Question about volts, AA batteries, and sight line red lasers

OK, so I bought some of those sight-line red lasers, for attaching to saws, CNC machines etc. I also bought battery packs for them (separate vendor). The battery packs were recommended for them. The packs take 3 AA batteries, which are 1.5v each. So, run in series, doesn’t that mean the pack provides 4.5v? And if so, does it stand to reason that the little lasers could be powered by 5v power from my control box (which has its own 5v power supply)?

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Answering my own first question: seems I am correct about the 4.5 v.

Quoting from this site:

Three AA’s in series gives us a voltage of 4.5 V (3 times 1.5V). You could also add another battery for a total of 6V and regulate the voltage down to what your circuit requires.

Does anyone have any advice on whether the difference between 4.5v and 5v is within tolerance or not for the little sight-line red lasers?

I don’t know the answer to your question, but the lasers are a smart idea. :smiley:

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Idk about the specific diode in your devices, but guessing it won’t hurt to do some tests. Adafruit provides voltage supply specs for the laser pointer they sell, 2.8-5.2V:

It would be a fair assumption that your lasers can also handle a tad over 5V. Current when driving leds near Vf can be a bit unpredictable, but I’m not sure if laser diodes behave the same. If you have a multimeter with current measuring abilities, you could measure draw to make sure it won’t be too much for your existing 5v source.

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Thanks guys!

I seriously considered running 5v from the control box (and I had already tested it with a multimeter and confirmed it was spot on 5v), however, since one battery pack with 3 batteries will indeed power two of the lasers, I am just going to use the batteries. In fact I already soldered the laser wires to the battery pack and used double stick tape to attach the battery pack. I’m currently whipping up a bit of printed mounts to attach the lasers. Exciting stuff.

Stuff that runs off of batteries has to be tolerant of large voltage changes. Because batteries themselves do in voltage when then discharge.

Alkaline batteries are the common disposable type. It looks like they range from about 1.6V to 1.0V (4.8V to 3V for three):

I would have wired the lasers to 5V and assumed that would work :slight_smile:. Most electronics protect themselves from a wide range of input power. It is a nasty world out there in power supplies.

Other battery types have different voltage ranges. One thing you have to watch out for in rechargeables is that some devices don’t stop sucking current when the voltage gets too low. That can damage rechargable batteries. I trust it in smart stuff, out things with a hard switch that I will turn off. But I watch out for cheap kids toys that sit in a box for months draining when no one is playing with them.

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Good to know! I may yet wire the lasers to the 5v power supply, but for now I’m up and running with the battery pack. I am using normal (not rechargeable) batteries.

Coming soon on my plasma build thread: video with full SketchUp design process from start to finish, on going from this:

BEFORE:

… to this:

AFTER:

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I think you will be fine. New AA batteries can be 1.6V, perhaps higher when they are warm, so it has to tolerate 5V anyway.

I once toasted one of those small, super cheap laser pointers that contains button cells by supplying 5V DC. It had three little button cells that were alkaline 1.5V. In that case I think the device was depending on the limited supply current of the button cells, and I’m guessing they skipped a current-limiting resistor (or whatever). I think even if I had supplied 4.5V from a bench supply, it still would have drawn too much current and toasted itself.

In your case, being driven by AA batteries and not button cells, they can’t get away with excluding some kind of current control, so you should be fine feeding it with a supply capable of higher current.

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Thanks!

That is interesting. Using the two lasers to create the crosshairs. I may have to try this too. I already have the lasers (and battery compartments too). Once I start cutting with my LR3, I may play around and do this. Thanks for the idea.

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I finally got the video posted on YouTube of the newly designed printed holders for laser diodes making the crosshairs. I also posted about it here under Hardware Development, with link to the printable files.

Link for downloading files: Printables

Pasted from Printables:

Description

This video not only shows how these laser crosshairs are installed and work on my DIY plasma rig, but also details how I designed these holders from scratch — from start to finish using SketchUp (free 2017 version, the last free version that could be installed locally on a computer).

LowRider 3 CNC DIY Plasma PART 13 - Laser Targeting! - SketchUp Creation Process Tutorial!

Full details on my DIY CNC plasma rig:

BEFORE (no laser crosshairs):

00. Laser Holders for LR3 Plasma CNC - BEFORE

AFTER:

p01. Laser Holders for LR3 Plasma CNC IMG_3107 - COVER IMAGE

I may yet wire the lasers to the 5v power supply in my control box, but for now I’m up and running with the battery pack that holds three AA batteries. I am using normal (not rechargeable) batteries.

Print / assembly info:

  • Prints as oriented.
  • Prints without supports.
  • Suggested: either 2 perimeter walls (0.6 nozzle) or 3 perimeter walls (0.4 nozzle).
  • 20% infill
  • I printed using 0.6 nozzle with 0.3 layer height and 0.6 wall line width, but they should also print well with 0.4 nozzle using same settings (emulating 0.6) or regular settings.
  • Use two M3 x 10mm screws, one in each holder, to tighten the flanges to “clamp” the laser diodes into the holders.

Product links for items mentioned or related*:

  • Laser Modules — (2 Pack) Red “Line” Laser Generator 650nm 5mw Diode Lasers —
    https://amzn.to/3WLuKoK
  • Battery Holder with Switch — (4 Pack) 4.5V, from 3x 1.5V AA Batteries — Amazon.com
  • Heat Gun — 1800W, 122°F-1202°F(50°C-650°C — Amazon.com
  • XFasten Double Sided Woodworking Tape w/Yellow Backing 2.5 Inches x 30 Yards —
    Amazon.com

My PayPal tip jar: https://paypal.me/design8studio

Various LowRider 3 CNC remixes:

View all my models and remixes on Printables:

*Amazon product links are affiliate links.