The LEDs are flickering in a light tent (Puluz 60cm)

If I buy a new power supply it's either going to take an age or cost a
bucket in shipping.
Output 12V 2A 'constant current', dimmable.

So,
Why might it be flickering? Are these things servicable?

Does it matter if I replace it with something different that isn't
constant current but constant voltage?
Because I can't seem to find a 24W constant current driver operating at
12V, is that going to matter?

Any input.....

On 04/01/2021 15:41, R D S wrote:
The LEDs are flickering in a light tent (Puluz 60cm)

If I buy a new power supply it's either going to take an age or cost a
bucket in shipping.
Output 12V 2A 'constant current', dimmable.

So,
Why might it be flickering? Are these things servicable?

Does it matter if I replace it with something different that isn't
constant current but constant voltage?
Because I can't seem to find a 24W constant current driver operating at
12V, is that going to matter?

Any input.....

There's actually 2 strips with a Y splitter, so 12W would suffice (2 of)
and i'd keep some degree of dimmability.

In article ,
R D S wrote:
Does it matter if I replace it with something different that isn't
constant current but constant voltage?
Because I can't seem to find a 24W constant current driver operating at
12V, is that going to matter?

A plain LED is current driven. Voltage as such doesn't much matter. If you
have an adequate power supply of known voltage you use (in the simplest
form) series resistors to set the current. Multiple LEDs might be a
mixture of series and parallel connection, though. You'll find calculators
online to give you the correct series resistors for various combinations.
You'll need to know the supply voltage and the LED parameters.

If you can't find a suitable LED driver power supply.

--
*Happiness is seeing your mother-in-law on a milk carton

Dave Plowman London SW
To e-mail, change noise into sound.

R D S wrote:

Does it matter if I replace it with something different that isn't
constant current but constant voltage?
Because I can't seem to find a 24W constant current driver operating at
12V, is that going to matter?

If it's a constant current LED driver, the it's odd for it to specify a
single voltage, rather than a range (e.g 25V to 70V) for a random one on
RS website

Also 2A sounds rather high.

Photo of existing driver?

Dave Plowman wrote:

Multiple LEDs might be a
mixture of series and parallel connection, though. You'll find calculators
online to give you the correct series resistors for various combinations.
You'll need to know the supply voltage and the LED parameters.

And each physical LED may internally be comprised of several actual
LEDs, so the voltage can be surprisingly high.

On 04/01/2021 15:41, R D S wrote:
The LEDs are flickering in a light tent (Puluz 60cm)

What's a light tent?

If I buy a new power supply it's either going to take an age or cost a
bucket in shipping.
Output 12V 2A 'constant current', dimmable.

So,
Why might it be flickering? Are these things servicable?

PSU doesn't like the load or a dry joint somewhere. I have noticed that
LED streetlamps seem to fail this way with monotonous regularity.

Does it matter if I replace it with something different that isn't
constant current but constant voltage?
Because I can't seem to find a 24W constant current driver operating at
12V, is that going to matter?

Any input.....

Constant voltage may well kill the LEDs or at the very least shorten
their lifetime. A series resistor with a constant voltage supply will
work OK but the resistor will get a bit warm try 1R 5W or 0.5R 2W.

--
Regards,
Martin Brown

On 04/01/2021 16:09, Andy Burns wrote:
R D S wrote:

Does it matter if I replace it with something different that isn't
constant current but constant voltage?
Because I can't seem to find a 24W constant current driver operating
at 12V, is that going to matter?

If it's a constant current LED driver, the it's odd for it to specify a
single voltage, rather than a range (e.g 25V to 70V) for a random one on
RS website

Also 2A sounds rather high.

Photo of existing driver?

https://drive.google.com/file/d/1JtQ...ew?usp=sharing

Reading the cautions, i'm thinking everything on that label should be
taken with a pinch of salt.

R D S wrote:

https://drive.google.com/file/d/1JtQ...ew?usp=sharing

Reading the cautions, i'm thinking everything on that label should be
taken with a pinch of salt.

I'd say not putting it in water or fire are good ideas.

It mentions batteries, I take it there aren't any?

On 04/01/2021 17:05, Andy Burns wrote:
R D S wrote:

https://drive.google.com/file/d/1JtQ...ew?usp=sharing

Reading the cautions, i'm thinking everything on that label should be
taken with a pinch of salt.

I'd say not putting it in water or fire are good ideas.

It mentions batteries, I take it there aren't any?


No batteries.
And I keep it away from the damp place anyway.

R D S wrote:

Andy Burns wrote:
R D S wrote:

https://drive.google.com/file/d/1JtQ...ew?usp=sharing

It mentions batteries, I take it there aren't any?

No batteries.

You mentioned a splitter inside the tent, can you measure the voltage there?

R D S wrote:
The LEDs are flickering in a light tent (Puluz 60cm)

If I buy a new power supply it's either going to take an age or cost a
bucket in shipping.
Output 12V 2A 'constant current', dimmable.

So,
Why might it be flickering? Are these things servicable?

Does it matter if I replace it with something different that isn't
constant current but constant voltage?
Because I can't seem to find a 24W constant current driver operating at
12V, is that going to matter?

Any input.....

Here's another picture for context. This shows enough of the
product, so you can understand the application. "Well-lit
handbags at dawn."

https://flutter-shop.com/953249/prod...dc-12v-2a.html

*******

The supply is two 1A constant current sources.
The output voltage is the "compliance" voltage.

When the adapter runs no-load, the output voltage
on each barrel connector should be 12V. But maybe
not perfectly steady. A proper (theoretical) constant
current source, the voltage would rise to infinity if
such a thing existed and no load were applied. If
testing with your multimeter, you start on the 1000V DC
range first, and dial down as you develop some trust
it's a 12Vmax output.

Instead, when we make constant current sources, they're
non-ideal, and their ideality stops at the compliance
voltage. When the voltage gets to 12V, it can no longer
rise higher, and the "constant current" behavior stops
at that point.

The device can provide 1 ampere per lead-set. Even if
we short it out, 1 ampere flows through the short.

If we connect a 1 ohm resistor to a lead-set, the 1 ampere
flowing through 1 ohm, develops 1 volt. The power is
1 amp times 1 volt or 1 watt. The unit does not make
12V in that case. That's because it is a constant current
source. The output voltage happens to be 1 volt, because
we've placed such a heavy load on it.

You could run about four 2.5V white LEDs off a 12V compliance
source. When you connect the four LEDs, 10V drops across
the LEDs while 1 ampere flows. The load receives 10W total
power.

This blackbox is, in effect, a "dual buck puck". Two channels
running at 1 ampere each. We could connect a 10 ohm 25W
power resistor and verify that we're getting the voltage
and current expected from it. That would be a load test.

The danger with any constant current source, is they tell
a lie about the compliance voltage. And open circuit, it
rises to some absurdly high DC value. That's why, being
chinese, you'd be careful to not trust the ratings on it.
You can characterize the device by placing test loads on it
and see if it behaves as a constant current source.

In terms of internal stress, the max stress is when the
output is shorted. It doesn't stop running when shorted
(unlike a voltage-regulating wall wart). Since it's a
constant current source, it is designed to produce 1 ampere
of current per leadset, even if the voltage developed
across the load is zero volts. a second stressful condition
for a constant current source, is being operated open-circuit.
But the compliance voltage feature, says the voltage should
not be rising to infinity when no load is present.
(If a constant current source is made using vacuum tubes,
yes, you can get absurdly high voltages then :-) Nothing
says someone won't try to make a closer-to-ideal source.)

Since this is a photography light tent application, the
regulator should be a bit more precise than your average
"buck puck". You could use two separate buck pucks to replace
the defective item.

You could also use a laptop adapter, two LM317 regulators in
constant current mode, and make a solution that way. If
the output of the LM317 is shorted, it gets extremely hot
(which doesn't happen to the buck puck idea). But an LM317
or a circuit related to it, is something I have the parts
in the house, to put together right now.

I've lost my only electronics store, so I can't just drive
off and buy an NTE970 if I want any more. I have to get
crap shipped, which takes days. The NTE970 is an LM317,
but in a package that bolts nicely to various lines of
heat sinks.

My kitchen light runs off an LM317 inspired constant current
source, so I've already done one of these.

See, hobbyists are already out there doing this sort of thing.
Here, a person after my own heart, is using a laptop adapter
to power four LEDs. R3 sets the current flow level. R3 must
have sufficient power rating for the job.

https://static-resources.imageservic...hting-leds.png

Paul

On 04/01/2021 16:34, Martin Brown wrote:
On 04/01/2021 15:41, R D S wrote:
The LEDs are flickering in a light tent (Puluz 60cm)

What's a light tent?

Martin, just Google for Puluz 60cm.

I did.




--
Adam

On 04/01/2021 15:41, R D S wrote:
The LEDs are flickering in a light tent (Puluz 60cm)

If I buy a new power supply it's either going to take an age or cost a
bucket in shipping.
Output 12V 2A 'constant current', dimmable.

So,
Why might it be flickering? Are these things servicable?

What do you mean flickering. Is this to the eye or are you shooting
video at 60Hz?

Because it says constant current it sounds to me like there are no series
resistors or current limiting in the leds. If you bung on a supply, say
unregulated or regulated, you could end up with a lot of dead burned out
leds. As for serviceable, well that very much depends on your abilities and
whether you can get the psu apart. Flickering is odd, sounds like it might
be just a capacitor inside the unit to me, but beware, there are many
designs all of which are pretty lethal when uncased, especially if its
switch mode.
Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"R D S" wrote in message
...
The LEDs are flickering in a light tent (Puluz 60cm)

If I buy a new power supply it's either going to take an age or cost a
bucket in shipping.
Output 12V 2A 'constant current', dimmable.

So,
Why might it be flickering? Are these things servicable?

Does it matter if I replace it with something different that isn't
constant current but constant voltage?
Because I can't seem to find a 24W constant current driver operating at
12V, is that going to matter?

Any input.....

On 04/01/2021 23:26, Fredxx wrote:

What do you mean flickering. Is this to the eye or are you shooting
video at 60Hz?

Visible to the eye.

On 04/01/2021 17:20, Andy Burns wrote:
R D S wrote:

Andy Burns wrote:
R D S wrote:

https://drive.google.com/file/d/1JtQ...ew?usp=sharing

It mentions batteries, I take it there aren't any?

No batteries.

You mentioned a splitter inside the tent, can you measure the voltage
there?

I keep forgetting to take my meter into work.

Anyway, I have one of these that i've had attached to another LED strip
in the past,
https://www.overstock.com/Home-Garde...8/product.html

Is that the right sort of thing for the job?

R D S wrote:

I have one of these that i've had attached to another LED strip in the
past,
https://www.overstock.com/Home-Garde...8/product.html

Is that the right sort of thing for the job?

Depends if you believe the "constant current" label on the other PSU, if
you do then no, it's not the right thing, but the 12V/2A label on the
other PSU doesn't sit with it being constant current, so maybe.

R D S wrote:
On 04/01/2021 17:20, Andy Burns wrote:
R D S wrote:

Andy Burns wrote:
R D S wrote:

https://drive.google.com/file/d/1JtQ...ew?usp=sharing

It mentions batteries, I take it there aren't any?

No batteries.

You mentioned a splitter inside the tent, can you measure the voltage
there?

I keep forgetting to take my meter into work.

Anyway, I have one of these that i've had attached to another LED strip
in the past,
https://www.overstock.com/Home-Garde...8/product.html


Is that the right sort of thing for the job?

The flickering in your existing unit, will be
easiest to catch on a multimeter, "in the current domain".
We could stick an ammeter in series.

Dual Source Box (+) ------------- ammeter ------------- LED array ---+
| 1 amp
(-) -------------------------------------------------+

(+) ----------------------------------- LED array ---+
| 1 amp
(-) -------------------------------------------------+

Working on circuits like this is easier, if you have a male and
female barrel connector of the same size that the unit uses, as
this can allow fitting measurement equipment (your multimeter)
for doing circuit characterization *before* buying anything.

The voltage level, if monitored at the (+) point and (-) point,
doesn't vary nearly as much when there is flickering. Only if the
power goes out completely for some reason, would the intelligence
collected from the ammeter, match the voltmeter.

Sometimes the flicker is caused by a dimming feature. The unit in
question has a knob to set the light level. Dirt in the potentiometer
could cause flicker. Any time the SMPS for a LED light supports
dimming, there is also the possibility of something modulating
the control voltage and "making it flicker". Flicker can even
be caused by dirty connectors or a broken wire in the cabling.

*******

Remember, that the unit puts out a constant current on each of two
cables. It puts out 1 amp on each cable. This means the power
source you start with, need not be more than a total of 2 amps.
For example, common laptop adapters put out 19V at 3A max,
as an example of something that has both enough volts and enough amps.

The voltage of the supply source you retrofit, only has to be
high enough to forward bias the LED array. We don't know at the moment,
what the operating voltage of the LEDs are. The source claims to have
a compliance voltage of 12V (12V max in other words) while putting
1 ampere through each of the two lead sets. The LEDs are allowed
to use any voltage which is less than 12V.

Assuming the LEDs are not using the full 12V at the moment, we
could draw a picture.

This would help with adjusting the current flow.

50W 10 Ohm Ceramic Potentiometer (need one for each of two lead-sets)

https://www.amazon.co.uk/Ceramic-Pot.../dp/B00K82TJMA

3 ohm 10W wirewound resistor, pair

https://www.amazon.co.uk/sourcing-ma.../dp/B08NX2SJ4K

Circuit looks like this:
+--------+
| |
v |
12V 2.1A src (+) --------- 3 ohm 10W --- 10ohm pot -+---- LED (+)

(-) ---------------------------------------- LED (-)

The purpose of the 3 ohm, is to prevent catastrophes caused by rotating
the pot too far. With the circuit as shown, total path resistance varies
from a low of 3 ohms to a high of 13 ohms. Even if you accidentally
rotate the pot all the way to one side (or the other side) of its
travel, the resistance can never be below 3 ohms.

Let's say the LEDs in the light tent, currently have 9V across them.
A 3 ohm resistor with 1 ampere through it, would have a 3V drop.
9V for the LEDs plus 3V across the resistor solution, gives 12V from
the supply.

Now, if the LEDs have a higher voltage than 9V across them at the moment,
we need to find out what that voltage is, so we can intelligently
select our resistors. We don't want to make the 3 ohm resistor
have a too-small resistance value, because then we've made the
circuit less-safe against "children-fingers" :-) You know, the
people who must turn every knob they can find.

When I was younger, and some kids came over to the house
while I was not there, one of the knobs on my stereo got
broken. Apparently, one of the kids *stood on it* :-)
That's how evil they can be :-) You have to build things
to that standard of strength and durability. "A pots no good
unless you can stand on it."

Recommended steps:

1) Acquire two sets of male and female barrel connectors
compatible with the lead sets. This is helpful if
needing access to the conductors for making measurements, and
doing it without hacking the existing wires all to bits. We want
the project to be neat and tidy when finished, and not a
mess of electrical tape. The first part of the project,
could benefit from some multimeter measurements, just to make
sure of what we're doing.

2) Make a measurement of the voltage across the LEDs. We know the
current is still (most of the time) 1 ampere per lead set.
Knowing the LED voltage, is to *make sure* we're buying
the correct power supply.

3) Once the LED voltage is known, we can fine tune our choice
of wirewound pot. The circuit shown above does not allow dialing to zero
intensity, like the original control allowed. With the circuit
above as shown, it might allow 25% to 100% light level.

You could also buy a bench supply and put it in CC mode
and drive the LED that way. Likely needs a fat wallet.
You would need one of these for each lead-set. This would also
be exposed to "children-fingers" with disastrous results. This
has plenty of power to "burn" the LEDs.

https://www.amazon.co.uk/MATRIX-Adju.../dp/B07WP3HV6G

When setting a bench supply like that in CC mode, you short
the output and adjust the current flow for the desired current (1 amp).
Then, with the short removed, set the voltage to any value which
is higher than the LED forward voltage. If the LEDs use 10V, then
setting the bench supply to 11V should be fine, while the CC current
limit is what really controls things. The advantage of the bench
supply, is not having the messy wirewound pot sitting there.

The cheapest I could do this, is a laptop adapter, plus a handful of
fixed resistors. I used to be able to get power resistors for
pretty cheap at the electronics store, making it possible to buy
a variety of values. The prices these web sites charge
are outrageous by comparison. The web makes gouging easy.
(Think Radio Shack and how they used to sell packages of
two 1/4watt resistors in a blister pack, like they were
diamond rings or something.)

Paul