AWG of Ampere and Length

Hello :wave:,
We are thinking of building a ROV with my friends.The motors we will use draw 10 amps. We will use 6 motors and add 10 amps in excess. When we calculated the power supply and cable, we reached a result of about 70 amps and we calculated an amazing thickness of 4awg. However, we see that no such cable was used in any ROV. Did we miscalculate, or do we really need to use such a thick cable and a 70 amp power supply? Thank you very much for all the answers.
Motor Link=

Sorry, but that site link looks VERY Spammy. If you’re not a troll, please resend with a PDF or simialr instead, thanks.

@Howard_Pippen You are right. I edited the link so that it would not be misunderstood. :slightly_smiling_face:

18 AWG will easily handle 10A as long as it is short or under water, but you may want to check the voltage drop. Consider how many of those motors are going to be running at high power at the same time and for how long.
If you are talking about powering the thrusters through the tether cable, consider a compact DC/DC converter (Vicor is my preferred brand) to run high voltage/low current on the tether and whatever the motors need in the ROV. My usual work ROV runs 150VDC at the bottom end of the tether, worst case 250VDC at the top of the tether. Yes, we lose up to 100V of voltage drop in the tether, but it is water cooled. Bigger commercial work ROVs run up to 7500V on the tether.

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@Douglas_Butler Unfortunately, there is a 50 volt limit in a contest we are planning to participate in.

I see. Can you buffer it somewhat with onboard batteries, so if the motors need to all run simultaneously for a few seconds they can, then the battery will slowly recharge through the tether?

If these are 4S (14.8V) motors needing 70 amps if running simultaneously (14.8V * 70A = 1036W), you could use a DC/DC converter as Douglas_Butler suggests and supply 50V * 21A = 1050W, and only need 16AWG. Ref American Wire Gauge Chart and AWG Electrical Current Load Limits table with ampacities, wire sizes, skin depth frequencies and wire breaking strength Admittedly I’m using chassis wiring as the basis, but the cable’s going to be water cooled, no?

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I’m sorry I answered late. As you said yes, if we go up to those current values, we will use li-po batteries. Yes cable is water cooled. Thank you very much for all the answers. :smiley:

Also, if you are looking to optimise the design for endurance and/or peak thrust, read the rules of the contest…is your design limited to 50vdc maximum at any point or 50vdc at the ROV?