General LED question - batteries and amperage draw

[Will91]

Hi all:

I'm thinking about adding some flashing LED's to my child's ride on vehicle (Power Wheels). I'm looking at something like this by Sho Me..

http://www.able2products.com/update/11_8200_v1.htm

It says each LED unit draws 0.05 amps and is powered by 12VDC and there is a controller that I would have to buy too. I'm hoping I can just use a bunch of alkaline batteries in series (by finding something at RadioShack to hold them) but I'm not sure if alkaline batteries have the amperage capacity to provide constant 12VDC for any length of time - especially for four of these LED units. I couldn't find the mAh rating of Duracell batteries on their site - can anyone give me an idea of the typical mAh capacity of a battery and whether they think four of these LED units at 0.05 mA each will work with a regular battery pack without having to go to a 12VDC lead acid rechargeable battery (such as those used to actually power the electric ride on vehicle). Note, many owners of these vehicles actually tap into the vehicle battery system, but I don't want to do this. Thanks!

 

[Curt R]

Hi Will:

This is a list of the most common batteries, buy US made units as some of the imported types can have as
much as one-half of their listed capacity.

PRIMARY TYPE DISPOSABLE BATTERIES

HEAVY DUTY ZINC
N 1.5 VOLT 460 mA
AAA 570 mA
AA 1100 mA
C 2900 mA
D 6500 mA

ALKALINE
N 1.5 VOLT 720 mA
AAA 1150 mA
AA 2850 mA
C 8350 mA
D 18000 mA

SUPER ALKALINE
AAA 1.5 VOLT 1450 mA
AA 3350 mA
C 10500 mA
D 22500 mA

LITHIUM
1/3 N 3 VOLT 170 mA
AA 1.6 VOLT 2600 mA
CR2 3 Volt750 mA
CR123 3 Volt1400 mA

6.0 VOLT DISPOSABLE LANTERN BATTERIES
SQUARE CARBON ZINC 8000 mA
SQUARE ALKALINE 26000 mA
RECTANGULAR CARBON ZINC 15700 mA
RECTANGULAR ALKALINE 52000 mA

Two 6 Volt Alkaline batteries at 26 amps will power one inch of that light for about 500 hours.

Have fun.

Curt

 

[Will91]

Hi Curt and a belated thank you for your reply.

Question, with a stack of 1.5V AA batteries to nomially equal 12VDC, mAhr is NOT additive, correct? So in other words, the power capacity of the stack is still the same spec as just one battery in the stack, right?

I'm now looking at some LED units that draw significantly more power (0.5A per unit x 4 = 2A). Even so, at 2850 mAhr, I should get close to 90 minutes of illumination time, right? Or, I could go with two 6V lantern batteries in series for even longer run time, correct?

Again, many thanks.

 

[gswitter]

I'm now looking at some LED units that draw significantly more power (0.5A per unit x 4 = 2A). Even so, at 2850 mAhr, I should get close to 90 minutes of illumination time, right?

Alkaline AA cells can't maintain that high of a load. AA's are absolutely an option (if you're OK with about 50-60 minutes of runtime), but you'll need to go with a different chemistry. Check out the graphs in this thread.

 

[Will91]

Thanks gswitter. I just called Duracell and they say their regular AA battery is only 1500mAhr. I'm looking at putting these lights on a child's ride on vehicle (Power Wheels) and they will only be on for short periods of time. I don't know why they don't put these specs on their site - it would be nice to see this spec for their regular batteries, vs. camera batteries, etc. Basically, every choice except rechargeable (although I'm considering a Maha charger and Eneloop batteries). I will have to study the info in the link you provided but it is good to hear the AA batteries will be fine (even if only for a short time).

 

[Curt R]

Voltage, (V), times Current, (I), equals Watts, (P), of a single battery. With two batteries in series the voltage
doubles, the current stays the same. With two batteries in parallel the voltage stays the same and the current
capacity doubles. No matter what or which way, add the the watt total of all the batteries and divide by voltage
output to get current capacity. And do not confuse power capacity, (P), with current capacity, (I), of a battery stack

AA batteries, (Alkaline), are rated for capacity, (C), in (mAh), at a constant draw of 25 mA. At a draw of 1 Amp the
capacity in mAh is 45% or less of the rated capacity, dependent on brand. Alkaline batteries are at their best
when the current draw is at no more than 1/4 C or less.

Curt

 

[LukeA]

...(although I'm considering a Maha charger and Eneloop batteries)...

That is the best-performing option and the cheapest in the long run, especially because the LED products you linked to here (which I hope are for being seen rather than seeing with) draw 0.05A per inch rather than 0.05A total.