9 volt battery question

[oldrocker]

This may be a dumb question but here it goes.  Is there any difference or an advantage cost wise for using six 1.5 volt batteries as oppsosed to using one 9 volt.  I realize you would have to make more room to house the battery compartment.  Also the weight of the stomp box would increase dramatically.  Would there be any problems with how long the batteries would last and would the guitar effect work any different?  I feel stupid asking this question but I was wondering if this has been done before.

[rhdwave]

I believe that the 4 1.5 volt batteries will actually give more life.  I recently read this in Effects Projects for Musicians...so it should be accurate.

[Connoisseur of Distortion]

it would last a lot longer, i suspect, but otherwise nothing would change.

however, those packs for AA batteries are poorly shaped for stompboxes... as in, waaaaaay too big. you might need to use bigger enclosures for them, ones with more depth. i suspect that the usual 125B, 1590B, or 1590BB will not have enough clearance for a battery pack to fit under the lid!

[Mark Hammer]

The lifespan of the battery isa function of the current drawn from it, compared to the current it is capable of supplying.  Batteries are rated in ampere-hours.  If a battery can supply 0.5 ampere-hours, then it can power something that need 100ma for 5 hours in theory, or something that draws 10ma for 50 hours.

The amount of current it can supply is a function of the chemical capacity to provide all those electrons.  More "stuff" in the container means more electrons for the passing.  This is one of the reasons why flashlights have traditionally used C or D cells, or larger.  If a device is supposed to be for emergency use, AND it consumes lots of current, then it starts to get pretty useless as something that will see you through an emergency.  Most household flashlights WILL work from penlights (AA) or even 9v batteries in some instances, but they will not likely see you through to when the lights come back on because the current such batteries can supply is insufficient, given the current demands of the bulb.

So, all other things being equal, D's have more current capacity (in terms of ampere-hours) than C's, C's more than AA's,  AA's more than AAA's, and six AAA's have more than a 9V, and a 9v likely has more current capacity than three coin-size lithiums.

I say "all other things being equal" because:
a) different types of batteries have different tendencies towards forming high internal resistances that limit current delivery
b) batteries differ in terms of how much current they can give on demand (e.g., the old Polaroid pola-pulse battery was essentially 4 very flat, thin, 1.5 batteries that by virtue of the large surface area between them, pass a LOT of current for brief periods - which is why they were used for flashes)
c) batteries have a tendency to self-recharge to some extent, reversing the chemical state created when current passes, with some doing it more than others.

Six AA's or even AAA's will provide much longer usable battery life than a 9v battery will.  IN some instances, this will be just what you need, while in other instances the difference may not be enough to see you through and an adaptor is really warranted.  The Line 6 Tone Core pedals will all run off a fresh 9v alkaline, but not for very long because the current demand is so high.  The manufactuer included a battery compartment and connector mostly for situations where use of an adaptor was momentarily inconvenient.  For instance, trying a pedal out in a store.  I suppose the pedals could have been built to accommodate 6 AA batteries, but my sense is the disadvantage of the larger case would have negated the advantage provided by longer battery life.  The battery life would not have been extended by an amount that one could consider useful or practical, anyways.

As has come up in discussion here frequently, there is absolutely nothing wrong with buying yourself a six-D-cell holder, filling it with batteries, and using THAT as your power supply for multiple pedals.  It will be pure DC (can't get much better voltage regulation than that!), provide the same voltage to everything, and provide enough current capability that, unless you're running 4 or 5 digital pedals, it should last a while.  If the batteries/holder are mounted on the pedal-board, that's one less thing you have to find an outlet for, too, which can be a real convenience for some folks.

[KORGULL]

Hi, I recently built a Ruby amp into a Hammond 1590BB size box. I used an eight AA battery holder from Radio Shack and it just fit. I could tell that the lid touches the batteries, but it did close and screw down all the way without any problems.

[oldrocker]

Well I guess I have my answer.  With longer battery life using 6 1.5v's is not worth increasing the box size for most stomp box applications.  My application for the effects I'm building is for studio use strictly so I'm now considering changing all my 9 volt battery clips and replacing them with 120v to 9 volt adapter jacks.  Originally I was thinking about cost because of the increase in price between 9 volts and AA's.  Most of the boxes I use for my effects units are sit on a shelf design with no bypass circuit since they are either on or off and not switched while playing.  Although I liked the fact that I wasn't taking up space on my power strips.  Now I'm thinking of some how daisy chaining the power to the effects and just removing the need for batteries altogether.  Thanks for the responses.  There was a lot of useful comments and suggestions.

[calpolyengineer]

One thing to note when using multiple batteries. In series, battery voltages add, but the capacities do NOT. In parallel, the capacity adds, but the voltages don't. So for instance, a 9V battery has about 675mAh. If you hooked up two 9V in series, the combo still only has 675mAh, not 1350mAh. AA batteries typically have about 1200mAh, so you would get about twice the life out of AAs vs 9V. I would say it definately isn't worth the extra space.

-Joe

[stm]

Some food for thought here:

1) You can also put two 9V batteries in parallel for twice the energy storage. Much simpler than 4xAA or 6xAA, and you still have 9V, and if you just have one battery available you can still make it work at the price of reduced battery life.  If you are paranoid about installing batteries with different voltages you can add them with a pair of shottky diodes in series, however this is unnecessary for 9V batteries IMHO.

2) I've found recently some MAXIM DC-DC converters that have programmable outputs between 5 and 15V (MAX632) which accept as input any voltage from 3.5 to 12V or so.  Such a device would allow you to have constant 9V output until the battery is really depleted.  Efficiency is on the order of 85%, so I'm not sure if you will get longer overall life or not.

3) Regarding lead-acid gel batteries for UPS, I found you can "take out" the theoretical Ah (ampere-hour) energy only at very low discharge rates. At moderate to high discharge rates the effective energy you can take out is greatly diminished.  In other words, if you put two batteries in parallel (twice the energy storage) you'll get MORE THAN TWICE the operating time because of the reduced discharge rate imposed on each battery.

Now my question is: is this also applicable to alkaline and carbon composition batteries?  What about those Duracell ULTRA batteries which are supposedly designed for higher discharge rates?

[JimRayden]

2) I've found recently some MAXIM DC-DC converters that have programmable outputs between 5 and 15V (MAX632) which accept as input any voltage from 3.5 to 12V or so.  Such a device would allow you to have constant 9V output until the battery is really depleted.  Efficiency is on the order of 85%, so I'm not sure if you will get longer overall life or not.

How about an emergency switch? You happily run the circuit straight from the battery and when the battery runs dry in the middle of a gig, you just flip the regulator into the circuit and get some bonus time to finish off before changing the battery?

----------
Jimbo

[stm]

How about an emergency switch? You happily run the circuit straight from the battery and when the battery runs dry in the middle of a gig, you just flip the regulator into the circuit and get some bonus time to finish off before changing the battery?
----------
Jimbo

It's a clever idea.  A DPDT switch would allow having "true bypass" for this supply circuit.  Such a supply design poses many advantages:

1) Taking the most energy out of a 9V battery
2) Using 4xAA or even 3xAA batteries instead of a PP3 cell and still have 9V
3) Regulating unregulated external DC power in the range from 5V to 12V into 9V
4) Stabilizing some voltage-sensitive circuits like those with JFETs that need precise voltage references
5) Powering some circuits with 10, 12 or even 15V instead starting from a single 9V battery. Consider BBD's from the MN30xx family, which would have better noise, headroom and THD specs.

[Dave_B]

It's worth mentioning that a 9v is made with 6 1.5 volt cells wired in series.  Pry one open sometime to see what I mean.

For anyone who knows, would those be AAAA's?