Electric Gauntlet for Phone, Flashlight & Laser Pointer: Battery Selection Guide

[Stephenk53]

I plan on creating a gauntlet that can power my phone, a flashlight and a laser pointer, preferably all at once. However I am having trouble picking a battery for it, I already have the laser pointer and flash light from previous purchases. The flashlight is normally powered by 4 aa batteries in series while the laser pointer uses 4 coin batteries (I will have to double check). I could just get a battery for each individual function but I would like to instead have a single battery pack. I would like it to have at least 7ah.

For now I only want help in picking a battery then after that I will try to design the gauntlet to meet it's needs myself and then get it checked before purchase

 

[berkeman]

I would like it to have at least 7ah.

At what voltage? And from the datasheets, it looks like Alkaline "D" cells only have a few AHr capacity (3-ish). Rechargeable batteries will have less.

https://www.duracell.com/en-ca/techlibrary/product-technical-data-sheets

 

[anorlunda]

Do you mean gauntlet as in a glove?

I think the easiest way to do that is to select phone/pointer/flash that are all able to be powered by USB. Then I would buy one of those battery+USB devices. Those devices cost only a few dollars and they come in many shapes, capacities, and sizes. Below is a random image of one such device.

 

[anorlunda]

What about safety? If the gauntlet and battery take a blow, the battery might catch fire or explode while on your hand.

 

[Stephenk53]

I would like around 6v, earlier I found some rechargeable d cell batteries that are rechargeable at 1.2v at 10ah, so I though of getting 5 in series to be 6v then I would have it go to the flashlight or laser pointer at 6v and would go to the phone through a car phone charger that would bring it to 5v. However I would like to be able to recharge all of the batteries at once also I have worried that the d cells may take damage due to the cold weather since if I recall corectly they were rated to a minimum 50F (10C) to 86F (30C), and I live in New England where we often get temperatures far below that, and occasionally above.

For clarification it would fit around my wrist up to my elbow if needed. As far as taking a blow I was planning on encasing it in metal, I have some metal left over from taking apart some stuff earlier and I can always get spare metal from my school. (technically not my school but I attend a robotics club there and we often get scrap metal that I likely could use)

 

[anorlunda]

You can buy 3.6V lithium batteries in D format. They work better than other chemistries in very cold temperatures.

Phones use USB chargers. A pointer and flashlight may tolerate higher/lower voltages, it depends on the brand. You could test them in advance. That's much simpler than trying to change the voltage.

Safety still concerns me. See this video. D cells hold even more energy than a phone battery.
How about a layer of Nomex between the battery and your skin? Nomex is not heavy or expensive.

Be safe

 

[Stephenk53]

You can buy 3.6V lithium batteries in D format. They work better than other chemistries in very cold temperatures.

Phones use USB chargers. A pointer and flashlight may tolerate higher/lower voltages, it depends on the brand. You could test them in advance. That's much simpler than trying to change the voltage.

Safety still concerns me. See this video. D cells hold even more energy than a phone battery.
How about a layer of Nomex between the battery and your skin? Nomex is not heavy or expensive.

Be safe

Good idea, I will look at some lithium batteries and get back to you.

 

[Stephenk53]

Assuming the devices can handle the voltages do you think these work? They are not d batteries but I can wire them in series parallel.
https://www.amazon.com/dp/B074CSCWRL/?tag=pfamazon01-20

 

[anorlunda]

Assuming the devices can handle the voltages do you think these work? They are not d batteries but I can wire them in series parallel.
https://www.amazon.com/dp/B074CSCWRL/?tag=pfamazon01-20

Yes.

Also look for the size 18650 . Those are the batteries used in the Tesla Roadster. Good price performance point.

 

[Stephenk53]

I haven't tested if they can handle the voltages yet since I am currently at school, but I made a quick design, it is the fourth circuit diagram I have made before so it isn't perfect.

 

[Stephenk53]

Alright here it is

 

[anorlunda]

Not bad. You realize that the resistors will eat up a big fraction of the battery energy?

The flashlight and the pointer may possibly work with just 3.7v. It is worth testing before building a circuit.

A prefab car charger? Like this?

It puts out 5v, but it takes in 12-24v the car's voltage. So, to use that you need to increase the voltage, not decrease it with a resistor.

But simpler still, you can also get 3.7v USB chargers. https://www.ebay.com/itm/1-Efan-IMR-21700-4800mAh-3-7v-40a-High-Drain-Battery-w-Efest-K1-USB-Charger/232596710041?epid=12011364117&hash=item3627d82299:g:gPcAAOSwGPxaMiQh

 

[Stephenk53]

I know the resistor would use up charge but i thought it was needed to get the right current. I will test the laser pointer and flashlight once I get home. I will try getting a 3.7b usb charger like you mentioned

 

[anorlunda]

Try them at 3.7v not 7.4v.

 

[Stephenk53]

Okay

 

[Stephenk53]

I tested them with 3v since I happened to have some aa batteries and the flashlight works fine, as for the laser pointer I could not find it but I do have a laser diode mixed in with my spare electronics scrap, that I think is from a dvd player. So I will test that tonight

 

[anorlunda]

Good start. But it is possible the pointer will work at 3.7v but not at 3v.

 

[Stephenk53]

I just found and tested the laser pointer and it works at 3v. I also used an ohms law calculator so I could quickly double check the current of the flashlight and since it says it is a 5mw and normally works at 4.5v it uses 1.111ma with 4050ohms of resistance. The resistance sounded too high to me so can you double check that

 

[anorlunda]

Electronic things are not linear. That means that Ohm's Law is not useful predicting their behavior.

The current values you showed in your circuit diagram are maximum values. That means they might draw any current less than the max.

So I suggest you forget about currents. The device either works or doesn't work at the voltage you provide.

The exception may be the cell phone. Many of them are "smart" That means if they have a weak charging source, they slow down the charge rate, so it would take a lot more time to charge.

So, you said the flashlight works, the pointer works, and there is a 3.7v USB charger. I think you're all set without any special circuit or resistors. The simplest is to use one AA size battery for each device. Don't bother to connect them to each other. When you buy the lithium batteries, you can also buy a recharger for them.

I hope you can find a small square of Nomex to line the inside of the gauntlet to protect your hand.

Good luck