Please help this mechanical guy dim my lights and make my DW happy....

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blw2

blw2

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Dumb question for those electrically inclined, bit it has been a very long time since I have tinkered with DC circuits
I guess seeing these complicated circuits out there for dimming LED's  has me scratching my head and doubting myself....

I have an overhead 2 bulb fixture over my sofa, and another over my dinette.
They are not controlled by the house light switch.  the only control is the spst switch on the fixture itself.

I was thinking of trying to find either a spdt or dpdt switch at radio shack (mini rocker style), so that I could rewire the fixture so that we could light either one of both of the bulbs as needed
BUT
I'm afraid that won't go dim enough for DW's preference while TV watching, etc....

So
I'm thinking about wiring in a small potentiometer.

Any reason that wouldn't work without additional circuitry or resistors?

I might in the future want to switch out the filaments for LED's but no short term plans for that since we mainly camp with hookups.... so I'm thinking a small potentiometer form radio Shack mounted right in the fixture might do the trick.....
 
Just be sure to calculate the proper wattage for the potentiometer.  If you ever change to LEDs, the pot probably won't work with those.
 
I doubt you can find a potentiometer with the power handling capacity to do what you want.  Most potentiometers are rated at 1/2 watt to 1 watt - your light bulbs use about 24 watts each.

If you dim one to half brilliance the single bulb will draw 12 watts, with the potentiometer having to dissipate another 12 watts.  This is well beyond the power rating of a simple volume control.

I suggest using something like this.  Although it's meant to dim LEDs, it has an 8 amp output (96 watts), which means it is capable of dimming several incandescent light bulbs (or lots of LEDs).  Essentially it's a potentiometer coupled to electronic circuitry that boosts it's power handling capability.
 
You need a rheostat instead of a potentiometer.  I submit that the fact that you can dim your 12V dash lights would prove it's practicality.  It may be difficult to get one small enough in physical size to be appropriate to install in your 12V light fixture, but it certainly can be done.
 
My little bit of input....  Wattage of the rheostat is still important; even just a 5 watt RHEOSTAT is of substantial physical size.

  I'll let someone else calculate the requirement.

 
ok, makes sense now that you point it out...... how about this......

Would a dimmer switch from Home Depot, designed to dim AC lights in your house work?
 
That's what the device I referenced above is - a 12 volt dimmer.  At less than 4 bucks with free shipping it's a no-brainer.  Just put it in line with the power feed going to the lights.

120 volt dimmers from Home Depot won't work - they're the wrong voltage.
 
Lou Schneider said:
That's what the device I referenced above is - a 12 volt dimmer.  At less than 4 bucks with free shipping it's a no-brainer.  Just put it in line with the power feed going to the lights.

120 volt dimmers from Home Depot won't work - they're the wrong voltage.
Click to expand...

Yep, i see your point.... no brainer, and I appreciate the suggestion....except I've also got to mount the thing and make it look good....  You're certainly helping me to understand the limitations...

I guess I never really understood what is inside of a residential dimmer.  Don't get why the voltage matters..... watts is watts I figured..... but I can believe there's more to it....

 
Watts is watts - but watts is also voltage x amps.

At 12 volts, for a given power you're handling 10 times the amperage than you are at 120 volts.  This means you need 10 times the current handling capacity at the lower voltage.

Plus most of the Home Depot dimmers are electronic devices, which require the correct input voltage to power themselves.

In short, you're talking apples and oranges.
 
Our two bulb fixtures have 2-position switches (plus off of course), and I put lower wattage bulbs in the single bulb positions so we have a choice of low or high level lighting.
 
Residential dimmers aren't simple rheostats, but use circuitry to pulse width modulate the power to the light.  A rheostat would have to dissipate too much heat to work in a residential environment.  A rheostat is just a potentiometer with only 2 terminals used.
 
You can get 12v dimmers of either the resistance type (rheostat) or the PWM type (pulse width modulated). PWM will work with leds but rheostats won't. Briefly, a rheostat alters the voltage while PWM alters the duty cycle time but keeps the voltage normal. Leds don't like to have their voltage reduced, so PWM is the only way to go.

You don't need complex circuits to dim Leds if you are using pre-made bulbs. The circuit diagrams are for those engineering their own light fixture or bulb from scratch, while the retail packaged bulbs already have circuitry in them.

Here are some rheostat type dimmers:
http://www.ebay.com/itm/12v-Single-On-Off-Switch-Dimmer-Control-Black-RV-Camper-Trailer-Home-Marine-Boat-/171427927052
http://www.ebay.com/itm/NEW-12V-15AMP-ROTARY-DIMMER-SWITCH-AT-RLD-1-005-RV-MARINE-EGGSHELL-WHITE-/371210638906

And a PWM type for either incandescents or leds:
http://www.ebay.com/itm/Brilliant-Light-Dimmer-Dial-Module-RV-Star-Lights-12v-/171070095930?pt=Motors_Car_Truck_Parts_Accessories&hash=item27d492823a&vxp=mtr
http://www.ebay.com/itm/New-12V-8A-Light-Dimmer-Bright-Adjustable-Controller-Single-Color-Light-/261398999708?pt=US_Lighting_Parts_and_Accessories&hash=item3cdc98329c
 
blw2 - Here is a dimmer marketed specifically for your RV incandescent bulb dimming.

Ned - I meant to specify a high wattage wire wound rheostat.  I just got tired of typing. ;D
 
Brad, Lou's comment:

Watts is watts - but watts is also voltage x amps.
Click to expand...

is essentially the reason that the giant high tension power lines run the voltage up in the thousands for long distance transmission of power. You can get the same power at a much lower voltage, but it would require more current, thus requiring (among other things) much thicker wire and other heavier duty stuff to handle it without burning up. Of course there's also the difference between AC and DC, which is more complex than it seems on the surface, as they behave differently in certain kinds of circuitry. Don't mix it.
 
Man, this talk makes me happy I have dimmers built into all my lights. I suppose I'll be sad it the Intellitec Multiplex system ever goes bad, but it's nice to be able to have the amount of light needed with just a push of the button. The dimmers are built into the system.

Ken.
 
Larry N. said:
Brad, Lou's comment:

is essentially the reason that the giant high tension power lines run the voltage up in the thousands for long distance transmission of power. You can get the same power at a much lower voltage, but it would require more current, thus requiring (among other things) much thicker wire and other heavier duty stuff to handle it without burning up. Of course there's also the difference between AC and DC, which is more complex than it seems on the surface, as they behave differently in certain kinds of circuitry. Don't mix it.
Click to expand...
Ooooh, AC volts and DC volts and little ohms.......sorry, lost my head. (sang to the tune of "Mairzy doats".
 
[quote author=Molaker]
Ooooh, AC volts and DC volts and little ohms.......sorry, lost my head. (sang to the tune of "Mairzy doats".
[/quote]
What the heck is "mairzy doats"? 
That wouldn't be Mares eat oats, would it?

Mares eat oat,
and does eat oats,
and little lambs eat ivy
Kids'll eat ivy too,
wouldn't you?
 
Just Lou said:
What the heck is "mairzy doats"? 
That wouldn't be Mares eat oats, would it?

Mares eat oat,
and does eat oats,
and little lambs eat ivy
Kids'll eat ivy too,
wouldn't you?
Click to expand...
Exactly, but it sounds like you never heard the original song.  Here's the lyrics as sang in the original song years ago.
 
Oh! I've heard it all right, and sang it as a kid.  We delighted in NOT telling anyone who asked, just what the words really were.

EDIT: I forgot to mention that the Nursery Rhyme is much older than the little song you linked to.
 
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