How long does a 9v battery actually last?

[gutsofgold]

How long should a 9v last in a regular opamp based fuzz/distortion box assuming it has an LED?

I just realized I forgot to drill for the DC power jacks on two boxes...that are already painted!
If I can get away with buying batteries at a reasonable rate, I'll just leave the boxes the way they are because I LOVE the way they turned out and wont risk chipping the paint.

[petemoore]

How long should a 9v last in a regular opamp based fuzz/distortion box assuming it has an LED?
  Pretty long, many hours at least I guess. What's the current draw of the pedal, what kind of battery etc. etc....nah.
  Way I figured it is measure the voltage on the battery while watching the clock, and it depends on how low a battery you or the circuit considers still 'last'ing.
  I remember them lasting best between about 9.5v or so to about 7v, at which point the circuits generally start acting funny...depends, FF's seem to like LV suppy.
  I just realized I forgot to drill for the DC power jacks on two boxes...that are already painted!
If I can get away with buying batteries at a reasonable rate, I'll just leave the boxes the way they are because I LOVE the way they turned out and wont risk chipping the paint.
  You have a switch on the battery, input jack battery lift switch trick ?

[R.G.]

How long should a 9v last in a regular opamp based fuzz/distortion box assuming it has an LED?

Honestly, there is no way to tell from that because a "regular" opamp based fuzz distortion box with an LED does not exist. They're all over the map. They could be from 1ma up to 100ma for similar circuits.

Batteries are rated in ma-hours, that being the number of hours the battery will last when you pull out a constant 1ma. If you pull 10ma, they last about the ma-hr rating divided by ten, etc. It's not exact, but it's close. "Exhausted" is a sloppily defined point too. As noted, about 7V or so on a 9V battery is where most makers would say it's all over, but obviously some effects would keep running at that voltage.

Batteries vary too. Old carbon-zinc ones were commonly 100-160ma-hr. Modern super alkaline may be 500ma-hr.

Your best way to guess is to measure the current your effect draws, then doing a min-max calculation on the kinds of batteries you buy.

[Processaurus]

Drilling your boxes won't be any harder on them than stomping on them and transporting them around...  I use little bits of flat rubber to protect mine when I throw them in the vise to drill them.

I looked up mAh for alkalines and found this shop, interesting comparison between different sizes of batteries.  Made RG's idea of having a 6 pack of D cells on a pedalboard seem much more reasonable when you know they got your back with 16500 mAh. 

lemme see 9v coppertops are $1.25 in bulk, 580 mAh,  = .21 cents per mAh
6x D cells (to equal 9v) in bulk are $7.14 ($1.19 apiece), 16500 mAh = .043 cents per mAh

so it'd cost about a 5th as much to power the pedals with D cells than 9v's


I haven't been able to find a long skinny commercial D cell battery holder that is 6x, end to end, as would be ideal to go along the back of a pedalboard.

[jakenold]

Drilling your boxes won't be any harder on them than stomping on them and transporting them around...  I use little bits of flat rubber to protect mine when I throw them in the vise to drill them.

I looked up mAh for alkalines and found this shop, interesting comparison between different sizes of batteries.  Made RG's idea of having a 6 pack of D cells on a pedalboard seem much more reasonable when you know they got your back with 16500 mAh. 

lemme see 9v coppertops are $1.25 in bulk, 580 mAh,  = .21 cents per mAh
6x D cells (to equal 9v) in bulk are $7.14 ($1.19 apiece), 16500 mAh = .043 cents per mAh

so it'd cost about a 5th as much to power the pedals with D cells than 9v's


I haven't been able to find a long skinny commercial D cell battery holder that is 6x, end to end, as would be ideal to go along the back of a pedalboard.

But those D-cells are huge! 

[stm]

This was addressed in detail here:

http://www.diystompboxes.com/smfforum/index.php?topic=41922.msg362255#msg362255

and here:

http://www.diystompboxes.com/smfforum/index.php?topic=41922.msg362294#msg362294

The second post contains an approximation for 9V alkanline battery based on the avaliable manufacturer's datasheet.

[puretube]

How much?

[mdh]

I haven't been able to find a long skinny commercial D cell battery holder that is 6x, end to end, as would be ideal to go along the back of a pedalboard.

DIY it! I was into model rockets when I was a kid, and one time I really wanted to do a launch, but the old 12V lantern battery that I used to power my launcher (and play with my DIY solenoids and electromagnets, etc.) didn't have enough juice to burn up the rocket engine igniter. So I ran in the house, crammed some AA or maybe C cells into an unsuspecting length of plastic pipe, et voila! the launch was saved.  You really only need one end of the battery pack to have a spring, and you can salvage that from any prefab battery holder.  Sure, there are some details to work out, but the obvious thing would be to take a piece of pvc or abs pipe of a close enough diameter, cement a cap on one end, and a fitting for a screw cap on the other end.  Put yer contacts in those caps, drill holes for wires, and you're good to go.

[earthtonesaudio]

Get batteries for free.  There are several places around my town that have public drop-off of batteries for recycling.  Whenever I need them, I grab a bunch of 9V's out  of there, and either use the tops for battery clips, or recharge them...

That's right, recharging alkaline "non-rechargeable" batteries.  I haven't bought batteries in a long while. 

Here's the DIY method for the recharger:
http://www.afrotechmods.com/reallycheap/batteries/batts.htm

[mac]

My Rangemaster has 6 x AAA alkaline batts, at 0.25ma or so they should last for centuries.
But most likely batts will start to leak. So I have to keep and eye on them.

I haven't been able to find a long skinny commercial D cell battery holder that is 6x, end to end, as would be ideal to go along the back of a pedalboard.

Maybe at www.batteryholders.com/d-cell.shtml

mac

[Mark Hammer]

One frequent source of battery drain is the status LED.  If you have a "garden variety" LED in there, consider trading up to a superbright LED.  For the same current, they glow a lot brighter, which means you can get all the glow you need for a fraction of the current.  If a 2k2 series resistor gets you sufficient brightness right now, then you should be able to get away with at least 12k using a superbright.

[earthtonesaudio]

One frequent source of battery drain is the status LED.  If you have a "garden variety" LED in there, consider trading up to a superbright LED.  For the same current, they glow a lot brighter, which means you can get all the glow you need for a fraction of the current.  If a 2k2 series resistor gets you sufficient brightness right now, then you should be able to get away with at least 12k using a superbright.

+1 to that.  A couple of my fuzz face derivatives consume more than 3x the power when the LED is on.  I'll have to get some superbrights.  Thanks for the tip!

[gutsofgold]

One frequent source of battery drain is the status LED.  If you have a "garden variety" LED in there, consider trading up to a superbright LED.  For the same current, they glow a lot brighter, which means you can get all the glow you need for a fraction of the current.  If a 2k2 series resistor gets you sufficient brightness right now, then you should be able to get away with at least 12k using a superbright.

I will keep this mind, thanks!

[Mark Hammer]

Not to harp on it too much (yeah, like THAT ever stopped me! ), but batteries can also be extended by doing whatever you can to maximize the visibility of whatever LED you do use.  So, setting it against a dark background, either by using a dark colour for the chassis, or by sticking it in a black plastic bezel, can give you the latitude to cut back on the current to the LED even more and maybe squeeze a few more hours out of the battery.

As I have written here many times, nonrechargeable batteries CAN be "rejuvenated" in a charger, but there are some stringent ground rules for doing so productively and safely:
1) Never leave the battery unattended in the charger for longer than an hour, and even then you should touch it once in a while to make sure it isn't getting too warm.  Not a bad idea to recharge for an hour, let it cool off, for a few hours, then give it another 60-minute zap at a later point.  Batteries can explode, and even if it happens in a manner that might not be dangerous, it can still be very messy, so you want to avoid it by being extra vigilant.
2) Unlike true rechargeables, carbon-zinc and alkalines don't charge up better the lower the voltage.  You can easily bring a carbon-zinc back up to something over 9v if it has dropped to maybe as low as 7.5v, but once you get below 7.5v, don't be looking to put that much more life back into it.  Still, it is possible to make batteries that are juuuuuuuuust starting to show their age look and behave a little younger.  Like putting makeup and a T-shirt on an adult.  Works if they're a 35 year-old, but not so much if they're 55.
3) The rejuvenation does not have the same staying power as a true recharge.  In other words, even if you do manage to bring an alkaline 9v back from 8.2 up to 9.7V (done it many times), it takes less time for that battery to drop back down to 8.2v than it did when it was brand new.  It certainly lasts for a useful period of time, but we aren't talking about maintaining how long the battery remains in peak performance for the same time period as a true rechargeable.

How come battery companies don't tell you that you can do this?  Well, do YOU want to explain to your great aunt who can barely operate the TV remote the guidelines for re-using nonrechargeable batteries?  I didn't think so.

While it is feasible to extend the usable lifespan of 9v batteries, one should have realistic expectations and make a point of observing safety precautions.  Having said that, suggestions for using battery packs of D-cells that share their current across pedals are spot on.

[mac]

I have been recharging alkalines for months for my mp3 player. I built a very easy circuit, 40-60ma, batteries never get hot.
Instead of the normal 8hs they last 3hs.
Thanks Mark.

mac

[earthtonesaudio]

I have been recharging alkalines for months for my mp3 player. I built a very easy circuit, 40-60ma, batteries never get hot.
Instead of the normal 8hs they last 3hs.
Thanks Mark.

mac

Got a schematic for that circuit?

[mac]

http://www.diystompboxes.com/smfforum/index.php?topic=53001.0

Not quite sure which is the ideal Vcc voltage that must be used to charge a single 1.5v alkaline. I use a wall wart that put 3v to be safe. A rough estimation is 3v - 1.2v = 1.8v, so the batt can be left hours without being over charged. NOrmally I charge batts for about 4-5hs. They read 1.65v but  this voltage starts to decrease slowly with time.

mac