Electronics potting and trace ampacity

CorbettROV · 2009-05-17T16:54:32+00:00

Hi everyone, this is my first post on this forum - I happened to stumble upon it and it seemed like I may be able to get some answers I've been looking for here. I am a high school student currently working on an underwater robot, and I had some concerns: 1. I am looking to pot my electronics for my underwater ROV in a super hard 4 to 1 epoxy resin. Someone told me that if potting is what I want to do, that's the way to go. What are your opinions on this? 2. I am looking into buying a custom PCB for my electronics. I have already designed it, and my only concern is about the capacity of the traces. I will be running up to 10 amps through 1 or 2 of the traces, and up to 3 amps through some of the others. Will I need to specify a heavier copper or thicker traces for this? I will not be running any current through the traces for a sustained amount of time. Maybe thirty minutes at the most, and during that time the usage will be sporadic. EDIT: I have just modified my PCB design to include 3.81mm traces with 2 oz copper for the traces carrying a high current. If it would be helpful, I could post my design - I designed it in the Pad2Pad software and the suffix is ".pcb". Thanks, Jacy

Electronics potting and trace ampacity

CorbettROV

Member

Updated: Oct 15, 2024

Views: 2.4K

Hi everyone, this is my first post on this forum - I happened to stumble upon it and it seemed like I may be able to get some answers I've been looking for here. I am a high school student currently working on an underwater robot, and I had some concerns:

1. I am looking to pot my electronics for my underwater ROV in a super hard 4 to 1 epoxy resin. Someone told me that if potting is what I want to do, that's the way to go. What are your opinions on this?

2. I am looking into buying a custom PCB for my electronics. I have already designed it, and my only concern is about the capacity of the traces. I will be running up to 10 amps through 1 or 2 of the traces, and up to 3 amps through some of the others. Will I need to specify a heavier copper or thicker traces for this? I will not be running any current through the traces for a sustained amount of time. Maybe thirty minutes at the most, and during that time the usage will be sporadic.

EDIT: I have just modified my PCB design to include 3.81mm traces with 2 oz copper for the traces carrying a high current. If it would be helpful, I could post my design - I designed it in the Pad2Pad software and the suffix is ".pcb".

Thanks, Jacy

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Rifaa

Member • May 17, 2009

Hmm, you are right with high current tracing, It will be safe if you could use thick copper wires to route the traces, just to be on safe side if you a potting the PCB.
I suggest that you run the PCB at it's peak load without potting and in an sealed environment typical to the environment the PCB will be once in water resistant resin.
If you use high grade potting that can insulate and transfer heat to the out side, it will be best. If not, the traces and the components should not over heat in a sealed environment.
Test it thoroughly and seal the PCB, cause once sealed you cannot melt the potting easily to rectify any fault.
I like to see what you are doing, the theory and Pictures too if you can 😀
Cheers

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CorbettROV

Member • May 18, 2009

Hi, thanks for the help. I can't really post pictures, as we have just finished our current season (the competition was on May 9th) and we did not win do to failure of one of our controller boards. Next year, the electronics will be different and I don't have these components yet to post any pictures. I could post pictures from this year if you are interested.

I am mostly wondering about the possibility of overheating (and maybe melting) components if I put too much current through the traces. If someone could let me know about the real ampacity of these traces I have described (3.81 mm wide with 2 oz copper). As I said, we will not be putting power through the lines for an extended period of time (60 minutes at the most) and the usage during this time period will be sporadic.

I'm also wanting to make sure the the specific potting substance I want to use (4 to 1 super hard epoxy resin) will work for my purposes. The manager of the plastics store I went to said this would probably work, but he doesn't know a lot about electronics and the like.

Thanks, Jacy
Thanks,

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Rifaa

Member • May 18, 2009

it is called hot pot testing ( or something like that)
If you are sealing the electronics then you shud test the unit in a sealed environment that has no heat ventilation for an extended period of time to see whether the components could with stand the abuse. About the traces it solely depends on the PCB manufacturing techinics, I suggest you clear the insulation and coat the tracks with thick solder, it will definitely help, and after checking the PCB to see if it operates at 75 degree Celsius without over heating for around an hour, you can be sure it can with stand indefinitely once it's molded in resin, cause resin will help to transfer heat to exterior.
Next technic is to mount heat sinks in every component that would create heat so much that it's not possible to touch. and when potting be sure not to cover up the entire heat sink so that free air cannot touch the heat sink surface, cover the sink as least as possible, this would definitely keep the components cool.
When buying resin, check the websites of that typical resin and do some testing before hand.
Cheers

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CorbettROV

Member • May 18, 2009

Ok, thanks - I'll look into that.

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CorbettROV

Member • May 18, 2009

Alright - I have some epoxy questions. I can't find any specific data as to potting for the epoxy I'm looking at. Right now I'm looking at the TAP Plastics 4-to-1 super hard epoxy resin. If anyone has had any experience with this that would be helpful. I just want to make sure that they will be waterproof and will stay that way. I have also taken a look at Epoxy Inc's 20-3001 NC which seems good, but I'm not sure how expensive that would be.

Thanks, Jacy

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Rifaa

Member • May 19, 2009

Let me get some info on the resin and I'll tell you later what I did to water resist one of my project.
In the mean time Hot Pot test your PCB.
Only after that you can cover it with resin. isn't it.
and one more thing, please remember to seal the tracks with high temp varnish ( which has electrical insulation properties ) if you coat any tracks with solder after thorough cleaning the flux with thinner or alcohol , it would prevent solder oxidization.

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CorbettROV

Member • May 19, 2009

I fixed the problem of trace width, so I won't need to coat the tracks with solder. I can't test my PCB, as I don't even have it yet... :/
I won't be doing this for a bit, I just want to get all my research done early.

Thanks a lot, I look forward to hearing what you find out.

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Rifaa

Member • May 19, 2009

here is what u need,

#-Link-Snipped-#
Go thru it and you'll know what to do. It's no biggie

And please do share us what you are doing, Jacy.
it would inspire others and who knows, you could be great contributor

Regards
Rifaa

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CorbettROV

Member • May 19, 2009

I actually found a great looking epoxy at epoxies.com. I emailed them, and they said that this one would work perfectly. It is the 20-3001 NC. They are also willing to donate it to us.

I will post a thorough description of what I am working on in a while, I am at school now.

Jacy

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CorbettROV

Member • May 19, 2009

Alright. Here we go.

One of my best friends and I are building an underwater remotely operated vehicle (ROV) for a regional Marine Advanced Technology Education (MATE) competition. We have competed in this for the past two years, and have gotten more technologically advanced each time. The first year, we got 3rd. The second, we did not place. One of our motor controller boards stopped working the night before the competition.
I will include pictures of this year's robot at the end of the post.

Next year, we are planning on revising a few things, but mostly our electronics. This year, we used 3 Pololu TReX Jr. motor controllers to control 6 motors. Next year, we will stick with the same concept, but use TReX motor controllers, rather than TReX Jr.'s. The difference between the two is the amperage capacity. The Jr.'s support 2.5 amps per channel, and the TReX's support 13 amps. The problem we had this year was the boards being over-amped.

Waterproofing was another issue. This year, we used a waterproof, ABS box with pass-through gromets that were supposedly waterproof. Turns our we got water in the box. Fortunately, nothing was ruinedbecause of that. We decided to pump silicon caulk into our box to keep the water out. That worked great for keeping the water out, but it shrunk and pulled out the connections on our boards. We spent hours removing that, and then tried filling the box with mineral oil. With the pressure differential underwater, this worked great, but as soon as the robot came to the surface, oil started leaking out, to our great chagrin. This was less than a week before the competition. Our last attempt at waterproofing involved encasing the boards in parafin wax. This worked fine, until one of the chips burned out the night before the competition. Boo hoo. Next year we are going to use epoxy and make sure nothing can go wrong in that area. I will be improving the control program to include speed control with a Logitech Dual Action gamepad. The first year, we used direct switches wired through the tether. It did not work that well. This year, we used the logitech gamepad, but still only had digital control. Next year, we want ful analog control.

Overall, there were many design flaws this year, which we are working out for next year.

Pictures of this year's robot:
(I'm the one in the red shirt with the tan shorts and my partner is the one in the red shirt with white shorts.)

(first attempt at waterproofing)

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Rifaa

Member • May 19, 2009

Wow. dudes.. This is really great. You will inspire a lot of kids like u, out there.
I must say for teens you did one hell of a job. 😁

The only thing you guys are lacking is experience in this field, but you are getting there, If you have found us sooner you could have won first place.

About the amperage of the boards, you jumping from 2.5 to 13A. I'd say that's over kill but you will be on the safe side. I think it would be expensive.
The resin you told was great, it would help you to seal the PCB.

How about sharing your bot as a CE project. You could make a thread in the mini project and explain all the do's and don'ts.
But I guess that will be after the competition.

Anyways best of Luck!!! you guys, break a leg ;-) ( did I say that right )

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Kaustubh Katdare

Administrator • May 19, 2009

Off topic:

Great going, fellas 😀 You make us proud!

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CorbettROV

Member • May 20, 2009

The amperage jump is overkill, but there is nothing in between :/

Thanks guys! I will Post it in the projects section after next year, when hopefully we do win first place!

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Ashraf HZ

Member • May 26, 2009

This is great stuff! The challenge of waterproofing electronics for underwater use is interesting. I'm doing a project for a different environment.. the atmosphere =P Do check it out when you have time:

#-Link-Snipped-#

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