Name of widget to control amps?

[M Philbrook]

In article <XnsA624E6D421BAmeadowmuffin@216.168.4.170>, email@no.no
says...

Tim Wescott <seemywebsite@myfooter.really> wrote in
news:iKmdneo5oM4EWMHKnZ2dnUU7-NmdnZ2d@giganews.com:

On Sat, 11 Jun 2016 16:30:01 -0500, Kris wrote:

Hello,

This is the "Basics" group, and yeah, I have a question that's most
definitely basic...

I want to purchase a small widget for a 12V DC setup to keep the voltage
constant but control the *amperage* from 0 to a maximum of 3. I'm
having a difficult time pinning-down what it's called - I *think* what I
need is a "varistor" or a "potentiometer", but the info I've turned up
in my searches sems contradictory.

Many thanks to any kind soul who will let me tknow the correct name so I
can order the right thing =

It's called a "magic box", because the load itself will determine how
much current will flow for a given voltage.

Think about a resistor: E = IR means that the voltage is _always_ the
resistance times the current. Conversely, the current is _always_ the
voltage divided by the resistance. So 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.


Oh....! OK, Thank you, Tim!, I had thought one could be varied while
keeping the other constant....

I'll be collecting all the info that the group members have generously
given, and print it out for study in the morning - and meanwhile, I think
I'd better just *exactly* follow the instructions at the website for the
salt+vinegar steel etching using a 9V battery, and make sure I'm *much*
more clear on all of this before I even think about fooling around with a
wall-wart =

Thanks again!,

- Kris

I see what you're looking for and using solid state devices means you
could be burning things out, unless you have proper arc protection.

For etching and current limiting, the easier thing you can do is use a
series of incandescent lamps in parallel, each in a socket to pop them
out of circuit to adjust current. Or use a switch on each one.

A 25Watt 12 volt lamp will give you 2 amps, a smaller one less and if
you combine them in parallel you can beef it up or have a smaller one
only for low current.

Lamps change their resistance when loade.

That is about as simple as I can come up with and you can get the
parts at an auto parts store or Walmarts.

Of course you could go the route of using a Rheostat in series, plan
to pay money for a large one..

Jamie

 

[George Herold]

On Saturday, June 11, 2016 at 5:30:05 PM UTC-4, Kris wrote:

Hello,

This is the "Basics" group, and yeah, I have a question that's
most definitely basic...

I want to purchase a small widget for a 12V DC setup to keep the
voltage constant but control the *amperage* from 0 to a maximum of 3. I'm
having a difficult time pinning-down what it's called - I *think* what I
need is a "varistor" or a "potentiometer", but the info I've turned up in
my searches sems contradictory.

Many thanks to any kind soul who will let me tknow the correct name so I
can order the right thing =

- Kris

Hi Kris, I think what you want is called a lab bench (or bench) power supply.
These devices will allow you to set a voltage and a maximum current.
For 12V and 3A you should be able to get one for ~$100 or so.

We resell some made by Volteq (use to be called Mastech..
everyone changes their name.)
http://www.volteq.com/

They are cheap, but seem to work fine.

George H.

 

[George Herold]

On Monday, June 13, 2016 at 8:14:13 PM UTC-4, John G wrote:

It happens that George Herold formulated :
On Saturday, June 11, 2016 at 5:30:05 PM UTC-4, Kris wrote:
Hello,

This is the "Basics" group, and yeah, I have a question that's
most definitely basic...

I want to purchase a small widget for a 12V DC setup to keep the
voltage constant but control the *amperage* from 0 to a maximum of 3. I'm
having a difficult time pinning-down what it's called - I *think* what I
need is a "varistor" or a "potentiometer", but the info I've turned up in
my searches sems contradictory.

Many thanks to any kind soul who will let me tknow the correct name so I
can order the right thing =

- Kris

Hi Kris, I think what you want is called a lab bench (or bench) power
supply. These devices will allow you to set a voltage and a maximum current.
For 12V and 3A you should be able to get one for ~$100 or so.

We resell some made by Volteq (use to be called Mastech..
everyone changes their name.)
http://www.volteq.com/

They are cheap, but seem to work fine.

George H.

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.

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.

 

[John G]

It happens that George Herold formulated :

On Saturday, June 11, 2016 at 5:30:05 PM UTC-4, Kris wrote:
Hello,

This is the "Basics" group, and yeah, I have a question that's
most definitely basic...

I want to purchase a small widget for a 12V DC setup to keep the
voltage constant but control the *amperage* from 0 to a maximum of 3. I'm
having a difficult time pinning-down what it's called - I *think* what I
need is a "varistor" or a "potentiometer", but the info I've turned up in
my searches sems contradictory.

Many thanks to any kind soul who will let me tknow the correct name so I
can order the right thing =

- Kris

Hi Kris, I think what you want is called a lab bench (or bench) power
supply. These devices will allow you to set a voltage and a maximum current.
For 12V and 3A you should be able to get one for ~$100 or so.

We resell some made by Volteq (use to be called Mastech..
everyone changes their name.)
http://www.volteq.com/

They are cheap, but seem to work fine.

George H.

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.

 

[amdx]

On 6/13/2016 7:14 PM, John G wrote:

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 little, 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. :-? ;-)

I think I did that, a while back.

> http://www.instructables.com/id/Adjustable-constant-current-source-4mA-to-3A/

Mikek

 

[Ralph Mowery]

In article <itGdnTn9vrnT0cLKnZ2dnUU7-fPNnZ2d@westnet.com.au>,
john.g@green.com says...

It happens that George Herold formulated :
On Saturday, June 11, 2016 at 5:30:05 PM UTC-4, Kris wrote:
Hello,

This is the "Basics" group, and yeah, I have a question that's
most definitely basic...

I want to purchase a small widget for a 12V DC setup to keep the
voltage constant but control the *amperage* from 0 to a maximum of 3. I'm
having a difficult time pinning-down what it's called - I *think* what I
need is a "varistor" or a "potentiometer", but the info I've turned up in
my searches sems contradictory.

Many thanks to any kind soul who will let me tknow the correct name so I
can order the right thing =

- Kris

Hi Kris, I think what you want is called a lab bench (or bench) power
supply. These devices will allow you to set a voltage and a maximum current.
For 12V and 3A you should be able to get one for ~$100 or so.

We resell some made by Volteq (use to be called Mastech..
everyone changes their name.)
http://www.volteq.com/

They are cheap, but seem to work fine.

George H.

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. :-?
;-)

For less than 2 bucks shipped from China he can use this device with
anything that will put out enough voltage and current.

From ebay number 191015464867

 

[Jasen Betts]

On 2016-06-11, Kris <em@il.no> wrote:

Hello,

This is the "Basics" group, and yeah, I have a question that's
most definitely basic...

I want to purchase a small widget for a 12V DC setup to keep the
voltage constant but control the *amperage* from 0 to a maximum of 3. I'm
having a difficult time pinning-down what it's called - I *think* what I
need is a "varistor" or a "potentiometer", but the info I've turned up in
my searches sems contradictory.

Many thanks to any kind soul who will let me tknow the correct name so I
can order the right thing =

- Kris

https://www.amazon.com/Lithium-Battery-Charger-Board-Module/dp/B00PAHOFQ8
(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.

--
\_(ツ)_

 

[Jasen Betts]

On 2016-06-12, Bob Engelhardt <BobEngelhardt@comcast.net> wrote:

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

I don't know how one can adjust both voltage & current, but maybe
someone here can explain that.

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

--
\_(ツ)_

 

[Nobody]

On Sat, 11 Jun 2016 22:37:50 -0500, Kris wrote:

Thanks! Yeah, I really need to study all the info. I thought I could be
varied while keeping V constant OR V veried with I constant, but it doesn't
seem to work that way at all.

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.

 

[amdx]

On 6/15/2016 8:44 PM, Nobody wrote:

On Sat, 11 Jun 2016 22:37:50 -0500, Kris wrote:

Thanks! Yeah, I really need to study all the info. I thought I could be
varied while keeping V constant OR V veried with I constant, but it doesn't
seem to work that way at all.

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.

That would be a constant current regulator, it's probably been mention
1/2 a dozen times in this thread.
Mikek

 

[Beauvine]

Nobody <nobody@nowhere.invalid> wrote in
newsan.2016.06.16.01.44.04.289000@nowhere.invalid:

On Sat, 11 Jun 2016 22:37:50 -0500, Kris wrote:

Thanks! Yeah, I really need to study all the info. I thought I
could be varied while keeping V constant OR V veried with I constant,
but it doesn't seem to work that way at all.

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.

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

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

 

[Kris]

amdx <nojunk@knology.net> wrote in news:njt5fb$lik$1@dont-email.me:

On 6/15/2016 8:44 PM, Nobody wrote:
On Sat, 11 Jun 2016 22:37:50 -0500, Kris wrote:

Thanks! Yeah, I really need to study all the info. I thought I
could be varied while keeping V constant OR V veried with I
constant, but it doesn't seem to work that way at all.

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.

That would be a constant current regulator, it's probably been
mention
1/2 a dozen times in this thread.
Mikek

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

 

[Kris]

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

 

[Kris]

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)).

- Kris

I don't know how one can adjust both voltage & current, but maybe
someone here can explain that.

 

[Beauvine]

M Philbrook <jamie_ka1lpa@charter.net> wrote in
news:MPG.31c7c34c709ecbc0989ef4@news.eternal-september.org:

In article <XnsA624E6D421BAmeadowmuffin@216.168.4.170>, email@no.no
says...

Tim Wescott <seemywebsite@myfooter.really> wrote in
news:iKmdneo5oM4EWMHKnZ2dnUU7-NmdnZ2d@giganews.com:

On Sat, 11 Jun 2016 16:30:01 -0500, Kris wrote:

Hello,

This is the "Basics" group, and yeah, I have a question that's
most definitely basic...

I want to purchase a small widget for a 12V DC setup to keep the
voltage constant but control the *amperage* from 0 to a maximum of
3. I'm having a difficult time pinning-down what it's called - I
*think* what I need is a "varistor" or a "potentiometer", but the
info I've turned up in my searches sems contradictory.

Many thanks to any kind soul who will let me tknow the correct
name so I can order the right thing =

It's called a "magic box", because the load itself will determine
how much current will flow for a given voltage.

Think about a resistor: E = IR means that the voltage is _always_
the resistance times the current. Conversely, the current is
_always_ the voltage divided by the resistance. So 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.


Oh....! OK, Thank you, Tim!, I had thought one could be varied while
keeping the other constant....

I'll be collecting all the info that the group members have
generously given, and print it out for study in the morning - and
meanwhile, I think I'd better just *exactly* follow the instructions
at the website for the salt+vinegar steel etching using a 9V battery,
and make sure I'm *much* more clear on all of this before I even
think about fooling around with a wall-wart =

Thanks again!,

- Kris

I see what you're looking for and using solid state devices means you
could be burning things out, unless you have proper arc protection.

For etching and current limiting, the easier thing you can do is use
a
series of incandescent lamps in parallel, each in a socket to pop them
out of circuit to adjust current. Or use a switch on each one.

A 25Watt 12 volt lamp will give you 2 amps, a smaller one less and
if
you combine them in parallel you can beef it up or have a smaller one
only for low current.

Lamps change their resistance when loade.

That is about as simple as I can come up with and you can get the
parts at an auto parts store or Walmarts.

Of course you could go the route of using a Rheostat in series, plan
to pay money for a large one..

Jamie

Thank you for your reply...

 

[Kris]

omnilobe@gmail.com wrote in news:66a08993-b4ca-4dea-b0ef-
eec27f5af5d9@googlegroups.com:

> Rheostat, 18 watts

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

Thanks!, I'll look for that!

- Kris

 

[Kris]

Jasen Betts <jasen@xnet.co.nz> wrote in
news:njrjgf$ssk$2@gonzo.alcatraz:

On 2016-06-11, Kris <em@il.no> wrote:
Hello,

This is the "Basics" group, and yeah, I have a question that's
most definitely basic...

I want to purchase a small widget for a 12V DC setup to keep the
voltage constant but control the *amperage* from 0 to a maximum of 3.
I'm having a difficult time pinning-down what it's called - I
*think* what I need is a "varistor" or a "potentiometer", but the
info I've turned up in my searches sems contradictory.

Many thanks to any kind soul who will let me tknow the correct name
so I can order the right thing =

- Kris

https://www.amazon.com/Lithium-Battery-Charger-Board-Module/dp/B00PAHOF
Q8 (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.

Ah!, interesting! Thank you!

- Kris

 

[Kris]

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

 

[Kris]

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

 

[Krid]

Still trying to post the graphic...




Kris <main@no.no> wrote in
news:XnsA62AD9FFBF9meadowmuffin@216.168.4.170:

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