I hate it when my cordless drill gives up in the middle of a job. It seems that the supplied battery packs just don't cut it. So I opened up the battery pack and replaced the NiCads with much longer lasting NiMH batteries. Now I get a much longer use between charges.
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Signing UpStep 1: Disassemble the battery pack
My battery pack had 4 Torx screws (I later replaced with regular Phillips screws for easier access). Inside you'll find 10 NiCad batteries. They appear to be just a bit smaller than 'C' cells, and all attached together in series. 1.2 volts X 10 cells = 12 volts. The cells are marked as 1300 mAH which is why they don't last very long. You will probably want to photograph the arrangement of batteries since you will need to make a new pack look just like this. Also notice the thin insulator that keeps the top battery from shorting against the batteries on the bottom.
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The one thing I took away from this, that i will be grateful for as long as I can remember, is the Soldering Video. That little trick/tip is going into the printed long-term storage
The new transformer is a Honeywell 120/208/240V, 60 cy, primary to 24 VAC 40VA secondary. I am sure the 40 VA would take some time to charge a 18 volt drill motor battery. All of the instructavles I have read deal strictly with batteries. None mentions the care and feeding of the chargers. Care to share any helpful hints?
I am not a professional so I needed someone with brains to clarify my idea.
Unless you're putting dozens of those cells in parrallel, 40VA is gonna DESTROY them.
I'll give you a summery of my research and calculations, as best I can.
Bear in mind, my power supply is going to be a 30 volt HP printer power-brick.
That brought my current limiting resistor VERY low ohmage, and wattage. 10 Ohm, and 1/4 watt.
Now, since you're starting with 40 volt...
The charging voltage is going to be approximately 1.4 v per cell.
You have what, 15 cells? (15 x 1.2 vdc nominal = 18 vdc)
So you need 1.4 x 15 = 21 vdc to charge.
24 v (supply voltage) - 21 vdc = 3 vdc voltage drop across the resistor.
Your cells are probably 2.5 Ahr. You need to charge C/10 , or 0.25amps.
R = E/I = 3 v / 0.25 = 12 ohms.
3 v / 12 ohms = 0.25 A
3 v x .25 A = 0.75 watts
I would upgrade to a 1w or eve a 10w resistor. they're only a dollar, and the added safety is worth it, imho.
You'll have to check VERY carefully. but if all the packs are NiCd, then 12-14 hours with the charger, and resistor described should give you a full charge. It should also be safe if you forget and leave it on a little too long. NiCd can survive almost indefinite charging at 1/10C rate. The extra energy gets converted to heat, and exits the battery through the cell wall.
Bear in mind, quick chargers like my original, have very sophisticated circuitry... but mine charged at almost 1C. it did shut off after that though, as a safety feature. Charge at 1C for 10 hours, and you better have the fire-department on speed-dial, cause around hour 3, it's gonna go Fwoosch!
Consider some googleing on "homemade NiCd chargers.
Tons of info is to be had at RC groups. they use packs much like these to fly their planes(though they're starting to switch over to li-po and li-fe)
Doh, just forgot.. you'll have to measure the ACTUAL voltage, under load, because you're gonna get a voltage drop over the rectifier. You're going to have to recalculate using the lower, measured voltage.
I certainly appreciate your rapid reply.
I am not that much into electronics, and had to re-read your reply several times to boil it down to my level. I am more mechanical and my dabbling into electronics is fixing things broken. Determine what is bad, cut out the old and replace it with a like item. Your reply was a real insight in how to determine (calculate) the needed resistor.
An amazing bit of info can be had on these new-fangled gadgets (computers) if a person knows where to look for it. I wish computers had been available when I was young. I pre-date Television!!
Correct me if I am wrong, but this is what I determined from your reply.
18 volt batteries have 15 1.2 volt cells.
To charge these cells will require 21 volts @ .25 Amps for 12 to 14 hours for a full charge.
To drop the 24 volt output from the transformer, after it has gone thru the rectifier, will require a 12 ohm 1 watt (or better yet a 10 watt) resistor.
Now if I can just figure out the 40VA output of the transformer...Many years ago I have read how the VA is calculated, but it escapes me now.
I REALLY appreciate your thorough explanation of my question.
Have a GREAT DAY, WEEK, and YEAR
Just happens, I post-date color TV.
Though i do remember, vividly, when the Internet switched and we all started using the WOrldWideWeb.
When I started, we Gophered instead of Googled.
If, and that's a pretty big IF, i got my numbers right then...
12 ohm, 1Watt(or higher) resistor should take your power supply, and turn it into a very crude 1/10C "slow charger" for your 18V battery packs.
Pardon me while I plagiarize.
The only difference between W and VA is the power factor. The power factor, unless known, is an approximation. For purposes of our calculations, we use a power factor of .85. The VA value is always higher than the value for W.
W to VA W / .85 = SAME VALUE EXPRESSED IN VA
VA TO W VA * .85 = SAME VALUE EXPRESSED IN W
that's AFTER the transformer is rectified.
I actually have absolutely NO idea what'd happen if you fed the unrectified AC into the battery(though I have a pretty good guess, and it involves letting out a lot of magic smoke. You know, the stuff that makes electronics work until you let it out?)
Thanks
I've taken apart my Makita 18v Cordless drill 2.6ah NiMH battery because it would not charge (flashing red and green). I've tested all the cells and they all read 1.34v so i'm thinking its one of the three components that is stopping the battery from charging (see image). It was hard work getting the cells out of the case and i think this may be an indication that the battery may have been over heated at some point. The charger is working fine with my other battery although that battery is also starting to loose power quickly.
Does anyone know what each of these components do and how I can replace \ bypass one or all three to get the battery to charge again?
Info: the red component was glued to the top of one of the other cells in the pack.
rectangular Klixon component is just a fuse,
The red component is a thermal cut-out\reducer switch used for reducing the power input when on the charger if overheating occurs,
The yellow component is a thermal cut-out\reducer switch used for reducing the power output when on the battery is in the drill but overheating occurs due to heavy usage.
All components worked on this battery, so i guess the batteries can no longer hold a charge.
Hope this info helps some one.
No need to warm batteries up anymore with Li-ion
I thought I was the only Mcgiver left but I see not. When I was a child, my Dad and mom called me “screwdriver fingers” due to the fact that I had to tear something open and see how it worked; even though not broken I just could not resist
I did the battery thing about tens years ago when I discovered the “C” batterers matched my flashlight. Aside from all the data and info in above links, if you can imagine and interpolate you can do this in about most everything
Thank God, Men are still men
MAC.
Take your two packs, and rebuild one good one out of them.
With the now empty battery case, rebuild it will ALL fresh cells.
That should get you the best bang for your buck/euro/pound.
Keep any extra good cells for when, not if, WHEN, your newly repaired pack
kills another of it's cells. When you run out of THOSE spare cells... recycle all the old cells, and rebuild with new tabbed cells for what is now the third lease on life for that battery pack :-)
Now, we're 10-15 years into the future of your tool, and it's probably worn out. Time for a new cold-fusion powered drill.
As for buying the new tabbed battery cells... don't we all buy them from the same Chinese manufacturers?
Check the image in step three.
If the battery is freshly charged, that "light bulb load" is pretty important.
It helps bleed off the "surface charge" on the cells, and gives you a "working voltage" to measure.
Test the cell voltage after 2-3 min of running the light.
If you're "lucky" like I am...
I ran my batteries in a sawsall, till it quit sawing.
hen took apart the packs that weren't performing(one lasted less than 3 min of sawing)
When i took apart my Bosch 24V pack, most of the cells tested fine with the volt meter.
FIVE of them tested ZERO volts.
Guess which cells were bad? ;-)
This only really works if its a few bad cells, and you run the battery to "dead".
The down side is, if a cell is only starting to die, this may not catch it.
example: http://www.discounttommy.com/Shop/Control/Product/fp/vpid/3433762/vpcsid/0/SFV/32282
I'm also working on my two Milwaukee 18V "Power-Plus" batts. Using the same trick, one seems now to be the usable battery for the drill I had loved--the drill turns solidly again! The other batt may be too far gone. It did go from 0V to ~3.2V, though. The charger doesn't accept it yet. I'm nowhere near ending the fight for it: I'll cut it open and go NiMH, if necessary.
Big box HW stores want $70-$80+ for such Milwaukee 18V batteries: Well, I then knew that the expensive drill screw wished to turn into myself! Amazon was somewhat more reasonable: $50+, yet, I haven't checked lately. Thus, I haven't used my originally priced $200+ drill for a couple of years. I was about to give up and purchase Skil or B&D--or even cheapo HFT or Big Lots!
(These Milwaukee batteries don't use the familiar vertical post most drill batts often use. Three side-shielded terminals "slide" horizontally into the drill bottom or the charger. As for checking such unmarked terminals for polarity, use a voltmeter to find the terminals which give a positive voltage reading--perhaps after charging. For this Milwaukee 18V "Power Plus" ni-cad battery, apparently the terminal on the far left (terminal side up and terminals facing you) is neg (-)--the one directly next to it, on the right, is the positive terminal (+).)
Thanks for the great inputs here!
CJQ