I would like to use a SparkX Power Meter - ACS37800 (Qwiic) to measure and log ( with SparkFun 9DoF IMU Breakout - ICM-20948 (Qwiic)) a 72 vdc voltage.
Should I do this with a step down dc-dc transformer? If so, will the voltage change be linear?
Or could 2x SparkX Power Meter - ACS37800 (Qwiic) in parallel cover the 72 vdc (since the board is limited to 60v max)?
Transformers only work with AC so that’s out. Connecting meters in parallel will result in both seeing your full battery voltage. Meters are typically high impedance so connecting them in series will also not work.
What you want is a resistor voltage divider to lower battery voltage. Connect two same value resistors in series and measure voltage across one resistor and you should measure 1/2 your battery voltage.
Thank you. I’ll explore voltage divider using the SparkX Power Meter - ACS37800 (Qwiic) to measure across one resistor.
Transformer was not the right word. I should have said DC to DC Converter - a unit like this: https://www.amazon.com/Pro-Chaser-regul … hdGY&psc=1
If you use a DC to DC converter your output voltage will always stay the same regardless of battery voltage. Right up until the battery is depleted, then the output will fall to zero.
Ahhh. thank makes sense. Thank you!
Yes, you can use a step-down DC-DC transformer to measure and log a 72 VDC voltage with a SparkX Power Meter - ACS37800 (Qwiic) and SparkFun 9DoF IMU Breakout - ICM-20948 (Qwiic). The voltage change will be linear, but there will be some losses due to the efficiency of the transformer.
To do this, you would connect the positive terminal of the 72 VDC voltage to the input of the step-down transformer, and the negative terminal to the ground of the transformer. The output of the transformer would then be connected to the positive terminal of the SparkX Power Meter, and the negative terminal of the SparkX Power Meter would be connected to the ground of the transformer.
The SparkFun 9DoF IMU Breakout - ICM-20948 (Qwiic) can also be powered by the step-down transformer. To do this, you would connect the VOUT pin of the transformer to the VIN pin of the IMU, and the GND pin of the transformer to the GND pin of the IMU.
Another option is to use two SparkX Power Meter - ACS37800 (Qwiic) boards in parallel. This would allow you to measure and log voltages up to 120 VDC. To do this, you would connect the positive and negative terminals of the 72 VDC voltage to the positive and negative terminals of the first SparkX Power Meter board. Then, you would connect the positive and negative terminals of the first SparkX Power Meter board to the positive and negative terminals of the second SparkX Power Meter board.
The two SparkX Power Meter boards would then need to be connected to the SparkFun 9DoF IMU Breakout - ICM-20948 (Qwiic) using an I2C multiplexer. This would allow you to read the data from both SparkX Power Meter boards on the same I2C bus.
Which option you choose will depend on your specific needs. If you need to measure voltages up to 120 VDC, then using two SparkX Power Meter boards in parallel is the best option. If you only need to measure voltages up to 60 VDC, then using a step-down DC-DC transformer is a simpler and more cost-effective option.
I hope this information is helpful. Please let me know if you have any other questions.
https://npr.brightspotcdn.com/dims4/def … cotty1.jpgYes, you can use a step-down DC-DC transformer to measure and log a 72 VDC
Connecting meters in parallel will NOT allow you to measure twice the voltage. Both will see the same voltage. Also, as Scotty is pointing out, there is no such thing as a DC/DC transformer, and as has been mentioned previously, using a regulator to drop the 72v won’t help since the regulator will have a constant output regardless of change on its input (for reasonable changes)…
There are two ways to be able to measure 72v with that board:
Use a voltage divider to drop the 72v to something close to 60v. Allow for headroom (ie. make sure the highest you can get on the 72v rail gets dropped to 60v), power dissipation in the resistor divider, and the input impedance of the board
Change the rSense resistor on the board. See page 19 of the data sheet https://cdn.sparkfun.com/assets/d/f/8/5 … asheet.pdf for info on selecting the resistors
As for the pcb layout, it looks like the limiting factor is the spacing between the LO terminal and the pour connected to IP-
but I think we are OK there.
/mike
