[GreenKeys] Given that energy can be neither created or destroyed ...

[Bob McConnell]

Roy Morgan wrote:
> 
> On Dec 1, 2008, at 4:34 PM, John Hensley wrote:
> 
>> ... how many machines can you run on a loop and still maintain
>> a good voltage (120V DC) and recommended current (30ma - 60ma) ??
> 
> I can't say.. others no doubt will.,
> 
>> .. and does each machine need a separate loop control?
> 
> No.. if there is one loop current control, it is enough.  Adding more 
> would only reduce the loop current and make need to readjust back to the 
> right current value.
> 
> Roy

I think the only sure way to find out is to try it. The machines need to 
be in series with a single loop control, so it is the total reactance of 
the coils that limits the number. Most early loop supplies were around 
135V, with very low impedance, so there was enough power for several 
devices in a loop. Still, since there is significant inductance 
involved, nearly half a henry per selector IIRC, the signal distortion 
increases much faster than the resistance alone would suggest. The only 
pure resistance is in the rheostat and the wire. But the selector 
magnets and power supply characteristics vary enough that it is 
difficult to predict how they will work under extreme load. You may need 
to adjust the selectors a bit when you get more than a couple connected. 
With a solid state supply, the back voltage from too many selectors 
after the contact opens may fry the output circuit. Make sure it has 
enough snubber diodes to protect it.

I believe some installations had repeater/regenerators available when 
they needed to string multiple devices together from a single source.

Bob McConnell
N2SPP