# Measuring high currents and high voltages with arduino.

Hi guys,

Lately i've been trying to find some ways to measure voltages till 50 volts, and current up to 15 amps. The suggestions that are given on the internet are mostly using a voltage divider for the voltage, and a shunt for the current, but since my voltages are way bigger than the most topics my question is = which resistor i should use for the voltage divider(it must be pretty small), and what kind of shunt(since i found out that the values are being shown as mV per A)?

Sorry for my bad english, and I hope that someone is willing to comment.

as the voltage is above 50 i would urge to use opto couplers. cheapo is to use 555 as a frequency maker this will drive the coupler and you count the pulses.

or here.

Current Transducer/30A

Lately i've been trying to find some ways to measure voltages till 50 volts,

AC or DC ?

which resistor i should use for the voltage divider(it must be pretty small), and what kind of shunt

Take a look at these

To measure voltages up to 50 V, it is fine to use a 10:1 voltage divider on the analog input (90K and 10K resistor).

For current up to 15 A, a sensor like this will work well: https://www.pololu.com/product/2452 (other models available for higher currents.

Hello,

At first let me thank you all, For the voltages i guess I'm going for the 10:1 voltage divider, and I think I'm going for a non-invasive current measurer because whenever an evasive current measurer breaks, the whole electricity stops flowing. But that leaves me another problem; i need to measure both AC and DC(on different spots in the schematic). And most of the non-evasive are AC only(i've only seen one on ebay).

For the voltage divider i do have another question: Can i just use the small resistors like the ones that you use for small 5 volt projects for the voltage divider with 15 amps and 50 volts, or do i have to buy special ones, since i can't seem to find resistors of a size that seem big enough to handle that amount of electricity.

Thanks.

Current sensing resistors can be had fro rs components etc.

You wont find thep in shops.

For 15 a fsd a 0.3 ohm resistor will give a full scale output of just under 5 v

That will dissipate 67.5 watts so a 100 watt resistor would do.

However thats a lot of loss.

Normally a smaller resistance would be used say 10 milliohm which would give a dissipation of 2.5 watts. The downside is fsd will only be .15 volts so an amplifier is needed

For the voltage divider, most common resistors of the wire ended type are rated between 100 to 250 v anyway. Just check with the supplier

Non invasive current transformers . Do they work at dc ?.?

Non invasive current transformers . Do they work at dc ?.?

No.

for the voltage divider with 15 amps and 50 volts

You misunderstand the entire process. Voltage and current are measured independently.

The voltage divider needs to conduct only a very small amount of current, which is the maximum voltage divided by the total resistance. So, my example of 90K and 10K resistors will conduct 50V/100 kOhms = 0.5 milliamperes. The power dissipation of the resistors is (50V)^2/100 kOhms = 0.025 watts, so 1/4 watt or 1/2 watt resistors are more than adequate for the voltage divider.

DC current must be measured "invasively", that is you must have a sensor in series with the current carrying conductor. This can be either a very small resistor, which develops a voltage drop to be measured, or a Hall effect sensor with the current carrying conductor as part of the sensor, as in the Allegro ACS series I linked earlier.

For AC current, you can use a current transformer as the sensor, which is noninvasive.

I don't think a current shunt can "break" if it is rated for the current you are measuring.

jremington:
No.

I recall hearing of a tecnicque where this was possible theoretically.
I think a coil was used to impose an ac field to the magnetic circuit which made measurment possible.
I have no idea on the method though.

Do you heve any idea of the search terms to use please.

jakob4614: Lately i've been trying to find some ways to measure voltages till 50 volts

If it were not for the 50V i would have recommendet a INA226 from Texas Instruments. But that only goes to 36V but has everything in a nice package.

You get everything you want over the I2C bus, voltage and current with very high resolution using a very small shunt.

Hello and thanks to everyone,

I recently found a 60 mV/50 A shunt and i think it should work when i would use an amplifier. Could someone please confirm that i am right?

Thanks

jakob4614 wrote:

I recently found a 60 mV/50 A shunt and i think it should work when i would use an amplifier. Could someone please confirm that i am right?

Yes, with a suitable op-amp to scale that shunt to the range you want, so you will have 0 to 15 Amps on the shunt give an output of 0 to 5vdc if your Arduino has a 0 - 5vdc analog port.

Be aware though, that the shunt will not provide you any electrical isolation to your Arduino system. Therfore, the shunt needs to be placed with one end at zero volts (0vdc) potential, and that this also needs to be tied to your zero volts of your Arduino.

Or, you could use an op-amp in an instrumentation amp configuration with suitable CMRR.

My suggestion is you use an Allegro device, such as a ACS758-050U, google it. They cost about \$10 AUD and are very easy to use and do provide full electrical isolation and you simply feed the output of this device into your 0-5vdc analog input.

Paul

Boardburner2: Do you heve any idea of the search terms to use please.

google measure DC current then pick on anything that does NOT look arduino related. http://www.kew-ltd.co.jp/en/support/mame_02.html or http://scienceshareware.com/how-to-measure-AC-DC-current-with-a-hall-effect-clamp-.htm

This is the type of current shunt we use where I work.

rockwallaby:
My suggestion is you use an Allegro device, such as a ACS758-050U, google it.
They cost about \$10 AUD and are very easy to use and do provide full electrical isolation and you simply feed the output of this device into your 0-5vdc analog input.

Paul

Thanks

So that means i don’t need a shunt anymore?

That is correct, the ACS758-xxx is, in effect a shunt, with the current sensing element as a hall effect sensor. I have used these and am quite impressed.

I am currently (pun, yes, I know) doing an update to my renewable energy system, with new Lithiums on the way and I am wanting to monitor many things, such as solar input, micro-hydro input and inverter output. I looked and thought hard over the ways in which I could measure the current, and while using the old traditional method of 'copper' shunt with op-amp had some appeal to me, I kept coming back to thinking that using a device like the ACS758-xxx was going to be far easier to install and connect to my control system.

With these ACS devices, you can get both uni-directional as well as bi-directional. Uni-directional devices output a voltage signal from 0v to 5v, with 0Amps giving 0 volts, and full scale giving near to 5 volts.

Bi-directional devices can measure the current flow in both directions and so they sit at Vcc/2 or 2.5 volts for 0Amps and give lower values for lower amps and higher volts for higher amps.

For me, I prefer to use uni-directional so I can get the full scale range over 0v to 5v for reading into the analog input.

Some of the smaller devices, such as the popular ACS712-xxx are bi-directional.

Hope what I wrote makes sense for you.

Paul

jakob4614: So that means i don't need a shunt anymore?

Yes, the Allegro Hall Effect Current Sensors are very nice devices. But they just measure current, not Voltage.

And they do not like other strong magnetic fields, since they are hall effect sensors.