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Topic: Battery voltage dropping upon connection (Read 937 times) previous topic - next topic

rptort

I wasn't sure where to post this cuz its not a mechanical/high voltage issue, but it does have to do with power. I need a 5V supply for my circuit but I also need a small battery. So I'm using two stacked coin cell batteries (3V each) and regulating that down to 5V. However upon connecting the power to the circuit, the voltages on the battery and the output of the regulator drop quite a bit. Is this simply because the battery can't source enough current to the circuit?

Thanks!

RuggedCircuits

Yes, it's quite possible. Coin cell batteries generally aren't used for significant currents, and likely have high internal resistance.

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retrolefty

#2
Mar 24, 2012, 08:32 pm Last Edit: Mar 24, 2012, 08:34 pm by retrolefty Reason: 1
Quote
However upon connecting the power to the circuit, the voltages on the battery and the output of the regulator drop quite a bit. Is this simply because the battery can't source enough current to the circuit?



That is correct. The battery has to be selected for the maximum load current it is being asked to supply. Also how long you wish to battery to be able to supply that load current is another selection criteria you must make.

Lefty


Grumpy_Mike

Quote
Is this simply because the battery can't source enough current to the circuit?

How much current are you asking of it?

jackrae

If they're something like CR2032 then they are rated at less than 1mA, which is a lot less than your micro is demanding.  Coin cells are really not suitable as a power source for anything other than memory retention or running RTCs.









rptort

They are CR2032 and I'm supplying a couple op amps (used as noninverting and inverting amplifiers), four potentiometers, and an ATtiny84 microcontroller. I don't know much about batteries, but I saw that the CR2032 had 225mAh capacity. I know that's only capacity, but I figured it could source enough current for my application. Any other ideas on a small battery that would source enough current?

jackrae

You really are into the AAA category as a minimum, but it all depends on how much current you are actually drawing and how long you wish the batteries to last (number of hours of constant use)

winner10920

I think a cr2032 can only supply 30ma max ata dead short, in reality i got 22 shorted thru my multimeter

rptort

I'd really rather not use something like a AAA...plus I need 5V. What about an A23? I found that while searching the Internet. Seems like they're really only used for small transmitters and things of that nature that don't pull much current, but with it being 12V could that work if I regulated it down?

Sorry if these are ignorant questions...again I'm pretty unfamiliar with this kind of thing. Thanks.

kf2qd

You are going about this backwards. You need to first figure out what the current demand is of the device you are trying to power. Then you need to determine how long you want it to run. THEN you can look at what battery you need to give that performance.

You are trying to run a diesel locomotive on a scooter engine.

You are going to have to either use a bigger battery, or eliminate functions until the battery you want to use can support the load.

rptort

Okay in that case, what is the easiest way to determine the total current demand of my device?

kf2qd

Get a millampere meter and put it in the circuit and operate it. Look at peak current demands.

Mud

as a newbie i don't yet know the "dos and don'ts", so forgive my ignorance, but what about vehicle remote cells?
12V 23A 1/2 AAA alkaline batteries. Small/lightweight with a fair longevity. i've never used them for anything with motors, so i don't really know their limitations, but couldn't these be rigged to fit the purpose or are the 12V 23A just too much? Price isn't excessive either.

Grumpy_Mike

Quote
but what about vehicle remote cells?

What about them. Link to one please.

However, it sounds like a very big battery considering the OP was using a coin cell to begin with.

takao21106

#14
Mar 28, 2012, 05:35 pm Last Edit: Mar 28, 2012, 05:38 pm by takao21106 Reason: 1

If they're something like CR2032 then they are rated at less than 1mA, which is a lot less than your micro is demanding.  Coin cells are really not suitable as a power source for anything other than memory retention or running RTCs.


CR2032 can power a very small 5x6 scrolling message for 2 days but that's it.
It has peak current of a few mA since the LEDs are so small they have their own resistance.
I also have PIC related web domain.

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