Replace AAA batteries with a rechargeable battery

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fixit · #1 Post by **fixit** » Mon 21 Apr 2014, 02:43

I am looking to replace AAA batteries with this AGM battery.

4.5 AH 6 VOLT

It would power 3 flashlights that have 9 LEDS each that each use 3 AAA batteries.

I would also get a NOCO Genius 6v 12v 750 mA Wicked Smart Battery Charger G-750 to charge the battery.

I also know that I will have to reduce the voltage.

What do you think ?

Andy

greengeek · #2 Post by **greengeek** » Mon 21 Apr 2014, 06:46

Sounds like a good idea to me. I just did something similar - I put 3 LED torches in series and ran them off a 12v battery. Each torch normally runs off 4.5volts (3 x 1.5 v AAA cells) so I figured that 3 x 4.5 = 13.5v which is a close enough match for the 12v battery.

It'll be a bit more difficult to use a 6v battery - two torches in series probably wont work off a 6v battery (might be worth a try though...). Any chance you could get two of those 6v batteries and put them in series to make 12v?

If you are sticking with the 6v battery and putting the 3 torches in parallel you will need to use a voltage dropping resistor (probably 1/2 watt power rating) in series with each torch. Is that the sort of thing you were planning? I looked at doing that in my torches, and it would have been simple because they already had an easily accessible dropping resistor (suitable for the 4.5v supply), but then I decided to do the 3 torches in series.

If you are going to attach the battery charger while the torches are connected it might be wise to keep an eye on what voltage the charger climbs to - could easily go way above 6v during the charge phase and that might be harmful to the LEDS if it goes too high.

I don't know how reliable my series torches will be in the long term as I only completed it last weekend... Hoping it should be good. Certainly seems bright

.

fixit · #3 Post by **fixit** » Mon 21 Apr 2014, 19:06

Thanks for the help.

I am going to hook them up in parallel.

I will disconnect the battery when charging the battery.

PANZERKOPF · #4 Post by **PANZERKOPF** » Mon 21 Apr 2014, 19:55

fixit wrote: I also know that I will have to reduce the voltage.
What do you think ?

Most flashlights should have internal DC/DC converter with automatic voltage
regulation so small difference of input voltage is not a problem.

chironÂ² · #5 Post by **chironÂ²** » Tue 22 Apr 2014, 04:09

Actually, what the resistor does, it reduces the CURRENT. You can operate LEDs with pretty much any voltage, as long as the current is limited. So best bet would be to run them off 6V and replace the resistor accordingly. If you want to be on the safe side, you can integrate a step down converter. Then you could also use the torches with the charging device attached. Plus you would gain some battery time, becaus lights then would start to get dim when the battery reaches 4.5V, whereas with a series resistor, lights would go dim as soon as the battery starts dropping in voltage.

Burn_IT · #6 Post by **Burn_IT** » Tue 22 Apr 2014, 10:23

By the way you should remember that a 12v car battery is actually 13.2 volts as the cells output 2.2 volts each. Similarly a 6V car battery is 6.6Volt.

Moat · #7 Post by **Moat** » Tue 22 Apr 2014, 11:54

Burn_IT wrote:By the way you should remember that a 12v car battery is actually 13.2 volts as the cells output 2.2 volts each. Similarly a 6V car battery is 6.6Volt.

Yes - and that little additional voltage might actually be enough to overdrive the LED's, shortening their lives considerably. LED's - unlike most metallic conductors - actually decrease in resistance as they heat up. That can lead an overdriven LED to "thermal runaway", where the decreased resistance allows more current flow, which causes more heat, which lowers the resistance, which allows more current, etc... until PooF! Magic smoke gets released, or the LED's get dim over a short span of time - or just fail. All of the while being driven at a constant voltage.

That's why LED's (as chiron mentioned above) are spec'd as current limited devices (with a rated maximum current), and not strictly as voltage limited. They do have a forward voltage (Vf) at which they will reach their rated current, but it can vary by a few tenths of a volt between LED's - even within the same batch. Best to regulate current, or stay well below the overdriven, thermal runaway threshold if using a voltage regulator. Cheap lights use dropping resistors and the (alkaline) batteries' own internal resistance/Vdrop under load as a coarse but inexpensive way to limit current - but are often a bit overdriven anyways (for the "Wow!" factor), and typically won't last anywhere's near their stated life before dimming noticeably or failing outright (often stated as 10,000 to 100,000 hours).

Also, the quality of the LED (i.e. - manufacturer) can have a huge influence on longevity and tolerance to being overdriven. Some of the better LED's (i.e. - Cree, Nichia, Phillips/Lumileds) can actually increase slightly in brightness over the first 100 hours or more, when driven at their rated current - while other cheap, no-name import LED's might not even make it to 100 hours, before dimming significantly - the little 3 and 5mm (T3-5?) epoxy-encapsulated, 20-30mA LED's generally being worse than the high-power, =>1 watt, silicone-encapsulated/copper heatsink LED's in that regard.

Lots of info here (too much, really) - http://www.candlepowerforums.com/vb/for ... styleid=24

Bob

Ted Dog · #8 Post by **Ted Dog** » Tue 22 Apr 2014, 14:22

Replaced my RV... Caravan 12v lamps with LEDs The newer generation light output is far better than past and price for 10 was same as price for one of first gen. leave two sets running at all times. They have built in regulators to handle full range from dead battery to solar open circuit voltage. What is nice is no change in output light. Lost main power one night and my TV stopped working.. but lights did not flicker or dim when automatically change over to battery banks. Was planning on getting new TV till I heard the reset beep from the system automatic switch back to mains. TV worked again...

Great LED lights.

Ted Dog · #9 Post by **Ted Dog** » Tue 22 Apr 2014, 14:41

NOCO Genius be careful using this and running LEDs at same time. The Battery chargers of that type have very messy spikes ( on purpose) to charge batterys and reduce sulfate build up on battery. Its a good charger for batteries but should not be run in parallel with a load.. All my chargers are shunt type with clean voltage so do have a sulfate issue I deal with directly by planned over voltage monthly ( I directly attach 120watt solar cell for a day for open cell and disconnect my AGM battery bank durable the event )

fixit · #10 Post by **fixit** » Wed 23 Apr 2014, 22:57

I decided against the Noco.

It charges at 750 Mah when 450 - 500 would be better for a 4.5 Ah battery.

linuxbear · #11 Post by **linuxbear** » Fri 25 Apr 2014, 19:04

I built a rechargeable battery pack and put it in a candy tin. It has a USB output so I can plug many things into it, but my main rule when putting this together was that I had to have a voltage regulator inside the candy box. I do not care for surprises and have no intention of "letting the smoke out" of my Tablet or phone.

greengeek · #12 Post by **greengeek** » Fri 25 Apr 2014, 19:39

linuxbear wrote: I had to have a voltage regulator inside the candy box.

Did you use an 'of-the-shelf' regulator of some kind, or build one from discrete components? I am currently wanting to build a regulated +5v usb power supply that I can drive from the 15v input to my Toshiba laptop (don't get enough power from the inbuilt usb ports and it causes problems with my usb HDD)

fixit · #13 Post by **fixit** » Sat 26 Apr 2014, 23:01

http://www.ebay.com/itm/New-LM317-Adjus ... 4864845f4f

This will reduce the voltage to any voltage from 1.25 -> 28 volts.

chironÂ² · #14 Post by **chironÂ²** » Mon 28 Apr 2014, 03:39

This kind of regulator (linear voltage) just turns the surplus energy (difference in voltage x current) into heat. Not quite what you want with batteries, they drain as fast as without a regulator. You would need a switching converter. They usually have efficiencies >90%. And are in the same price range.

Geoffrey · #15 Post by **Geoffrey** » Mon 28 Apr 2014, 06:17

what about two diodes in series with the supply line to the LED's, silicone diodes have 0.7volt voltage drop so if you have two on a 6volt battery that will give 4.6volts output,

Code: Select all


voltage drop of 0.7 volts per diode

                    |\  |       |\  |
   6v in          | \ |  +   | \ | +  4.6v out
+------------------|  >|------| >|------------------>
                    | / |       | / |
                    |/  |       |/  |

linuxbear · #16 Post by **linuxbear** » Mon 28 Apr 2014, 18:45

greengeek wrote:
linuxbear wrote: I had to have a voltage regulator inside the candy box.
Did you use an 'of-the-shelf' regulator of some kind, or build one from discrete components? I am currently wanting to build a regulated +5v usb power supply that I can drive from the 15v input to my Toshiba laptop (don't get enough power from the inbuilt usb ports and it causes problems with my usb HDD)

i chose an off the shelf 5v. regulator because it was easier. Also, I think it had a little metal heat sink which I attached to the tin with a screw

linuxbear · #17 Post by **linuxbear** » Mon 28 Apr 2014, 18:51

greengeek wrote:
linuxbear wrote: I had to have a voltage regulator inside the candy box.
Did you use an 'of-the-shelf' regulator of some kind, or build one from discrete components? I am currently wanting to build a regulated +5v usb power supply that I can drive from the 15v input to my Toshiba laptop (don't get enough power from the inbuilt usb ports and it causes problems with my usb HDD)

... or the simple solution might be a powered USB hub? I velcroed mine to the back of the monitor so I am only plugging one USB plug into the laptop. The rest are plugged into the hub which supplies about 5 volts and 500ma to each port

greengeek · #18 Post by **greengeek** » Mon 28 Apr 2014, 20:51

linuxbear wrote:... or the simple solution might be a powered USB hub? I velcroed mine to the back of the monitor so I am only plugging one USB plug into the laptop. The rest are plugged into the hub which supplies about 5 volts and 500ma to each port

Yes, that is exactly what I am hoping to do. It's just that I wanted to supply the power to the hub direct from the 15v power cord that feeds the PC, rather than having an extra mains powered adapter power cord strung up to the hub.

I thought it would be nice to have the one 15v supply cord to the PC, and piggyback that up to the hub by going through a 15v to 5v reducer on the way (more velcro

)

fixit · #19 Post by **fixit** » Mon 28 Apr 2014, 23:04

I can't find any .7 volt Zener diodes.

Maybe if I go to a 12.6 volt battery, I can find one that will reduce down to 4.5 volts.

greengeek · #20 Post by **greengeek** » Mon 28 Apr 2014, 23:08

I think you can use a standard silicon diode as a 0.6v zener just by using it in "forward bias". (All a zener is is a chain of diodes placed end to end and biased backwards)

Not all silicon diodes have exactly a 0.6v drop though - some may give you the 0.7 you are looking for.

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Replace AAA batteries with a rechargeable battery

Replace AAA batteries with a rechargeable battery

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