| Author | Message | ||
| Bill moldenhauer (12.73.231.58)
Rating: |
Awhile back someone mentioned adding resisters to 24v lights to run them at 12v does anyone know what size resisters. my thought is this all the 24v wiring is in place the only place you are changing it is at the light I bought all new leds for my mci-9 and thought this would be the easiest way to do it | ||
| Doug (68.83.22.144) Rating: N/A |
MCI makes a kit for the conversion of headlights | ||
| BrianMCI96A3 (65.160.209.132) Rating: N/A |
Bill, I've done a little experimenting doing exactly what you are going to do. It all depends on the specs for the light itself. For instance, my lights are rated at 104ma max draw @ 14v By using Ohm's law... Resistance is equal to Voltage divided by Amperes. Dividing 14V by 104 milliamps then, gives you roughly a resistance of 134 Ohms Since a coach charging system will max out at 28V, and one of my lights has a resistance of 134 ohms if we add a resistor of say 150 ohms (134 + 150 = 284 ohms)and use another of Ohms laws Amperes are equal to Voltage divided by Resistance... Then, 28V divided by 284 ohms is equal to 98.5 milliamps... Being a little below specs, ought to work out perfectly. One other thing, in tests a 1/2 watt resistor got hot to the touch but not hot enough that you couldn't hold it firmly between your fingers. Still, to disapate the heat better, I am going to try using 2 watt resistors a much bigger heat sink. Brian | ||
| Stephen Fessenden (Sffess) (65.154.176.203)
Rating: N/A |
I don't know if the resistance measured across the whole unit including LEDs and ballast resistor will be correct, But you arrived at the correct additional ballast. You need to do the calculation with the remaining volts after subtracting the voltage drop for the LEDs. Probably 2 to 6 volts for the resistor. The voltage used (as a voltage drop) by the LEDs does not enter the calculation. So if you had a 10 volt total drop accross the LEDs (3-5 in series, probably 4 or 5 series strings in parallel to use 104 ma.) the remaining voltage drop across the resistor would be 4 volts. 4 volts divided by 104 ma is 38.5 Ohms. Add another 14 volts, all voltage drop accross the resistor, 18 volts divided by 104 ma is 173 Ohms. Pretty close this time, but remember to use the desired milliamps and the VOLTAGE DROP ACROSS THE RESISTOR ONLY to calculate the total reistance needed. Since you know the milliamps and the additional voltage that you want to drop accross the additional resistor, you can also calculate that you need: 14 Volts divided by 104 milliAmps = 135 Ohms additional, Which is what you did. Your additional resistor would need to be able to dissipate at least 1.45 watts. You should be able to measure the milliAmps on a multitester. Most will handle this range through the meter. If you are getting near the design milliAmps at 26 volts with the batteries not charging, you have the right ballast. No need to be under specs at all, since LEDs last 100,000 hours at their design milliamps. By the way, I learned on this board about the importance of putting LEDs in series in a lighting system, for efficiency. LEDs are so new for lighting that I find most people do not know that and think of designing will all parallel LEDs off one resistor. Spread the word. | ||
| CoryDane RTSII (66.155.188.169) Rating: N/A |
I was paging through some of those "Hobbyists" catalogs, they sell some fairly cheap converters for 24 to 12vdc. They won't carry the whole bus 12v system but will carry a light or two. I recall the other trick is to run two 12vdc lights in series. "Imagine" cd | ||
| Larry Baird (Airhog) (159.115.185.216)
Rating: N/A |
I have a question along the same lines. I just put Jakes on my 8V71, and the truck I got them off was a 12 volt, I have a 24 volt. Do I need to drop the voltage for the Jakes? | ||
| BrianMCI96A3 (65.160.209.132) Rating: N/A |
Stephen, it's late and my brain isn't up to trying to figure out exactly what you mean... But I wonder, since two 12 volt lights in series will equal a 24V light fixture, just as CoryDane has mentioned... And (if you know the specs) since Ohms law: Voltage divided by the Amperage MUST tell you the resistance of one 12V light fixture... Then... if you add a resistance equal to a 12V light fixture in series WITH a 12V light fixture, wouldn't you have a 24V fixture? I'm thinking if you know the specs for ANY 12V light, you can find it's resistance, add a resistor of equal value, and viola 24V light... without having to know voltage drops or even touching a meter My actual measurements show a little less current draw than the specs, but in any case I thought that a 2 watt resistor was just the ticket. Pretty simple... easy to remember, easy to figure out. Brian | ||
| FAST FRED (63.234.22.103) Rating: N/A |
The big proiblem is 12V takes 2X the amps of 24V. Are the existing coach wires large enough to have the amperage doubbled? Very doubtfull , as cost was a consideration in selecting those 24V wires. Simplest would just to run 12v bulbs in series. FAST FRED | ||
| Phil Dumpster (24.16.243.37) Rating: N/A |
You can't add resistance to a 24 volt lamp to make it work on 12 volts. Going the other way is possible. The easiest way to find the correct resistor value is to run your subject lamp on 12 volts while measuring the current with an ammeter. From that, use Ohms law to determine the hot resistance of the subject lamp. Use that figure for your dropping resistor value. Now your lamp will work on 24 volts with that resistor in series. While running two 12 volt lamps in series on 24 volts is an elegant solution, when one burns out the other stays dark too. The best and simplest solution, believe it or not, is to find a DC to DC converter with enough capacity to handle the exterior coach lighting. Then you can use standard 12 volt automotive bulbs. | ||
| BrianMCI96A3 (65.160.209.132) Rating: N/A |
Fred while I understand what you are trying to get at, in this instance you are wrong. In actuallity, the LED lights Bill is talking about draw perhaps a TENTH of the original incandescent light, AND if you add the proper resistance to the 12V fixture you will have created a 24V light with exactly the same amperage draw in the entire circuit as the 12V light, about a TENTH of the original. Phil, you are right adding resistance to a 24V light will not give you a 12V light fixture on a 12 V circuit, BUT adding an equal resistance to a 12V fixture on a 24V circuit will give you a 24V light, which is what Bill and I were describing. Since Stephen is right and LED lights last upwards of 100,000 hours, if 2 LED lights tied together work well as a 24V light fixture, then the NEXT owner MIGHT have to repair one years down the road. Brian | ||
| Buswarrior (Buswarrior) (64.229.209.232)
Rating: N/A |
Hello Bill. If that set of LED's were purpose built for the coach, they might be ready to go straight in without any adjustment. The manufactured LED tailights have a wide voltage tolerance. The big names do something like 5 to 35 volts. I know of a 24 volt coach that has been running around for the last 5 years with LED brake lights that were installed in ignorance by a junior mechanic who thought it would be good to retrofit instead of fixing the old socket. He'd never heard of 24 volt systems. That inspired us to do the research and not let him work on the old bus anymore... Only tricky side effect is the brake light dash indicator doesn't light, due to the amp draw being too low (simulating a burned out bulb, which is the purpose of the little beggar. In a fleet situation, no one is going to put a fix for that in, but a busnut can make up a cheater circuit to fool it into working again. So, check your LED's, you may be pleasantly surprised to find no mods required! happy coaching! buswarrior | ||
| Tim Brandt (Timb) (12.8.192.60)
Rating: N/A |
West marine now sells 24-12 converters of varying amperage: http://mastercatalog04.westmarine.com/0622.asp They also sell several led light fixtures starting on this page http://mastercatalog04.westmarine.com/0677.asp | ||
| BrianMCI96A3 (198.81.26.45)
Rating: N/A |
Phil, not only are you correct that adding a resistor will not make a 24V light work on a 12V circuit, but re-rereading Bill's original post, that is exactly what Bill was asking! But perhaps Bill meant it the other way around? Bill, what say you? Were you looking to make a 12V LED light work on 24V Or a 24V LED light to work on 12V? Brian | ||
| njt5150 (68.243.175.255) Rating: N/A |
Why not just use a vanner and have 12 volt any place you need it? | ||
| Mike Eades (Mike4905) (206.148.124.184)
Rating: N/A |
The question about the jake brakes is yes you need 24 volt jake soleniods on a 24 volt system. I ahd to replace a bad jake on my 4905. Luke and Bill at U.S. Coach changed it and put in a 24 volt jake. works perfect. Mike | ||
| Bill Moldenhauer (12.74.16.214)
Rating: N/A |
12v lights running on a 24v system This was supposed to be the first question the wiring does not come in to question because i will be adding the resistor at the fixture runing two bulbs in series is okay till one burns out then you have two out ( which would be 2 brake lights or 2 tail lights)The head lights are already 12v a rsistor is about $.29 a dc to dc convertor could be $$$$$ I alreadt have an equalizer that was for the video system and could use that with 24v relays for the 12v lights but would have to upgrade all the wiring So thats why i thought a simpleresistor at each light would be the quick ticket | ||
| njt5150 (68.243.250.225) Rating: N/A |
Simple ticket is just run the wires from the vanner... Then everything runs correctly like it should not rigged.. | ||
| BrianMCI96A3 (65.160.209.132) Rating: N/A |
Whew... then what I wrote before does apply to you. Actually Bill, the fact is that the amount of current that your 12V LED lights draw would not be a problem for the 24V wiring in your coach if you wanted to use relays and 12V for them. You have to remember that the original incandescent lights drew at least ONE AMPERE of current each, through the circuit... LED lights have a current draw in MILLIAMPS... My LED lights draw 104 milliamps MAXIMUM, and a THOUSAND milliamps equal 1 AMP The bottom line is: If you chose to run your lights on 12V you would need to hook up TEN LED lights like mine on the same 24V wire to draw as much current as the original incandescent! So you DO NOT need to replace all the wiring to run 12V through them, unless you want to run MUCH smaller wires more appropriate to their current draw to run your LED lights Brian | ||
| BrianMCI96A3 (65.160.209.132) Rating: N/A |
Bill, you are right, the simple answer would be a resistor for each 12V light. But, as far as two LED lights in series being a problem, when being used for turn signals, you are wrong there. Experiments I have done, confirm the observations I have made of LED lights on trucks... individual LEDs may burn out inside the lamp, the light stays lit...as will the other lamp in the series. AND you have to remember that many LED lights are rated to last as much as 100,000 hours and THAT is equal to leaving your lights ON for ELEVEN YEARS and 4 MONTHS. Which is why.... I used two 12V lights in series for my brake lights... and my rear turn signals... and my front turn signals. Brian | ||
| Stephen Fessenden (Sffess) (65.154.177.247)
Rating: N/A |
Brian, the problem with just using Ohms law for the whole light is that the LEDs may not follow it like a pure resistance. We both came up with the same answer and it helps me to go through the math since I am designing replacement clear tail lights with clear LEDs that light red or amber. Should look neat if I ever get it done. I have all the LEDs and backup lights to mount them in. Just have to sit down and do it. Used to use perfboard to make them. I have found that it is easier to drill 3/16" holes in plexiglass of some type and push the LEDs into the holes than to mount them on perf board like I did the inside lights. You can use a second matching piece of drilled plastic to push all the LEDs firmly into position. Great way to build interior lights and step lights. | ||
| CoryDane RTSII (66.155.188.191) Rating: N/A |
Is the problem that you do not want to run wire? Is your coach finished to the point where running wire is a problem? I thought all buses had the 12vdc tap at the battery. A resistor will work theoretically, but you can never change the bulb wattage, or bulb style unless you change the relay too. If you are putting in incandescent bulbs, put two 12v bulbs of the same number/wattage in series for the fixture. I am sure a florescent will work the same way but they make florescent ballasts for 24v you can buy. LED can use a resistor, actually requires one. Just what are you installing? There are more answers for specific lamps. "Imagine" cd | ||
| BrianMCI96A3 (65.160.209.132) Rating: N/A |
Stephen, I see what you are saying... but, when I made my calculations I measured the actual resistance of the lights while they were lit. Plus, though Ohm's law doesn't cover everything, it is pretty specific, if you know or can measure amperage draw, and applied voltage, Ohms Law will tell you the actual resistance. CoryDane, Bill is planning on installing pre-made 12V LED lights. Brian |
