How many mA is a 9v battery?

[samzeppelin]

How many mA is a 9v battery?
Thanks

/sam

[JimRayden]

Well, actually what is measured on batteries is the milliampere hours ( I think it was that). Virtually you can suck as much amps from a battery as you fancy but the mAh sets the "durability". If you use more amps, you also get less battery life. If you know the mAh of a battery, you can divide it by the amount of mA you're using to get the lifespan of the battery in hours.


------------
jimbo

[samzeppelin]

ok.......
but How many mA is a 9v battery? (if i use it for one pedal?)
/sam

[JimRayden]

The correct question would be: how much does the pedal draw? If you have an ampmeter, connect it to the circuit in series with the battery.

It completely depends on the pedal itself.


----------
jimbo

[Marek]

You can count with somewhere about 500 mAh ( miliampere per hour )

If your effect draws 10 mA your theoretical battery life will be 500 / 10  = 50 hours. If it draws 100 mA your battery will last only 5 hours.  

You can not get 3 A out of a 9V "E-cell"  since it only has 0,5 mA.  

The capacity  of a (standard 9V) cell is only theoretical, because batteries have the funny custom of loosing their capacity even if they are not connected to anything at all.

Hope that was the right answer to your question.

Greetings,
Marek

p.s. I wrote this to my best knowledge. If any of it is wrong, please correct me. Thanks.

[zachary vex]

i think you might be asking how many mA you can squeeze out of a 9V battery, maximum.  to determine that, you need to put a digital meter straight across your 9V battery when you've got the 10A current setting chosen.  it will be in the 100-500 mA range, i imagine, depending on the type and age of the battery.  when drawing near the maximum of a battery's possible current output, you severely shorten the lifetime of the battery.  that's why digital delays often suck batteries dry in a matter of minutes, and leave them warm to the touch!

a well-designed guitar effect shouldn't draw more than 10-15 mA of power, and preferably well below that.  at least you can get a few gigs out of a battery if it's in that range.  maybe even a short tour.  8^)

[Paul Perry (Frostwave)]

Zach is too modest to say, but some of his boxes draw so little current that I would not be suprised if the batteries lasted LONGER with the unit switched on :wink:
as for how long a battery lasts, you get more total lifetime ma/hour out of a battery if it is run at a low current, and if it is run intermittently.

[zachary vex]

You can count with somewhere about 500 mAh ( miliampere per hour )
...

almost... 500 mAh is millampere-hours, which is milliamperes times hours, not divided-by (per).  500mAh means 500mA delivered for one hour.  strangely enough, it's basically an electron count...

one amp is 6.241 506 x 10^18 electrons/second.  since it's a number of electrons per unit of time, multiplying it by time makes that measurement a simple count of total electrons!  we can figure out the real number of electrons represented by 500 mAh by doing this simple math:

one hour is 3600 seconds.

one amp is 6.241506 * 10^18 electrons per second.

500 mA is half of that, or 3.12 * 10^18 electrons/sec.

500 mAh is 500 mA times 3600 seconds which is [3.12 *10^18] * 3600, or 1.123 * 10^22 electrons.

11,230,000,000,000,000,000,000 electrons, or to give it some perspective... in dollars, approximately how much the Iraq war has cost us and our children.  8^)

[puretube]

so, next time we`ll give B*ush a battery-powered toy to play war...  :lol:

[Triffid]

Why ruin a decent thread or even forum with political view points?

[zachary vex]

oops, sorry. just trying to put things in perspective.  i couldn't come up with another way of suggesting such a large number.

[Triffid]

sorry for the hasty remark...  I did appreciate your input on the matter, I'm sure you've done much work to keep your pedals low on power.

[Alex C]

What should be considered or focused on when trying to minimize current draw when designing a circuit?  (How do you do it, Vex?)

[Mark Hammer]

I might point out that one of the things that varies across battery types and brands is the extent to which the battery design itself limits current delivery.  All 9v batteries incorporate six 1.5V "cells" inside the metal casing.  In some instances (ultracheap carbon-zinc batteries) the cells are essentially Chicklet-sized "slugs" stacked on top of each other, with a large area of conduction between them.  In pricier industrial-quality alkalines, the cells are essentially miniature AAA cells (AAAA?), with metal tabs spot welded between them as contacts.  It is my understanding that the old cheap ones can deliver lots of current initially, because of the contact/surface area, but the contact area rapidly becomes higher impedance such that the capacity to deliver lots of current does not continue until the battery's last dying gasp.  In contrast, alkalines cannot deliver as much instantaneous current when new, but are able to deliver it for a much longer period of time over the lifespan of the battery because of the higher quality inter-cell contact that does not degrade with use.

Though not in use as much since the advent of digicams, Polaroid cameras used cartridges which came with their own internal "Polapulse" battery for the flash and camera motor.  These are 6v batteries that are about half the dimensions of a credit card (with the package being much bigger) and *maybe* 1/4 in thickness.  These batteries also contain multiple cels, but because of their considerable surface area between cells, in comparison to 9v battery cells, they could deliver VERY big chunks of current for brief instants, without much in the way of long-term lifespan, which is exactly what you want when you want to run a flash and motor off a battery 24 times.

This is the long answer to Sam's question.  The number of ma deliverable by a battery will depend on its general design.  Some are designed to "give up" all their current freely and die quickly.  Some are designed to ration it out more conservatively and last a long time.  

This is partly why some musicians *say* they prefer to use certain kinds of batteries for certain sorts of effects.  This is most typical of high-gain distortion circuits where some folks say they like carbon-zinc batteries like the red Eveready Classic, especially when the battery is near death or unusably low voltages.  My guess is that what they like is the manner in which the battery delivers as much current as it can for transients, but sags immediately thereafter, not unlike some sorts of tube-based power-supplies.  If the circuit goes from enough current to less than enough (and I suspect that may be accompanied by momentary changes in supply voltage as well) over the lifespan of a note, that can produce some interesting sounds.  Note that this is NOT the same thing as simply reducing the supply voltage of a wall-wart.  If the wall-wart is rated at 9v and you drop it to 8v or less, it is still capable of supplying more than enough current at a stable voltage of your choice.  This is likely not the same as what happens with a battery.

One final note.  MaH rating generally corresponds to cell volume (more stuff inside = more potential charge).  So, AA cells can deliver more current for a longer period than AAA, C more than AA, and D more than C.  Since the cells in a 9v battery have LESS volume than an AAA, you can imagine that a 6-pack of AA batteries will last *much* longer than a 9v battery.  Every once in a while, when someone raises the problem of a noisy/hum-laden power source in their work environment, at least one of us here will pop in and suggest using a 6-pack of D-cells as the "floor-wart" to power a bunch of stompboxes.  You won't get the sag that comes from a single 9v battery, but it can dependably supply a pedal board with pure DC for a pleasingly long period.

[Johan]

your typical non-alcaline 9v battery holds about 120-150mAh, some Alcalines can get up to 500mAh but most die after about 350-400mAh ( and that is less than 10hours in a Boss DD-3...)
I have gone over to use "Ultralife" 9volt lithium batteries ( the kind made for use in smokedetectors) and they are specified to deliver up to 1200mAh..yes, they cost about tvice as much as a duracell but they last four to five times longer...put one of those in a crybaby, and you dont have to replace it for the next couple of years...

Johan