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# Buck Converters

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(@robotbuilder)
Member
Joined: 5 years ago
Posts: 2147

"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."

So the question is unanswered? What didn't make sense is the "output voltages" as I thought there would only be one output voltage? I can't find the warning at the link provided or any circuit details. If the negative (or ground) rails are connected then connecting to the output voltage would simply short out the output of the converter?

A long time ago while teaching myself the fundamentals of electronics I really tried hard to have a good understanding of how circuits actually worked beyond being "magic" boxes with labels like "buck converter" on them. Those many years ago the only circuit I remember made use of a transformer which of course electrically separated the input voltage from the output voltage which was useful when the input was 240v from the mains!

It all depends of course if you want to build with understanding at some lower level or are happy to hook together circuits following a set of instructions without any understanding.  I started with simple components and thus had no choice but to understand at the lower level.  Although in those days like today you could solder up an electronic kit and pretend you understood it.  The same is true of programming.  Today with the Arduino even low level stuff well suited to assembler code like turning a LED on and off is all done in C.  And like electronic modules you can use C functions without a clue how they work.

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

Posted by: @casey

So the question is unanswered? What didn't make sense is the "output voltages" as I thought there would only be one output voltage?

The plural "voltages" refers to the input voltage and the output voltage.  One of each.  That's two voltages.

The warning is to not connect the ground side of these two voltages together.  In other words, don't connect the ground of the input voltage side to the ground of the output voltage side as this will cause the unit to burn  up and fry itself.

This would be ok if you keep the battery ground separate from whatever you are driving with the output voltage.   But if the ground of the source battery is connected to a main grounding frame along with the device  you are attempting to power, then poof.  It's all over.

So as long as  you can keep the source battery totally isolated from everything else, this converter will work.  But typically most batteries are also connected to a main ground frame (as in a car).  So you wouldn't want to use it in that situation to power a sound system that is also grounded to the car frame.  That would  be another Poof.

You could use it to power a sound system that you had sitting on the seat next to you in the car that wasn't grounded to the car.   But if anything on the sound system  is grounded to the car ground, poof.

It's just a converter that needs special attention.  Not something that you'd typically want to bother with.  It can work, as long as you make sure the source battery ground is NEVER grounded to the unit you are powering.  But one little mistake and poof.  The manufacture takes no responsibility.  It's your fault for allowing the grounds to come in contact with each other.

DroneBot Workshop Robotics Engineer
James

(@robotbuilder)
Member
Joined: 5 years ago
Posts: 2147

Posted by: @robo-pi

This would be ok if you keep the battery ground separate from whatever you are driving with the output voltage.   But if the ground of the source battery is connected to a main grounding frame along with the device  you are attempting to power, then poof.  It's all over.

Ok I misread it.  Actually the first time I read it I seem to remember reading it that way but became confused with trying to figure out what else they could mean. I still don't get it. Looking at the circuit diagram of a buck converter the negative input and output terminals (0 volt reference points) are already connected internally?

Can you show me where the frying takes place?

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

Posted by: @casey

I still don't get it. Looking at the circuit diagram of a buck converter the negative input and output terminals (0 volt reference points) are already connected internally?

Most buck converters are built like that.   I just checked all mine and they all have common grounds.

The product Steve was pointing to is apparently different.  Until we can see the schematic for that exact product I can't tell you why it fries when the grounds are connected.

I can tell you this, I've owned similar products in the past an I can vouch for the fact that they do indeed burn  up when the grounds are accidentally touched.  Shamefully I confess that I didn't pay attention to the rule.  I can also vouch for the fact that destruction of the converter is instantaneous.   At least mine blew up instantly.  No overheating and smoking to warn that it's about to blow.  Just instant sparks and flames and it's done faster than you can say, "Oh no!" ?

At least when connected to a 12 volt car battery.

DroneBot Workshop Robotics Engineer
James

(@tentoes)
Member
Joined: 5 years ago
Posts: 28

If I may add a bit to this exchange, is that I recently learned that most all “switching-type” buck regulators will create some RF noise, as I recently learned in my HAM radio class (USA Technician level, KJ7LNV).

The class instructor mentioned with dismay the fact that so many of the new, LED light sources use switching regulators that emit RF noise that HAMers find annoying.

(@tentoes)
Member
Joined: 5 years ago
Posts: 28

@casey

I agree wholeheartedly!  And he does it with highly professional video effects and preparation that is also evident in Bill’s work on the Dronebot Workshop!

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