panel meter needs independant supply ...

M

mark krawczuk

Guest
hi, i`ve finished building a power supply with , fixed 5,9,12,15 volts and
adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the adjustable
side ( i powered the meter from the fixed 9 volts) it came up with a 1 in
the display, anyways if i powered it from a 9 volt battery the panel meter
worked perfect. looks like it needs a independant 9 volts supply.

is there any way around this , by using the power supply i already have
to power the meter , instead of a battery ?

thanks,
mark k
 
On Dec 19, 9:44 am, "mark krawczuk" <krawc...@adam.com.au> wrote:
hi, i`ve finished building a power supply with , fixed 5,9,12,15 volts and
adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the adjustable
side ( i powered the meter from the fixed 9 volts) it came up with a 1 in
the display, anyways if i powered it from a 9 volt battery the panel meter
worked perfect. looks like it needs a independant 9 volts supply.

is there any way around this , by using the power supply i already have
to power the meter , instead of a battery ?

thanks,
mark k
Click to expand...
Yes, many of those panel meters do not like being ground referenced on
the supply side. Some have a link or can be easily moded for a common
supply, but others can't.
You didn't supply any details on the meter, nor your power supply
configuration, so it's kinda hard to help...
If you have a spare isolated tap on your transformer you can use that.

There has been talk about this recently on the group, search the
archives.

Dave.
 
What David said is correct. I went through that experience a couple of years
back. Ever since I have been asking specifically if the meter can be used with
a common negative, and they all eventually admit shyly that the answer is NO.

Luke Tubnor at Jaycar's tech support went through this with me at some length,
having already been there in his own experimentation. You can sort of fudge it
if you are only using it as a voltmeter, but if you want to switch it between
voltage and current then that fudge isn't a goer.

If you havent got an isolated uncommitted secondary, the easiest ways -
seriously - are either to get a small transformer and connect that to provide
the separate (microamp) supply, or build a small isolated DC-DC switcher off
your bridge oputput.

It's a real bummer.
 
rebel wrote:
What David said is correct. I went through that experience a couple of years
back. Ever since I have been asking specifically if the meter can be used with
a common negative, and they all eventually admit shyly that the answer is NO.

Luke Tubnor at Jaycar's tech support went through this with me at some length,
having already been there in his own experimentation. You can sort of fudge it
if you are only using it as a voltmeter, but if you want to switch it between
voltage and current then that fudge isn't a goer.

If you havent got an isolated uncommitted secondary, the easiest ways -
seriously - are either to get a small transformer and connect that to provide
the separate (microamp) supply, or build a small isolated DC-DC switcher off
your bridge oputput.

It's a real bummer
Click to expand...
Many years ago I built a simple inverter type circuit for a LCD display
power supply. It used a nand logic chip and a few other components. Have
a look around.
 
"Davo" <Dave@gmail.com> wrote in message
news:494afd5c$1_6@news.peopletelecom.com.au...
rebel wrote:
What David said is correct. I went through that experience a couple of
years
back. Ever since I have been asking specifically if the meter can be
used with
a common negative, and they all eventually admit shyly that the answer is
NO.

Luke Tubnor at Jaycar's tech support went through this with me at some
length,
having already been there in his own experimentation. You can sort of
fudge it
if you are only using it as a voltmeter, but if you want to switch it
between
voltage and current then that fudge isn't a goer.

If you havent got an isolated uncommitted secondary, the easiest ways -
seriously - are either to get a small transformer and connect that to
provide
the separate (microamp) supply, or build a small isolated DC-DC switcher
off
your bridge oputput.

It's a real bummer

Many years ago I built a simple inverter type circuit for a LCD display
power supply. It used a nand logic chip and a few other components. Have a
look around.
Click to expand...
Been there, done that, use a SRS-1209 miniature DC-DC converter module.

Google for it.

JD
 
On Fri, 19 Dec 2008 09:26:45 +0800 rebel <me@privacy.net> wrote in Message
id: <93slk4t0q1fi0s7rsrgrtt8aggdapr1crm@4ax.com>:

What David said is correct. I went through that experience a couple of years
back. Ever since I have been asking specifically if the meter can be used with
a common negative, and they all eventually admit shyly that the answer is NO.

Luke Tubnor at Jaycar's tech support went through this with me at some length,
having already been there in his own experimentation. You can sort of fudge it
if you are only using it as a voltmeter, but if you want to switch it between
voltage and current then that fudge isn't a goer.

If you havent got an isolated uncommitted secondary, the easiest ways -
seriously - are either to get a small transformer and connect that to provide
the separate (microamp) supply, or build a small isolated DC-DC switcher off
your bridge oputput.

It's a real bummer.
Click to expand...
Some panel meters do not have that limitation:
http://www.mpja.com/prodinfo.asp?number=16565+ME
http://www.mpja.com/prodinfo.asp?number=12306+ME
For instance.
 
On Fri, 19 Dec 2008 05:22:16 -0500, JW <none@dev.null> wrote:

On Fri, 19 Dec 2008 09:26:45 +0800 rebel <me@privacy.net> wrote in Message
id: <93slk4t0q1fi0s7rsrgrtt8aggdapr1crm@4ax.com>:


What David said is correct. I went through that experience a couple of years
back. Ever since I have been asking specifically if the meter can be used with
a common negative, and they all eventually admit shyly that the answer is NO.

Luke Tubnor at Jaycar's tech support went through this with me at some length,
having already been there in his own experimentation. You can sort of fudge it
if you are only using it as a voltmeter, but if you want to switch it between
voltage and current then that fudge isn't a goer.

If you havent got an isolated uncommitted secondary, the easiest ways -
seriously - are either to get a small transformer and connect that to provide
the separate (microamp) supply, or build a small isolated DC-DC switcher off
your bridge oputput.

It's a real bummer.

Some panel meters do not have that limitation:
http://www.mpja.com/prodinfo.asp?number=16565+ME
Click to expand...
which is a LED type. They don't have any problem sharing a neg rail. In fact
it is almost a requirement on most common units.

http://www.mpja.com/prodinfo.asp?number=12306+ME
Click to expand...
which is more interesting (although from USA).

Mind you, many of the cheaper ones claim to be able to do it, but can't deliver.
Having been thusly disappointed before, I wouldn't get overly excited until I
had seen it perform.
 
On Fri, 19 Dec 2008 20:10:31 +0800 rebel <me@privacy.net> wrote in Message
id: <pj3nk4d1btm4h1ghttdo4a16j4u42u5s27@4ax.com>:

On Fri, 19 Dec 2008 05:22:16 -0500, JW <none@dev.null> wrote:

On Fri, 19 Dec 2008 09:26:45 +0800 rebel <me@privacy.net> wrote in Message
id: <93slk4t0q1fi0s7rsrgrtt8aggdapr1crm@4ax.com>:


What David said is correct. I went through that experience a couple of years
back. Ever since I have been asking specifically if the meter can be used with
a common negative, and they all eventually admit shyly that the answer is NO.

Luke Tubnor at Jaycar's tech support went through this with me at some length,
having already been there in his own experimentation. You can sort of fudge it
if you are only using it as a voltmeter, but if you want to switch it between
voltage and current then that fudge isn't a goer.

If you havent got an isolated uncommitted secondary, the easiest ways -
seriously - are either to get a small transformer and connect that to provide
the separate (microamp) supply, or build a small isolated DC-DC switcher off
your bridge oputput.

It's a real bummer.

Some panel meters do not have that limitation:
http://www.mpja.com/prodinfo.asp?number=16565+ME

which is a LED type. They don't have any problem sharing a neg rail. In fact
it is almost a requirement on most common units.
Click to expand...
I can't speak for every place that sells them, but many of the LED meters
at http://www.mpja.com/products.asp?dept=52 do not. I don't believe it has
anything to do with whether they are LED or LCD, but rather the A/D
converter or input amps.
 
"mark krawczuk" <krawczuk@adam.com.au> wrote in message
news:hbidnSHAh_n1T9fUnZ2dnUVZ_vWdnZ2d@adnap.net.au...
hi, i`ve finished building a power supply with , fixed 5,9,12,15 volts and
adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the adjustable side
( i powered the meter from the fixed 9 volts) it came up with a 1 in the
display, anyways if i powered it from a 9 volt battery the panel meter worked
perfect. looks like it needs a independant 9 volts supply.

is there any way around this , by using the power supply i already have to
power the meter , instead of a battery ?

thanks,
mark k
Click to expand...
This is what I used the last time I needed an isolated supply for a cheap little
LCD meter (a month ago)

http://www.discovercircuits.com/PDF-FILES/ISOLATED9VSUPPLY2.pdf

I have used in the past a 4011 quad NAND gate to do exactly the same thing.
Scroll right to the bottom of the page for "floating supply..."

http://www.techlib.com/electronics/regulators.html

These are good for a couple of mA and work fine with an LCD meter. Not sure how
much current an LED meter draws.

PH
 
hi, mine is a led panel meter , and draws up to 60 ma , the schematic you
mentioned only has a 1ma ?

mark k



"Peter Howard" <bbrover109@bbbigpond.net.au> wrote in message
news:4vg3l.3389$cu.2049@news-server.bigpond.net.au...
"mark krawczuk" <krawczuk@adam.com.au> wrote in message
news:hbidnSHAh_n1T9fUnZ2dnUVZ_vWdnZ2d@adnap.net.au...
hi, i`ve finished building a power supply with , fixed 5,9,12,15 volts
and adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the adjustable
side ( i powered the meter from the fixed 9 volts) it came up with a 1
in the display, anyways if i powered it from a 9 volt battery the panel
meter worked perfect. looks like it needs a independant 9 volts supply.

is there any way around this , by using the power supply i already have
to power the meter , instead of a battery ?

thanks,
mark k


This is what I used the last time I needed an isolated supply for a cheap
little LCD meter (a month ago)

http://www.discovercircuits.com/PDF-FILES/ISOLATED9VSUPPLY2.pdf

I have used in the past a 4011 quad NAND gate to do exactly the same
thing. Scroll right to the bottom of the page for "floating supply..."

http://www.techlib.com/electronics/regulators.html

These are good for a couple of mA and work fine with an LCD meter. Not
sure how much current an LED meter draws.

PH
Click to expand...
 
On 2008-12-21, mark krawczuk <krawczuk@adam.com.au> wrote:
hi, mine is a led panel meter , and draws up to 60 ma , the schematic you
mentioned only has a 1ma ?
Click to expand...
you'll need a bigger converter for that (scrounge an 0509 from an old thin
ethernet card? they're good for 222ma )

or use an op-amp to shift the input voltages:

http://www.jprelec.co.uk/docs/PImages/pdfcopies/375-102.PDF
 
"mark krawczuk" <krawczuk@adam.com.au> wrote in message
news:Z-adna7cbLFvUdDUnZ2dnUVZ_qvinZ2d@adnap.net.au...
hi, mine is a led panel meter , and draws up to 60 ma , the schematic you
mentioned only has a 1ma ?

mark k
Click to expand...
Yep, a milliamp or two which doesn't help you if your LED panel meter draws
fifty times that.

Other posters mentioned the possibility of a tiny mains transformer,perhaps
salvaged from some small mains powered junkbox device like a radio or even the
guts of a low current plugpack. Depends on how good your junkbox is.
That SRS-1209 DC-DC converter mentioned by another poster is available in
Australia from
http://www.computronics.com.au/meanwell/srs/
56mA out for $7.10 plus of course whatever they want to bite you for postage.
They look very handy in a DIP sized package. I may even get some myself to save
me reinventing the wheel next time around.

PH
 
On Dec 19, 9:44 am, "mark krawczuk" <krawc...@adam.com.au> wrote:
hi, i`ve  finished building a power supply with , fixed 5,9,12,15 volts and
adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the  adjustable
side ( i powered the meter from the fixed  9 volts) it came up with a 1 in
the display, anyways if i powered it from a 9 volt battery the panel meter
worked perfect. looks like it needs a  independant  9 volts supply.

 is there any way around  this  , by using the power supply i already have
to power the meter , instead of a battery  ?

thanks,
mark k
Click to expand...
As a lateral thinking idea for your next project, use a $20 DMM from
jaycar etc instead of a panel meter. Make it visible via a cutout with
connections made internally, and provide a 9v supply from your main
supply. Will be cheaper and easier.
 
On Sun, 21 Dec 2008 14:00:02 -0800 (PST), geoffjunkster@gmail.com wrote:

On Dec 19, 9:44 am, "mark krawczuk" <krawc...@adam.com.au> wrote:
hi, i`ve  finished building a power supply with , fixed 5,9,12,15 volts and
adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the  adjustable
side ( i powered the meter from the fixed  9 volts) it came up with a 1 in
the display, anyways if i powered it from a 9 volt battery the panel meter
worked perfect. looks like it needs a  independant  9 volts supply.

 is there any way around  this  , by using the power supply i already have
to power the meter , instead of a battery  ?

thanks,
mark k

As a lateral thinking idea for your next project, use a $20 DMM from
jaycar etc instead of a panel meter. Make it visible via a cutout with
connections made internally, and provide a 9v supply from your main
supply. Will be cheaper and easier.
Click to expand...
Huh? Same problem exactly that the O/P raised.
 
Hi Rebel,
Jaycar have a small PCB kit which uses radio IF coils and and an
oscillator circuit creating an isolated supply to drive an LCD panel meter.

cheers,
Dex


rebel wrote:
On Sun, 21 Dec 2008 14:00:02 -0800 (PST), geoffjunkster@gmail.com wrote:

On Dec 19, 9:44 am, "mark krawczuk" <krawc...@adam.com.au> wrote:
hi, i`ve finished building a power supply with , fixed 5,9,12,15 volts and
adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the adjustable
side ( i powered the meter from the fixed 9 volts) it came up with a 1 in
the display, anyways if i powered it from a 9 volt battery the panel meter
worked perfect. looks like it needs a independant 9 volts supply.

is there any way around this , by using the power supply i already have
to power the meter , instead of a battery ?

thanks,
mark k
As a lateral thinking idea for your next project, use a $20 DMM from
jaycar etc instead of a panel meter. Make it visible via a cutout with
connections made internally, and provide a 9v supply from your main
supply. Will be cheaper and easier.

Huh? Same problem exactly that the O/P raised.
Click to expand...
 
Hi Rebel,
Oatley Electronics may have it also can't remember exactly, so many
websites so little time.

cheers,
Dex


Dex wrote:
Hi Rebel,
Jaycar have a small PCB kit which uses radio IF coils and and an
oscillator circuit creating an isolated supply to drive an LCD panel meter.

cheers,
Dex


rebel wrote:
On Sun, 21 Dec 2008 14:00:02 -0800 (PST), geoffjunkster@gmail.com wrote:

On Dec 19, 9:44 am, "mark krawczuk" <krawc...@adam.com.au> wrote:
hi, i`ve finished building a power supply with , fixed 5,9,12,15 volts and
adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the adjustable
side ( i powered the meter from the fixed 9 volts) it came up with a 1 in
the display, anyways if i powered it from a 9 volt battery the panel meter
worked perfect. looks like it needs a independant 9 volts supply.

is there any way around this , by using the power supply i already have
to power the meter , instead of a battery ?

thanks,
mark k
As a lateral thinking idea for your next project, use a $20 DMM from
jaycar etc instead of a panel meter. Make it visible via a cutout with
connections made internally, and provide a 9v supply from your main
supply. Will be cheaper and easier.
Huh? Same problem exactly that the O/P raised.
Click to expand...
 
On 2008-12-21, Jasen Betts <jasen@xnet.co.nz> wrote:
On 2008-12-21, mark krawczuk <krawczuk@adam.com.au> wrote:
hi, mine is a led panel meter , and draws up to 60 ma , the schematic you
mentioned only has a 1ma ?

you'll need a bigger converter for that (scrounge an 0509 from an old thin
ethernet card? they're good for 222ma )
Click to expand...
I was wrong - actually 56mA, same as the 1209 mentioned previously
4mA to few for you, (maybe enough if you leave "half a digit" dark)
 
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