How Does One "Provide" A Different Level Of Current?

[xpnctoc]

I was just reading a old manual for a train signal whose color changes are driven by a motor coil which rotates a color lens disc. In the "Do's and Don'ts" section it says "Don't apply excessive operating current to the motor coil." I don't understand how one can provide excess current. I thought a power source provides a voltage level and is "rated" for a current draw but that it is up to the load to draw (or attempt to draw) whatever current it needs. Can someone help me understand what the manual could mean?

 

[Audioguru]

The person who wrote the wrong things does not know anything about electricity. It should say "do not apply excessive voltage to the motor". Does the manual say the voltage that should be used?

 

[xpnctoc]

Actually, it doesn't say what the expected voltage is. The entire manual is written in very general terms, which makes me think there may have been different units manufactured to different specs. I read an article on refurbishing these signals that suggests the optimal voltage is 12VDC, but I don't know where the author got that information. I hooked up the signal to a 12VDC supply and it seems to work just fine. But then I read that quote about providing too much "current" and it got me all confused and paranoid about inadvertently burning out the motor.

 

[BobK]

Reminds me of the very old SNL skit "The Pepsi Syndrome", where the reactor is about to melt down and the operators are arguing the meaning of the line in the instruction manual that says, "You can't have too much water in the reactor."

Bob

 

[duke37]

A train signal may be controlled from a current source. If the cable is broken, there could be an indication of a fault. Just supplying a voltage does not give any indication that there is a connection.
Railway slave clocks are driven with a current source to allow for long distance resistive cables. I have just wound a couple of bobbins for these (30,000 turns!)

 

[Irv]

Isn't this exactly like a great big moving-coil (analog) meter? They are driven by current thru the coil, not voltage (even the voltmeters).

 

[turbogt16v]

May i join in,
My knowledge of electricity is poor.
And i have that problem understanding power that device uses.
So if we have 12v 600a power source, and we have a bulb that is rated 60w,will bulb only draw 5a of current?

 

[Audioguru]

60W/12V= 5A. but only when the light bulb is at its normal very hot operating temperature because an incandescent light bulb draws a much higher current before its filament is 2000 degrees C.

A DC motor's current is also much higher before it is up to its normal speed.

 

[davenn]

So if we have 12v 600a power source, and we have a bulb that is rated 60w,will bulb only draw 5a of current?

no it will only draw the max current the PSU can supply and the lamp will glow dimly

where do you think it will get 5A from when the PSU can only supply 600mA ?

 

[Irv]

He said he had a 600 *amp* supply. I don't think that's what he meant, but if he does,
it should be able to power a 60 watt bulb without much sweat.

Lifting that supply will require much sweat, however.

 

[turbogt16v]

Yes i meant 600amp,but only so i can understant it, not to use practicly

So to sum it up. U dont worry about ampers, u only need to pass the rated amperage of the circle or device

 

[davenn]

Thread closed, not going anywhere useful