Nicad Battery Q for the guru's

[ruddycrazy]

G'day Guy's,
                 Well had an hour to spare today before picking up the kids from school so for a bit of fun I stripped my old B & D fire storm 18 volt cordless drill to see if it still worked. I put my Lion cell package and no worries it started spinning and no way could I stop the chuck. So next job was to ind the old batteries for it and see if there was any life left in them. A few years ago the charger let the magic smoke out and I couldn't buy a replacement so I forked out for another drill. I did remember that ol' fire storm was a top drill so for a bit of a laugh I put the first battery I found on my 30 volt 3 amp PSU. It measured 0.67 volts and at first the PSU went into current limit @ 3 amps, the voltage on the battery soon rose up to match the PSU voltage then the current dropped to just under 3 amps. I had the voltage set to 22.5 volts as the old charger was a 23 volt 1 amp one. I charged the first battery for about 20 minutes and it was holding 19 volts off charge so I went and had a go at drilling a 8mm(5/16") thru some 1/4" plate, the first hole it ripped thru and the drill said the battery was still charged so went for 10mm this time and it did drill it ok but the voltage reading was off the screen. I put a DMM on the battery and it was sitting on 16.75 volts, so time to find the second battery and do the same thing.

              Now ages ago I did read about charging nicads and my rusty memory remembered when the battery is charged the current will drop off a bit and the temp will rise. Ok back to the second battery the current limit stayed on a bit longer with this one but it did rise up in voltage so I let it charge @ 22.5 volts with 2.5-3 amps going in for about 40 minutes. I did notice the current drop about .2 amps and the temp rose to about 33 degrees C ( the ambient temp 17C). I did see the current slowly rise up again so I thought right thats charged.

            Now is my rusty memory right with the charging regime for those nicads as if I can bring these batteries back to life, ok not with the full AH they had before but to a useable state then I'll make a new  charging circuit for them.

            I've got both batteries at rest now and I got yet another car to fix so I'll got get that done and take the sitting voltages reading again and hopefully they have held the voltage.

Regards Bryan

P.S. Ok checked both one was sitting on 20.1 volts and was steady for the time I was up the shed, the other was 18.3 volts and dropped 0.1 volt while I was there. So hopefully that first one might come good but as the second one that might be a suspect one.

[Bruce S]

Bryan;
 Your memory is spot on  .
That one that dropped is toast, there is a cell inside that has gone into reverse pole charge, and can be dangerous, in that it could cause a thermal run away for the rest of the pack.
NiCds like to be constant current charged, when you have the chance  setup a charging so the voltage is at 21.00(full mark before the heat really gets going and a current of C/10 or even C/5 if your in a hurry.
Don't use the C/20 settings for these, the slow charging won't be enough to wake up the cells from their long rest. I've stopped doing the longer slower charge after doing some tests on several packs the C/10 and C/5 seem to be the best for the Sub-Cs that I have. Notice that I stated 21.00 ! this is about 98% full and the NiCds seem to love being abused like this, plus I can jump on the charged packs sooner. The full mark when the Neg-Z kicks in is 1.43V/cell once you push them past that is when the heat gets going at 1.40V/cell they will feel warm put that's about it. This is working fine for my packs both small and large.
Hope this helps;
Bruce S

[ruddycrazy]

Hi Bruce,
             Thanks for the tips mate, last night I did a bit of a trial with that suspect battery. I got to drill 9 off 8mm holes then the battery went flat. When I put it back on charge the psu wouldn't go off current limit and noway would it go over 18 volts. The temp didn't go over 31 C but as soon as I took it off charge the voltage dropped so yea it must have a cell or two that went south. The other battery very slowly dropped and after about 3 hours it was down to 17.6 so it might be suspect also.
            In my research last night I did read the best way to charge nicads is not using CC but pulsing the charge with a sec second burst then a 5ms reverse pulse. It did say by using this method one can get double the life out of the nicads so that might be the wya I'll go when I make my own charger.

           Also I did read one can give a dead nicad a high voltage pulse to bring them back to life. Now I do have here some 1500uf 420 volt caps and I could use my 90 volt psu to charge the cap up then use a resistor to ensure only a small current pulse goes into the nicad.

          The local battery guy said he charges $79 to repack drill batteries so that might be the way to go down the track when I'm working again.

Regards Bryan

[Bruce S]

Bryan;
I have heard of GHurd doing the high-voltage zap and it works from what I've heard.
Possibly once he wakes up from his evening shift he'll drop by  to lend a sentence or two.

The pulsing thing on charging is tricky at best. I'll drop a pic in here to show what happens when it doesn't work.
It's NOT pretty at all. Wait til you see the battery pack, Almost got sent to the dog house for this trail in the house 

the unit going down to 17.6, try doing a charge full discharge recharge a couple cycles, since it came up and started working, it may only need a few usage cycles to get back to being useful.
 
IF you weren't so far away I'd send you all the sub-Cs you could stand.
Norm is first on the list though  he's the real guru of re-building these.
On the repack, we have a website I've used that does the same thing, they have been reliable for the most part, but I would ask what the mAh of the replacement batteries are.

Best of luck!
Bruce S

[ruddycrazy]

G'day Bruce,
                 The good battery pack was sitting on 17.4 volts this morning so I got it on charge again, I put a 5 ohm 5 watt resistor in series and the current is about 300mA going in. It's currently sitting on 19.46 volts after an hours charge so it won't be long hopefully and it will be fully charged. Now with the second pack I pulled it apart and 6 cells were showing zero voltage. The rest were around 1.2-1.3 volts.
                I have an old laptop battery here and I pulled it apart and everyone measured zero. I flashed each battery for about 10 seconds using my Lion 3 pack and everyone bounced back to 1.2-1.3 volts. Now the BIG Q I got now is how do you guys build your packs as I reckon spot welding would be the best. I have had some success in the past just soldering but with those 2 off 1500uf 420 volts I'm thinking I might be able to make a small spot welder out of them.

               My idea is now with 6 dead cells in the second pack and 8 good ones out of the laptop battery I'll make some packs up to power some garden lights and use a 5 watt pv panel and circuit to keep em topped up. This will hopefully keep the missus happy and the best part I'm having a heap of fun doing all this. down the track I'll get that second pack done by the local guy but for now one batterypack will do and I got my trusty fire storm cordless drill going again.

Regards Bryan

[ghurd]

I have heard of GHurd doing the high-voltage zap and it works from what I've heard.

I think the common old time term is "Spark the Whiskers".  Maybe 'Zap the whiskers'?  Something like that.

Something like a 12V battery and #24 wire, then do some 12V to 1.2V charging via just twitching the #22 wire on the nicd, so it makes some sparks.
The idea is to make a few sparks.
The idea is to NOT supply charging current!
Repeat a few times.
Check the nicd voltage.
If it is not something like 0.7V or more, repeat another time or 2.
It works in the first few tries, or it won't work at all.

Might get a few more cycles out of the cell, but the cell will be problematic and not last much longer.
(may be OK for a AA in some situations, but I would not build a pack containing that cell)

It must be a dangerous operation.
Nothing I could recommend from the standpoint of the safety issues.

Take safety precautions.
Better yet, don't try it at all.
The 'cd' in nicd is not good stuff to mess with.
G-

PS-  Can rebuild the drill battery pack yourself with Norm's methods.  The hardest part is figuring out how the pack comes apart so it can be put back together later, because they were not intended to be taken aprt and reassembled.
Most in the US use Sub-C cells, even if they don't look like it before opening them up.

[Bruce S]

Bryan;
I wanted to get back with you on the pulsed charging idea. NOW I'm not the best at building these as I usually kludge things together to see if it something I want to work with or am curious about trying out.


This unit is a 12Vdc 10Ahr small pack that I use for various stuff. I have about a dozen of these.
I'm not sure you can tell the wire gauge from the pic, but it is stranded 12awg.
I built up a pulse charger that included the reverse and this is what I got from it.
When I saw the ends and that it was smoking, I pulled the entire circuit away from the supply voltage and chalked it up to experience.

Bruce S

[Bruce S]

Bryan;
I wanted to weigh in on the rebuild as well.
I can get small one-off cut pieces cheap (free)of  stranded 12awg wire, so that's what I use to build up my packs.
I do not do a form of spot welding, too lazy to build a unit up  .
I use a good hot 180 watt soldering iron, let it  come up to full hot temp and solder the tin pieces together.
Actually I have an older 16Ahr pack that I keep charged for my still, I use it ( when not distilling car fuel  ) with a 300 watt MSW to do the soldering, that way if I get a tech-support call and leave the iron on  the dead pack will fix that for me.

I've burnt my fingers enough doing this but if you spread them apart fully and then solder each one you can then re-bend them back down pretty easily. I tend to work on separate cells , building one part let it completely cool and work on another while it cools.
Its the hot iron that is important. Too little and it starts to cook the batteries internally , as they absorb the heat from the iron.

Hope that helps
Bruce S
What GHurd said it true, most of the battery packs seem to have been formed about the packs rather than the packs built to be rebuild-able, BUT places are doing just that.
Norm has done a ton of stuff with the ones he has and is still find ways to re-do them even nicer.

Having fun is always the best way to go!!

[Norm]

Byran,
    I'll show you guys my idea of how to best power a
cordless power tool...especially a cordless drill.....my thoughts are its a waste of time
to have a cordless drill ....I mean if I'm too far away from a receptacle.....why not
have a NiCad power supply of 18 volts nominal voltage 3.9 amp/hr. (45 NiCad c-size
, 1.2v each) and using a 10 guage stranded wire cord about 6-8 ft. and an adapter
plug in place of the cordless battery ( a few of you have already done this with a 
car battery) now this NiCad battery pak will weigh  about 5 lbs. with a eye ring if you're
up on a ladder and can hook it on a rung...
First step is to dissassemble 3 of the batteries
to disassemble ....take a utility knife and cut the length of the shrink wrap including
the end fold over .......
Okay ....some pics

next cut fold over on each end as marked, this allows the corner to hinge open and
all 3 stacks slip out, then you remove wires and cut the connecting ribbon in between
the batteries cuts easily with a utility knife....(*careful those little corners are sharp
and can cause at least small cuts that will sting for a week ! *)
Now place in freezer for about an hour....then you canseperate them quite easily
with a table knife, take the middle one and turn it end for end ,glue them back together, some 12 guage stranded wire....twisted and soldered across the terminals
each end......a short piece of wire soldered onto the formered mentioned wire  and
inserted into the top of the tab end of a male quick connector  and crimped where
the top of the connector is flush with the top of the cell....do the same with the other
end put the 3 back into the shrink wrap cover and after taping back together ,cut
a slit on both sides of the connectors and across the top providing access to the connector. Now connecting 3 of these 6v paks into series gives you a 3.9 amp/hr.
18 volt battery that should last 3 times as long as an 18 volt cordless drill battery.
enjoy !
Norm.

Of course you can just disassemle one 18 volt NiCad , use 12 guage wire , bypass
the thermistor and cutting the package like I've shown is the best way to open and
close it back up when you are done.