How to Make a Rechargeable D Size 2 Cell Flashlight Using Laptop Batteries Rev1

7/31/2019 How to Make a Rechargeable D Size 2 Cell Flashlight Using Laptop Batteries Rev1

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10-25-2011

4-08-2012 Rev. 1

How to make a rechargeable D size 2 cell flashlight using laptop batteries

Disclaimer: If you dont know what you are doing, dont try this. Talk to someone whoknows electricity and electronics and let them show you. Laptop batteries can bedangerous when used incorrectly.

This document has no author or copyright. Please copy as much as you want andimprove on the design. This is just one way.

Start by taking apart a laptop battery. Ill use an old discarded Dell laptop battery.

Notice the label says it has lithium-ion batteries and its voltage is 14.8 and its capacity is3.6 AH (ampere-hours).

Youll need the following tools: scissors, sharp pointed instrument, side-cutters.

Take off the label and youll see this.

.Next stick the pointed instrument under the plastic.


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This allows you to slide the side-cutters under the plastic and cut it. You are trying not todamage the batteries as you take it apart.

After you expose all the batteries, only a couple of double-stick tape is holding thebattery pack in-place. Youll need a screw driver to carefully pry the battery off the tape.


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Cut away any wires that are soldered to metal strips. Do not cut away the metal stripsyet.

You will notice there are eight batteries that make up the laptop battery. Also notice thattwo batteries are in parallel and that there are four pairs of batteries in series. If you goback to the first picture it says a fully charged laptop battery will measure 14.8 volts.14.8 volts divided by 4 equals 3.7 volts. So a fully charged individual battery will

measure 3.7 volts and higher if left charging. The label also says it has a 3.6 AHcapacity. That means each pair of batteries can put out 3.6 amps in one hour. If you useless current then the battery lasts longer. However, if there are numbers on the batteryand you look up the specs, it will tell you that its capacity is 3.7 volts 1.2 AH which istypical. Two batteries in parallel will give 2.4 AH, not 3.6 as it say on the label. Thenewer laptop batteries they are making have square batteries inside. This cant be usedfor flashlight batteries.

Begin cutting the metal strips so you end up with four pairs of batteries.

Dress up the pair of batteries by cutting any extra metal strips close to the terminals. Fileany sharp edges until they are smooth.


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Next is the circuit well use to charge the batteries.

I use this circuit with a usb cable and a 5 volt usb source. The 2N5638 is a junction fetwired as a constant current source. With the 150 ohm resistor, the current is always 25 to30 milliamps no matter what the load is and the input voltage can go up to 30 volts.

Another junction fet is J105 with higher current spec but lower maximum voltage. Thisfet can handle higher currents with a different resistor.

The following circuit shows how the constant current device is wired to charge yourlaptop batteries.

I used the 2N5638 circuit because it can regulate current at 5 volts. Notice that the J105does not begin regulating at about 7 volts.

A note of CAUTION: Do not charge your laptop batteries at currents greater than 35milliamps. There are not any over temperature protection built into the charging circuitlike a regular laptop battery. It will take a couple of days to charge the battery to 3.7


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volts at 35 milliamps. You can consider this a trickle charge circuit. If the battery feelswarm when charging then something is wrong and you should stop. For that matter if thebattery feels warm when you are using it then you are drawing a lot of power in a shorttime and should be careful. Even though it is a trickle charge, do not forget to stopcharging after a couple days. Use a digital voltmeter to measure if the battery is at 3.7volts. I have measured up to 4 volts when leaving it in the charger too long.

To be extra clear on how to hook up the constant current device, I have redrawn thecircuit.

When you make the constant current device, you dont have to use a circuit board. Justtwist the correct leads together and solder with wires. You can make more than one at atime.


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Next, the pair of batteries tend to flop around when you put it in the D size

flashlight, so I hot glued a piece of dowel to the batteries. One on each side. The

dowel is 1/2 inch long and 7/16 inch in diameter.

I then solder a #6 zinc plated steel washer in the middle of the plus side of the

battery.

Next, the pair of batteries are not as long as two D size cells, so I made a spacer to makeup the difference. The wood dowel is 1 inch long and 1 inch in diameter. I usedtwo flat head #8 x 5/8 sheet metal screws, 2 #10 brass washers and a straight piece ofwire.


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Screw in the #8 screws in the center at the two ends with the brass washer underneath.Drill a small hole through the dowel off to one side of the center and attach the straightpiece of wire to the two screws.

This was the makeup of the spacer in the old revision. The new revision uses 3/16 x

1 inch fender washers on both sides and two flat head #8 x 5/8 sheet metal screws.

You can use a straight wire or a 2.2 ohm resistor depending on if you are using anincandescent bulb or led.

Next is how I made up the charging circuit, you may want to do it differently. Thedifficulty is how do you attach the charging wirings to a flat surface? I had somecylindrical neodymium magnets so I thought I would use that. I also had some coppertape with conductive adhesive which I wound around the magnet.

The magnets were 3/16 inch in diameter and inch long.


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I put solder on the end of the wrap of copper tape so it would not unravel and solderedwires to the magnets. Be very careful to not over-heat the magnet when soldering wiresto it. If you do, it weakens the magnet and it stays weak. I leave the four magnetsconnected in a row to act as a heat sink while putting solder on the magnet

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Magnet and constant current device.

I then use a usb cable from a discarded mouse or keyboard and an ac-to-usb adapter forthe 5 volt source. I found this more convenient than using a transformer with a 5vdc

output.

By the way, the black and red leads from a usb cable are always the power leads. Red forpositive and black for negative. But always check by plugging into a usb port and testwith a meter. Assemble the charging unit by soldering the wire from the constant currentdevice to the red wire of the usb cable and the black wire to the black wire of the usbcable. I put shrink tubing over each solder joint, then shrink tubing over both wires.


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I then use hot glue over the exposed solder joints like the magnet and constant currentdevice so the wires dont break off from too much handling. The hot glue also protectsthe constant current device.

Assembled charging circuit.

Next buy the cheapest D size 2 cell flashlight you can find.

Revision 1: I no longer use masking tape around the batteries. I hot glue inch x

7/16 inch dowel to the batteries and solder a #6 zinc plated washer to the plus side.Also, the spacer has fender washers at the ends. Put the dowel in first and then the

battery, plus side up. The spacer length was sized for an Eveready flashlight. Other

models may require a longer length of dowel.

Put in the spacer, battery plus side up and screw on the cap with the flashlight bulb.Turn it on and you will have a very bright light. If the light doesnt turn on, whack theflashlight on the side. Sometimes the battery doesnt make good contact with theflashlight bulb. If it does light up, the flashlight bulb will probably burnout in about 15minutes. Every 2 cell flashlight comes with a PR2 incandescent bulb. This bulb cant


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handle the current coming out of the lithium-ion batteries. You have to look for areplacement bulb named PR3. This will handle the current and probably be very brightfor about 2 hours before you need to recharge the battery.

You can find all the electronic parts from Mouser Electronics, even the PR3 bulb.Website is www.mouser.com. For the PR3 bulb you have to search for 606-PR3. Ofcourse you can buy your parts from any electronic store.

Let me backtrack a little. You have 4 pairs of batteries that you have recovered from thelaptop battery. They all may be bad, either shorted or open. You may find some that aregood. If you dont find a good battery, you need to open up more discarded laptopbatteries. When you take out the batteries from the laptop battery and measure them,they usually will measure zero volts. Then you hook up your charging circuit and startcharging them. Always measure the current first when you hook up the charging circuit.If the battery is open, there will be no current reading and you can discard (recycle) thatbattery. If you have current, you have a chance that the battery is good and will chargeup to 3.7 volts. Let it charge a couple of hours, then take off the charging circuit andmeasure the battery voltage. If there is some voltage then you have a good chance thatthe battery is good. However, you are not done yet if it does charge up to 3.7 volts.

When the battery charges to 3.7 volts, remove the charging circuit. Set the battery asidefor several weeks, then measure the voltage again. If it still is at 3.7 volts, you probablyhave a good battery that will hold its charge for months and can be used as a flashlightbattery. But if the voltage is less than 3.7 then eventually it will discharge to zero overtime and this battery is not suitable for flashlights.

Another thing to note is that if you look up the specs for the PR2 or PR3 bulbs, you willsee that it is only rated for 15 hours of life! So the next part of this document is how toreplace the incandescent bulb with a 1 watt white led.

Revision 1: I have put together a new charging circuit. Use this charging circuit if

you dont want to bother monitoring the voltage on the charging battery. Thiscircuit will not overcharge your batteries no matter how long you leave it on the

charger. It should fully charge your battery in two days. If you leave it charging

longer, the battery voltage will be a little higher than 3.7 volts. It will not

overcharge your battery to 4 volts. The maximum it can charge your battery to is

about 3.875 volts. The following picture is the schematic and physical layout of the

new charging circuit. It uses a chip TL431 which is a precision zener. The zener

volt can be set where you want it and it is this chip that prevents the battery from

overcharging.


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Some pictures of the assembly of the charging circuit. Ive just replaced the

constant current device with the TL431 chip. The wires to the usb cable is the same

and the wires to the magnets is the same. I put a little more hot glue around the

magnets.

Some pictures after soldering the wires.

Underneath look.


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Device with wires attached.

Underneath view.

Wires cut for usb cable and magnets. White jewelry cord holding the wires together

instead of plastic tyrap.

Hot glue covering the whole device and wires.

Magnets with hot glue all around. Short wires soldered to usb cable and shrink

tubed.


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Shrink tubing over usb cable and wires. Assembled unit.

I put the charger in a zip lock bag with instructions on how to connect the charger.

Instructions for replacing the incandescent bulb with a one watt led.

First buy some 1 watt white leds. However, dont buy the semi-hemisphere type.

There is a dark area in the center of the circle of illumination with this type of led. Buythe type that looks like an hourglass.


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This is the underside of the hourglass led.

That round metal surface is the heatsink of the led. When you receive your led, theheatsink may be isolated from both the positive and negative lead. Or it may be tied

to the positive lead or tied to the negative lead. I have received leds that fell into the

three categories. Depending on the type you receive will change how the led is

mounted on the metal case.

Usually there are no instructions as to which lead is the positive and which is thenegative. You can use a coin battery like the CR2032 or your digital multimeter. Ifusing your multimeter, use it in the measuring ohms position, lowest setting. Make surethat plus voltage is really coming out of the red lead. You are looking for the led to lightonce the correct polarity is found. Do not power the led with double A batteries or thelike. The coin battery like the CR2032 is current limited. Meaning it can put out onlyabout 20 milliamps when shorted. Plus if you have the polarity reversed, the 3 volts outwill not breakdown the led.

We will be using the incandescent bulb metal case to hold the l watt led. So if you are

willing to remove the bulb from the PR2 or PR3 lamp, try the following procedure.

First tape the bulb with masking tape. This helps to wiggle the bulb and not burn yourfingers if the bulb becomes hot.

Next use a solder sucker to remove the solder from the bottom of the bulb.There is a tiny wire that you must break free from the solder left on the bulb.Next you use your soldering iron to heat up the metal part of the bulb, put the solderingiron right where the solder is next to the flange of the bulb. This is where the other wire


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is connected to the bulb. If you are lucky, the glue that holds the bulb to the metal casewill melt and you can wiggle the bulb out.

Clean out as best you can the remaining glue in the case of the bulb. Especially the area

opposite the V cut in the metal flange.

If you are unlucky and the glue does not melt no matter how hot or how long you leaveyour iron on the solder spot by the flange then its time for another method. It appears tobe some type of epoxy holding the bulb to the metal case. What I do then is use a microtorch to heat the metal case, holding the masking tape with a long-nose plier. I see gasescaping from the bottom of the metal case where you sucked out the solder. The gas canburn. Let it burn until it stops burning. Then I put the bulb on a metal tray and break theglass. The I dig out the glass from the metal case. The glue looks carbonized and easyto scrape from the metal case.

Next cut some copper strips from a piece of copper metal. I think the piece I had was onemil thick.


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Tin in the center on both sides on the copper strip. We are going to solder the metal stripto the heatsink of the led. The width of the copper strip is the same as the diameter of theheatsink on the led.

Put a little solder on heatsink of the led.

Next solder the copper strip to the underside of the led.

This is why you put solder on both sides of the copper strip. Lay the copper strip on topof the heatsink of the led. Heat the solder of the copper strip, let the solder underneathmelt along with the solder on the heatsink of the led, joining the two.


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Soldering the copper strip only applies to leds with the heatsink tied to the negative

lead or the heatsink is isolated from both the negative and positive leads.

If you have an led with the heatsink tied to the positive lead, use a silicon

compound/glue to attach the led to the copper strip. Do not solder the copper strip

to leds with the heatsink tied to the positive lead. We will be using silicon

compound/glue to electrically isolate the copper strip and still have heatsinking

capacity with the silicon compound/glue. We want to mount the led to the metalcase with the negative lead of the led touching the case always. The positive lead of

the led will always be the wire at the tip of the metal case.

Picture of the silicon compound/glue and the led attached to the copper strip. You

can see the white silicon compound/glue around the led and isolating the copper

strip from the heatsink. After the silicon compound/glue has dried, test with an

ohmmeter that the copper strip is electrically isolated from the positive lead.

Next bend the leads of the led about 90 degrees.

Take an insulated #30 gauge wire and solder it to the inside of the positive lead of theled.


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Solder only on the inside. Do not get any solder on the outside. Next you will put 3/64thinch shrink tubing over the connection.

Next you will put some solder on the negative lead of the led, both sides of the lead.

Next you file the flange where the v shape is cut out. File both sides so you can put alittle solder there.


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Then you place the led in the metal case. The negative lead of the led goes into the v cutin the flange. Try to center the led in the metal case and see where the negative lead ofthe led ends up. Thats where you will tack solder the lead to the case.

Strip the insulation from the wire so only bare wire shows from the bottom of the metalcase before tack soldering the led in-place.

The led should be centered in the metal case as much as possible. Notice the positivelead of the led is not touching the metal case because of the shrink tubing.


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Bare wire sticking out of the bottom of the metal case.

Add solder to build up the base.

Cut the excess lead and trim the copper strip around the flange with a scissors.


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You can make more than one led bulb at a time.

Of course you should test your led bulb at this point to see if the led still works. It couldhave overheated during its construction.

Revision 1. Remember, the pictures above assume you are mounting leds with the

heatsink tied to the negative lead or isolated from both negative and positive leads.

Do not solder the copper strip to leds with the heatsink tied to the positive lead.Attach the copper strip to the heatsink with the silicon compound/glue. Soldering

the negative lead to the V of the flange and the wire to the tip of the metal case is the

same for all three categories.

Finally assemble your flashlight. You will have to change the straight wire in yourspacer with a 2.2 ohm or watt resistor. Place the wooden spacer in the flashlightfirst. Then the battery with the positive pole up, and then the top of the flashlight.The led bulb is inserted in the cap just like an incandescent bulb. Make sure theflashlight you are buying has a metal holder for the flashlight bulb because we are using

that as a heatsink for the led. With the 2.2 ohm resistor limiting the current through theled to about 90 milliamps, the flashlight should be bright for a couple of hours. When thelight gets dim, then its time to recharge. Or if you measure the batterys voltage and itsbelow 3 volts. It can go as low as 2.4 volts and still look kind of bright.

You could probably use a 2 ohm watt resistor instead of 2.2 ohm. It was a resistor Ihad around. You could try using the straight wire and not insert the 2.2 ohm resistor.The led will probably draw about 105 milliamps. However, after a while the led will acterratic and flicker. If you open your flashlight youll find the metal housing for the led


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bulb quite hot. Your heatsink has overheated. I put in the 2.2 ohm resistor to limit thecurrent to around 90 milliamps so the heatsink wouldnt overheat.

I dont know if it will be difficult to find the hourglass led from the electronic companieslike mouser or digi-key. I get my hourglass leds from www.dealextreme.com, sku #13286. Price is around $2.60. The other place is www.goodluckbuy.com, sku # 64689.Price for 5 pack is around $6.50.

You are not limited to making rechargeable flashlight batteries. You can make the

batteries into many different voltages and capacities.

I like to use the nine volt battery clips as connectors. I hot glue all the exposed metalssurfaces to prevent accidental shorts.


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This is my fathers old portable drill with ni-cad batteries that long since failed. I openedit up and took out the ni-cad batteries, brought out the power connection leads to a 9 voltbattery clip. A rubber band around the lithium-ion battery holds it in place and thebattery clips make them replaceable and I have a working portable drill again. Anyportable tool with failed batteries is fair game.

Any bad rechargeable battery, ni-cad or lithium-ion I find I place in the recycle box atHome Depot.

I like using 9 volt battery clips to connect and disconnect my batteries. Duracell 9 voltbattery clips are the best because the clips are mounted on a type of stiff thick paper.Other brands of 9 volt clips are mounted on plastic. These melt when you try to reusethem and solder wires to the back of the clips. I can reuse only so much Duracell typebattery clips because I dont use 9 volt batteries that much. So Ive started to make myown battery clips, Mouser sells the male, female clips and the rivets to hold them. I canmake as many as I want now.

Some final notes: test the constant current charging circuit when you make it by shorting

through the digital multimeter in the milliamp setting. It should read anywhere between25 to 35 milliamps, around there. The 5 volt charging circuit is only to charge batterycells to 3.7 volts. If you are planning on putting more battery cells in series, you need toup the source voltage. The source voltage always has to be higher than the final batterycell voltage for the cells to reach full charge. When you take apart the laptop battery andhave the cells lined up in series, number them 1, 2, 3, 4. That way if you want to seriessome cells, series them in the way they originally were hooked up. The metal stripsconnecting the batteries should all be shiny. If any are discolored, that usually means oneor more of the batteries has been leaking. Of course that battery is no good. The batteryusually leaks from the positive end, so a discolored metal strip on the negative side of abattery and a shiny metal strip on the positive side of the battery could mean its still

good.

Test the no overcharging circuit by measuring the voltage at the magnets. It should

be around 3.875 volts. The 150 ohm resistor in the circuit is to limit the current

from the 5 volt usb adapter to around 36 ma. The precision zener shunts some of

that current so about 34 ma is available to charge a battery with zero volts. The

charging current will decrease as the battery voltage reaches 3.7 volts.

Documents

How to Make a Rechargeable D Size 2 Cell Flashlight Using Laptop Batteries Rev1