New lights for my passenger cars.

[Madman]

I have swopped out the incandescent lamps in three of my passenger cars for LEDs powered by two AA cells.




Before, with incandescent lighting.

I see that I am going to have to figure out how to position the photos on the posting. I posted the last photo, above, before any of the others.

 

[annieshalt]

[H3]the same lights i fitted to my passenger cars last weekend .total cost ,£1.00 plus batteries which last for 24hrs. by using re/chargeable ones =endless hours of lighting at very little cost. just going to buy more sets today. they do them in red,white or blue.[/H3]

 

[Madman]

I bought a set of Christmas tree lights, for about $6.00, with fifty LED lights on it. Enough LEDs to outfit six cars, each with eight lights. I did a test before I decided to do the changover. I powered four LEDs with two AA batteries. It was still going strong at 48 hours when I disconnected it. That gave me ample proof that this type of lighting was possible.

 

[Bram]

I presume that no resistors were used then ?

 

[Spule 4]

The only real problem I have with LEDs is they make everything look like the front of a Lexus IS350.....if they could get some that were not blue but a warmish white-to-yellow, I would be sold.

BUT, they are great for a lack of energy consumption, so I guess that is the trade off between these and Edison lamps?

 

[Doug]

Maplin sell warm white LEDs, but Rapid don't.

 

[Rosco]

So can you make up LED circuits without resistors?

 

[Neil Robinson]

So can you make up LED circuits without resistors?

Yes, but IMHO it's better to always include one unless there is some other form of current limitation. Resistors typically cost less than 2p each bought in bulk, and not that much more if purchased individually from a shop.

 

[Rosco]

Thanks for the info Mr Robinson and Mr Ross. Great help indeed.

 

[CoggesRailway]

Very nice- in some ways the incandessent looks more cosy though.. i wonder if yellow LEDs would look better? Either way it's a great job. That stuff is all voodoo to me....

 

[CoggesRailway]

sorry should have read the thread better!

 

[Bram]

Very informative and helpul thread for a complete numty where electrickery is concerned, many thanks guys

 

[Neil Robinson]

For anyone who is somewhat concerned about leds and resistors the two links below should prove helpful.

http://led.linear1.org/1led.wiz

http://led.linear1.org/led.wiz

If you are unsure of a value, just click on the relevant question mark button.

 

[corgi]

I in the past managed to aquire a considerable number of signal diodes that fell off the back of a truck.
If there is a possibility of providing reverse voltage I stick a resistor in one leg and a signal diode in the other leg.

As Neil says resistors are cheap.

 

[corgi]

So can you make up LED circuits without resistors?

Yes, but IMHO it's better to always include one unless there is some other form of current limitation. Resistors typically cost less than 2p each bought in bulk, and not that much more if purchased individually from a shop.

You can BUT if using a power source equal to the voltage required by the led as max voltage input.

However, I agree with this suggestion by Neil. IF you do it properly, then there should be no problems and using a resistor between power supply and led is the proper way when using a voltage ABOVE that of the max of the led. AAs are 1.2v NOT 1.5v as people believe. (PP3's are 8.4v NOT 9v and are only 110 to 150 milliamps.) AA rechargeable can go as high as 1.2v @ 3600 milliamps these days. When the rechargeable are used & after recharging, they can exceed their nominal 1.2v and go over the top...this will blow a LED IF a resistor is not used. Alkaline batteries are expensive to run and then throw away. Use rechargeable batteries and resistor(s)..make solder joints and wiring neat and insulate soldered joints from each other or expect trouble in future!

I would suggest MADMAN cover his joints in the picture shown above with hot glue and mount the leds in a LED holder that can be glued to the roof and still allow the led to be changed.

On the other hand you could use flexi surface mount leds ..say - a three strip or two 3 strips and connect them to a power source (9v PP3 rechargeable) under the floor via a simple on/off switch (no resistors required as they are built into the flexi strip sections). PP3's and AA's can be mounted in a number of different holders these days and the AAs have very neat slim boxes complete with switch either in 2 AA or 4 AA types..

Hope this helps.

I wish to correct the false statement regarding AA's and (v batteries, and to confirmit I have just put my multimeter to them.
AA's alkaline will give 1.6v new at no load, an alkaline 9v will read 9.6v new at no load.

Similar figures will apply to general purpose and heavy duty batteries. The lower voltages are to be expected on rechargeables.

 

[Doug]

My rechargeable AA batteries (Energizer ones) always read about 1.35 volts when newly charged, but drop to around 1.2v when partly used.

 

[Madman]

So if using AA Alkaline batteries, even if the LED is rated at 3 volts, should a resistor still be required? I have been performing experiments with two AA batteries hooked to LEDs. So far the LEDs have been lit for days on end without incident. I am curious to see whether the LEDs will stay lit as the battery power runs out. In other words, how low a voltage will a 3 volt LED run on.

 

[Madman]

So if I hook up a 3 volt LED to two 1 1/2 volt batteries, 3 volts, and place a resistor between the positive battery terminal and the anode, the LED will still light with all of it's brightness?

Or if I had three 3 volt LEDs wired in parallel, as in my passenger cars, and had the same three volt power source, but placed a resistor between the positive leg of the bus bar and the anode, the three LEDs would light and all be protected?

 

[Neil Robinson]

So if I hook up a 3 volt LED to two 1 1/2 volt batteries, 3 volts, and place a resistor between the positive battery terminal and the anode, the LED will still light with all of it's brightness?

Simplistically, if you choose a suitable resistance value, yes.
Personally, I would add another 1.5V battery to the circuit and use a resistor calculated using 4.5V supply and the current quoted for the typical light output. The link below should help with this. Using a suitable resistor to limit the current to a modest value will extend the battery life.
http://led.linear1.org/1led.wiz
Should you choose to click on LED Basics on the above link you will find a lot of further information.

Or if I had three 3 volt LEDs wired in parallel, as in my passenger cars, and had the same three volt power source, but placed a resistor between the positive leg of the bus bar and the anode, the three LEDs would light and all be protected?

With leds in parallel I recommend a separate resistor for each parallel path.
In all cases the polarity of the led matters, but the polarity of the resistor doesn't and it may be connected to either the anode or cathode of the led.

 

[don9GLC2]

So if using AA Alkaline batteries, even if the LED is rated at 3 volts, should a resistor still be required? I have been performing experiments with two AA batteries hooked to LEDs. So far the LEDs have been lit for days on end without incident. I am curious to see whether the LEDs will stay lit as the battery power runs out. In other words, how low a voltage will a 3 volt LED run on.

The links that Neil Robinson gave are very useful. I was considering trying to write a technical explanation for non- technical readers, but it has already been done. Look at

http://led.linear1.org/why-do-i-need-a-resistor-with-an-led/


Using a battery to power the leds is less likely to cause problems than using a mains powered supply, but because of their different characteristics rechargeable batteries are a bigger risk to leds than disposable batteries. My advice to anyone who is uncertain of the technology is to use resistors. They are inexpensive and can save early failures of your leds. Why risk this? (a dark-emitting-diode!) You can calculate the values using the links that Neil provided.