Sawsall batteries

These guys have been doing my batteries used in production for years. I'm very happy!

I use 18v driver drills as nut drivers. The guy at Voltman had me explain what we were doing and said to use NiCad. Call and ask.

Lasers!

My better half has voltman recorded as the place to go. You must have told me before. I have CRS (can't remeber s%^&) but my honey takes care of me.

Karl

It took me twenty minutes with Google to figure out who the were. I remember them being somewhere in Ohio that I used to go Walleye fishing in the river in the spring...CRS! BUT, in the spring, the fishermen are elbow to elbow on the river bank and the fish only hit tiny chartreuse jigs tipped with a Shiner and a slow retrieve bouncing off the bottom. SEE...I remember the important stuff!

Yeah, light sabres (limiting reach) attached to RC heli rotors! I expect that he could sell tickets to bystanders if he ran 'em at night, making the whole project pay for itself.

-- A paranoid is someone who knows a little of what's going on. -- William S. Burroughs

I believe that the cells are made by A123 Systems.

The "buzz" is that these are the best you can get. They are some flavor of Li and are able to be fast charged without overheating.

But I haven't actually used them myself. The last time I looked (about two years ago) they were about four times as expensive as regular NiMh cells. So I put them in the "would be nice" category.

Looks like the prices are still pretty high, but if you need the performance I would give them a try.

DOC

Buy my junk...

Me too, even less. But I expect great things (it's called "The Optimism of The New Owner").

I have the 12v Milwaukee Li-ion impact driver and it is HALF the weight of my 14.4v NiCd driver-drill (2.2lbs vs. 4.4lbs). I LOVE the light weight. There are 2 batteries available, one twice the capacity (& twice the weight) of the other. I got a big one as a "free" bonus when buying the kit and sold it. Lighter is so much better.

The battery has only run down once and I switched to the back up. My use is very intermittent.

The Li-ion charge curve (charge vs. voltage) has a knee: quite steep up to about 3.9v and then much flatter to 4.25 (full charge). The charge process uses constant current up to the knee and then constant voltage. Charging time is about the same for each phase.

The charge (energy) at the knee is about 1/2 the max. But operating the battery below the knee about doubles its life. So using the battery below the knee allows it to charge in 1/2 the time, but only gives half the run time (a wash except for the swapping time) & doubles the life. That's what I think my Milwaukee charger is doing. Sounds like your Makita is doing that, too.

Too soon to tell. Check back in a couple of years.

I haven't paid enough attention to say. But it would be comparing old NiCd's to new Li-ion's, so that's no use.

I am more impressed that I thought I would be. Half of it is the light weight & the other half is the impact-ing drive. It's a delight every time I use it.

Bob

And where does it say the sawzall draws 10 Amps? ...lew...

Karl, I work for a maintenance department. We run DeWalt battery tools (got started with Black & Decker commercial grade way back when and once started.....) We've run the 18 volt stuff since it came out using NiCad. I remember when the parts lady got us a new drill with the "new fangled" Lithium batteries. It seems like it was just a bit ago. We've used and worked the daylights out of these things. The Lithium seems to have a fresher, stronger feel and sound in use. They seem to last longer than the NiCad (very subjective, non-measured, unscientific observation). When they die, they don't just start to run down - they die!!!! We have tried several companies on rebuilds of NiCads. We've not had good luck with them, so we buy factory replacements. The dollar difference between rebuilds and factory is not much - we get a substantial discount at Graingers and the commercial tool house we use.

I had my first lithium not take a charge about 2 weeks ago. My comment was that these were way too new to have a problem. I do date and mark the stuff my crew uses. I said, "See, look at this date . . . . . . . . . . . . . . . . . Spring 2006." Time flies when your having fun.

I wish I could help you more on your decision, but this has been mine.

Thanks. I think I'll take your suggestion and buy two new batteries. Then rebuild a couple more.

I think I'll stay away from lithium this time around.

Karl

I think a lightweight, 12v sawzall connected to a paralleled string of

7AH batts on your belt would be the optimum tool. $150 would get you a couple of sawzalls and half a dozen batts to play with. Add $10 for a pack of blades and roll of wire and you're set.

-- "A patriot must always be ready to defend his country against his government." --Edward Abbey

Karl Townsend wrote in rec.crafts.metalworking on Sat, 19 Mar 2011 12:28:35 -0500:

Also be sure to STOP using the saw as soon as you notice a drop in speed/power. Continuing to draw power from a multi-cell pack can damage the cells. I can't stress this point enough.

...

Hmm...

Wish I new the facts here. I've also been told I'm sticking 'em back in the charger too soon. Should run 'em nearly flat.

Karl

That depends on the battery chemistry. NiCd's are almost indestructible, NiMH's are practically worthless, and I hear those lithium things are as temperamental as a prima donna.

Good Luck! Rich

Probably only if it's made in Mississippi.

"Karl Townsend" wrote in message news: snipped-for-privacy@4ax.com...

The short answer is: Stop as soon as the tool slows.

The long answer is: If there is just one cell in the pack you can run it flat and the cell voltage will drop to zero volts. Bad in terms of number of cycles you can get out of the battery but not really destructive. You can find datasheets online to get specific recommendations but none recommend going all the way down to zero. Go to

, click on literature then nicd-nimh batteries then nicd/technical manual for one example. All of the discharge curves stop at 1.0 V because the voltage is dropping off of a cliff by then (a little more current drawn from the cell makes the voltage drop a lot more, so there is very little energy left in the cell). Now put two identical cells in series, and run the pair flat. Since they are identical (you can already tell where this is going, can't you? :-)) they both reach zero volts at the same time and the current stops flowing. Again, taking a cell all the way down is harsh but not catastrophic. Now have two cells in series but let one cell have more capacity than the other. As the pair discharges, the weaker cell will reach zero volts first and as the stronger cell finishes discharging towards zero volts it will actually partially charge the weaker cell backwards - that's really bad :-). Now think about an 18 V battery pack made from 1.2 V NiCd or NiMH cells - that's 15 cells in series. If all cells discharge equally to 1.0 V the pack voltage will be 15 V, not much less than 18 V so you can probably tell the tool is starting to slow but it is still at 15/18=83% of the starting voltage so the speed is probably only down 17-20%. That's where you should stop, because those discharge curves say that even though the pack voltage is 15 V the energy left in the pack is tiny, so you won't get but a few more minutes anyway. The real reason is that if one cell is noticeably weaker than the rest, so that it is down to zero volts by the time the rest are only down to, say 1.1 V, the pack voltage will still be

14*1.1 + 0 = 15.4 V and even if you stop at 15 V you will have already reverse charged that one cell enough to damage it. That means you really can't tell if you have a weak cell by voltage on such a high voltage pack with so many cells. Reverse charging a cell will at best completely kill any capacity it might have still had, and at worst can cause overheating and rupture if you are really sucking out the current. Works the same for NiCd and NiMH, and probably the same for Li but I don't know the discharge curves so don't know when to stop with Li.

----- Regards, Carl Ijames

My newest Milwaukee packs have very little drop in output before they stop cold. They also have a charge indicator, so there is some control and programming built into the packs.

Pete Keillor

Karl Townsend wrote in rec.crafts.metalworking on Sun, 20 Mar 2011 18:17:39 -0500:

That would depend on how smart the charger is. If the charger is a timed shutoff kind, then yes, run them down to the point that you notice loss of power.

If your pack and charger have three terminals, it is likely to have a thermal cutoff at the least. This kind of charger dumps current into the pack and the temperature sensor (third contact) will terminate charge on temperature rise.

The next smarter ones will charge some, then sample the voltage, charge more, sample again. Each voltage sample is compared to the one before. When the pack is near full, the voltage will drop slightly. These usually have a thermal back up, or will stop after a certain time.

If your chargers are post 1995, I would be sure not to run the packs dead. Stop when you notice any power loss. And if possible, let the pack cool to room temperature before charging.

The problem is that not all the cells are exactly equal. One or more will go dead first, and any further discharge of the pack will be forcing the dead cells below dead.

Yep, what you said, Dan. Chargers vary a lot, from cheap ones that actually kill batteries unless they're not watched/monitored very carefully, to combination analyzers/chargers.

Some folks (way too many) are still mentioning the negative issue of so-called "memory effect", when there was no real effect.. it just doesn't apply to rechargeable cells. Misuse and neglect are responsible for poor performance from good quality rechargeable cells.

The trouble with many battery pack temperature/thermal switches, is that they're often selected for safety (shut off in case of charger failure to prevent excessive pack temperatures/fires), and are typically in the 65 C/149 F range, which is too hot.. the cells are very likely being damaged at those temperatures. Many of the thermal switches are sensing air temperature within the pack case, not the actual cell temperatures, where the cells' core temperatures will likely be extremely excessive and rapidly damaging the cells.

One aspect of using new replacement cells, which isn't always mentioned, includes several/numerous charge/discharge cycles of new battery packs before putting them into service. The new NIMH sub-C and D cells that I started using show significant performance improvements (actually measured, not guessed) after 5 to 10 cycles. Some of the MRC charger models mentioned earlier, have controlled discharging capabilities which will show how many mAh have been drawn out of battery packs (also how many mAh have been added during charging).

Discharging of rechargeables should never include running the cells down to nearly dead.. regardless of what anyone says. Discharge cycles should be a controlled, specific to the Ah capacity, current draw to bring the charged cells down to about 80% of fully charged (to about 1V or not below 0.6V per cell, at most). These discharge levels are from cell manufacturers and data from real scientific study approaches where the goals were peak performance and long-term reliability.

For critical applications, such as endurance performance competition (not kids with RC toys), individual cells are thoroughly tested and matched before combining them into battery packs, prior to use.

Users that believe that they're saving time by not changing out battery packs, or getting the most per charge by continuing to run a cordless tool (or other rechargeable-powered device) until it just won't work any longer, are sacrificing the life of the cells.. this is one reason why many newer electronic devices shut down before their battery is depleted.