Battery choice: 9V vs 6 AAs

I'm fixing a kid's toy that was damaged by corrosion (stored with the batteries). The only damaged part was the battery compartment, so I opened it up, clipped off the internal wires to that bit, soldered extensions on them & ran those through holes in the case, in order to put an external 6 AA holder on. As it turns out, the 6 AA battery holder I bought clips onto a 9 V battery attachment, which I had in stock. As I was putting this together, I realized that 6 AAs in series make about 9 V, so I'm wondering why a toy would run on 6 AAs when 1 9V would be smaller & easier?

(Yes, I know it should be "cells" rather than "batteries".)

Thanks.

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Reply to
Adam Funk
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Look up the amount of current the AAs can supply vs. the 9 volt.

Reply to
Tom Biasi

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The capacity of the AAs is much greater than the capacity of the 9V. 

John Fields
Reply to
John Fields

As well as being way cheaper per amp-hour.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

It's simpler, change one battery rather than six.

It's generally cheaper, or rather, the outlay at a given time is less with a 9v battery, though of course you probably buy batteries more often.

Less space is required, which might be a factor.

Take one of the old 27MHz license free walkie talkies, that all ran off

9v. If they'd used 6 AA batteries, They'd either have to make the case longer or wider to fit those extra batteries, and even if the per unit cost is tiny, it adds up over the production run. Likewise the 9v battery needs just the connector, while AA need a battery holder.

There were 9v batteries before transistor radios, though bigger units if I get the picture properly. Then transistor radios came along, and they added the 9v battery. For lots of things, it's not optimum, but it's cheaper. You can buy little caps that fit onto 9v batteries to add a switch and an LED bulb, nice little flashlights. 9v is overkill, but you need more than one 1.5V battery to light the LED, so the 9v battery is simpler and cheaper.

Michael

Reply to
Michael Black

HAHA.

Got these elcheapo meters from Harbor Freight. At one time they were on sale for like $3.99. I looked at a nine volt battery in the store and it was $4.99.

Actually if you can grab their coupons, they actually give these meters away for free sometimes. Meter = free. Battery = ridiculous.

Reply to
jurb6006

As has been mentioned, 6 AA cells have a lot more capacity than one 9 V battery. To put some numbers on it:

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Look at the first graph in both data sheets. At a constant 10 mA load, the 9 V will last about 60 hours, while the stack of AAs will last about

320 hours; the AAs last 5.3x as long. In the second graph, at a constant 100 mA, the 9 V is good for 3 hours, while the AAs are good for about 27 hours; the AAs last 9x as long.

You do pay for it in weight and size; the 9 V battery is 45 g and about

22.8 cm^3, and the 6 AAs will be about 144 g and about 50.4 cm^3.

Looking at pricing, Wal-Mart sells a two-pack of Rayovac 9 V batteries for $5.47, or $2.735 each. They sell a 4-pack of Rayovac AAs for $2.97 ($0.743 each) or an 8-pack for $4.97 ($0.621 each). This makes a string of 6 AAs cost something around $3.73 to $4.46; more expensive than the

9 V battery, but also better performance.

Matt Roberds

Reply to
mroberds

Do the math, and you see that the capacity/weight tradeoff is better for AA than 9V, too. I realize that you'd need to redo the computations with constant power rather than constant current, but I suspect the AA cells will still come out ahead most of the time.

For a new-equipment design, I'd lean toward a pair of AA cells and a boost regulator, unless there's some really compelling reason not to.

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Tim Wescott 
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Reply to
Tim Wescott

Like if the toy has a motor?

Reply to
Tom Biasi

Years ago the 9 volts were made of flat cellsand not in much of a case. Later they were made of what looks like AAA cells or so. I have not opened one up in a while, so don't know what they look like now.

Reply to
Ralph Mowery

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And all that bluster has what to do with the capacity of a 9 volt 
battery made from 1.5 volt AA cells VS the capacity of your 
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Reply to
John Fields

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Thanks, Ralph, posting what you're clueless about is ever so 
helpful. 
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Reply to
John Fields

Way high production products have different economies than most of what I work on.

If the toy has a motor then I'd lean toward a 3V motor instead of a 9V motor, running straight off the batteries.

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Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

The Duracell data sheets have curves for constant power, constant resistance, and even constant temperature. I just grabbed the constant current numbers because that was the first chart in both sheets. :)

Availability is another factor, too. If you go to the general store, AAs are available in everything from 4 packs up to 20 packs or more, and they have a lot of them. 9 V batteries come in 1, 2, or 4 packs, and they have some. D batteries come in 4 or 8 and they have some. C batteries come in 2 or 4 packs, but they don't stock many of them.

As a user, I like designs that use AA cells. If it doesn't take much juice at all, or I don't think I'll use it often, I'll put primary cell(s) in there. If it takes a lot, I can often run NiMHs, but still have the option of using primary cells if I am caught short.

Matt Roberds

Reply to
mroberds

Maybe he was suggesting getting the meter for free with the coupon, and then using the 9v battery in something else.

I was suprised a couple of years ago to find that the cheap DMM I bought at the hardware chain store here used a 9v battery. "Everyone knows a DMM should use AA batteries".

Michael

Reply to
Michael Black

I wasn't sure if that was a transition, or just different companies doing things differently.

Yes, I remember the stack of cells and then about 20 or 25 years ago taking a 9v battery apart for something, and finding the "AAA" batteries inside. But I wasn't taking apart a lot of 9v batteries, so I wasn't sure if there was a pattern or not.

Michael

Reply to
Michael Black

One thing (maybe the *only* thing) in favor of 9V batteries is that their snap-in contact system seems to be much more reliable than that of standard cylindrical cells, especially chains of cells.

(This may be an unfair comparison, since 9V batteries are usually only found in low-current applications, and it may be that the higher current in the multi-cell products is the culprit causing the terminal corrosion.)

Best regards,

Bob Masta DAQARTA v7.60 Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusiq generator Science with your sound card!

Reply to
Bob Masta

Maybe my Fluke meter is not any good because it uses a 9 volt battery. Guess that I should ask for my $ 350 back.

Reply to
Ralph Mowery

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I think Michael Black's comment was supposed to be joke-ish since - 
as far as I know - all  battery-operated DMMs are powered by 9V 
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Reply to
John Fields

I don't know, I was thinking someone had mentioned Fluke used 9v batteries.

But my 1984 Radio Shack DMM uses AA (two), my 1996 Radio Shack DMM uses 3 AA, but the cheap one from the hardware store uses a 9v. It surprised me, that's all.

Michael

Reply to
Michael Black

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