Dimming Rechargeable 18650 3100 MAH 20A Batteries in a Pack

Thread Starter

PropsGuy

Joined Jun 20, 2019
7
Hello,

I'm a film guy working on a low budget project with a handheld "technological prop" whose main feature is a very bright light. Form factor being small, we were looking at flashlight options and our target for the tech is the Ace X80 tactical flashlight.

Specs here: http://www.acebeam.com/x80

14 volts I believe. The battery pack consists of 4 rechargeable 18650 3100 MAH 20A batteries, protected.

More info here:

https://www.batteryjunction.com/acebeam-imr-18650-3100mah-lithium-ion-battery.html

The art direction calls for dimmable light as an effect. My question: is it feasible to add a dimming switch or circuit (or both) to safely adjust the brightness of the torch? How would that effect the battery circuitry? Would it require switching to unprotected batteries, or is that a bad design decision? Also, could a 18650 battery rated at 3400 MAH work in the same circuitry, or would that be a problem?

Also, is that something I could put together fairly simply with good soldiering skills and a diagram and parts list? I am not an electrical engineer, obviously, but I am quite good with building things and technology, so the practical aspects are inside my wheelhouse. The proper safety, feasibility, and circuit design are not, so I could use some counsel.

Thanks!
 

crutschow

Joined Mar 14, 2008
25,698
You could likely add a PWM circuit controlling the current to the LEDs, such as one using a 555 timer, but you'd have to determine where in the circuit would be best to connect the added circuit.
Intercepting the wires to the LEDs may be the easiest.
Also need to determine where this circuit would physically reside.
There's likely little extra room inside the torch.

It should have no effect on the battery or its circuitry.
 

Alec_t

Joined Sep 17, 2013
11,758
Intercepting the wires to the LEDs may not be a simple matter though, given that the torch contains LEDs of different colours which, presumably, are individually selectable?
I think any additional dimmer circuit would have to be external, but then obviously would need the torch case to be drilled for wires to pass through. That could compromise the 'waterproof to 30 metres depth' rating.
Also, could a 18650 battery rated at 3400 MAH work in the same circuitry, or would that be a problem?
Providing the discharge-current rating is adequate and the physical size matches that should be ok (but I wouldn't mix cells of different capacities).
 

mvas

Joined Jun 19, 2017
537
Hello,
I'm a film guy working on a low budget project ....
If you "film" this event and you decide to use PWM, ie a flickering LED, then ...
verify that there will not be any artifacts between the PWM On/Off frequency and the "film" speed.

I would do a variable constant current source ...
 

Thread Starter

PropsGuy

Joined Jun 20, 2019
7
but you'd have to determine where in the circuit would be best to connect the added circuit.
How would I proceed with that?

As far as fitting extra circuitry - the form factor is not the torch, the torch fits inside the final piece. There should be adequate room for any additional circuitry.

Intercepting the wires to the LEDs may not be a simple matter though, given that the torch contains LEDs of different colours which, presumably, are individually selectable?

Providing the discharge-current rating is adequate and the physical size matches that should be ok (but I wouldn't mix cells of different capacities).
The different light settings (high, max, and ultramax) employ groupings of LEDs - but I'm not sure normal usage targets individual LEDs.

I think people are getting the wrong idea about the torch - it's material resources, not finished product. I expect to destroy it in the process as far as casing, or any waterproofing is concerned. That's how prop building goes.

If you "film" this event and you decide to use PWM, ie a flickering LED, then ...
verify that there will not be any artifacts between the PWM On/Off frequency and the "film" speed.

I would do a variable constant current source ...
Can you elaborate on the variable constant current source? Because film is the verb, not the medium - shooting digital on this project as you smartly assumed. What kind of flicker rates are we talking about here? Can that be improved by adjusting that metric in the circuit or chip?
 

dendad

Joined Feb 20, 2016
3,625
A lot of LED torches have a current source built in. You may be able to modify that to control the current.
An investigation is in order to see what you have to start with.
 

oz93666

Joined Sep 7, 2010
737
The flashlight you have linked to has "Highly focused beam for maximum distance" ..I don't think this is what you want for filming ... shone on a wall 10 meters away it will probably give a circle of light about 1 meter in diameter the rest will be dimly illuminated ...

Dimming flashlights is also problematic for reasons already mentioned.

You need to excplain how tight a beam you want , spotlight effect or illuminate whole area ??? and how much power???
 

Thread Starter

PropsGuy

Joined Jun 20, 2019
7
A lot of LED torches have a current source built in. You may be able to modify that to control the current.
An investigation is in order to see what you have to start with.
Are there any resources for what a typical torch circuit on this device might look like? I'm still trying to track down the actual schematics but the company is Chinese and those might be a trade secret.

The flashlight you have linked to has "Highly focused beam for maximum distance" ..I don't think this is what you want for filming ... shone on a wall 10 meters away it will probably give a circle of light about 1 meter in diameter the rest will be dimly illuminated ...
:) Thanks but I'm not looking for advice on the effect itself - it's dialed in. For the record, this torch performs beyond what you describe in field tests - shown on any light colored wall 10 meters away, it would "blow out" the wall on a camera monitor.


This website is stripping the time modifier - action can be seen at 17:10.

We're shooting outside, so that doesn't matter. My requirements as far as performance goes essentially IS that flashlight, minus the need for the casing, but including size, lenses and output dynamics. I appreciate you're approaching it from an engineering standpoint. That's not quite what we do when the budget is low (most films). We put on an eyepatch and start hacking away like pirates until the battle's won, so to speak. You get used to sawing up brand new tech rather quickly.

I'd be open to a home-cooked system from scratch, but it's not a Marvel film, and this has the LED configuration baked in. We might go with a fewer lumens torch option, once the DP gets back to us, but even with half the lumens, the essential problem remains - dimming.

Back to what Alec_t mentioned about individually selected LEDs - found a diagram of the Single Button UI, which looks annoyingly complicated. It also suggests there is a chipset that controls the range in a specific manner.

Question: does this complicate matters? Can the dimming switch be placed in a position in the circuit that bypasses that functionality to render all modes effectively dimmable?

Want to thank everyone replying as well, I appreciate your time and experience.
 

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Thread Starter

PropsGuy

Joined Jun 20, 2019
7
You will probably have to trace the circuit and work out how it operates.
Something like from this web site may be inside it.
https://www.lightmalls.com/flashlight-diy-accessories
That site is great resource, thank you. As far as "working out how it operates" - I'm not an engineer. I can build an operate an Arduino and make some cool things happen - but as far as how the actual electrical signals propagate through the system, how voltage differences create information states, how timing becomes a language - none of that is in my wheelhouse. Arduino is Plug n Play, standing on the shoulders of giants, or at least the engineers.

Is there anyone out there who can take the given power source, and the given load from the LEDs and a simple switch and draw a basic diagram of what it "should" look like? I understand the control chipset will complicate things, but that complication should also be within a small finite design footprint given the UI. I'm not looking to the community to reverse engineer the exact circuitry, but a basic blueprint, that identified locations for possible dimmer introduction in the schematic would put me on the right track and give me a sense of the scope - since true scope eludes me in my ignorance.

Trying to get as much information as possible so I don't fry the unit with poorly planned bending.

Alternatively, is there a method for hiring small scale engineering work through this site? Or another site that might offer that kind of resource?

Perhaps I have the wrong perception of the matter, but I view this problem as something fairly simple. It feels like not being able to cook, and thinking cookies are some kind of mysterious wonder, when the recipe couldn't be simpler. So, here I am not knowing how to cook circuitry..
 

Yaakov

Joined Jan 27, 2019
1,612
What is the action of the dimming? Are they set shots at different intensities or dynamic?

If the former, maybe you should consider optical filters, possibly a variable ND. It will mean heat but it’s easy and certain.
 

Thread Starter

PropsGuy

Joined Jun 20, 2019
7
What is the action of the dimming? Are they set shots at different intensities or dynamic?

If the former, maybe you should consider optical filters, possibly a variable ND. It will mean heat but it’s easy and certain.
Exterior night shot. Just to be clear - the light is practical, and the effect is practical. Hero Prop is a piece of technology that emits extremely bright light. But it sits on the ground and points upward. Not quite a burn transition or a fade to white, but overexposure is an element of the shot for sure. The effect is a dramatic rise in light intensity. Takes place in a forest with low enough canopy to catch the effect, but not so low as to bounce it all back into the shot. If it didn't need light to emanate from the prop itself, I'd just have the lighting guys set up a 10K on the floor. But it's seen and a major reveal so, here I am..

Are you suggesting putting an ND on the torch lens? Or shooting with an ND on camera to achieve the effect? I thought in camera, but you mentioned heat. On the unit itself is an interesting solve I hadn't thought of, but it won't work here. It has to "do the thing" without being touched or manipulated.

Lots of ways to skin this cat. Really just looking for tech advice on bending this flashlight circuit to introduce dimming behavior. Also, wondering if the LEDs are required to be wired in series for dimmable functionality to occur..
 

Yaakov

Joined Jan 27, 2019
1,612
A variable ND on the prop. I suppose you could motorize it if dimming proved impractical. IF you use PWM you may have a problem with strobing depending on frame rate.

Making it dim is not impossible, but since PWM might not work for you, it could be tricky.
 

Thread Starter

PropsGuy

Joined Jun 20, 2019
7
A variable ND on the prop. I suppose you could motorize it if dimming proved impractical. IF you use PWM you may have a problem with strobing depending on frame rate.

Making it dim is not impossible, but since PWM might not work for you, it could be tricky.
Motorized ND lens is not happening - too complicated, and budget too small. PWM looks promising actually, there's been huge development cycle dealing with dimmable LED house lights. Not that I'll be working at 110v but the design wave made a huge impact on what's available commercially.

Definitely looking deeper into PMW.

I'd love to get input on this chipset from Maxim Integrated

https://www.digikey.com/en/product-...rated/max16819-20-high-brightness-led-drivers

It seems like the right idea, but I think the voltage range is more in line with household appliances..
 
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