We were trying to measure the current using a multimeter on a specific PWM signal — the maximum PWM signal we plan to use in our ROV — to determine the maximum current draw. However, we weren’t able to identify where the issue occurred during the measurement.
Based on the attached report ( link ), we’re now planning to determine the PWM signal we’ll actually use and then estimate the corresponding maximum current for each thruster from that.
Would this approach be reliable, or would you recommend a different method to accurately determine the maximum current?
It is not expected to measure any current coming via the PWM signal - it is a servo-style PWM signal, and is so a square wave sent at 50hz, varying the duration of a pulse between 1 and 2 milliseconds - not traditional PWM.
To measure the current consumed by an ESC powering a thruster, you would connect your multimeter in current measuring mode in series with the wire going from the positive terminal of your DC power source to the ESC powering the thruster. You’d then send the PWM servo signal, via the Navigator or a servo-tester, and observe the power consumed.
Where the thruster is will determine how much current is consumed. The T200 and T500 product page include detailed information comparing current consumption with thrust and servo-signal - this was determined in a large tank, with very brief pulses of movement, as sustained operation causes the water to move in the tank in such a way that current, and thrust, are reduced from initial peaks. The technical details on product pages have a lot of effort put into them to be as comprehensive as possible, alongside guides for the product.
Are you trying to determine the maximum current consumption of a BlueROV2? This is typically limited by the battery supplying the vehicle, to around 1 kW, or 60 amps continuous. It’s rare to achieve this in normal operation - you would need to be operating at 100% gain, and driving aggressively…. the current consumption and battery voltage are also monitored by the vehicles power module…
Just to explain what we were trying to do earlier:
We initially attempted to measure the current coming from the ESC while changing the PWM signal, so that we could see how much current corresponds to each PWM value. However, that didn’t work as we expected, and we weren’t sure where the issue was.
To keep the project moving, we decided to try a different approach. Based on the graph from this report (linked earlier), we plan to determine which PWM range we’ll actually use — for example, setting a limit at 1700 µs or less — and then ensure that the current at that PWM level doesn’t exceed around 5A per thruster.
Once we confirm that, we’ll distribute the available power accordingly between all thrusters.
We just want to make sure this method makes sense — using the PWM vs. thrust/current data to estimate the maximum current for our setup — or if you’d suggest a more reliable way to determine it.
Appreciate your help and the detailed explanation earlier!
If you tried to measure the wires in the motor wires going from thruster to ESC, this is actually an AC current and not a DC one! One wire only carries ~ 1/3rd of the total current being used by the motor. That’s why it’s best to measure the DC (red and black) wires going to the ESC.
It’s fairly unusual for an ROV to run all its thrusters at the same time, at the same thrust level. Additionally, if you’re using ArduSub, there is a built-in feature to automatically limit throttle levels to keep current draw below a desired threshold. Are you using BlueOS and ArduSub? If so, simply set BATT_WATT_MAX as desired - see more detail in this thread.
I’ve just double-checked, and it seems the part of my comment you’ve linked to was actually incorrect, because the BATT_WATT_MAX parameter is limited to specific vehicle types (not including Sub), and was mistakenly showing up in all of them.
The relevant parameters for ArduSub are covered in the Pilot Control - Responsiveness documentation, which I’ve also edited my original comment to link to
