Batterys in parallel and in series?

I am designing a circuit with some space restrictions. Unfortunately i can only put 3 AAA batterys in it. I need at least 1.8 volts for the circuit to be operational, so 2 AAA NiMh batterys in series is rated 2.4 volts. If i have this can i also add a single parallel battery, for added Mah. The diode i will be using has a forward voltage drop of .33v at 1 amp. These batterys will have a load of about 500 Ma. Will the (very bad) schematic i have work? Also, will the output voltage of the batterys be somewhere around 3v? One more question, will the load be shared between the batterys?

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Re-design7 years ago
I wouldn't bother adding the third battery.  It's like a chain, it's limited by its weakest link.  What will happen is you pack will only supply the mah of the single battery and then it will be run down.  your other two batteries will be half run down and will only supply 1.2 volts or less, but the resistance of the dead battery will reduce this so you probably won't get any voltage thru the circuit.

Just use 2 batteries and buy the best batteries you can afford.  Then you will get the max use out of them per charge.
astroboy907 (author)  Re-design7 years ago
k... Thanks for clearing this up! Glad i didnt start my project and then have it die halfway before i expected it too. If i redesigned the entire thing, and had it so you can put 4 batterys in the enclosure, then i could have 2 packs of 2 batterys, put the batterys in series, then connect the packs in parallel?  + Diode protect them from charging each other... Would this work? Re-design, Best AAA batteries that looked pretty good were either 1800 or 2300 mah each... If i enlarge the enclosure im pretty sure i can put in AA's and have it run for a long time... Thx!
4 batteries would work great.  wire each pair in series then  connect the two packs + to + and - to -.  You won't need the diode unless you need the diode to drop the voltage.
astroboy907 (author)  Re-design7 years ago
Oh, one more thing, re-design wouldnt the batterys try to recharge each other or would they be safe due to polarity? (and the fact that the batterys in eack pack are in series)

If you put two fresh batt. on one side then two dead batts on the other side they would but if they are close to the same freshness the there is not a problem.
jimc45677 years ago
 Just wire them up in series. This will give you about 3.6 volts. 
astroboy907 (author)  jimc45677 years ago
jimc4567, I was looking for more capacity, not necessarily more voltage, though putting them all in series would give slightly more runtime, as the current would drain out faster than the voltage (maybe? someone correct me if i am wrong...). I believe this would allow to use the batterys until they are completely dead (a good thing in this case, its good to have extra runtime)

Lemonie, I like that idea (i should try it sometime) but i would prefer rechargeable batterys to non, and im not sure if those cells would have very good Mah

I believe the easiest thing to do would be to re-design the casing (i was originally going to do it in a tic tac box, but i can upgrade to a tic tac big pack box :) :)

Thx All! :)
seandogue7 years ago
If you don't have an even number of batteries or all of the batteries are in series, I would not recommend operating like this.you'll end up with a couple of partially discharged bateries and one dead one...makes for messy replacement cycles and unanticipated system voltage droop, since the by-itself battery will deplete just as fast as before, since the current thru it will  not change AT ALL.
lemonie7 years ago
You could get a 9V battery and take it apart - they usually have 6 cells inside them, smaller than AAA.
(use 2 parallel pairs)

Won't work as shown, you have 1.2V shunted with 2.4V. The batteries will die.

astroboy907 (author)  steveastrouk7 years ago
Thx! :)