| Author | Message | ||
| Joebus (Joebus)
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I have purchased a couple of 7" S/T/T red LED tailights for my MC8. But they are 12 volt, my coach is 24. What resistors would I use? Thanks | ||
| Gary Stadler (Boogiethecat)
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Hook them to 12 volts and measure the current.... report back and I'll figure the resistor value for you... | ||
| John Jewett (Jayjay)
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Why not use an LR24 voltage regulator and not have the heat dissipation problem of the resistors? A couple of bucks at most electronics suppliers. ...JJ | ||
| Gary Stadler (Boogiethecat)
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Um... what exactly is an LR24? I've been in the electronics biz for 40 years and never heard of one... and google gets me nothing. Assuming it is some sort of non-switching voltage regulator, it would dissipate exactly the same amount of heat as does a resistor, probably cost a lot more, and is likely going to take much more in the way of wiring than a simple resistor... ...and yes a resistor does dissipate some heat, so what? If sized properly it's no big deal. Everything electrical dissipates heat. A simple resistor is going to be a no-brainer to install, cost less than a dollar, be as reliable or more so than the LEDs it's working with, as long as it's value is calculated properly. Knowing the current the LEDs draw on 12 volts allows that to be calculated in a heartbeat using ohms law... | ||
| Richard Bowyer (Drivingmisslazy)
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I do not know if it is proper to do so, but when I needed to drop the voltage from 12 volts to 6 volts for some instruments in the dash of a car I was restoring, I used a zener diode rated at 6.5 volts. It never got hot and dropped the 12 volts down to the proper voltage. I believe they have different wattage ratings, but Gary will be the one to answer that. Richard | ||
| Gary Stadler (Boogiethecat)
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Hi Richard, Yes, a zener diode will work fine- if it doesn't get hot, it could be the perfect answer. Zener diodes can be though of as a "self calibrating resistor that drops a fixed voltage across itself regardless of the load". If, as Richard did, you buy a 6 volt zener and hook it in series with some doodah and then hook that combination to 12 volts, it will "eat" 6 volts and leave the rest for the doodah as you did on your dash instruments. In doing this, it will dissipate heat just as if it were a resistor, so you need to buy one that is rated with enough wattage to do the job. Little zeners that look like small diodes will be rated at 1/2 to 5 watts and they can be purchased all the way up to 50 watts or so, but by this size they are in stud packages that need to be bolted to heatsinks. But with LED tail-lights and markers, a zener is a great idea (Richard is one step ahead of us once again with great ideas!!) Basically you can try a 12 volt zener in series with your LED lights, and if it doesn't get hot, it's happy. If it gets too hot to comfortably touch, a larger wattage is in order. The "burning finger method" is an easy to calculate wattage without resorting to current meters and ohm's law for those of you who cant or dont want to go there... 12 volt zeners Mouser part numbers: ( www.mouser.com ) 12 volt 1 watt: 78-1N4742A for 7 cents 13 volt 5 watt: 610-CZ5350B 50 cents | ||
| Richard Bowyer (Drivingmisslazy)
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A great big bow from Richard! Thanks Gary. BTW, these things are really cheap aren't they. I had not bought one for 10-15 years or more and had just about forgot about them and am surprised at how cheap they have gotten. Took me about 10 minutes to even remember their name. LOL Richard | ||
| Richard Bowyer (Drivingmisslazy)
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Gary, could a person utilize two 5 watt, 12 volt zener's in parallel to drop 24 volts to 12 volts? Probably be good for a little over one amp which should be good for most LED'd. In the same vein, and depending on price and availability, could you use two 6 volt units in series to accomplish the same thing? Richard | ||
| Gary Stadler (Boogiethecat)
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Possibly. The problem when you use two in parallel is that they won't usually be manufactured at exactly the same voltage, so one will likely take the whole load and the other just sit there. You could put maybe 20 ohms in series with each one to help balance them but now you're getting messy... easier to just buy a 10 watt, 20 watt or even a 50 watt zener, mount it on a heatsink and be done with it. The problem I'm finding is that these days there aren't any "easy" suppliers for zeners bigger than 5 watts. Guess if you need bigger in electronics, there's probably a better way to do it (not so brute force) so they aren't in a big a demand as in the old days. Nte Inc makes them NTE5254A is a 50 watt 12 volt and NTE5188A is a 10 watt 12 volt You can find NTE distributors here: http://www.nteinc.com/NET_St_lst/Disty.html My guess is that thru "distribution" channels, you'll have to jump thru hoops to buy small quantities. It may be better to ask for 1 or 2 free samples- quite often if you give them a good enough story and sound like you'll be using them later in a manufacturing project, they'll just give you a few. Good luck.... Yup Richard, take that bow!!!!!  | ||
| Richard Bowyer (Drivingmisslazy)
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Maybe better to just use a five watt at each light fixture rather than trying to do all the clearance lights with one diode. Richard | ||
| Gary Stadler (Boogiethecat)
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That'd work for sure. Even a 1 watt would probably be fine on a marker. Either way, it is a great idea Richard! If you use zeners, they have polarity. Hooking them in series with your marker one way will make it VERY bright, the other way a lot less bright. The proper polarity is the less bright direction. | ||
| Tom Caffrey (Pvcces)
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Since a lot of those LEDs like 20 milliamps, the one watt zeners could be made to handle a bunch of them. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| Richard Bowyer (Drivingmisslazy)
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Yea, about 4 of them I would guess. Richard (Message edited by drivingmisslazy on May 31, 2006) (Message edited by drivingmisslazy on June 01, 2006) (Message edited by drivingmisslazy on June 01, 2006) (Message edited by drivingmisslazy on June 01, 2006) | ||
| Gary Stadler (Boogiethecat)
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Um well, 12 volts at 1 watt means the current thru the zener is 83Ma. So one 1-watt zener could handle four LEds, oops, not 40.... Now I get to bow!!! | ||
| Richard Bowyer (Drivingmisslazy)
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Yep, you get to bow, and I need to get a calculator! Richard | ||
| Bryce Gaston (Busted_knuckle)
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Where can I find these Zeners? 731-885-7460 BK | ||
| Gary Stadler (Boogiethecat)
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Bryce, if you need some 1W ones, email me your address and I'll send you some. Bigger ones you'll have to buy thru distribution... Gary | ||
| Richard Bowyer (Drivingmisslazy)
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BK, check here. Richard http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLD,GGLD:2004-50,GGLD:en&q=z ener+diode | ||
| Bryce Gaston (Busted_knuckle)
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Thank ya'll! Gary, I'll get with ya as soon as I figure out what it is I need LED's have been put on hold right now, more important stuff like making it go Whoa! (I gotta spend some outragous euro's on 4 new slack adjuster's on the Setra ! Having to adjust automatics every couple days is getting to be a PIA!) Bryce |