What's Wrong With Nicd?

[Punx0r]

Just a musing really.

Having received a lipo charger I thought I'd try it out on something expendable first. I have a 6 D-cell maglite in my car powered by nicds rescued from used emergency lighting (3 cell sticks in this case).

Everyone knows nicds have a high self-discharge rate (I've been told they run dead in a month). The torch cells get charged when I remember - usually 12-18months. In this case it's been a good 18 months. The sticks measured 3.80V and 3.81V and the torch was still bright The (dis)charger reported 2Ah (to 1V/cell).

The sticks are date stamped 1992. I have some other cells somewhere that are about five years older. They worked fine when I tested them about a year ago.

I've read reports of large-format nicd's giving 20-30 year service lives in aircraft and EV applications - despite being neglected.

The internet reports they have good charge/discharge rates, low peukert and fairly idiot-proof.

I hear they (like nimh) don't like being paralleled, but aside from this, what is really so wrong with them?

 

[dogman dan]

They don't like being paralelled. Thats enough unless you have a fairly short trip to do. And tend to have a so so C rate. That can make em less than ideal for ebikes. You can discharge em paralelled all you want, but then you gotta charge em not paralelled. Heavy suckers, not as bad as lead but close.

I've run nicads in drills for years and years. Every day kind of professional use. They work good for that, but you mess up bad if you charge em too soon after a discharge. After enough cycles, the self discharge gets to be a real pain since they won't hold a charge overnight.

 

[1000w]

Nickel–cadmium is toxic, heavy metals are not very helpful for the environment.
Just mentioning another angle.
Cheers.

 

[liveforphysics]

You need to make sure the total desired capacity of the pack can be achieved in a single parallel cell.

This generally means about 7Ah is your limit (F-size cell). (it's possible to do parallel strings with diodes and completely separate chargers for each string, but it's quite a PITA)


If you can get quality well matched cells (tough to find these days because pretty much all good Tier1 mfg's stopped making them about 5-10 years back), you could make a NiCd pack that would last 10-20years of service on an ebike.

Keep in mind, when these things blow up, it's scary, you won't get burned, you will get shrapnel blasted into you like a shotgun.

Charging is also way more complex than dealing with Lithium, you need temp sensing to really properly charge them, and voltage decreases towards the last ~10% of capacity, so you really need a charger setup to detect that peak and not over-charge past it or they can explode.


That said, right NiCd charger, a string of good quality cells that has the capacity you need, and you could have a heavy and bulky, but super long lasting pack.

 

[Punx0r]

I think it's slightly out of date (no lipo), but there's a summary table of different battery characteristics here:

http://batteryuniversity.com/learn/article/whats_the_best_battery

The C rates aren't amazing compared to lipo, but they're much better than lifepo or laptop cells.

Regarding charging, I can't recall a hearing of temperature being a problem (inc. 30 min charges) or a cell exploding. Not saying it doesn't happen, but can't be *that* common.

If I find myself with hands on a load of used D cells I'd certainly use them as a range extender pack. The use of laptop cells on here looks very interesting, but just too fragile and too much hassle for me.

Thinking about it, I bet the packs in emergency lights get periodically replaced (internet suggests 3-5 years), so there must be companies with crates of usable waste cells.

 

[dogman dan]

Long as you don't abuse it.

I put my Ebikes-ca 8 ah nicad packs on a 5304 motor, and quickly killed em. Ran em too hard at too high a c rate. Both packs have one or two bad cells in them now. They heat up fast when charged, so the charger won't put much more than 2 ah into the pack nowdays. I squeezed another summer out of em, running my lawnmower. But it was charge em 3-4 times to mow the lawn. Now I mow the entire lawn with 5 ah of lipo.

FWIW, Justin said on his website don't run a 5304 on 8 ah nicads. He said use 16 ah for that. YUP.

 

[Ypedal]

I have bikes.ca nicad packs still in service ( 2006 or so ? ) they deliver 6ah as of last year when i bench tested it.

watch justin's video on youtube *( will see if i can dig it up ) he has a well documented history of them going ballistic... stories of them shooting contents thru walls.. :lol:

 

[Punx0r]

It's interesting to hear that commercial nicd ebike packs are available.

I suppose they are fairly heavy, but miles better all round compared to SLA

 

[John in CR]

My 120 4.5ah nicads, solar cells, and extra hubbie bearings are my $hit hits the fan stash, so I'll be ebiking long after some "event". I don't put any stock in the 2012 thing, but a big quake could change things here for quite a while. They're better than lead, but other than the cycle and shelf life they don't hold a candle to lithium.

John

 

[SamTexas]

2 things not yet mentioned:

1) No need for LVC. You can run them down to zero volt. No worries about long term storage.
2) Very high self discharge rate.

 

[Punx0r]

Interesting. I thought running them flat was bad, because the weaker cells would be reversed, and so damaged?

Regarding self-discharge, as mentioned in the OP the lighting cells I have appear to have a very low self-discharge. On the other hand, my dad has some hitachi drill packs that have good capacity, but will barely hold a charge for 24 hours. I, though, have a ~15 year old Bosch drill that still delivers near-new performance despite sitting on a shelf for up to 12 months at a time (and still having usable capacity i.e. not self-discharged).

I did buy some cheap subC nicd cells from china to replace a dead pack in a little floor sweeper. One was DOA, the "good" ones did maybe a dozen cycles powering a 20W motor before dying. So I guess there are good ones and shit ones.

Thinking about it, before I pulled the sticks apart, I think the older (~20 years) lighting cells were marked SAFT. Probably explains why they still work :lol:

 

[SamTexas]

Interesting. I thought running them flat was bad, because the weaker cells would be reversed, and so damaged?

That's a related but different issue. As far as individual cells are concerned, you can take them down to zero volt. But in series, yes they can reverse. I have not experienced the reversing myself, probably because all my cells are of the same capacity so they all go down to zero (or close to zero together) at about the same time. But the reversing is also applicable to Lithium battery, which I have deliberately made it happen.

Self discharge for Nickel battery (NiCad and NiMh) are horrible compared to Lithium battery.

... I, though, have a ~15 year old Bosch drill that still delivers near-new performance despite sitting on a shelf for up to 12 months at a time (and still having usable capacity i.e. not self-discharged).

That's hard to believe for NiCad battery.

 

[Punx0r]

It was the first power tool I ever bought Other drills have come and gone since, but I still use the little Bosch every now and again. It's small and fits in places, or as a second drill to avoid having to keep changing bits. I used it lap valves on a couple of 16V cylinder heads a few weeks ago.

I attribute its longevity to having good quality cells. It's "fast" charge capable (50 min). Cheaper tools took 5-6 hours and I'm guessing the cells were inferior, with poor C rates.

You've got me curious so I just dug out my other set of lighting cells (individuals). These haven't been charged for 18 months either. Five ranged from 1.25 to 1.22V, the sixth was at zero It's on the charger now, seeing if it'll come back.

I also pulled out a cheap 7.2V 1800mAh RC pack. I can't tell you when it was last charged, must be at least two years ago. Terminal voltage is 7.22V.

 

[SamTexas]

I also pulled out a cheap 7.2V 1800mAh RC pack. I can't tell you when it was last charged, must be at least two years ago. Terminal voltage is 7.22V.

I have thrown away all my NiCad cells and it's been at least a year since I last played with them. So this is from memory: Your 7.2V pack should have 6 cells in series. At 1.20V average per cell, there isn't much energy left in it. Best way for you to verify is to use that pack now (before recharging) and note how long it last. Then recharge the pack fully and repeat the test. That will tell you how much self discharge has happened since you last charged it.

 

[999zip999]

Makita blue 9.2v forever.

 

[dogman dan]

I put a lot of miles on makita 9v drills. They seemed to have very good cells in the packs.

The 8 ah nicad ebike packs aren't really avaliable anymore. Grin has no stock left of them I think.

With drill packs, I've learned the hard way to not run them down too deep, which helps them stay balanced. Edit.. Balanced as in, you don't create one wrecked cell that has no capacity.

But you can let em self discharge to nothing with little harm. Edit,,, It's the high discharge rate deep discharge that seems to wreck a drill pack.

 

[SamTexas]

With drill packs, I've learned the hard way to not run them down too deep, which helps them stay balanced.

The only risk involved in running the pack down too deep is the remote chance of reversing one or more cells. Remote because you would most likely give up way before it could happen because the pack is already too weak to provide any useful output. Why do you need to keep them in balanced? Every time you charge a NiCad (or NiMh) pack, the pack is balanced once the charge is complete (just like lead-acid battery).

 

[Punx0r]

Ok, so the RC pack, whilst showing 7.22V terminal only put 35mAh into the discharger :lol: Recharging it took 300mAh. I think it's toast...

Regarding the 15 y/o Bosch drill pack I've just tested it: 1.4Ah rated capacity, it put 1.33Ah into the discharger (to 0.85V/cell). I'm impressed. It's done hundreds of cycles, been abused, shorted, neglected etc in it's life.

 

[SamTexas]

Ok, so the RC pack, whilst showing 7.22V terminal only put 35mAh into the discharger :lol:

Good! So there is no need to revisit/modify the Nickel based battery's high self discharge rate.

Regarding the 15 y/o Bosch drill pack I've just tested it: 1.4Ah rated capacity, it put 1.33Ah into the discharger (to 0.85V/cell). I'm impressed. It's done hundreds of cycles, been abused, shorted, neglected etc in it's life.

Just like what people have been saying earlier in this thread. NiCad is tough and long lasting.

 

[dogman dan]

Perhaps balanced was the wrong techincal term for it. I edited the comment to clarify my meaning.

 

[Punx0r]

Ok, so the RC pack, whilst showing 7.22V terminal only put 35mAh into the discharger :lol:

Good! So there is no need to revisit/modify the Nickel based battery's high self discharge rate.

I make that a 12% SOC, not great, but it is knackered

As I mentioned though, the lighting cells and the drill pack hold usable charge for 12-18months (not tested longer).

Just like what people have been saying earlier in this thread. NiCad is tough and long lasting.

Yes, I believe I said it in the OP


Ant

 

[SamTexas]

As I mentioned though, the lighting cells and the drill pack hold usable charge for 12-18months (not tested longer).

My last comment on this subject because I'm starting to sound like a broken record: What's usable? Less than 20% energy left? Possible. 40% or more, hard to believe. Signing off.

 

[Punx0r]

Dunno TBH. I take these things from storage and illuminate something, or drill a few holes or drive some screws. Then think "that's overdue a charge".

To me, if a battery (of any chemistry) has been sat and drops near to, or below 0% SOC then I'd say it had self-discharged. Perhaps I'm easily pleased to find any battery left sat for a year has any usable capacity remaining.

Really, I was just countering the claims I've heard that nicd typically goes from 100% SOC to O% in a month. I didn't mean to hammer the point, or to give the impression that I thought nicd was particularly good when it came to self-discharge rates.

I'll be sure to bump this thread if I get my hands on a crate of used lighting packs

 

[SamTexas]

Really, I was just countering the claims I've heard that nicd typically goes from 100% SOC to O% in a month.

Jeez, I'm back. Whoever said the above is totally clueless. NiCad self discharge rate is around 20% per month. And I bet the variation from that 20% is large. I don't think there's an absolutely correct rate. Really signing off this time.

 

[Ypedal]

nicad cells in a pack, can be drained to 0v and recover, but only at a very slow rate ( like forgetting your controller connected ) .. if you bonehead an over-discharge with 20 amps... say bye bye to the weakest cell !!! :wink:

so does lithium to an extent.