[TowerTalk] (another)Problem That Needs Ideas,

Wed Dec 8 16:24:36 EST 2004

Chuck,

Any time you have to drive a control voltage at significant current down a
long line the resistance of the line forms a voltage divider with the load
and drops your voltage. What you really want in this case (long lines
feeding a resistive/inductive load, motors, relays, etc.) is a constant
current source. That way you don't care how long the line is. There is a
real simple circuit configuration to do that on the data sheet of several
versions of a three pin adjustable voltage regulator (LM317, LM338, and some
others). 

It only requires the regulator and one low ohm resistor. If you need a weird
value resistor you can tweak it by paralelling several if you have trouble
getting just the right value. You really don't need an engineering degree to
do this. Three pins on one part, and two on the other. You can get the LM338
in a 5amp version with a TO-3 package (needs a heat sink for full power
though). 

If memory serves me (please verify with the data sheet before trying this)
you put the resistor in series with the regulator's output pin and connect
the adjustment pin to the other side of the resistor along with the load. I
think the resistor value in ohms was equal to the current desired in amps.
You start with a power supply of enough voltage to handle the drop, and the
constant current will insure that you get enough current for starting and
yet prevent over heating. This is REAL simple and works great. The circuit
is toward the back pages of the data sheet on several of these regulators
from different vendors. 

You can figure out the current you needed if you don’t have a spec for your
motor or relay by running it through an amps meter with short leads and the
voltage it is specified for. Then set up a current source for that much
current and supply the current source with a higher voltage. 

I drove a 3V screwdriver motor through 1000' of wire using a 24V supply and
it worked perfectly, never overheated or stalled. 

– Tom Scott §§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§
          27005 NE Neill Road     Newberg, Oregon     97132-9446
503-538-5839 Home   503-330-6867 Cell   503-554-9468 Fax   KD7DMH

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Chuck Dietz
Sent: Wednesday, December 08, 2004 12:37 PM
To: towertalk at contesting.com
Subject: RE: [TowerTalk] (another)Problem That Needs Ideas

I have been using 24 volts on 12 volt coil relays for years and I have never
had a failure.  Occasionally I have left a switch on with a relay energized
for as long as a week.  The higher voltage also compensates for resistance
in the lines to the relay too.

Chuck W5PR 

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of w9ge
Sent: Wednesday, December 08, 2004 1:52 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] (another)Problem That Needs Ideas

I have a two port six pack that I have relegated to the back bench because
of relays not always pulling in.  It is tough on amplifier tubes to be
running into an open!  My rotator has no  brake, so cannot try that method. 
A very light touch on the offending relay always makes em pull in however. 
73 bob de w9ge
----- Original Message -----
From: <n4gi at tampabay.rr.com>
To: <towertalk at contesting.com>
Sent: Wednesday, December 08, 2004 8:06 AM
Subject: Re: [TowerTalk] (another)Problem That Needs Ideas

> Don't have an RCS8V, but it reminds me of a problem I occasionally 
> have with a sixpack switch...  One or two of the ports on one side are 
> intermittent unless I click the brake of my ham rotor 50 feet above 
> it.
>
> If I don't hear anything when I turn things on, I can click the brake 
> a couple of times, then the relay engages.  I think it's the 10M port.
>
> Odd, but I just have lived with it.  Dirty contacts?
>
> 73,
> Blake N4GI
>
> ----- Original Message -----
> From: Bill Jackson <k9rz at radiks.net>
> Date: Tuesday, December 7, 2004 8:21 pm
> Subject: Re: [TowerTalk] Problem That Needs Ideas
>
>> Pat,
>>
>> I have an Ameritron RCS-8V which has been in service for almost 20 
>> years.Shortly after I purchased it new, I started having intermittant 
>> problems similar to yours, especially in cold weather.  This was the 
>> case until I discovered the relay arms were touching the inside of 
>> the plastic cover and would only partially actuate.  The cure was to 
>> place a couple of flat washers between the plastic case the and the 
>> chassis in all four corners,increasing the clearance between the case 
>> and the relays. It has operated
>> flawlessly ever since.
>>
>> I would try operating the switch with the cover off to see how the 
>> relaysactuate.
>>
>> 73 de Bill
>>
>>
>> _______________________________________________
>>
>> See: http://www.mscomputer.com  for "Self Supporting Towers", 
>> "Wireless Weather Stations", and lot's more.  Call Toll Free, 1- 
>> 800-333-9041 with any questions and ask for Sherman, W2FLA.
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
> _______________________________________________
>
> See: http://www.mscomputer.com  for "Self Supporting Towers", 
> "Wireless Weather Stations", and lot's more.  Call Toll Free, 
> 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
> 

_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.

_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.

_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk