Dash/LED req's

So im making a new little dash unit that has LEDs for neutral, turn, and oil indicators but i burned out 4 LEDs tonight. What do i need so the 10 amps or whatever its recieving doesnt burn them out?

 

Your supply should be 3 VDC at about 10 milliamps each (this is for the standard LED's, you might have different types, but I'm going to assume you don't). If your running higher than that, you might experience some short lived LED's. You may have to solder in a resistor to "sink" the heat and current to keep those LED's alive.

 

well the ones i got are set for 12 volts and 10 mA. But if i put in a resistor wont that basically up the power usage so theres no benifit in using LEDs?

 

Those lights can be sorta finnicky about power in. I suggest getting some 320# resistors, otherwise you'll continue to burn them out, and ensure that they are mounted with the resistor on the NEGATIVE side, with this, you should have no problems with them working. I blew my fair share of LED's without this knowledge.

 

helpful as always Ian. Thankyou.

 

I am puzzled Fox. You said the LED's you bought were designed for 12 VDC so it confuses me that you would have them blow out on you. Did they arrive with a small pigtail containing a resistor? The addition of the resistor will not raise your power consumption greatly, you will still see a great deal of benefit in reduced wattage demand. The LED sucks less than half a watt and the resister shouldn't pull more than 2 watts. The 1157 bulb pulls about 30 watts as I recall so your still making out. The addition of a resistor as ION suggested is a good start (near as I can figure, your LED's original resistor is not doing a bit of good), however I must politely disagree with the resistor placement. In the education I received, current flows from positive (excess of electrons) to negative (absence of electrons). To place the resister after the load (the LED) would invite the whole of the current to pass through the LED before it got to the resistor, negating its purpose. I would suggest the resistor be placed on the input (positive) side to prevent more blown LEDs. The positive side is the anode and the negative side is the cathode (typically flat side of the base). I would suggest you hit Wikipedia for Light Emitting Diode, neat guide with a good picture of where everything is in case you have questions. Good luck.

 

well, 2 of them dont have a resistor and are blown, not very surprised, but the other two, for oil and neutral have the resistor built in the negative pigtail and are blown. Also i must add, they did work for a few minutes.

 

I agree with Robert, put the resistor first then the diode!

 

I like your idea although I am looking at drop in replacement LEDs for the dash lights. WWW.SuperBrightLEDs.com Can anyone tell me what type of incandescent bulbs are used? I can't find a reference to them in the Haynes book and I haven't had a chance to pull them out and look. I'd like to know which ones to order. The above website lists the follwing but I'm not sure which to get:
BA9s
BA7s (midget flange)
12MB
756
I'd appreciate any help.
-Moe
p.s. I'd like to convert to LED's all around... any sources for an LED compatible flasher relay?

 

they have 1 type of electronic flasher at advance auto parts that is cool, i was gonna use it but I ended up not. Its the only one that doesnt flash twice as fast if a bulb is missing. Meaning that it wont flash twice as fast because LEDs wont be detected.

 

hey Rob, since you are the electric whizz, im not going to blatently disagree with you. maybe i heard or read wrong. But when you look into a standard LED theres a big triangle shaped piece(cathode) and the little triangle piece over top (annode) and the resistor goes on the cathode side. so either i have some freaky deaky LED lights that work backwards or have the cathode and annode mixed up. I could have also sworn electricity moves the other way(-ve towards +ve) Maybe you can clarify.

 

Well as for which side i know which side. You put it on negative side. Thats the side electrons flow from. Electrons are negatively charged and flow outwards.

I just didnt know what kind of resistor to use. I used to be able to read the color strips on them but i have now forgotten how to do so.

 

I'm an electronics tech and you should always use a resister when hooking up a diode.
It doesn't matter if you put the resister first or last. The voltage is divided between the resister and the diode based on resistance at a specific voltage.
At the 12v a 10 ma diode will have 1,200 ohm, you can't measure this with an ohmeter because the Diode lets more currect through as the voltage goes up.
With a 330 ohm resister you will drop the diode voltage from 12 to 9.5 volts, but since your voltage is probably closer to 14 volts with the motor revving you should wind up with about 11 volts. Personnally I would use a 220 ohm for full brightness. Polarity is negative to the stripe, if youre not sure hook it up to a 9v battery, it will only light if the polarity is correct and the 9v won't fry it.

 

I used to burn up LED's in class with a 9 volt battery just because I liked the weird ozone stink they made went they exploded! All the LED testers I use use 3 volts or less. phred, I'm with you on the placement of the load resistor, I was hopeful that there would be some change in the issues Foximus was having. I'm assuming a full 14 volts flowing but I'm totally curious as to why the LED's Foximus bought with the resistors in place already are blowing as well. Foximus, you simply must provide us a better picture of what is in place on your machine. There seems to be a mystery afoot. ION, I'm aware that different schools of thought teach different ways of current flow. I use the one I was taught with (spare electrons,+, flow to lack of spare electrons,-), but you should be able to use the converse just as easily. The triangle you refer to wouldn't be the pad inside the LED lens would it? I'm racking my brain trying to figure out the configuration you described and the internals are all I can think of that come close. Another note to all, I didn't see this continuation on the forum, I only caught this thread browsing for a previous post with a parts/tool supply link. I'm sorry I've not been attentive to this issue, I'll flag it now.

 

I reread the packages on the LEDs I bought... Silly radio shack. says 12 v on the front, on the back it says 9v-12vmax. So when id floor it and the alternator surged up i guess the 14-15v flow killed it. Either way i just used different ones and its working now. As i have pictures in my thread of the light box.

 

I'm going to bet it says 12 volts peak. This means that it can sustain life but only for a brief period of less than a second before it succumbs to current overload.

 

glad to hear you got things all ironed out!

just to clear up the "which way electricity flows" thing. Heres how it goes.

Conventional theory was basicly formed by benjamin franklin, so at that point no one understood anything about electrons or any of that. Just that there is a charges, and when you have a diffrence in charges it creates a flow, called electricty. "Positive" and "negative" were then arbitrarily assigned to each of the charges, and it was ASSUMED that elecrtricity flowed from neg. to pos.
Then we discovered electrons, and realized that electricity is really just the flow of electrons. So we figured out a way to see which way the electrons flowed. Turns out electrons flow from positive to negative, and we had been wrong all along. This is called "electron theory" and is the technically correct one. However since this seems backwards, and it doesnt actually matter which way ellectrons flow, so long as we are consistant, most people still talk about conventional theory, even though it is dated and technically incorrect.

As for where in the circuit a resistor goes in relation to a LED, as long as they are wired in series it makes no diffrence where the resistor is, as all electrons must pass through both the resistor and the LED before returning to ground. The electrons are not altered by passing through the resistor, which is why current flow everywhere in the system is the same in a series circuit. However since there resistances are diffrent the voltage drops are diffrent, and inversly proportionate. So really the point of the resistor is "step down" or eat some of the voltage.

Hope that clears things up for someof you who were still confused about the flowof electricity.

 

Brian, your reply was enjoyable. I'm glad we have this wealth of experience to help along eachother. I'm not the brightest bulb on the end of the lightpost, but I do avoid shocking myself regularly. The last publication I read on electron flow (Lord help me if I can remember the name of the book) stated that there was no definitive direction but for simplicity and understanding, either train of thought would work so long as it was consistantly observed (you already said this, I'm rambling). I'm using my training/education from 20 years back and it has been functioning for me all this time, but it's cool. I'm glad that the various ways to figure out the problem are there so that we can find the best way to the answer!!!

 

You know all the confusion here is caused buy a simple thing... Both schools of thought are kinda right. In highschool physics class we're taught that electrons flow from negative to positive, and oddly enough we remeber that, because thats what phyisists believe, and then in any electrical or electronics course you take they specifically tell you that current flows from postive to negative, and forget about witch way the electrons go (because that'll just confuse you).

So when you talk about any kind of electric circuit, current flows from positive to negative. Unless you're talking to a Phyisist. :roll:

 

And the other theory of the theory that its not the electrons that is the current , only the potential , the current could be the holes that the electrons create when moving so that is the work force? , we all so smart we are yet all this time and the consensus of which way it goes is still not really known yet? , my ten cents too....

 

Well said Nooz.

 

Electronics tech and engineer here! phred is correct in his figuring for the leds.