Electronics > Beginners
Is it possible to combine current?????
RivaultUser:
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 mA
The 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 NPN
Please help................
c4757p:
The current required is IC/hFE. IC is the current you are trying to switch with it, and hFE is 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 to sense it 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?
Rerouter:
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,
amspire:
--- Quote from: RivaultUser on March 15, 2013, 01:20:27 am ---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 mA
The 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 NPN
Please help................
--- End quote ---
I 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.
RivaultUser:
--- Quote from: c4757p on March 15, 2013, 01:27:05 am ---The current required is IC/hFE. IC is the current you are trying to switch with it, and hFE is 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 to sense it 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?
--- End quote ---
Thx for your reply man, but sadly My stepper motor is fixed and I can't do anything about it
It's for my school project, I chooe to make energy from water and I'm stuck in here
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