Power Supply Voltage

Thread Starter

What595654

Joined Feb 11, 2021
6
I purchased two identical power supplies rated DC 28-38V at 3A. But, when I measure the voltage, they both show 52 volts. Is this correct? Because of the 52 volts

I added a step down converter to hit 30 volts but I am worried, because my converter is not rated for that high. Only 38V I believe.

Also, when I measure the amps on a 30-32V 1.7 amp 50 watt LED, I get 1.4 amps.

I purchased another power supply labeled +24V. It goes up to 28V. When I test the same LED, I get .46 amps.

Lastly , I have a 30V 1A power supply. When I test the same LED, I get .75 amps.

Am I misunderstanding something, or are all these power supplies faulty/ or not honest about their ratings?
 
Last edited:

AlbertHall

Joined Jun 4, 2014
11,317
Some supplies have a voltage regulator and will give the specified voltage as long as they are not overloaded.
Some supplies are not regulated and will give higher voltages on no load, and as the load is increased the voltage will fall until, at the rated output current, the voltage will be approximately the rated voltage.

The unregulated supplies typically use a transformer, rectifier, and smoothing capacitor only.
 

dl324

Joined Mar 30, 2015
12,871
Welcome to AAC!
I purchased two identical power supplies rated DC 28-38V at 3A. But, when I measure the voltage, they both show 52 volts. Is this correct? Because of the 52 volts
As noted, unregulated supplies specify their loaded output voltage. Put a load on the supply and increase it in steps to 3A. Make sure you use the appropriate wattage resistors.
 

Thread Starter

What595654

Joined Feb 11, 2021
6
Welcome to AAC!

As noted, unregulated supplies specify their loaded output voltage. Put a load on the supply and increase it in steps to 3A. Make sure you use the appropriate wattage resistors.
Well, I have burnt 3 voltage regulators already. Two were rated 37V 2A and one was 36V 8A. Is this the reason they all started smoking?

How can I test these power supplies safely? How can I lower their voltage safely? Is there a better power supplies to use? Voltage regulators rated for that high of voltage are expensive.
 

Thread Starter

What595654

Joined Feb 11, 2021
6
Welcome to AAC!

As noted, unregulated supplies specify their loaded output voltage. Put a load on the supply and increase it in steps to 3A. Make sure you use the appropriate wattage resistors.
Well, I have burnt 3 voltage regulators already. Two were rated 37V 2A and one was 36V 8A. Is this the reason they all started smoking?

How can I test these power supplies safely? How can I lower their voltage safely? Is there a better power supplies to use? Voltage regulators rated for that high of voltage are expensive.
 

Thread Starter

What595654

Joined Feb 11, 2021
6
Which supplies did you buy?
The simplest solution is to buy a regulated supply.
No connection drawings, no photos, no datasheets, no vendor page links - exactly what are you expecting us to do?

ak
This is the power supply. I have the 100 watt 30-32V 3.5A LED at the bottom.
IMG_20210211_155628.jpg

I am new to this, so I didnt know what I needed to share.
 

Attachments

BobTPH

Joined Jun 5, 2013
3,318
Power supplies come in 2 basic varieties, constant voltage and constant current. The one you show is obviously constant current since it gives a range of 28-38V and a current of 3A. It is designed to work with an LED that draws 3A at a voltage somewhere in its stated range.

The LED you are using says 3.5A at a voltage of somewhere between 30 and 32 V. At 3A its voltage will be somewhat less than that, but you don’t know exactly at what voltage. If it is 28V or more your power supply would power it happily at 3A. But it is probably less than the the 28V minimum, which is why the current is less than you expect.

Bob
 

Thread Starter

What595654

Joined Feb 11, 2021
6
Power supplies come in 2 basic varieties, constant voltage and constant current. The one you show is obviously constant current since it gives a range of 28-38V and a current of 3A. It is designed to work with an LED that draws 3A at a voltage somewhere in its stated range.

The LED you are using says 3.5A at a voltage of somewhere between 30 and 32 V. At 3A its voltage will be somewhat less than that, but you don’t know exactly at what voltage. If it is 28V or more your power supply would power it happily at 3A. But it is probably less than the the 28V minimum, which is why the current is less than you expect.

Bob
Thanks. That makes sense. I have a feeling i was sold a fake 100 watt led then, because it only puts out 1.35 amps, which is similar to the 50 watt leds I have. Strangely though, the little lights inside the 100 watt led cob appear to be more densely packed, more of them, than the 50 watt one, but draws the same amps. I bought the 50 watt and 100 watt from the same seller same type. So, i think i am going to request a refund.
 

MrChips

Joined Oct 2, 2009
23,541
Your tests of the power supplies are not appropriate.

These are constant current supplies. Hence you need to test for current, not voltage.

If the constant current supply is rated at 3A @ 28-38V then it will output 84 to 114W.
You need a resistor (or resistive load) between 10 and 12Ω that can dissipate 125W or higher if you want to test it properly. Measure the voltage across the load to estimate the current.

You cannot lower the voltage with a voltage regulator. This 3A constant current supply is designed to output 100W. The voltage will keep on rising until it pumps out 3A or the limit on the voltage supply is reached. If your load cannot handle 100W it will blow. That is why your voltage regulators will keep on blowing.

This power supply is suited to the 100W LED and not the 50W LED.
The power supplies are not at fault. They are not properly matched to the load.
 
Top