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Buck Converters

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codecage
(@codecage)
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I was just looking at some step down (12 V to 5V) buck converters to use along with some 12V batteries on my DB1.  And one of them had a warning about not connecting the ground side of the input and output voltages together as this would destroy the converter.

Is this the case for all buck converters?  I have not used any buck converters in the past, but have not seen this warning on any others I have looked at.

Since we are using a common ground on DB1, this would not be a viable solution to derive the needed 5 volts for the rest of the electronics.

SteveG


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
 

Today the world's in turmoil
as the people disagree
they argue with each other
"You're wrong!" They so decree!

But in the world of robotics
in a Canadian abode
the solution to all our problems
has kindly been bestowed

A single engineer
who's heart is solid gold
is designing a wonderful robot
that's a pleasure to behold

Yes, the robot's friendly
and can help with all our chores
but far beyond these attributes
it will bring an end to wars

The secret's in its circuity
that we all must learn to heed
a lesson for humanity
that must forever be decreed

No social peace is possible
nor is it likely to be found
until we learn from DB1
the grace of common ground

?

DroneBot Workshop Robotics Engineer
James


   
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egers
(@egers)
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@robo-pi

Where did you learn poetry?


   
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Robo Pi
(@robo-pi)
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Posts: 1669
 
Posted by: @egers

Where did you learn poetry?

I didn't.  I just spit it out and hope it doesn't look like vomit.  ? 

But yeah there are technical secrets behind my poetry.  I do use RhymeZone.   It certainly helps to have a large database of rhyming words to choose from.   But of course there's more to it than just rhyming words.  Rhyming words alone isn't nearly enough.    There needs to be a story or message behind the poem and things need to make sense.

Here was my thinking when I wrote the above poem.

The term "Common Ground" from  Steve's original post is part of what sparked this poem.   I obviously also had in my mind how uncivil the world currently is.  My first thought was, "If the world could only find common ground how nice that would be".  And instantly my second thought was "Hey there's a poem here!"

So the next question, "What do I want the poem to be about?"

Then I thought, "I got it!  Let's make Bill a hero by having DB1 save the world via common ground" ? 

So off to RhymeZone I go with keyboard in hand.  I've already got the story plot, let's see if we can make a  poem out of it.  The poem you see is the result of that inspiration.  It's just a matter of juggling words from that point forward.

Got to have inspiration FIRST.  And when the inspiration hits, don't let it pass by without jumping on it.

Can't let those poems get away when they're knocking at the door. ?

DroneBot Workshop Robotics Engineer
James


   
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codecage
(@codecage)
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@robo-pi

Wonderful poetry, but still looking for an answer on the common ground of buck converters!  ? 

SteveG


   
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Robo Pi
(@robo-pi)
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Sorry, I didn't mean to derail your thread.

I don't know what to tell you.  I just checked my buck converters and they have the grounds connected together on the board so you couldn't separate them if you wanted to without cutting traces.

I can't imagine how it could damage a buck converter to share common ground with the supply voltage.  Are you sure the warning isn't some sort of misprint?  Maybe they meant that to connect either positive voltage to the ground of the other side would damage the board? I can see that being a problem. 

But I can't imagine why it should hurt the board to connect the two grounds together.  That's a strange one there.

Where did you get the boards?  Can you post the warning message?

DroneBot Workshop Robotics Engineer
James


   
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codecage
(@codecage)
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Topic starter  

@robo-pi

I enjoyed the poem, so no problem there.  Just had to post something after LMAO with the poem.

I don't have the converters, just was looking through the assortment I was finding on Amazon and came across the one with the warning.  None of the others had this warning so it got me to thinking (always a bad thing) what gives here.  Most of the ones I found were limited to 3A at 5V, but the one that warned about the common ground was capable of 10A.

My first thought was eventually we could be putting more than 3A worth of electronics requiring 5V, so was reading about this particular converter when I came across this warning (with typical Chinglish translation):

Note:>> this DC converter is non-isolated designed,when you power on ,
remember do not connect the two negative electrodes together(usually the black cable) ,
even touch,otherwise ,the converter will burn down/damaged ,
please be carefull.if you connect the black cable together ,the converter burn down ,
we do not resend or refund ,please know this problem.

Here is the link on Amazon: 12V to 5v 3A Step Down Converter

SteveG


   
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Robo Pi
(@robo-pi)
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Posted by: @codecage

non-isolated designed

Translation:  They screwed up the design but manufactured it anyway.  And now they need to unload them.

Posted by: @codecage

we do not resend or refund ,please know this problem.

Translation: Yes!  It's a horrible "problem" that they are dumping onto you and they no longer want any parts of it. ? 

At least you  have to give them credit for warning you up front. ? 

Go with Bill's DB1 design and find one that has "Common Ground". ? 

DroneBot Workshop Robotics Engineer
James


   
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robotBuilder
(@robotbuilder)
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https://www.emea.lambda.tdk.com/il/KB/The-benefits-of-using-nonisolated-DCDC-converters.pdf
https://www.cui.com/blog/isolated-vs-non-isolated-power-converters

Without seeing their circuit design I am not sure how they might have messed it up?

 


   
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codecage
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@robo-pi

I think I'll just get a couple 3A ones for now as that should be more than enough for the time being!  Can always add more and split the 5V loads between the different terminal strips in the design.

SteveG


   
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codecage
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@casey

Now I'm even more confused!  Reading the links you provided it looks like the non-isolated converters share a common ground anyway.  That seems to be different than what the Chinglish warning was all about!  Any chance you can clarify?

SteveG


   
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robotBuilder
(@robotbuilder)
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Being self taught in basic electronics my knowledge has big gaps in it so although I have a general understanding of the principles involved it is best a fully trained electronics guy explains things.

Here is an example of building your own buck converter.

https://hackaday.com/2016/06/04/how-does-a-buck-converter-work-anyway/


   
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Spyder
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@codecage

I picked up an assortment of those things for various projects, and I still have a few left. I can't visibly see the traces, so I just put a meter on them all. There's a buck/boost, and 2 bucks, all 3 say common negative

bucks

   
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Robo Pi
(@robo-pi)
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Posts: 1669
 
Posted by: @codecage

@robo-pi

I think I'll just get a couple 3A ones for now as that should be more than enough for the time being!  Can always add more and split the 5V loads between the different terminal strips in the design.

That's what I would do.  Unless you actually have a single item that draws more than 3A just use multiple smaller ones.

DroneBot Workshop Robotics Engineer
James


   
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codecage
(@codecage)
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@robo-pi & @spyder

Thanks guys!  That's one of the great things about this forum.  We get to bounce ideas around and sometimes come up with solutions that we hadn't thought of before. Sort of like not being able to see the forest for the trees.  And then all of sudden we see the light, like coming into a clearing in the forest and there's the sun shining down on you.

SteveG


   
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