Any electrical guys around.

[_chris_]

I bought some small LED lights a while back off of ebay and I want to use them in all my cubbies and storage spots in my boat but I need to know how to hook them up. I have tested a couple on a 12 volt battery and they blow immediatly(Probably because they are 3.4 volt led's) Does anyone know how I should wire them up? I have heard if I just do them in series to total 12 volts they will be fine but I am not sure. here are the specs from when I bought them if it helps.

Size (mm)
3mm

Lens Colour
water clear color

Forward Voltage (V)
12v DC

Reverse Current (uA)
12v/DC

Luminous Intensity Typ Iv (mcd)
6000 - 8000

Life Rating
100,000 Hours

Viewing Angle
20 Degree

Absolute Maximum Ratings
( Ta = 25?C )

Max Power Dissipation
PM = 80 mw

Max Continuous Forward Current
IFM = 30 mA

Max Peak Forward Current
IFP =75 mA

Reverse Voltage
12 V

Lead Soldering Temperature
240 ? C ( < 5 Sec )

Operating Temperature Range
- 25 ? C ~ + 85 ? C

Preservative Temperature Range
- 30 ? C ~ + 100 ? C

 

[QC]

Re: Any electrical guys around.

Hey chris, moved this over to Electrics as there are more EE types hanging over here. Would have got the answer either spot, but maybe faster here. Good luck.

 

[_chris_]

Re: Any electrical guys around.

Thanks.

 

[jeffnick]

Re: Any electrical guys around.

Most LED's use a current limiting resister in series to let them operate at the proper voltage.​

You can wire enough LED's in series to make them work. I wired 4 3.2V LED's in series and encased them in epoxy for my license plate light.

But when done this way you should use a fuse in the circuit because if one LED fails in the 'closed' position, the rest will be overvoltage and will fail as well, potentially leading to a direct short and perhaps a fire caused by the heat of that short.​

 

[_chris_]

Re: Any electrical guys around.

Now I got another question. circuit and series= OK but what if I hav 10-20 3.4v lights would that be a problem as they would not be getting enough power? Where can I find a current limiting resister? and if I do can I run the 10-20 lights?

 

[Bifflefan]

Re: Any electrical guys around.

Now I got another question. circuit and series= OK but what if I hav 10-20 3.4v lights would that be a problem as they would not be getting enough power? Where can I find a current limiting resister? and if I do can I run the 10-20 lights?

Radio Shack...

 

[4JawChuck]

Re: Any electrical guys around.

Here is a resistor calculator for determining what size resistor needed for wiring your LED's, you would put a resistor on each leg of the LED's in this scenario.

http://home.cogeco.ca/~rpaisley4/LEDcalc.html

 

[_chris_]

Re: Any electrical guys around.

Radio Shack...

I just ran by there and they no nothing, he could only tell me which drawer to look in.

Here is a resistor calculator for determining what size resistor needed for wiring your LED's, you would put a resistor on each leg of the LED's in this scenario.

http://home.cogeco.ca/~rpaisley4/LEDcalc.html

Thanks but I am still confused, can someone help me out here? I want to plan on running 20 of these lights, I would assume I could do this off of one switch. I don't know if I am using the calculator right.

 

[chuckz]

Re: Any electrical guys around.

You can run 10 to 20 LED's but not in one series circuit. Each LED drops about 2 volts. To drive 10 LED's in series requires a 20 volt source (2V * 10).

In a parallel circuit the limiting factor is current. 10 LED's in parallel each drawing 10 mA (0.010 A) requires 100mA (0.1A).

You can buy LED's from E-Bay with the limiting resistors for the voltage you are connecting to (12 to 15 VDC). It is much cheaper than buying the resistors at Radio Shack.

Each LED requires one resistor. The resistor value is 12 volts/10 mA =120 ohms. The power rating is 12 volts*10mA=0.12 watts. So in theory you could use an 1/8 watt resistor but for dependability use a 1/4 watt resistor.

Resistors come in specific value, the resistors you want is anywhere from 120 to 150 ohms. Exact value is not critical.

Here is a link where you can buy the resistor for $1.95 per 100:
http://www.action-electronics.com/resistor.htm You may have to look around for other sources if this supplier has a minimum order policy.

Also try Parts Express.

Also, 20 LED at 10 mA each is 200 mA, so you need a switch that is rated for more than 200 mA. Almost any switch will handle this current.

 

[_chris_]

Re: Any electrical guys around.

So are you saying I could run 6 in a series per switch and be fine? And if so what resister should I look for?

The problem is I already have these lights and would like to use them, I don't mind spending a few bucks on the resistors or even hooking them up to a couple of switches so I guess my question is what is the max I could hook up to my 12v batery and what resister to go with?

 

[chuckz]

Re: Any electrical guys around.

Wire the LED's in parallel so if one fails the rest stay lit.

 

[_chris_]

Re: Any electrical guys around.

So let me get this right. If I run the led's in parallel I can run 10-20 led's on one switch as long as each led has its own resistor of 1/8 or 1/4 watt and 120 to 150 ohms and a 200 mA switch? Am I reading this correct?

 

[metriccrescentwrench]

Re: Any electrical guys around.

OK Chris, to use these LEDs individually you need to put approximately a 320 Ohm resistor in series with each LED. Anything close will be fine, standard values that are close would be 300 or 330 Ohms. If you want to use multiple LEDs in series then put 4 in series and they'll be ok. (That's based on the rating you gave of 3.4 Volts)

DON'T use the 120 Ohm resistor someone else suggested, that would be too much current for the LED's. They're rated at a max continuous current of 30 mA. At a nominal battery voltage of 13 Volts the resistor needs to drop 9.6 volts (13 - 3.4 = 9.6). From Ohm's Law (E=IR) 9.6 = 0.03R; R = 320.

 

[_chris_]

Re: Any electrical guys around.

Thanks, so 320 ohms for just one LED and no resistor if I run 4 in a series? Now what about parallel? If I run a live 12volt positive and negative wire down my side cubbies on my boat can I hook up say 10 LED's here and there as long as each one has a 320 ohm resistor, correct?

 

[4JawChuck]

Re: Any electrical guys around.

If you use a 320 ohm resistor on each LED you can use inexpensive smaller 1/2 watt resistors, if you use the calculator you can calculate the wattage needed for the resistor.

When I ran your values through the calculator it said 350 ohms per resistor at 13.5 VDC and 30 milliamps using 3.0 VDC per LED, don't forget the battery is being charged at 13.5 volts when underway...using 3.0VDC for each LED ensures you under the max for each light if the voltage goes higher than 13.5 VDC.

I would think a parallel circuit would be better than series since finding a burnt out light would be easier and wouldn't take out a whole bank as it would if they were in series.

 

[_chris_]

Re: Any electrical guys around.

Thanks for everything (and I just figured out how to use the calculator) so I will be giving this a try. My plan is to run a 12v(13.5v when running) power supply down the length of each side of my boat in the cubbies and put an LED every foot or two with a 320 ohm 1/2 watt resistor on each one. I will probably be around 20 or a few more when done and I think it will give some nice light for those evenings I am on the water. Please let me know if I am doing something wrong and I will post up some pics when I am done.

 

[metriccrescentwrench]

Re: Any electrical guys around.

That sounds good. 20 of these will pull only a bit more than a half amp, so you could easily run these off a 1 or 2 amp fuse (you did plan on taking power from a fused circuit didn't you?).

 

[_chris_]

Re: Any electrical guys around.

That sounds good. 20 of these will pull only a bit more than a half amp, so you could easily run these off a 1 or 2 amp fuse (you did plan on taking power from a fused circuit didn't you?).

I did I have learned in my younger years that a fuse is there for a reason. I had a stereo power wire catch on fire while driving down the highway just as I was passing a fire truck, talk about a major deal then, they shut the highway down all for a wire. I cut it as soon as I pulled over and it was all good but the FD had to do a full inspection before I could drive off.

Do you think this will be a major drain on the battery? In the next year or so I am gonna run dual batteries but don't want to start the project until after the season.

 

[bruceb58]

Re: Any electrical guys around.

There are plenty of LEDs that are available with internal current limiting resistors. Rather than adding a resistor to the ones you have, I would just buy the ones that have them included. Makes life way easier.

 

[_chris_]

Re: Any electrical guys around.

UPDATE: I went to Radio Ripoff and grabed 20 resistors and went home and soldered them on to the LEDs and made my chistmas light string. I put it in place in the boat and hooked it up and couldn't be more happy with the results, it gives a nice ambient light. I love it, I tried to take some pics but they did not turn out. Now I need to hide the wire and make something to hold the LEDs where I want them to shine properly. I will let you all know when I am done.