Rechargeable battery question

ally shipped from the factory with nicds and a charger.

panel; recharge and store. The store is a very low trickle charge. Becau se it's from the early 80s, I'm assuming it's just a current limited charge r (dumb charge) as it takes 14 hours to charge the entire group.

sts they don't like this type of charge, so I'm back at looking at regular nicads for it.

anyone know if anyone is making a quality nicad battery anymore? In the o ld days, I'd buy Sanyo nicads and although they'd often advertise less mah per cell than others, they seemed to last almost forever.

Over here they're banned now. FWIW I had good results years ago with very o ld nicads, but yeah, the capacity isn't hot.

I also wouldn't ignore the possibility of just using cheap new NiMH, if the capacity is enough.

NT

There are a LOT of variables here. It would be helpful to know what it is. Are the batteries in series, parallel, separate supplies? Is the OFF power drain really zero? Is it gonna sit for a long time between uses?

'80's nicads were probably about 500maH. With eneloops, that 14 hour charge might become 56 hours. If there are 14 cells in series, there's a lot of opportunity to have at least one cell reversed by the time you sense any symptoms. Keep doing that and you'll kill 'em all eventually.

The best strategy is to charge the cells externally in a proper charger and put 'em back in when you're ready to use it.

There are many charging strategies, but depend heavily on the usage patterns and actual cell configurations.

There's quite a bit on charging Eneloop cells here: Plenty of warnings to NOT use really fast chargers and really dumb (trickle) chargers.

Can I suggest yet another alternative? 14 NiCd cells, at 1.35v each =

18.9V total. If you replace the AA cells with five 14500 LiIon cells, which are the same physical size, that would be: 5 * 3.6 = 18.0v There are plenty of smart chargers available for the RC market that can deal with a 5s battery pack. I have one of these: Checking the specs, it charge 1 to 6 cells so it should work. If you need AC power, LiFePO4 charging, PC connectivity, upgradeable firmware, and terminal voltage adjust, the V2 version is what you want:

I use nothing by the cheapest cells, which sucks because they usually only have about half the capacity and lifetime of a decent cell. However, they're cheap, and my use in mostly flashlight is not critical. I haven't tried this brand, but at $1/ea, it's worth trying.

One potential problem with LiIon is if your unspecified device runs on

+10 and -10 volts. 5 cells won't work but 6 cells might. It all depends on the operating voltage range of your unspecified device and on how it's wired/designed/configured.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Thanks, but the link takes me to page after page of cells. Can you disclose exactly which link is the one you've verified as reasonable cells? Better the devil you know than to take a random shot.

I've had horrible luck with any 18650's with "ultra" or "fire" in the name. I'd like not to repeat that with 14500's.

inally shipped from the factory with nicds and a charger.

nt panel; recharge and store. The store is a very low trickle charge. Bec ause it's from the early 80s, I'm assuming it's just a current limited char ger (dumb charge) as it takes 14 hours to charge the entire group.

gests they don't like this type of charge, so I'm back at looking at regula r nicads for it.

es anyone know if anyone is making a quality nicad battery anymore? In the old days, I'd buy Sanyo nicads and although they'd often advertise less ma h per cell than others, they seemed to last almost forever.

old nicads, but yeah, the capacity isn't hot.

he capacity is enough.

or it might be easier to ask for a pile of NiCds on ebay

NT

inally shipped from the factory with nicds and a charger.

nt panel; recharge and store. The store is a very low trickle charge. Bec ause it's from the early 80s, I'm assuming it's just a current limited char ger (dumb charge) as it takes 14 hours to charge the entire group.

gests they don't like this type of charge, so I'm back at looking at regula r nicads for it.

es anyone know if anyone is making a quality nicad battery anymore? In the old days, I'd buy Sanyo nicads and although they'd often advertise less ma h per cell than others, they seemed to last almost forever.

Trying to avoid that :) It's a Teknetics 9000 metal detector. Back when i t was new, it was a high end detector. I don't know where I got it or even when, but there it is in my collection. My brother lost some keys last fal l and has a pretty good idea where they are. He was going to buy a detecto r but I told him I have one so that's what prompted my inquiry.

Series, but in two different banks of 8 and 6. If I feed in a dc supply on the 8 cell bank, the LCD display comes to life and the controls affect the display. If I put a supply on the 6 cell bank, it draws current but the L CD doesn't light. No, I haven't powered both simultaneously. I will before I order any batteries to confirm it's working.

I think so. There is a physical switch for power.

Probably, although these are fun toys and I do have several acres of unclea red woods on my property to explore. One of my best friends has a house bu ilt in 1798 with an original rock wall and outhouse, so there's that.

I agree, but one of the banks of batteries had a leakage and several of the very thin battery contacts have disintegrated away. If I install batterie s in it, it would be far more convenient to not have to physically remove t hem for charging.

I may have to rebuild the battery box with new contacts and go with externa l charging as you suggest. I was just looking for an easier way out (which is my defining personality trait...)

Thanks everyone.

A few years ago I pickedup a Eneloop battery pack for a bearecat scanner.

It takes longer to charge, since the charger is a fraction of the eneloop capacity. I never had over heating issues. It probably never fully charged, but it's always ready to use.

Avoid the trickle charge.

Test it out, you'll be happy with the eneloops.

Cheers

at's

If you only need it once for a single job, I would just use alkaline batter ies for a quick and easy fix. If necessary, use a couple battery holders a nd mount them externally. I assume that the circuitry will tolerate the sl ightly higher voltage, but if you are concerned, you could use one or two f ewer cells in each pack.

Sorry. I meant the link to show an example of typical LiIon batteries of all sizes, brands, and qualities. I usually avoid making product recommendations unless I've used or tested the product. I can't provide a reliable source of 14500 cells because I have yet to purchase any that I consider to be acceptable.

The problem with buying by brand name is that there are so many counterfeit cells on the market, that chances are good that even an honest vendor might be fooled by a disreputable distributor. "Can you identify the fake LG HG2 18650 Battery?" Lots of articles on how to spot fake cells. For a while, I was having too success by weighing the cells, but todays fakes are filled with carefully measured amounts of sand making the fakes impossible to spot by the weight. My best source of 18650 cells are used laptop battery packs. The catch is that they don't have a "button top" on the + terminal making them difficult to use in some holders.

In 14500 cells, everything I've purchased on eBay has been lacking. I haven't had time to run any discharge curves on the 14500 cells, such as these for various 18650 cells: I carry around a flashlight with 14500 cells that has a rather short operating time and probably doesn't meet the printed specs.

To: John-Del Before you run out and buy a pile of know to be good 14500 for powering the unspecified device, I suggest you buy some cheap 14500 cells on eBay, which are sure to be inferior and possibly counterfeit. Test the unspecified device and its charging system using cheap cells. Once it's working, then go shopping for good batteries.

So, where to get good 14500 cells? I have no idea. I just checked Digikey and Mouser. Nothing found. I tried NewEgg and found the same bogus brands as on eBay. Nitecore is probably a good (relabeled) brand, but the price is too high: I found an article recommending brands: but no sources. There's also the risk of buying counterfeits.

Bottom line... Sorry, I can't answer your question at this time.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Lotsa people recommending tiny magnets to replace the button top. I asked about the series resistance and was assured it wasn't a problem. I spot-weld a tab on top and fold it over until it's tall enough.

Best source for 18650 cells I've found is this:

Has six 18650 cells. Only 1.5 Amp-Hours, but they're rated for 30A peak discharge. Six for $10 is tough to beat.

If you saw the tabs in half, you can solder to the tab...if you're quick about it.

The pack works great as a replacement for two series lead acids in my weed whacker, but the voltage is too high for most things. If my analysis is correct, there's no protection disconnect. The reason the pack is cheap is that, it looks like, they monitor the cells and send a bit stream to the tool. The tool makes the decision about discharge protection. The charger makes the decisions about charge protection...so it seems. Good news is that there's a battery gauge. If you can use all 24V and watch the gauge, you can keep from over-discharging the cells...YMMV.

AS I recall, there was a ban on individual cells in the US. Don't know if it's true, but it's still a BIG liability issue for sellers. People seem to throw in any battery that fits and make smoke. You can't rely on anything you read on EBAY. You can't even buy one and test it. The next purchase of the same part from the same vendor may be completely different.

I tried NewEgg and found the same

If that were true, then all the 19.2v laptop batteries, which consist of 6 lithium ion cells in series, would also be dying from cell reversal. I've seen dead cells in such battery packs, but usually when the other cells are near death. It's just a question of which cell blows up first.

You can kill series batteries several ways with cell reversal. The most common is during discharge and charge. The problems can happen with any chemistry if a cell is discharged to zero. Lithium Ion batteries have battery protection circuitry (usually called a BMS or battery management system) to prevent individual cells from dropping below 2.7 to 3.0V which might kill the cell. Something like these: A BMS will also protect against over voltage and over charging and might include a charger and balancing circuit.

Keeping all the cells at the same voltage is also a problem. For that, there is the "balanced charger" such as the Imax B6 V2 I previously mentioned. The battery pack has an extra connector with wired going to the junction between adjacent cells. There are various schemes for balancing. Most common is if the voltage across a cell is too high, the balance charger adds some resistance across the cell to draw away some of the charging current, so that the other cells can catch up.

Balance chargers are very common in the RC (radio control) and power tool areas, where running unprotected LiPo batteries without BMS boards is common.

I agree, with one possible exception. The battery holders found in consumer devices are not known for being rugged and reliable. The springs make lousy connections, they become intermittent when banged around, or they contacts go high resistance when an alkaline cell leaks. This is not the best environment for precision LiIon charging. I'm beginning to think that my suggestion of using 14500 cells in series might be susceptible to these mechanical problems and that 5S battery pack of 18650 cells, with welded nickel strips, and proper XT60 connectors, might be a better choice.

Yep. I don't know what's appropriate for a metal detector. If it's lightly used, a single battery pack, as I mentioned above, would be easy to remove when the device is not in use. (Anything is better than fumbling with 14 cells, as I do with my MFJ-269 antenna analyzer. The pack could also be charged externally. Hmmm... yet another project.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Yet, you describe why that doesn't happen, for a protected battery pack, in the next paragraphs.

For unmonitored series connections, the shape of the discharge curve matters. Lithium voltage decreases gradually. By the time you trigger shutdown, the cells may be unbalanced, but likely not damaged. NiMH has a flatter voltage that drops suddenly at the end. Minor imbalance can cause one cell to drop by more than a volt before any symptoms are visible. For 14 in series, one cell can go from 1V to 0V with only about 7% change in voltage.

For unmonitored devices like NiCd or NiMH cordless drills... The speed drops, but you've got only one more hole to drill. That last hole damages a cell. That weakened cell is the first to go next time. Increase in self-discharge also means that if it sits on the shelf for a month before you need it again, it runs out of charge far faster than the other cells, compounding the problem. Eventually it shorts. Now, all the rest get overcharged. I suggest that practice is why most unmonitored drill batteries fail.

I've seen dead cells in such battery packs, but usually

Yep.

I bought an assortment of magnets to replace the button top on an

18650 cell. They're not quite the right size, but work well enough in my various flashlights. My spot welder died and I haven't bothered to work on its replacement. When I get something working, I'll go back to spot welding fake button tops (made by pounding a home made die set with a big hammer). I measured the resistance of the magnet with a ESR meter and found the resistance to be negligible. I forgot the exact value. Bug me if you want the numbers.

I hadn't heard of any such ban and couldn't find anything searching with Google. There are various limits to how many cells can be shipped and how they should be packages, but no ban that I could find.

I prefer "Trust, but verify".

Well, I bought 10 cells on eBay twice from the same vendor and received the same junk cells twice. Like these but from a different vendor:

I just realized that I don't have any 14500 data, so I dug out the West Mountain Radio CBA-II discharge tester and ran a graph: The cell is labeled 1200 ma-hr. Nominal, normal, or typical for a

14500 LiIon cell is 750 ma-hr. My test produced about 225 ma-hr capacity, which is well below 750 ma-hr nominal. The cell is junk.

Also, there's a problem. Capacity is measured at 0.2C. For a nominal

750 ma-hr rated capacity, 0.2C would be 150 ma test current. That would require 5 hrs to run the test. It's also well below where I normally run these batteries in my various flashlights. Testing the battery at operating conditions makes more sense, so I measured the current of my cheap junk Chinese flashlight at 850 ma and ran the test at 850 ma which would only require 1.1 hrs. If I had run it at 150 ma, it capacity would have been somewhat higher, but nowhere near the nominal 750 ma-hr.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

If you use magnets you might consider grabbing the magnets out of a dead hard drive, neodymium is IIRC the strongest fixed magnet made, and it has very low resistance.

What do you like for a small spot welder? I've been thinking of getting one.

Those magnets are much too big I have a fairly large pile of such hard disk magnets that I bought at a local flea market. Very handy, but not for making button tabs.

The magnets I bought were some of these: in 6mm x 1mm and 6mm x 2mm. 1mm is a bit thin but works for most battery holders. 2mm is a bit too thick but works ok in a few holders. The magnets stick fairly well to the stainless battery case. I had to punch out a few sticky back vinyl "washers" to keep the magnets centered.

I looked at what was available and decided that I didn't like anything that was also affordable. So, I'm building my own. Nothing fancy. The biggest automotive starting battery I can find (I want cold cranking amps), a large high current relay, a less than 1 second timer board to drive the relay, a foot switch to start the timer, some heavy gauge wire, and some machined parts for the copper electrodes. It didn't take much testing to determine that if I wanted to weld something, I want DC, and to use AC if I wanted to blow a hole in something. There are several YouTube videos describing how to throw something together. For example: "Simple and dirt cheap Spot Welder for lithium cells" It needs 2 electrodes, no ground clamp, and heavier gauge wire.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Stable/controlled pressure is very important. You can make a serviceable electrode pair from a small arbor press and some hobby store brass. I use #6 solid copper wire for the electrode and a file to shape the end. The trick is to make sure that the current doesn't go thru any part of the probe actuation assembly. I could put up some pix if anybody cares.

You need a lot of energy in a short time to melt the nickel without overheating the bottom of the cell. At the risk of repeating myself, the secret is to use an energy pulse, not a current or voltage pulse.

I started with a microwave transformer and some logic to count full cycles of 60 Hz. to keep the transformer from saturating arbitrarily. I used 4-6 cycles for a weld. If you try to do it without the full cycle counter, the transformer ends up at some arbitrary point on the B-H curve and saturation effects can raise havoc with your welds. Repeatability was horrible. I could make some very nice welds, but not enough in a row to make a battery pack. Starting the pulse at a zero crossing and counting cycles improved repeatability dramatically, but it was still crap. Problem is the low voltage is very intolerant of contact resistance variation.

I tried discharging a cap, but at the time, I didn't have anything that would switch the required current. And I didn't have a storage scope so I could see what I was doing. Turns out that it's harder than I thought to instrument a welder. When the pulse fires, everything on the bench jumps. Getting a scope to trigger on a specific part of the waveform was just wishful thinking.

I tripped over a Unitek CD welder for $17 shipped on EBAY and snapped it up. It can put 7V across a milliohm. Welds got instantly very much more repeatable. Since it's an energy pulse rather than a current pulse, it's much more tolerant of resistance variations. It's only 125 Watt-Seconds, so it works great on thin nickel for low current stuff. It won't weld the thick links for high current stuff.

Turns out that hobby store brass sheet can be cut into battery tabs. It welds very easily. I wouldn't use it for anything high current tho.

Forgot to mention that rebuilding battery packs rarely works these days. Back in the NiCD days, there was a chance. With Lithiums, not so much.

IF you remove the battery, the protection chip goes into disabled mode. Even if the cells are good, the laptop won't work. I only succeeded on ONE Lithium battery pack because it used a PIC processor and I was lucky that resetting the PIC restored control.

I haven't tried, but I expect the same applies for Lithium cordless tools and most everything else.

That's not a problem for this thread, but might influence your motivation for building a welder.

On 4/16/2018 6:01 AM, mike wrote: ...

Since the brass melts at a much lower temperature than the nickel/stainless steel, is it actually a weld (both metals melted)? Or is it more of a braze, with only the brass melted?

You can pick all the nits you want. It makes the connection.