Is it possible to combine current????? - Page 1
Forum section: electronics / beginners

author: RivaultUser
author_rank: Contributor
timestamp: March 15, 2013, 01:20:27 am
content: Okay, here's my situation :I have a handmade generator that only can provide me 2mV ( i know i know that its pathetic ). So my idea is I want to power up my transistor base with that. But I don't know how much current flows in the 2mV ( well, i assume it's small less that 0.7 V )So is it possible to combine a current, i want to combine that with my other generator which can draw enough mAThe problem is :I'm still a newbie and i dont know how much current my base transistor need to power up ( i have bc547 and 2n3904,, both of them are NPNPlease help................

author: c4757p
author_rank: Super Contributor
timestamp: March 15, 2013, 01:27:05 am
content: The current required is IC/hFE. ICis the current you are trying to switch with it, and hFEis the DC common-emitter gain - assume around 100 for these transistors. Actually, look it up, it's in the datasheet.You are going to have a hard time doing anything with 2mV. I would suggest putting more turns of wire on that thing to get more voltage out of it. (Have you wound the wire in two directions? You may be getting a lot more voltage but cancelling voltages. Make sure you wind consistently.) If you just want tosenseit you can use a comparator - hang the "generator" off a virtual ground so you don't have to compare that close to the comparator's ground. (If you don't know what I mean, start Googling terms now. I think you have some learnin' to do before this is going to get anywhere.) But you're not going to get any power out of that.What exactly are you trying to do?

author: Rerouter
author_rank: Super Contributor
timestamp: March 15, 2013, 01:35:16 am
content: sounds like your mixing units there, i'm going to assume 2mA rather than 2mV,next step, how did you measure this 2mA? was it across the mA terminals of your multimeter or calculated from the drop across a resistor? or some other thing?once you clear that up we should be able to work out roughly what voltage it can generate, otherwise find a known resistor, e.g. 100 or 1000 ohms, and see what voltage you get across it while operating your generator, if its greater than 0.7 then you should at-least be able to turn on the transistor,next up combining it with another generator, yes it is possible, but probably not worth it, its the same for 2 batteries in parallel unless they are matched the more capable or charged one will be dumping charge into the lesser one trying to balance the voltage,and finally, a transistor switches on the moment you give it more than 0.7V for general ones, then any current fed into it at that voltage is able to flow between collector and emmitor (multiplied by beta)so if you have a transistor with a beta of 100, and you are able to feed it 2mA at 0.7V into its base, then you can use it to pass 200mA between collector and emmitor before saturating,

author: amspire
author_rank: Super Contributor
timestamp: March 15, 2013, 01:38:41 am
content: Quote from: RivaultUser on March 15, 2013, 01:20:27 amI do not understand what you are asking. Did you mean 2mA rather then 2mV? A transistor base will not draw any measurable current at 2mV. You need probably at least 400mV on a transistor base to get any measurable effect.How much current do you need to "power up" an BC547? Depends on the circuit. You can use them at a 1 uA collector current if you want which means the base is drawing much less then 1 uA.

author: RivaultUser
author_rank: Contributor
timestamp: March 15, 2013, 12:07:15 pm
content: Quote from: c4757p on March 15, 2013, 01:27:05 amThx for your reply man, but sadly My stepper motor is fixed and I can't do anything about itIt's for my school project, I chooe to make energy from water and I'm stuck in here

author: RivaultUser
author_rank: Contributor
timestamp: March 15, 2013, 12:09:15 pm
content: Quote from: amspire on March 15, 2013, 01:38:41 amIt's really 2mV, I measured it when the generator start spinning.

author: RivaultUser
author_rank: Contributor
timestamp: March 15, 2013, 12:15:19 pm
content: Quote from: Rerouter on March 15, 2013, 01:35:16 amWell, I'm going to focused on the combining the current first.......Let's say that my generator cannot give enough current to saturate the transistor base, can I connect my generator with a capacitor ( pararel & charged ) to give the current an extra current from the capacitor ?

author: Rerouter
author_rank: Super Contributor
timestamp: March 15, 2013, 12:19:44 pm
content: while 2mV seriously sounds like you have problems with your generator, yes you should be able to use a capacitor to slowly accumulate a large enough voltage to at-least turn the transistor on, probably supplying uA to the base, so unless you use a darlinton arrangement you will not be able to pull more than possibly 1-10mA through the transistor,

author: Harvs
author_rank: Super Contributor
timestamp: March 15, 2013, 12:25:54 pm
content: A stepper motor doesn't have a permanent magnet core, making it totally unsuitable as a generator (I.e if it had no residual magnetism you would get nothing out of it.) just find yourself a standard dc motor out of some small toy and you should be converting a reasonable amount of energy.

author: Harvs
author_rank: Super Contributor
timestamp: March 15, 2013, 12:30:24 pm
content: Woops I just read the initial post where you said it was handmade. Honestly with a decent magnet core and few dozen turns it's not hard to make something work, so I'd look there.Why are you calling it a stepper then?

author: XynxNet
author_rank: Regular Contributor
timestamp: March 15, 2013, 01:15:21 pm
content: Please take a picture of your setup. 2mV seems way to low. Maybe there is a fault in your setup.

author: Marco
author_rank: Super Contributor
timestamp: March 15, 2013, 01:19:22 pm
content: Quote from: RivaultUser on March 15, 2013, 12:07:15 pmIf it's one with permanent magnets then you are probably doing something wrong ... those can be used as generators and will generate more than 2 mV, are you sure you are correctly rectifying the outputs? (They will generate AC current pulses, not a DC output voltage like say a toy DC motor would.) Googling for stepper generator will get you plenty of web pages and youtube videos showing how you have to wire it up with diodes to do this ...If it doesn't have a permanent magnet and it's not an option to replace it, then your only option is to give up (although personally I would re-examine your opinion of impossibility and just replace it any way).

author: SeanB
author_rank: Super Contributor
timestamp: March 15, 2013, 04:20:45 pm
content: Stepper will give more than 2mV, bog standard 12V ones from a printer will light a LED when turning it by hand slowly, so you probably are trying to measure DC voltage or current. Steppers give AC when turned, so try placing a LED across the windings, it will probably light quite brightly.