MJLJ - any worries when potting in epoxy?
Moderators: JeffC, rdoherty, stieg, brentp
MJLJ - any worries when potting in epoxy?
After reading the bits about MJLJ not being specced up for heavy vibrations, I'm wondering if there's anything dissapating enough heat that potting the board in epoxy to help with vibration would be a problem?
The MJLJ processor draws
The MJLJ processor draws very little current, so no- there shouldn't be any problem.
The LM2003 device handling the user outputs is spec'd to 500ma per output, there probably would be some heat generated with prolonged use at the edge of that current limit. However, this is an open collector setup- as in, it switches ground to your external circuit, using the programmable outputs does not draw current from the MJLJ power supply.
Before considering an epoxy potting I would suggest soldering all of the chips that would otherwise be socketed; bolting down the voltage regulator, and making sure the pressure sensor, if outfitted with such, is secured to the board using a zip tie or screws (zip tie preferred). Those measures should get you a long way towards tolerating high vibration environments.
The LM2003 device handling the user outputs is spec'd to 500ma per output, there probably would be some heat generated with prolonged use at the edge of that current limit. However, this is an open collector setup- as in, it switches ground to your external circuit, using the programmable outputs does not draw current from the MJLJ power supply.
Before considering an epoxy potting I would suggest soldering all of the chips that would otherwise be socketed; bolting down the voltage regulator, and making sure the pressure sensor, if outfitted with such, is secured to the board using a zip tie or screws (zip tie preferred). Those measures should get you a long way towards tolerating high vibration environments.
Also..............
Be careful of the CT mismatch of the epoxy....i.e. while setting, the epoxy will move, and you need to be very careful that it does not cause dry joints....the odd component is fine as you dont use that much...but coating the entire cct board is potentially not a good idea......
A better solution (IMHO), is look at the board, decide what components are potentially susceptible to moving and use some electronics grade silicone.
A better solution (IMHO), is look at the board, decide what components are potentially susceptible to moving and use some electronics grade silicone.
Good point
I was intending on using the low contraction stuff through, but I think I might just go with securing the components better and see how it goes, the case is suspended on rubber mountings so it shouldn't be too bad.
-
Oliver Sedlacek
- Posts: 68
- Joined: Mon Sep 13, 2004 8:45 am
- Location: The Chalfonts
- Contact:
Use candle wax
I've used candle wax for circuit board protection in the past. I know you can buy all sorts of stuff specifically for protecting electronics, but candle wax has the advantage that you can get it off again. I've used it on my megajolt for waterproofing rather than vibration resistance, as I solder all my components anyway.
-
capri_turbo
- Posts: 122
- Joined: Tue Jan 10, 2006 8:17 pm
- Location: North Yorkshire, UK
Potting thru hole components
We do this at work and had problems originally... when the potting compound goes off, it'll move and shrink etc., which can actually break legs of components and pull solder joints and pads etc. What we do now is to use "Silcoset" first... a pliable silicone rubber compound... we pot the board with Silcoset to just cover all the components, and then use the epoxy over the top of this... works great and our stuff is mostly I.S. too.
Silcoset is unfortunately
Silcoset is unfortunately only available in relatively large quantities. A litre just to do one board is a bit hard to justify for most people.
The only problem we've had with candle wax is it has too low a melting point for our Australian environment.
Beeswax (available from about any craft shop) has a higher melting point and works well. Steam will melt it to repair the board. Not as reliable as hot melt glue for heavier components particularly in extreme cold conditions but quite adequate otherwise.
Most conformal coating materials designed for PC boards are soluble in alcohol so easy to clean off.
We had similar problems in early days with missile components. Wax was the first layer followed by epoxy (no RTV silicone rubber back then!).
No I.S. here but a fair bit has gone to places like Antarctica.
The only problem we've had with candle wax is it has too low a melting point for our Australian environment.
Beeswax (available from about any craft shop) has a higher melting point and works well. Steam will melt it to repair the board. Not as reliable as hot melt glue for heavier components particularly in extreme cold conditions but quite adequate otherwise.
Most conformal coating materials designed for PC boards are soluble in alcohol so easy to clean off.
We had similar problems in early days with missile components. Wax was the first layer followed by epoxy (no RTV silicone rubber back then!).
No I.S. here but a fair bit has gone to places like Antarctica.