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Topic: Overvoltage Protection Circuit (Read 220 times) previous topic - next topic

twiens99

Hi

I'm been working on my first electronics Project for a little while now. Mostly Researching the net to find what I need.

I'm trying to build in an overvoltage protection circuit into my project.

The Project is going to be powered by my Truck Batteries, And may be subject to Voltage spikes when the the Truck is being started up. (or by any unknown factor that it may see)

I've included a simple Circuit Diagram with the Part numbers. You can ignore the motor part, that will be the rest of the project, which includes a Buck Converter, arduino Nano, some Relays, a Fan. And A ThermoElectric cooler. Pretty sure I've got that part figured out as I can Breadboard that part out. But I have no way of testing the overvoltage circuit properly.

I'm sure there are other ways of doing this, but this is the best that I could come up with.


The Circuit consists of a 1500W TVS Unidirect Diode With a Breakdown Voltage of 15V
Followed by a 10uF 100V Capacitor
Followed by a Power Choke Inductor 15.75kHz 0.075Ohms Rated to 6.6A (Which is more than my total Draw of my project)
Followed by a 1000uF 50V Capacitor
Followed by another 1500W TVS Unidirect Diode With a Breakdown Voltage of 15V
This is all in Parallel with the rest of the project. (See Schematic)


One of the things that I am totally unsure about is the second diode, Which way would you orient it. Same as the first? or Flipped? I have no idea, Can't seem to find this answer out there. My thinking is Flipped.


I'm basing this circuit off of somebody elses 12V Project.


If Anybody can help a fellow newbie out That would be Great!

Thanks

wvmarle

So that are zeners, not regular diodes.

What's the purpose of that series of capacitors, zeners and a choke? That motor doesn't seem to get much if any protection from it.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Wawa

Seems you wanted to make a "Pi filter" (Google it, images), but mixed a few things up.
Leo..

DVDdoug

The buck regulator should provide some "filtering" and you may not need any further protection.

The way Zener protection works is it essentially "shorts out" when you go over the Zener voltage, and the fuse blows.    In a signal circuit you can replace the fuse with a "current limiting" resistor, but in a power supply circuit you can't have a resistor in series.

A single Zener will clamp between (about) zero and +15V.   Back-to-back Zeners will allow -15 to +15V (which you don't want).   

The LC circuit is doing more harm than good...   The inductor prevents current from instantly flowing...  The spike appears across the inductor until it's magnetic field builds-up so the voltage is not across the Zeners and they don't kill the spike.

Once current starts flowing the capacitors start charging-up.   With a long-term over-voltage, the capacitors will fully-charge and voltage will appear across the capacitors, so again the Zeners are not doing anything.

twiens99

So it seems the guy that I got the idea from.... Doesn't know what he's talking about...lol.

I think I'm gonna just leave circuit the way it was before I got the bright idea of complicating it way over my head.


But In the future I'd like to be able to "Protect" a circuit that would be installed on a vehicle.


This seems like something that should be straight forward, and done all over the internet, but for some reason I can't seem to find it.

What would you guys do to accomplish this?

wvmarle

Protecting a power supply is a different problem than protecting a signal, as you want to quench voltage spikes while letting a lot of current pass through unhindered.

You can protect quite well against voltage spikes using a capacitor, which smooths out such spikes. Makes sure the cap is rated to take at least the highest level spike you expect to ever see. So in automotive that would have to be a 150-200V rated cap. An inductor and second cap would allow for smoothing even more, with the inductor trying to keep the current constant. Indeed the Pi circuit as mentioned above.

You may add a (Schottky) diode in the circuit to protect from reverse voltages (electrolytic caps take very bad to that), but make sure it can handle the current and power dissipation.

Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Wawa

Don't see why you would use a cap rated for "100-200volt".
A 25volt cap should be more than enough, especially if it has a TVS diode across.
18volt breakdown standoff is a good value.
Leo..

ted

.I will remove 220uH (capacitor maybe too ), it is not much inductance but is make circuit worse

wvmarle

Inductor can be beneficial for your circuit if wired in the correct way.

An inductor goes in the power line, it's for keeping current constant, while a capacitor goes between the positive and negative wires, it's for keeping the voltage constant.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

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