On 21 Oct, 01:03, "Bill Daniels" bildan@comcast-dot-net wrote:

As frank pointed out, winches comsume very, very little energy. Roughly
1kW/Hr or a liter of diesel which could easily be biodiesel. An electric
winch, if it could be powered from the grid, would comsume less than 10
cents worth of power per launch.

I'm bored, so thought I'd play with some numbers ...

I've launched ASH-25's to 1,600' on the wire. At 750kg that's a PE
gain of 750kg x 10 N/kg x 500m = 3.75MJ. There's also a PE gain in
half a ton of wire rope going up 250m: 500kg x 10 N/kg x 250m =
1.25MJ. KE is small in comparison, so that's a nice round 5MJ per
launch.

That's 1.4kWh, but allowing for 85% efficiency in the electric motor
you'd need 1.6kWh. Typical domestic prices here are around 12.5p /
kWh, so that's a nice cheap 20p/launch.

The downside is that you need that energy awful fast. 5MJ over 50
seconds is 100 kW (probably what 200bhp diesel winches get to wire
after transmission losses). That gives two problems.

First of all, you need a very hefty supply. On 415V 3-phase AC, and
assuming a 0.85 power factor, that's a line current of 100 kW /
[sqrt(3) x 415 x 0.85] = 163A. That's definitely non-trivial.

Secondly, you wouldn't get the electricity on a domestic tariff.
Industrial contracts take account of peak power as well as energy
used: the club would need a 100kW supply infrastructure despite only
using, on average, a tiny fraction of that capacity. The power company
will want to recoup the cost of the supply, and that will push the
price up considerably.

The logical alternative would be to use a local energy storage
facility: a great big Li-ion battery bank in the winch would help a
lot. With a 20% service factor (one launch every five minutes) the
average power requirement would come down to 20kW. Still too much for
a standard domestic supply, but a 40A 3-phase supply is pretty
standard. The downside there is that the batteries and associated
supply kit would be horribly expensive.

I believe Tost used to offer a (mobile?) electric winch, and I'd be
interested to know what the power supply arrangements were. As far as
I can see they don't do winches of any sort any more.

I'm sure electric winches could work very well, but I think they'd do
best as fixed installations. Are any in use?

Ian