| Author |
Message |
don (Bottomacher) (66.216.217.11)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 08, 2004 - 8:30 am: | |
I'm uncommonly thick in the area of electronics, and I can't figure this out by the archives. I want to replace my 24 volt lights on my MC9 with LEDS, but I can't find any available. Can someone tell me how to add a resistor to 12 volt LED lights that will allow me to accomplish it? Thanks in advance for your help.
Don |
Marc Bourget (209.142.38.81)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 08, 2004 - 9:16 am: | |
Look at Gumpydog's site. http://www.gumpydog.com/bus/MC9_WIP/Lighting/Exterior_Lighting/Turn_Signals/turn_signals.htm
This is one of several LED pages. It has the overall best discussion in view of the general nature of your question.
He has some further experiments planned. If you can be patient he may develop all your answers. |
Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 08, 2004 - 12:45 pm: | |
Hook your 12 volt lights to a 12 volt battery and measure what current is being drawn. Then use ohms law to figure how much effective resisance the light is, and you'd use that number for the series resistance you need to operate on 24 volts. Then you must also use ohms law to figure the wattage of the resistor.
For example:
Say your light draws 100ma (.1A) on 12 volts. This gives the light an effective resistance of
(volts/amps=ohms)
12/.1= 120 ohms
You'd need to basically double the resistance to operate on 24 volts, so you'd want to put a 120 ohm resistor in series with the lamp for 24 volt operation.
Now you have a 120 ohm resistor passing 100ma of current- use ohms law to figure the wattage:
volts x amps= watts
12v x .1A= 1.2 watts
You'd want to make the resistor bigger just for fudge factor, so a 5 watt resistor would be great though a 2 watt resistor would probably work fine as long as it has plenty of air space to carry away the heat it will make... no matter what resistor you use it will need to have some air. If you bury it in foam or tightly enclose it, the heat it creates will not have anywhere to go and it will toast.
For turn signals or brake lights its not such a problem but for night lights that are always on, you have to make sure the resistor can get cooled. |
BrianMCI96A3 (205.188.116.135)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 08, 2004 - 12:47 pm: | |
I've followed Gumpydog's directions and built a number of 24v LED light fixtures, and I plan on having LED fixtures throughout the coach.
I also replaced all of the turn/stop/tail lights with LED units, using a mixture of 24v fixtures that I built following Craig's instructions, and a grouping of factory 12v LED lights that I wired in series to create 24V lights
When it came to the clearance lights I found a really great deal on 12v units and purchaced enough to replace them all.
There are three obvious ways to approach wiring up 12v led lights to a 24V system.
The first is to wire the lights in series, as I did with the turn/stop/tail lights.
(two 12V lights in series creates one 24V fixture)
The second is to power the CIRCUIT with 12V (from one side of the battery bank.
The third is to do as Don is asking about and install a resistor inline with the 12v light creating a 24V fixture.
For a number of reasons, the third choice was precisely what I had in mind for the clearance lights.
So I did a number of experiments with resistors
and I was not very happy with the results.
In the initial trials, I used marginally sized resistors (the right ohms, barely the right watts, because I had them on hand) and was surprised at just how really hot they got!
I then purchased resistors that were four times the wattage of the first resistors, it handled the load just fine and was not anywhere near as hot as the first resistor, but it was still HOT... I could hold the resistor in my finger tips but not for long before it became uncomfortable!
That got me to thinking... I really don't want a lot of heat buried in the roof of the coach.
And then even if I oversized the resistors to the extent that they might only be warm to the touch, I realized that my original idea was to create a very energy effcient coach and any waste heat is just that, a waste.
So, the long answer is, I'm going to power the clearance light CIRCUIT with 12V from one side of the battery bank.
Don, to create a 24V fixture from one 12V light, you will need a resistor equal in ohms to the ohms of the 12V light itself.
The wattage of the resistor ought to be, in my opinion, at LEAST 4 times the wattage draw of the 12V light.
Brian |
BrianMCI96A3 (205.188.116.135)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 08, 2004 - 1:06 pm: | |
I agree with Gary, for a 1.2 watt light I'd go with a 5 watt resistor, or as I mentioned, at least four times the wattage of the light, because as Gary said a 2 watt would probably work, but it will still give off a good deal of heat.
Brian |
Bill Moldenhauer (12.74.6.61)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 08, 2004 - 6:41 pm: | |
I powered mine off the 12v side
of the battery
found the switch for clearance lights and wired one side 12v and the other to the led's
took about 20 minutes
1980 mc-9 |
don (Bottomacher) (66.216.217.11)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 08, 2004 - 9:13 pm: | |
Gentlemen, thank you all! I should have made it clearer. I know how to wire in series for running lights; it's the turn signals and brake lights that had me floored. Another thing- does a resistor resist the same amount regardless of voltage? Do I need to be able to tell the Radio Shack genius what volts, watts, and ohms I need? Can I simply insert the correct resistor in the ground wire of the pigtail? Are resistors at all weatherproof, like in the light housing with the usual almost effective gaskets? Thank you all again
Don |
JimMC9OH (209.190.8.70)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 09, 2004 - 10:57 am: | |
Got my 24v LED's at NAPA in Grove City OH (truck parts) |
don (Bottomacher) (66.216.217.11)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 10, 2004 - 9:01 am: | |
Jim, do you have the stock number? The folks here look at me like I'm speaking Swahili when I ask for 24v leds. Thanks
Don |
Marc Bourget (209.142.38.81)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 10, 2004 - 9:46 am: | |
They way I read Gumpy's site and the links he included, I understand that resistors are rated for watts output in addition to resistance in ohms.
You have to look at the volts running thru the load to see what amount of heat you are going to shed by imposing the desired resistance on the circuit.
You have to pick a resistor with sufficient wattage capability to stay within the heat load that will be generated.
Also, don't ignore the benefits of a heat sink. It'll go a long way towards keeping the resistor "healthy" and helping you to throw away all that nice energy you've stored in your batts through careful, diligent (and expensive) monitoring and charging of your system!
Onward and Upward
Marc Bourget
(just tongue in cheek, not sarcastic! :^) ] |
DrivingMissLazy (66.168.175.51)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 10, 2004 - 10:38 am: | |
Marc, FYI, I believe resistors are rated in WATTS for the amount of heat (watts) they can dissipate in free air rather than OUTPUT.
BTW, I am not aware of heat sinks being commercially available for resistors in these low wattage ranges, but these resistors are very inexpensive. |
Marc Bourget (209.142.38.81)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 11, 2004 - 2:14 am: | |
Dear Richard,
Poor choice of words on my part (Watt did you say?) LOL
I've seen resistors mounted to an aluminum plate as a radiator/heat sink.
Electrician who hooked up my father's tow'd to his Prevost dropped the voltage with a cascade of serial and parallel resistors all attached to a 5" x 7" Aluminum Plate. Not the way I would have approached it, but it works.
Onward and Upward
Marc Bourget |
DrivingMissLazy (66.168.175.51)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 11, 2004 - 10:00 am: | |
Yea, that sounds like a good idea that I had never thought of. That is the nice thing about the board, there is seldom a day that I do not learn something. Thanks.
Richard |
John that newguy (199.232.240.75)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 11, 2004 - 4:10 pm: | |
I dunno if this is of any help to you:
http://www.powerstream.com/dc1.htm
Rather than tap off 1/2 the battery and continually drain one
battery more than the other, I would prefer to do it with a
dc to dc converter. This will not only give me the 12 volts,
but enough amps to power any other 12 volt device I have. |
JimMC9OH (209.190.8.16)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 28, 2004 - 9:57 pm: | |
Sorry it took so long to get back.Willstop by there tommorow and ask(9-29) |