Wires...?

F

fungus

Guest
Spurred on by my first LED light setup, I'm now doing the hallway...

The setup is this: There's a 12V switching power supply connected to a
small current regulator board ("CRB"). The CRB fixes the output
current to 850mA. After that come the LEDs.

I did the initial test on the table. The LED current was 850mA as it
should be, output from the CRB was 10.5 Volts. I left it running for a
day, all the voltages/currents were good.

So ... I moved into the hallway and started putting it together. I
put the PSU on the floor and ran a length of lamp wire up to the CRB
which is at ceiling level. When I switched it on it looked a bit dim.
I measured the LED current and it was only 450mA. Weird.

On investigation I found that the voltage at the PSU was 12V but at
the other end of the piece of wire it was only 11V. The CRB didn't
have enough voltage margin to power the LEDs properly.

The PSU has a little trimmer pot on it to adjust the output voltage. I
tweaked it up to 13V and everything started working properly again.

Why would I get this voltage drop? I measured the resistance of the
wire and it's 0.1-0.2 Ohms - background noise level for my multimeter.
I thought it might be some sort of coupling issue because the CRB is
switching on/off quickly so I looked the CRB"s input voltage with an
oscilloscope. It was perfectly flat, nothing to see. I even tried
putting a ceramic capacitor across the CRB input to see if it would
help and it made no difference. The voltage drop along the wire was
still a whole volt.

(Note: The output voltage from the CRB is also perfectly flat - it's
not outputting a PWM signal to the LEDs)

As a second test I moved the CRB next to the PSU (a six inch piece of
wire) and put a longer wire between the CRB and the LEDs (this wire
was slightly shorter/thicker then the lamp wire).

The voltage drop from the PSU to the CRB went down to 0.1V - much
better! (but still measurable)

But ... the voltage output from the CRB went up from 10.5V to 11.5V. I
didn't gain anything. I just moved the missing Volt from one wire to
another!

Can anybody shine a light on what's happening here?

This setup works and I assume the PSU will be OK outputting 13V (it's
only at 40% of rated current) but it bothers me. Either copper wire is
nowhere near as good as I imagined (in which case how does the phone
company stay in business?) or there's something going on that I don't
know about.
 
On Sun, 27 Nov 2011 04:04:16 -0800 (PST), fungus
<openglMYSOCKS@artlum.com> wrote:

Spurred on by my first LED light setup, I'm now doing the hallway...

The setup is this: There's a 12V switching power supply connected to a
small current regulator board ("CRB"). The CRB fixes the output
current to 850mA. After that come the LEDs.

I did the initial test on the table. The LED current was 850mA as it
should be, output from the CRB was 10.5 Volts. I left it running for a
day, all the voltages/currents were good.

So ... I moved into the hallway and started putting it together. I
put the PSU on the floor and ran a length of lamp wire up to the CRB
which is at ceiling level. When I switched it on it looked a bit dim.
I measured the LED current and it was only 450mA. Weird.

On investigation I found that the voltage at the PSU was 12V but at
the other end of the piece of wire it was only 11V. The CRB didn't
have enough voltage margin to power the LEDs properly.

The PSU has a little trimmer pot on it to adjust the output voltage. I
tweaked it up to 13V and everything started working properly again.

Why would I get this voltage drop? I measured the resistance of the
wire and it's 0.1-0.2 Ohms - background noise level for my multimeter.
I thought it might be some sort of coupling issue because the CRB is
switching on/off quickly so I looked the CRB"s input voltage with an
oscilloscope. It was perfectly flat, nothing to see. I even tried
putting a ceramic capacitor across the CRB input to see if it would
help and it made no difference. The voltage drop along the wire was
still a whole volt.

(Note: The output voltage from the CRB is also perfectly flat - it's
not outputting a PWM signal to the LEDs)

As a second test I moved the CRB next to the PSU (a six inch piece of
wire) and put a longer wire between the CRB and the LEDs (this wire
was slightly shorter/thicker then the lamp wire).

The voltage drop from the PSU to the CRB went down to 0.1V - much
better! (but still measurable)

But ... the voltage output from the CRB went up from 10.5V to 11.5V. I
didn't gain anything. I just moved the missing Volt from one wire to
another!

Can anybody shine a light on what's happening here?

This setup works and I assume the PSU will be OK outputting 13V (it's
only at 40% of rated current) but it bothers me. Either copper wire is
nowhere near as good as I imagined (in which case how does the phone
company stay in business?) or there's something going on that I don't
know about.
Click to expand...
With a little back of the envelope math: Assuming you're using AWG 14
zip cord, that's about 2.5 ohms/1000 ft. Assuming a 20-ft run from the
PSU to the CRB, each leg would be about 0.05 ohms. Swagging some
efficiency for the CRB to make the math easy, assume it's pulling 1 A to
supply 0.85 A. The expected drop across each feeder leg would then be
0.05 V. So, 12 V across the PSU should drop to 11.9 V across the CRB.

Either you're running AWG 24 (25 ohms/1000 ft -> 0.5 V/leg @ 1A -> 11 V)
or you're pulling 10 A through the CRB or you've got a high resistance
connection somewhere.

--
Rich Webb Norfolk, VA
 
On Nov 27, 1:40 pm, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
Either you're running AWG 24 (25 ohms/1000 ft -> 0.5 V/leg @ 1A -> 11 V)
or you're pulling 10 A through the CRB or you've got a high resistance
connection somewhere.
Click to expand...
I did suspect the screw terminals but they've been connected
and disconnected several times over the last day or so and
nothing changed in any of the measurements.

Maybe I could check that out in more depth.


PS: I've always wondered how things like heaters
need 13 amp cable (here in Europe) but the plugs
and switches they use to connect to the supply
seem to have quite small contact areas...
 
fungus wrote:
Spurred on by my first LED light setup, I'm now doing the hallway...

The setup is this: There's a 12V switching power supply connected to a
small current regulator board ("CRB"). The CRB fixes the output
current to 850mA. After that come the LEDs.

I did the initial test on the table. The LED current was 850mA as it
should be, output from the CRB was 10.5 Volts. I left it running for a
day, all the voltages/currents were good.

So ... I moved into the hallway and started putting it together. I
put the PSU on the floor and ran a length of lamp wire up to the CRB
which is at ceiling level. When I switched it on it looked a bit dim.
I measured the LED current and it was only 450mA. Weird.

On investigation I found that the voltage at the PSU was 12V but at
the other end of the piece of wire it was only 11V. The CRB didn't
have enough voltage margin to power the LEDs properly.

The PSU has a little trimmer pot on it to adjust the output voltage. I
tweaked it up to 13V and everything started working properly again.

Why would I get this voltage drop? I measured the resistance of the
wire and it's 0.1-0.2 Ohms - background noise level for my multimeter.
I thought it might be some sort of coupling issue because the CRB is
switching on/off quickly so I looked the CRB"s input voltage with an
oscilloscope. It was perfectly flat, nothing to see. I even tried
putting a ceramic capacitor across the CRB input to see if it would
help and it made no difference. The voltage drop along the wire was
still a whole volt.

(Note: The output voltage from the CRB is also perfectly flat - it's
not outputting a PWM signal to the LEDs)

As a second test I moved the CRB next to the PSU (a six inch piece of
wire) and put a longer wire between the CRB and the LEDs (this wire
was slightly shorter/thicker then the lamp wire).

The voltage drop from the PSU to the CRB went down to 0.1V - much
better! (but still measurable)

But ... the voltage output from the CRB went up from 10.5V to 11.5V. I
didn't gain anything. I just moved the missing Volt from one wire to
another!

Can anybody shine a light on what's happening here?

This setup works and I assume the PSU will be OK outputting 13V (it's
only at 40% of rated current) but it bothers me. Either copper wire is
nowhere near as good as I imagined (in which case how does the phone
company stay in business?) or there's something going on that I don't
know about.
Your meter is not telling you the truth about the wire?
Click to expand...

You are border lining your current limiting board due to the 1 diode
drop voltage (0.7) that is going to take a sharp
drop. I only assume you're using a bipolar type limit circuit ?

So in one case you may have a high R cord and then next case
insufficient voltage range to make up for the loss in the CRB.

Remove 1 led out of the string.


Jamie
 
On Nov 27, 1:40 pm, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
Either you're running AWG 24 or you're pulling 10A
through the CRB or you've got a high resistance
connection somewhere.
Click to expand...
Aha!

I was using a piece of solid-core telephone wire because
the last few inches will be visible so I wanted a thin wire
going up the wall instead of a huge chunk of mains cable.

I just measured it with my micrometer and googled "AWG".
It comes in at around AWG 25. It's not 20 feet long but
between that and all the screw connections it probably
adds up.

So...if I wanted to fix it I could run a thicker wire up to
the last few inches then switch to the thin wire.

OTOH I can leave it as-is. It works, I know nothing
sinister is happening and the CRB stays cooler the
closer the input&output voltages are to each other.

Anyway, mystery solved - I'm an ignoramous who
needs to keep the AWG chart handy.
 
"fungus" <openglMYSOCKS@artlum.com> schreef in bericht
news:194e69b3-8aab-4f55-b1a1-719f3938c1fa@gi1g2000vbb.googlegroups.com...
Spurred on by my first LED light setup, I'm now doing the hallway...

The setup is this: There's a 12V switching power supply connected to a
small current regulator board ("CRB"). The CRB fixes the output
current to 850mA. After that come the LEDs.

I did the initial test on the table. The LED current was 850mA as it
should be, output from the CRB was 10.5 Volts. I left it running for a
day, all the voltages/currents were good.

So ... I moved into the hallway and started putting it together. I
put the PSU on the floor and ran a length of lamp wire up to the CRB
which is at ceiling level. When I switched it on it looked a bit dim.
I measured the LED current and it was only 450mA. Weird.

On investigation I found that the voltage at the PSU was 12V but at
the other end of the piece of wire it was only 11V. The CRB didn't
have enough voltage margin to power the LEDs properly.

The PSU has a little trimmer pot on it to adjust the output voltage. I
tweaked it up to 13V and everything started working properly again.

Why would I get this voltage drop? I measured the resistance of the
wire and it's 0.1-0.2 Ohms - background noise level for my multimeter.
I thought it might be some sort of coupling issue because the CRB is
switching on/off quickly so I looked the CRB"s input voltage with an
oscilloscope. It was perfectly flat, nothing to see. I even tried
putting a ceramic capacitor across the CRB input to see if it would
help and it made no difference. The voltage drop along the wire was
still a whole volt.

(Note: The output voltage from the CRB is also perfectly flat - it's
not outputting a PWM signal to the LEDs)

As a second test I moved the CRB next to the PSU (a six inch piece of
wire) and put a longer wire between the CRB and the LEDs (this wire
was slightly shorter/thicker then the lamp wire).

The voltage drop from the PSU to the CRB went down to 0.1V - much
better! (but still measurable)

But ... the voltage output from the CRB went up from 10.5V to 11.5V. I
didn't gain anything. I just moved the missing Volt from one wire to
another!

Can anybody shine a light on what's happening here?

This setup works and I assume the PSU will be OK outputting 13V (it's
only at 40% of rated current) but it bothers me. Either copper wire is
nowhere near as good as I imagined (in which case how does the phone
company stay in business?) or there's something going on that I don't
know about.
Click to expand...
Well, Ohms law stands. R=U/I=1/450=2R2 or 2.2 Ohm, which has to account for
the wire (twice), the ampmeter and various contactresistances. Guess you
have not taken them all when measuring ohms, besides this meters are not
known for there lack of accuracy measuring below 10 Ohm. (Unless you have a
very good=expensive and callibrated one.)

If you want to get an idea of the wire resistance you better use a curent
source of - let's say - 1A or 2A. Then short the wires at one side, connect
the source at the other and measure current and voltage simultanuously at
that side. Be sure to measure the voltage at the wires side, not at the
source side. Supposing you have reasonable good meters you'll find the
resistance using Ohms law as mentioned.

Be aware that doubling the thickness of the wire will reduce its resistance
by four.

As for telephone companies, they use currents way below 100mA (depending on
where you live) and voltages up to 48V. But they sure have to be aware of
line losses.

The phenomenon you encountered is well known and power supplies are often
equiped to deal with it. They have separate sense lines to measure the
voltage near the load and regulate the power output to be correct at that
point.

petrus bitbyter
 
"petrus bitbyter" <petrus.bitbyter@hotmail.com> schreef in bericht
news:4ed25ab5$0$16304$e4fe514c@dreader37.news.xs4all.nl...
"fungus" <openglMYSOCKS@artlum.com> schreef in bericht
news:194e69b3-8aab-4f55-b1a1-719f3938c1fa@gi1g2000vbb.googlegroups.com...
Spurred on by my first LED light setup, I'm now doing the hallway...

The setup is this: There's a 12V switching power supply connected to a
small current regulator board ("CRB"). The CRB fixes the output
current to 850mA. After that come the LEDs.

I did the initial test on the table. The LED current was 850mA as it
should be, output from the CRB was 10.5 Volts. I left it running for a
day, all the voltages/currents were good.

So ... I moved into the hallway and started putting it together. I
put the PSU on the floor and ran a length of lamp wire up to the CRB
which is at ceiling level. When I switched it on it looked a bit dim.
I measured the LED current and it was only 450mA. Weird.

On investigation I found that the voltage at the PSU was 12V but at
the other end of the piece of wire it was only 11V. The CRB didn't
have enough voltage margin to power the LEDs properly.

The PSU has a little trimmer pot on it to adjust the output voltage. I
tweaked it up to 13V and everything started working properly again.

Why would I get this voltage drop? I measured the resistance of the
wire and it's 0.1-0.2 Ohms - background noise level for my multimeter.
I thought it might be some sort of coupling issue because the CRB is
switching on/off quickly so I looked the CRB"s input voltage with an
oscilloscope. It was perfectly flat, nothing to see. I even tried
putting a ceramic capacitor across the CRB input to see if it would
help and it made no difference. The voltage drop along the wire was
still a whole volt.

(Note: The output voltage from the CRB is also perfectly flat - it's
not outputting a PWM signal to the LEDs)

As a second test I moved the CRB next to the PSU (a six inch piece of
wire) and put a longer wire between the CRB and the LEDs (this wire
was slightly shorter/thicker then the lamp wire).

The voltage drop from the PSU to the CRB went down to 0.1V - much
better! (but still measurable)

But ... the voltage output from the CRB went up from 10.5V to 11.5V. I
didn't gain anything. I just moved the missing Volt from one wire to
another!

Can anybody shine a light on what's happening here?

This setup works and I assume the PSU will be OK outputting 13V (it's
only at 40% of rated current) but it bothers me. Either copper wire is
nowhere near as good as I imagined (in which case how does the phone
company stay in business?) or there's something going on that I don't
know about.

Well, Ohms law stands. R=U/I=1/450=2R2 or 2.2 Ohm, which has to account
for the wire (twice), the ampmeter and various contactresistances. Guess
you have not taken them all when measuring ohms, besides this meters are
not known for there lack of accuracy measuring below 10 Ohm. (Unless you
have a very good=expensive and callibrated one.)

If you want to get an idea of the wire resistance you better use a curent
source of - let's say - 1A or 2A. Then short the wires at one side,
connect the source at the other and measure current and voltage
simultanuously at that side. Be sure to measure the voltage at the wires
side, not at the source side. Supposing you have reasonable good meters
you'll find the resistance using Ohms law as mentioned.

Be aware that doubling the thickness of the wire will reduce its
resistance by four.

As for telephone companies, they use currents way below 100mA (depending
on where you live) and voltages up to 48V. But they sure have to be aware
of line losses.

The phenomenon you encountered is well known and power supplies are often
equiped to deal with it. They have separate sense lines to measure the
voltage near the load and regulate the power output to be correct at that
point.

petrus bitbyter
Click to expand...
Oops.

These meters are known for their lack of accuracy.
These meters are not known for their accuracy.

petrus bitbyter
 
On Nov 27, 3:54 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
Your meter is not telling you the truth about the wire?
Click to expand...
Maybe...I'll have to revisit that.

    You are border lining your current limiting board due to the 1 diode
drop voltage (0.7) that is going to take a sharp
drop. I only assume you're using a bipolar type limit circuit ?
Click to expand...
I dunno. It's a prebuilt board (based on the MBI6651 if you want
to google it).

   So in one case you may have a high R cord and then next case
insufficient voltage range to make up for the loss in the CRB.
Click to expand...
Looks like it was the cord. I hadn't realized ten feet of
copper had such a high resistance (and my meter
wasn't measuring it for some reason).



    Remove 1 led out of the string.
Click to expand...
Not really possible... I've already got the lamps in place.

(Some cute little lamps I bought in Marrakesh last week... :)
 
fungus wrote:

On Nov 27, 3:54 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Your meter is not telling you the truth about the wire?



Maybe...I'll have to revisit that.


You are border lining your current limiting board due to the 1 diode
drop voltage (0.7) that is going to take a sharp
drop. I only assume you're using a bipolar type limit circuit ?



I dunno. It's a prebuilt board (based on the MBI6651 if you want
to google it).


So in one case you may have a high R cord and then next case
insufficient voltage range to make up for the loss in the CRB.



Looks like it was the cord. I hadn't realized ten feet of
copper had such a high resistance (and my meter
wasn't measuring it for some reason).




Remove 1 led out of the string.



Not really possible... I've already got the lamps in place.

(Some cute little lamps I bought in Marrakesh last week... :)
I didn't find much of a PDF on that however, what I did find does state
Click to expand...
the on switch resistance of being 0.45 ohms. So it looks like you're
losing some head room there and you should count that value in on your
calculations.

Also, for 850ma, using 24 awg is way to small!

Jamie
 
On Nov 27, 4:43 pm, "petrus bitbyter" <petrus.bitby...@hotmail.com>
wrote:
Well, Ohms law stands. R=U/I=1/450=2R2 or 2.2 Ohm, which has to account for
the wire (twice),
Click to expand...
Yes of course...it'll be double the resistance. That's where
the other missing volts are. My wire is twice as long as
I think it is...
 
On Sun, 27 Nov 2011 06:14:27 -0800 (PST), fungus
<openglMYSOCKS@artlum.com> wrote:

On Nov 27, 1:40 pm, Rich Webb <bbew...@mapson.nozirev.ten> wrote:

Either you're running AWG 24 or you're pulling 10A
through the CRB or you've got a high resistance
connection somewhere.


Aha!

I was using a piece of solid-core telephone wire because
the last few inches will be visible so I wanted a thin wire
going up the wall instead of a huge chunk of mains cable.
Click to expand...
Yes, I should have picked up on that with your aside on how the
telephone company does it. IIRC the nominal gauge for premise telephone
wire is AWG 24.

I just measured it with my micrometer and googled "AWG".
It comes in at around AWG 25. It's not 20 feet long but
between that and all the screw connections it probably
adds up.
Click to expand...
Add 0.1 ohm per connection (connector pair). That's not exact, of
course, but a good place to start for estimating. You'll have at least
four, so about another half ohm or so gets added in for the whole run,
out and back.

So...if I wanted to fix it I could run a thicker wire up to
the last few inches then switch to the thin wire.

OTOH I can leave it as-is. It works, I know nothing
sinister is happening and the CRB stays cooler the
closer the input&output voltages are to each other.

Anyway, mystery solved - I'm an ignoramous who
needs to keep the AWG chart handy.
Click to expand...
Nah, it's just easy to forget to include the voltage drop across long
runs if you're accustomed to mostly dealing with on-PCB measurements.

WireTronic <http://www.wiretron.com/> has a handy free PC app that
includes, among other things, an AWG to resistance converter.

AWG is a dB-style scale, though, so easy enough to do in your head given
one starting point (e.g., AWG 10 is 1 ohm per 1000 ft). AWG 20 would
then be 10/1000, 30 is 100/1000, 33 is 200/1000, and so on.

--
Rich Webb Norfolk, VA
 
On Nov 27, 8:40 pm, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
Nah, it's just easy to forget to include the voltage drop across long
runs if you're accustomed to mostly dealing with on-PCB measurements.
Click to expand...
Yep, that's the problem.

WireTronic <http://www.wiretron.com/> has a handy free PC app that
includes, among other things, an AWG to resistance converter.
Click to expand...
I found this web page: http://www.daycounter.com/Calculators/AWG.phtml
 
On Nov 27, 6:11 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
 Also, for 850ma, using 24 awg is way to small!
Click to expand...
The power dissipation is tiny - less than 1 watt per meter.
Is there really a problem apart from having to factor it
into the voltage calculations?
 
On Nov 27, 6:11 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
I didn't find much of a PDF on that...
Click to expand...
Here's the datasheet for the actual board I'm using:

http://www.sure-electronics.net/download/LE-LL11114_Ver1.0_EN.pdf


Here's the schematic:

http://www.sure-electronics.net/download/LE-LL12113_Schematic.pdf


I just noticed I can make my board more efficient by
removing a reverse voltage protection diode...doesn't say
how much more efficient though.
 
fungus wrote:

On Nov 27, 6:11 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

I didn't find much of a PDF on that...


Here's the datasheet for the actual board I'm using:

http://www.sure-electronics.net/download/LE-LL11114_Ver1.0_EN.pdf


Here's the schematic:

http://www.sure-electronics.net/download/LE-LL12113_Schematic.pdf


I just noticed I can make my board more efficient by
removing a reverse voltage protection diode...doesn't say
how much more efficient though.
Click to expand...
That is a buck boost converter and very simple indeed.

There are a lot buck converters in that style on the market that
can be used. I see that one starts off at 9 volts and can work its
way up to something like 26 volts.

P.s.
Don't remove that diode, it most likely is helping the kick back
from the buck to not get into other things via those diode pairs.

Jamie
 
On Nov 27, 8:40 pm, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
IIRC the nominal gauge for premise telephone
wire is AWG 24.
Click to expand...
I measured the diameter at 25 - pretty close!
 
On Nov 27, 10:17 pm, fungus <openglMYSO...@artlum.com> wrote:
The power dissipation is tiny - less than 1 watt per meter.
Click to expand...
Wait, it's even less than that. It's about 0.85 Watts over my
long piece of wire. Per meter it's only 0.06 Watts.

In the name of science I just tried lighting up some LEDs
with a ten foot piece of 33 SWG transformer wire to see
what happens.

Answer: It works fine. It's been lit up for over an hour and
all voltage/current readings are correct.

I was expecting the wire to get hot, maybe even melt,
but if it's getting any warmer it's not enough to feel.
 
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