Name of widget to control amps?

Oh Dear, :-? We are back in the cycle seen so often in this and some othere "Technical" groups where some so called "Xperts" B-) want to display their very limited knowledge to the world. and completely ignore the ability of the questioner.

The OP wants to know about a simple school boy experiment and comes from a position of knowing very litle, if anything about electricity. Now you want to sell him a Bench Supply costing over $100 to start with. GET REAL! propose a solution that fits the situation please. :-? ;-)

--
John G Sydney.

I think I did that, a while back.

Mikek

Huh.. well geesh I don't know what he wants. If you are getting started in electronics a bench supply is not a bad place to start.

If he's got the 12V supply he can make a 3A current limit with a Fet (pchan?), a pnp and a (0.6V/3A=) 0.2 ohm resistor.

George H.

(same product available from many vendors)

don't get the 3A version the they overheat IME but the 5A version can be adjusted down to 3A and only gets warm.

you'll need more than 12V in to get 12V out, but not much more.

--
  \_(?)_

you set a limit on voltage out, current out, and sometimes power in and whichever limit is reached first reduces the other parameters

--
  \_(?)_

Oh, if you keep V constant, I *will* vary if R varies (e.g. due to a change in the distance between the electrode and the work, or the properties of the surface, or the concentration of the electrolyte, or whatever). Similarly, if you keep I constant, V will vary if R varies.

What's needed is something which will respond to changes in R by varying V to keep I constant.

I suspect that the approach with batteries (constant V) boils down to trying to keep R reasonably constant so that I remains reasonably constant.

That would be a constant current regulator, it's probably been mention

1/2 a dozen times in this thread. Mikek

Nobody wrote in news: snipped-for-privacy@nowhere.invalid:

Actually, I want constant V but varying I - that's what I don't know how to do and it is the I-varying-widget whose name I don't know ;)

I *think* it's called a varistor, but I don't know. I probably ought to write to DigiKey and see whether they'll tell me; it's just such a nothing- burger question when they have large-scale customers to deal with ;)

THanks, though!

- Kris

amdx wrote in news:njt5fb$lik$ snipped-for-privacy@dont-email.me:

But I want to vary the current and keep V constant; so I guess that means I need to order a "Constant Voltage Regulator" for my setup...

Thanks!

- Kris

Bob Engelhardt wrote in news: snipped-for-privacy@news4.newsguy.com:

Well, I want to adapt that setup so I can use a wall-wart. I have a 12 V one that puts out 3 Amps. I don;t have great molility any more, so I want to avoid batteries that need to be replaced.

Since the original plan does use batteries, though, my guess is that 3A is much higher than necessary, but the higher voltage is what gives the better results for both etching and anodizing, so I want to maintain the 12V, and vary the Amps to the minimum that will do the job.

OK, I'm confused now, because everything I've been reading emphasizes the voltage and ignores the current...

Maybe I should skip this idea completely and just try to use a diamond bit and my Dremel, if I can rig up a support for it (my hands aren't all that steady, that's why I was hoping that the NaCl+Vinegar etching would be do- able)...

THanks, though!

- Kris

Bob Engelhardt wrote in news: snipped-for-privacy@news4.newsguy.com:

Thanks, though that's actually the opposite of what I want. But it *is* an idea for where and how to search ((I'm not an E-Bay person, so I didn't think to look there)).

- Kris

M Philbrook wrote in news: snipped-for-privacy@news.eternal-september.org:

Thank you for your reply...

Robert Roland wrote in news: snipped-for-privacy@4ax.com:

YES, the resistance, what is the thing called that changes resistance? I'm pretty sure I've seen photos of ones where you just turn a knob *or* move a slider to vary the resistance, but what is it called...?

Or, to put it visually: (trying to attach an image...)

=ybegin line=128 size=16045 name=Widget.png

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=yend size=16066 crc32=a9b7bb79

snipped-for-privacy@gmail.com wrote in news:66a08993-b4ca-4dea-b0ef- snipped-for-privacy@googlegroups.com:

OH, for some reason, I'm just seeing this today (17 June)

Thanks!, I'll look for that!

- Kris

Jasen Betts wrote in news:njrjgf$ssk$ snipped-for-privacy@gonzo.alcatraz:

Ah!, interesting! Thank you! :)

- Kris

Robert Roland wrote in news: snipped-for-privacy@4ax.com:

YES! Resistance variation. "omnilobe" had mentioned a potentiometer and a rheostat, though I only saw those posts pop up today (ah, the mysteries of the "intertubes", Heh! ;) ), so I'm going to go look those up.

Meanwhile, I'm trying to post a drawing to show more clearly what I mean ;)

Thanks!

- Kris

=ybegin line=128 size=16045 name=Widget.png

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=yend size=16045 crc32=a9b7bb79

=ybegin line=128 size=16045 name=Widget.png

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=yend size=16045 crc32=a9b7bb79

Still trying to post the graphic...

Kris wrote in news:XnsA62AD9FFBF9meadowmuffin@216.168.4.170: