Adjusting a constant current supply?

[Uncle Peter]

How easy would it be for me to change the current rating of a constant current supply? One from a CREE LED light fitting, which I think is very roughly 0.5 amps at 7V. I want to lower the current, the voltage is ok.

--
Did you hear about the guy who finally figured out women?
He died laughing before he could tell anybody.

 

[Daniel]

On 16/04/14 06:11, Uncle Peter wrote:

How easy would it be for me to change the current rating of a constant
current supply? One from a CREE LED light fitting, which I think is
very roughly 0.5 amps at 7V. I want to lower the current, the voltage
is ok.

My memory of teaching Power Supplies (about 15 years ago), the constant
current was maintained but keeping the voltage developed across a
particular resistor constant, so, in theory, by increasing the value of
the resistor, a lower current would develop the same voltage across the
sensing resistor.

However, you would have to determine which resistor and which value .....!

Daniel

 

[Uncle Peter]

On Wed, 16 Apr 2014 13:01:00 +0100, Daniel <dxmm@albury.nospam.net.au> wrote:

On 16/04/14 06:11, Uncle Peter wrote:
How easy would it be for me to change the current rating of a constant
current supply? One from a CREE LED light fitting, which I think is
very roughly 0.5 amps at 7V. I want to lower the current, the voltage
is ok.

My memory of teaching Power Supplies (about 15 years ago), the constant
current was maintained but keeping the voltage developed across a
particular resistor constant, so, in theory, by increasing the value of
the resistor, a lower current would develop the same voltage across the
sensing resistor.

However, you would have to determine which resistor and which value .....!

Thanks for the tip, I'll run it on a bench with a dummy load and test some resistor voltages, then try changing one a little.


--
Your mouse has moved. Windows must be restarted for this change to take effect.

 

[Daniel]

On 16/04/14 22:23, Uncle Peter wrote:

On Wed, 16 Apr 2014 13:01:00 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 06:11, Uncle Peter wrote:
How easy would it be for me to change the current rating of a constant
current supply? One from a CREE LED light fitting, which I think is
very roughly 0.5 amps at 7V. I want to lower the current, the voltage
is ok.

My memory of teaching Power Supplies (about 15 years ago), the constant
current was maintained but keeping the voltage developed across a
particular resistor constant, so, in theory, by increasing the value of
the resistor, a lower current would develop the same voltage across the
sensing resistor.

However, you would have to determine which resistor and which value
.....!

Thanks for the tip, I'll run it on a bench with a dummy load and test
some resistor voltages, then try changing one a little.

If you've got a circuit diagram of your power supply, and you can
determine which resister is the "sensing" resister, replace it (for the
time being) with a variable resistor/rheostat in the same ohmic range as
the sensing resistor until you can determine what value resistor you
want to stick in.

Daniel

 

[Uncle Peter]

On Thu, 17 Apr 2014 13:42:41 +0100, Daniel <dxmm@albury.nospam.net.au> wrote:

On 16/04/14 22:23, Uncle Peter wrote:
On Wed, 16 Apr 2014 13:01:00 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 06:11, Uncle Peter wrote:
How easy would it be for me to change the current rating of a constant
current supply? One from a CREE LED light fitting, which I think is
very roughly 0.5 amps at 7V. I want to lower the current, the voltage
is ok.

My memory of teaching Power Supplies (about 15 years ago), the constant
current was maintained but keeping the voltage developed across a
particular resistor constant, so, in theory, by increasing the value of
the resistor, a lower current would develop the same voltage across the
sensing resistor.

However, you would have to determine which resistor and which value
.....!

Thanks for the tip, I'll run it on a bench with a dummy load and test
some resistor voltages, then try changing one a little.

If you've got a circuit diagram of your power supply, and you can
determine which resister is the "sensing" resister, replace it (for the
time being) with a variable resistor/rheostat in the same ohmic range as
the sensing resistor until you can determine what value resistor you
want to stick in.

I've got one of those multi-resistor-bank boxes with dials on the top for units, tens, hundreds, etc, so I can select any resistance with it. Very handy!

--
Some "chinese english" instructions for an automatic light switch, needless to say I did not attempt to follow them during the installation....

The surface design is facility, comely but not losing generosity, it will not have accidented feeling after installation.
Wide working voltage: you will not be worried when you go all over Europe carrying it.
You could fix the sensor with two screws on the junction box in circular one, also fix it with special installation shelf.
In a word, whether the junction box installation orientation is true, it makes the installation flatly.
The lamp will be on automatically when you knock at the door or say "I am coming back".
It will make your home warmer and more romantic.
Penetrate the setscrew into installation hole, block on radiator to aim at the installation hole on connection box.
Let electrician or experienced human install it.
The unrest objects can't be regarded as the installation basis-face.
Don't open the case for your safety if you find the hitch after installation.
If there is any difference between instruction and products, please give priority to product, sorry not to inform you again.

 

[Uncle Peter]

On Thu, 17 Apr 2014 13:42:41 +0100, Daniel <dxmm@albury.nospam.net.au> wrote:

On 16/04/14 22:23, Uncle Peter wrote:
On Wed, 16 Apr 2014 13:01:00 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 06:11, Uncle Peter wrote:
How easy would it be for me to change the current rating of a constant
current supply? One from a CREE LED light fitting, which I think is
very roughly 0.5 amps at 7V. I want to lower the current, the voltage
is ok.

My memory of teaching Power Supplies (about 15 years ago), the constant
current was maintained but keeping the voltage developed across a
particular resistor constant, so, in theory, by increasing the value of
the resistor, a lower current would develop the same voltage across the
sensing resistor.

However, you would have to determine which resistor and which value
.....!

Thanks for the tip, I'll run it on a bench with a dummy load and test
some resistor voltages, then try changing one a little.

If you've got a circuit diagram of your power supply, and you can
determine which resister is the "sensing" resister, replace it (for the
time being) with a variable resistor/rheostat in the same ohmic range as
the sensing resistor until you can determine what value resistor you
want to stick in.

This is a partial drawing of the circuit diagram of the power supply. I can't see half of the circuit connections as they go underneath the unknown microchip!
http://petersphotos.com/temp/PSU.jpg

--
Some "chinese english" instructions for an automatic light switch, needless to say I did not attempt to follow them during the installation....

The surface design is facility, comely but not losing generosity, it will not have accidented feeling after installation.
Wide working voltage: you will not be worried when you go all over Europe carrying it.
You could fix the sensor with two screws on the junction box in circular one, also fix it with special installation shelf.
In a word, whether the junction box installation orientation is true, it makes the installation flatly.
The lamp will be on automatically when you knock at the door or say "I am coming back".
It will make your home warmer and more romantic.
Penetrate the setscrew into installation hole, block on radiator to aim at the installation hole on connection box.
Let electrician or experienced human install it.
The unrest objects can't be regarded as the installation basis-face.
Don't open the case for your safety if you find the hitch after installation.
If there is any difference between instruction and products, please give priority to product, sorry not to inform you again.

 

[Daniel]

On 23/04/14 08:02, Uncle Peter wrote:

On Thu, 17 Apr 2014 13:42:41 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 22:23, Uncle Peter wrote:
On Wed, 16 Apr 2014 13:01:00 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 06:11, Uncle Peter wrote:
How easy would it be for me to change the current rating of a constant
current supply? One from a CREE LED light fitting, which I think is
very roughly 0.5 amps at 7V. I want to lower the current, the voltage
is ok.

My memory of teaching Power Supplies (about 15 years ago), the constant
current was maintained but keeping the voltage developed across a
particular resistor constant, so, in theory, by increasing the value of
the resistor, a lower current would develop the same voltage across the
sensing resistor.

However, you would have to determine which resistor and which value
.....!

Thanks for the tip, I'll run it on a bench with a dummy load and test
some resistor voltages, then try changing one a little.

If you've got a circuit diagram of your power supply, and you can
determine which resister is the "sensing" resister, replace it (for the
time being) with a variable resistor/rheostat in the same ohmic range as
the sensing resistor until you can determine what value resistor you
want to stick in.

This is a partial drawing of the circuit diagram of the power supply. I
can't see half of the circuit connections as they go underneath the
unknown microchip!
http://petersphotos.com/temp/PSU.jpg

O.K., that's more than I expected, thanks.

(I'm really guessing that the 280ohms you measured is the 282ohm
resistor next to it, but that's by-the-by)

The NPN transistor that you question mark as "Low Freq" ... I would be
expecting it to be as High Freq Switching Tranny, which would, somehow,
by "driven On/Off/On/Off by the IC in middle of the diag, causing an
On/Off/On/Off current to flow through the coil/Transformer, and these
pulses are transformer coupled across the coil/Transformer, to be
rectified by the diode and filtered by the capacitor and 4.7kohm
resistor across the output.

Are you sure this is a "constant current supply"?? Depending on the
arrangement of the pins of the coil, this could just be a fairly regular
variable voltage PS.

Do you have access to an Ohmmeter?? If so, with the device switched off,
and unplugged, can you measure the resistance from each connected
terminal of the coil to each other terminal?? I'm really only interested
in connection/no connection, not the actual ohmic values. Are you right
in calling it a coil rather than me calling it a transformer!!

Daniel

 

[Uncle Peter]

On Wed, 23 Apr 2014 13:08:37 +0100, Daniel <dxmm@albury.nospam.net.au> wrote:

On 23/04/14 08:02, Uncle Peter wrote:
On Thu, 17 Apr 2014 13:42:41 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 22:23, Uncle Peter wrote:
On Wed, 16 Apr 2014 13:01:00 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 06:11, Uncle Peter wrote:

My memory of teaching Power Supplies (about 15 years ago), the constant
current was maintained but keeping the voltage developed across a
particular resistor constant, so, in theory, by increasing the value of
the resistor, a lower current would develop the same voltage across the
sensing resistor.

However, you would have to determine which resistor and which value
.....!

Thanks for the tip, I'll run it on a bench with a dummy load and test
some resistor voltages, then try changing one a little.

If you've got a circuit diagram of your power supply, and you can
determine which resister is the "sensing" resister, replace it (for the
time being) with a variable resistor/rheostat in the same ohmic range as
the sensing resistor until you can determine what value resistor you
want to stick in.

This is a partial drawing of the circuit diagram of the power supply. I
can't see half of the circuit connections as they go underneath the
unknown microchip!
http://petersphotos.com/temp/PSU.jpg

O.K., that's more than I expected, thanks.

(I'm really guessing that the 280ohms you measured is the 282ohm
resistor next to it, but that's by-the-by)

No, there are two in series. They are marked as such. I didn't measure any, except to determine which way round the figures or bands were written when unclear.

The NPN transistor that you question mark as "Low Freq" ... I would be
expecting it to be as High Freq Switching Tranny, which would, somehow,
by "driven On/Off/On/Off by the IC in middle of the diag, causing an
On/Off/On/Off current to flow through the coil/Transformer, and these
pulses are transformer coupled across the coil/Transformer, to be
rectified by the diode and filtered by the capacitor and 4.7kohm
resistor across the output.

Are you sure this is a "constant current supply"?? Depending on the
arrangement of the pins of the coil, this could just be a fairly regular
variable voltage PS.

It's designed to have three CREE LEDs connected to its output in series. If I connect different LEDs, or a resistive load like a torch bulb, it behaves very differently (as though it's confused). It's not behaving like I'd expect a constant current PSU to behave. It seems designed specifically for LEDs and is changing according to what I connect. For example when I connected three LEDs which have a lower forward voltage to it then the expected CREEs, it gave out less volts AND less current and lit them almost correctly. I would have expected it to give more power until it hit either a voltage or current limit, probably blowing the LEDs. Could it be "clever" like a NiMH charger and is sensing how the LEDs are behaving? Open circuit it only gives out 1.5V.

Do you have access to an Ohmmeter?? If so, with the device switched off,
and unplugged, can you measure the resistance from each connected
terminal of the coil to each other terminal?? I'm really only interested
in connection/no connection, not the actual ohmic values.

This is the transformer close up: http://petersphotos.com/temp/Transformer.jpg
This is the underside: http://petersphotos.com/temp/Transformer%20pins.jpg
The numbers on the photo correspond to the measurements below:
1-2=1.65 Mohms
1-3=open circuit
1-4=2.3 ohms
1-5=open circuit
1-6=open circuit
2-3=0.5 ohms
2-4=increasing reading, as though the ohmmeter is charging a capacitor
2-5=open circuit
2-6=open circuit
3-4=increasing reading, as though the ohmmeter is charging a capacitor
3-5=open circuit
3-6=open circuit
4-5=open circuit
4-6=open circuit
5-6=0.1 ohms

Are you right
in calling it a coil rather than me calling it a transformer!!

Yes, transformer. As in two coils together I wrote coil for some reason or other....

--
Five out of four Americans have trouble with fractions.

 

[Daniel]

On 24/04/14 04:04, Uncle Peter wrote:

On Wed, 23 Apr 2014 13:08:37 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 23/04/14 08:02, Uncle Peter wrote:
On Thu, 17 Apr 2014 13:42:41 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 22:23, Uncle Peter wrote:
On Wed, 16 Apr 2014 13:01:00 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 06:11, Uncle Peter wrote:

My memory of teaching Power Supplies (about 15 years ago), the
constant
current was maintained but keeping the voltage developed across a
particular resistor constant, so, in theory, by increasing the
value of
the resistor, a lower current would develop the same voltage
across the
sensing resistor.

However, you would have to determine which resistor and which value
.....!

Thanks for the tip, I'll run it on a bench with a dummy load and test
some resistor voltages, then try changing one a little.

If you've got a circuit diagram of your power supply, and you can
determine which resister is the "sensing" resister, replace it (for the
time being) with a variable resistor/rheostat in the same ohmic
range as
the sensing resistor until you can determine what value resistor you
want to stick in.

This is a partial drawing of the circuit diagram of the power supply. I
can't see half of the circuit connections as they go underneath the
unknown microchip!
http://petersphotos.com/temp/PSU.jpg

O.K., that's more than I expected, thanks.

(I'm really guessing that the 280ohms you measured is the 282ohm
resistor next to it, but that's by-the-by)

No, there are two in series. They are marked as such. I didn't measure
any, except to determine which way round the figures or bands were
written when unclear.

The NPN transistor that you question mark as "Low Freq" ... I would be
expecting it to be as High Freq Switching Tranny, which would, somehow,
by "driven On/Off/On/Off by the IC in middle of the diag, causing an
On/Off/On/Off current to flow through the coil/Transformer, and these
pulses are transformer coupled across the coil/Transformer, to be
rectified by the diode and filtered by the capacitor and 4.7kohm
resistor across the output.

Are you sure this is a "constant current supply"?? Depending on the
arrangement of the pins of the coil, this could just be a fairly regular
variable voltage PS.

It's designed to have three CREE LEDs connected to its output in
series. If I connect different LEDs, or a resistive load like a torch
bulb, it behaves very differently (as though it's confused). It's not
behaving like I'd expect a constant current PSU to behave. It seems
designed specifically for LEDs and is changing according to what I
connect. For example when I connected three LEDs which have a lower
forward voltage to it then the expected CREEs, it gave out less volts
AND less current and lit them almost correctly. I would have expected
it to give more power until it hit either a voltage or current limit,
probably blowing the LEDs. Could it be "clever" like a NiMH charger and
is sensing how the LEDs are behaving? Open circuit it only gives out 1.5V.

Do you have access to an Ohmmeter?? If so, with the device switched off,
and unplugged, can you measure the resistance from each connected
terminal of the coil to each other terminal?? I'm really only interested
in connection/no connection, not the actual ohmic values.

This is the transformer close up:
http://petersphotos.com/temp/Transformer.jpg
This is the underside: http://petersphotos.com/temp/Transformer%20pins.jpg
The numbers on the photo correspond to the measurements below:
1-2=1.65 Mohms
1-3=open circuit
1-4=2.3 ohms
1-5=open circuit
1-6=open circuit
2-3=0.5 ohms
2-4=increasing reading, as though the ohmmeter is charging a capacitor
2-5=open circuit
2-6=open circuit
3-4=increasing reading, as though the ohmmeter is charging a capacitor
3-5=open circuit
3-6=open circuit
4-5=open circuit
4-6=open circuit
5-6=0.1 ohms

Are you right
in calling it a coil rather than me calling it a transformer!!

Yes, transformer. As in two coils together I wrote coil for some
reason or other....

O.K., are you counting 1 through 6 starting at your drawings top left
pin on the coil and counting anti-clockwise??

If so, could it be that you are forward-biasing the diode and you're
charging the cap connected to pin two of the coil?? Try re-measuring
with ohmmeter connected other way around to reverse-bias the diode.

Probably same-same with pins 5 & 6. Measure both ways.

I'm guessing pins 2 and 3 are not actually connected to the other
transformer windings but may or may not be connected to each other via
another winding on the transformer (0.5 ohms). Are you sure pin 3 is not
connect to anything outside the transformer??

Pins 1 & 4 primary winding, pins 5 & 6 secondary winding plus, maybe,
pins 2 & 3 another secondary winding

If what I thought was a variable resistor is just another 280 ohm (or
1.8kohm) resister, is there actually a variable resistor anywhere in the
circuit??

Is there any Brand Name and model number which might help find a circuit
diagram somewhere online?? Any info on a back panel/whatever??

Daniel

 

[Uncle Peter]

On Thu, 24 Apr 2014 13:53:25 +0100, Daniel <dxmm@albury.nospam.net.au> wrote:

On 24/04/14 04:04, Uncle Peter wrote:
On Wed, 23 Apr 2014 13:08:37 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 23/04/14 08:02, Uncle Peter wrote:
On Thu, 17 Apr 2014 13:42:41 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 22:23, Uncle Peter wrote:
snip

snip

If you've got a circuit diagram of your power supply, and you can
determine which resister is the "sensing" resister, replace it (for the
time being) with a variable resistor/rheostat in the same ohmic
range as
the sensing resistor until you can determine what value resistor you
want to stick in.

This is a partial drawing of the circuit diagram of the power supply. I
can't see half of the circuit connections as they go underneath the
unknown microchip!
http://petersphotos.com/temp/PSU.jpg

O.K., that's more than I expected, thanks.

(I'm really guessing that the 280ohms you measured is the 282ohm
resistor next to it, but that's by-the-by)

No, there are two in series. They are marked as such. I didn't measure
any, except to determine which way round the figures or bands were
written when unclear.

The NPN transistor that you question mark as "Low Freq" ... I would be
expecting it to be as High Freq Switching Tranny, which would, somehow,
by "driven On/Off/On/Off by the IC in middle of the diag, causing an
On/Off/On/Off current to flow through the coil/Transformer, and these
pulses are transformer coupled across the coil/Transformer, to be
rectified by the diode and filtered by the capacitor and 4.7kohm
resistor across the output.

Are you sure this is a "constant current supply"?? Depending on the
arrangement of the pins of the coil, this could just be a fairly regular
variable voltage PS.

It's designed to have three CREE LEDs connected to its output in
series. If I connect different LEDs, or a resistive load like a torch
bulb, it behaves very differently (as though it's confused). It's not
behaving like I'd expect a constant current PSU to behave. It seems
designed specifically for LEDs and is changing according to what I
connect. For example when I connected three LEDs which have a lower
forward voltage to it then the expected CREEs, it gave out less volts
AND less current and lit them almost correctly. I would have expected
it to give more power until it hit either a voltage or current limit,
probably blowing the LEDs. Could it be "clever" like a NiMH charger and
is sensing how the LEDs are behaving? Open circuit it only gives out 1.5V.

Do you have access to an Ohmmeter?? If so, with the device switched off,
and unplugged, can you measure the resistance from each connected
terminal of the coil to each other terminal?? I'm really only interested
in connection/no connection, not the actual ohmic values.

This is the transformer close up:
http://petersphotos.com/temp/Transformer.jpg
This is the underside: http://petersphotos.com/temp/Transformer%20pins.jpg
The numbers on the photo correspond to the measurements below:
1-2=1.65 Mohms
1-3=open circuit
1-4=2.3 ohms
1-5=open circuit
1-6=open circuit
2-3=0.5 ohms
2-4=increasing reading, as though the ohmmeter is charging a capacitor
2-5=open circuit
2-6=open circuit
3-4=increasing reading, as though the ohmmeter is charging a capacitor
3-5=open circuit
3-6=open circuit
4-5=open circuit
4-6=open circuit
5-6=0.1 ohms

Are you right
in calling it a coil rather than me calling it a transformer!!

Yes, transformer. As in two coils together I wrote coil for some
reason or other....

O.K., are you counting 1 through 6 starting at your drawings top left
pin on the coil and counting anti-clockwise??

No, sorry. Labelled now: http://petersphotos.com/temp/PSU.jpg

If so, could it be that you are forward-biasing the diode and you're
charging the cap connected to pin two of the coil?? Try re-measuring
with ohmmeter connected other way around to reverse-bias the diode.

Probably same-same with pins 5 & 6. Measure both ways.

For ones that I saw charging, I tried both ways.

I'm guessing pins 2 and 3 are not actually connected to the other
transformer windings but may or may not be connected to each other via
another winding on the transformer (0.5 ohms). Are you sure pin 3 is not
connect to anything outside the transformer??

There's quite a few connections I can't see - surface mount resistors underneath the transformer, tracks that run underneath the chip, etc.

Pins 1 & 4 primary winding, pins 5 & 6 secondary winding plus, maybe,
pins 2 & 3 another secondary winding

If what I thought was a variable resistor is just another 280 ohm (or
1.8kohm) resister, is there actually a variable resistor anywhere in the
circuit??

I can't see anything that can be adjusted.

Is there any Brand Name and model number which might help find a circuit
diagram somewhere online?? Any info on a back panel/whatever??

No, the only markings are things like C6, R7, etc to identify components.

--
Imagine you are a child in your mother's womb, can you detect light?
Only during ballet practice.

 

[Daniel]

On 24/04/14 23:12, Uncle Peter wrote:

On Thu, 24 Apr 2014 13:53:25 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 24/04/14 04:04, Uncle Peter wrote:
On Wed, 23 Apr 2014 13:08:37 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 23/04/14 08:02, Uncle Peter wrote:
On Thu, 17 Apr 2014 13:42:41 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 16/04/14 22:23, Uncle Peter wrote:
snip

<snip>

O.K., are you counting 1 through 6 starting at your drawings top left
pin on the coil and counting anti-clockwise??

No, sorry. Labelled now: http://petersphotos.com/temp/PSU.jpg

If so, could it be that you are forward-biasing the diode and you're
charging the cap connected to pin two of the coil?? Try re-measuring
with ohmmeter connected other way around to reverse-bias the diode.

Probably same-same with pins 5 & 6. Measure both ways.

For ones that I saw charging, I tried both ways.

I'm guessing pins 2 and 3 are not actually connected to the other
transformer windings but may or may not be connected to each other via
another winding on the transformer (0.5 ohms). Are you sure pin 3 is not
connect to anything outside the transformer??

There's quite a few connections I can't see - surface mount resistors
underneath the transformer, tracks that run underneath the chip, etc.

Pins 1 & 4 primary winding, pins 5 & 6 secondary winding plus, maybe,
pins 2 & 3 another secondary winding

If what I thought was a variable resistor is just another 280 ohm (or
1.8kohm) resister, is there actually a variable resistor anywhere in the
circuit??

I can't see anything that can be adjusted.

Is there any Brand Name and model number which might help find a circuit
diagram somewhere online?? Any info on a back panel/whatever??

No, the only markings are things like C6, R7, etc to identify components.

O.K., thanks for all this, Peter, but from what you've told me and what
I can work out, this is not a Constant Current Power Supply, it is
merely a 12 Volt Power Supply which can deliver up to approx 300mA
output Current.

Let's see! If you can connect a D.C. Voltmeter across the D.C. out
terminals you should, obviously, measure 12V. Now connect a 40 ohm
resistor across the output. From Ohm's Law, R = V/I so 12V/0.3A gives 40
ohms. Voltage should remain 12V across the output terminal and output
current would be 0.3Amps, the supplies rated maximum.

Now, increase the resistance to, say, 50 ohms. I expect the output
current will have reduced (from Ohm's Law I = V/R = 12V/50 =) 0.24A,
well below the supplies Current rating of 0.3A so no problems and the
output voltage will still be 12 volts.

Now, reduce the resistance to, say, 30 ohms to try to draw more current
from the supply (from Ohm's Law I = V/R so 12V/30 gives 0.4A. Does this
happen??

I'm guessing that the Supply will not supply 0.4Amps because the output
Voltage will have fallen below the 12Volts it's supposed to still be
supplying.

Daniel

 

[Uncle Peter]

On Fri, 25 Apr 2014 10:57:47 +0100, Daniel <dxmm@albury.nospam.net.au> wrote:

On 24/04/14 23:12, Uncle Peter wrote:
On Thu, 24 Apr 2014 13:53:25 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 24/04/14 04:04, Uncle Peter wrote:
On Wed, 23 Apr 2014 13:08:37 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

On 23/04/14 08:02, Uncle Peter wrote:
snip
snip

snip

O.K., are you counting 1 through 6 starting at your drawings top left
pin on the coil and counting anti-clockwise??

No, sorry. Labelled now: http://petersphotos.com/temp/PSU.jpg

If so, could it be that you are forward-biasing the diode and you're
charging the cap connected to pin two of the coil?? Try re-measuring
with ohmmeter connected other way around to reverse-bias the diode.

Probably same-same with pins 5 & 6. Measure both ways.

For ones that I saw charging, I tried both ways.

I'm guessing pins 2 and 3 are not actually connected to the other
transformer windings but may or may not be connected to each other via
another winding on the transformer (0.5 ohms). Are you sure pin 3 is not
connect to anything outside the transformer??

There's quite a few connections I can't see - surface mount resistors
underneath the transformer, tracks that run underneath the chip, etc.

Pins 1 & 4 primary winding, pins 5 & 6 secondary winding plus, maybe,
pins 2 & 3 another secondary winding

If what I thought was a variable resistor is just another 280 ohm (or
1.8kohm) resister, is there actually a variable resistor anywhere in the
circuit??

I can't see anything that can be adjusted.

Is there any Brand Name and model number which might help find a circuit
diagram somewhere online?? Any info on a back panel/whatever??

No, the only markings are things like C6, R7, etc to identify components.

O.K., thanks for all this, Peter, but from what you've told me and what
I can work out, this is not a Constant Current Power Supply, it is
merely a 12 Volt Power Supply which can deliver up to approx 300mA
output Current.

That would seem very odd as it's powering LEDs without any current limiting resistor! No wonder the LEDs have a very short life!! Or are CREE LEDs self limiting?

Let's see! If you can connect a D.C. Voltmeter across the D.C. out
terminals you should, obviously, measure 12V.

Now connect a 40 ohm
resistor across the output. From Ohm's Law, R = V/I so 12V/0.3A gives 40
ohms. Voltage should remain 12V across the output terminal and output
current would be 0.3Amps, the supplies rated maximum.

Now, increase the resistance to, say, 50 ohms. I expect the output
current will have reduced (from Ohm's Law I = V/R = 12V/50 =) 0.24A,
well below the supplies Current rating of 0.3A so no problems and the
output voltage will still be 12 volts.

Now, reduce the resistance to, say, 30 ohms to try to draw more current
from the supply (from Ohm's Law I = V/R so 12V/30 gives 0.4A. Does this
happen??

18 ohms, 8.55 volts.
27 ohms, 12.45 volts.
36 ohms, 12 volts.
47 ohms, 10.8 volts.
56 ohms, 10.7 volts.
Open circuit, 12.73 volts.

27 ohms (being about a 6 watt load) seems to make the PSU happy, that's about what the CREEs draw.

But I can't explain why it drops the voltage at 47 and 56 ohms, unless it's a universal supply designed for 3 or 4 LEDs?

And why the slightly higher voltage at 27 ohms than at 36 ohms?

I'm guessing that the Supply will not supply 0.4Amps because the output
Voltage will have fallen below the 12Volts it's supposed to still be
supplying.

--
The German for nipple is "Brustwarze" - or "breast wart".

 

[Daniel]

On 26/04/14 06:37, Uncle Peter wrote:

On Fri, 25 Apr 2014 10:57:47 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

<Snip>

Now, reduce the resistance to, say, 30 ohms to try to draw more current
from the supply (from Ohm's Law I = V/R so 12V/30 gives 0.4A. Does this
happen??

18 ohms, 8.55 volts. > > > >0.475Amps
27 ohms, 12.45 volts.> > > >0.4611Amps
36 ohms, 12 volts. > > > >0.333Amps
47 ohms, 10.8 volts.> > > >0.2298Amps
56 ohms, 10.7 volts.> > > >0.191Amps
Open circuit, 12.73 volts.> > >0.000Amps

Not very "Constant Current"ish!! Mind you, not very "Constant Voltage",
either!!

I'd just guess a poorly regulated Voltage, Power Supply.

Daniel

 

[Uncle Peter]

On Sat, 26 Apr 2014 10:43:00 +0100, Daniel <dxmm@albury.nospam.net.au> wrote:

On 26/04/14 06:37, Uncle Peter wrote:
On Fri, 25 Apr 2014 10:57:47 +0100, Daniel <dxmm@albury.nospam.net.au
wrote:

Snip

Now, reduce the resistance to, say, 30 ohms to try to draw more current
from the supply (from Ohm's Law I = V/R so 12V/30 gives 0.4A. Does this
happen??

18 ohms, 8.55 volts. > > > >0.475Amps
27 ohms, 12.45 volts.> > > >0.4611Amps
36 ohms, 12 volts. > > > >0.333Amps
47 ohms, 10.8 volts.> > > >0.2298Amps
56 ohms, 10.7 volts.> > > >0.191Amps
Open circuit, 12.73 volts.> > >0.000Amps

Not very "Constant Current"ish!! Mind you, not very "Constant Voltage",
either!!

I'd just guess a poorly regulated Voltage, Power Supply.

I guess I just treat it as a shit power supply and find a resistor to go with the smaller LEDs to make the current correct.

It and the 3 CREE LEDs only cost Ł3, so I guess I shouldn't have expected anything cutting edge. Mind you, that's maybe why the bloody CREEs died early! I had every one of the batch replaced under warranty, then couldn't be bothered the second time. Or then again it could be because the heatsink on the LEDs was too hot to touch for more than 1 second, which I would think was also uncomfortable for the LEDs!

--
Women do not snore, burp, sweat, or fart.
Therefore, they must "bitch" or they will blow up.