battery life caculations

[MrDEB]

using AA batteries rated at 2000mah using 3 in series = 4.5v but if I put another 3 AA batteries in parallel would this increase the 2000 to say 4000mah?
circuit draws 18ma but it runs only 30 seconds every 3 minutes which calculates out at 6660 minutes but placing the extra battery pack in parallel will I double the mah of the total battery pack?
Trying to be conservative
Would love to go with C or D batteries but no room in enclosure..

 

[Sceadwian]

It won't quiet double it, and you'll have charging considerations, series + parallel packs need to be balanced every now and then moreso than a simple series pack. If you don't change the charger to accommodate the life of the pack at least as far as the number of charge/discharge cycles go will probably go down a little bit, also because two cells never match, let alone three in series let alone three series two parallel you'll probably increase the zero power drain of the batteries as the stronger of the batteries tries to charge the weaker one's and the cells internal resistances leach out just a little bit more power when not being used.

No thought given to a Lithium pack? Least as long as you can match the voltage you need.

 

[crutschow]

I believe the op is taking about non-rechargeable alkalines since he said he's getting 4.5V from three batteries in series. In that case there certainly should be no problem with putting two banks in parallel (as long as they are all replaced at the same time).

 

[Sceadwian]

In the OP's application for a primary cell what you say is generally true, though you'll still have to de-rate for cell imbalance from assembly variances. You can't simply slap packs in parallel.

I would said a conservative measure of total pack capacity that would transfer would be 98% or so, at least for primary cells. But as the duty cycle lessons the pack will self drain faster than a single cell will.

 

[MrDEB]

Yes this is using Alkline non rechargable batteries.
Circuit utilizes an 18F1220 PIC and an LM386. Have an LED but planning on removing it rom circuit.
Thanks for the input people. Now to locate a better amp than the LM386?. Only amplifyig a square wave so quality is really not a consideration per say.

 

[MrDEB]

may have found alternative to the LM386
The LM4871 has a higher output but slightly higher quiescent current.
any opinions?

 

[audioguru]

Your battery will be 4.5V only when it is brand new. Its voltage will quickly drop to only 3.6V when the amplifier IC will not work then the voltage will drop slower to about 3V when it should be replaced.

The minimum supply for an LM386 is 4V when its undistorted max output into 8 ohms is only 75mW. A speaker will sound faint like headphones laying in a chair. A square-wave will produce only 150mW which will sound only a little louder.

Use a TDA2822M bridged amplifier IC. It is also in an 8-pins case, has a minimum supply of 1.8V and does not need a huge output coupling capacitor. With a 4V supply its undistorted output is 550mW into 8 ohms or 1100mW with a square-wave.
Its idle current is 1.5 times more than the LM386.

 

[MrDEB]

NOTE the output is connected to a piezo tweeter (am reworking the bird/bat repellent unit)
will look at the TDA2822.
My problem is the tweeter is 3.5 x 3.5 square with 1.75 " (mounted its 1.5" aprox into the enclosure)
Still need to put batteries inside. was looking at https://www.mouser.com/ProductDetail/Bulgin/BXS013-1/?qs=DiYbA0fqsPpzvzoLpQircQ==
then one can install new batteries without opening the entire enclosure which is $18 by itself (https://www.mouser.com/ProductDetail/PacTec/84446-510-332-OD56-20/?qs=nRD1PKnFC2F2P2%2bi2Box%2bQ==) Polycarbonate for outdoor use.
If I can find a smaller piezo that can be used outdoors?
this designing is not easy but kinda interesting as well as fun.
using Google Sketchup to check parts fit.

 

[audioguru]

With only a few volts peak-to-peak into a piezo tweeter then it will not be loud enough to repel anything. The loudness drops as the battery runs down.
The low loudness might attract curious birds, bats, dogs, deer or polar bears. If somebody tries it in Florida then it might attract alligators and criminals.

 

[MrDEB]

Increase voltage perhaps?

I contemplated increasing the voltage and using (already in circuit) a LDO 5v reg.
Too many variables. At present, the Kritter Ridder scares the hell outta birds at 200 yards (using the H bridge amp) but that IMO would be too loud for in town use. YES you can hear the unit mounted on a car going 50mph towards you using the H bridge at a 200 yard distance. THANKS for the design. I tried using 330 ohm resistors in place of the 1k but the unit didn't work? Presently using the LM386 to rid area of bats (15khz +)
Trying to decipher a data sheet and use a dust boot https://www.electro-tech-online.com/custompdfs/2012/01/c1221_21.pdf
the switch I am looking at states a size on the thread but??
https://www.sci.com.tw/PRODUCTS/switch/(R13) PUSH SWITCH/R13-512.htm
what is M7*0.75

 

[audioguru]

I contemplated increasing the voltage and using (already in circuit) a LDO 5v reg.

A low dropout 5V regulator does not have an output of 5V when its input is only 4.5V or less. Its input must be at least 5.5V.

At present, the Kritter Ridder scares the hell outta birds at 200 yards (using the H bridge amp) but that IMO would be too loud for in town use.

In this thread we are talking about using a bridged audio amp which is almost the same as an H-bridge.

YES you can hear the unit mounted on a car going 50mph towards you using the H bridge at a 200 yard distance.

Doppler says that the frequency increases when a sound source is moving towards you. Then the 25kHz will be maybe 30kHz. Can anybody hear 30kHz?
But maybe the piezo piece of junk is distorting badly and causing sub-harmonics which can be heard.
The frequency decreases when the sound source is moving away.
Haven't you heard an airplane, fire truck or ambulance go past?

I tried using 330 ohm resistors in place of the 1k but the unit didn't work?

What are you talking about? There is no schematic in this thread.

 

[MrDEB]

OUPS no schematic

The two resistors R1 and R2 are 1k and it was suggested to change to 330 to lower the capacitance of the P channel mosfets. The input voltage is 12-14v
https://www.electro-tech-online.com/attachments/combo-hot-png.44892/.
sorry about leaving out the schematic.
On the LDO reg--I must of had a brai freeze- dUH only have 4.5 v input.
Maybe up the battery voltage so I increase the output of the TDA2822 and solve the low voltage supplying the LDO reg.

 

[MrDEB]

change of plans to eliminate ANY exposed componets (push button etc)
go with a hall sensor https://www.mouser.com/ProductDetail/Honeywell/SS41/?qs=sGAEpiMZZMtdU8v/CHkq39AvnkiVL6ci
use a mosfet to do the actual switching of power off/on

 

[Diver300]

what is M7*0.75

It is a metric thread size. 7 mm diameter with a thread pitch of 0.75 mm.

https://www.newmantools.com/tech/threadmf.htm

That is a really, really odd thread size as threads between 6 and 8 mm are rarely used. Also, it is metric fine, as metric coarse, which is the standard one, would be 1 mm pitch at 7 mm diameter.

However, the nuts that hold switches and potentiometers into panels are supplied with the switches, so it's not as though you have to buy the nuts separately.

 

[MrDEB]

The rubber boot screws onto the thread so I am outta luck using an external push button. Looking at some polycarb enclosure that have doors rated to IP67. COST? waiting to hear back. Using these I can put the batteries and everything else inside same enclosure
**broken link removed**
planning on using 6-12 AA batteries. Need at least 9 volts (using a protection diode to prevent reverse polarity.)Cheaper than using a P mosfet.

 

[KMoffett]

Besides the other comments, except for trying to make a ~1/2" thick battery pack, why use series/parallel AA batteries? Just move up to C or D cells.

Ken

 

[MrDEB]

I need the voltage. I could go with C batteries aif the ;inked enclosure is cheap enought.
At present the enclosure I was going to use costs $18 plus the battery enclosure ( weather proof)https://www.mouser.com/ProductDetail/Bulgin/BXS013-1/?qs=DiYbA0fqsPpzvzoLpQircQ== Now were up to $30 just for the enclosure but only 4.5 volts (3 - AA batteries) plus running outta room.
I want to be able to change batteries without removing the main enclosure top and bottom (https://www.mouser.com/ProductDetail/PacTec/84446-510-332-OD56-20/?qs=nRD1PKnFC2F2P2%2bi2Box%2bQ==.
LOTS of roadblocks when designing a product for market.