[GreenKeys] Loop supply voltage

[hwhall@aol.com]

The loop will have an adjustable current limiting resistor in series. That sets the current in the loop when the loop is in a steady state. And they are DC loops.

Wayne
WB4OGM

On Saturday, January 18, 2025 at 09:07:04 PM MST, steve bennett via GreenKeys <greenkeys at mailman.qth.net> wrote:

Harold,

I get it about the inductance.
But once the coil reaches steady state you are just left with the resistance in a DC circuit.
So if the goal is to have 60mA at steady state 100v is way too much. What am I missing?
The loop supply is DC correct? Maybe that is where I'm confused. Is the loop AC?

-Steve

On Saturday, January 18, 2025 at 10:37:22 PM EST, Harold Hallikainen via GreenKeys <greenkeys at mailman.qth.net> wrote: 

You normally need a higher voltage,  typically around 100 volts with a
series resistor to set the current. The selector magnet has a high
inductance so that limits how fast the current can increase. V=L × dI/dt.
So, the rate of current increase is V/L. Higher voltage makes the current
increase faster. Another way of looking at it is T=L/R. The time constant
for the current increase is L/R. A bigger series R makes the current
increase faster. So, you need higher voltage, at least on space to mark
transitions. Otherwise, the selector magnet armature will not pull in fast
enough or, for holding magnets, the current will not be hogh enough to
hold the armature at ssmple time.

Harold


On Sat, January 18, 2025 8:11 pm, steve bennett via GreenKeys wrote:
> GKs,
> Â  Â Yet another M15 question.Please check my math. I'll be really
> embarrassed if I screwed up ohms law.My selector magnets are in series and
> reading a total of about 200 ohms.This means to get 60mA I need to apply
> 12V?
> I thought loop supply voltage was way higher than that, like up near
> 100vAm I confused? Wouldn't be the first time.
> -Steve
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