A weird battery tale

[Mark Hammer]

I picked up some 9V batteries from the dollar store.  Specifically these.  I didn't think much of the "for low drain devices" labelling, any more than I take the "heavy duty" labels on the package to heart.

When I'm working on pedals, I tend to simply keep a 9V battery around, clipped to a barrel-type 2.1mm plug so I can easily power up a pedal for however long I need to, in order to verify everything works prperly.  I suppose I could probably use a bench supply, but the bench is too damn cluttered as it is.

I was verifying the functioning of some Forty-Niner pedals I had made for some people, using a fresh 9V.  I had tested them previously and they all seemed fine.  But now they sounded awful.  I couldn't get low drive settings on them.  The Tone control didn't seem to work, and the frequency-booster sort of worked but displayed no variation in where the boost was happening.  If I tried to turn the gain down to get a milder sound, it sounded weak and sputtery.  What the?  Had I misjudged them when I first wired them up, and been too lax with the quality check?

I was beginning to doubt my workmanship.  I checked over the boards.  Maybe I had installed an electro the wrong way around.  Maybe I had misread the value of the current limiting resistor supplying V+.  But no, everything checked out. The battery certainly wasn't to blame because it read 9.6V on the meter.  What the heck is wrong?

Just for the heck of it, I changed batteries to a more conventional carbon-zinc and the pedals came alive, doing everything they were supposed to.  And the battery I was using read 8.1V!!

Boy, when they say "for low-drain devices", they mean it!  I have no idea how these may be different internally or compositionally, but if you feel the need to power a pedal with a battery these are NOT your best friend!

[amptramp]

There has been a lot of research into making batteries more capable of handling large discharge currents.  A battery that is designed for low discharge currents would not have the wide conductors that connect the six internal cells and may use a different (or no) depolarizing agent.

There are a number of things that would make a battery suited to low drain only and many of them make the internal resistance of the battery higher than normal.  If you are using a battery to maintain memory contents, the current is very low because you are only feeding leakage currents.  If you use this battery in a high-drain circuit, the series resistance of the battery may cause various stages to fight against each other, so a pedal with no internal regulation and dependence on a stiff power supply will not operate properly.

[willienillie]

At our dollar store the batteries are branded Sunbeam, and the package also mentions "low drain" applications.  I was under the impression that those were carbon-zinc (zinc-carbon?) batteries, though I don't think it actually says that anywhere on the package.  They last a good while in wahs and fuzzfaces for sure, but I don't expect them to do as well as alkalines.  I think that type has shelf-life issues too.

And the battery I was using read 8.1V!!

In circuit or out?

[Mark Hammer]

Out.  I like to "rejuvenate" my carbon-zincs by sticking them in the charger for a bit, as long as they haven't dropped below 7V or so.  Gotta keep a close watch on them to make sure they don't get hot.  But I can keep a 9V usable for many purposes for a year or so.  This one was probably about that old.

[willienillie]

8.1v out of circuit could be 7v in circuit, depends on the circuit of course.  Charging non-rechargeable batteries is all you, man.

[Rob Strand]

The open circuit voltage isn't a good measure of charge state.    When batteries get old the internal resistance goes up and the terminal voltage drops under load.

Heavy duty batteries are carbon batteries.  They have a poor shelf life.   I rememeber 9V batteries in DMMs (with old school power switches) going flat within a year with virtually no use.  I'm suspecting your battery is old stock.

These days I only use Alkaline batteries, they last for 5 to 10 years on the shelf; although some brands can leak in that period.

The Alkalines have a lower internal resistance than Carbons.   See AMZ web-site for the numbers on good and flat batteries.

Note increase in impedance for old batteries,
http://www.muzique.com/lab/batteryz.htm

I guess the bottom line is perhaps those circuits need a regulator so they still sound good down to 7.2V or so.   That would be very easy to do on circuits with series resistors on the power rails;  you might need to keep some resistance though.

[PRR]

A Canadian dollar store? So this is a $0.63 9V battery? About 1/6th the price it should be?

The dollar stores are known to adulterate products down to the price. Even Name-Brand dish-soap that was more water than soap.

Weigh it against a "normal" cell. Is it just short-weight?

Analyze the chemicals (yes, not worth it). I'm sure there's black-stuff behind a battery factory which fills up a case with stuffing without filling with too much juice (don't want to dent the sale of the good batteries).

EDIT: RayOVac low-drain seems to have been a standard product for smoke detectors and such, but discontinued. Maybe your dollar-store went to the clearance sale? How old is the one you got?

[Mark Hammer]

A Canadian dollar store? So this is a $0.63 9V battery? About 1/6th the price it should be?

The dollar stores are known to adulterate products down to the price. Even Name-Brand dish-soap that was more water than soap.

Weigh it against a "normal" cell. Is it just short-weight?

Analyze the chemicals (yes, not worth it). I'm sure there's black-stuff behind a battery factory which fills up a case with stuffing without filling with too much juice (don't want to dent the sale of the good batteries).

EDIT: RayOVac low-drain seems to have been a standard product for smoke detectors and such, but discontinued. Maybe your dollar-store went to the clearance sale? How old is the one you got?

I don't know if it's a date code, but on the bottom of the battery, it says 06/20, so I don't think it's that old.  Nothing on the packaging to indicate a probable manufacture date.  But yes, it does feel a little lighter than other carbon-zincs I have.

In general, it is getting harder and harder to find 9V batteries, as fewer and fewer devices require them.  I'm not going to pay $9 for a Duracell at the supermarket checkout.  So I keep an eye out for which Dollar stores still sell them.  This particular store had two brands, and I was familiar with Rayovac, who have been making decent batteries for a long time; almost as long as Eveready (1906, vs 1890).

[Rob Strand]

See Rayovac specs,
https://www.rayovac.com/support/product-resource-library.aspx

and click on, "Alkaline and Heavy Duty Application Notes & Product Data Sheet"

or click on,
https://www.rayovac.com/support/~/media/C89F67DD5B5F4CA1AE5C6C85569B8D27.ashx

Look at page 14, then the table,

With a 270 ohm load (27mA current when voltage drops to 7.5V) it only takes 0.9 hours of use to drop to 7.8V, 7.5hrs to drop to 6.6V.   Very roughly the 7.8V end-point implies about 59 ohms of internal resistance.   The AMZ website figures are showing about 25ohm when new/fresh.

If your '49 pedal doesn't have any current limit resistors on the +ve rail it could draw 25mA to 30mA so you are going be hit that region pretty quickly.

If the battery is old  then it might get there straight out of the box, maybe even at a much lower load current.  If the battery is not even a full spec "heavy duty"/"low drain" it will also reach that point sooner.

[MaxPower]

There's an old circuit that uses an obsolete chip (voltage doubler?) to convert 3v from a couple of AA batteries to 9v. Something about the output floating so you can stack the 3v input on top of the 6v output to get 9v. The reason for doing this being that the AAs will provide a lot more current than a 9v. Or so the article claimed. Oh, and AAs being cheaper.

Would it be any better than a voltage tripler using diodes and caps?

Edit: Wait, with the voltage drops/losses would you need a quadrupler? Quintupler? Sextupler? Octopler? Err... 9v battery?

[Mark Hammer]

See Rayovac specs,
https://www.rayovac.com/support/product-resource-library.aspx

and click on, "Alkaline and Heavy Duty Application Notes & Product Data Sheet"

or click on,
https://www.rayovac.com/support/~/media/C89F67DD5B5F4CA1AE5C6C85569B8D27.ashx

Look at page 14, then the table,

With a 270 ohm load (27mA current when voltage drops to 7.5V) it only takes 0.9 hours of use to drop to 7.8V, 7.5hrs to drop to 6.6V.   Very roughly the 7.8V end-point implies about 59 ohms of internal resistance.   The AMZ website figures are showing about 25ohm when new/fresh.

If your '49 pedal doesn't have any current limit resistors on the +ve rail it could draw 25mA to 30mA so you are going be hit that region pretty quickly.

If the battery is old  then it might get there straight out of the box, maybe even at a much lower load current.  If the battery is not even a full spec "heavy duty"/"low drain" it will also reach that point sooner.

Thanks.  The good news is that I built it without a battery snap.

[Electric Warrior]

EDIT: RayOVac low-drain seems to have been a standard product for smoke detectors and such, but discontinued. Maybe your dollar-
I don't know if it's a date code, but on the bottom of the battery, it says 06/20, so I don't think it's that old.  Nothing on the packaging to indicate a probable manufacture date.  But yes, it does feel a little lighter than other carbon-zincs I have.

That's the "best used before" date according to the website: https://www.rayovac.com/products/batteries/zinc-carbon/9v-1-pack-zinc-carbon.aspx

[anotherjim]

Am I right that the 49er opamp has no power supply cap but it's Vref does? The 4049 has a cap but it's behind 100R.
So if the 9v wiggles any, the Vref won't. That could be the trouble.
Temporarily tack a 100uF cap on the opamp 9v and try the weak battery again.

I know the circuit takes too much current for normal battery operation anyway, but would be interesting to see if there is a cure.

[j_flanders]

In general, it is getting harder and harder to find 9V batteries, as fewer and fewer devices require them.  I'm not going to pay $9 for a Duracell at the supermarket checkout. 

1.99 euros for 9V alkalines  at IKEA.

They also sell the cr2032 which are used in clip on tuners.
At 1,50 euros for 8 cells, instead of the 9,95euros for 2 duracells!

[Mark Hammer]

Am I right that the 49er opamp has no power supply cap but it's Vref does? The 4049 has a cap but it's behind 100R.
So if the 9v wiggles any, the Vref won't. That could be the trouble.
Temporarily tack a 100uF cap on the opamp 9v and try the weak battery again.

I know the circuit takes too much current for normal battery operation anyway, but would be interesting to see if there is a cure.

But the same +9V point with the 100uf cap also feeds the op-amp.  I'm unclear how and where a second one would be added.

As for "best before" dates on batteries, I view them more as a "Hey, it's not OUR fault" disclaimer from the company.  I have batteries I've rejuvenated that are several years past their expiry date.  Naturally, manufacturers strongly urge against this because, unlike true rechargeables, non-rechargeable batteries placed in a charger and ignored for too long have a tendency to attract one's attention with a loud noise and "redistributed contents".  I can bring an older Duracell alkaline back above 9V with a 1hr restorative stay in the charger, if it hasn't already sunk too low, but it would now be assigned to a pedal that only draws 5ma or less.  But when you have dozens and dozens of pedals, and far more than you have PSU outputs for, such miserly practices can be called for.  Dead-ish 9V - particularly those you can't get a "tongue tingle" from - are also handy for testing LEDs.

[anotherjim]

I was going by the Forty Niner schematic I found on Ampage. The power supply is called 9v, the opamp pin8 is called 9v and the 4049 has 100R/100u power filter fed from 9v. So by that, it didn't look as though the opamp has a filter.

[Rob Strand]

I have batteries I've rejuvenated that are several years past their expiry date.  Naturally, manufacturers strongly urge against this because, unlike true rechargeables, non-rechargeable batteries placed in a charger and ignored for too long have a tendency to attract one's attention with a loud noise and "redistributed contents".  I can bring an older Duracell alkaline back above 9V with a 1hr restorative stay in the charger, if it hasn't already sunk too low, but it would now be assigned to a pedal that only draws 5ma or less.

I do the same sort of thing.   It does work and it's certainly a handy method to keep the show going when you haven't got another battery handy.

Years ago I did a lot of research and testing on charging dry-cells.  Tried all sorts of charge currents and pulse methods.  At the end of the day some brands charge-up better than others and some brands end-up leaking regardless of how low the charge rate is.   Generally brand names like Everready and Duracells were better than cheap stuff.  Alkalines work better than Carbons.   Non-rechargeable Lithiums don't charge.

Like you found,  you can never get them back to a low-impedance suitable for driving any sort of a load, especially once they have been drained to near empty.   So charging works for light-loads where you just need to kick the voltage up a bit.

Another thing I found is after you charge them, if they are left for long periods a lot of the charge is lost.   It seems to self discharge.   The voltage certainly drops off too.

[PRR]

> 9V batteries from the dollar store

"A friend of mine bought a box of pencils from a dollar-store here. He got home and found no lead (graphite) in the pencils at all - they were just solid wood! Fake pencils!"
https://www.diyaudio.com/forums/instruments-and-amps/351095-proco-rat-clone-doesnt-post6160420.html

[Electric Warrior]

Those are called "drum sticks" 

[Mark Hammer]

> 9V batteries from the dollar store

"A friend of mine bought a box of pencils from a dollar-store here. He got home and found no lead (graphite) in the pencils at all - they were just solid wood! Fake pencils!"
https://www.diyaudio.com/forums/instruments-and-amps/351095-proco-rat-clone-doesnt-post6160420.html

Is he sure they weren't just DIY chopstick kits that you could whittle down in either Chinese or Japanese style?