Hi all,

I'd like to record (with a PC maybe it would be easier) the current consumption of a DC motor.
The motor is mounted on a machine and he will perform his movements continually for hours, so we can see its power consumption.
Since I want to see the exact trend of the signal, I need to record it with a scope.

I know there are other tools to do this current log, but I want to buy a scope also for other uses, so I take two birds with one stone

So could you give me some advice to understand which model is suitable for my needs?
And also: to measure corrent is ok a normal amperometric clamp connected to the scope?
Requested features:
- it should be connected to a pc in order to log some hours of data.
- 4 channels
- bandwidth could be low..
- current measurement clamp to connect to the scope.

Thanks

 

I'd use data acquisition for this. My tool is a LabJack U3-HV, but there others such as Dataq. These inexpensive solutions presume you have a computer to dedicate to the task.

I'd also consider the Kill-o-watt. Not sure it has the details you want.

 

Can you break one of the wires going to the motor to insert a low resistance shunt? If so, monitoring a time-varying DC motor current then just requires a simple current monitoring IC, typified by the ZXCT1009 and its brothers.

Use a PC USB data logger to sample the voltage out of the ZXCT1009, and pick a sampling interval sufficiently fast to catch the details of the motor current dynamics you are interested in.

 

You could probabally set something up with one of these http://www.syscompdesign.com/assets/images/Datasheets/CGR101-Datasheet-4.5.pdf and a Honeywell current sensor, the other channel would record voltage.
http://sensing.honeywell.com/products/current_sensors they have DC versions.
Max.

 

If you've got a deep pocket you can buy a DC clamp Ammeter/logger with a USB/Bluetooth interface for a PC.

 

Thank you all for the replies

Can you break one of the wires going to the motor to insert a low resistance shunt? If so, monitoring a time-varying DC motor current then just requires a simple current monitoring IC, typified by the ZXCT1009 and its brothers.

this is very interesting! Thank you!
The motor can absorb up to 30A.
If I put 1 ohm shunt resistor, in the worst condition, the current across the resistor will be about 30 A, and the voltage across 30 V.
I need to find some current sense amplifier more suitable for my values.

Regarding the other replies: I need a scope also for other measurements, so I take two birds with one stone. So for sure I will by one, but since this will not happen in a short time, in the meantime I can try the current monitoring IC..

 

1 ohm is not low.

0.001 ohm is low. Monitoring 30 mV is easy.

 

Yes, the ZXCTxxx series is intended to be use with current shunts that are typically a few milliOhms or less. 30A through 1mΩ produces a voltage drop of only 30mV.

 

yes, but not so easy to find into my collection of resistors
I found some 1 ohm 10 W resistors, I'll put some of them in parallel..

 

I will use some 1 ohm resistors put in parallel.. 10 W each. It should be enough

 

Accurate Current Shunts are a special component made for the purpose. They have a four point connection scheme to preserve accuracy.

 

even more interesting!
Thank you Mike, your answer are always very useful

 

I get shunts like that from China off EBay for a fifth the price.

 

yes, but with 40 days delivery time to Italy

 

yes, but with 40 days delivery time to Italy

Then you better place the order today.