change polarity@15 mins on DC transformer<total beginner--single project>

[Poxy]

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...

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.

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.

 

[David L. Jones]

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...

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.

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.

Nice solution.

Dave

 

[The Real Andy]

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...

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,

 

[The Real Andy]

There's something odd about this. The application (which he won't explain to
us) is fairly sophisticated yet the basic knowledge is about nil. Sorry
mate, not trying to be unhelpful but what exactly are you trying to do? Why
do you want to 'switch polarity'?

Maybe the OP is onto something that he chooses not to reveal. Fair
call I say.