shortest acceptable Life span of Battery?

[Steben]

What I am getting at is: at what point it starts getting useless to put a battery clip in a stompb?
What is the minimum lifetime of a battery at which you'e not annoyed.

I have this Phase45 with green LED and 1k LED-resistor. What current does the LED draw? 6mA? It uses 4558's. Let's say 10-15mA in total? That's about 20 hours lifetime, 10hours with rechargeables. That's ok, isn't it?

[gez]

I have this Phase45 with green LED and 1k LED-resistor. What current does the LED draw? 6mA? It uses 4558's. Let's say 10-15mA in total? That's about 20 hours lifetime, 10hours with rechargeables. That's ok, isn't it?

If you use 'low current' LEDs, 2mA (or less even) is all you need to get decent brightness and makes for a battery friendly circuit.

Most op-amps consume just a few mA so your total current draw probably isn't as high as you've reckoned on.  Data sheets will give you a better idea, or measure it with a meter and see.

I install battery compartments in all my boxes regardless of how much juice they consume.  I use a PSU,which is my preferred choice, but like the option of a battery as a backup for emergencies...

[gez]

PS  There are battery friendly op-amps that consume miniscule amounts of current when ticking over.  ICL761*/ICL762* series for example.  The (extremely) low input bias current means you can get away with reasonably large bias resistors too.  All helps...

http://www.datasheetarchive.com/semiconductors/download.php?Datasheet=932714

My favourite op-amps.  Don't look much on paper, but sound great (well, with my setup they do), plus you get rail-to-rail output swing so they're great for 9V circuits where headroom can be an issue.

[Processaurus]

9v are expensive if you have to replace them a lot.  I wouldn't even bother putting an option for a  battery in a pedal that took more than 15-20mA.  Manufacturers only do so for more power hungry pedals so stores can demo them easily.  They're worried about selling it, but you're worried about using it.  Not really a good model for DIY, unless you're also selling them through a store.  Also, getting rid of the battery is a good way to free up space in a box, simplify wiring, etc. 

My p45 takes 7-8mA, no LED.  I don't think your LED is a big deal if you're doing the flashing indicator thing, remember its only drawing power half the time.  You can always use a high briteness LED like Gez suggested, for optimal power comsumption.


I think alkaline 9v have about 300-500mAh supposedly, so you could get around 30-50 hours of battery life for your P45.  Those nice lithium duracell ones are rumoured to have about 1200mAh, even though they cost twice as much.  I was impressed after having had one in my rat for like, 2 years of consistant use.

[Steben]

Thanks, guys.
Some basic but worthy reflections I see.
Low-current LED's and low power opamps make a big difference...

Normal LED with 4558's = 5 + 8 = 13mA
lc LED with TLC2262's = 3 + 0.5 = 3.5mA

[Mark Hammer]

The Line 6 Tone Core pedals have a battery compartment, but ask for 70ma current from an external supply.  As digital pedals, they are designed to give something like 6hrs of life from a fresh alkaline 9v.  The Behringer Acoustic Modeller I picked up the other day is an all-analog that draws 25ma.

As more and more players use more and more pedals at once, and powered pedalboards as an outcome of that, companies can assume with relative safety that batteries will be the sole source of power under under a few circumstances:
1) when trying it out in a store (where searching for the right adaptor and an available outlet for the adaptor that will let the pedal reach the amp one is hoping to direct the customer to is a pain in the neck)
2) the "my first pedal" customer who is likely to be a kid with an amp that has a 6" to 8" speaker and the pedal is likely to be a fuzz with low current demands anyways

Of course many of the people who would find a site like this one to be of interest are probably the sort of player that would be interested to try out differentorders of pedals, in which case the flexibility afforded by being able to know that a pedal with a battery in it will still have some juice to try out without having to screw around with adaptors... is nice.

I seem to recall Anderton saying somewhere that 10-15ma was a reasonable limit on current draw to aim for.
Like others, I recommend superbirght LEDs as a sensible, and pretty painless way to reduce overall current draw on a pedal.

One of the things that never really gets discussed here is quiescent current vs "active duty" current.  Keep in mind that even when bypassed, current is still being applied to the semiconductors, and when the semiconductors are asked to "do" something, current draw will go up.

There are some effects which you use for a little bit then bypass (a ring modulator or octave down box would be an excellent example of this), and there are effects which you tend to leave on for long periods of time (chorus and compressor are examples of this).  Of course, if the pedal is engaged for brief periods of time, the role of current draw in the LED is not such a big deal since it will spend a lot of its time dark.  If its a compressor that oone leaves on all the time, then an LED will have significant impact on batery life.  Personally, I only stick indicator LEDs on things where it is difficult to tell right away if its on or off, but that's me.

IN the case of semiconductors, they are ALWAYS "on".  The question then becomes one of how much current they draw when you ask them to do what you want vs how much they draw when they're off-duty and out for a smoke while the boss is away.  I doin't know enough about semis to know what that contrast could possibly be, but it stands to reason there will be instances where the current draw when "on" in a pedal you intend to leave on for lengthy periods is not that much higher than when "off", where in other cases the current draw when on (and playing) is substantially different than when off.

There are a few things to consider here.  One is that there may be serious limits to what you can infer about current consumption from simply powering up an otherwise sound asleep circuit and hooking up your meter (it is essentially being measured under "bypass" conditions).  Another is that battery life may be more a product of how one intends to use the pedal (punch-ins vs set and forget) than anything else.