Hi

This may be a stupid question , but I purchased a set of 100 miniture Led lights to put around a small tree ( dead) in my garden , they are run off 3x AA Batteries , but they are only lasting a couple of nights before the batteries become flat .
Not sure how to calculate the resistance of these , my feeling is that the inline resistor is not the correct one ! .
cheers
Spike

 

Hello,

What kind of batteries are you using?
The zinc-carbon will have a much shorter life than alkaline batteries:



More info on this page:
https://batteryuniversity.com/learn/article/primary_batteries

Bertus

 

Hi

This may be a stupid question , but I purchased a set of 100 miniture Led lights to put around a small tree ( dead) in my garden , they are run off 3x AA Batteries , but they are only lasting a couple of nights before the batteries become flat .
Not sure how to calculate the resistance of these , my feeling is that the inline resistor is not the correct one ! .
cheers
Spike

There's just not a whole lot of power available in those little batteries. A quick Google search says 2000-3000mAh is typical for alkaline AA batteries.

Let's say you chose resistors to limit each LED to only 1mA, which is not much current. You'd have 100mA for the whole string. At 2000mAh, that would equal roughly 20 hour run time.

Adding more resistance would extend the time some, but at the expense of brightness. Are you happy with how they look now? Would you still be happy if they were half as bright? How long were you expecting to make these batteries last? You can certainly made adjustments, but you'll need to have realistic expectations.

 

Hi
Thanks for your reply , they are Panasonic Alkaline ones ! .
cheers

Spike

Hello,

What kind of batteries are you using?
The zinc-carbon will have a much shorter life than alkaline batteries:

View attachment 166277

More info on this page:
https://batteryuniversity.com/learn/article/primary_batteries

Bertus

 

There's just not a whole lot of power available in those little batteries. A quick Google search says 2000-3000mAh is typical for alkaline AA batteries.

Let's say you chose resistors to limit each LED to only 1mA, which is not much current. You'd have 100mA for the whole string. At 2000mAh, that would equal roughly 20 hour run time.

Adding more resistance would extend the time some, but at the expense of brightness. Are you happy with how they look now? Would you still be happy if they were half as bright? How long were you expecting to make these batteries last? You can certainly made adjustments, but you'll need to have realistic expectations.

Hi
Thanks for your reply , they are quite bright at the moment , I don't understand why they would sell these and not last very long , they where sold has Christmas lights , well you would expect them to run longer than a 2/3 times 4 hour periods ! , and they were not bought from a cheap store ! .
cheers
Spike

 

Were these light strings specifically intended to be used on Christmas trees (or something else that would be on for extended periods of time)? Many LED light strings powered like this are intended for applications, such as camper cabinets, that are only one for a few seconds at a time and that spend the vast majority of the time off. In those applications they last for months and even years.

 

Were these light strings specifically intended to be used on Christmas trees (or something else that would be on for extended periods of time)? Many LED light strings powered like this are intended for applications, such as camper cabinets, that are only one for a few seconds at a time and that spend the vast majority of the time off. In those applications they last for months and even years.

Hi
Thanks for your reply , they were definetly listed has christmas tree lights .

cheers
Spike

 

Outdoor christmas tree lights

 

Even though leds don't consume much , if you have 100 of them they will soon flatten your battery ...

if you want longer life they will be so dim they will hardly be visible ... I know the product you mean , the manufacturer doesn't care ,they look impressive in the shop , by the time you realize the problem you've already bought them.

No way around this except change to rechargeable batteries

 

Hi
Thanks for your reply , they are quite bright at the moment , I don't understand why they would sell these and not last very long , they where sold has Christmas lights , well you would expect them to run longer than a 2/3 times 4 hour periods ! , and they were not bought from a cheap store ! .
cheers
Spike

But how where they intend to be powered? I find it hard to believe that someone would sell lights and not give you a way to power them. Instead of a battery, consider a wallwart. Then just plug the wallwart in and don't worry about it.


As we say, "You can't get blood out of a stone". Each of those LEDs is going to consume current to light them. Your battery is only going to be able to supply so much current befor it is depleted. There is nothing magical that will make them light any longer aside employing a more sophisticated current limitation such as a switching current source.

 

Those things are cheaply produced in mass. The intent is to sell something to a consumer. They work until they don't. And there's no warranty. If you modify them then there's no loss.

Instead of a battery, consider a wallwart.

Good advice. Quick and easy. An old cell phone charger MIGHT light them, but it might not be powerful enough. The voltage is typically 5 volts, which is slightly more than your 3 batteries, but they also typically run at around 500 to 700 mA. I don't know if that can light your lights. It's worth a try though. If you have one laying around from an old cell phone then cut the end off and, using a multi-meter, determine the positive and connect it. See if it works.

CAUTION: WALL WARTS ARE NOT INTENDED FOR OUT-DOOR USE. There's a potential for deadly shock. If you DO use a wall wart then I'd suggest you put it in a tupperware container and seal it in so no moisture can reach it. However, I still advise against it. But out of curiosity, see if it can light them up. It just might work.

 

CAUTION: WALL WARTS ARE NOT INTENDED FOR OUT-DOOR USE. There's a potential for deadly shock. If you DO use a wall wart then I'd suggest you put it in a tupperware container and seal it in so no moisture can reach it. However, I still advise against it. But out of curiosity, see if it can light them up. It just might work.

Exactly. My advice would be to make sure the wall wart and its wiring are covered. Then add proper outdoor wiring to the lights. It can be purchased at most home improvment stores.

 

If you really don't want to plug in for whatever reason, another option would be bigger batteries. Wikipedia says D batteries typically have 12,000-18,000mAh capacity, or roughly 6 times what AAs can deliver. So, if getting six times as much life out of them would be worth it, just rig up a battery pack with 3 D batteries and wire it in to replace the AAs.

 

Those things are cheaply produced in mass. The intent is to sell something to a consumer. They work until they don't. And there's no warranty. If you modify them then there's no loss.
Good advice. Quick and easy. An old cell phone charger MIGHT light them, but it might not be powerful enough. The voltage is typically 5 volts, which is slightly more than your 3 batteries, but they also typically run at around 500 to 700 mA. I don't know if that can light your lights. It's worth a try though. If you have one laying around from an old cell phone then cut the end off and, using a multi-meter, determine the positive and connect it. See if it works.

CAUTION: WALL WARTS ARE NOT INTENDED FOR OUT-DOOR USE. There's a potential for deadly shock. If you DO use a wall wart then I'd suggest you put it in a tupperware container and seal it in so no moisture can reach it. However, I still advise against it. But out of curiosity, see if it can light them up. It just might work.

Hi
Thanks for your reply , that is what I have just done , had a charger 4.5/4.7 v @ 200 mLA , works perfectly .
Thanks to all for your input , great site , great people .
Spike

 

Use 4 strings of light, 25 LEDs each.
Switch them by timing diagram below.
They will look very attractive, still bright
and battery life will last 20 times longer.