# Can't set amperage on 400w 15A DC-DC step up boost converter 10-60 volts

#### jobee

Joined Mar 10, 2023
21
Hello folks,
I'm just new to the forum. I'm looking for help using a 400w 15A DC-DC step up boost converter 10-60 volts.
I watch many youtube video of people who can set voltage and amperage with that.
But I can't do the same. Here is my project : I want to power a COB LED 30-34v 200w.
I have a DC Power 28 volts 400 w that I plug to the DC-DC step up boost. I can set the voltage to 33V using my multimeter.
And after when I plug the COB LED with the multimeter as amperemeter it's not working. Actually there current is going to the LED but the voltage is blocked at 28 volt and amperage to 4A. If I turn the small screws on the Convverter, nothing happens.
I attached two drawings to explain it. (Not very technical drawings
Could you please give me help !

Jonathan

#### Attachments

• 1.8 MB Views: 11
• 2 MB Views: 12

#### Papabravo

Joined Feb 24, 2006
21,323
It is a mistake to think that you can control both the current and the voltage independently. Ohm's law tells you that with voltage, current, and resistance if two of them are fixed, the the third is determined by those two. In the case of a power supply if you set the output voltage and the load is fixed, the load will draw EXACTLY as much current as it needs. No more, and no less.

You might be confusing a settable current limit with the ability to control the current, but that is a different matter entirely.

#### jobee

Joined Mar 10, 2023
21
It is a mistake to think that you can control both the current and the voltage independently. Ohm's law tells you that with voltage, current, and resistance if two of them are fixed, the the third is determined by those two. In the case of a power supply if you set the output voltage and the load is fixed, the load will draw EXACTLY as much current as it needs. No more, and no less.

You might be confusing a settable current limit with the ability to control the current, but that is a different matter entirely.
Yes, that's right, I finally understand I can't control both the current and the voltage independently.
And yes, I try to deliver 6 amp in constant current for the LED. That's why I believed I have to set first the voltage to 33V and after set a 6 amp in constant current. Because this converter has 2 screws, as I understood, one for volt and one for ampere.
But when I plug the amperemeter it like it "inibates" the role of the Step-Up. Also I don't know how to be sure to have a 6 amp in constant current.

#### Papabravo

Joined Feb 24, 2006
21,323
The immutable rule of DC-DC conversion schemes is:

The output power will ALWAYS be less tahn the input power. Sometimes it will be much less.
When you have a boost converter, raising the output voltage will limit the output current. In your example you have: 33V @ 6 Amperes is 198 Watts. Assume for the sake of argument that the conversion was 80% efficient, this would require 198/0.8 = 247.5 watts of input power. Your power supply has 28 V @ 4 Amperes which is only 112 watts. Therefore, I am hardly surprised by your results.

#### jobee

Joined Mar 10, 2023
21
The immutable rule of DC-DC conversion schemes is:

The output power will ALWAYS be less tahn the input power. Sometimes it will be much less.
When you have a boost converter, raising the output voltage will limit the output current. In your example you have: 33V @ 6 Amperes is 198 Watts. Assume for the sake of argument that the conversion was 80% efficient, this would require 198/0.8 = 247.5 watts of input power. Your power supply has 28 V @ 4 Amperes which is only 112 watts. Therefore, I am hardly surprised by your results.
Thank's again for your answer. I must have expressed myself badly. Actually, the power supply is 28 V @ 400 watt (14 Amp). I speak of "4 amp", this is this the current showed on the amperemeter when I plug it. It is like the amperemeter "interfer" to the circuit. I can't change the values of the converter when I plug the ampermeter. It stays on 28 volts and 4 amp

#### Papabravo

Joined Feb 24, 2006
21,323
Thank's again for your answer. I must have expressed myself badly. Actually, the power supply is 28 V @ 400 watt (14 Amp). I speak of "4 amp", this is this the current showed on the amperemeter when I plug it. It is like the amperemeter "interfer" to the circuit. I can't change the values of the converter when I plug the ampermeter. It stays on 28 volts and 4 amp
I'm not sure what that ammeter is measuring but if it has that reading with no load then I would call it meaningless. I'm not familiar with the term "interfer"; what is that? You also need to consider the operational limits of the DC-DC converter. What is the maximum input power level it can handle?

#### jobee

Joined Mar 10, 2023
21
I'm not sure what that ammeter is measuring but if it has that reading with no load then I would call it meaningless. I'm not familiar with the term "interfer"; what is that? You also need to consider the operational limits of the DC-DC converter. What is the maximum input power level it can handle?
The measure of 4 amp is made with load, I mean when the power supply is connected to the converter that is connected to the COB LED. But whatever, by "interfer" I meant that it's like the amperemeter has an effect on the circuit that cause problem to use of the converter. Also I think all is ok regarding to the specs of the converter :

Input voltage: DC8.5V-50V
Input current: 15A (MAX) exceeds 8A please improve heat dissipation
Quiescent current: 10mA (12V liter 20V, the output voltage, the higher the current will increase too quiet)
Constant] range: 0.2-12A

Actually my main problem is that, if I can set the right voltage with the converter, I can't set a constant current of 6 amp that I'm supposed to can do. Because LED has to work with constant current, I heard.

#### BobTPH

Joined Jun 5, 2013
9,299
You are trying to set both the voltage and current. To use that converter as a constant current source, you set the voltage at maximum and set the current to the desired level. Then it can set the voltage needed to achieve that current.

Despite the specifications, it sounds like your LED requires more than 33V to draw 6A. What is the max continuous current specification for your LED module? That is the current you should use and the voltage will be whatever it is.

Also, I hope you have a massive heat sink, because at 200W, the COB will have to dissipate about 100W. If you have operated it without a heat sink it is probably damaged.

#### LowQCab

Joined Nov 6, 2012
4,312
When working with LEDs, the important Specification is Amperes ( Amps ).
Buying stuff from China is a big risk.
You never know what You might get,
and the advertised "Wattage" is usually a greatly inflated number.

You need to make sure that You have adequate Heat-Sinking capabilities for the LEDs.
This is extremely important.

Next,
You need to know how much Continuous-Current ( Continuous-Amps ),
that the LEDs are rated for.

Next,
Set your Power-Supply for maximum-Voltage, and minimum-Current
BEFORE
You turn the Power-Supply "On".

Next,
Turn the Power-Supply "On".
Then slowly increase the Current-Potentiometer.
at some point, the LEDs should start to get bright.
STOP,
Turn "Off" the Power-Supply.
Connect an Ammeter between the Power-Supply and the LEDs.
Turn the Power-Supply "On".
Increase the Current-Potentiometer until the Ammeter reads the Current that You want,
but DO NOT exceed the recommended Current rating of the LEDs.

If You can not get the Current as high as You would like,
then You need a stronger Power-Supply.

If the LEDs get too Hot, they will POP !!!
.
.
.

#### jobee

Joined Mar 10, 2023
21
You are trying to set both the voltage and current. To use that converter as a constant current source, you set the voltage at maximum and set the current to the desired level. Then it can set the voltage needed to achieve that current.

Despite the specifications, it sounds like your LED requires more than 33V to draw 6A. What is the max continuous current specification for your LED module? That is the current you should use and the voltage will be whatever it is.

Also, I hope you have a massive heat sink, because at 200W, the COB will have to dissipate about 100W. If you have operated it without a heat sink it is probably damaged.
Thanks a lot !
yes the specs are Forward Voltage / Forward Current: DC (30-34V / 6A). I can't see any "continuous current specification".
I used a laboratory power supply to test first (a 60V / 5 A), it seems to work as described with this specs (DC (30-34V / 6A))
Yes I have massive heatsink with fan.
You said "To use that converter as a constant current source, you set the voltage at maximum and set the current to the desired level. ". You mean that I have to set the voltage at maximum (60 volt for this converter), but I can't plug the converter with 60 volts on my LED? Or I start with the minimum amperage?

#### jobee

Joined Mar 10, 2023
21
When working with LEDs, the important Specification is Amperes ( Amps ).
Buying stuff from China is a big risk.
You never know what You might get,
and the advertised "Wattage" is usually a greatly inflated number.

You need to make sure that You have adequate Heat-Sinking capabilities for the LEDs.
This is extremely important.

Next,
You need to know how much Continuous-Current ( Continuous-Amps ),
that the LEDs are rated for.

Next,
Set your Power-Supply for maximum-Voltage, and minimum-Current
BEFORE
You turn the Power-Supply "On".

Next,
Turn the Power-Supply "On".
Then slowly increase the Current-Potentiometer.
at some point, the LEDs should start to get bright.
STOP,
Turn "Off" the Power-Supply.
Connect an Ammeter between the Power-Supply and the LEDs.
Turn the Power-Supply "On".
Increase the Current-Potentiometer until the Ammeter reads the Current that You want,
but DO NOT exceed the recommended Current rating of the LEDs.

If You can not get the Current as high as You would like,
then You need a stronger Power-Supply.

If the LEDs get too Hot, they will POP !!!
.
.
.

Yes, thanks a lot, that are great instuctions. When you say to set the maximum-VoltageI on the converter. You mean the maximum voltage of the LED (also 34 volts) or the maximum voltage that the converter can deliver (60 volts)?
Also yes, I won't go to the maximum amperage. The specs are Forward Voltage / Forward Current: DC (30-34V / 6A). I guess "continuous current" required is about 33V.

#### jobee

Joined Mar 10, 2023
21
Yes, thanks a lot, that are great instuctions. When you say to set the maximum-VoltageI on the converter. You mean the maximum voltage of the LED (also 34 volts) or the maximum voltage that the converter can deliver (60 volts)?
Also yes, I won't go to the maximum amperage. The specs are Forward Voltage / Forward Current: DC (30-34V / 6A). I guess "continuous current" required is about 33V.
And yes, I have a massive heatsink with fan.

Thanks for all !

#### jobee

Joined Mar 10, 2023
21
And yes, I have a massive heatsink with fan.

Thanks for all !
Hum, you said "
Set your Power-Supply for maximum-Voltage, and minimum-Current
BEFORE
You turn the Power-Supply "On"."
Before to turn ON. So you mean, to set to the maximum voltage of the converter (60 volts) but after you don't seem to tell me to set the voltage to 34 volts? How do I do ?

#### LowQCab

Joined Nov 6, 2012
4,312
What I mean is that the Voltage-Limit is irrelevant,
as long as it is high enough to cause the desired Current to flow through the LEDs.

LEDs need to have their Current Regulated, NOT THE VOLTAGE,
the Voltage required to achieve the desired amount of Current
will vary substantially, depending upon the the Temperature of the LEDs.
.
.
.

#### jobee

Joined Mar 10, 2023
21
What I mean is that the Voltage-Limit is irrelevant,
as long as it is high enough to cause the desired Current to flow through the LEDs.

LEDs need to have their Current Regulated, NOT THE VOLTAGE,
the Voltage required to achieve the desired amount of Current
will vary substantially, depending upon the the Temperature of the LEDs.
.
.
.
So, practically, you mean I do this steps :

1/ Set your Power-Supply for maximum-Voltage, and minimum-Current of the converter
BEFORE
You turn the Power-Supply "On"."
2/ Plug a voltmeter
3/ Turn On the power supply
4/ Set the voltage to maximum voltage required for the LED (34 volts)
5/ Slowly increase the Current-Potentiometer.
at some point, the LEDs should start to get bright.
STOP,
6/ Turn "Off" the Power-Supply.
7/ Connect an Ammeter between the Power-Supply and the LEDs.
8/ Turn the Power-Supply "On".
9/ Increase the Current-Potentiometer until the Ammeter reads the Current that You want,
but DO NOT exceed the recommended Current rating of the LEDs.
Is that right ?

#### jobee

Joined Mar 10, 2023
21
So, practically, you mean I do this steps :

1/ Set your Power-Supply for maximum-Voltage, and minimum-Current of the converter
BEFORE
You turn the Power-Supply "On"."
2/ Plug a voltmeter
3/ Turn On the power supply
4/ Set the voltage to maximum voltage required for the LED (34 volts)
5/ Slowly increase the Current-Potentiometer.
at some point, the LEDs should start to get bright.
STOP,
6/ Turn "Off" the Power-Supply.
7/ Connect an Ammeter between the Power-Supply and the LEDs.
8/ Turn the Power-Supply "On".
9/ Increase the Current-Potentiometer until the Ammeter reads the Current that You want,
but DO NOT exceed the recommended Current rating of the LEDs.
Is that right ?

I tried the step 1 to 4
1/ Set your Power-Supply for maximum-Voltage, and minimum-Current of the converter
BEFORE
You turn the Power-Supply "On"."
2/ Plug a voltmeter
3/ Turn On the power supply
4/ Set the voltage to maximum voltage required for the LED (34 volts)

But when I plug the LED and turn-on the power supply, LED already light on although I turn the Current to minimum before.

#### LowQCab

Joined Nov 6, 2012
4,312
No Voltmeter is needed, ( except maybe just for your personal interest ).

Set the Voltage to "Maximum", ( whatever that might be is not important ).

At the start of the adjustment procedure,
the Current-Limit-Control should be set to "Minimum".

This is where an Ammeter is REQUIRED.
A Volt-Meter will NOT substitute for an Ammeter.

Slowly increase the Current-Limit-Control until the desired Current is achieved.

If You can't achieve the desired Current-level through the LEDs,
You will have to get a stronger Power-Supply.
.
.
.

#### LowQCab

Joined Nov 6, 2012
4,312
The LEDs may partially "turn-On" at a very low Current-Level.
.
.
.

#### jobee

Joined Mar 10, 2023
21
Wow !!!!!
This works. Exactly like you said !
Amazing !
One billion thanks !

#### jobee

Joined Mar 10, 2023
21
Here is the procedure, for any people asking the same question.
1/ Set your converter for maximum-Voltage, and minimum-Current
BEFORE You turn the Power-Supply "On"."
2/ Turn On the power supply
3/ Slowly increase the Current-Potentiometer.
at some point, the LEDs should start to get bright.
STOP,
4/ Turn "Off" the Power-Supply.
5/ Connect an Ammeter between the Power-Supply and the LEDs.
6/ Turn the Power-Supply "On".
7/ Increase the Current-Potentiometer until the Ammeter reads the Current that You want,
but DO NOT exceed the recommended Current rating of the LEDs.