Need trouble shooting help (pics) - Page 1
Forum section: electronics / beginners

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 20, 2019, 05:42:11 pm
content: 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 20, 2019, 05:52:15 pm
content: 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.shtmlThe 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?

author: fourtytwo42
author_rank: Super Contributor
timestamp: February 20, 2019, 06:01:21 pm
content: 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.

author: rstofer
author_rank: Super Contributor
timestamp: February 20, 2019, 08:03:27 pm
content: 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.PDFhttps://www.onsemi.com/pub/Collateral/2N3903-D.PDF

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 20, 2019, 10:05:27 pm
content: If we knew which YouTube video you got your information from, we could either:a) Help you understand what the video was trying to sayorb) 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 20, 2019, 10:31:29 pm
content: 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 usedhttps://www.digikey.com/schemeit/project/to draw these diagrams. Quick and easy.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 21, 2019, 04:39:05 am
content: I goofed by not giving enough information. The video washttps://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)

author: ArthurDent
author_rank: Super Contributor
timestamp: February 21, 2019, 06:04:37 pm
content: 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.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 21, 2019, 08:00:44 pm
content: Only now getting a chance to review the responses. Before today (or last night) I had never even heard of anemitter 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 usuallyareshown, 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.

author: ArthurDent
author_rank: Super Contributor
timestamp: February 22, 2019, 01:37:19 am
content: Here are the two very different circuits.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 01:13:04 am
content: 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.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 23, 2019, 02:23:36 am
content: 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.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 23, 2019, 02:33:12 am
content: QuoteEr.... 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":

author: ArthurDent
author_rank: Super Contributor
timestamp: February 23, 2019, 03:17:20 am
content: Try this.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 03:53:17 am
content: Ha! Yes! The biggest reason I do that is because I don't trust breadboards for good connections.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 03:58:59 am
content: Oh wow! I love that!

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 04:07:49 am
content: "Er.... I'll wager it draws quite a bit more than that when supplied with 12 volts, or even 5 volts."See photo.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 04:11:10 am
content: You are too cool to do that for me! Thanks Arthur. Transistors ordered. Replicating your drawing will be my first order of business.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 23, 2019, 01:41:40 pm
content: Quote from: billbyrd1945 on February 23, 2019, 04:07:49 amYes... 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.Quote from: billbyrd1945 on February 21, 2019, 04:39:05 am

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 23, 2019, 02:24:44 pm
content: 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.

author: madires
author_rank: Super Contributor
timestamp: February 23, 2019, 02:44:41 pm
content: If the goal isn't to explain a BJT emitter follower then an n-channel MOSFET would be a much better choice.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 03:14:08 pm
content: 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.

author: ArthurDent
author_rank: Super Contributor
timestamp: February 23, 2019, 04:56:31 pm
content: 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.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 05:13:36 pm
content: 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 seesome kindof a transistor behave in the way that is should. See video athttps://youtu.be/k0bCO1eJzIohttp://pdf1.alldatasheet.com/datasheet-pdf/view/82713/ETC/C945.html

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 05:16:07 pm
content: "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.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 23, 2019, 07:41:41 pm
content: Quote from: billbyrd1945 on February 23, 2019, 05:16:07 pmAh..... no.Ma is not a usual electronics abbreviation. The capital "M" usually would indicate MEGA, that is, MILLIONs of amperes.The correct abbreviation for "milliAmps" is mA. Not Ma.So in your original post where you stated the current, you either misplaced a decimal and/or used the wrong abbreviation. I even quoted and bolded your text, up above, so you could see where you made your error.Believe it or not, these little nitpicking things are important, and it does a beginner a real disservice for someone else to "know what you meant" instead of pointing out the error so it doesn't get made again.As far as reading and interpreting data sheets for transistors... usually on the first page on top you may find the most critical information you really need: the pinout, the maximum collector-emitter voltage, and the maximum rated collector current. And the usual application information may help you select the proper transistor for your application. A "saturated switch" BJT would be better than an audio amplifier for turning on your motor. And of course a mosfet would suit the actual application better but would teach little about the use of a BJT.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 07:55:57 pm
content: "I goofed by not giving enough information. The video washttps://www.youtube.com/watch?v=8DMZSxS-xVc.And I used the same transistor (PN2222A). The motor I have just happens to draw .056mA"As far as I can tell, the only time I mentioned a current capacity was small m, large A. But it should've been amps rather than mA as Arthur pointed out. And don't think I don't appreciate your eye for detail. I retired from a medical career where such errors could kill. As to the datasheets, I can read what they say, just not yet sure what it means. But I'll get there. Do you think that the "audio" feature would have any bearing on the pulsations?

author: ArthurDent
author_rank: Super Contributor
timestamp: February 23, 2019, 07:56:54 pm
content: In the video I don't see the 4.7K current limiting resistor in series with the +5 VDC and the transistor base. Not having the resistor in the circuit could be very bad for the transistor.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 23, 2019, 08:01:34 pm
content: One other thing that should be pointed out is this: That little motor when given 12 volts, unloaded and running freely, draws about 54 or 56 mA, well within the max collector current of the small transistors, as you've shown. But at initial startup it will draw more, maybe a lot more, maybe enough to blow or stress the little transistors. Ditto if the motor is heavily loaded or stalled. The initial startup surge will be over quickly once the motor is running at speed so the transistors may survive even if the peak current is over their "absolute max" rating.The surging you see in your video could be caused by a number of things but my first guess would be the power supply sagging. I'd also change the transistor just on spec.You will find either mosfets, or BJTs inside the typical compact fluorescent bulb. I've seen both, and same brand bulbs may use either circuit. You can experiment with either type in this present motor circuit. You will usually find at least 4 diodes of the 1n400x variety or equivalent, the two transistors, a big electrolytic cap and some smaller film caps. I usually don't bother with the resistors or inductors in the CFL circuit but they too can be scavenged if you really need them for something. Be careful not to break the glass, there is a tiny amount of mercury inside.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 23, 2019, 08:05:36 pm
content: Quote from: billbyrd1945 on February 23, 2019, 07:55:57 pmOr you could have moved the decimal three places to the right and said "56 mA" which would have been completely correct.QuoteNo, it just means the transistor is optimised for rapid oscillation (audio) and varying signal amplitude. A 'saturated switch' type is designed to be fully on or fully off, and wastes slightly less power.I'm looking into the pulsations now.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 09:06:53 pm
content: "In the video I don't see the 4.7K current limiting resistor..."Oh crap! I can't be trusted to do anything! I'll put it in now and try again.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 23, 2019, 09:31:13 pm
content: Interesting. I placed the 4.7K resistor, connected the 12VDC without the 5VDC base voltage. The motor started immediately. That disappointed me because I assumed the previous magic had evaporated. Then, just for kicks, I decided to unplug the power supply and discharge the transistor with my fingers, a maneuver I only learned about a couple of days ago. I reconnected the 12VDC. The motor did not run. I plugged in the 5VDC and everything was as before. Yipee! Then I observed something new: I unplugged the 5VDC and saw the motor continue to run. No, wait a minute, it stopped. I repeated the process several times. One would swear it was notgoingto stop, but then it would. I decided the wall wort must have some kind of residual energy after being unplugged. Breaking the circuit at the 12VDC produced the instant on/off that I was hoping for. As to the pulsating-- gone.

author: ArthurDent
author_rank: Super Contributor
timestamp: February 23, 2019, 10:34:05 pm
content: Leave the 5 VDC supply plugged in and disconnect the +5 lead from the 4.7K resistor. When you touch the +5 to the resistor lead, the motor will start and when you remove it, the motor will stop.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 23, 2019, 10:38:35 pm
content: Quote from: billbyrd1945 on February 23, 2019, 09:31:13 pmTransistors do not "hold a charge" like that. Certainly not for low-voltage DC circuits such as yours.Your power sources are "black boxes" that are not behaving like you imagine they should.Even one of those $10 volt/amp panel meter things would show you what voltages and currents you are really dealing with. For example...https://www.amazon.com/ZRM-Digital-Voltmeter-Ammeter-Display/dp/B07DZTPSLS

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 24, 2019, 01:05:02 am
content: "Leave the 5 VDC supply plugged in and disconnect the +5 lead from the 4.7K resistor."Right. That's what I meant in my last sentence.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 24, 2019, 01:20:13 am
content: "Transistors do not "hold a charge" like that."I didn't mean to imply that. I suspected the 5v wall wort (or is it "wart") was responsible. And even if it is, I'm fine with that. I'm sure the YouTuber didn't intend for anyone to think of unplugging a transformer as a switch in itself. I'm tickled that merely disconnecting the 12VDC (or the 5V wire) provides instant on and off. It's working perfectly and drawing 0.056AMPS. Finished project photo attached. Thanks to everyone! This means a lot to me!

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 24, 2019, 02:36:23 am
content: Beautiful! I like the way you used the dowels to hold the connecting posts. All you need now is to find a little 3-prong socket connector so you can easily change transistors to see how different ones behave, and a 10k potentiometer to substitute for the fixed resistor. The idea is to find the greatest resistance that will still allow enough current through to turn on the transistor fully.I found an ideal "socket" for a transistor on the end of a little cable I scavenged from a discarded CRT television that I found on the roadside. The blue screw blocks from Vellemann are ideal for mosfets in the TO-220 or TO-247 style packages. (The smaller ones need legs bent a bit, the larger ones are exact fit without bending.)

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 24, 2019, 02:57:06 am
content: Quote from: Richard Crowley on February 23, 2019, 10:38:35 pmActually it would be more correct to say that "BJTs don't hold a charge like that." Mosfets, which are charge-actuated devices, can and do hold a gate charge, staying 'on' (for Nch types) as long as that charge persists. It can indeed be charged or discharged with a finger!(the finger charge demonstration action happens after about 5 minutes in)(Looks like the narrator was confused about lowside/highside switch arrangements, but never mind that.)But of course bipolar junction transistors don't work like this.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 24, 2019, 03:37:03 am
content: Too cool! That (one with a pot and connectors) will be my next project. Still going to keep this one for posterity.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 24, 2019, 03:46:11 am
content: "Transistors do not "hold a charge" like that."I misunderstood you. I thought you were referring to my thoughts about the wall wart retaining some energy. In reality, you were telling me that the finger shorting doesn't work on BJTs. Uh... yep, I stepped in it again. I had been watching vids about MOSFETS and forgot that I had changed my focus to the transistor project. So I don't know why there was some kind of state change when I did it. Hmm. I probably did something else at the same time and got confused.

author: ArthurDent
author_rank: Super Contributor
timestamp: February 24, 2019, 03:04:11 pm
content: I would not replace the fixed 4.7K resistor with a 10K pot as suggested because when the pot is turned to one end there will be approximately zero ohms in series with the transistor base which will have a maximum drop to ground of about 0.7 volt and you could damage the pot.A better way for speed control is to connect a 1K to 10K pot (it's not that critical) between +5 VDC and your common point and leave the 4.7K resistor in series with the pot wiper and the transistor base. You can now adjust the speed of the motor.What you will now find is that instead of the transistor acting as a switch and dropping about .7 volts, it is acting as a resistor between the +12 VDC and the motor. When the motor is receiving a low voltage and turning slowly, the transistor will be dropping the majority of the voltage at whatever current the motor is drawing at that speed. This power must be dissipated as heat and the transistor may get quite warm. That is why audio amps and your bench supply have large heatsinks and often fans to remove the heat from the transistors they use.

author: billbyrd1945
author_rank: Regular Contributor
timestamp: February 24, 2019, 04:02:11 pm
content: Thanks Arthur. Will do.