I have an old favourite Makita 6v cordless drill/driver that is no longer taking a charge. The batteries are of the semi-permanent NiCd variety. I can't find a replacement for them so I was thinking of making my own battery pack out of AA rechargeable batteries. Easy enough to solder together 4 AAs.
The question is, can I use NiMH batteries instead of the original NiCd? If I do, will the original AC charger work to charge up the NiMHs? I'm not sure how the two battery types differ in terms of charging needs.
Here's what I know so far (and please somebody correct me if I'm wrong):
NiCds and NiMH have different charging characteristics. Smart chargers for NiCds usually use negative delta-v detection to sense when the battery is charged. In other words, when a NiCd cell reaches capacity its voltage actually drops a bit, the smart charger senses this and stops charging.
When NiMH reach capacity they can go either negative delta-v or zero delta-v, so it depends on the cell. I think they also rise in temperature, so you have chargers that may detect this rise in temperature and stop charging.
NiCds can tolerate bigger current draw and are more tolerant to overcharging (if using a 'dumb' trickle-type charger). I also think you get more recharge cycles for NiCd than for NiMH. NiCds also work better in the cold although this may not be applicable to you.
You may want to look into the required charging current for the NiMH cells you are considering to see if your charger is compatible. You have to charge the cells at their rated capacity, in other words if the cells are rated 1500mAh you need a 1.5 amp charging current for a 'quick charge'.
As for soldering cells, you can do so but be very very quick, don't let the cell heat up or you'll damage them. Use a soldering iron with a wide tip so you have enough surface for a good and quick heat transfer; you may need to hold a smaller iron longer and this may damage the cells. I use dad's old Fuller 50W with a quarter inch tip.
Use the copper braid from a old length of coax cable to connect them, then use heat shrink tubing to package them up. Start by shrinking the ends first then the middle so the pack will be tighter.
To make a long story short, try to find NiCds with the same characteristics as the old cells.
I think you and I are working on a similar project: I'm looking to build a battery pack for a bike light, either NiCd or NiMH (I'm very much leaning on NiCd), and I'm looking to built it myself using
7000mAh D-cells. I'll be using a modified DeWalt 9107 (smart) charger to charge 'em up.
===> Nothing to correct; that's a pretty good writeup! ===>
Basically, for the OP, try to stick with the same battery type as the charger is/was meant for; you'll get better and more reliable use of the batteries. Batteries care about their charging rates for their longest life. "Better" batteries without the proper charging specs could, not will, result in a short charging life. Charging voltages (and thus rate of charge) varies with the type of battery. Another tip for soldering: lightly sand the battery solder locations wiht a high grit sandpaper (220 is good) and wipe down with medicine-cabinet alcohol; do not touch the solder surfaces with your fingers. And do solder as reasonably quickly as you can. If you flub it, wait ofr the battery to completely cool inside before you apply heat again. Batteries store heat for several minutes.
While the other posters who mentioned different charging rates are correct, there's also the issue of discharge rate. NiMH batteries have pretty good discharge rates, but not quite as much as NiCd. This is important, because those power tools demand a lot of power. While in this case the difference isn't huge, it may be enough to underpower your drill, shortening your battery life as well as the life of the drill.
Also, NiMH batteries don't hold their charge very well. You can pick up a NiCd battery after several weeks and expect it to be near fully charged. NiMH batteries will be stone cold dead in a month, which brings another issue, which is one cell will almost surely die completely or have it's life seriously shortened with a full discharge. The weakest battery will be drained first, and the others will send a reverse current through it, which is bad.
It's best if you stick with NiCd.
As an aside, you can buy these things with the tabs already soldered on. Soldering directly onto battery terminals is a big pain. The price difference is insignificant.
If you are like me, I don't give much thought to charging rates, and decline rates, and interest rates. I just want to know that my batteries are gonna work. There's nothing like going to do something, and your batteries are dead.
Right now, I have three Makita 9000 9.6 batteries. I would rate one an 8, one a 6, and one a 3. It is time to get new ones, but hell, they cost as much as a new drill. With batteries. AND charger.
Think I will bite the bullet this time and get a DeWalt.18v. I really like the little Makita, but no sense spending money on something that is going to crap out at any time.
Don't be too quick with that. I know a few unhappy DeWalt owners due to clutch problems. Our maintenance supervisor just dumped his DeWalt in favor of a Craftsman. I don't know if it was this group or the woodworking groups where there were recent complaints about the ability to set the torque for screws.
My Craftsman batteries are powerful, but was surprised to see they only used sanyo kr-1300sc nicad battery cells.
In an earlier thread.
" That's ok, but I hated adding less powerful cells to my better packs so decided to order some powerful new 1.2 V cells that are even better than what they replace. I got them at
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DKid. " They sell very powerful nicad cells that are double the power of the standard Craftsman cells. And they come with solder tabs at no extra charge.
I have a Bosch 14.4 drill and am very happy with it. The nice feature is that you don't have to use 2 hands to tighten the chuck. The motor/gear has a lock when off, so you only tighten it with one hand. I also bought one for my son. I also bought a Craftsman 19.somthing volt kit with drill, recip saw, circular saw and light for my son. This kit is real nice and is very powerful. I was even thinking of getting one for me, however, I have most of the tools already. But, my "Tool Shop" recip is a poor excuse for a tool. It vibrates wildly, is pretty weak and the battery doesn't last. I gues that's why they are that cheap. I do, however, like my
18 volt DeWalt circular saw. It is really a great tool.
But his drill I assume comes with a charger. In this case he would no longer be able to use this charger correct? That would be a bad idea since Im sure the battery caseing and whatnot is designed specifically for this charger.
I would stick with the same battery type, there is no reason to change is there?
If you want to add power, put the batteries in parallel. If you have enough space, you will double the power and/or usage time of your 'battery pack.' Perhaps that is what these 'powerful' cells have, parallel cells inside 1 unit.
NiMH discharges at about twice the rate of NiCd. That is nowhere near as bad as you claim. As well, topping up NiMH is easy, whereas partial discharge gives problems with NiCd unless you have a conditioning charger.
If you use the tool a lot on a continual basis, NiCd is the way to go. If you use it occasionally, NiMH wll be better, though you may have to top up the charge first. If you've got loads of money, Li Ion is better than either.
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