Basic stamp & wall wort''s
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Posts: 46,084
A 'typical' 'unregulated' wall wart for 12 VDC
simply has an AC transformer, with a half or
full-wave rectifier on it, and probably an output
capacitor. It's rated for a certain current at
that rated voltage. Below that current, the
output voltage can be higher than the rating.
(Not by a whole lot -- I'd expect a 12V DC
wall wart to measure open-circuit at around
16 volts).
When you use these, you are expected to have a
linear regulator, with a 'local' input capacitor and
a 'local' output capacitor near the regulator.
For your application, a single 7812, 12 volt
regulator would be enough for your relays,
and you could use the Stamp's on-module
regulator for its power, driving Vin from
your regulated 12 volt DC line.
On the other hand, if your relays can handle the
ripple coming out of the wall-wart,
you are already in good shape.
Note that a 'regulated' wall wart has the regulator
built in to the wall-wart itself, so it should have
much steadier voltage over a broader range of currents.
Note they also cost $10 to $20 more than their
unregulated brothers.
The failure mode of an unregulated wall-wart I would
assume to be from age or overheating -- I'd guess it
would mostly fail open. If the transformer shorted,
I'd guess it would burn out the rectifiers, and again
fail open.
A regulated wall-wart could burn-out its regulator,
and then you could get a little more voltage -- but
I don't know if this would be enough for damage.
I've only seen switching supplies fail dramatically,
where the output voltage goes from +5 DC to 120 VAC.
--- In basicstamps@yahoogroups.com, "John Walton" <john@l...> wrote:
> Well, of all the 'odd' posts I see on the list and the answers they
> receive, I'm surprised this one made it through without so much as 1
> reply. For the record, I'm going with the wall wort, wish me luck!
>
> -John
>
>
>
Original Message
> From: ufi911 [noparse][[/noparse]mailto:john@l...]
> Sent: Monday, January 12, 2004 7:47 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Basic stamp & wall wort's
>
> I'm about to deploy a very simple valve control module using a BS1.
>
> Its controlling a couple of relays switching 120 vac (very low
> amperage).
>
> I want to power the stamp & relays with 12 VDC. Can I use a wall
> wort? My concern is if the wall wort fails, is the result going to
> be the end of my stamp? I know nothing is guaranteed, but if the
> wart were to fail and send say 30 VDC to the stamp, I would have to
> rebuild the entire project. Now, if it were to fail and LOOSE
power,
> I can simply replace the power source.
>
> Or should I buy some kind of cheap power supply?
>
> Thanks in advance,
>
> -John
simply has an AC transformer, with a half or
full-wave rectifier on it, and probably an output
capacitor. It's rated for a certain current at
that rated voltage. Below that current, the
output voltage can be higher than the rating.
(Not by a whole lot -- I'd expect a 12V DC
wall wart to measure open-circuit at around
16 volts).
When you use these, you are expected to have a
linear regulator, with a 'local' input capacitor and
a 'local' output capacitor near the regulator.
For your application, a single 7812, 12 volt
regulator would be enough for your relays,
and you could use the Stamp's on-module
regulator for its power, driving Vin from
your regulated 12 volt DC line.
On the other hand, if your relays can handle the
ripple coming out of the wall-wart,
you are already in good shape.
Note that a 'regulated' wall wart has the regulator
built in to the wall-wart itself, so it should have
much steadier voltage over a broader range of currents.
Note they also cost $10 to $20 more than their
unregulated brothers.
The failure mode of an unregulated wall-wart I would
assume to be from age or overheating -- I'd guess it
would mostly fail open. If the transformer shorted,
I'd guess it would burn out the rectifiers, and again
fail open.
A regulated wall-wart could burn-out its regulator,
and then you could get a little more voltage -- but
I don't know if this would be enough for damage.
I've only seen switching supplies fail dramatically,
where the output voltage goes from +5 DC to 120 VAC.
--- In basicstamps@yahoogroups.com, "John Walton" <john@l...> wrote:
> Well, of all the 'odd' posts I see on the list and the answers they
> receive, I'm surprised this one made it through without so much as 1
> reply. For the record, I'm going with the wall wort, wish me luck!
>
> -John
>
>
>
Original Message
> From: ufi911 [noparse][[/noparse]mailto:john@l...]
> Sent: Monday, January 12, 2004 7:47 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Basic stamp & wall wort's
>
> I'm about to deploy a very simple valve control module using a BS1.
>
> Its controlling a couple of relays switching 120 vac (very low
> amperage).
>
> I want to power the stamp & relays with 12 VDC. Can I use a wall
> wort? My concern is if the wall wort fails, is the result going to
> be the end of my stamp? I know nothing is guaranteed, but if the
> wart were to fail and send say 30 VDC to the stamp, I would have to
> rebuild the entire project. Now, if it were to fail and LOOSE
power,
> I can simply replace the power source.
>
> Or should I buy some kind of cheap power supply?
>
> Thanks in advance,
>
> -John