# Current produced by 3 AA batteries

#### MoneyJohn

I am aware that AA batteries are calculated in terms of Ah and not A, and volts, still is there any way to calculate how much current in A that 3 AA batteries can produce? The details, First, I don't have much understanding of electricity. I do not try to deal with any electric related stuff but this felt simple so I thought of trying. Son has Snap Circuit sets that use 3 AA batteries. Now that he has a lot of time on hand and gets bored easily, he is running batteries like a set per 6 hours/day or so. He is using rechargeable batteries, still, I thought maybe it is easier to just put it on USB power using a phone power bank. Did some YouTubing and found a guy using dowels https://www.youtube.com/watch?v=UzruV5pH1RU Only difference is, he used a transformer and I chose to use a phone power bank. I was just focused on 5V produced by 3 batteries. I 'assumed' the current drawn will be dependent on the circuit. Snap Circuit didn't like these batteries and they didn't work (but worked with 3 AA batteries). Everything seemed OK so I tried in one of the LED lamps I had that uses 3 AA batteries. It lit up but soon one of the functions failed. It has On/Off/Auto setting. The auto setting has a motion-sensing sensor. Now it works on On but not on Auto. I opened up the lamp and smelled something burnt. I am quite confused about why it stopped functioning and smell something burnt. Is it because the current was too high from the power bank (between 1-2.5A). And why the LED lamp works but Snap Circuit doesn't. Any educated guesses? (P.S. - I admit, many may not know what circuits I am talking about but I don't know how best I can put this question. Pls ask if any more info needed.)

#### supton

3 AA's is 4.5V that will dip down to like 3V at end of life. 5V from a USB battery is likely 5V (it can be as low as 4.5V from a computer, especially when under load on a small gauge cable). And it'll be 5V until the battery is depleted. I wouldn't think 0.5V would matter to the LED widget. I'm going to guess either infant mortality or poor design. Assuming that no one applied more than 4.5V (any chance your son decided that, if 3 was good then maybe 6 was even gooder?). Edit: under heavy current draw the AA's will droop in voltage too. It's possible that any high current draw device in the kit may have been expecting that phenomenon, but the 5V bank was not dipping under load. So I suppose there is that effect.

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#### terry274

Are the batteries in parallel or series? That would make a difference in the volts supplied.

#### MoneyJohn

Originally Posted by terry274
Are the batteries in parallel or series? That would make a difference in the volts supplied.
Parallel. 3 batteries in parallel but the middle one with opposite polarity.

#### kschachn

Originally Posted by MoneyJohn
Parallel. 3 batteries in parallel but the middle one with opposite polarity.
What? If they are in parallel then they will be in parallel, not with one reversed. if one is reversed then that indicates they are in series unless there is some sort of funky wiring in the holder. What voltage are you getting out of the pack? Batteries in parallel is somewhat odd for several reasons.

#### supton

Originally Posted by MoneyJohn
Originally Posted by terry274
Are the batteries in parallel or series? That would make a difference in the volts supplied.
Parallel. 3 batteries in parallel but the middle one with opposite polarity.
I think you mean they are physically parallel to one another. But electrically they are in series. If you remove the batteries and look at the tabs/springs you should see that the batteries go + to - and so forth.

#### Quattro Pete

Originally Posted by MoneyJohn
Originally Posted by terry274
Are the batteries in parallel or series? That would make a difference in the volts supplied.
Parallel. 3 batteries in parallel but the middle one with opposite polarity.
If you're getting 4.5V (3x1.5V) out of them, then that means they are in series, not parallel.

#### djb

The Snap Circuit battery pack has a hidden 'PTC' (Positive Temperature Coefficient) resistor. That limits the current if there is a short circuit, which is a common occurrence. The PTC resistor works by dramatically increasing its resistance when it heats up. That allow almost full voltage for typical loads, and almost full current briefly, but then the current is very limited until the load is removed and the resistor cools down. Using rechargeable batteries in the supplied battery case is the easiest way to solve your battery usage problem. We can talk about internal resistance and the complexity of how much current different types and brands of batteries can supply in different conditions, but that is of academic interest only.

#### Kawiguy454

Basically that PTC is a really cheap way to power the circuit without the cost of a real voltage regulator. when voltage input is higher even .5 volts that PTC reacts to limit current but that extra voltage gets converted to heat inside it and puts the device above its temperature maximum. As part of powering circuits he needs to understand voltage, current and Resistance relationship. He should be encouraged to purchase a voltage regulator kit and bypass the battery pack to power his stuff. This is how the old timers would approach it and learn something along the way. just pulling a kit out of a box to see a light blink dosent really teach the fundamentals and how to resolve problems.

#### MoneyJohn

Originally Posted by Quattro Pete
Originally Posted by MoneyJohn
Originally Posted by terry274
Are the batteries in parallel or series? That would make a difference in the volts supplied.
Parallel. 3 batteries in parallel but the middle one with opposite polarity.
If you're getting 4.5V (3x1.5V) out of them, then that means they are in series, not parallel.
Thanks, As I said in the OP, my knowledge of electricity is zero. From the explanation, it looks that they are physically parallel but in series.
Originally Posted by djb
Using rechargeable batteries in the supplied battery case is the easiest way to solve your battery usage problem. We can talk about internal resistance and the complexity of how much current different types and brands of batteries can supply in different conditions, but that is of academic interest only.
No, this pretty much answers the question. I will just get some new rechargeable AA batteries for him to use so that he will have a set always charged. But I am still confused about what in the LED light circuitry blew that one of the functions doesn't work. I actually had high hopes because I was planning to go away from rechargeable batteries and replace all such lights with 5V USB power but now I am not too sure because of my lack of understanding.

#### supton

Can you post a picture of the bad module? Open it up even. There is many ways to make a blinking light, and speculating about what blew won't get anyone anywhere.

#### PandaBear

Originally Posted by MoneyJohn
Originally Posted by terry274
Are the batteries in parallel or series? That would make a difference in the volts supplied.
Parallel. 3 batteries in parallel but the middle one with opposite polarity.
I think you need to understand what it means by parallel or series first. https://globalsolarsupply.com/wp-co...ecting-batteries-series-and-parallel.gif Regarding to why USB power works but battery doesn't, it is likely because battery's current is limited much more than a USB power. USB power can be a much higher current depends on the "charger" you use, like, 2A. I highly doubt a AA battery in series can provide 2A unless lithium and connected in parallel.

#### user52165

Great God - whatever happened to science in the classroom? Like elementary school. Re, the OP series vs parallel

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#### JimPghPA

Originally Posted by MoneyJohn
Originally Posted by terry274
Are the batteries in parallel or series? That would make a difference in the volts supplied.
Parallel. 3 batteries in parallel but the middle one with opposite polarity.
Ohhhhhhhhhhhhhhhh "First, I don't have much understanding of electricity." Well at least he got that part right.

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#### SpitFire6

Hi, 3 x Alkaline = 4.5v 3 x NiMH rechargeable = 3.6V Are you allowed to run rechargeable cells in it? There are 1.5V rechargeable out there in AA format. Costly & AHr is not great though Cheers, Iain.

#### Dave9

Alkalines aren't good for much over 1A, and (good quality) NiMH closer to 4A, but with either, the closer you get to, or exceed that, the more the voltage will droop, so the shorter the usable capacity will be before you need new batteries, or recharged batteries, or to let the tool rest till the battery recovers a bit, but then will still have a less than idea usable battery life. This is a bit of an aside because most devices use batteries appropriate for their purpose, meaning that besides some LED flashlight, most are designed to run for multiple hours from a set of batteries. You can then calculate out what the average current is if the device seems to run in about the same power mode the whole time, to get an average current, but for devices with higher on-load current, you would need to use an ammeter to measure that peak current. Odds are that a phone charger would be sufficient to power it, but as mentioned above you need to measure current to be certain and to consider that there are a wide range of phone charger capacities too, older ones could do maybe 400mA and newer, particularly for bigger more expensive phones or tablets, upwards of 2A or even more. However, circuits using 3 x AA (or AA, or a single Li-Ion cell) to power illumination (flashlight function) LED are a different story. That tends to be a cheap design depending on the battery voltage being a certain amount over the LED forward voltage and even a little in excess of that, can put a lot more current through the circuit than the designer intended because the design was too cheap to start out with a sufficiently higher battery voltage then a buck regulating LED driver to regulate current. It may be possible to modify the device to incorporate this, but the choice of batteries is a different matter. Sometimes you can rewire a battery compartment to take 2 x 14500 Li-Ion cells in series then this buck regulator but it is all a bit fiddly to try to shoehorn it into a product casing that likely doesn't have a lot of empty space in it to do that. Ultimately the best non-fuss solution is going to be continuing to use good quality (like Eneloops) NiMH and have a spare pair and decent smart/rapid charger for them. If you want to fuss anyway, there is little we can state with certainty without seeing a schematic of the circuit(s) involved.

#### PandaBear

Originally Posted by SpitFire6
Hi, 3 x Alkaline = 4.5v 3 x NiMH rechargeable = 3.6V Are you allowed to run rechargeable cells in it? There are 1.5V rechargeable out there in AA format. Costly & AHr is not great though Cheers, Iain.
The 1.5V vs 1.2V debate is way overblown. For high current application they don't expect voltage to stay consistently at 1.5V or 1.2V the entire duration until it suddenly drop to 0, it is a curve that gradually goes down.

#### Quattro Pete

Originally Posted by SpitFire6
Hi, 3 x Alkaline = 4.5v 3 x NiMH rechargeable = 3.6V
You're not going to get anywhere close to 4.5V out of alkaline batteries if you try to pull high current from them.

#### CR94

Originally Posted by Quattro Pete
You're not going to get anywhere close to 4.5V out of alkaline batteries if you try to pull high current from them.
Or if more than a small fraction of their capacity has already been consumed. They don't maintain relatively constant voltage through their useful life the way some other types do.