Author Topic: How do you tell what "type" of power a DC power supply is?  (Read 6759 times)

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Offline DW1961Topic starter

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How do you tell what "type" of power a DC power supply is?
« on: July 22, 2020, 05:36:48 am »
I ordered some LED strips that came with the best power supplies I could find on Amazon. Those were 12V 5 Amp models. There is one I am ordering tomorrow that is 24V 2.5 Amps.

The 24V models says, "Only for LED lighting." I know some of you have mentioned different types of DC power and supplies. I know I'm eventual going to mix them up, so what's the difference and how can I test them--or can I--to designate which ones are which type of DC power?
« Last Edit: July 28, 2020, 05:11:47 pm by DW1961 »
 

Offline bob91343

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #1 on: July 22, 2020, 05:46:36 am »
I can't imagine a power supply that only can be used for LED lighting.  Perhaps it's constant current or something.  Read the specs.
 

Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #2 on: July 22, 2020, 06:06:44 am »
I can't imagine a power supply that only can be used for LED lighting.  Perhaps it's constant current or something.  Read the specs.

Yep, something like that. Just not sure what.
 

Offline Vovk_Z

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #3 on: July 22, 2020, 04:38:49 pm »
I can't imagine a power supply that only can be used for LED lighting.  Perhaps it's constant current or something.  Read the specs.
Possibly, it can be non-isolated from mains too, and have very weak or almost absent EMC filters.
 

Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #4 on: July 22, 2020, 06:10:37 pm »
Constant current vs constant voltage?

Switching vs linear?
 

Offline coromonadalix

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #5 on: July 22, 2020, 08:22:47 pm »
Some led strips will need a led driver, the leds are controlled in current

Some led strip have the limitting current resistors integrated in the led voltages paths inside it, if its a clear led strip like many, youll be able to se them and the leds arrangements, and normally a simple 24vdc psu will be okay. I used some psus with a small adjustable voltage trimpot, dropped them at 22 vdc, just to drop the intensity a little.

Example: a led driver have a voltage range  say between 18 to 32 volts (seen some like this in the past)  for a 24vdc strip, but the current is limitted, the voltage will adjust itself with the load applied / given by the led strip.

Normally a led driver are  most of the time directly connected to the led, no resistors needed ...  like the 100watts leds  10x10 matrix, they work at least at 32-36vdc and NEED a led driver to work reliably.
« Last Edit: July 22, 2020, 08:24:32 pm by coromonadalix »
 
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Online John B

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #6 on: July 22, 2020, 10:46:13 pm »
Do you have a link to the 24V 2.5A power supply? It would be explicitly labelled as constant current if that's the type of LED driver that it is. I've seen power supplies labelled as "LED only" power due to the fact that they have horrible noise and ripple, that's all.
 
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Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #7 on: July 23, 2020, 06:35:29 am »
Do you have a link to the 24V 2.5A power supply? It would be explicitly labelled as constant current if that's the type of LED driver that it is. I've seen power supplies labelled as "LED only" power due to the fact that they have horrible noise and ripple, that's all.

Sure, it says (CV) on it so I assume that means constant voltage, not current?

1029510-0


I don't even know why I wanted that model. I can't use it for computers and and I can only use it with 24V PSU, so I don't know what I was thinking.
« Last Edit: July 23, 2020, 06:37:41 am by DW1961 »
 

Offline magic

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #8 on: July 23, 2020, 08:29:08 am »
Maybe it's constant voltage but not stable with capacitive loads :-DD

If you are curious, order it, test it, write an Amazon review. Isn't this why they are offering it to you for free in the first place? :)

edit
I'm kidding, I have no idea what it is and if there is anything special about it. Externally, looks like any other switcher. Certainly not linear.
« Last Edit: July 23, 2020, 08:31:00 am by magic »
 

Online Zero999

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #9 on: July 23, 2020, 08:44:25 am »
It's just an ordinary switched mode power supply. Any special claims made about it will be purely marking.
 

Online John B

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #10 on: July 23, 2020, 10:09:28 am »
It looks sketchy. I'm not sure I'd trust a cheapo AC/DC pack off ebay/ali-whatever anymore, certainly not one that is "UL LIGTED"  :-DD

I've had too many bad experiences, fake specs, bad reliability, even completely random modules shoved inside the plastic pack you see. Not to mention the safety risk you take in isolation and potentially starting fires.
 

Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #11 on: July 23, 2020, 05:03:39 pm »
It looks sketchy. I'm not sure I'd trust a cheapo AC/DC pack off ebay/ali-whatever anymore, certainly not one that is "UL LIGTED"  :-DD

I've had too many bad experiences, fake specs, bad reliability, even completely random modules shoved inside the plastic pack you see. Not to mention the safety risk you take in isolation and potentially starting fires.

UL Ligted?  HAHAHAHA, NICE catch!

So, back to the original question, what is the difference in DC PSU? Does it matter what "type" they are regarding what you can run with them?

I'll start another thread about portable DC power supplies and how to tell if they are any good or not. I guess my question is can you use any quality 12V portable supply with any 12V application, regardless of type of power it delivers?

PS--I'm not plugging in anything to my "good" electronics before I know it's a good supply.
 

Offline capt bullshot

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #12 on: July 23, 2020, 05:08:48 pm »
Might be just for regulation and applied standards reasons.

Lighting is a different kind of equipment than e.g. a general purpose power brick, so it's tested and declared conforming to different standards.
I bet the load device (wether it's actual LED lighting or something else that can cope with the provided output) can't read that fine print and will just work ;)
Safety devices hinder evolution
 
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Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #13 on: July 23, 2020, 06:10:26 pm »
Might be just for regulation and applied standards reasons.

Lighting is a different kind of equipment than e.g. a general purpose power brick, so it's tested and declared conforming to different standards.
I bet the load device (whether it's actual LED lighting or something else that can cope with the provided output) can't read that fine print and will just work ;)

Yeah, I think you are just right on that too. Reading this page really clarified things. Most all LED light strips or multi-light LED system us CV drivers. One poster above said it might be because ripple and some other undesirable artifact is present becasue it is a 'dirty' supply, but LEDs don't care about ripple (maybe). Constant Voltage is the LED standard.
https://www.ledsupply.com/blog/constant-current-led-drivers-vs-constant-voltage-led-drivers/

Incidentally, my SONY laptop power supply (made by Light-on) says CC/CV on it so I guess it can do both. That makes me wonder if laptops need both? IF so, we know for sure one reason that power supply says for "LEDs only."
 

Offline capt bullshot

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #14 on: July 23, 2020, 06:31:21 pm »

Incidentally, my SONY laptop power supply (made by Light-on) says CC/CV on it so I guess it can do both. That makes me wonder if laptops need both? IF so, we know for sure one reason that power supply says for "LEDs only."

That'd be rather uncommon. Usual laptop bricks have CV output, and some kind of overload limiting / shutdown mechanism (which of course might be some kind of CC operation). I've never seen a laptop that relied on CC operation of its supply.
Safety devices hinder evolution
 
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Offline TimFox

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #15 on: July 23, 2020, 07:52:32 pm »
Reading the label, it appears to be a constant-current power supply for 2.5 A (2500 mA), with a compliance (maximum voltage across load) of 24 V.  However, I don't think that is correct:  instead it is probably a constant-voltage supply ("CV") at 24 VDC, with a maximum current of 2.5 A.  A switch-mode constant-current supply is great for driving LEDs in series without extra loss from a series resistor, but it looks like that strip includes SMD resistors.
« Last Edit: July 23, 2020, 07:55:39 pm by TimFox »
 
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Online John B

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #16 on: July 23, 2020, 09:35:19 pm »
Might be just for regulation and applied standards reasons.

Lighting is a different kind of equipment than e.g. a general purpose power brick, so it's tested and declared conforming to different standards.
I bet the load device (whether it's actual LED lighting or something else that can cope with the provided output) can't read that fine print and will just work ;)

Yeah, I think you are just right on that too. Reading this page really clarified things. Most all LED light strips or multi-light LED system us CV drivers. One poster above said it might be because ripple and some other undesirable artifact is present becasue it is a 'dirty' supply, but LEDs don't care about ripple (maybe). Constant Voltage is the LED standard.
https://www.ledsupply.com/blog/constant-current-led-drivers-vs-constant-voltage-led-drivers/

Incidentally, my SONY laptop power supply (made by Light-on) says CC/CV on it so I guess it can do both. That makes me wonder if laptops need both? IF so, we know for sure one reason that power supply says for "LEDs only."

CV/CC power supplies can be thought of as either maximum condition being met. So for a maximum of 24V and 2.5A, it will attempt to push 2.5A through the load, up to a maximum output voltage of 24V, or it puts out 24V up to a maximum load of 2.5A, after which the output voltage reduces to keep the current at 2.5A.

This would describe supplies designed for lighting, however I don't see why a laptop charger would function that way. CV power supplies generally have a hiccup mode when the max output current is exceeded. They don't gradually reduce voltage, it cuts out completely for a second or two then reattempts power.

I also wouldn't overlook the noise and ripple. LED installations involve long lengths of wire, which in conjunction with the power supplies inherent conducted interference can contribute to a noisy environment. In the past that has given me problems with magnetic pickups and noise on my scopes

You can always get a quality CV driver then use a second step down CC module to run LEDs. That's a more flexible way to implement dimming. I usually buy Meanwell drivers from the usual electronic parts suppliers. There's nothing particularly special about Meanwell, but they have a large range of voltages, power levels, form factors, CC/CV supplies etc generally at a decent price.

Also, avoid PWM dimming methods for controlling lights. They produce the most interference.
« Last Edit: July 23, 2020, 09:37:08 pm by John B »
 
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Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #17 on: July 24, 2020, 12:28:21 am »

Incidentally, my SONY laptop power supply (made by Light-on) says CC/CV on it so I guess it can do both. That makes me wonder if laptops need both? IF so, we know for sure one reason that power supply says for "LEDs only."

That'd be rather uncommon. Usual laptop bricks have CV output, and some kind of overload limiting / shutdown mechanism (which of course might be some kind of CC operation). I've never seen a laptop that relied on CC operation of its supply.

Well, that's Sony for you. This laptop is one of the last Sony manufactured, and it's 6 years old and I've had zero problems with it, including the battery pack.
 

Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #18 on: July 24, 2020, 12:29:18 am »
Reading the label, it appears to be a constant-current power supply for 2.5 A (2500 mA), with a compliance (maximum voltage across load) of 24 V.  However, I don't think that is correct:  instead it is probably a constant-voltage supply ("CV") at 24 VDC, with a maximum current of 2.5 A.  A switch-mode constant-current supply is great for driving LEDs in series without extra loss from a series resistor, but it looks like that strip includes SMD resistors.

It says right on it, "(CV)."
 

Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #19 on: July 24, 2020, 01:14:15 am »
So the question remains, how do you know what DC supply to plug into a device? Will the device have that information on it? Or do most application use CV?

As long as LED strips have resistors, CV is the supply to use. According to that source I posted, CV power is virtually all applications for premade LED strips.

But what about other applications?
 

Online John B

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #20 on: July 24, 2020, 03:02:55 am »
Yes most applications utilise a CV power supply. When there's a single load circuit, like a string of LEDs, then it makes more sense to implement CC power supplies.

In this case the current is limited by the resistors in the LED strips, within certain margins. The current goes up and down with temperature, but is kept to an acceptable limit due to the resistors.
 

Offline james_s

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #21 on: July 24, 2020, 04:20:37 am »
Any decent equipment will have the power requirements listed right on it, or at the very least in a datasheet.

I haven't played with any of those power supplies that say they're for LED use only but I suspect they skimp on output filtering if they have any at all. It doesn't really matter if your LED strip is flickering at 20kHz, you're not gonna see the flicker, but if you try to power an electronic device from a power supply that has a load of ripple in the output it will wreak havoc.
 

Offline DW1961Topic starter

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #22 on: July 24, 2020, 06:09:45 am »
Any decent equipment will have the power requirements listed right on it, or at the very least in a datasheet.

I haven't played with any of those power supplies that say they're for LED use only but I suspect they skimp on output filtering if they have any at all. It doesn't really matter if your LED strip is flickering at 20kHz, you're not gonna see the flicker, but if you try to power an electronic device from a power supply that has a load of ripple in the output it will wreak havoc.

No doubt. I should get a analyzer. I could just TEST EVERYTHING! I should also get a variable power supply, too. I see them all over Amazon for 100 bucks.
 

Offline james_s

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #23 on: July 24, 2020, 06:53:30 am »
Anyone who does anything at all with electronics should have a multimeter, even if it's just a basic $20 model. A bench power supply with CV and CC modes is very handy but there are substitutes you can use in a pinch to accomplish most things.
 
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Offline AndyC_772

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Re: How do you tell what "type" of power a DC power supply is?
« Reply #24 on: July 24, 2020, 08:16:44 am »
Might be just for regulation and applied standards reasons.

Lighting is a different kind of equipment than e.g. a general purpose power brick, so it's tested and declared conforming to different standards.

^^^ This.

If a power supply is sold with a CE mark, then it's sold as being compliant with all applicable standards.

If the set of standards which apply is different - say, because it's being used with computing, communications or other equipment, instead of the type of equipment for which its testing and certification applies - then it's no longer compliant.
 
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