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| Potting an electrolytic capacitor will make it last longer? |
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| Kirkhaan:
--- Quote from: Hero999 on August 25, 2018, 06:27:29 pm --- As far as explosion is concerned, I think it will depend on the hardness of the potting compound, with the softer, more elastic compounds being safer, than the harder more rigid ones. --- End quote --- Indeed, and when applying the more harder/rigid potting compound, often special rubber caps are placed on top of the ELCAP, leaving some room for the pressure relief valve to open and electrolytic to get out. This way no excess pressure is build up and the ELCAP can die in a controlled (and safe) way... |
| Wolfram:
--- Quote from: voltsandjolts on August 25, 2018, 06:59:35 pm ---There are thermally conductive potting compounds such as Dow Corning TC6020 with conductivity of 2.72 W/mK, whereas RTV3120 is around 0.001 W/mK. --- End quote --- This sounds unrealistically low. The only number I found in this range were in this datasheet: http://media.erapol.com.au/wp-content/uploads/files/products/silicone/condensation/Dow%20Corning%20Silastic%203110.pdf , but given in the units of calories per second centimeter celcius, corresponding to 0.24 W/mK. Other sources place RTV silicone in this ballpark as well (around room temperature): https://www.sciencedirect.com/science/article/abs/pii/S001122759700146X |
| Kjelt:
They are potted because they are outdoor drivers. Besides the driver has a thermal protection, an ntc measured by the microcontroller. Most metal indoor drivers from Philips have a thermal spot printed on the housing, that is where the temp is measured. Normally potting would distribute the heat over the device. |
| In Vacuo Veritas:
--- Quote from: treez on August 25, 2018, 06:21:10 pm ---Thanks, but i assume that in a totally enclosed enclosure, the potting compound would always make it easier for heat to get out of the capacitor? Yes i did think of the need-to-vent too....but philips potted over the can top......probably only about 5mm of potting covering the can top though....so could still explode out..... presumably no 'lytic explosion would be enough to fracture the 1.5mm thinck plastic enclosure --- End quote --- Are you really an engineer? Which breakfast cereal did your degree come with? |
| T3sl4co1l:
Potting probably reduces the diffusion of electrolyte, but I wouldn't count on it to help significantly, you're stopping rubber with rubber. Also, that electrolyte has to go somewhere. Most of it will remain diffused inside the potting, but some of it may condense in pores and interfaces in and around the potting, which could be an electrolysis/corrosion hazard just the same as any leaky cap is (but more limited, to such locations). Conductivity: air sucks, particularly when the device is compact and there is little room for airflow within the enclosure. Typical figure is 0.045 W/mK, but this is going to be a hand-wave because heat diffuses rather than conducts, and some convection always occurs. It can be much higher where convection (chimney effect) takes place, but this requires more room, or more temperature differential. Speaking of, temperature differential. Convection only requires that, and gravity. Putting some components inside a closed metal box incurs two convection steps, so the peak internal temp rise is almost double (very roughly speaking!), compared to the case for an open or well-ventilated enclosure. A fan can be desirable inside a sealed enclosure, for this reason. Better is just to design it so everything sinks heat to the enclosure directly. These may be of interest, http://www.cde.com/resources/catalogs/MLP.pdf but good luck budgeting for it ;) Tim |
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