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Registered Member #4346
Joined: Tue Jan 17 2012, 10:16AM
Location: Slovenia
Posts: 9
For Ethernet I will use fiber.For motors I "reserved" 1800w, lights 100-200 wats, instruments, manipulator and other electronic will take the rest. Of course there will not be powered all motors at the same time. I saw solution with Coax, but I will have 3 cameras, sonar... a lot of data to transfer and we choose to use fibre and hv wires together in tether. Tether must be thin and neutraly buoyanced because of rov maneuverability. Maybe, but again maybe we could use 2x2 twisted wires of Cat for ethernet instead fiber.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
Sulaiman wrote ...
in which case a hvdc supply down the wires makes more sense with a step-down/buck converter at the receiving end.
2000/48 is an awfully high ratio for a buck converter. AFAICS you would need either a transformer based converter or something like this together with an inverter :
(It's essentially an inverse voltage multiplier, hard to believe it took someone till so recently to come up with one ... but I can't find any other references quite like it, it's similar to switched capacitor converters but it's single switch approach makes it seemingly unique.)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I think that thing can't be more than 50% efficient, like any other inductorless converter. (Note the "dissipater element", 306.)
Also, there might be only one switch, but it needs to stand the full input voltage. Making the HV switch is the hard part, so if you have to do it anyway, you might as well build a conventional step-down converter.
A while ago, there was a device called an "ISBT", which was basically a cascode of a power MOSFET and a large HOT type BJT, all in one multi-pinned package. They had very high voltage ratings and were intended for flyback supplies running off a 560V DC bus. Something like that might be worth trying for the switch.
TV cameras are connected to their control units by a "triax" cable. This is a coax cable with two screens: the outer one is ground, the inner one carries high voltage power, and the centre conductor carries all the signals, multiplexed. Maybe if you're on a commercial budget, you can find the power supply modules that they use for this.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
Presumably the dissipater is there to limit inrush current. AFAICS the theoretical efficiency when fed with a sine is the same as that of a voltage multiplier, higher than 50% (the sine allows efficient capacitor charging without an inductor).
For DC->DC it wouldn't be inductor less, you'd feed it through an inductor and use two switches, which is still pretty good.
The HV switch is the hard part, but not the bulky part ... a capacitor/diode only divider would have the same advantages as a multiplier, more compact than a transformer.
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power transfer through thin wires
