Connecting two buck boost boards for a split supply?

[Tinkerer99]

Hi folks,
Just bought a cool buck boost converter which i'll power from a laptop power supply.
Would there be a problem if I powered two of these and connected the +ve output of one board to the -ve output of the other to have a split supply?
Thks

 

[bertus]

Hello,

The drawn setup will only work when the converters are fully in/out isolated.

Bertus

 

[Tinkerer99]

Can I use a multimeter to figure out if the lines are isolated? If so, how?

 

[Delta Prime]

On non-energized equipment
Resistance check! If input common &
Output common are connected than
thay are not isolated.
Quick,Dirty Inaccurate,

 

[Bluejets]

Think you will find the negative is common so no.

 

[Bluejets]

What voltage split are you aiming to get and at what load current?
Do you have a link to the specs of the board you show?

Point being it may be possible to use just the one board, run to output up to 30v (for say a 15v split) then add a couple of linear regulators positive and negative along with a couple of capacitors and create a zero volt rail that way.

Still need to isolate from original input common overall.

 

[Tinkerer99]

On non-energized equipment
Resistance check! If input common &
Output common are connected than
thay are not isolated.
Quick,Dirty Inaccurate,

Resistance between in/out common was 760k. Then I measure the + in/out and I got 2k resistance increasing up to 12k over 10 seconds. Guess something was charging up. Then I went back to the ground common and now it read open circuit.
Can I assume it is isolated?

 

[Harald Kapp]

Can I assume it is isolated?

You can assume what you like, but it is highly unlikely that this module is isolated. Tell us the make and model (or a link to the datasheet or the website where you purchased this module) so we can have a more detailed look at the module.

 

[Delta Prime]

Resistance between in/out common was 760k.

I would expect greater than 1 Mega ohm isolated resistance both power rails for floating (again isolated outputs).make,model,year of your unit under test. Please.

 

[Delta Prime]

Then I measure the + in/out and I got 2k resistance increasing up to 12k over 10 seconds. Guess something was charging up

Again Quick,Dirty ,Inaccurate
It works for me because I know what to expect.
I Apologize for any confusion I my have caused you....
I'm still learning how to convey information.

 

[Tinkerer99]

You can assume what you like, but it is highly unlikely that this module is isolated. Tell us the make and model (or a link to the datasheet or the website where you purchased this module) so we can have a more detailed look at the module.

DC Buck Converter 60W 5A Power Supply Module with Cooling Fan LCD Display

Product descriptionDescription:Input voltage: 5.5-30V (When the input voltage is 5V, the voltage can be increased or decreased, but the voltage and current measurement is not accurate; when it is lower than 4.7V, the undervoltage protection)Output voltage: 0.50-30VOutput current: up to 6AOutput...

www.makerfocus.com

Low cost Chinese stuff. Bought a couple of days ago via Amazon. The item box had model dp60 label on it.

 

[Delta Prime]

An isolated buck converter (Fly-Buck) uses a synchronous buck converter with coupled inductor windings to create isolated outputs.
I see nothing to sugest the use of this topology. I sumitt your outputs are not isolated,therefor can not be used for your application.

 

[bertus]

Hello,

The two large chips are a processor and a lcd driver.
The two small chips cant be read.

I assume the converter is not isolated, so you can not connect the outputs in series.

Bertus

 

[Tinkerer99]

Thanks Delta, Bertus, and Harald,

How about this? What if I create a mid-voltage rail using discrete components at the input, like a virtual 0ve rail, creating a split supply? See pic? Wouldn't that work?

 

[Delta Prime]

Thanks Delta, Bertus, and Harald

All three in the same sentence.
I'm going to play the lottery.
I will defer to my superiors.

 

[Bluejets]

I doubt (as quoted previously) that the input/output is common isolated....so once again.....no.

 

[Delta Prime]

@Tinkerer99 Can you change the color of you're avatar, please.
.

 

[Harald Kapp]

Hello,

The two large chips are a processor and a lcd driver.
The two small chips cant be read.

I assume the converter is not isolated, so you can not connect the outputs in series.

Bertus

+1. No transformer, no isolation.

 

[Tinkerer99]

Thks for all the replies,
Last attempt... Each converter gets its own separate linear power supply (transformer, bridge rect, smoothing cap).
Now surely....!! ??

 

[Bluejets]

Possibly...if you keep the outputs totally isolated from everything else.
It really depends on what your final application is and there may well be some regulation problems or other so far unseen.

Why don't you just buy a split supply unit?
Cannot understand why some will bend over backwards just to be different, no matter on the possibly complexity of the outcome.