9V Battery or 2 x AAA with 9V Converter

Why not two AA cells? That's closer to the size of a 9V battery.

Check the data sheet for the TL496 -- dry cell batteries are useful down to about 0.9V per cell; you really want something that will function down that far, or at least down to 1V/cell.

I don't think you mean efficient, I think you want to know which will last longer. From this page, ( I guess that,s what you said)

I see an alkaline AAA has a 1000mAh capacity and a 9v has 500mAh capacity. I would think, (that means you must verify) because of the voltage differences the equivalent of the 9 volt at 3 volts is 1500mAh minus the efficiency of the converter. I think the 9V would last a bit longer, not sure it is worth the extra circuitry though. Mikek

The convertor is only 80 or 90% efficient, so clearly the 9v is more effici ent - but I think thats not what you meant. If you mean cost efficient, 9v batteries are terrible compared to 1.5vs. Only you can price your circuit, your batteries, and know your use thus calculate the Total Cost of Ownershi p for each option.

I always avoid 9v except when they have a big advantage, since they're far worse value.

NT

On a sunny day (Tue, 13 May 2014 07:22:35 +1000) it happened snipped-for-privacy@protec.com wrote in :

Design your circuit for 3.7 V LiPo. Use a voltage converter if you have to. Use a USB charger chip and micro USB connector for charging. This is perhaps more expensive (a little) in the short run, but saves batteries and environment. I think this is the current trend. A 1Ah Lipo with build in protection is almost the same price as a 9V block these days. Peak current capability is also higher, charge retainment is good. And Lipo needs less space, less weight than 4 AAA. Saves the battery connector pack, the need to have a housing with a battery lid or compartment, and prevents leakage etc, people putting them in the wrong way around, etc etc. And if the Lipo goes bad after some years .. sell them a new device (Apple?). Or solder in a new one...

Never use AAA cells. You get twice the capacity in a AA cell at about a third the cost.

I know people who use the type of battery in the remote to pick between brands of TVs. I try to run make everything I own AA cell compatible.

No matter where you go, you can find chickens, 7.62 ammo, and AA cells.

The most annoying things are low current devices that will only run on two AAA cells and will not work with NiMH rechargables at all. My phones LED display when the phone is off hook for instance.

Only in the USA and some third world countries.

AA cells are the only one of those three commonly stocked in Europe.

Have you ever seen this offered as a cost-effecive integrated, drop-in package, e.g. with the battery, charger, converter, and connectors?

If not, looks like a good opportunity for someone.

Kevin Grant

If you're building one, these guys have some interesting modules.

--- According to this chart from:

Battery Type Capacity (mAh) Typical Drain (mA)

--------------------------------------------------- D 12000 200

the AAA cell has a capacity of 1000mAH with a 10mA drain, and the 9V battery has a capacity of 500mAH with a 15mA drain.

Neglecting the TL496 for a moment, and assuming a 15mA load on the

During that time, the load will be dissipating 9V * 15mA, or about

Since I = P/E, then, the AAA's would have to supply 135mW/3V = 45mA into the perfect converter.

The AAAs have a capacity of 1000mAH so, with a 45mA drain, they'd last for 1000mAH/45mA, or about 22 hours.

Unfortunately, the 1000mAH capacity is for a load current of 10mA, so the 45mA load would shorten the battery life even more.

Then, on top of it all, the converter isn't perfect, so its less than 100% efficiency will also take its toll on the 3V battery's life.

Just for grins, if we say that the converter is running 80% efficient with a 135mW load on its output, then its input will need about 169 milliwatts to do the conversion and, for a 3 volt battery, that comes to about 56mA.

According to the constant current curves at:

a 50mA load will get you about 21 hours to 1V cutoff, so I suspect

John Fields.

Thanks for explaining the calculations in detail.

So, if I understand correctly, due to the effect of the voltage step up, the AAA's have a shorter life than the 9V battery, 22 vs 33 hours, even though they can supply twice as many mAH's at 3V.

Assuming the converter will operate down this low, its output would then be 3V?

Not many circuits would even continue to operate below that. I would think a more practical cut-off for a 9V supply would be 5 or 6V.

Kevin Grant

I wouldn't take this table as Gospel. Lantern batteries typically have cells half again as large as D cells and so should have half again the capacity. Some are actually made with D cells and a filler in the bottom. Those should have exactly the same capacity as D cells.

I wonder where this web site got their data?

You say I can't find chickens and ammo in Europe? What about Poland?

There are some controllers that will keep running down to 2V, but can't start there. That is because they bootstrap power to the chip from the DC/DC output using a LDO.

That is, sometimes the datasheet curves show low voltage operation, but the electrical tables won't indicate operation at low voltage.

This is the electrical equivalent of I have fallen and can't get up.

I can't seem to open that link. You do see my point though, right? It is very unlikely in my opinion that the lantern battery with much larger cells would not be able to supply as many mAHr as a D cell.

Perhaps this is because the data given was from lantern batteries which were made using D cells. I see the stated drain current is half again as high for the lantern battery, so that may explain the difference in rated capacity if they were tested at those values.