A question on current

Discussion in 'General Electronics Chat' started by elecbeg, Nov 13, 2009.

1. elecbeg Thread Starter Active Member

Sep 7, 2009
30
2
I think I have been reading to much lately as I have lost the understanding of basic voltage v current.

The question I need answered is:

If you was to use a step up transformer, obviously the voltage goes up as the current goes down. But say the starting values were 6V at 1A, how low could you take the current before it stops working?

I know this is basic as anything, but I have lost it completely and can't seem to remember what is going on. I know there is a limit to how low the current can go, cus I know you can't get say 500KV from the above mentioned values lol.

Just to give you a bit about me, I understand ( or used to! ) how electricty works, I have built many simple and intermediate circuits.

So please help me before I think drinking guinness has killed a few to many brain cells

2. thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
Transformers can be wound to handle a huge variety of currents, though not in a universal package.

Otherwise, I'm unsure I understand your question. Drawing more than 1Amp on the primary, or secondary? What is the turns ratio?

3. elecbeg Thread Starter Active Member

Sep 7, 2009
30
2
hmm, what I mean is, if there is a 6V line at 1A goin to the primary, and ignoring the size required of the transformer, it steps up the voltage to 6MV, which means the current would go down to the micro if not nano amp. What is the lowest amp reading you could get?
There has to be a point where it wont let you increase the voltage anymore because the amps would run to low to create any power.

I know its a very simple thing but its one of them brain freeze moments for me

Last edited: Nov 13, 2009
4. russ_hensel Distinguished Member

Jan 11, 2009
820
47
In simple theory as long as you conserve energy ( and therefore power ) you can go as high as you want, the sky, the planets...... Other things like insulation breakdown eventually mess this up.

5. elecbeg Thread Starter Active Member

Sep 7, 2009
30
2
In that case, for example with tesla coils - I know not the most practicle subject, but why do they draw so many amps to create there voltage if you can create high voltage regardless of how many amps you have available?

6. davebee Well-Known Member

Oct 22, 2008
539
46
I don't think there is any limit to how low a current you can go. There is probably a limit to how low you'd be able to measure, as eventually the current noise will become much larger than the current you're trying to measure.

But on the other hand, there are very real limits to how high the voltage can go in practice, as charges will jump across insulation and air and even vacuum when the voltages get high enough, so when the voltage get so high that the transformer breaks down, you won't be able to test for currents any lower than that winding ratio.

7. studiot AAC Fanatic!

Nov 9, 2007
5,005
515
There is no known lower limit to current which is charge/time as time is considered to be a continuous quantity.

Charge however is quantised, the smallest known charge is the charge on the electron or proton.

8. elecbeg Thread Starter Active Member

Sep 7, 2009
30
2
Thanks for all your help, I got up this morning and it just all made sence again.

I must say, this furom is amazing, I have posted a few things on here and the replies are always fast and helpful.

9. alphacat Active Member

Jun 6, 2009
186
0
In the case of transformer, isnt it always:
Ip * Vp = Is * Vs? (neglecting losses)

So if 1A flows through the primary inductor, and 6V drops on it,
then
6M volts would drop on the secondary coil (assuming 1:10^6 ratio), and 1uA would flow through it.
Isnt it correct?

10. russ_hensel Distinguished Member

Jan 11, 2009
820
47
Yes conservation of energy for the ideal transformer.

11. studiot AAC Fanatic!

Nov 9, 2007
5,005
515
A bit old fashioned now, but I have an 7 decade ratio transformer on my bench.

These wonderful gadgets were used for measurement of low voltages or currents before modern sophistry was available.

They are extremely simple, sensitive and reliable.