So... I need to measure the 320V DC rail.
Is it smart to go about it this way, or should I implement some kind of inbetween system?
Since its dc, and both arduino and op amp are supplied elsewhere, having a common ground shouldn't be a big deal?
If something was to happen, those 2W zeners would probably burn those weak resistors out open before ADC gets it.
I know HV buisness is always concerning, but I realy need this project done for school, it will probably never see any use, filtration before and after, and fusing/driving/protections are on seperate schematics.
Another option I thought of, would be to wind currentsense arround the + wire, and use 2 dividers and optocouplers to detect over and under voltage, but this could get me analogue measurement so I would prefere it...
Is there perhaps another way to separate the HV side, or this is enough...
by GND here I mean COMMON, AC GND will be done differently on the input filter
Of course, be careful and the Arduino should be earth grounded for additional safety.
If the resistors are high-enough in resistance you won't fry anything.
I assume you know Ohm's Law and you can calculate power dissipation as voltage X current, or Voltage squared/R.
And you can calculate the "worst case" power dissipation in the Zeners.
The op-amp looks like trouble because of the voltage difference between the inputs and the power supply pins. Maybe put the current sense on the ground side.
I don't know what sort of op-amp (or comparator?) you plan to use but it seems to want a common-mode range that includes +320v dc, have a true differential input, and an output range that can go down to 0v. Incompatible requirements methinks. Voltage measurement using a potential divider is standard operating practice, the zener is redundant.
you assume correctly, 2W is actually an overkill but I have them arround.
I didnt get to the grounding yet, but I will certainly read a book on it before this is finished.
thanks for the quick reply, sure, current sense will go low
the op amp part is still undecided, but it should only measure the drop of the sense resistor, or i might just wind it, like a hall probe, just needs to signal slightly under the fuse rating to stop the thing...
I thought as much for the zenners, but they can't hurt should there for any reason be a spike, even tho the caps are quite large, I will drive a welding transformer, 25A fuse is underpowered, and swapable, but it should be enough, IGBTs are 45A, and the rectifier bridge is indestructible...
Its stuff I had arround...
I know there are alot of ICs that separate grounds, just wanted to know if i should go that far, since everything else is galvanic separated from the arduino...
So sense resistor is 1 ohm, suppose current is 1A so it drops 1v.. One opamp input is at 320v, the other at 319v, the ouput needs to be something less than +5v. As I said these are incompatible requirements, the op amp needing a positive supply rail somewhat over 320V!
What load current do you have to supply? You have a 25A fuse so must expect quite a large current - the sense resistor will get very hot, and also contributes to the output impedance of the supply.
You have to isolate the current sensing, and a Hall sensor seems the easiest way. Not a good idea to put the current sensing in the negative rail because then the output is floating slightly. Or you might use a current transformer on the AC supply to the rectifier.
Sure, I was kind of worried about the resistor, I could even go with a shunt, but op amp complicates things, and building a buck boost just for the electronic fuse/IGBT response sensor does seem counter intuitive...
I can't do it on the AC side since those capacitors can probably still do some damage even without the mains, thus the physical fuse, and it should signal to stop firing the switches/close the relay/shut off the driver, and log fault...
Main reason for the 25A fuse would be the H-bridge short prevention, so it can be as strong as the switches.
Another fuse after the output filter can deal with the expected current, even tho the overcurrent sensor here might be faster then both, while giving feedback on switch activity.
I was split about the opamp and the Hall, thanks for the imput
The only safe way is to buy an isolating dc to dc transducer or isolating ADC .
You can’t risk potential dividers as a fault could leave the high voltage onto the Arduino and may be you .high voltage and low voltage sides need physical separation , so the H V cannot be touched .
You need qualified assistance for this .
25A 300v =7.5kw, not a hobby project
Or … do all this on the ac side of the power supply , where transformers can be used .
Where does the AC input to the bridge rectifier come from? If directly from the mains without a transformer then the whole circuit is live and dangerous. You cannot connect any part of it to earth as doing so will short out the rectifier via the neutral - earth connection.
Please leave the original schematic where it is and post a revised one as a reply, otherwise the comments that have been made will no longer make sense.
by schooll I mean senior college, I'm not likely to kill myself, and tese sensors are in the development proces, thats why I asked, there is a load of components I haven't heard of yet.
Driver is opto coupled, and this is the last piece of the puzzle...
Mains comes from the input filter that will provide earth...
I know... Isnt't that the case with any HV work, I don't want to bother my mentor with everything
Even tho I seem chill, I am not taking this lightly at all
I am taking every possible step, those capacitors would kill me in an instant, I know that very well, what I asked here is for an oppinion on how to implement a voltage/current sensor, there is much more to this whole thing.
The transducer is highly apreciated...
relax
You will smoke all the components and probably smoke the PC when plugged into the Arduino.
If you are seriously proposing this circuit, any company hiring you to design stuff better have a good insurance policy, and death benefits, just saying.
you assume correctly, 2W is actually an overkill but I have them arround.
