Name of widget to control amps?

[Jasen Betts]

On 2016-06-17, Kris <email@no.no> wrote:

Bob Engelhardt <BobEngelhardt@comcast.net> wrote in
news:njkkar01dr7@news4.newsguy.com:

On 6/12/2016 4:59 PM, Bob Engelhardt wrote:
On 6/11/2016 8:24 PM, Kris wrote:
... THe practical
application I'm looking at is doing some small-scale metal etching
using a
12VDC source using the emthod described here:
http://byo.com/stories/issue/item/3113-etch-your-kettle-projects
...

That link does not talk about current, so I suppose that your 0 - 3 amps
was found somewhere else?

Anyhow, in that application, the load resistance is going to vary a lot,
depending upon the electrolyte and your technique. So, I would say that
your need is to regulate the current. You can use your 12v source, but
the voltage doing the etching will vary as the load resistance varies.
And you don't care if it does! Your current will be constant at
whatever value you set. In the end, it is the current that is doing the
etching.

HTH,
Bob

Here is a widget that might do your job:
www.ebay.com/itm/321921444650

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)).

one of those adjustement screws will do the thing you want.

--
\_(ツ)_

 

[amdx]

On 6/17/2016 1:35 PM, Kris wrote:

Bob Engelhardt <BobEngelhardt@comcast.net> wrote in
news:njkiel01cdd@news4.newsguy.com:

On 6/11/2016 8:24 PM, Kris wrote:
... THe practical
application I'm looking at is doing some small-scale metal etching
using a 12VDC source using the emthod described here:
http://byo.com/stories/issue/item/3113-etch-your-kettle-projects
...

That link does not talk about current, so I suppose that your 0 - 3
amps was found somewhere else?

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.


Anyhow, in that application, the load resistance is going to vary a
lot, depending upon the electrolyte and your technique. So, I would
say that your need is to regulate the current. You can use your 12v
source, but the voltage doing the etching will vary as the load
resistance varies. And you don't care if it does! Your current will
be constant at whatever value you set. In the end, it is the current
that is doing the etching.

HTH,
Bob

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

It has already been explained that ohms law is V = I x R.
If you vary R the I will change and V will stay the same*.
If you make I constant (Say 2A) and vary R then V will change, but it
will only change enough to keep the current constant. (2A)
You will be varying R because of your solution, contact area, and
pressure.
The voltage is only important in that it must be high enough to cause
the current flow you want with the R caused by your solution, contact
area, and pressure.
If it were me, I'd try a constant current regulator and practice on
test pieces until I found the current that allow me to get the best effect.
I don't think it is very critical. My daughter used a 9v battery and
some electrolytic (I don't now what) to etch her boyfriends initials on
a stainless steel water bottle.
It looked good to me.

*In a perfect device V would stay the same, wall warts, batteries and
power supplies have some internal resistance and the V could drop
slightly. Nothing for you to worry about, but I had to mention it
so others wouldn't bring it up.

 

[Rheilly Phoull]

On 18/06/2016 10:28 AM, Kris wrote:

Robert Roland <fake@ddress.no> wrote in
news:4tdqlbllsrdvbm6cg6jlnlj8k0vfrp4dbe@4ax.com:

On Sat, 11 Jun 2016 21:14:49 -0500, Tim Wescott
seemywebsite@myfooter.really> wrote:

a 10 ohm resistor on a 12 volt
supply will flow 1.2 amps -- the only way to change the current is to
change the voltage.

...or the resistance.

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

If you take that lm317 cct and use a rheostat in place of the resistor
you will have good control of the current. Bear in mind as said before
you will need to supply about 3v (to be sure) above the desired
operating voltage.

 

[Nobody]

On Fri, 17 Jun 2016 13:24:55 -0500, Kris wrote:

> But I want to vary the current and keep V constant;

I wouldn't be so sure about that. The rate of material removal will be
proportional to the current. The voltage only matters insofar as it
affects the current.

In essence, you need to transfer a certain amount of charge in order to
transfer a certain amount of material. Current is charge per unit time. So
a constant current will tend to remove material at a constant rate,
whereas a constant voltage will tend to remove material faster or slower
as the resistance varies (primarily due to the variation in the distance
between the electrode and the work).

so I guess that means I need to order a "Constant Voltage Regulator" for
my setup...

Most power supplies (including batteries) are roughly constant voltage.

An unregulated supply (such as a battery) will exhibit a reduction in
voltage as the current increases. For a battery, the reduction will be
roughly proportional to the current drawn as a fraction of the
short-circuit current, so if you aren't drawing anywhere near the
short-circuit current, the drop won't be significant.

Regulated supplies will make an effort to maintain a constant voltage as
the current varies.

 

[Nobody]

On Fri, 17 Jun 2016 13:35:52 -0500, Kris wrote:

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

That's because constant-voltage supplies are cheaper and easier to obtain
than constant-current, and you're (presumably) looking at sites dealing
with this as a hobby rather than electrochemical machining (ECM) as an
industrial process.

Constant-current will almost certainly work better, but a bench PSU with
constant-current mode will cost between $50 for Cheap Chinese Crap and
hundreds of dollars for something from a well-known manufacturer. Whereas
batteries and some wire will cost a couple of dollars.

 

On Fri, 17 Jun 2016 21:39:02 -0500, Kris <mail@no.no> wrote:

Robert Roland <fake@ddress.no> wrote in
news:4tdqlbllsrdvbm6cg6jlnlj8k0vfrp4dbe@4ax.com:

On Sat, 11 Jun 2016 21:14:49 -0500, Tim Wescott
seemywebsite@myfooter.really> wrote:

a 10 ohm resistor on a 12 volt
supply will flow 1.2 amps -- the only way to change the current is to
change the voltage.

...or the resistance.

Still trying to post the graphic

This newsgroup is a text only newsgroup, which means that you will not
be able to post binaries here. Try the dropbox and just post a link to
your pictures.
Eric