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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Sure it is, that's why I recommended to modify a surplus one instead of building from scratch. 48V is a standard voltage after all.
As luck would have it, the same guy who did the microhydro system also has two DIY SMPS projects on his site. However they are old designs using BJTs.
Taking a step back and looking at the problem on the system level: Would it really be that hard to just make the tether wires a bit thicker (or reduce your ROV's power budget) so you can feed 220V, 50Hz, or 320V DC down it, into an unmodified 220V to 48V SMPS.
If feeding 220V AC down there, do choose a SMPS with a PFC front end as this will reduce the RMS current in the wires.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
0joze0 wrote ...
what is equation for calculating losses on cable ?
I'm pretty sure its just standard I^2R losses... At line voltage (~300VDC) you need to send 8A, which corresponds to 300W of losses in the cable. Run a voltage doubler and you'll only need 4A, which is just 80W of losses.
Registered Member #4118
Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140
Actually, 8A is about 600W of losses. You forgot to account for the current coming back through another 5 ohms of wire. It shouldn't be too hard to design a switching converter. Just calculate your component values with this and use a TL494 for feedback.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
If it is a bottom crawling vehicle weight would not be a problem going down. However, coming up, the issue of catastrophic failure could be handled by an air bladder which might be inflated through tubing provided in the umbilical cord.
Because of the shunts in MOTs, I dont think they transform equally well in both directions.
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power transfer through thin wires
