Date: Mon, 25 Oct 2010 09:58:45 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
Subject: Re: [TowerTalk] 5 x conductor rotor cable ?
On 10/25/2010 7:16 AM, Jim Thomson wrote:
> Who makes 5 x conductor rotor cable ?
This is nothing more than an Ohm's law problem combined with the cost of
the cable. When I needed a 350 run from my shack to my Yaesu rotor, I
used two runs of 3-conductor power cable from the shack to the base of
the tower (250 ft), and then found some surplus 8-conductor #18 to go
120 ft up the tower to the rotor. In that multi-conductor cable, I
doubled up on the pairs going to the motor.
## I came to the same conclusion, after doing the maths. I have a
1000' roll of 10 ga stranded RW-90 pwr cable... u can lay this stuff
outside all you want. One plan was to use 3 x runs of 10 ga from
shack to base of crank up tower, a distance of 75'. [150' of loop resistance]
Then smaller ga stuff, to go 100' up the side of the tower.[200' of loop
resistance].
The previous owner used RG-58 for the magnetic pulse leads. The pulse leads
can be any ga,
like 22-26 ga. I can use any ga wire from shack to base of tower... like 3
x 6ga's. But I require
LIGHT cable going up the side of a crank up. I have one coax + another control
cable [for 40m relays
+ 80m compressible coils, etc], so want to keep the total cable weight down.
In your situation, I would first study what the sensing circuit is.
If you think RFI might be an issue, run shielded twisted pair
for that circuit.
## good point. RG-58 is probably a good idea for the digital sense leads. The
GH manual
sez if coax used for the sense leads, the braid can also be grnded at top and
bottom of tower
+ SPG.
##see above. It's a 45 lb small K7NV PP, which uses a spinning magnet on the
end of the
motor shaft. No pot used. The control box is a GH unit, that's modified for
small PP's. It outputs 27 vdc under a 9.3A load. I measured 23.2 vdc right
at the PP itself. This is on the carpet right now, with a single 22 ga
wire to
the CW..and a single 22 ga to the CCW... and paralleled 22 ga for the COM.
[also used 22 ga for the digital sense pulse leads]. The GH box and PP are
only 3' apart.. and all wires are short, for testing. The 22 ga wire runs
stone
cold with 9.3A flowing. The START UP current is a whopping 16.12 A ..but only
lasts
1/3 sec. I used the 100 msec record/ min/max/average feature on my Fluke 87
to measure
all this. [ the fluke shows 22A MAX, when on the 1 msec 'snap shot mode']
## OK, the above is with the speed control set to MAX..and NO ramp up/down
being used.
Now if speed control set to max, and ramps used [ PWM].... then the START UP
current is
only 10.15 A [1/4 sec], then drops to 7-8 A...while speeding up... then hits
a max of 9.2A.
Interesting enough, even when speed set to a crawl, it still sucks 7.4A
## apparently, IF you can manage to get 24 vdc to the [small] PP under load,
the torque is
phenomenal, like 25K in lbs [1250 ft lbs, that's running torque, not start up
torque,which is a myth].
I added torque compensator's to the yagi's, so the mast torque is very
little....in high winds.
IF I can manage to get 18-24 vdc at the PP itself, I will be happy. It has
GLOBS of torque.
## remoting the PP pwr supply to the base of a tower + relays will work...
but then you have
NO PWM... unless the PWM board, etc, is also moved to base of tower. Either
method requires
120 vac to be run out to base of a tower. The PWM feature in the GH box is
superb. There is
no pwm on either of my tic rings. With PWM, no more bringing 585 lbs to a
crashing halt.
## Tnx to folks, for all the various suggestions. If this was a fixed tower,
I would just run 3 x 10ga's from
shack to PP. [You can go 300' with 10 ga wire]. Being a crank up, I want to
cut the cable weight
if possible.. + it has to flex, since it is retracted during the day. With
big ga wire from shack to base of tower,
I can afford to use smaller than optimum wire going up the tower.
Jim VE7RF
73, Jim K9YC
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