27 Led Light Mod





Introduction: 27 Led Light Mod

And yes, It's yet another Harbor Freight 27 Led light mod ! I get these free from HF, and thought I might make one a little more useful. These lights are quite bright, even with the cheap batteries provided. I would recommend, even if you don't mod them, that you take a look inside. These batteries can ruin your light, depending on how long they've been sitting on the shelf. I was thinking one day after a power outage, that these little lights could be powered by a 12 volt DC adapter. I already had an adapter, that will provide multiple voltages from a 12 volt source. I'll put in a link to the one I have.

Remember, safety is YOUR responsibility. This is a DC only device. Do not use with AC current ! This Information is for educational purposes only.

Tools and Materials :

1. 27 Led Light - Harbor Freight.

2. Soldering iron and solder.

3. Light gauge wire

4. Power Jack

5. Step drill bit (optional)

6. Hobby Knife

7. Small heat shrink tubing (optional)

8. DC Adapter

9. 12v Socket extension cord

10. Here's a coupon for a free light. This way if you destroy it, at least it didn't cost you anything ;) Expires 1/3/18

So on to step one.

Step 1: Take It Apart !

These things are fairly easy to take apart. First take out the 3 screws on the back. There's a convenient magnet on the back, to keep the screws handy. Next remove the batteries, and then the four screws that hold on the front panel. Finally remove the 2 screws that hold the Led circuit board. Be careful when you move the Led board from its slot, that you don't break the wires.

Step 2: Modify Center Section

I disconnected the wires from the center battery section, to make it easier to work on. I then used a step drill or Unibit to drill through the peg on the battery section. You could probably use a standard drill if you're careful. I didn't want to crack to plastic, hence the step drill. After the peg is gone, I enlarged the hole with a hobby knife. You need to make room for the power jack, which is installed next.Just below the new cutout there is a thin wall. You will need to cut a half moon shape there for the wires from the jack.

Step 3: Drill Hole for Jack

I used masking tape to mark for the jack hole. There is a mold line in the plastic of the battery case. I centered the mark on that and used the center of the cutout I made earlier to mark the center horizontally. I used my hobby knife to make a small indent for the drill bit. Then with the step drill I drilled a hole slightly smaller than my jack. I did this so I could make flats in the hole to match the jacks barrel. Your jack may not have these flats. I used my hobby knife to make the flat sections. I just took a little off at a time, checking with the jack for fit. You don't won't to make the hole too big. I installed the jack and tightened the lock nut with needle nose pliers. This was just a test fit, I soldered on the wires and added heat shrink before installing the jack permanently. That is the next step.

Step 4: Install the Jack

I started the wiring by tinning the ends of the wires with solder. I soldered the wires to the jack and added some heat shrink tubing. I put the jack in the hole made earlier, and threaded the lock nut over the wires. I cut the wires to length and soldered them to the positive and negative connections. You probably want to run the wires around the screw posts as shown. That way you won't crush them when you put it back together. You can find polarity of the points, by looking in the battery box. I don't know if polarity actually matters here, but I connected the wires the way they were originally.

Step 5: Button It Up !

Now you can put it all back together. Be careful when tightening the screws, the plastic posts are easy to strip. Don't ask me how I know, ;) I tested the light first with the supplied batteries. Just to make sure it still worked. I removed the AAA batteries. I set the adapter on the 4.5 volt setting and hooked it up to a 6 volt battery I had sitting around. Voila , what do you know, it works !

I'm sure with this adapter, it will work on any battery from a 6 volt to a 12 volt. I tried it on a 6 volt wall wart type adapter and it worked, but it flickered badly. Probably not a regulated adapter. You'll probably want to remove the AAA batteries before running on an external battery. I don't know if it will hurt the AAA,s, but no need to chance it.

This thing will probably run for weeks on a fully charged 12 volt battery. Haven't tested that yet, but I will, and will post an update later. Hope this is useful to someone. Let me know how you use this, Enjoy,


P.S. I know somebody will say, Man, that's a lot of stuff hooked up, for what was a portable light ! Well, this is true. But to be able to run it on many different types of batteries may come in handy. Unless you have stock in a AAA battery company, that is. ;)



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    65 Discussions

    Updated links and added recent coupon for free light, enjoy !

    WARNING: If you reverse the polarity to an LED you will cook it for sure.There is even the chance it will physically pop. Also putting any amount of current on to a non-rechargeable battery WILL cause extreme heat and the thing might explode.

    7 replies

    Don't get me wrong, I'm it saying reverse polarity won't hurt leds, I'm just saying in my experience luckily it hasn't been an issue for me. I'm also not working with high voltage on my leds.

    Did this the other day by accidentally reversing the power from a pair of AA batteries. Piece nailed me in the cheek!

    Led 1.jpgLed 2.jpg

    Talk about popping, wire an electrolytic capacitor backwards...boy it blows like a big ol firecracker. Amazingly loud. Never had it hurt an LED though. It just doesn't light.

    I've worked with many, many leds, mainly with Arduino and adding them to my rc vehicles and never once had an led burned up or popped from reverse polarity. They just don't work with reverse polarity. Set it properly and they work fine even after reversing it.

    If you dump too much voltage and current into an led it has the potential to pop.

    I was actually wondering about this instructsbke becsuse I'd imagine that something designed to run on 4.5v isn't going to handle 12v very well at all for very long. I'm not surprised it works on 6v but surely the lifespan of the light will be decreased.

    Well, I do not say anywhere in this instructable that I run this light directly on 12 volts. Many people are reading that into the instructable, but this is not what I said. Please read the instructable carefully again. All five steps ! Thanks,


    Commented on and answered, several times, thanks,


    Great! thanks for posting....Anyone know a way to find technical spec's for these types of lamps. I've just rigged one up to the Arduino and altered fade tempo and intensity. Just wondered if I could determine what the LED's are and the resistors needed for other projects. Thanks.

    Great project! I've been modifying those free lights for years using old car cell chargers which put out around 5 volts. Or you can attach a USB cable to the light and power the light through any USB port (wall charger or lap top).

    LED lights.JPG
    1 reply

    Wow, great idea ! You've got the transformer and the cigarette connector all in one. Makes a smaller footprint. I believe I have one or two of those chargers . I may have to mod a few like that, ;-) thanks for the comment,


    Thankyou very much for your post, you know I live in a romote village in Papua New Guinea and house lights are more needed here, I spend alot on AAA battaries, but now you have brighten up my mind that I will buy a 12 volts (10 watt ) solar panel + 12 volts (7amph) battery + solar charge control, I will make a 6 volts rectifier for each of this 4.5 volts led lights that can light till morning.

    1 reply

    This is exactly the use I made this mod for, :-) I'm so glad it is useful to you. Show your friends how you do it. Maybe they will benefit as well. Thanks for the great comment !


    Glad I saw this. We have a lot of those, we also got ours free from HF. Thank you!

    1 reply

    Thanks for the pointers. From personal experience don't EVER connect any type of power source that is meant to "charge" rechargeable batteries. These devices will ramp up the voltage while monitoring the amperage draw. With LEDs, they'll burn out before the charger backs down the voltage and basically think it is a bad battery. Fixed voltage wall plug type transformers should be ok to use but test the DC output with a free Harbor Freight multimeter (sorry no coupon link). Keep in mind some power supplies rated at 12 Volts DC may read 16 volts, which may be due to the fact that the multimeter doesn't put a load on the transformer. Some power supplies may also say 12VDC but put out 15VDC, something like a 500mAh car battery trickle charger(comes to mind). The main reason for this is when you want to charge your car battery, if it's voltage is 12.35V (not bad, but not fully charged), 12.00VDC would do nothing, because its voltage potential is lower than the battery you want to charge. Now LiPo batteries are a whole different subject, with many dangers, including the kind that burn things and go BOOM. You're on your own with those. Where did you get the DC female jack? Is this a standard Radio Shack item, or have you found them cheaper online(or in bulk)? What I'd like to find are some micro USB jacks to install like you did with the plug in jack, then any of these commonly available USB battery packs could be used to run this or anything else of similar voltage. I think rechargeable batteries would be a great step for this item but i also don't know what wiring mods need to be done, but i'm sure plenty of readers could weigh in on the subject. And my final statement or complaint is an addition to your comment about owning stock in a AAA battery company. Wow, that couldn't be more spot on if you tried. If you use rechargeables as an example, 1000mAh is about the most "juice" a AAA can hold (NiMH), but AAs often are rated at 1800-2200 mAh (I think I've seen 2300mAh too) which is 2 amps x 1.35 V (+/-) or 2.7 watts of power vs 1.35 watts for the best AAA but they cost the same or more because of their compactness. BS. I'll take a device that holds 3 x AA batteries over one that uses 3 AAAs, ANY DAY of the WEEK. But the product manufacturers are convinced that 3 or 4 AAAs are Sooooo much better than 3 AAs. Give me a break. Cut the price of AAA batteries(alkaline, carbon, whatever) to half of the comparable AAs of get rid of them.

    1 reply

    If you click on the #4 Power jack, it will link to the jacks I used. Usb jacks are a good idea. I had the dc jacks from another project, so I used them. Of course they also work with the dc adapter I use also. Thanks for the info, Cheers,