Introduction: 27 Led Light Mod

Picture of 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 !

Picture of 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

Picture of 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

Picture of 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

Picture of 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 !

Picture of 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. ;)


bwayne64 (author)2017-09-26

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

GeorgeP165 (author)2016-10-14

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.

DNMEBOY (author)GeorgeP1652016-10-14

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.

GeorgeP165 (author)DNMEBOY2016-12-07

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

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.

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

DNMEBOY (author)GeorgeP1652016-10-14

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.

bwayne64 (author)DNMEBOY2016-10-15

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,


bwayne64 (author)GeorgeP1652016-10-14

Commented on and answered, several times, thanks,


ssolley (author)2016-11-25

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.

techman2000 (author)2016-11-01

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).

bwayne64 (author)techman20002016-11-02

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,


I have one of these Harbor Freight lights (who doesn't?) and making a lamp out of it never occurred to me. Great idea. Thanks bwayne64

You're very welcome, glad you found it useful,


john tom marej (author)2016-10-21

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.

bwayne64 (author)john tom marej2016-10-21

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 !


debra.ridleyhurst (author)2016-10-19

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

You're very welcome, glad it was useful,


RaymondC66 (author)2016-10-16

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.

bwayne64 (author)RaymondC662016-10-16

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,


jeasterl (author)2016-10-16

Use a 3 c or d-cell holder with cheep batteries it should go many times longer and still be portable

bwayne64 (author)2016-10-14

Please read the entire instructable, thanks


David the R (author)2016-10-14

That's why the DC adaptor is used and set to 4.5 volts.

HoppyH1 (author)2016-10-13

Rather than removing the batteries, I would simply replace them with rechargeable batteries which would allow you to disconnect from the adapter and still have a fully charged light

bwayne64 (author)HoppyH12016-10-13

The whole point of this mod, was to use a 12 volt battery externally.
Obviously rechargeable is an option. It could run for days on a large
battery like this. Not sure how many days you'd get with rechargeables.
In fact the jacks not even necessary for using rechargeables.

cheever3k (author)2016-10-13

If you don't mind, I'm just curious: how do you get these for free?

I'm in Tallahassee, and I love these lights too. Thanks for the coupon.

clarkt (author)cheever3k2016-10-13

Go to Harbor Freight. Sign up for their flyer. It will arrive periodically, and there is always 2-4 free items (with purchase of another item). You can always find cheap stuff that you can use. The thing arrives in your mail once or twice a month. I love harbor freight.

bwayne64 (author)cheever3k2016-10-13

I usually just search Google for free 27 led light Harbor Freight coupon and set the search tools time setting to 1 month. That gets me everything recent. Most times I use the image search. Then I can check the expiration date. As mentioned below, there are flyers and magazines that have the coupons also. Also you and print as many copies of these coupons you want. You could get one per day if you wanted to. Of course you have to purchase something. I usually go once a month and use a 20 % off coupon on whatever I buy. If I were closer I would go once a week. Hope this helps.

ac1ac (author)cheever3k2016-10-13

Look for Harbor Freight coupons. They are in all sorts of magazines. They give these away, and many other items for free with any purchase, and sometimes with no purchase required. You can also sign up on line and they will send them to you in email and in the snail mail form. If all else fails, go to any HF and they all have supplies of sales flyers on the counters and they all have coupons. I am lucky enough to live pretty close to a store and have about 20 of these lights as well as other flashlights, multimeters, tool sets etc.

Gordyh (author)cheever3k2016-10-13

Sign up here.

NickB6 (author)cheever3k2016-10-13

To get them free, you need to buy something at HC. It can be anything. I have several of these and the little black flashlights lying around that I got free. They work great. I buy small cheap stuff like a $1 set of utility knives or 50 cent box cutter and they give you the light free with the coupon.

bwayne64 (author)2016-10-13

All this talk of rechargeble batteries and charge circuits gave me another idea !

I have a camera that comes with a charging cradle. It would be awesome to have one for these lights. Just sit it in the cradle and charge it up. If I had a 3d printer I could print up the cradles hard parts. I'm a fairly good 3d modeler, so that part would be easy peezy. Oh well I'll do it the old fashioned way, with my two little pinkies, ;) I'll put up the instructable when I have something.

GrampaDave54 (author)2016-10-08

been wanting a good cheap hack for these lights. have you thought of doing a rechargeable setup?

bwayne64 (author)GrampaDave542016-10-10

Yes sir, I'm not sure if theres room in the case for a bigger battery. But you can definitely use rechargeable aaa's in it. Now to build a circuit to charge to batteries without taking them out, ;)

barista (author)bwayne642016-10-13

I used the innards of one of these®-Battery-Balance-Charger-2800mAh/dp/B009LIUD90
Wii balance board battery pack

bwayne64 (author)barista2016-10-13

Thanks I'll ck it out, Cheers

ed-romes (author)bwayne642016-10-13

the very fact that you said take out the batteries shows that your mod will charge them I once did something like this for a portable radio to use while I was driving a truck with no radio and was tired of buying d cells so I wired it up to use the cig lighter and put in rechargeable it ran for years and my battery cost was far less

bwayne64 (author)ed-romes2016-10-13

Actually, I said remove the batteries, because I didn't know if the batteries which are akaline, would be damaged by the external power source. I also remember that when I first hooked up the external source, I noticed that even with the adapter set at 1 and 1/2 volts the light remained the same brightness. Then I remembered that I left the batteries in, facepalm ! LOL. I just try to err on the side of safety. As for rechargeable batteries, they need a pretty specific voltage, amperage combo to be charged safely. That was why I mentioned a charging circuit earlier. Just look at the new Samsung phone issues. Even the big boys get it wrong sometimes. Thanks for the comments, they are much appreciated.

LarryS41 (author)ed-romes2016-10-13

Please be careful, merely attaching an external power source is not a charging circuit. You could wind up with a light fire from over change

ed-romes (author)LarryS412016-10-13

Larry I grew up in a tv repair shop so I know the dangers far more than most but as I was playing the radio that used a configuration of to 8 batteries it was necessary to have rechargeable batteries to keep from burning out the power circuit with 12 to 16 volts depending on the lead acid battery charge and as I was next to the radio I could smell if it was getting warm and take out a battery or unplug the cable !!!

jchavis2 (author)bwayne642016-10-13

I carry a flashlight around with me and on full power, the batteries only last 3 hours, so I just use rechargeable NiMH AAA batteries. They costed about $3 each, but they last for over 1000 charges.

However, if you insist on an onboard charger, you can get a usb LiPo converter/charger similar to a power bank from Adafruit for about $6. They charge 5V USB to the 4.2V needed to charge the LiPo battery and also convert the 3.8V from battery back to 5V for the LEDs.

stangaroo (author)GrampaDave542016-10-13

You can make these rechargeable with a USB power pack that you use to recharge your cellphone.

bwayne64 (author)2016-10-13

Really enjoying all the comments guys ! In my opinion this is where the real good ideas are found. People adding to the design of things and improving on them. To everyone commenting about the polarity on leds and me using 12 volts, please read the entire instructable before commenting. I know a wee but about electronics. I was talking about the polarity of entire circuit. I'm going to hook it up both ways to see if I can make the magic smoke. But follow the instructable where I mention marking the wires for polarity. I think some people are just excited when they think they see an error, and rush to comment. I've done it , and then deleted my comment when I read further into the instructable. Its OK, I have no problem with actual corrections, they help me make my project better. Keep the comments coming, guys and gals ! I love em !

JohnW51 (author)2016-10-13

YES, polarity matters. LEDs are Light Emitting Diodes. Diodes conduct electricity on only one direction. Wiring them backwards would produce no light and could damage the diodes.

bwayne64 (author)JohnW512016-10-13

This is true for individual LEDs. Wasn't sure about this particular circuit. Guess I got it right, cause it works just fine, ;)

ed-romes (author)2016-10-13

I saw your response to my statement and yes an unrelated power could over time cause heating as the batteries are charged with out discharging but as most older cig lighter are only active while the key is on that was seldom a problem but your set up is slightly different as a power outage or a disconnect from the main power would serve to discharge that energy keeping things safer as I am trained from my youth in both electronic and electricity I know a few ways that most here would not !! Like your regulated power supply should have a circuit for protecting rechargeable batteries where a car generator would not be so kind to a nice over a lead acid battery !!

Bollebof (author)2016-10-13

I just forgot te report a resistor is needed to reduce the chargecurrent

from 5 Volt to the needed 4.5 Volt. It seems a very little difference but

charging without any resistor foor ad your are longer period of you can forget the chargingtime , your batteries can be destroyed. A resistor of about

40 to 100 Ohms / 0.5 Watt will do the job. The value depends on the

capacity of the 3 batteries. I used 3 pcs of 2500 mA . I never had an

empty battery and you are fully free to go anywhere. You can use a car-

lighter-charger of a pc usb-slot. read the charge rate on the batteries !

To be absolutely sure about a safe chargingrate use half the recommended

chargecurrent.. O.K. it takes a bit longer to charge them full, but now you

can overcharge in time without blowing up the batteries. And again measure

with a multimeter the charge-current before closing up the lamp.The advised

10% rule is much too high in practice. That is the main reason so many

drills and wireless phones are laying around with dead batteries. The factory

will happily sell you new batteries and still you have the problem of over-

charging. Believe me , I changed the canopener, phones, portophones,

mp3 player, you name it, the charge-current by placing a simple resistor

in the chargestand or housing and reduce so to about 25 to 50 % of the

original current . For Li-Ion batteries it is a totally different story. My advise

is then to use the Original chargers of specific chargers from China for

just a few dollars ( euro) For expirienced user only !!!!


Cor den Hollander

The Netherlands.

arvevans (author)2016-10-13

If you re going so far as to add rechargeable batteries and a charger to this unit, why not add an output jack and use it to power Arduino projects, charge your cell phone, and power other electronic devices.

Bollebof (author)2016-10-13

I have the very same lamp and as soon as the batteries were dead I drilled also

a hole for a 3.5 mm mono jack and put in 3 recharchables batteries and connected the batteryleads to the jack. Now you can easely recharche

with every 5 Volt charger , in the car or from the pc or laptop. Normal batteries

get often oxidated in a car, recharchebles not. I use the lamp now for more then a year without any problem. My English is not 100 % but I think everbody knows

what I mean. Watch carefully how to connect the wiring to the jack.

Alway check with a multimeter.

Cor den Hollander

The Netherlands.

tbt10f (author)2016-10-13

Excellent 'ible. One improvement would be to use a jack that disconnects the battery pack when the cord is plugged in.

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