KR> POT OHM OR K?

[Glenn Martin]

On 10/20/2011 5:46 AM, John Martindale wrote:
> Well actually Jeff, the current in the circuit stays the same. Refer
>
John. You are incorrect in this situation. Adding the resistance of the 
rheostat (as we increase the dimming effect) increases total circuit 
impedance. ALTHOUGH this is accompanied by a SLIGHT decrease in 
resistance of the lamps (due to the lamps having a  positive temperature 
coefficient of resistance) this effect is STILL not enough  to be 
considered of any consequence in this application. THUS, since the 
dimmer's resistance ADDS to the resistance of the lamps (which for all 
practical purposes has not changed) TOTAL circuit resistance INCREASES. 
Since the applied voltage remained the same (12V) and Total Resistance 
INCREASED, Total circuit current decreased as a result, and power  
decreased. The converse is true as we increase brightness.



-- 
Glenn Martin

KR> POT OHM OR K?

[John Martindale]

Well actually Jeff, the current in the circuit stays the same. Refer

http://www.allaboutcircuits.com/vol_1/chpt_5/2.html

The brightness is a function of power (watts) which equals volts times amps.
Since amps remain the same, a resistor/rheostat drops the voltage across the
bulb thus dimming it. The associated voltage drop across the resistor times
the amps equals the watts that the resistor must give off as heat. The sum
of the voltage drops must equal the voltage of the battery (12volts).

In summary, electrons out of a battery terminal equals electrons in at the
other. Those little fizzers have to go somewhere :-).

John Martindale
29 Jane Circuit
Toormina NSW 2452
Australia

ph:61 2 6658 4767
m:0403 432179
email:john_martind...@bigpond.com

-Original Message-
From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net] On Behalf
Of Jeff York
Sent: Wednesday, 19 October 2011 2:46 AM
To: KRnet
Subject: Re: KR> POT OHM OR K?

Ok, It has been a long time since I was in Electrical Engineering 101.
.snip

KR> POT OHM OR K?

[John Martindale]

Well actually Jeff, the current in the circuit stays the same. Refer

http://www.allaboutcircuits.com/vol_1/chpt_5/2.html

The brightness is a function of power (watts) which equals volts times amps.
Since amps remain the same, a resistor/rheostat drops the voltage across the
bulb thus dimming it. The associated voltage drop across the resistor times
the amps equals the watts that the resistor must give off as heat. The sum
of the voltage drops must equal the voltage of the battery (12volts).

In summary, electrons out of a battery terminal equals electrons in at the
other. Those little fizzers have to go somewhere :-).

John Martindale
29 Jane Circuit
Toormina NSW 2452
Australia

ph:61 2 6658 4767
m:0403 432179
email:john_martind...@bigpond.com

-Original Message-
From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net] On Behalf
Of Jeff York
Sent: Wednesday, 19 October 2011 2:46 AM
To: KRnet
Subject: Re: KR> POT OHM OR K?

Ok, It has been a long time since I was in Electrical Engineering 101.
.snip

KR> POT OHM OR K?

[Glenn Martin]

On 10/18/2011 1:19 PM, Jeff Scott wrote:
>   The biggest issue with the one I pointed to on ebay (which is the one I am 
> using) is the 1 amp limitation. It doesn't take a lot of incandecent bulbs to 
> add up to 1 amp, although most modern panels are far less than that. When 
> this unit hits a 1 amp or higher draw, it crowbars and shuts off. You have to 
> shut it off for 30 seconds for it to reset. However, you can also buy 8 amp 
> units as well. I can't imagine anyone would be pulling that kind of current 
> with their panel lights. The advantage to it is that it is a switching power 
> supply, so does not have to dissipate heat like a resistive rheostat.
>
>   Jeff Scott
>   Los Alamos, NM
This current limit can be overcome by using the PWM to drive a 2N3055 
Transistor, the output of which connects to the Lamps/LED's. The 3055 is 
capable of delivering up to 15A. If you send me  schematic of this PWM, 
I can show you how to add it into the circuit. There are other 
transistors which are available at Radio Shack which would also be 
appropriate, Such as the TIP31.

If you like to build things on your own, the following link  shows how 
the 555 timer is used for this purpose:

http://pcbheaven.com/circuitpages/LED_PWM_Dimmer/

I personally would use LED's over incandescent bulbs any day, twice on 
Sundays.

-- 
Glenn Martin
KR2 N1333A, Biloxi, MS

KR> POT OHM OR K?

[Jeff Scott]

This is a good discussion Jeff.

 Actually, the LED controlling device works very nicely with LEDs and 
incandecent bulbs. I have both LED and incandecent lights on mine in the Cub. 
I'll also be using a combination of both when I refit the lights on the KR this 
fall. 

 The power supply does not work by limiting voltage. Instead, it uses Pulse 
Width Modulation (PWM). That means it varies the duty cycle of the 12v being 
quickly switched on and off to it's output. As it turns out, the light 
intensity varies at the same rate with both the LED and incandecent bulbs. 
Using this unit also provides an easy avenue to upgrade your lighting to LED 
lighting in the future as you would already have the controller in place. And 
it really costs no more than a good quality rheostat. ($15)

 The biggest issue with the one I pointed to on ebay (which is the one I am 
using) is the 1 amp limitation. It doesn't take a lot of incandecent bulbs to 
add up to 1 amp, although most modern panels are far less than that. When this 
unit hits a 1 amp or higher draw, it crowbars and shuts off. You have to shut 
it off for 30 seconds for it to reset. However, you can also buy 8 amp units as 
well. I can't imagine anyone would be pulling that kind of current with their 
panel lights. The advantage to it is that it is a switching power supply, so 
does not have to dissipate heat like a resistive rheostat.

 Jeff Scott
 Los Alamos, NM


- Original Message -

 Ok, It has been a long time since I was in Electrical Engineering 101. But, I 
believe this is a case where Ohms law needs to be applied to figure out the 
correct type of pot to use. In fact, I think you actually want to use a 
rheostat. Ohms law states that V = I X R or voltage equals I (amperage) times R 
(resistance) . Since you know your voltage is 12 VDC and you are trying to 
calculate the needed resistance then you can calculate Ohms law the following 
way. R = V / I If your calculations show that you are trying to dissipate much 
more then 1 watt, then as I recall you are going to have heat build up. So you 
may need to consider the value of R and have a heat sink. Remember, the more 
heat the greater the chance the pot or rheostat with heat up and eventually 
fail. The below item that Jose is recommending is for LED use which is 
different then calculating a pot for incandescent bulbs. I do not believe you 
could safely use a device designed for LED control on an incandescent bulb. 
But, it has been more years than I want to admit since I was an engineering 
student but, I am pretty sure I am right. An incandescent bulbs brightness is 
controlled by limiting the amperage to the bulb. A LED's brightness is 
controlled by the voltage to it. So as I recall for an LED you would want a 
variable power supply type of device with a voltage regulator at its core. By 
design it would be solid state and not be as big a heat source as say a pot or 
Rheostat. The ebay device in which Jose is pointing to is for LED use. Yes, the 
ad states at the bottom that it can be used for incandescent bulbs. I am not 
sure how well it would work because it is a voltage limiting device. My two 
cents worth and I qualified its been a while. Jeff York Georgetown Scott County 
airport 2010 KR Nationals Peoples Choice and best interior 2011 Air Fest Best 
Experimental and Best Instrument panel

KR> POT OHM OR K?

[Jeff York]

Ok, It has been a long time since I was in Electrical Engineering 101. But, I 
believe this is a case where Ohms law needs to be applied to figure out the 
correct type of pot to use. In fact, I think you actually want to use a 
rheostat. 


Ohms law states that V = I X R or voltage equals I (amperage) times R 
(resistance) . Since you know your voltage is 12 VDC and you are trying to 
calculate the needed resistance then you can calculate Ohms law the following 
way. R = V / I

If your calculations show that you are trying to dissipate much more then 1 
watt, then as I recall you are going to have heat build up. So you may need to 
consider the value of R and have a heat sink. Remember, the more heat the 
greater the chance the pot or rheostat with heat up and eventually fail. The 
below item that Jose is recommending is for LED use which is different then 
calculating a pot for incandescent bulbs. I do not believe you could safely use 
a device designed for LED control on an incandescent bulb. But, it has been 
more years than I want to admit since I was an engineering student but, I am 
pretty sure I am right.


An incandescent bulbs brightness is controlled by limiting the amperage to the 
bulb. A LED's brightness is controlled by the voltage to it.  So as I recall 
for an LED you would want a variable power supply type of device with a voltage 
regulator at its core. By design it would be solid state and not be as big a 
heat source as say a pot or Rheostat. 

The ebay device in which Jose is pointing to is for LED use. Yes, the ad states 
at the bottom that it can be used for incandescent bulbs. I am not sure how 
well it would work because it is a voltage limiting device.

My two cents worth and I qualified its been a while.

Jeff York
Georgetown Scott County airport
2010 KR Nationals Peoples Choice and best interior
2011 Air Fest Best Experimental and Best Instrument panel 




From: Jose Fuentes <jose.fuen...@gmail.com>
To: KRnet <kr...@mylist.net>
Sent: Tuesday, October 18, 2011 10:31 AM
Subject: Re: KR> POT OHM OR K?

Thanks, that's a great IDEA I will move to that one, just purchased it, much
perfer a solid state version.

Joe

On Tue, Oct 18, 2011 at 9:54 AM, Jeff Scott <jscott.pla...@gmx.com> wrote:

> I would suggest not using the old heat dissapating resistive dimmers and go
> to a solid state LED dimmer.
>  <
> http://www.ebay.com/itm/LED-Dimmer-12-volt-panel-dash-mount-on-off-12V-DC-/320764532724?pt=LH_DefaultDomain_0=item4aaf0e57f4
> >
>  This is a switching controller, so works very well with LED or incandecent
> lighting. This particular unit is $15 and very compact. It maxes out at 1
> amp. There are others on Ebay that carry up to 8 amps. I used this for the
> internal lighting in my SuperCub and have another one I'll be mounting in
> the KR soon.
>
>  Jeff Scott
>  Los Alamos, NM
>
> - Original Message -
>
>  On 2:59 PM, Jose Fuentes wrote: > Hi everyone, > > does anyone recommend a
> good POT OHM/K value for use as a dimmer? > Joe
> ___
> Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp
> to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net
> please see other KRnet info at http://www.krnet.org/info.html
>



-- 
Jose Fuentes
Founding Father (one of and former Vice Prez) of Capital City.NET User's
Group
Former Microsoft MVP
http://blogs.aspadvice.com/jfuentes
___
Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp
to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net
please see other KRnet info at http://www.krnet.org/info.html

KR> POT OHM OR K?

[Jose Fuentes]

Thanks, that's a great IDEA I will move to that one, just purchased it, much
perfer a solid state version.

Joe

On Tue, Oct 18, 2011 at 9:54 AM, Jeff Scott  wrote:

> I would suggest not using the old heat dissapating resistive dimmers and go
> to a solid state LED dimmer.
>  <
> http://www.ebay.com/itm/LED-Dimmer-12-volt-panel-dash-mount-on-off-12V-DC-/320764532724?pt=LH_DefaultDomain_0=item4aaf0e57f4
> >
>  This is a switching controller, so works very well with LED or incandecent
> lighting. This particular unit is $15 and very compact. It maxes out at 1
> amp. There are others on Ebay that carry up to 8 amps. I used this for the
> internal lighting in my SuperCub and have another one I'll be mounting in
> the KR soon.
>
>  Jeff Scott
>  Los Alamos, NM
>
> - Original Message -
>
>  On 2:59 PM, Jose Fuentes wrote: > Hi everyone, > > does anyone recommend a
> good POT OHM/K value for use as a dimmer? > Joe
> ___
> Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp
> to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net
> please see other KRnet info at http://www.krnet.org/info.html
>



-- 
Jose Fuentes
Founding Father (one of and former Vice Prez) of Capital City.NET User's
Group
Former Microsoft MVP
http://blogs.aspadvice.com/jfuentes

KR> POT OHM OR K?

[Jeff Scott]

I would suggest not using the old heat dissapating resistive dimmers and go to 
a solid state LED dimmer.
 

 This is a switching controller, so works very well with LED or incandecent 
lighting. This particular unit is $15 and very compact. It maxes out at 1 amp. 
There are others on Ebay that carry up to 8 amps. I used this for the internal 
lighting in my SuperCub and have another one I'll be mounting in the KR soon.

 Jeff Scott
 Los Alamos, NM

- Original Message -

 On 2:59 PM, Jose Fuentes wrote: > Hi everyone, > > does anyone recommend a 
good POT OHM/K value for use as a dimmer? > Joe

KR> POT OHM OR K?

[Jose Fuentes]

Here is the part

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem=160665003749=ADME:L:OC:US:1123

got to wait a couple weeks now.

Joe

On Tue, Oct 18, 2011 at 6:44 AM, Jose Fuentes <jose.fuen...@gmail.com>wrote:

> I found and purchased a wire wound one on eBay for $9 delivered. 25w 0
> to 10 ohm exactly like what AS sells for 35.
>
> Joe
>
> Sent from my Windows Phone
> From: Roger
> Sent: 10/18/2011 6:29 AM
> To: KRnet
> Subject: Re: KR> POT OHM OR K?
> Joe, a lot depends on the circuit that it's in, but for experimental
> purposes with your result sofar, try a 5kOhm linear taper and if that
> still doesn't do enough, try a 2kOhm. You may need to use a wirewound
> pot rather that plastic depending on how much current you are dissipating.
> Cheers, Roger
>
> On 2:59 PM, Jose Fuentes wrote:
> > Hi everyone,
> >
> > does anyone recommend a good POT OHM/K value for use as a dimmer? I got a
> > 10k one and well I have to go to the very end to get it to go on and I
> have
> > very little room (very fine turn) to dimm while I have 75% of the turn
> that
> > does nothing.
> >
> > Was trying to remember my electronics information, I think it's the
> higher
> > the resistance the more adjustment I will get so if 10k isn't enough
> maybe
> > 20-30k?
> >
> > Though I could be wrong, granted they seem to have started out at 10k on
> the
> > store I got it from.
> >
> > Joe
>
> ___
> Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp
> to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net
> please see other KRnet info at http://www.krnet.org/info.html
>



-- 
Jose Fuentes
Founding Father (one of and former Vice Prez) of Capital City.NET User's
Group
Former Microsoft MVP
http://blogs.aspadvice.com/jfuentes

KR> POT OHM OR K?

[Jose Fuentes]

I found and purchased a wire wound one on eBay for $9 delivered. 25w 0
to 10 ohm exactly like what AS sells for 35.

Joe

Sent from my Windows Phone
From: Roger
Sent: 10/18/2011 6:29 AM
To: KRnet
Subject: Re: KR> POT OHM OR K?
Joe, a lot depends on the circuit that it's in, but for experimental
purposes with your result sofar, try a 5kOhm linear taper and if that
still doesn't do enough, try a 2kOhm. You may need to use a wirewound
pot rather that plastic depending on how much current you are dissipating.
Cheers, Roger

On 2:59 PM, Jose Fuentes wrote:
> Hi everyone,
>
> does anyone recommend a good POT OHM/K value for use as a dimmer? I got a
> 10k one and well I have to go to the very end to get it to go on and I have
> very little room (very fine turn) to dimm while I have 75% of the turn that
> does nothing.
>
> Was trying to remember my electronics information, I think it's the higher
> the resistance the more adjustment I will get so if 10k isn't enough maybe
> 20-30k?
>
> Though I could be wrong, granted they seem to have started out at 10k on the
> store I got it from.
>
> Joe

___
Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp
to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net
please see other KRnet info at http://www.krnet.org/info.html

KR> POT OHM OR K?

[Craig Williams]

There are some lamp dimmer circuits here.

http://www.rst-engr.com/kitplanes/

Craig
www.kr2seafury.com




From: Jose Fuentes <jose.fuen...@gmail.com>
To: KRnet <kr...@mylist.net>
Sent: Monday, October 17, 2011 5:42 AM
Subject: KR> POT OHM OR K?

Hi everyone,

does anyone recommend a good POT OHM/K value for use as a dimmer? I got a
10k one and well I have to go to the very end to get it to go on and I have
very little room (very fine turn) to dimm while I have 75% of the turn that
does nothing.

Was trying to remember my electronics information, I think it's the higher
the resistance the more adjustment I will get so if 10k isn't enough maybe
20-30k?

Though I could be wrong, granted they seem to have started out at 10k on the
store I got it from.

Joe
-- 
Jose Fuentes
Founding Father (one of and former Vice Prez) of Capital City.NET User's
Group
Former Microsoft MVP
http://blogs.aspadvice.com/jfuentes
___
Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp
to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net
please see other KRnet info at http://www.krnet.org/info.html

KR> POT OHM OR K?

[Roger]

Joe, a lot depends on the circuit that it's in, but for experimental 
purposes with your result sofar, try a 5kOhm linear taper and if that 
still doesn't do enough, try a 2kOhm. You may need to use a wirewound 
pot rather that plastic depending on how much current you are dissipating.
Cheers, Roger

On 2:59 PM, Jose Fuentes wrote:
> Hi everyone,
>
> does anyone recommend a good POT OHM/K value for use as a dimmer? I got a
> 10k one and well I have to go to the very end to get it to go on and I have
> very little room (very fine turn) to dimm while I have 75% of the turn that
> does nothing.
>
> Was trying to remember my electronics information, I think it's the higher
> the resistance the more adjustment I will get so if 10k isn't enough maybe
> 20-30k?
>
> Though I could be wrong, granted they seem to have started out at 10k on the
> store I got it from.
>
> Joe

KR> POT OHM OR K?

[Jose Fuentes]

Hi everyone,

does anyone recommend a good POT OHM/K value for use as a dimmer? I got a
10k one and well I have to go to the very end to get it to go on and I have
very little room (very fine turn) to dimm while I have 75% of the turn that
does nothing.

Was trying to remember my electronics information, I think it's the higher
the resistance the more adjustment I will get so if 10k isn't enough maybe
20-30k?

Though I could be wrong, granted they seem to have started out at 10k on the
store I got it from.

Joe
-- 
Jose Fuentes
Founding Father (one of and former Vice Prez) of Capital City.NET User's
Group
Former Microsoft MVP
http://blogs.aspadvice.com/jfuentes