Harbor Freight Drill Charger Mod

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Introduction: Harbor Freight Drill Charger Mod

WARNING: PERFORMING THIS MOD WILL PROBABLY COMPLETELY VOID ANY WARRANTY YOU MAY HAVE.

You may notice the charger included with Harbor Freight rechargeable drills (at least the Drill Master 66965) is not a "float" charger, meaning you CAN NOT leave the battery on the charger for too long otherwise you will destroy the battery.  

This Instructable fixes this issue.

This limits the charging current to approximately 100 milliamps which is less than 10 % of the 1200 milliamp rating of the battery thus OK for a constant “FLOAT” charger. Note - Allow no less than 14 hours for full recharge of a fully discharged battery but you may leave ON after that time.

Step 1: Open the Charger

Turn the charger base over.  There are 4 screws. Take them out.  Remove bottom of charger.

Step 2: Make Your Resistor

Take 3 Radio Shack 10 ohm/ 1 watt resistors (Radio Shack # 271-151, BUY 2 PACKS) clip them short, and solder them in series.
(yes, I know my soldering STINKS.) Cut a piece of shrink tubing to cover the resistor  and heat to shrink around it.

Step 3: Insert Resistor Into Charger Base and Close

Clip red wire in the charger.  Strip the covering to expose appx 1/4" of the wire on each.
My pictures aren't great but I forgot to add shrink tubing to one end to cover the solder connection.
Shove it in and replace the cover.

This limits the charging current to approximately 100 milliamps which is less than 10 % of the 1200 milliamp rating of the battery thus OK for a constant “FLOAT” charger. Note - Allow no less than 14 hours for full recharge of a fully discharged battery but you may leave ON after that time.

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    21 Comments

    user

    I had been doing this type of mod on the current series of DrillMaster Drills that come with battery 68413 and use the 68420 model charger. It was a manual charger just like this one that would burn up quickly if left in for more then a few hours, but now it looks like Harbor Freight finally got a automatic charger is their latest series of drills. I got one off of ebay and I tested it and it works! It really does shut off after the battery is charged! I got another on the way now too. I think you can find it just searching for drillmaster automatic charger.

    Why not just spend $5 on an electric timer at Harbor Freight, plug the charger into it, and recharge the battery for only 4-5 hours?

    Where is that 5 dollar timer? Have a link? Also trickle charging ensures the battery is always charged when you go to it. The timer will turn off and the battery will start to discharge.

    I did this mod. Results were a bit different. BEFORE mod - 1.14A (1140mA), AFTER MOD - .562A (562mA) - Measured at the battery posts that touch the battery. Voltage 30.5v

    Battery pack is 1300mAh so full charge should be reached in about 2.5 to 3 hours? Need to add more resistors to bring it down to approximately 100mAh

    So it cut the current about 1/2. Still a bit high. Interestingly, the charger output is listed on the charger as 400mA

    Harbor Freight Drill 69651 (Purchased Dec 22, 2014)

    Charger Model Number XR-DC240400

    These chargers must be made in various locations. I have two
    of them & the output on both was 300 - 310 mA@35.2 V.After reading the posts here, I added 410-Ohm resistors to one charger (since they
    come 2 to a package, no sense in wasting the other one)Now the unmodified charger puts out 310 mA initially
    & tapers down to 240mA after about 1/2 hour.

    The modified
    charger puts out 140mA tapering down to 130 after 1/2 hour.To be on the safe side I labeled them MAX 5
    HRS & MAX 10 HRS respectively.Thanks
    for the advice guys.

    Harbor Freight Drill 68287 (Purchased Dec 18, 2014)

    Charger & batteries both numbered 69652

    Chargers marked24V DC400mA

    I just got my hands on a HF drill (68851) and it came with a really crappy charger (68859). I'm really careful about reading reviews on HF stuff before purchase (thus that specific drill). Reading the reviews on the charger though, say very similar things to the complaints you remedy in your instructable here.

    1st night charging the battery, I only charged it for an hour, and had to unplugg it for 20 min to let it cool; it was already getting that electronic burning smell.

    Would I need to plug my information into an equation for a different amount of resistance to drop the current to "Float charge" specifications? Specs: 7.2-24VDC, 1.3A.

    Not sure what the output Amperage is on that model. You need to know what it's delivering to the battery. Then add resistors accordingly.
    http://www.sengpielaudio.com/calculator-ohmslaw.htm

    I cannot locate any type of connection in which to insert the adapter plug into the base (battery section). The box pictures a connection on the certer of the back but no opening exists anywhere in which the plug would fit.

    The battery won't have an adapter hole. The charger will.
    What model do you have?

    You could very easily use a switch that would short the ends of the resistor network and be able to chose fast or trickle charging...