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Enough power ?

Started by Andy K April 20, 2014
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 for the battery.

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

What do you think ?


Andy 
On Sunday, April 20, 2014 10:59:17 PM UTC-4, Andy K wrote:
> 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 for the battery. > > > > I also know that I will have to reduce the voltage. > > > > What do you think ? > > > > > > Andy
Excellent decision to replace AAA batteries with AGM batteries. A 4.5AH 6V battery will supply 4.5 A for 1 hour, or 2.25 A for 2 hours, etc., before recharge. One could build a simple charger, using the fact that for this case, the maximum charging current would be 0.45 A, or 450 mA. Note that VRLA/ sealed lead acid batteries are VERY rugged.
On Mon, 21 Apr 2014 13:57:18 +1000, <dakupoto@gmail.com> wrote:

> On Sunday, April 20, 2014 10:59:17 PM UTC-4, Andy K wrote: >> 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 for the battery. >> >> >> >> I also know that I will have to reduce the voltage. >> >> >> >> What do you think ? >> >> >> >> >> >> Andy > > Excellent decision to replace AAA batteries > with AGM batteries. A 4.5AH 6V battery will > supply 4.5 A for 1 hour, or 2.25 A for 2 > hours, etc., before recharge.
not quite. the 4.5ah rating is at the 20hr discharge rate. the ah rating will be lower at faster discharge rates. also hr needs a float charger that will provide a maximum of 450ma *and* limit the output voltage. it's not hard with an lm317, but for longest life and best performance (especially if you are likely to forget to remove the charger when finished) you should get a small 3 stage charger that is sized for this battery.
On Sunday, April 20, 2014 9:59:17 PM UTC-5, Andy K wrote:
> 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 for the battery. > > > > I also know that I will have to reduce the voltage. > > > > What do you think ? > > > > > > Andy
I did a test 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. Thus I have to limit the current to keep them from burning out. :-) Andy
> I did a test 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. > > Thus I have to limit the current to keep them from burning out. :-) > > Andy
It is really best to current limit supplies to diodes. There are COTS chips for this. If you don't mind low efficiency, I think there is some hack of a shunt regulator to make it into a current limiting device.
On Tuesday, April 22, 2014 11:40:33 PM UTC-5, miso wrote:
> > I did a test which validated a comment I saw that "LEDS will use all th=
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>=20 > > current they can." >=20 > >=20 >=20 > > A nine LED light used .125 amps when powered by 3 AA batteries. >=20 > >=20 >=20 > > That same light pegged out the .25 amp scale when powered from a 1.5 am=
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>=20 > > 5.0 volt source. >=20 > >=20 >=20 > > Thus I have to limit the current to keep them from burning out. :-) >=20 > >=20 >=20 > > Andy >=20 >=20 >=20 > It is really best to current limit supplies to diodes. There are COTS chi=
ps=20
>=20 > for this. If you don't mind low efficiency, I think there is some hack of=
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>=20 > shunt regulator to make it into a current limiting device.
I am looking for something that will not allow the LEDS to draw more than 5= 00 mA. Would this work ? 1 Piece - 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 ef= ficiency) 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 =E2=84=83 to +85 =E2=84=83) (o= utput power 10W or less) Full load temperature rise: 40 =E2=84=83 Load regulation: =C2=B1 0.5% Voltage regulation: =C2=B1 0.5% Dynamic response speed: 5% 200uS
In article <a6e98c89-4e1b-4079-874d-6d3015236458@googlegroups.com>, 
andrewkennedy775@gmail.com says...
> > On Tuesday, April 22, 2014 11:40:33 PM UTC-5, miso wrote: > > > I did a test 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. > > > > > > > > > > Thus I have to limit the current to keep them from burning out. :-) > > > > > > > > > > Andy > > > > > > > > It is really best to current limit supplies to diodes. There are COTS chips > > > > for this. If you don't mind low efficiency, I think there is some hack of a > > > > shunt regulator to make it into a current limiting device. > > I am looking for something that will not allow the LEDS to draw more than 500 mA. > > Would this work ? > > 1 Piece - 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
use a LM317 in current limiting mode. Jamie
On Thursday, April 24, 2014 2:39:40 AM UTC+1, Maynard A. Philbrook Jr. wrote:
> In article <a6e98c89-4e1b-4079-874d-6d3015236458@googlegroups.com>, > andrewkennedy says... > > > On Tuesday, April 22, 2014 11:40:33 PM UTC-5, miso wrote:
> > > I am looking for something that will not allow the LEDS to draw more than 500 mA. > > > Would this work ? > > > 1 Piece - This DC to DC Step-Down Adjustable Power Supply Module is based on the LM2596 switching regulator.
> use a LM317 in current limiting mode. > Jamie
Or a transistor. LED goes from e to 0v, base has resistors from + and 0v rails NT
On Sun, 20 Apr 2014 19:59:17 -0700 (PDT), Andy K
<andrewkennedy775@gmail.com> wrote:

>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 for the battery. > >I also know that I will have to reduce the voltage. > >What do you think ? > > >Andy
--- If the flashlights all work OK as is, I think that - instead of connecting three of them in parallel and driving them with a current source - you'd be much better off connecting them in series and driving them with a voltage source. John Fields
On Sunday, April 20, 2014 7:59:17 PM UTC-7, Andy K wrote:
> 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 also know that I will have to reduce the voltage.
The AAA batteries have enough internal resistance to drive (some) LEDs in parallel with the 'right' current. It's wasteful, though, because battery capacity must be derated for the high drain condition. With 4.5V to play with, you could use a voltage reference, amplifier, and pass transistor to regulate the current. Or, you could use a series resistor (different resistor for each of the LED arrays, they match because they're thermally close). Or, you could use a two-transistor, three resistor current mirror (different mirror for each of the LED arrays). Or, you could go with a full switchmode regulated LED drive (overkill, IMHO). If you want long battery life in emergency, consider a bright/dim switch, too.