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Old 11-24-2011, 10:39 AM   #21
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I'm just catching up on old threads and found this one. Being a model RR guy as well as a camper, we find lots of uses for resistors, diodes, capacitors, etc on our club layout. I second the "resistors get hot" motion and I might suggest a diode instead...it is essentially a switch that turns the power on and off so fast it's not visible to your eye, but the result is that the bulb gets less voltage and appears dimmer. We use this trick on Lionel 022 turnouts that tend to melt the red/green lens covers when you supply adequate switch machine voltage to them. Diodes are your friend for dimmer bulbs (as long as you don't need a controllable dimmer.)
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Old 11-24-2011, 10:57 AM   #22
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Hey train guy-- I think you are talking about low voltage AC and these
guys are talking about low voltage DC.
I don't think a diode will work for cutting DC voltage.
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Old 11-24-2011, 11:23 AM   #23
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Diodes will drop voltage even for DC (wired forward bias).
Reaching into the "Way Back" machine I believe it is .5 volts drop per diode. You could wire several in series to get the DC voltage drop you need without hardly any heat generated.

OR you could just buy a voltage regulator solid state device for 5 volts and plunk it into the circuit. http://www.ebay.com/itm/5-Volt-5V-DC...-/290592255754

Just a buck each.

Someone more "current" on solid state devices should chime in here.
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Old 11-24-2011, 02:59 PM   #24
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Quote:
Originally Posted by Shasta1 View Post
Is there a resistor that can be used to cut 12v in half?

I'm wanting to dim a couple of bulbs to half brightness.... is there a simple and inexpensive solution to this? The bulb is the 1141 size base.


Don't know if this is what you're looking for. I think it may help though. DC bulbs ratings
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Old 11-24-2011, 06:24 PM   #25
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Originally Posted by Shasta1 View Post
Is there a resistor that can be used to cut 12v in half?

I'm wanting to dim a couple of bulbs to half brightness.... is there a simple and inexpensive solution to this? The bulb is the 1141 size base.
I used Hi-Temp black grill paint on my Sconce wall light bulb (12 V). Reduced the output where we could leave it on while watching TV. Bulb has lasted 2 years so far. No downside,heat,smell,ect. No $ investment,used spray paint left over from grill! Youroo!!
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Old 11-24-2011, 07:41 PM   #26
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Way Back Machine

In a normal silicon diode at rated currents, the arbitrary cut-in voltage is defined as 0.6 to 0.7 volts. The value is different for other diode types Schottky diodes can be rated as low as 0.2 V, Germanium diodes 0.25 to 0.3 V.

Diode - Wikipedia, the free encyclopedia

When a diode is "forward biased" (meaning current is flowing in the "ON"
direction), a silicon diode will "use up" 0.6 to 0.7 volts "turning on."

"Reversed biased" (meaning trying to push current in the opposite direction) the diode will prevent electron flow and the diode will be "OFF."
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Old 11-27-2011, 07:27 AM   #27
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I stand corrected!

And to taranwonderer sorry, I was remembering my old Lionel AC trains.
I guess HO and others are DC.

I think to answer the OP, just get a lower wattage bulb and be done with it.
LED is a great option also.
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Old 11-28-2011, 09:11 PM   #28
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Quote:
Originally Posted by herk7769 View Post
Diodes will drop voltage even for DC (wired forward bias).
Reaching into the "Way Back" machine I believe it is .5 volts drop per diode. You could wire several in series to get the DC voltage drop you need without hardly any heat generated.

OR you could just buy a voltage regulator solid state device for 5 volts and plunk it into the circuit. 5 Volt 5V DC Voltage Regulator 1 Amp L7805CV 7805 | eBay

Just a buck each.

Someone more "current" on solid state devices should chime in here.
From what I've seen, the 78XX series if regulators have changed quite a bit in the last few years.

Where I could reliably use a 7805 to drop the 12-VDC source voltage to 5-VDC for TTL devices with little to no heat sinks, I now have to use quite a bit of sink and ventilation.

I think the mfr's have cheapened the circuitry of the product to where it contains only a zener and a dropping resistor, instead of a transistor, resistor and zener.

I've noticed that even on the simplest circuits, that when I use a Radio Shack or similar regulator, that I have the heat that I used to have by just using a dropping resistor. These guys are also power hogs. You can buy more efficient ones for about a buck apiece; look at the specs!!!

There is no reason for a properly designed "valve" to use more than 5-10% of applied power to drop input voltage to a desired level. This all converts to heat and battery losses.

Even mini-inverters used in 12-VDC equipment to activate memory generate higher than applied viltages at 70-to 80% efficiencies.

Posted, tired, with a drink, and no editing!
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Old 11-28-2011, 11:46 PM   #29
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Originally Posted by Shasta1 View Post
Is there a resistor that can be used to cut 12v in half?

I'm wanting to dim a couple of bulbs to half brightness.... is there a simple and inexpensive solution to this? The bulb is the 1141 size base.
Replace the 12 Volt DC bulbs with 24Volt DC bulbs
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Old 11-29-2011, 07:59 AM   #30
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Replace the 12 Volt DC bulbs with 24Volt DC bulbs
Simple and effective. "Brilliant"
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Old 11-29-2011, 10:43 AM   #31
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Quote:
Originally Posted by herk7769 View Post
Diodes will drop voltage even for DC (wired forward bias).
Reaching into the "Way Back" machine I believe it is .5 volts drop per diode. You could wire several in series to get the DC voltage drop you need without hardly any heat generated.

OR you could just buy a voltage regulator solid state device for 5 volts and plunk it into the circuit. 5 Volt 5V DC Voltage Regulator 1 Amp L7805CV 7805 | eBay

Just a buck each.

Someone more "current" on solid state devices should chime in here.
Those voltage regulators are available in several different
voltages, including the 6v ( 1/2 12vdc) model. Like the 7806
for example. Available in several cases depending on power
dissipation required. TO-220, TO-3, etc.... I "think" that I
remember the 7806 is available in 2.2amp version as well
as lower current versions.
[Remember to use the HIGHEST "12v" your system produces
when calculating power dissipation in the regulator!]

As you say, you can probably find 'em on ebay. If not, places
like mouser.com, digikey.com, allied.com and other electronic
parts suppliers will have them. Three pin, fixed voltage regulators
are ...old... technology and available in surplus electronic stores
generally........

cheers,
johnd

PS remember that when using diodes in the supply side (+), they
do *NOT* regulate voltage, only "drop" it. So as your 12v
supply goes up and down, the voltage to the load will
vary likewise............
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Old 11-29-2011, 10:45 AM   #32
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Originally Posted by herk7769 View Post
Simple and effective. "Brilliant"
Or
Put two 12 dv bulbs in series at each light fixture.

It's all Ohms Law
E= I X R
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