Hello forum, ive been thinking of making a circuit that can measure 230 volts and maximum of 64 amps.
This is to be used in a fusebox that can run 230v and 400v. the box has 12 fueses each on 16 amps. what we want to do is display the voltage/current on each of the 12 fuses, and on the 3 phases.
It dossnt have to do this simuntainously for all 12 fuses.
So im thinking of having 3 measuring devices, so i can monitor the all the pases in the 3-phase simuntainously.
Ive read about the Voltage divider, and that its practically lethal.
My question to you guys is:
What is the best/safest way of measuring voltage and current.
What is the best way of routing the 12 fuses through the measuring array. Relays, FETS etc, etc.
I will try to have the drawings for the IO schematic for the fusebox uploaded later.
The idea was to be able to measure the 3 phases simuntainously aswell as measuring current running over the 12 fuses indevidually. measuring voltage is the main aspect of this deal, since the input voltage is not that important.
This is to be used as a psu on stages, so the power drawn from this is the biggest variable. We want to use this as a tool to check that we balance the loads properly, and just because we can really.
I worked in a large industrial oil refinery that used tons of both single and 3 phase power systems. They too often required that current was roughly balanced in multiphase power systems.
This was normally done with three CT transformers on the main wires feeding ( for 3 phase power) a service panel for a building, outside equipment enclosure, etc.
It would be a little unusual to also monitor each fused/circuit breaker circuit due to the added expense and not really required to tell if the total system was in balance or not. One could just turn off all the branches and turn only one circuit at a time to get a reading on what each branch's current draw is. However your desire to be able to monitor each branch is possible, just takes more money, more sensors, etc.
CT transformers, while simple, safe if installed properly, are not real compatible with an Arduino. A CT outputs a low value AC voltage (across it's burden resistor) where the amplitude is proportional to the current flowing in the single primary wire being measured. As a arduino analog input pin cannot directly measure a AC voltage, one requires a signal condition circuit between the ct output and the arduino analog input. This would normally be a rectifying/filtering and scaling to allow for proper calibration of this AC to DC measurement. Also note that CT accuracy specs assume a linear resistive load is being powered. If the load has a high reactive component like AC motors, switching type DC power supplies, then CT measurement accuracy will suffer unless the signal conversion/calibration circuit is designed to utilize true RMS correction feature.
I think the present generation of AC hall-effect sensors promise to both lower the expense and complexity of AC power current measurements, as they solve a lot of the interface problems while maintaining the isolation properties with CTs. I haven't personally used any, but I would think that someday the they will replace most CT applications.
CT's cost like 10$ am i right? and in a world where a box like this would cost thousands of dollars to get produced i think we should be able to afford buying 13 of them.
So how would you go around to convert the AC signal the CT produces into a usable signal for the arduino?
As for the load, it will mostly be amplifiers and dimmers, not sure if it will affect the stable reading from the CT, since the transformer has a gigantic coil and a large capacitor array to feed the speakers with sufficient power.
CT's cost like 10$ am i right? and in a world where a box like this would cost thousands of dollars to get produced i think we should be able to afford buying 13 of them.
I think $10 each might be a low estimate. A lot depends if you are buying from a retail distributor or a surplus or e-bay type seller. Don't know if the following is representative. 404 Error - Electro Industries/GaugeTech
So how would you go around to convert the AC signal the CT produces into a usable signal for the arduino?
Measuring mains voltages is much more problematic - the use of a small step-down transformer is the right sort of thing, but again protection is needed against line spikes and the AC level needs shifting suitable for the A/D conversion.
3 phases of current and voltage means 6 values to sample many times per mains cycle, squared, averaged and square-rooted to give RMS readings... I think you can get about 6 analogRead's per millisecond which should be enough.