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I am trying to set up a disposable battery pack to recharge phones, I was able to find online a female usb cable connected to 4 AA that charges fine. when testing with 8 d-cell in series, charging 3 phones at the same time, each one charges at about 430 mah, with 8-11 volts.

My base question is what would I need to do to charge multiple phones at once, ideally without a regulator, only usb connections and d-cell batteries. When testing for a few hours the d-cells would heat up then stop discharging enough to actually charge the phones, is this because of a limitation to power output when the phone is above a certain%, or the batteries heating up and stopping themselves from discharging?

I have the idea of running 2 sets of 4 parallel d-cells in series. I can add more d-cell batteries, I would assume i need a steady 1500 or so mah input to actually get any charging to happen, and am trying to incorporate fans for active cooling

I don't know much about batteries or electronics in general other than a base understanding, and my own google searches have not yielded much results.

nick
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    Supplying straight 11V to a USB socket is a good way to blow up some parts. Aside from that, this seems like a fabulously expensive way to charge your phone. What's wrong with a power bank? – vir Mar 16 '24 at 04:25
  • @nick you are trying to do exactly what power banks do, but with non-rechargeable D-cells instead of rechargeable lithium cells. You need almost identical electronics to do that, to buck or boost voltage of batteries to 5V, or whatever voltage the phone would like to negotiate with the powerbank. So no, it can not be done with just batteries and a USB connector, let's hope you did not damage your phone already by directly connecting it to batteries. Also, mA is an unit of current, mAh is an unit of capacity. And I bet you might already be able to buy a device that already does do that. – Justme Mar 16 '24 at 09:26
  • Why wouldn't you just use 4 D-cells in place of the AA cells, since you say that the 4 AA-cell system "charges fine"? – Nedd Mar 16 '24 at 09:27
  • Vir, when going camping, having 4 or 5 rechargeable battery packs isn't as easy, we play music and movies and stuff at night, so have disposable batteries, or even rechargeable d cell batteries, but just a box of them is way cheaper than battery packs. Atleast over the course of 5 or 6 days – nick Mar 16 '24 at 12:32
  • Justme, you are right I can definitely buy a portable pack, I responded to Vir with why I'm looking for an alternative. I am wondering if 8 can just buy 3 packs, and hook up the d cells to the already existing hardware – nick Mar 16 '24 at 12:33
  • Need, I want more capacity, and I'm a glutton for 3d printing so I have to make my own thing – nick Mar 16 '24 at 12:36
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    Why not buy yourself a handcranked USB generator - less weight to carry into the jungle, will work forever and, when you fall asleep, the music will stop :-) – Robin Iddon Mar 16 '24 at 13:01
  • Robin thats a great idea, i have 1 already, and it works pretty well, but my little sister, her friends and my friends also have phones, and its not the most feasible to hand crank everyone's phones. if there was a hand crank battery maybe, but still – nick Mar 16 '24 at 14:57

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USB is normally 5 volts and is allowed to be up to 5.5 volts. 6 volts is out of specification, and 12 volts is much too high and creates a high risk that you'll permanently break the phone. (On the other hand, you might not. Maybe your phone is safe from this. Other people's phones might not be.)

If someone else plugs their phone into 5.45 volts and it breaks, it's their fault. If they plug their phone into 6 volts and it breaks, it's your fault and you will have to pay for their new phone.

You should get some type of converter/regulator module that will convert any voltage to 5 volts. They are quite cheap and plentiful at any electronics supplier. Search for 'buck converter' (decreases voltage), 'boost converter' (increases it) or 'buck/boost converter' (does either). It will be a little circuit board with somewhere to attach input and output wires. If you can't solder then see if you can find one with screws for the input and USB connectors for the output.

Some are adjustable with a knob or you can get one that's pre-set to 5 (or 5.5) volts.

Important numbers to look at are the output voltage, allowed input voltage, and maximum current.

A buck converter can only decrease voltage, so even if it says the output is adjustable 3V to 30V, to get a 5V output the input must be higher than 5V (probably higher than 6V - leave some safety margin). Likewise, a boost converter would need an input lower than 5V (probably lower than 4V).

If yours is adjustable, setting the voltage a bit higher than 5 volts (but not more than 5.5) isn't a bad idea, since the voltage will drop a little between the converter and the phone when it starts pulling current.

AA, AAA, C and D cells start at about 1.6 volts each when brand new, drop down to 1.5, then slowly drop to about 0.8 volts by the time they are completely empty. So make sure the converter you choose can handle the brand new battery voltage as well as the completely empty voltage, so you can use all the power in the batteries.

To charge several phones at once, simply connect them in parallel. In parallel, the amperage adds up. I'd estimate about 2A per phone, to make sure I get a big enough voltage converter. The actual amount will probably be less than that.

Phones can adapt their charging speed depending on how much the power source says it can provide. A very easy and standard signal is to simply connect the two data pins to each other. This tells the phone it can use 1.5 amps. If you want to charge more phones more slowly, you could try one of the other signals to tell them to slow-charge.

user253751
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  • Most phones use Type-C and will negotiate higher voltage. The phones will complain about slow charge or won't charge at all, if you provide only 5V and they cannot negotiate higher voltage or how much current is available. – Justme Mar 16 '24 at 17:29
  • @Justme My phone charges just fine on 5V with the data pins shorted together. I'm not sure they can charge much faster than that anyway. You might be thinking of tablets and laptops, which use more power and have much bigger batteries. – user253751 Mar 16 '24 at 17:43
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    I get your phone works like that but it might not be what OP has. You need to think all the phones or at least all the phones the OP ever wants to charge. – Justme Mar 16 '24 at 17:46
  • @Justme I don't think other phones have much bigger batteries than mine. There's only so much space in a phone sized plastic box to fit a battery into. – user253751 Mar 16 '24 at 17:48
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    It's not about the size of the battery but what kind of charger the phone wants to see. Even low end Android phones have had Type-C port for years and expect the charger to be able to negotiate 9V or 12V. – Justme Mar 16 '24 at 17:51
  • @Justme I normally charge my low end Android phone plugged into a type A port via adapter cable, since I don't have a type C charger. Works fine. Sometimes I also charge it via my own electronic box that outputs 5.5V with data pins shorted. Also works fine. Also works fine on other people's phones. Do you have any actual evidence for your statement that contradicts my real-world experience? – user253751 Mar 16 '24 at 17:53
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    My phone has Type-C and came with Type-A charger and cable between them. They will still negotiate up to 12V voltage. Your Type-A charger may be similar and it outputs 12V when your phone tells it to, and your phone may also be happy with 5V and not complain about it. I am just saying, not all phones work like yours do. – Justme Mar 16 '24 at 18:01
  • @Justme You still need to provide some evidence to back up this statement. – user253751 Mar 16 '24 at 18:03
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    For the evidence, please read Wikipedia page for Quick Charge. There should be enough evidence about standards, protocols and manufacturers who support QC over USB Type-A. You can also read what is printed on your charger. But also 5V protocols like BC exist up to 1.8A and maybe beyond that. 2.1A ports are proprietary. – Justme Mar 16 '24 at 18:16
  • thank you so much, i will look into boost/buck converters, and try to find one that fits, i am looking for fast charging options also, and to get into wireless QC charging when i can, but wanted to figure this out first. should i be adding fans to generally cool the batteries also or will the buck converter solve that issue as well? – nick Mar 16 '24 at 19:10
  • @Justme 1.5A is standard USB - see the hyperlink. – user253751 Mar 16 '24 at 21:56
  • @nick If they get hot, you can add a fan. If they don't get hot, you don't need a fan. If they get hot it also means you are also wasting power by using it too fast. You can get more power in total if you don't use it too fast. There's a reason phones and laptops use lithium-ion or lithium-polymer cells, not alkaline D cells. You can probably find wireless chargers that have a 5 volt input or some other voltage that you can get a converter for. – user253751 Mar 16 '24 at 21:56
  • @user253751 if i have a buck converter would i need to use one for each usb output, or am i good to have 4 or 8 usb ports in parralel? – nick Mar 17 '24 at 01:46
  • @nick you can put USB ports in parallel; make sure the max amperage is enough – user253751 Mar 17 '24 at 20:20