What about MOSFETs with substrate? I think I've seen a few, but I forget what numbers (if they were even 3Nxxx).
2N5819 has a case pin (TO-72), but that's no semiconductor connection.I've seen a few... certainly don't remember the numbers.
Tektronix used a few dual monolithic JFETs, too. TO-39-8 size.
Tim
Do a search and see what they cost now.
I did. Gasp! ...Jim Thompson
So you're saying that the difference between a 6AU6 and a 12AU6 is the power rating?
I ain't buying that one either.
Now you see why I tell people to wear a seatbelt, when reading newsgroups. :(
Robert Roland:
Because a ROV has motors and fins.
Yes, but no moveable shaft, let alone axle, went trough the hull.
Late at night, by candle light, Marco Trapanese penned this immortal opus:
The 1N4148 will likely survive a good bit of pressure due to its small size making for small surface area in relation to volume. Fuses, even hermetically sealed, will crush under less pressure. There are some with thick walled ceramic bodies but I don't know their ratings off-hand.
- YD.
Il 30/10/2010 04:06, YD ha scritto:
I got it. Thank you.
Marco
The hermetic seal makes a big difference. If the part is sealed, the body must be able to withstand the pressure difference, since the pressure inside will remain constant. This is exactly the same as a submarine. It is designed to withstand a certain amount of pressure difference. If the pressure difference goes too high, the hull will be crushed.
If the part is not sealed, the dielectric oil will enter the part and possibly (or probably) affect its electrical properties.
If the fuse was sealed, it would collapse at a certain pressure. How much pressure it would take, nobody knows. A fuse like that is, however, not sealed. You can, in fact, pull the end caps off with your bare fingers. If such a fuse was submerged in oil, the oil would enter the fuse and change the fuse's properties. Since oil has much higher thermal capacity than air, I'm guessing the fuse would withstand much more than its rated current before it blows.
Could you make your ROV a two-chamber solution? One pressure proof chamber for the electronics and one oil-filled pressured chamber for motors, shafts and stuff that can withstand the pressure. Electrical connections between the high-pressure and low-pressure chambers should be fairly simple, and you probably already have experience with those.
Robert Roland:
Do you have a vague idea of the number and thickness of wires (yes, at that pressure oil may migrate through the interstices among the strands) that will go to the electronics? And what about heath dissipation?
John Fields:
I don't think that 1.1 A will be sufficient for even a fin servo motor.
Do you think it's possible to find some that are not hugely expensive?
I would start with having a miniature pressure vessel turned from a bar of solid bronze, something big as half a beer can, and test the individual components, starting from the ones that are better left out of the pressure proof chamber, like power transistors and temperature sensors.
Marco's uncle should be able to do it.
The main problem are probably going to be the batteries.
Tim Shoppa:
Well, actually they don't need to, as the extra wire is used for either the base of the phototransistor or the output enable, so both are in fact optional.
Or maybe they do, since they need at least three wires on the output side, which is powered, while the simpler optos only need two.
John Fields:
So far, just a mere speculation on how to make ROVs that dive much deeper than "his" current ones.
Marco Trapanese:
No, but I expect it to be closer to the local ambient if the pod contains oil, which has an heat capacity much higher than air.
Il 30/10/2010 17:08, F. Bertolazzi ha scritto:
Please, may I answer by myself?
Like I said before, the question is not related to ROVs. I just have a oil-filled tank with some electronics that should withstand to that pressure. It's a test equipment so no problem about temperature or whatever else.
I thanks all the friends who answered.
Marco
John Fields:
Sure. In a solid there are only those two factors.
But, in a fluid, heath is transported mainly (almost exclusively) by convection, which is proportional to the fluid viscosity and its heat capacity.
Water is much more viscous than air and has about the same thermal conductivity, so how comes that a radiator is way more efficient in water than air?
Marco Trapanese:
You're welcome.
What did you say before about this? That the temperature in a pod is quite higher than the water's. Anything else I missed?
At last you say something about this application.
But not much. An entire tank with that pressure? What for? I suspect some Spectre ROV. :D
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