How to figure how long a battery will last

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Here is the basic math concerning pedal board effect pedals, and operation with a battery. Almost all modern guitar effect pedals have at least one or more 8 pin-IC Op Amp. Some have several Op Amps.
On average a 8 pin-IC Op Amp will draw around 5 mili-amps. or .005 amps.
Most people want a power light on their pedal board effect pedal. These lights are called LEDs. LEDs draw somewhere around 20 mili-amps, or .02 amps.
Really good 9 volt batteries are rated at 120 MAH, or 12 MAH. The MAH means mili-amp hours--how long it will last depending on current used. Lessor quality batters will last less than 120 MAH.
The math to figure how long a battery will last is pretty simple. One 8 pin Op Amp chip draws approximately 5 mili-amps. One LED light draws approximatley 20 mili-amps. Total draw would be 25 mili-amps.
Divide 25 into 120 and the answer is= 4.8 hours. All of these figures are averages. The question then is: "Are you willing to spend $3.00 on a good battery to get 4.8 hours of operation out of your pedal board effect pedal?
Some extremely simple electronics only using a couple of transistors and can draw much less than 5 mili-amps. I stress the word "simple" electronics. All of the figures above are averages, meaning some chips draw more, and some draw less. Same thing with LEDs, some draw more, and some draw less.

Ian Rae · From: Redditch, England

Does anyone use batteries when a mains PSU pays for itself in a week?
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Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Ian, the answer is yes--many! Many say they don't want the trouble of plugging something else in. In time, people realize batteries cost money, and go dead when you least expect it.

Greg Lambert · From: Illinois, USA

When I use batt's they are the rechargeable type.

Ian Rae · From: Redditch, England

It's the prospect of sudden death that puts me off - you can estimate the life of a battery but you can't predict it Smile

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Jack Stoner · From: Kansas City, MO

Like Keith, I see many people use batteries instead of a power supply. There are many reasons. I have a SansAmp interface unit and I use battery with that to avoid a ground loop hum and that its only used for very short periods for recording (the 9V battery is over a year old and still good) and more convenient without hooking up a power supply.

Bryan Bradfield · From: Lethbridge, Alberta, Canada.

6 D cell batteries, 9 volts of power.
Six times 2.1 x 5.5 mm center negative connectors.
Three times old-style 1/8" miniphone tip positive connectors.
Food container for enclosure.
Cable tie mounts for dressing and keeping connectors securely in place.
Double sided carpet tape holds everything down.
12 amps of power should provide lots of time between battery changes.
A 2 amp automobile fuse was subsequently added.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

I don't like to use a power supply on a pedal steel volume pedal. I don't keep any other effects pedals anywhere near my right foot, so that would be yet another separate power supply wire down where I have my foot. To my mind, this is just another annoyance and something else to potentially go wrong. I normally play steel, more than one guitar, occasionally something else (like a banjo) and sometimes have multiple amps and a pedal board with switching. I want no additional power supplies to contend with.

Sometimes I just plug the steel straight into an old Sho Bud volume pedal. Other times, I want to buffer the signal before the volume pedal. So in that case, I just use a buffer attached to my leg. I could build one into my old Sho Bud pedals, but I haven't seen a real reason to do that. But if I did, I'd just power it with a battery - and here's why:

A battery can last a very long time in a simple single-discrete-transistor buffer. For example, a simple JFET buffer without an on/off LED (I don't need an LED if it's gonna be on all the time) can draw as little as 100-200 Î¼A (0.1-0.2 mA or 100-200x10^-6 amps). So even considering a draw of 200 Î¼A, the battery life of a 120 mA (0.12 amps) battery should be something on the order of (0.12 amps)/(0.0002 amps/hour) = 600 hours, more or less. So for my typical 3-4 hour gig/rehearsal/session, that's something on the order of 150 3-4 hour playing periods, as long as I pull the plug when I'm not playing.

This is consistent with my experience using Brad's Freeloader buffer, and what Jim Palenscar is reporting with his new Goodrich pedal. My general MO is to replace the battery once a year in the Freeloader, whether it needs it or not. It's never gone dead on me yet in the (8-10, can't remember when I got it) years or so I've been doing this. I haven't even noticed a 9V battery going below 9V in that period - I always measure when I take it out, and I just repurpose it for a portable tuner or something else that is not mission-critical.

Now, I use a One-Spot for my pedal boards. Each of them has 8 powered pedals, and keeping them batteried up would be annoying and expensive. These pedals are not heavy current suckers, but I've been surprised how well the One Spot has managed to handle them all without any issues that I've noticed.

Jim Sliff · From: Lawndale California, USA

Batteries can also last for years in many gain-based pedals - clean boosts, distortion, fuzz pedals etc.

This site lists a huge number of effects pedals by manufacturer and their actual draw.

http://stinkfoot.se/power-list

If you use power supplies it's generally a bad idea to by cheap ones,. especially used ones that are used to power home telephones and other non-audio gear.

Most 9VDC pedals require regulated power supplies commonly known as "PSA" type, the Boss designation fr regulated supplies.

But cheap phone 9VDC power supplies are unregulated "ACA" types, and they will cause significant hum with pedals made after the mid-70's or so. Early pedals that are marked with "use ACA-type power supply" can be used with a PSA power supply - but only if it's on a daisy-chain with one or more PSA pedals.

There's more detailed info about this on the visual sound effects website.
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Tony Prior · From: Charlotte NC

as usual, odd guy out ! I use a PS, sometimes a good one sometimes a cheap one. BUT, the pedals needing power are behind me sitting on the amp. I use a dual wire thingy, I power 2 at a time .

If I'm using the Boss Multi Pedal rack then it's on the floor with the Boss Power Supply, but thats not very often.

In the photo, this is pretty much EVERY gig. No issues that I can detect.

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Jack Stoner · From: Kansas City, MO

I generally get a year out of the batteries in my Goodrich Matchbro. Not a big deal to use batteries in this.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Not trying to derail the discussion, but there are many low-current LED's that draw only 2ma. Also, COSTCO is now selling 9v Duracell batteries, 8-pack for $15. I use tons of batteries, so I always buy bulk at the warehouse stores when they have a special to get the best deal. Buying 2-packs or 4-packs at Walmart or Target is just wasting money.

ajm · From: Los Angeles

In the original post: "Really good 9 volt batteries are rated at 120 MAH, or 12 MAH."
I believe that there is a math error or typo here.
Actually, 120 MAH = 0.12 AH. (I pay attention about once or twice a year.)

Also: "Divide 25 into 120 and the answer is= 4.8 hours."
This would be OK, except the average 9v battery will/should last much longer in a "normal" BOSS/Ibanez type effect pedal.
Why? Because battery life also depends upon how much current is being drawn out of it at a given rate.
The 120 mah rate that you are using appears to be at a discharge rate of around 500 ma, which is huge for a "normal" effects pedal.

At one time I measured all of my effects pedals (or at least the dozen or so that I had wired up at the time).
- The most current hoggy of any of them was a BOSS GE7 EQ at 25 ma.
- An MXR Carbon Copy was (surprisingly) about 12 ma. (I thought that it would be much more.)
- Most of my pedals are lower, in the 15-20 ma range.

A couple of tid bits from the source of all knowledge (the internet):
- A circuit that draws 10 ma powered by a 9 volt rectangular battery will operate about 50 hours: 500 mAh /10 mA = 50 hours
- 9 Volt battery, 15 ma current draw, 500 mah (which calculates out to about 30 hours)

From Keith's second post: "Many say they don't want the trouble of plugging something else in."
They don't want to plug in an extra 9vdc wall wart, huh? This is probably OK if you are only using 1 or 2 or 3 pedals. That means that you are willing to plug in the 1/4 inch cables ("wired for sound") to their effects pedals before using them. Assuming of course that they unplug the 1/4 inch cables when they're not using them. Because if you don't, it will drain the battery. If you leave them connected, and you come back a week later, be sure to bring another battery, because the one in the effect may be dead.

Also, keep in mind that when your effects are wired for sound that even if they are not "effecting" and the LED is off, the electronics are still drawing current. Which means that the original calculations are for worst case. If you leave the effects wired for sound, but the LED is not on, the battery should last longer.

IMO the best, and maybe only, reason for using batteries is if you have an old vintage pedal and don't want to modify it to add a battery jack. Of course, there are adapter cables to connect to the existing battery clip and still use a 9vdc adapter.

Also, for whatever reason, some pedals just to do want to play well with others (I have one). The by product there is usually excessive hum. They want their own separate supply/wall wart, or a battery.

Another potential gotcha: Keep in mind that some effects use a positive ground (I have one). In that case, you need to use a battery, or a separate dedicated 9vdc adapter wall wart, or a DC supply "brick" with isolated outputs.

Another negatory for batteries (this one is obvious): Some pedals, particularly digital delays and reverbs, are current hogs.

So what does all of this mean? How should I know? But I do know that we'll be discussing it again before too long. ;>))

IMO, everybody needs to do whatever makes them happy.
And, you need to look at each set up individually.
If you only use 1 or 2 or 3 "normal" effects, and remember to de-wire for sound the 1/4 inch cables when you're not playing, batteries are probably workable for you.

If you are using 9vdc supplies, and something doesn't work (like excessive hum), you need to figure out why and take the appropriate steps. The solution is probably as simple as either using a battery or a separate wall wart for the problem child pedal.

FYI, my home goofing around setup right now consists of:
- 14 basic "BOSS type" "modern" effects (Why so many? Because it's FUN!!! And I very rarely use more than 3 at a time.)
- Two true bypass strips totaling 13 LEDs (Why true bypass strips? Signal loading. Brian Wampler has a very good video on this on Youtube.)
- One vintage fuzz that I don't want to modify.

I got tired of using/buying/replacing/checking batteries a LONG time ago.
I'm not going to unplug all of the 1/4 inch cables when I'm not using everything.
I also got tired of wall warts and all of their issues.

I use two home made regulated DC supplies.
The vintage "don't dink with it" effect (which also happens to be a positive ground) uses a battery. I unplug the 1/4 inch cable when I'm not using it in between sessions.

Like I said, whatever makes everybody happy.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

George Redmon · From: Muskegon & Detroit Michigan.

I never "Daisy Chain" multiple effect pedals with one of those small Ispot power supplies and a daisy chain cable. You're just asking for a ground loop. I use this Strymon unit.

Except for my Hilton volume pedal, and Hilton Legend Delay. I use Keith's power supplies.

When i want to use just one pedal, without taking the pedal off my board, or plugging in the whole board i use one of these 9 volt battery cables and a 9 volt alkaline battery.

Ian Rae · From: Redditch, England

Math police here. The correct abbreviation for milliamp hours is mAh. If you have a device drawing megamps, trade it Smile

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