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gregl
12-12-2011, 12:43 PM
Hey guys, I've got a DeWalt 18v drill with tired battery packs. They will run the drill but run time is way down. I charged one up and then took it apart and here is what I found:
-Most cells at 1.3 v.
-Two at 1.28
-Two a 1.29
-One at 1.4

-Total voltage charged: 19.5
-Voltage when drill is running but not under load: 18.4
-After running drill for 60 seconds voltage while running drops to 17
-Battery voltage no load after above run: 18.8

Most of the websites I've checked say to find the one or two bad cells and replace them but I don't see any individual bad cells. So is the whole set over the hill? Any rebuild options or should I just go for new packs? These are about 4 years old and only get part-time use.

I hate to drop a C-note on a pair of packs if these are salvageable.


THANKS!!

Black_Moons
12-12-2011, 12:51 PM
Try recovering them instead.. Try this.

Find a REALLY small load. Lets say 100mA.
R=V/I, 180ohms for 18v.
60W 120v bulb = About that. (240ohms on resistance. .less when cold). Less is OK, More is not. (less wattage that is)

Connect it across the 18v drill pack once its discharged enough to no longer spin your drill, And measure the voltage now and then. I believe those 18v packs are 15 cells, So you want to wait untill it hits 0.4v per cell, or 0.4v * 15, or about 6v

Once thats done, Recharge it fully, And repeat. Your charger may initial refuse to charge it due to low voltage, but most trickle charge it in that state and it should quickly perk up and start charging, Failing that find a 24v+ supply and hook the battery to it in series with the light bulb, untill the pack voltage exceeds 15v. (Should only take a minute or two)

Discharge to 0.4v per cell has been shown to actualy recover Nicad capacity. The only problem is discharge below 1v per cell can easily reverse some cells as the internal resistance is VERY high below 1v per cell, and any high current reverse is very damageing, Hence the use of very low current.

Thruthefence
12-12-2011, 12:51 PM
Test each cell individually under load, a 6V lantern bulb makes a good test light. I bet you find a few of them dropping down in voltage while the test light is hooked up.

While I am not an authority on "dry cell" nicads, I have been maintaining aircraft nicads for many years, and I assume the chemistry is similar. I have seen "reversed" cells in a 24V battery go as high as 6v. This is when the nominal voltage is about 1.3V.

What this means, is that assuming a 20 cell battery, you might have 19 cells at + 1.3vdc, and one cell at - 6.0vdc, for all intents & purposes, you now have a 18.7 vdc battery!

As for as nicads not developing a "memory", I wish someone would notify Saft America and Marathon, (the manufacturers of Aircraft Nicad batteries) so they can amend their maintenance & inspection schedules. Currently, the batteries require a full discharge, cell shorting, and recharge to 120% of capacity every 100 hrs of aircraft operation.

http://www.mptc.com/

http://www.saftbatteries.com/SAFT/UploadedFiles/Aircraft/PDF/tn5.pdf

Boostinjdm
12-12-2011, 12:52 PM
When my packs die I just buy all new cells. I don't mess around trying to find the weak ones. If you are capable and shop around, they can be rebuilt for about half of what a new pack costs.

gregl
12-12-2011, 01:00 PM
THANKS for the fast response, guys. Back to the shop to try your suggestions. Boostinjdm, you may be right in the end but my inherent cheapness won't let me do that until I've spent more than $100 worth of my time trying to save these!

Stu
12-12-2011, 01:45 PM
I have bought rebuilt cores from here:

http://mrwindystbs.com/index.php

The price per 18v core is $42. I'm not associated with them, just a satisfied customer.

Bill

armedandsafe
12-12-2011, 02:21 PM
I've wondered if buying one of these and stripping the batteries out would be a practical source for rebuild.

http://www.harborfreight.com/catalogsearch/result?keyword=battery+18

Pops

Evan
12-12-2011, 02:28 PM
You didn't say what type of cells they are.

bruto
12-12-2011, 02:56 PM
I've wondered if buying one of these and stripping the batteries out would be a practical source for rebuild.

http://www.harborfreight.com/catalogsearch/result?keyword=battery+18

PopsI've done that, or something like it, in the past, buying leftover/overstocked etc. battery packs and rebuilding others with the contents. It can work, but difficulty varies considerably with layout. I rebuilt a few batteries for an old Milwaukee, and extended its life for years. But when I opened up a DeWalt 18 volt battery, I found the way they're stacked rather intimidating, and I think it might be difficult to roll your own. You may find it less daunting, but I suggest anyone planning this open up a pack first and see what you're getting into.

atty
12-12-2011, 03:21 PM
Bruto's right. It's not a quickie job, as you have to do some planning on how you're going to lay out the cells and the connections. I suggest some close color prints of the existing one, so you have a guide as you go along.

One of the main incentives for rebuilding your own is that you can usually get Sub-C's with a considerably higher capacity than the original cells. I remember my first rebuild came with 1800 ma cells while 15 3300 ma cells could be had for an amount that was still far less than a whole replacement battery.....and if you opt for the replacement battery, you're likely to get the same low capacity cells as the original.

Like most things we venture into, the first time can be a bit of a challenge, but after that first one, it's a breeze.....plus you're going to wind up with a battery pack that is far superior than the original.

JoeLee
12-12-2011, 03:33 PM
If your going to pull it apart replace all of them. I think my Milwaukee 14.4 volt packs were sub C type nicads. I replaced them with nickel metel type. The cost of rebuilding each pack was less than half of a new one.

JL....................

DFMiller
12-12-2011, 03:54 PM
Replace all the cells together. The cells as they age change impedance. You want them as matched as possible. Putting two new ones in will not be a fruitful exercise. As Evan said you have not told us the chemistry? I expect NiMH. Around Vancouver there is a couple places that will rebuild your pack. I expect there will be lots of options on something as common.
Is there an option for getting a Lithium Ion replacement pack. For performance they kick NiMH big time. You do need a proper charger for them. I know there are some brands of drills that will take both types.

Dave

Black_Moons
12-12-2011, 04:18 PM
As a subnote, My discharge to 0.4 recommendation is only valid for Nicad.

Boostinjdm
12-12-2011, 06:18 PM
If your going to pull it apart replace all of them. I think my Milwaukee 14.4 volt packs were sub C type nicads. I replaced them with nickel metel type. The cost of rebuilding each pack was less than half of a new one.

JL....................

To my knowledge, Dewalt only used NICAD and Lithium cells. I tried rebuilding a pack with NIMH cells before and it was pretty much a failure. It wouldn't charge right, it got hot when charging, and it didn't last as long per charge as the NICADs.

Evan
12-12-2011, 06:42 PM
I have gotten some very good deals on brand new battery packs from Canadian Tire here. When a product is discontinued they will often have left over packs that only fit the discontinued product. They clear them out for sometimes 75% off or even cheaper for high quality units. I have bought quite a few that originally retailed for around $50 for as low as $10 bucks. All you need to do is move the batteries to the old pack, sometimes with minimal fuss.

darryl
12-12-2011, 09:01 PM
The last drills I've bought using nicads are about 10 years old. The batteries are starting to go now. They are 1.4 AH and the one supposedly superior drill uses 1.7 AH cells. There are a lot of 1.3 AH packs around, new. Makes me wonder whether these 'new' ones even have that much capacity. At any rate, this is old, old technology still being offered. Even a double A in NMH can have twice this power.

I saw combo kit the other day- drill, circular saw, and flashlight- 45$. Cheap crap I'm sure, but I had to check it out. 18v battery pack, light as a feather. Looking it over I finally saw where the rating was printed- 1 AH. On my way home, happily without the kit, I started thinking 'what a guy really needs is a propane powered drill'.

Well, maybe not, but a 1 AH battery pack? Who would offer such a thing? I guess it's like printers- comes with four drop of ink of each color:(

J Tiers
12-12-2011, 09:08 PM
The DeWalts , at least older ones, are NiCd.

I had two of them rebuilt at batteries Plus for $40 a pop.... I could barely buy the cells for that, and B-P gave a guarantee. No work on my part. What's not to like about costs the same or less, no work, guarantee, and more time for other things?

NiCd usually "go" by reverse charging the weakest cell(s) in the pack. You run the pack down too far, and one or more cells go to zero, after which they "reverse charge" as current flow through them. It ruins them.

That is if you are not rigidly committed to swapping packs when you notice a slow-down..... NONE of that "Ill just get one more hole" crap.....

I should mention that both of the ones I had done were ones with screws holding them together..... the older ones were glued, I didn't try them, maybe B-P can do them also.

Mike Burdick
12-12-2011, 09:38 PM
gregl,

Here's an option...

Harbor Freight sells a 18v battery for around $10.00 when on sale. For my 18v Milwaukee drill I buy the one shown in the link and take it apart and replace my old batteries with theirs. This way I don't need to weld the wires on the batteries! The charge doesn't last quite as long as the original Milwaukee but it does the job well. Perhaps those batteries will fit in the Dewalt case too.

http://www.harborfreight.com/18-volt-battery-67029.html

Bill736
12-12-2011, 10:50 PM
While we're on the subject, don't forget that most 12 through 19 volt drill motors will run nicely on the 19 volt batteries. I have a 16.8 volt Craftsman drill motor that was easily converted to accept the 19 volt NiCad battery packs with just a little terminal modification. Not all battery packs will easily fit into other drill motors, however, so some luck is involved. I can recall that Consumer Reports once observed that several battery powered drills using battery packs from 12 to 18 volts actually had identical motors . Over the last 25 years or so, I've had many battery powered drills, but I've never once burned out or wore out a motor. Getting replacement batteries at reasonable prices was always the problem, and that's what lead to buying new drill kits.

JoeLee
12-12-2011, 11:12 PM
To my knowledge, Dewalt only used NICAD and Lithium cells. I tried rebuilding a pack with NIMH cells before and it was pretty much a failure. It wouldn't charge right, it got hot when charging, and it didn't last as long per charge as the NICADs.

Nicads and NIMH should both charge without issues on the same charger. Lithium won't charge properly. As to your overheating ??????
My Milwaukee 14.4 packs are still holding out great a year later. The original nicads were about 750 mAh the replacments I bought are about 1650 or something like that. It was well worth the time.

JL.................

lakeside53
12-12-2011, 11:37 PM
"Smart" chargers often charge at the highest rate possible while monitoring and maintaining a safe temperature. Some battery packs have a thermister (or other device) inside for this purpose, some just read the terminal temperature. I can't put my NIHM batteries on the old Nicad charagers, but I can charge the NiCads in the later charger - it identifies the battery and adjusts accordingly.

My Makita NiMH batteries on the 1804 charger charge in as little as 30 minutes; the old nicads took forever on the orginal charger, but much faster on the 1804.

Boostinjdm
12-12-2011, 11:53 PM
Nicads and NIMH should both charge without issues on the same charger.

They can both be charged in the same charger, but not all chargers will do it. Apparently the run of the mill dewalt charger doesn't like NIMH. I believe that the more expensive yellow top chargers will do 'em all.

gregl
12-13-2011, 12:22 PM
Thanks everyone for your responses. I wasn't able to respond immediately because right after posting the thread, I changed my email addy here on the board. Apparently there is a bug in the board software that cancels the account when you do that. Daron Klooster at Village Press got me back in today and says they're working on a solution to the problem.

Evan: I don't know what type of battery is in the pack. They are the DeWalt XRP 18v packs. The individual batteries are plain wrap with no markings on them at all.

Anyway, the Harbor Freight pack swap looks interesting, and is a clever option. As far as other rebuild options, it looks like the price would come to within at least ten bucks of a new pack (which is $50). So if the whole set is toast, I think the expedient thing to do is just to bite the proverbial bullet and buy new packs with a warranty.

Thanks again guys.

Black_Moons
12-13-2011, 01:33 PM
Don't charge Nimh in a Nicad charger, Nimh require much more sensative shutoff circuity and MUCH lower 'trickle' currents that make Nimh not suitable for charging in a nicad circuit

Nicad are considered chargable in a nimh charger however.

Also, those '4+ hour' nicad chargers are the worst, because they typicaly contain the least intelligence and often overcharge, or continiously 'trickle' charge the battery past full charge, And will often ruin nicads if left in.
(4+ meaning any charger that takes over 4 hours)

J Tiers
12-13-2011, 09:18 PM
My 14.4V XRP are NiCd.

rdfeil
12-13-2011, 09:56 PM
My 18 Volt XRP's are also NiCd.

Dunc
12-14-2011, 08:15 AM
My DeWalt XRP's use NiCad. If/when replacement batteries are needed I intend to switch to the Li powerpacks. These are direct replacements, acc to DeWalt.