrawn in the conventional way)
It suffers from lack of enough current into the base of the transistor as @fourtytwo42 described.



2. Here is the same circuit except driving the base of the transistor from the +12V bus (as @fourtytwo42 described).
This has a better chance of working, but there is probably still too much current through the transistor.



3. Here is the more conventional way of controlling a higher-current and/or higher-voltage load.
This puts the transistor/switch in the "low side" of the load.
It allows you to control the current on/off with a low voltage (like 5V or 3.3V from a microcontroller, etc.)



4. And you can also control the "low-side" circuit from the 12V bus as shown here.



I used https://www.digikey.com/schemeit/project/ to draw these diagrams.  Quick and easy.

[billbyrd1945]

I goofed by not giving enough information. The video was https://www.youtube.com/watch?v=8DMZSxS-xVc. And I used the same transistor (PN2222A). The motor I have just happens to draw .056mA, the same as the solenoid he used. And yes, it does run properly on 12V. After I accidently smoked my only 2222, I found the 9014 in my limited inventory. At any rate, they both perform the same. That is, the motor only gets the 5v. My understanding was/is that the 5v turns on the base so that the 12v flows to the motor. My amateur diagram may not be representative of the actual circuit I built, or what the YouTuber built. But I can't point to any difference in my actual physical circuit. Maybe I've given enough additional info for you guys to help. Thanks for all the responses. I need to go back and study them more. Wanted to get this out before hitting the sheets. (Revised diagram attached)

[ArthurDent]

As others have said, the circuit you have constructed is an emitter follower and this circuit is commonly used with a zener to give a regulated output voltage. The output will always be the base voltage minus the base to emitter voltage drop so if you put 5 VDC through the limiting resistor you will get the approximately 4.4 VDC that others have mentioned. I have redrawn your circuit and next to it the basic regulator circuit that it is equivalent to. This makes it easier to see that they are the same type of circuit. The output as you have wired the circuit will never be more than 4.4 VDC.

So why did the circuit in the video work? The answer is you didn't copy the circuit properly. If you look at the frame I captured from the video you referenced you will see that the transistor is wired as a simple transistor switch and not an emitter follow. This circuit works much differently so when there is a base voltage that can deliver enough current to turn the transistor on it works just like a mechanical switch and the voltage applied to the load will be the 12 minus the small VDC drop across the transistor junction. This was one of the variations Richard Crowley drew yesterday but you might have missed the importance.

[billbyrd1945]

Only now getting a chance to review the responses. Before today (or last night) I had never even heard of an emitter follower. I'm going to read up on that before trying anything else.  Quite often, it's not possible to copy YouTube demonstrations because you can't see the breadboard very well and leads are coming into frame from who knows where. One should be able to use the schematics that usually are shown, but for noobs like me, that's not a very safe proposition. I still don't see how his circuit is different from mine except for the solenoid.

[ArthurDent]

Here are the two very different circuits.

[billbyrd1945]

Okay guys. I'm sorry to be so dense. Several of you have commented that I need to get with the program and draw my schematics in the traditional way for a start. I think I have some kind of a spatial disorder that makes it hard for me to use a scientific drawing as opposed to my third-grader's version. But I'm going to force myself to do it from here on. You never improve yourself if you don't try. So, going back to the bench to start over again. You can be sure I'll let everyone know if I can get this motor run wide open on 12v having been switched on with a mere 5v.

[rsjsouza]

billbyrd, great suggestions all around, but I just wanted to tell you something: I love your board with the glued parts and the written values on the wood. I don't know if nostalgia is influencing me, but I did a lot of these circuits assembled on wood - although I used nails to keep things together and the terminals were enough to hold the parts in place. 

[alsetalokin4017]

The motor I have just happens to draw .056mA,

Er.... I'll wager it draws quite a bit more than that when supplied with 12 volts, or even 5 volts.

As part of the learning experience please be sure that you locate your decimal point correctly and that you use conventional abbreviations. "mA" is short for milliamps, that is, thousandths of an ampere. To avoid confusion when writing decimal values less than one,  I always recommend not suppressing the leading zero: "0.056" is clearer than ".056" which doesn't inspire confidence: it could be a typo or... a misplaced decimal.

Also you can "breadboard" circuits pretty easily by laying out the schematic using a conventional organization, then pretty much duplicating that layout on your board. I use solid copper wire (stripped from 4-conductor phone wiring) inserted into small holes in the wood to make "power busses" and other connections for soldering, and I use sockets for transistors whenever possible. You can adapt 3-pin molex female connectors to make transistor sockets if you can't find actual ones. An example of my little "breadboards":

[ArthurDent]

Try this.

[billbyrd1945]

Ha! Yes! The biggest reason I do that is because I don't trust breadboards for good connections.

[billbyrd1945]

Oh wow! I love that!

[billbyrd1945]

"Er.... I'll wager it draws quite a bit more than that when supplied with 12 volts, or even 5 volts."

See photo.

[billbyrd1945]

You are too cool to do that for me! Thanks Arthur. Transistors ordered. Replicating your drawing will be my first order of business.

[alsetalokin4017]

"Er.... I'll wager it draws quite a bit more than that when supplied with 12 volts, or even 5 volts."

See photo.

Yes... and in your original post you said it drew .056 mA.  A thousand times less than what it actually draws. Thank you for confirming that you originally misplaced the decimal point.

I goofed by not giving enough information. The video was https://www.youtube.com/watch?v=8DMZSxS-xVc. And I used the same transistor (PN2222A). The motor I have just happens to draw .056mA, the same as the solenoid he used. And yes, it does run properly on 12V. After I accidently smoked my only 2222, I found the 9014 in my limited inventory. At any rate, they both perform the same. That is, the motor only gets the 5v. My understanding was/is that the 5v turns on the base so that the 12v flows to the motor. My amateur diagram may not be representative of the actual circuit I built, or what the YouTuber built. But I can't point to any difference in my actual physical circuit. Maybe I've given enough additional info for you guys to help. Thanks for all the responses. I need to go back and study them more. Wanted to get this out before hitting the sheets. (Revised diagram attached)

[alsetalokin4017]

Often a "12 volt"  can motor needs a little manual help to start running when it is supplied with much less voltage. Your original circuit could be "working" but the motor might simply be stalled. Try giving it a spin with your fingers.

Also, if you have any old CFL light bulbs or computer power supplies hanging around, you can scavenge lots of useful parts from them. The transistors in a CFL would work well for this demonstration.

[madires]

If the goal isn't to explain a BJT emitter follower then an n-channel MOSFET would be a much better choice.

[billbyrd1945]

So much help is flowing in that it's hard to keep up with my "thank you's". I've looked back over my post and don't see the decimal goof. Wouldn't be the first time I couldn't find something though. I love the idea of the CFL diode. I may just sacrifice one if I get to antsy to wait for my order to come in. Also may try the MOSFET route. I need to know how to use those too.

[ArthurDent]

I see the current in question as ".056Ma" when it should have been .056A. The difference between Ma and Amps. 56Ma would have been correct. I knew what you meant.

[billbyrd1945]

Eureka (sort of)!

This is the wiring schema suggested by Arthur. It positively works in the sense that it doesn't run on the 12VDC until turned on by the 5VDC. I don't yet know how to read a datasheet well enough to know if this transistor (c945 b444) is rated for this kind of load. I used it because I found in in the junk drawer and don't yet have my PN2222A as used in the YouTube video (the build that I wish to replicate). Readers should also know that I connected it incorrectly before I realized that the collector and base for this transistor are NOT ebc but, rather, ecb. Doing so made the transistor too hot to touch. So the pulsating (when correctly wired) may somehow be related to this. What do you think? Also suspect that the innards of the motor may be less that securely affixed. All things considered, though, I'm tickled sh*tless just to see some kind of a transistor behave in the way that is should. See video at https://youtu.be/k0bCO1eJzIo

http://pdf1.alldatasheet.com/datasheet-pdf/view/82713/ETC/C945.html

[billbyrd1945]

"I see the current in question as ".056Ma" when it should have been .056A. The difference between Ma and Amps. 56Ma would have been correct. I knew what you meant."

Ah! I see what you mean. I used the wrong label.