charlieaarons said:
I did a calculation a few years ago. For electric winches feet/sec times line pull divided by input ampsXvolts. I came up with 10-20% efficiency. For hydraulic winches feet/sec X line pull divided by psiXgal/min (all numbers converted into compatible units). I came with 90%. The difference is incredible; no wonder electric winches burn out. Needless to say I've used hydraulic winches ever since.
Can you elaborate? By my over lunch scribbles, I come up with this junk and want to know where I am wrong.
Mile Marker's 9000 lbs winch is rated at 1500 psi at 3.5 gpm max flow. This is in low range, line speed is 6.16 ft/min, 1 wrap of cable. So assuming 90% hydraulic motor efficiency, it takes 3.4 HP to do that. Then when you figure a rotary vane pump like a power steering pump has pretty lousy overall efficiency, it's gonna take a lot more than that from the crank. A typical vane pump efficiency is like 70%. It took 4.9 HP from the crank to supply 3.4 HP to the winch.
A Warn 9000 lbs winch is rated for 6.38 ft/min at 1 wrap. Their motors ratings say it will pull 460 amps at 12V at max pull. I dunno what the efficiency of their motor, but a series wound DC should be no worse than about 85%. That means it takes 6.3 HP to do that pull. A car alternator is around 65% overall efficient at converting mechanical power to electrical. The alternator took 9.7 HP from the crank.
It seems at max pull both are similar line speeds and the hydraulic system is no more than about twice as efficient. I also only assume a generic vane pump efficiency, I understand power steering pumps are pretty bad. If a car power steering pump is more like 50% overall efficient, then the hydraulic system took maybe more like 6.8 HP from the crank. There is a whole lot of wiggle room here, so I'd have to emphasize that this is a very, very big w.a.g.
