Disabling the low-power shutoff of a small boost circuit

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
80
I'm looking to purchase a charging/protection/boost circuit for some lithium batteries like the USB-C option seen here, but it has a low-power cutoff that will be annoying. I'm going to be using it to power an LED headlamp, but said headlamp already has some electronics in it so it won't be powered directly, and it will be frequently off for a few minutes at a time, then on again. I've looked at a lot of these types of circuits, I can't seem to find any that have all the features I want and are sans the low power cutoff (so if anyone knows of a nearly identical circuit sans cutoff, that would be great). How would I disable/bypass the cutoff? I'm guessing there's a cap and a resistor for feedback, and maybe I could increase the cap size and resistor size, to give myself more like an hour before cutoff? Or is that little tiny 8-pin chip reprogrammable, so I could just disable that "feature?" The easiest thing of course would be to just add a 100ohm resistor across the output but then if I forgot to turn that off it would discharge itself in about 4 days max which I don't want. So any ideas are welcome!

Also if this is the wrong forum I apologize, and please move it appropriately. Thanks!
 

LowQCab

Joined Nov 6, 2012
1,372
Can You create your own simple Circuits ?
or are You going to be relying on pre-built-Modules ?

Do You already have the Batteries that You want to use ? (Specifications)

Do You have Specifications/Schematic for Your Head-Lamp ?

Where is the Power-Switch ?

Do You intend to use a USB-Cable to transfer Power from the Battery to the Lamp ?
(not recommended)

How was the Head-Lamp originally intended to be Powered ?
.
.
.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
80
Can You create your own simple Circuits ?
or are You going to be relying on pre-built-Modules ?
I could make my own I think, I've done a few, but mostly worked with MCUs and just added to them, not many whole circuits from scratch, but I'm familiar with lots of components and I'm not opposed to building one myself, I only need a couple of them. Pre-built would just be easier and possibly cheaper for me.

Do You already have the Batteries that You want to use ? (Specifications)
I purchased some 21700, 3.7V, 5,000mAh lithium cells, 5C/25A rated output. They're no longer available so I have no link.

Do You have Specifications/Schematic for Your Head-Lamp ?
I can't find much besides the Home Depot page for the light: Coast FL74, but the gist is 500 lumens, 3 brightness settings, and a secondary button for separate green and red LEDs, designed for 3xAAA batteries. I've tested it and it physically works fine with a 5V USB cord cut, stripped and alligator clamped to its input terminals.

Where is the Power-Switch ?
Don't have a determinate place yet, but it will be somewhere on my head. And the main point is of course to make sure that I have only 1 button, which gives me an idea: if the button on the switch built into the light pulls down to ground, I can simply tie a wire in from the button back to the IC, because it works by being pulled to ground. I'm gonna test that and see because that might be the best option if it works.

Do You intend to use a USB-Cable to transfer Power from the Battery to the Lamp ?
(not recommended)
Yes m but only because it seemed convenient. I would also pretty gladly just hard wire it in to the projection circuit. (Why it's the USB not recommended?)

How was the Head-Lamp originally intended to be Powered ?
3xAAAs
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
80
Yes, it looks like the other button pulls to ground, so I should in theory be able to just wire the two in parallel across the switch. Hopefully they won't operate at such different voltages as to cause problems. I'll do some measuring and testing to see what voltage they are working at and see if I can connect them (I have some different but similar ICs to test with).
 

LowQCab

Joined Nov 6, 2012
1,372
USB Connectors don't do well with lots of movement
and/or rough conditions, and
many will corrode easily in an outdoor environment.

Personally I don't think remote Batteries is a good idea for your Project,
there are a lot more points of failure, dealing with wires, carrying-case, etc.

Rechargeable Dura-Cell Triple-A's and a Charger are cheap and they're everywhere,
and should give You at least ~3-hours of Light per Charge.

A BMS-Board, a Switching-Regulator, and a Battery-Charger, can certainly be done,
but it's a lot of aggravation to go through
just to get a couple more hours of Run-Time out of a cheap LED-Head-Lamp.
If You needed ~5-Watts worth of LED-Light, it might be a different story,
but in that case you'd be talking about something like ~3-pounds worth of Batteries.

I have a similar Head-Lamp, and I still haven't put new Batteries in it a year later,
but then again, I've only put around 4-hours on it.

A Cell-Phone "Re-Charger / Battery-Pack" could be another option,
they already have all the required Electronics built-in.
.
.
.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
80
USB Connectors don't do well with lots of movement
and/or rough conditions, and
many will corrode easily in an outdoor environment.

Personally I don't think remote Batteries is a good idea for your Project,
there are a lot more points of failure, dealing with wires, carrying-case, etc.

Rechargeable Dura-Cell Triple-A's and a Charger are cheap and they're everywhere,
and should give You at least ~3-hours of Light per Charge.

A BMS-Board, a Switching-Regulator, and a Battery-Charger, can certainly be done,
but it's a lot of aggravation to go through
just to get a couple more hours of Run-Time out of a cheap LED-Head-Lamp.
If You needed ~5-Watts worth of LED-Light, it might be a different story,
but in that case you'd be talking about something like ~3-pounds worth of Batteries.

I have a similar Head-Lamp, and I still haven't put new Batteries in it a year later,
but then again, I've only put around 4-hours on it.

A Cell-Phone "Re-Charger / Battery-Pack" could be another option,
they already have all the required Electronics built-in.
.
.
.
I'm willing to risk it with the USB connectors. I'm an electrician and it will definitely be used a lot, and in rough conditions, but I'm willing to risk it for now. And if it becomes problematic, I can turn to hard wiring.

Remote batteries are exactly what I want, something long-lasting, and balancing the weight from the front of my head. The highest cap rechargeable AAAs I can find on Amazon (that are of a reputable brand) are eneloop 950mAh. 0.95*3.6V=3.42Wh, 5*3.7=18.5Wh, 5.4 times greater. Even with efficiency losses of let's say 10% (most of the chips I've seen claim 93-95% efficiency, so that might be on the high side), that's still 4.87 times greater capacity. I've had to change AAAs 2x in one day some times using Duracells, so this is really what I think is the best way to go, all told. I've thought plenty about other factors, but this is how I want to do it (if I can figure it out reasonably). I'm considering using a Seeeduino Xiao because I have extras of those and they have a powersaver/sleep mode which I think takes it down to uA of current usage as it sits in standby, with a MOSFET for PWM control for brightness of the LED, and a tiny alert speaker for low voltage in case it sits too long or something like that. I know it's overkill but I know how to do it that way and make it work (but I've not exhausted other options yet).

Also please remember that my headlight maxes out at 500 lumens, which I do use fairly often. Based on my experience, it's going to be about 100 lumens/W, so yes, I will need 5W of power on a fairly regular basis (2/3 of the time I'm probably on medium or low, but I do use high some times). And a 21700 cell certainly is nowhere near 3 pounds, yet at 5W could run for over 3 hours. The rechargeable AAAs would run for 15 minutes or less, and probably be less bright the whole time at those power levels.

I've tried cell phone rechargers of various types, and they all have the auto shutoff problem so I have to click them on before I can click on my headlight even if it's only off for like 30 seconds (which happens when I have to talk to a coworker or am in a brightly lit area briefly). I also wanted something with a removable cell of 4-5Ah, so I can swap it and keep going, and so it wouldn't be as heavy or bulky as some of the bigger options.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
80
Here's the board I have in hand that I'm currently experimenting with.21700 holder PCB.jpg
The 8-pin seems to be a chip specifically designed to handle lithium battery charging (also, knowing this IC exists makes me more likely to just DIY my own circuit). I believe this data sheet is for it. I might be able to just reprogram it using I2C bus. Time to do some reading!

EDIT: Did some reading, the IC has a timer inside. I'll have to contact the manufacturer to see if there's a way to reprogram it or something.
 
Last edited:

DickCappels

Joined Aug 21, 2008
8,000
People use head-mounted lamps around here for nighttime hunting of small creatures. The lamps are often powered by motorcycle batteries carried in a sling over the shoulder. Easier for the shoulder to deal with the new weight than the neck.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
80
People use head-mounted lamps around here for nighttime hunting of small creatures. The lamps are often powered by motorcycle batteries carried in a sling over the shoulder. Easier for the shoulder to deal with the new weight than the neck.
As I've stated, I'm looking at using a 21700 cell, and those are really not very heavy, so I know it'll be fine. A motorcycle battery over the shoulder is extremely impractical for climbing in attics and under houses.
 

Thread Starter

LikeTheSandwich

Joined Feb 22, 2021
80
In my research I found out about the 555 timer, and the 555 calculator here on AAC. Did some experimenting with the calculator and I think it will do what I need so I'm gonna order some and try adding these to trigger the "key" every ~30 seconds or so. That should do what I ultimately need, and it's cheap. But whether it works or not, I think I'll try using some sort of ATTiny next time I need a timer.
 
Top