jono300

iTrader: (8)

Hi anyone able to tell me roughly how long between charges I will get if I were to run two flashing leds from the following battery ??

12V 0.8Ah sealed lead-acid battery on eBay, also Other Rechargeable Batteries, Rechargeable Batteries, Batteries Battery Chargers, Consumer Electronics (end time 18-Dec-08 18:36:01 GMT)

The battery is to be placed within an outside alarm bell box and as I say will power two so called ultra brite leds.

not sure just how little power leds actually take ?? but would imagine very , very little so would I be correct in saying that I should be able to get a good while ( 6/12 months out off one charge ?? )

The battery itself is said to only loose around 3% per month itself so that would suit my particular requirments just need to know regards the actual length off time between charges if anyone could work out / have a guess ??!!

hux309

The specs of the led would help.

jono300

iTrader: (8)

Okay sorry apart from them being 5mm not too sure exactly ??!!

the leds being used are as follows :

2 x 10mm GREEN LEDS, M/BRITE,12V READY WIRED, PC / CAR. on eBay, also, Modding LEDs, Desktop PC Components, Computing (end time 16-Dec-08 19:05:22 GMT)

have sent a message to the seller asking for tech info so will hopefully get back with an answer for you ??!!

cheers

tanyatriangles

iTrader: (2)

Have a look here: Rapid Electronics - Flashing 10mm LED

and here: Rapid Electronics - 10mm Bezel panel clips

Specs on that site give supply currents of between 6 and 70 mA, so that would give you a run time of between 11 and 133 hours.

jono300

iTrader: (8)

Okay thanks for that even if it was not excatly the news I was hoping for !!!
okay have heard back from the seller off these Leds and he informs me that they consume approx 10mA on each LED so I guess your run time figures dictate that the anwser to my question would " not long enough ""

ahg - back to the drawing board I guess !!

I do have two alternate flashing leds here that run off a small 3v lithium battery and they are said to last up to ten years on the original battery, just a bit confused as to wht these can run for so long even if they are no as bright as the new leds I have here- any idea ??

lastly !!!- okay then as I say have a small 12 v battery in the alarm bell box, these two flashing leds, other than running up and down the ladder every 100 hours or so what are my alternatives in getting power up to these two leds within the alarm box ??

the_msp

1. Bring up mains power and use a 12V power supply... something like this RS | Power Supplies | Power Supplies, Inverters, DC/DC Converters & Generators | Power Supply Units (DIN Rail & Panel Mounting) | Industrial Power Supply Units

2. If you cant use mains, use:

a) a battery with longer life (higher AH rating) or several in parallel...
b) a 555 circuit that uses a PWM (Pulse Width Modulation) to turn on/off the LED so fast that it uses less energy but you can still see it as being lit.

Search online there should be a lot of info as this is often a project done by NC/HNC Electrical/Electronic Engineering students.

AndyC_772

iTrader: (2)

You need more information to have any idea of how long the battery will last.

Leave the LED on 100% of the time, and assuming it uses a series resistor to control the current, it'll draw 10mA from the battery. So, your 800 mAh battery will last 80 hours powering one LED, or just 40 hours powering both.

How much longer it lasts will depend on what proportion of the time it spends turned on. If it's on 10% of the time then, in theory, the battery could last 10 times as long. But that will depend on the device that controls the flashing; it could waste a few mA all the time, in which case battery life will be reduced.

If you need longer battery life then you'd need a dc/dc converter or some other more sophisticated controller. An LED only actually requires 2V or so, which means the theoretical longest battery lifetime could be 6 times longer. For, say, a 0.5 second flash every 5 seconds that would give a battery lifetime of (80 x (5/0.5) * (12/2)) hours, or 200 days for a single LED, or 100 days for both.

A controller that would last that long would be a project for someone with reasonable electronics knowledge... maybe try Maplin or Ebay?

jono300

iTrader: (8)

Okay thanks so much for all your informative replies folks, appreciatte the advice and am certainly a bit wiser now !!

have decided that its deffinately got to be mains power, can get mains power to within the bell box but unfortunatly at £30 + each these power converters within the above link are out off the question for the simple job I require them for in terms off overal cost.

any other cheaper way off converting mains power to the 12v required by these leds ??

lastly - still confused as to why the two flashing leds powered within the lithium battery circuit will last up to ten years before the battery requires replacing / recharging ??

scunnered

iTrader: (1)

An ordinary lead acid battery will begin to sulphate if you let it run down without regular charging.
A deep cycle battery, or an AGM battery is more expensive in the short term but will probably work out cheaper as they would last much longer.

jono300

iTrader: (8)

Okay thanks for the info, to be honest choose the above 12 v batteries as they were recommended as ideal for long periods as back up batteries only suposdly loosing 3 % per month.

The only other battery I have here is a 12 v 8 or 10amp motorcycle battery, given the bigger amps off this anyone work out how long this would last for powering the leds ??

AndyC_772

iTrader: (2)

If it's rated at 8Ah, that means it'll (theoretically) delivery 8A for an hour, or 4A for 2 hours and so on. So, delivering 10mA it'll last 800 hours, or about a month.

How are you going to make the LEDs flash? That'll make a big difference, since the battery drain will be much less during the 'off' time.

To accurately calculate how long it'll last, you need to know:

- the 'on' current for the LEDs (total 20mA)
- the 'off' current, ie. how much is wasted by the flashing circuit even when the LEDs aren't on
- the current that's wasted in the controller when the LEDs are on
- the proportion of the time for which the LEDs are on
- the efficiency with which the 12V output from the battery is converted down to the 2V the LED actually requires. If it's just a resistor, which it usually is, then that's just 16%.

If you can get an LED driver / flasher which includes a dc/dc converter to drive the LED, rather than just a resistor, then you'll get much better theoretical battery life. Better to spend the money on this rather than big batteries IMHO.

Failing that, a 12V mains adapter, a flashing LED, a resistor and a mounting bezel will last forever and would be much simpler and cheaper.

dunx

iTrader: (3)

Try a low power LED with a solar panel and a battery, also turning it off in daylight would help. Easy fix, position near to a 240V socket and drill through the wall, plug in a 12V psu and it's sorted.

DunxC

jono300

iTrader: (8)

Yep cheers mate appreciatte the advice, have 100% decided to just go for the 240 volt method , bit more work but think it will prove a bit easier than replacing batteries every few weeks !!

have a small 240v to 12 v adapter here which I am sure I could utilise so thats fine, but just need to work out the best way off getting a mains cable from a socket thru to the rear off the alarm bell box, any tips ??

wagrain

just run 12volts to the bell box!

Did that on a workshop I had. Plugged an old psu with 12v output into an internal mains socket, then extended the 12v wiring using reclaimed speaker wire, fed out through the wall into the back of an old alarm bell box with a couple of flashing leds I had.
Job done for no cost!

jono300

iTrader: (8)

Yep another idea I suppose I could try, will have a think on see what I can come up with.

thanks again folks appreciatte all the advice given.

Huxley

Just go and raid an alarm company skip there is bound to be an old alarm panel in there just uses that for your 12v supply "Free" I have thrown away hundreds of them in the past, lots of then in working order !

jono300

iTrader: (8)

But surely you have to get the mains power to the actual alarm box in the first place ??!!

dont suppose you are throwing any away in the near future are you ??!!

Huxley

You can just put a plug on a flylead from the alarm panel then run a cable to the bell box ie. alarm cable, I dont like to say this but bt wire is sort of ok and hey presto

I will have a look at what I have got lying around if any

But you are still better off raiding an alarm company skip

Where are you ?

jono300

iTrader: (8)

Perfect mate, located up here in fife, scotland. just let me know if you can sort anything out ??

thanks again for now.