Losing electric in saltwater, I think

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micoma
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Losing electric in saltwater, I think

Post by micoma »

I don't really know what is happening. I run my ROV in saltwater. I have 24v from the surface to a 12v 15a converter onboard, then the relays. I am using Rule 1100gph bilge pumps. I have everything connected via quick disconnect plugs. Details can be seen at http://micomarov.weebly.com/. Anyway, test on the surface and everything runs like it should. But after being in the sea for some minutes, probably not more than 10, the motors stop working. I pulled it to the top and tested for voltage at the motor. They were getting little to no voltage. After a few minutes out of the water the voltage started returning until the motors worked as expected. The batteries were not run down. The container with the converter and relays is closed/waterproof and I can't see what it happening inside. It just does not make sense that being in saltwater would somehow suck the voltage away.
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olegodo
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Re: Losing electric in saltwater, I think

Post by olegodo »

Water causing a short in the quick disconnects?
rossrov
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Re: Losing electric in saltwater, I think

Post by rossrov »

Unplug the connectors (disconnects?) and see if there is any green colour on the pins. In saltwater, corrosion/electrolysis of this sort happens almost instantly. Would create a high resistance, stopping the motor.
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micoma
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Re: Losing electric in saltwater, I think

Post by micoma »

Yes there is green on the connectors. The yellow circle is the 24v power cables. But if the corrosion is causing the drop in voltage why does the voltage return once it is out of the saltwater? The more important question is how do I prevent whatever the problem is? Would it be enough to space the power cables further apart?
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olegodo
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Re: Losing electric in saltwater, I think

Post by olegodo »

The contacts are close enough so that the electricity jumps between the positive and negative contacts when they get wet. This is what is causing the corrosion. This shorts the circuit before the power reaches the motors and limits the flow of current to them. When you take it out of the water, the contact dries out and a short circuit is no longer made, hence the power returns to the motors.
Moving them further away from each other should help. Or waterproofing them completely.
rossrov
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Re: Losing electric in saltwater, I think

Post by rossrov »

The tether to ROV connection is arguably the trickiest part of an ROV project. In the case of your ROV, the connections must be sealed from the water. Search the forum for waterproof connectors, there are many examples. Alternatively http://www.homebuiltrovs.com/howtosealingwireexits.html or read some of the other "how to" pages that Steve has provided
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sthone
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Re: Losing electric in saltwater, I think

Post by sthone »

You could try filling the connector with dielectric grease before plugging it in. I'd make sure to disconnect the plugs and dry them out after a dive too. That kind of corrosion usually doesn't happen right away.

While it's a PITA I don't like to have removable tethers for a few reasons. The less connectors the less that can go wrong and I like to firmly attach my tether to the frame so if my rov ever gets stuck I can yank it free with the tether.

-Steve :sting:
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micoma
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Re: Losing electric in saltwater, I think

Post by micoma »

Thanks for everyone's help. Obviously the cheap connectors are not going to work. But I am not going to pay $100 for waterproof connectors either. And I still want to detach the tether. So I am going to try these http://tinyurl.com/mrajtud and see what happens. This has really been an interesting project. It has been a lot of fun figuring things out.
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KR2_Diving
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Location: Currently: NW Suburbs of Chicago. Originally: NE Wisconsin

Re: Losing electric in saltwater, I think

Post by KR2_Diving »

That is a very interesting looking plug! Best pricing I have seen!

I would be VERY interested to find out how well these work for you! Please keep us posted!
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