End the cycle of replacing AAA batteries :-)

[Magnum]

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

[Magnum]

I am looking for something that will not allow the LEDS to draw more than 500 mA.

Would this work ?

Code Select Expand

This DC to DC Step-Down Adjustable Power Supply Module is based on the LM2596 switching regulator.

Input voltage: 4-40V

Output Voltage: 1.5-35V (adjustable)

Output current: rated current 2A, maximum 3A (heat sink required)

Conversion efficiency: Up to 92% (the higher the voltage, the higher the efficiency)

Switching Frequency: 150KHz

Rectifier: Non-Synchronous Rectification

Module Properties: Non-isolated step-down module (buck)

Short circuit protection: current limiting

Operating temperature: Industrial grade (-40 ℃ to +85 ℃) (output power 10W or less)

I did an experiment  which validated a comment I saw that "LEDS will use all the current they can."

A nine LED light used .125 amps when powered by 3 AA batteries.

That same light pegged out the .25 amp scale when powered from a 1.5 amp 5.0 volt source.

So I concluded that I have to limit the current to keep them from burning out. :-) 

[dedndave]

that power converter is 80% efficient, at best
just put a resistor in series

R=(Vmax-Vled)/I

Vmax is the maximum battery voltage
Vled is the Vf of the LED - they vary, typically from 1.5 to 2.5 V
you can measure the Vf with the max LED current
I is the desired current
because I is a maximum value, calculate the resistor and chose the next higher value that's available

[Magnum]

Thanks SuperDave,

[dedndave]

 :t

[Magnum]

that power converter is 80% efficient, at best
just put a resistor in series

R=(Vmax-Vled)/I

Vmax is the maximum battery voltage
Vled is the Vf of the LED - they vary, typically from 1.5 to 2.5 V
you can measure the Vf with the max LED current
I is the desired current
because I is a maximum value, calculate the resistor and chose the next higher value that's available

Is the second project more efficient ?

http://johnarthur.wordpress.com/2008/06/08/an-efficient-voltage-regulator/

[dedndave]

88% is very efficient, even for a switcher
that's because they are using "new-fangled" stuff (highly techincal term)
that's about the best efficiency i've ever seen for a power converter

however, calculate the efficiency of the dropping resistor and compare
efficiency is an easy formula
n = Pout / Pin

[Magnum]

My charger is putting 180 Mamps into my battery. (SLA)

Why does the charger say 500 Mamps?

I will not let the battery get even close to being discharged to increase it's lifetime.

Andy

[dedndave]

the difference between the charger max output voltage, and the current battery voltage, will determine how much current is drawn
ok - some chargers are well-designed and have constant current outputs - not many

for NiCd batteries, it's a good idea to fully discharge and recharge them every now and then
otherwise, they develop "memory" and it shortens the battery life
this isn't the case for many of the newer types of rechargable batteries
it helps to read mfg specs on the specific battery you are using

[Magnum]

The battery initially had a voltage of around 7.0.

That would explain why it was only drawing 180 ma.

Andy

[dedndave]

i think i mentioned it before...
batteries are a science all their own   :P

i learned something interesting about batteries when i was working for Telonics
http://www.telonics.com/wildlife.php
we made tracking transmitters for all kinds of wildlife - and associated equipment

there are 2 basic transmitter types - those that are tracked directly
and those that send data to a satellite for later retrieval

either way, the battery is loaded in some sort of pulsing fashion
most of the time, very little current drain - occasional brief periods, a larger drain

batteries don't like that pulsing drain
we put very large capacitors across the batteries to take up some of the slack   :P
for larger animals, we might even use 1 farad low voltage caps
in fact, rather than allowing the battery to charge the capacitor,
we would connect the battery to a bench supply to charge it up, then connect it across the battery - lol
the end result was - a longer discharge cycle

[Magnum]

I have looked all over but can not find a battery holder for 18500 batteries.

Some places list this, 18650 17500 18500 Battery Clip Holder Box Case, but is misleading because all these batteries are different lengths.

Seems if they make 18500 batteries, someone ought to have made a holder ?

Thanks,
          Andy

[dedndave]

the 18500 seems to be the same size as a standard AA battery
at least, the sanyo one
the 18650 is longer



Vision makes a tube with "adapter" plugs



http://www.gotvapes.com/index.php?main_page=product_info&products_id=1606

[Magnum]

Mine are .7 inches in width, AA are around .5 inch.

There are too fat to fit in the holder.

Andy

[dedndave]

well - i am sure they have one, someplace - lol
or - you can make your own stuff   :P

http://www.mouser.com/Power/Battery-Holders-Clips-Contacts/_/N-5gbj?P=1yzvpu0