I converted a PCB UV Exposure box I made from Fluoro to UV LED's but on testing current draw
I found it to be well bellow what it should be unless I used an unregulated power supply.

Am I missing something?

Led strip with 120 X 3528 LED's,
40 Resistors marked 151, dimensions approximately 1.5 X 0.5
Wattage per LED 0.08W
Recommended drive mode 12v constant voltage.

1 X 12V regulated P/S Open circuit voltage 12.37VDC 1.5A Capacity

1 X 12V unregulated P/S Open circuit voltage 18VDC 1.0A Capacity

LED Strip connected to Regulated Power supply
voltage 12.37VDC
Current: 0.27A

Per LED: 0.00225
Wattage: 0.027

Similar results for other Regulated 12V Power supplies with =< 0.4A Current seems to vary
between different 12V regulated power supplies. Switch-mode and Transformer types.

LED Strip connected to Unregulated power supply
Voltage 13VDC
Current 0.8A.

Per LED: 0.00666
Wattage: 0.086


The unregulated P/S seems the right one, but why are the Regulated ones
down to three times lower.

If I measure across both I get 12.37 or so and 13VDC respectively which is the
voltage drop across the strip/s, so both currents should be pretty much the same?

 

Your numbers don't make sense.

Led strip with 120 X 3528 LED's,

120 x 3528 LEDs is 423,360 LEDs.
It look like 8 strips of 15 LEDs in the photo...120 LEDs
but you have 40 resistors.
That would be 3 LEDs per resistor. and 150 ohms in each series string of 3.
3.5V to 4.5V per LED x 3 = 10.5 to 13.5V per 3 LEDs

Meanwhile 0.63 volts of difference is causing 0.53 amps of change.
I'm not getting any sense of this and I have to go out into the real world right now.
Maybe I gave enough to get somebody else a clue.

 

120 x 3528 LEDs is 423,360 LEDs.

That's 120: 3.5X2.8mm smd LEDs. Google: 3528 (aka 1210)

It look like 8 strips of 15 LEDs in the photo...120 LEDs

Correct.

but you have 40 resistors.
That would be 3 LEDs per resistor. and 150 ohms in each series string of 3.

Correct.

Meanwhile 0.63 volts of difference is causing 0.53 amps of change.
I'm not getting any sense of this and I have to go out into the real world right now.
Maybe I gave enough to get somebody else a clue.

I don't follow, 530ma difference in .63 volts? So if it was more than 1 volt it would >100% difference. Not only that but why do I get different current draw when using different regulated power supplies at 12v.

1-In the following I am unable to confirm if they are 0.06w or 0.08 watt LEDs
2-not taking the resistors into consideration.

Assuming each LED is 0.08 watt
0.08w x 120 LED's = 9.6w
9.6w / 12.37v = 776ma - Actual regulated P/S = 270ma to 400ma depending P/S
9.6w / 13v = 738ma - Actual Unregulated P/S = 800ma +/- 20ma
Assuming each LED is 0.06 watt.
0.06w x 120 LED's = 7.2w
7.2w / 12.37v = 600ma - Actual regulated P/S = 270ma to 400ma depending P/S
7.2w / 13v = 553ma - Actual Unregulated P/S = 800ma +/- 20ma

To me the regulated P/S have no correlation as to what the actual current draw should be, yet alone the difference between different regulated Power supplies.

 

To me the regulated P/S have no correlation as to what the actual current draw should be, yet alone the difference between different regulated Power supplies.

That is correct, but I didn't have time to get the answer. Sorry. The external world suddenly got busy for me today. (Death in the family.)

 

I converted a PCB UV Exposure box I made from Fluoro to UV LED's but on testing current draw
I found it to be well bellow what it should be unless I used an unregulated power supply.

Am I missing something?

Led strip with 120 X 3528 LED's,
40 Resistors marked 151, dimensions approximately 1.5 X 0.5
Wattage per LED 0.08W
Recommended drive mode 12v constant voltage.

1 X 12V regulated P/S Open circuit voltage 12.37VDC 1.5A Capacity

1 X 12V unregulated P/S Open circuit voltage 18VDC 1.0A Capacity

LED Strip connected to Regulated Power supply
voltage 12.37VDC
Current: 0.27A

Per LED: 0.00225
Wattage: 0.027

Similar results for other Regulated 12V Power supplies with =< 0.4A Current seems to vary
between different 12V regulated power supplies. Switch-mode and Transformer types.

LED Strip connected to Unregulated power supply
Voltage 13VDC
Current 0.8A.

Per LED: 0.00666
Wattage: 0.086


The unregulated P/S seems the right one, but why are the Regulated ones
down to three times lower.

If I measure across both I get 12.37 or so and 13VDC respectively which is the
voltage drop across the strip/s, so both currents should be pretty much the same?

\Where did you get the need for 12 V from? It looks to me like you need 15 V.
Three 3.4 Volt LEDs rated at 20 mA and a 150 ohm resistor sounds like 15 V.
60 mA per board x 8 boards = 540 mA
So a power supply of 15 V at 540 mA, or slightly more, unregulated. Or 15 V at 540 mA or more, regulated. Maybe a 12 V unregulated supply rated at 1 Amp? Since you are not loading it down the voltage will be higher.

 

OK. Next day. I suspect that the difference in measurements is about a difference in the measuring instrument. For instance, the DC volt meter does not consider the AC component of a cheap power supply, but the current meter does correctly sense the sum of all currents.

Assuming each LED is 0.08 watt
0.08w x 120 LED's = 9.6w
9.6w / 12.37v = 776ma - Actual regulated P/S = 270ma to 400ma depending P/S
9.6w / 13v = 738ma - Actual Unregulated P/S = 800ma +/- 20ma

All of that just confuses the issue because the math is wrong.
Assuming some wattage for the LEDs, what happens if we change the applied voltage and expect the current to decrease when the voltage increases?
Hmmm...That doesn't correlate to any measurements of what is actually happening. Let's do it again!

Assuming each LED is 0.06 watt.
0.06w x 120 LED's = 7.2w
7.2w / 12.37v = 600ma - Actual regulated P/S = 270ma to 400ma depending P/S
7.2w / 13v = 553ma - Actual Unregulated P/S = 800ma +/- 20ma

No. That method won't work just because you did it twice.
An array of LEDs is not a self regulating, constant power device.

Try this: Connect your power supplies, one at a time, and measure the DC voltage on the array, then switch the meter to "AC voltage" to measure the ripple component of the power supply. Choose the power supply with the least amount of AC in its output.

Connect that power supply and measure the DC voltage across an LED and measure the DC voltage across a 150 ohm resistor.
Do that 2 or 3 times to show that the results are, or are not, pretty much the same for each group of 1 resistor and 3 LEDs.
I think they are because the photo shows about the same amount of light from each LED.
At that point, we will have a clue about the voltage required by the LEDs and the voltage across the resistors. Those numbers will describe the current and power that is actually happening for one of the power supplies.
When you have some actual measurements, you can begin to figure out that the LED voltage does not change much, the difference in the power supply voltages mostly shows up as more voltage across the resistors, and a large AC component doesn't measure correctly on your meter.