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Topic: Cheap Potting Material? (Read 230 times) previous topic - next topic

weldsmith

Hello all,

I have been working on this project for quite some time and have it completed with the exception of making the board durable and vibration proof. I have been looking at potting solutions but they are expensive. Does anyone know of a cheaper potting material. I plan to make hundreds of these boards that I would like to pot and this would save a lot of money.

Thanks in advance!
David Smith

Paul__B

Noting that in either case, it makes servicing impossible, I think you want conformal coating rather than potting, so simply dipping rather than potting with a particular compound will reduce the expenditure.

Tall components can sometimes be leaned together or you can provide a strut of some insulating material.

larryd

Remember 'Potting' may cause internal heating problems.

Expanded foam works.









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CrossRoads

You can also get Thermal Conductive Epoxy.
We used this to pot 328P boards that were to be used in Africa.
The boards were small, we found some silicon muffin tins (and maybe a spray release, has been a while), and cured the material in a $50 toaster oven we got from Target (2-3 hours at some warmish temperature) vs waiting weeks for it to cure on it's own.
https://www.digikey.com/en/products/detail/mg-chemicals/832TC-450ML/655660 
I forget if we weighed the stuff, or liquid measured it, to get the amount of each part to be used.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

Conformal coat comes in spray-on, or liquid to brush on, or dip in.
We used the UR Type when we did boards at work.
https://www.digikey.com/en/products/filter/coating-grease-repair/642?s=N4IgTCBcDaIMYHsB2AzBAnAtgQwDYAJFsAXEAXQF8g
Not really intended to help with vibration, potting would be better for that. Make sure your design is solid, or at least edge programmable (via some kind of connector, or wireless) before potting them up.
Potting may also interfere with wireless, depending on what is in it.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

And you might not need potting for all components, you may get by with just applying whatever is used around the tall/heavy/long lead components that are prone to vibration.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

This was a prototype in the thermal epoxy


Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

weldsmith

Thank you all!

I may not need to pot this unit. I have spot welded all of the heavier components with Che-set MS 35. I will have to test and see if it holds up. I am putting these in a metal box and shooting them with guns Lol! So I am see what I can get away with. Not doing anything (first step did not do well;). I feel to commercialize these I will half to pot them at least through the bottom and part way up the caps. I feel that I can get away with the heat issue. I not I will add a heat sink that protrudes through the potting material.

Spray Foam you when on the creativity side. I will do some testing :) !

Cross Roads, yes the thermal potting material makes it very durable. What did that cost you?
David Smith

CrossRoads

No idea now, that was in 2014-2015. We bought the 832TC-2L size, a liter of each part.
After assembling/potting/shipping 100 cards, customer decided they't rather do the potting locally vs paying the freight cost for the added weight from US to I forget which country in Africa that charged import fees based on shipping costs (and the fee was more than the FedEx shipping).
So we just did assembly and shipping after that, kind a relief as the potting was awkward for us.

That customer has since moved to Australia and I am working a different design for them, has turned into a Processor/WiFi card on a main board, with a daughter card to hold more components, stacked up to fit a certain outer footprint. From one side, looks like a 3 layer board.  Waiting to hear back on initial testing.

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

weldsmith

#9
Nov 21, 2020, 11:39 pm Last Edit: Nov 22, 2020, 12:17 am by weldsmith
CrossRoads, I have seen some of your designs before. Have you done any stepper driver designs?
David Smith

Paul_KD7HB

My experience with potting electronics. You want to be sure there is no place where the potting compound can leak from the housing. We used RTV to seal those places. Another day for that to cure.

Then we used the epoxy mix that was thinner than water. Why? So we could get all the air bubbles out of the device. Had to pour and then jiggle, turn the box this way and that way. Then after all the obvious air bubbles were out, waited until the epoxy began to set, and then topped up the box. Epoxy does shrink as it cures.

I bought the two-part epoxy from an EBAY seller. We only needed to buy every 3-4 months, so never set up an account.

Paul

weldsmith

Paul, not sure why I did not go to Ebay. I was looking in Newark. 96oz. for $60 is not bad.
David Smith

Paul_KD7HB


weldsmith

David Smith

CrossRoads

Stepper design - I've only used small geared steppers so far, and used ULN2003 to drive them, also discrete transistors, high current shift registers (TPIC6B595), and a H-bridge chip,  LV8548.


The design really depends on how much current you need to switch for the stepper.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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