change polarity@15 mins on DC transformer

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Hi,
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want to change the polarity from positive to negative every 15 minutes in a
continuous cycle.

 >This is the first time for me and it's a one off project. I would
like to do it as easily as possible--with instructions a child could
follow if that's ok. Is it possible to do it with a 'plug in'
'breadboard' ? (I don't even own a soldering iron--or meter).

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    K2813--Discovery Series Kit Multi 555 Timer for $20.
<Circuit uses a 555 timer IC as a building block for timer projects.
Supplied with components and PCB.>
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capacitor. [the transformer has a little pot that you turn with a screwdriver] I
can unscrew its case--but its very fiddly and fragile-looking inside--maybe I
should start over and get a kit transformer too--I found these on the DSE
catalogue... but I'm not sure if they're AC to DC--

1.) <General Purpose Transformer 12-0-12V @ 3.6VA
Secondary output: 12-0-12 volts. Secondary current: 150mA.
Terminations: flying leads.>
Related Searches: transformer | transformer 12 volt    M2854$4.98>
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2.) <    Transformer 0-24V @ 3A
Secondary output: 0-24 volts. Secondary current: 3 amps. Terminations:
solder lugs.> M2158.
Sorry I don't know more. Thanks for your help.


Re: change polarity@15 mins on DC transformer


use the 555 to switch a
small relay with two sets of change over contacts
or use 4 transistors in a full bridge configuration

: Hi,
: >I have a little transformer putting out 3 volts DC from 240 volt AC
mains and I want to change the polarity from positive to negative every
15 minutes in a continuous cycle.
:
: >This is the first time for me and it's a one off project. I would
: like to do it as easily as possible--with instructions a child could
: follow if that's ok. Is it possible to do it with a 'plug in'
: 'breadboard' ? (I don't even own a soldering iron--or meter).
:
: >Dick Smith Electronics has a kit called the 'Discovery series'
K2813--Discovery Series Kit Multi 555 Timer for $20.
: <Circuit uses a 555 timer IC as a building block for timer projects.
: Supplied with components and PCB.>
: >Is this what I need to buy? --should set the time interval...
:
: >But to change the polarity? I wouldn't have a clue. I read you need a
capacitor. [the transformer has a little pot that you turn with a
screwdriver] I can unscrew its case--but its very fiddly and
fragile-looking inside--maybe I should start over and get a kit
transformer too--I found these on the DSE catalogue... but I'm not sure
if they're AC to DC--
:
: 1.) <General Purpose Transformer 12-0-12V @ 3.6VA
: Secondary output: 12-0-12 volts. Secondary current: 150mA.
: Terminations: flying leads.>
: Related Searches: transformer | transformer 12 volt M2854$4.98>
: >
: 2.) < Transformer 0-24V @ 3A
: Secondary output: 0-24 volts. Secondary current: 3 amps. Terminations:
: solder lugs.> M2158.
: Sorry I don't know more. Thanks for your help.
:


Re: change polarity@15 mins on DC transformer



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I want to change the polarity from positive to negative every 15 minutes in a
continuous cycle.
Quoted text here. Click to load it
    K2813--Discovery Series Kit Multi 555 Timer for $20.
Quoted text here. Click to load it
capacitor. [the transformer has a little pot that you turn with a screwdriver] I
can unscrew its case--but its very fiddly and fragile-looking inside--maybe I
should start over and get a kit transformer too--I found these on the DSE
catalogue... but I'm not sure if they're AC to DC--
Quoted text here. Click to load it

DSE M2854 and M2158 are transformers and nothing more - AC in and AC
out. And since you admit you don't have a clue, I suggest you steer
clear of them because to connect them you have to work with mains
wiring - dangerous if you don't know what you are doing.  
Andy Wood
snipped-for-privacy@trap.ozemail.com.au

Re: change polarity@15 mins on DC transformer



snipped-for-privacy@cool.com.au wrote:
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I want to change the polarity from positive to negative every 15 minutes in a
continuous cycle.
Quoted text here. Click to load it

Not easily. You'll almost certainly have to do some soldering.
"Breadboards" are just a temporary way to trial a circuit, it's not a
permanant solution.

Quoted text here. Click to load it
    K2813--Discovery Series Kit Multi 555 Timer for $20.
Quoted text here. Click to load it

You'll need some sort of timer like this, yes.

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capacitor. [the transformer has a little pot that you turn with a screwdriver] I
can unscrew its case--but its very fiddly and fragile-looking inside--maybe I
should start over and get a kit transformer too--I found these on the DSE
catalogue... but I'm not sure if they're AC to DC--

You could use a DPDT relay to reverse the contacts to the DC plug.

Dave :)


Re: change polarity@15 mins on DC transformer



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small relay with two sets of change over contacts
or use 4 transistors in a full bridge configuration

Thanks--but I need specific help--on circuit design and exactly which
components to buy. Ideally I would use a pre-bought transformer and
just add the polarity switching circuit at the dc end--that way it's
idiot-proof 240 volt-wise. Is this possible?


David L. Jones wrote:
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and I want to change the polarity from positive to negative every 15 minutes in
a continuous cycle.
Quoted text here. Click to load it
    K2813--Discovery Series Kit Multi 555 Timer for $20.
Quoted text here. Click to load it
capacitor. [the transformer has a little pot that you turn with a screwdriver] I
can unscrew its case--but its very fiddly and fragile-looking inside--maybe I
should start over and get a kit transformer too--I found these on the DSE
catalogue... but I'm not sure if they're AC to DC--
Quoted text here. Click to load it


Re: change polarity@15 mins on DC transformer


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Yes.
Didn't you say you already had the 3V DC supply?
In that case you'll probably need another supply to power the timer.
Output of the timer drives a DPDT relay coil, DPDT relay contacts are
wired so the polarity gets swapped when the contact changes.
I failed ASCII ART at school.

It is possible to use plugpacks for both so there is no mains wiring
involved.

Dave :)


Re: change polarity@15 mins on DC transformer



David L. Jones wrote:
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OK thanks, yes, I have one 3V DC supply--so I need to buy another one
to power the timer. Can anyone draw me a wiring diagram or suggest a
site to find one on?
Thank you.


Re: change polarity@15 mins on DC transformer



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What are you trying to drive?

There should be tons of info on google. Do a search for h-bridge.

Re: change polarity@15 mins on DC transformer



The Real Andy wrote:
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to negative every 15 min. It's only for a hobby application. I thought of
getting a kit for the timer--but don't know how to switch the polarity from
positive to negative. If you can't help, that's
ok, I just thought I'd ask. Will search for h-bridge ...
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Re: change polarity@15 mins on DC transformer



snipped-for-privacy@cool.com.au wrote:
Oh--I see--the H-bridge is for driving a motor--no, I don't need to
drive a motor, I just need the raw current. 15min positive--15 min
negative in a continuous cycle.


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positive to negative every 15 min. It's only for a hobby application. I thought
of getting a kit for the timer--but don't know how to switch the polarity from
positive to negative. If you can't help, that's
Quoted text here. Click to load it


Re: change polarity@15 mins on DC transformer



found this power supply at DSE:  K3435
Features:
Can be used in a variety of ways as either a single or dual supply
Designed so that constructors can obtain many different voltages: +15V,
-15V, +/-15V, +18 to 22V, or less than 15V [I need 4.5V]
Power source required: Power adaptor or transformer (depending on
individual requirements)
Supplied with PCB and instructions only
Case optional (use H-2853)
PCB size:53mm x 71mm
Cat No.    K3435

If anyone thinks this would work, good--just need to work out how to
switch it from positive to negative every 15min-- or maybe use 2 of
them through an AC to  DC transformer--of course that may be easier
said than done...

snipped-for-privacy@cool.com.au wrote:
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positive to negative every 15 min. It's only for a hobby application. I thought
of getting a kit for the timer--but don't know how to switch the polarity from
positive to negative. If you can't help, that's
Quoted text here. Click to load it


Re: change polarity@15 mins on DC transformer


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We have already told you how to do it, but I'll re-cap.

You need:
1) A power supply for your "device"
2) A timer that can switch on/off at the 15min interval you want.
Connect the output of the timer to the relay coil.
3) A DPDT relay. See the link Andy posted on how to wire it up to
reverse the polarity when the relay switches.
4) A second power supply (probably 12V or 5V) to power the timer and
relay. This is only required if the voltage of your other supply is not
suitable for this.

Dave :)


Re: change polarity@15 mins on DC transformer



Thank you for your kind and patient help. I will look at the link. BTW,
 The price of these things varies from between $250 and $3000 US--and
as to the power output, I'm not sure, but they normally run on D cell
batteries--but I had an old 'plug pack' ...

David L. Jones wrote:
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Re: change polarity@15 mins on DC transformer



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In fact, you could use one of those common 24 hour mains timers - some of
them have plastic lugs at 15 minute spacings so you just need to push in
every second lug, and use it to power a low-voltage plugpack that energises
the relay.





Re: change polarity@15 mins on DC transformer


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Nice solution.

Dave :)


Re: change polarity@15 mins on DC transformer



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Sorry bout the delay, i been locked up on jury duty.

I still dont know what you a driving. Obviously not a motor. I suggest
that you use the simplest solution suggested by others, which is a
relay. As for the timer, if you know nothing about electronics, then i
suggest you use a manufactured timer from your local electrical
distributer. Alternativley, Jaycar or Altronics (IIRC) used to sell
pre built kits, i cant remember which, but i suggest you peruse there
range. That is providing that they are still sold. Perhaps others here
can confirm,

Re: change polarity@15 mins on DC transformer


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how much current do you need?

Bye.
   Jasen

Re: change polarity@15 mins on DC transformer



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I bet you don't!  Transformers do not put out DC.

Cheers,
Alf



Re: change polarity@15 mins on DC transformer



:
: > Hi,
: >>I have a little transformer putting out 3 volts DC from 240 volt AC
mains
: >>and I want to change the polarity from positive to negative every 15
: >>minutes in a continuous cycle.
:
: I bet you don't!  Transformers do not put out DC.


they do if they are a plug pack transformer

most mobile phone chargers output "current limited" and "regulated" DC

you can buy one for a couple of bucks

you should open one and have a look, you might learn somthing!

:
: Cheers,
: Alf

cheers dickwad
:
:


Re: change polarity@15 mins on DC transformer



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Except there not transformers, they are power packs. Quite a difference
in fact.

--
Regards

Kevin Martin

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