Max current of entire rov?


#1

I´m in contact with a supplier for sub sea wet connectors. My idea is to exchange the potted pass trough to such connectors. For that reason i need to know the realy maximum current from battery to electronic board and the current in one of the 3 motor wires.

0.75mm² Cable is basic supply. For higher current it will be "customer made" and i gues f....ng expensive.

Hope somebody could help?


#2

Hi Stefan,

I did some tries few days ago, and I obtained this (values a bit rounded-up for safety):

- Cape + BB + Webcam = 0.25A

- All above + Ethernet adapter online = 0.30A

- All above + led max pwr = 0.48A

- All above + all ESC on = 0.52A

- All above + Servo moving = 0.55A average, 0.78A starting

- All above + 1 motor = 1.10A max (starting)

- All on and 2 motors = 1.57A max

- 3 motors not tested, but probably around 2A or less. Say 2A to stay safe.

Ah, I forgot: voltage was 12V, from lab power supply.

Hope this helps.

Tiziano


#3

Hi Tiziano,

this helps a lot. What kind of motors you use? The suggest 800kv bl motors or something diffenrent?

2 A max is pretty low because i read some posts where the max current was stated with 30A or more. 24W of power consumption will be very easy to handle.

All the best

Stefan


#4

Hi Stefan,

I'm using these motors.

I forgot to mention that I tested all in air! :) ...in water is different.

Maybe the 2A is something like "motors-running" current, and not peak: I have to do some new tests.

My multimeter takes some time to update, so maybe I lost the peak value!

But.. it's all real data. :D

Let me know!


#5

Ok in water the consumption will raise up a little but if they are running software limited in water with lets say 5A it is enough. Im exited about further test from you. My focus is on diving depth and manouvering in small spaces.

Thanks for your work!


#6

Yes, I think 5A peak is realistic!

Now I'm working on power supply, based on 2 wires tether (but I'm using 2 pairs of wires attached in parallel:
too much resistance... a single 26 awg is 40 Ohm per cable, over 100m!!, total of 80Ohm roundtrip... too much! Using 2x26AWG in parallel is the half and it's good).

The project, in short, is:

- 30-48V from batteries running down on tether

- voltage regulator in the battery tubes set to (say) 10-12V to supply ROV & LT3652-based battery controller

- LiFePo4 batteries constantly charged and that can supply peak current when needed.

All the values are related to a constant 0.7A supply in the tether (motors off), used for ROV+Battery charging.

If all goes well, today I'll drop some new current measurement.

Unfortunately I'm stuck with the rest of the project because I'm waiting for both LT3652 and batteries. Let's see.

Have a nice day!


#7

I am also working on a tether/battery powered unit with 48VDC coming down the tether and a battery bank to supply peak loads.

Have you gotten to the point of testing with this setup? I would be interested in knowing if you see any brownout issues. Could you let me know what regulator you have selected? I was looking at something very large previously, but that was based on much higher current. I was assuming that each motor can pull 10A.

I recognize that is conservative, but I would love to know what you are seeing in practice. DCtoDC regulators can get kinda expensive when you require that amount of power.

Can't wait to see your results!


#8

Hi Michael,

unfortunately I had no spare time to do some tests (even with the current consumption measurement).

But I received my batteries and I'll receive soon the battery charge regulator chip.

Then I have to build the test circuit on breadboard and, if it works, I'll update a bit of things.

Actually I don't think to have the current for motors passing in the regulator.

The basic idea (under test) is that theter current is naturally limited by the cable resistance (the more the current, the lower the voltage at the tether end), and so, when the current request increases, the batteries will do the job.

The DC DC regulator is used only to mantain 10-12V over the BB, cape and so on. Since the current absorbed by the "ROV-brain" is not constant, I have a floating voltage, and that's no good at all.

Summarizing:

- DC DC regulator will mantain a constant voltage at the BB, cape and battery charger, with a max current rating of 1A (really requested is around 0,7A);

- Battery charge regulator mantains batteries fully charged without damaging them;

- when requested current is over 1A (and so, tether voltage goes down), batteries will supply the extra current.

Hope this helps and I hope it is not confusing (I'm writing fast, as I have to rush)!! :)

Obviously any advice is welcome!