Powering 3.7V IR Torch with USB?

[Victor Keys]

Hi,

I found this forum via a search. I was reading a thread similar to the info I was looking for but I didn't get the answer I needed so I decided to sign up and post my question. What I am attempting (hopefully) is to power this IR Torch (https://www.amazon.com/Evolva-Futur...&redirect=true&ref_=oh_aui_detailpage_o00_s00) with a USB power pack so I don't have to keep switching out batteries on my night fishing trips. My action cams are modded to see IR light and run on my USB power packs. The torch currently runs on a 3.7V 2600 mAh 18650 battery. Do I need to make a dummy cell with a resistor connected to a wire with a usb plug? Any help would be appreciated!!

-Victor

 

[audioguru]

If you do not use a proper Lithium-ion battery charger circuit then you will probably have a very hot fire or explosion.
If you remove the battery cell then the USB probably might not have enough current to drive the infrared light, after reducing the voltage to 3.7V too 4.2V. How much current?

 

[Victor Keys]

Yes I'm looking to remove the battery and either wire up usb directly to contacts (after stepping down voltage to 4.2?) or use some sort of dummy cell. Are you asking how much current the power pack supplies? Forgive my ignorance. This is foreign stuff to me but I had the idea in my head and was hoping I could make it a reality...with some help of course!

 

[audioguru]

You need to know the current draw of the torch and whether the USB can provide that much current. A silicon diode (rated for the current) in between the 5V of the USB and the torch will reduce the voltage to 4.0V to 4.2V.

 

[DirtyLude]

For Easy, DIY, I would buy a buck converter module and put it between your power bank and your flashlight.

If you search e-bay for '3a buck step down', you'll see some little adjustable switching regulators. If you need more current, then just search 'DC DC Buck' and order by price. The small ones a rated 3A, but they will likely do maybe 1.5A without cooling of some kind. Simple and easy to use. Just make sure you use a multimeter to adjust it to the voltage level you want. 3.7 volts and then hot glue the pot so it doesn't move.

As mentioned, you will need to know whether your USB power bank will be able to handle the current. You'll need to know how much current that flashlight uses. Some power banks will put out quite a bit of current. These aren't PC USB connections and many are rated for 2.1A and some will do more.

 

[audioguru]

A "power bank" has a little rechargeable battery in it, maybe the same capacity as used in the torch. The OP wants to avoid switching out batteries. He did not say if the "USB power pack" has a battery and if it does he did not say its mAh capacity. He also does not know how much current is used by the torch.

 

[Colin]

The torch will have a constant current circuit internally.
To find out if this is the case, connect a variable supply to the cell contacts and adjust the voltage from 3v to 4v. If the current stays the same you can gradually increase the voltage to 5v.
But the losses will take place in the constant current circuit and it may over-heat. That's why it is best to add a power diode to absorb some of the losses.

 

[Victor Keys]

I have a few 15,000 mAh power banks which I use for my gopros already. They have four usb outputs on each: a 2.4A, 2.1A, 1.3A, and 1A. The battery for the torch is a 2600 mAh and runs it for 2-2.5 hours. Also, my friend has a multimeter so can/should I use that to see how much amperage is drawn by the torch?

 

[Colin]

You need to determine the current because some USB ports are limited to 1 amp

 

[Victor Keys]

If I figure out the amperage draw of the torch and it's 1.2 or less then this would work here right? **broken link removed**

 

[Victor Keys]

Colin, as I stated above, my power banks will do 2.4 amps.

 

[Colin]

Before you start mucking around, do I what I say. You don't know what you are doing.

 

[DirtyLude]

If I figure out the amperage draw of the torch and it's 1.2 or less then this would work here right? **broken link removed**

That would work, but it's not good to push the specs of these chinese modules. You would be pushing that at its max. I've used these successfully. The slightly larger versions.
https://www.ebay.com/itm/Supper-min...804519?hash=item3aa5dca727:g:DFIAAOSw7aBVEOSH

As mentioned, your flashlight LED driver might be 5V tolerant. I have no idea how to find out, though.

Also, my friend has a multimeter so can/should I use that to see how much amperage is drawn by the torch?

Yes, use the multimeter to find out the current draw. Your friend should know how, if not there are a lot of tutorials on the web.

EDIT: You'll also need that multimeter to set the voltage level on the adjustable regulator, no matter which one you get. Make sure you do that and lock it down before attaching it to the flashlight.

 

[audioguru]

Why are you buying a cheap Chinese buck converter when the Chinese manufacturer is lying about its current? The datasheet of its American AMS1117 IC has its spec's stop at 1A. Above 1A the output voltage drops. But some of them produce 1.5A into a dead short (0V output).
I think your torch draws (2600mAh/2 hours=) 1.3A.

 

[DirtyLude]

Why are you buying a cheap Chinese buck converter when the Chinese manufacturer is lying about its current? The datasheet of its American AMS1117 IC has its spec's stop at 1A. Above 1A the output voltage drops. But some of them produce 1.5A into a dead short (0V output).
I think your torch draws (2600mAh/2 hours=) 1.3A.

Because. that's not a 1117 nor do they claim it to be. A 1117 is a linear regulator not a switcher. The 'repl' shortform in front of AMS1117 is saying it replaces an AMS1117. As you can see from the ad they throw in as many search words as possible to get hits. Any common search word that somehow relates will be thrown into the description.

 

[Victor Keys]

So it just dawned on me that I may have had the piece I needed sitting right in my house. I had an extra battery eliminator for my gopros kicking around (the connector that went to the gopro was broken) and after seeing the pictures of a buck step down I realized that that's exactly what my gopro battery eliminators used. I checked the gopro battery and it is 3.8v. I had my buddy meter the step down and it was reading 4.2V...perfect! The gopro draws ~1 amp so I thought it might just work. My buddy soldered up the usb cable and step down to the pill on the IR torch and it worked!! So we drilled a hole in the torch body and tucked the step down and wires in the battery chamber and it's all good to go. I want to thank you all for chiming in. It was much appreciated!!

 

[DirtyLude]

Nice, just make sure that thing isn't over heating, especially if you have it enclosed in the battery compartment.

You can do the reverse as well if you need to. I have a charger for my handsets that takes 10V for some odd reason. Attached a step up regulator to charge from a USB battery pack.
**broken link removed**

 

[Victor Keys]

Nice, just make sure that thing isn't over heating, especially if you have it enclosed in the battery compartment.

You can do the reverse as well if you need to. I have a charger for my handsets that takes 10V for some odd reason. Attached a step up regulator to charge from a USB battery pack.
**broken link removed**

I'll keep an eye on the temp when I have the light on for 1-2+ hours...make sure all is good...thanks for the tips!!