Sawsall batteries

On Sat, 19 Mar 2011 12:28:35 -0500, Karl Townsend


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
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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.
--

Dan H.
northshore MA.
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...

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
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Karl Townsend wrote:

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
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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 www.power-sonic.com, 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 15/18ƒ% 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
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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.
--

Dan H.
northshore MA.
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On Tue, 22 Mar 2011 00:28:37 GMT, snipped-for-privacy@privacy.net (dan) wrote:

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
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Pete Keillor wrote in rec.crafts.metalworking on Mon, 21 Mar 2011 19:07:25 -0500:

Built in circuitry in your packs is there to prevent over discharge. I'm guessing their Li. packs.
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Dan H.
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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.
--
WB
.........


"dan" < snipped-for-privacy@privacy.net> wrote in message
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The lithium packs that I'm familiar with (laptop, misc) are complicated.. and some types are potentially hazardous as far as overheating, but then almost any energy storage device is hazardous when mishandled.
Some good brands of NIMH cells with tabs are, IMO, good replacements for building battery packs for portable equipment, and although the technical aspects of charging differ between NICD and NIMH, the NICD chargers could also charge NIMH packs well.. if the charger a moderate-charging-rate delta peak sensing type (not a fast/high-rate/timer type charger).
When comparing cheap grades of different cell technologies, all bets are off, there's no point. Better grades of cells are in a separate class. The best quality/grades of cells have typically been from Japan. There are a lot of different specific cell characteristics for different grades of cells.. info from Sanyo or Panasonic give very good descriptions of their different grades.
Some sources state that NICD are better for cordless tool requirements of intermittent, moderately high drain, power. The equivalent cell size of a NIMH will provide considerably more Ah capacity, which can be a significant benefit for many applications (not primarily cordless tools).
When considering replacement of cells in older packs, one should also be considering upgrading to newer charging units. The old charger is likely to be out-of-spec and/or possibly near failure. I don't test/check out new chargers or cells unattended.. just the same habit as when charging LA lead-acid batteries.
For many of the HSMs here, replacing/bypassing the board of an existing charger probably isn't too complex, for reusing the old charger case receptacle for the existing OEM battery packs.
Some cordless power tool packs contain internal temperature protection circuits or other safety devices which shouldn't be ignored.
I've been using some universal Powerizer NIMH-NICD chargers for over a year with very good results. These are 2-wire chargers, although one or more models come with a temperature sensing lead to prevent battery pack overheating. There are some models that are AC line voltage input only, or DC input (auto/truck lighter socket cord, or AC adapter input).
Some of the MRC brand chargers have a wide variety of selectable features for different cell types and capacities.. generally limited to up to 12V maximum pack voltage, as they come supplied with 12V inputs for portable/mobile use (can also be used with 12VDC AC adapters).
--
WB
.........


"Winston" < snipped-for-privacy@BigBrother.net> wrote in message
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Karl Townsend wrote:

I only have about seven names in my filter, and the difference is dramatic! :-)

If they're individual cells, and they're NiCd, (nickel-cadmium), it _might_ help if you gave them a deep discharge through maybe a 1K resistor in series with a 1N4004 diode (forward-biased, of course), and then give them a good charge. You'd probably have to set aside a weekend, because you'd want to let them discharge to about .6 ~ .7V, (the diode forward voltage), or the voltage across the resistor is too low to measure (just two ways of determining the same thing); this could take all night, and you'd have to set aside the next day to charge them REAL GOOD. :-)
Like I say, it _might_ help, and it might not, but it's a lot cheaper to try it than just going ahead and throwing them away and buying a whole new set. :-)
Cheers! Rich
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On 3/17/2011 9:51 AM, Rich Grise wrote:

<snip>
I put 1 name in my filter and my experience is f'n great now.
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Depends, I guess. What's coming for my old 12V drill is a jumper cable adapter and a car battery (deep cycle would be better, spare car battery is what I have handy.) I'll get something else for when it "really needs to be cordless" but a lot of the time a short cord would be no problem, and it's reaching the end of being worth buying it new battery packs.
If you can put a good 24V lead-acid setup in a wheelbarrow, hand-cart, wagon, tractor-basket or golf cart (ie, fill in appropriate sort of mobility depending what you already use to get around the orchard) and throw 25-50 feet of leads on it plugged into the sawzall, it would beat the crap out of any small pack you can buy or make, and not cost much either. ie, your units you can't remember are likely milli-Amp-hours, so you have 3 amp-hour batteries, if they are going the full distance. One of the best-bang-for-buck golf cart batteries runs 200 amp-hours (@ 6 volts, so you'll need 4 of them) - so if you can put up with a cord, you get 66 times the use and only one battery to charge. Now, those are 62 lbs each, so you can see you'd need something to haul 4 of them around with, but you could also go smaller (ie, 12V 55 ah -you'd only need 2- @42.5 lbs each) and still beat the heck out of little packs. Or you could put a couple of 9 lb 12V 12AH in a backpack....
Doesn't work if you can't have any cord.
--
Cats, coffee, chocolate...vices to live by

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On Mar 17, 9:53 am, Ecnerwal

If you're going to have 50 feet of cable at 24V driving a heavy-duty sawzall (remember, he doesn't want 18V), that's gonna be some hefty cable. Fifty feet (100 foot round trip) of 10 awg will drop about a volt at ten amps.
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In article

If it drew 10 amps, he'd get less than 20 minutes to a 3-ah battery - possible, I suppose, but kinda short run-time. Actual length needed depends on size of trees and how bad the terrain is. I don't regard 10AWG as remotely heavy (2/0 is heavy, and 500 mcm is f-n obnoxious) - but two strands of 6 or 8 will take quite a few feet to even add up to the weight of the battery you won't have to pick up in this arrangement unless going for the small back-pack option, which has short wires. And it's far cheaper (battery, wire and charger) than the $600 small-pack rebuild. If the terrain is not friendly to park near the trees, a heavier cable could be brought to the bottom of the tree and a lighter cable to the saw from there, if voltage drop even became an issue. A 1.2-volt drop (10awg) may not be that big of a deal, depending on the saw's behavior - 6 awg would bring it down to half a volt at 50 (100 r.t.) feet.
I don't know what Karl is doing with his trees - some of the "modern" orchards around here would be all set with 15 feet of cord as they are sticking with small (dwarf) trees and less ladder work. Of course, they also have to support the trees so the brittle dwarf stock does not snap in the wind. The older orchards would need longer cords as they still have big trees.
--
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On Thu, 17 Mar 2011 14:58:26 -0400, Ecnerwal

cords aren't the answer. Just today we drug 200' of air hose out over the snow to run the shears. REALLY looking forward to the snow melting. You get twice the work done for half the effort. I had to rest this morning after getting hoses in place before I even started. Just finished our 150 trees for today. Only 3000 left.
Karl
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On Thu, 17 Mar 2011 15:31:21 -0500, Karl Townsend

Why aren't you programming CNC helicopters with rotary razorblades on top to do the work for you, Karl? That sounds like far too much work.
-- A paranoid is someone who knows a little of what's going on. -- William S. Burroughs
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wrote:

Lasers!
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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
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rangerssuck wrote:

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