real-world voltage reference?

[IanB]

Modern zinc chloride cells are way higher than 1.55 V out of the package. I just bought a couple of Sunbeam 9 V batteries from the dollar store (expiry date 9/2018) and one measures 10.1 V, the other 10.0 V. Assuming six cells, that gives about 1.67 or 1.68 V per cell. That's pretty typical in my experience. Fresh zinc chloride cells usually have a higher voltage than fresh alkaline cells.

[Alex Eisenhut]

Maybe keep one of these in a bowl?

https://en.wikipedia.org/wiki/Electric_eel

[ralphd]

What about primary lithium cells, like CR2032?

[SeanB]

What about primary lithium cells, like CR2032?

Fresh CR2032 is around 3V3, but the discharge curve, while it is pretty flat over a large portion, does have some slope along it, and there is a small drop from manufacture till it evens out for a long period.

It is a good power source for light loads, but not a very good reference if you want better than 100mV of resolution.

Basically look for a 2V5,5V,10V reference online, which are pretty cheap and good enough for most uses. Otherwise buy one of the AD references which have a guaranteed accuracy sped right from the factory. I bought an AD581KH, which is 10.00V out of the box, and it is both cheap, has only 3 terminals and is easy to use. Just supply it with 15V from a simple power supply ( 15VAC wall wart, bridge rectifier and capacitor, then a 7815 regulator to give 15V to drive it) and it gives 10.00V on it's output.

[Gyro]

From your increasing number of spot readings and the anecdotal observations from others about Alkaline battery starting voltages I don't see anything that tells me that your meter is actually reading out of spec - you're seeing some voltages higher than you expected but others lower or the same as you expected.

If you are really dead set on using a primary cell as a reference rather than a tightly specified 3 terminal semiconductor one then, in a non-Mercury/Cadmium world, you need to get yourself a Silver Oxide watch battery as I said several pages ago! It has the flattest discharge curve of any of the battery types.

All the silver Oxide datasheets say 1.55V with a flat discharge voltage until end of life. The discharge curves all show a small wiggle or drop over the first few hours, but if you load it with the resistance value specified on the relevant datasheet for around 50 hours, then you will be into the flat discharge region.

Just go and look up the datasheets for various manufacturers, Energiser, Renata, Maxell etc. Just type in "Silver Oxide battery datasheet" and they are all just a few clicks away. There really is no point in messing around with any battery technology, Alkaline, Lithium (better than alkaline but nowhere near as flat a Silver Oxide) etc that don't have a ruler flat specified discharge curve.

You really do need to to some basic research for yourself. 

Edit: Silver Oxide batteries are used in other things too, calculators, calipers etc. If it starts SR (rather than LR or CR) then it's Silver Oxide. Buy a new one, load it with the resistor compatible with its capacity (datasheet). Leave it 50 - 100 hours, measure it (still under load). Use a holder of some sort - DON'T solder to it (at best you'll damage its characteristics).

[SeanB]

Hard to get a SR cell these days though, you will typically get a LR cell, as the SR cells do contain Mercury inside. I know as I buy a lot of assorted cells for watches, and they typically might be marked as SR"compatible" but are an alkaline cell.

Just order the 2 terminal or 3 terminal VR online, the best accuracy grade you can afford. That way you have a simple check as to the accuracy of the meter at at least 1 range and at 2 points ( 0V and the selected point).

[Gyro]

No problems getting them in the UK (ROHS and all), I buy them for my calipers and height gauge. SR44 is the most common one. They don't last 5 minutes with LR44 due to the lower (steeper) discharge voltage.

Renata (Swiss) make loads of types for watches - but they use a numeric code rather than SRxx. All the datasheets are there on their website though. Just go to a jewelery shop.

I agree with you 100%, an accurate semiconductor reference / VR is  by far the most sensible way to go (series types are probably easier for the OP to apply than Shunt types). It's only his insistence on using a battery that is prompting the other advice. Even a TI  REF102C (Tightest grade) dip pkg can be had from RS in the UK for GBP10 (probably cheaper in the US), this gives 10V +/- 2.5mV untrimmed. Subtract the cost of a watch battery and the additional hassle involved and it's a no-brainer!

[ralphd]

My point was to see if there is a common household item like a battery that can be used as a voltage reference.
It would be useful to hobbyists that aren't going to spend $10 on a precision reference.
Anyway, I'll probably end up getting a max6126 just to satisfy my curiosity.  And maybe I'll find a common household item that others can use for a 1% reference...

[IanB]

Then how do you explain the 1.635V reading on the alkaline batteries?

A sample of new Sunbeam alkaline cells read between 1.626 V and 1.630 V.

[ralphd]

Then how do you explain the 1.635V reading on the alkaline batteries?

A sample of new Sunbeam alkaline cells read between 1.626 V and 1.630 V.

Thanks.
You don't have any fresh CR2032's around do you?
I only have 1 unused 2032 left, and it is about 2 yrs since I bought it.  I'm reading 3.331V from it.

[Alex Eisenhut]

My point was to see if there is a common household item like a battery that can be used as a voltage reference.
It would be useful to hobbyists that aren't going to spend $10 on a precision reference.
Anyway, I'll probably end up getting a max6126 just to satisfy my curiosity.  And maybe I'll find a common household item that others can use for a 1% reference...

Steel wool and drain cleaner??



More likely to have this lying around than a regulator tube or an eel, I think.

[Gyro]

My point was to see if there is a common household item like a battery that can be used as a voltage reference.

Ok, I understand your aim, just question the practicability using torch batteries of various brands and ages (since manufacture, not purchase)

As SR44s are a household item in my home (as previously explained)...

Fresh SR44:  1.5655V @ 21'C  Never loaded

I think you need to be including measurement temperature in your investigation due to their fairly large temperature dependence. Putting weak zinc carbon batteries in front of the household fire to revive them was once common practice.

[ralphd]

My point was to see if there is a common household item like a battery that can be used as a voltage reference.

Ok, I understand your aim, just question the practicability using torch batteries of various brands and ages (since manufacture, not purchase)

As SR44s are a household item in my home (as previously explained)...

Fresh SR44:  1.5655V @ 21'C  Never loaded

I think you need to be including measurement temperature in your investigation due to their fairly large temperature dependence. Putting weak zinc carbon batteries in front of the household fire to revive them was once common practice.

I mentioned the Wal-mart alkaline AAs were measured at 23C.
The CR2032s were in the basement, with a temperature around 21C.
Duracel and Energizer have expiry dates, so I still think it is plausible and even probable that a popular brand of batteries with a specific expiry date will have a narrow range of voltage.
Thanks for the SR44 reference.  As others have pointed out, many batteries are advertized as SR44 compatible, and are actually LR44 or AG13.
I found a Aliexpress seller offering a pair of 'genuine TI' REF5050IDGKR for under $4.  Under $2 a chip for a .05% reference seems like a pretty good deal...

[Kalvin]

Buy one of those cheap $5 5-digit voltage meters. Use the meter as is or salvage the reference**. Of build a buffer for the reference using a decent op amp, so you will have a cheap 5-digit volt meter and quite accurate voltage reference

** It is possible that the reference is actually software calibrated, so you should buffer the reference with a decent op amp and measure the buffered reference voltage, so you will know actual reference voltage.

[babysitter]

Consider sticking a button cell in your navel, under your armpits, under your tongue or up your A$$, and use it always at rest and at the same time of day. Natural oven controlled cell !

[Gyro]

Thanks for the SR44 reference.  As others have pointed out, many batteries are advertized as SR44 compatible, and are actually LR44 or AG13.
I found a Aliexpress seller offering a pair of 'genuine TI' REF5050IDGKR for under $4.  Under $2 a chip for a .05% reference seems like a pretty good deal...

I think any battery that actually has SR44 stamped into it probably is one (ironically you should be able to tell from its voltage, initial voltage for Alkaline appears higher)

True, you did state the temperature, but other measurements are coming in without temperature data. Given that this is an international forum ambient conditions from various locations are going to be a factor, as are brands - I've never heard of some of the ones people have posted  (probably not sold here).

Given the price of a pack of 4 Duracell batteries here you could afford a reasonable reference - as you indicated. BTW on this occasion I might be tempted to buy from a known source as it's not unknown for 'genuine' parts to be fake or re-marked as a more premium grade. However you could still do very well for the price of a pack of batteries - The  "Even a REF102C"  at £10 is pretty much the practical state of the art (buried zener), without going to ovened references - far tighter than you are needing. I was really just illustrating the degree of precision you can get for RELATIVELY little money these days You can go a LOT cheaper by reducing the initial tolerance a little as you have found

[Gyro]

@babysitter:

You are a true comedian  Your talent is clearly wasted on us

[SeanB]

New still in the wrapper Renata CR2032 Expiry 05 2020 3.288V.

[Alex Eisenhut]

Consider sticking a button cell in your navel, under your armpits, under your tongue or up your A$$, and use it always at rest and at the same time of day. Natural oven controlled cell !

Don't try that with an eel. Or steel wool.

[Ian.M]

... or at least, if thats what floats your boat, *please* don't tell us about it!

[ralphd]

New still in the wrapper Renata CR2032 Expiry 05 2020 3.288V.

Thanks.  Is that with a calibrated meter?

[ralphd]

Then how do you explain the 1.635V reading on the alkaline batteries?

A sample of new Sunbeam alkaline cells read between 1.626 V and 1.630 V.

That should make a reasonable comparison to the Wal-Mart "Great Value" alkalines I have.  Both cheap, made in China batteries.
If we take my highest reading of 1.636 and your top reading of 1.630 as being equal, that would mean my meter is +.37%.  I suspect my meter uses a cheap TL431B (+-.5%), so +.37% is in the range of what makes sense...

[SeanB]

Compared to accurate voltage references, and it agrees to within 6 counts, so pretty much good enough for me. If I want a more stable one I would have to get the Tek I have at work at present, as that has been verified with a Fluke calibrator. 2000 count though so I can only measure to 2 decimal places.

[Ian.M]

Some more data points for you:

Cheap far east Lithium 2032, approx 3 years old: 3.29V
Cheap far east alkaline AG13, approx 3 years old: 1.58V
4x Kodak Extra Heavy Duty (Zinc Chloride) D cell, expires 10-2015: 1.63V, 1.61V, 1.63V, 1.58V
Kodak Xtralife Alkaline 6LR61 (PP3), expires 10-2024: 9.50V
4x Kodak Xtralife Alkaline AA, expires 10-2024: all 1.62V
 
All readings taken with a Maplin Pg22 pocket multimeter (+/-2% + 2 digits) at 20 deg C - I'm down the boat and there's nothing better aboard.

[ralphd]

I forgot to mention the meter I'm using for my measurements is a Mastercraft (CT store brand) auto-ranging model 52-052-2.  Nothing obvious that would indicate who the OEM is.