$0.32/Wh NiMh. Too good to be true?

http://www.onlybatteries.com/showitem.asp?itemid=17177

Anyone has experience with this sub-C battery? Is the 2600mAh rating believable, verifiable?

Stubbornly determined to use a crappy battery eh?

dogman said:

Stubbornly determined to use a crappy battery eh?

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+1 !

Don't even bother to waste your time with those..

- nimh is too fragile, considering available options in lithium
- canot parallel nimh/nicad, you need to charge individual strings..
- C rate too low.. will not cope with ebike power levels
- Assembly nightmare..

Ypedal said:

dogman said:

Stubbornly determined to use a crappy battery eh?

Click to expand...

+1 !

Don't even bother to waste your time with those..

- nimh is too fragile, considering available options in lithium
- canot parallel nimh/nicad, you need to charge individual strings..
- C rate too low.. will not cope with ebike power levels
- Assembly nightmare..

Click to expand...

In the end I might give in and use Lithium. Lithium is superior in terms of energy density and higher discharge rate, but its weaknesses are too great to ignore:
- disastrous consequence when overcharged
- total loss when overdischarged
Nickel based batteries don't share those characteristics.

SamTexas said:

Nickel based batteries don't share those characteristics.

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How sure of that are you ? :wink:

Ypedal said:

SamTexas said:

Nickel based batteries don't share those characteristics.

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How sure of that are you ? :wink:

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What do you mean? Are you saying that Nickel batteries would explode when overcharged? I haven't tried that so I can't be 100% sure. But I have discharged them to ZERO and was able to recharge them. So 100% sure on the discharge side.

I ran big F cell 13AH NiMh packs for several years and it ain't no picnic. Sure, they can be useful for a low power system you may not use frequently although it takes several cycles to wake 'em up. But they don't seem to mind sitting around in discharged 0V state, in my experience.

But suck with low C rate and less than advertised capacity at high discharge rates - and they do get HOT while charging. Almost all nickel charging schemes employ temp cutoff. Sure, they can vent. Maybe not as flammable as Lipo but they can pop.

Also much less individual cell monitoring (high number of cells makes impractical) so in some ways they could be more dangerous than Lipo. At least with Lipo you don't go in with any false sense of security relying on "notions" about what's safe...

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=23105

SamTexas said:

- disastrous consequence when overcharged
- total loss when overdischarged

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depends on chemistry.. i've overcharged LiMn konions to around 4.5v before by accident and there were no disastrous consequences at all.

i've also revived many 0v resting LiMn to a useable state again.

[youtube]QuYYhXizTOg[/youtube]

Why bother when you can get lipo for $0.40/Wh?

SamTexas said:

Ypedal said:

dogman said:

Stubbornly determined to use a crappy battery eh?

Click to expand...

+1 !

Don't even bother to waste your time with those..

- nimh is too fragile, considering available options in lithium
- canot parallel nimh/nicad, you need to charge individual strings..
- C rate too low.. will not cope with ebike power levels
- Assembly nightmare..

Click to expand...

In the end I might give in and use Lithium. Lithium is superior in terms of energy density and higher discharge rate, but its weaknesses are too great to ignore:
- disastrous consequence when overcharged
- total loss when overdischarged
Nickel based batteries don't share those characteristics.

Click to expand...

The order of powerful battery explosions in my experience has been as follows:

#1. Lead Acid. By a huge margin. Datacenter battery rooms have exploded entire facilities to rubble just from a ventilation fan control error. The best couple battery explosions on this board have also been lead-acid batts.

#2. NiMH. The cans dont normally have vents (and often it seems the types with vents (which by design have to be VERY high pressure) don't function anyways). Anytime something causes them to off-gas (over-charge etc), they explode like mini-gernades. Shrapnel, cans shot like shotgun slugs into walls and things, total mechanical destruction of things around them.

#3. Lithium round cells. Lithium cans must have vents by design, but like NiMH, vents in cans are a sketchy thing as best. Overcharge causes electrolysis in the electrolyte, it off-gasses, builds pressure, and vents with a BANG that can rival NiMH.

#4. Lithium Polymer. Virtually impossible to explode, however, it can vent a gnarly fireball out of the pouch that can encompass and burn objects near it. The fire only lasts for about 5 seconds, but it's powerful enough to melt, burn, damage, or catch on fire flammable objects near them. It would be tough to be life threatening (because it happens rather slowly and you get a big hiss of white smoke as warning to get away), but if you couldn't get away from them and you had enough of them, you could burn to death (like in a car with a giant LiPo pack).

Let me make sure that I understand you correctly before I respond.

YOU ARE TELLING EVERYONE THAT LITHIUM BATTERY IS SAFER THAN NIMH AND LEAD-ACID. RIGHT OR NOT?

hands on track record trumps myths..

the accidents that did happen, were more violent SLA,

Don't think that Nickel cells are " safe " and cudly, they have the potential just like any battery.

I've overdischarged all cell types, and over charged them rarely... only sparks i've had so far were done on purpose.

Long and hideous history of lead acid explosions, often burning the face off idiots jumping cars and other equipment stupidly. Classic case, 6v tractor battery jumped from the truck 12v battery.

Mostly though, I just think that particular example was a really lame cell to try to make an ebike battery out of. We're getting meaner trying to snap you out of it.

You really want nickel? I have two E bikes CA nicad packs here at the house. 24v 8 ah, 20 cells per pack. Both have problematic cells in them and are a bitch to charge now because the problem cells get hot and stop the charge early. (everbody that's had that problem with a drill raise your hand, yup, its everbody). I haven't posted them for sale because I wouldn't want to wish them on anybody. But if you really want em, a buck a cell plus shipping and you can have em. At least they are F cells. Sort out the hot ones and you'd have enough good cells left for a 36v 8 ah pack. Lots of cycles left in the good cells, but too heavy for me to bother with. You'd get a 24v charger if you wan to make one good 24v pack.

It'll be safe all right, if you use a temp sensor charging em. It's just a pita now to deal with trickling in power slow enough to charge the bad cells in there. the good cells just end up undercharged over and over.

dogman said:

Stubbornly determined to use a crappy battery eh?

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No kidding.. i can't believe this guy. I don't know why he asks things as he won't listen to good recommendations on chargers, batteries, motors, or anything else by me + multiple other people even when clearly shown graphs, data, and links to good and easily understandable info.

SamTexas said:

Let me make sure that I understand you correctly before I respond.

YOU ARE TELLING EVERYONE THAT LITHIUM BATTERY IS SAFER THAN NIMH AND LEAD-ACID. RIGHT OR NOT?

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In my experience (both personal and on this forum), yes. The biggest most dangerous blasts have been lead. Second biggest NiMH, third biggest round lithium cells, forth biggest lithium polymer fireballs.

There is a very dangerous type of lithium battery, which is the non-rechargeable little 123 size flashlight cells. Unlike any ebike cells, they use metallic lithium, and are just a really bad idea for both safety and use of resources.

FWIW we are talking about currently sold lipo. Some laptops did come with some lipo that was causing fires. It's gone now.

What's really dangerous on ebikes and other EV's is simple short circuits. Those can burn the house down just fine, or burn the vehicle while you ride. It doesn't matter what chemistry in that case. It's far more common than lipo explosion.

I will grant this though, you do have to watch overdischarging lipo and lifepo4. One screwup and you lose the cells. However, my 30 years of experience with nicad and nimh in drills says you screw up with those and you get to buy new batteries too. Just different ways to screw up, like charging too hot. Or leaving lead acid uncharged very long. Either way, you can't completely ignore your battery and get away with it much, with any chemistry.

neptronix said:

dogman said:

Stubbornly determined to use a crappy battery eh?

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No kidding.. i can't believe this guy. I don't know why he asks things as he won't listen to good recommendations on chargers, batteries, motors, or anything else by me + multiple other people even when clearly shown graphs, data, and links to good and easily understandable info.

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You mean I need to listen to dumb reasoning, logic just because it was answered?

SamTexas said:

neptronix said:

dogman said:

Stubbornly determined to use a crappy battery eh?

Click to expand...

No kidding.. i can't believe this guy. I don't know why he asks things as he won't listen to good recommendations on chargers, batteries, motors, or anything else by me + multiple other people even when clearly shown graphs, data, and links to good and easily understandable info.

Click to expand...

You mean I need to listen to dumb reasoning, logic just because it was answered?

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Lol, ok. I see how this is going to go down. I'll stop giving you feedback then.

SamTexas said:

What do you mean? Are you saying that Nickel batteries would explode when overcharged?

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Abso-freakin'-lutely they will. I had a 6 cell 3300 mAh RC pack blow in my workshop. Spewed carbon dust all over $50,000 worth of HP logic analyzer.

liveforphysics said:

There is a very dangerous type of lithium battery, which is the non-rechargeable little 123 size flashlight cells.

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You mean like the little 4Sevens Quark Mini 123 S2 flashlight that hangs out about 2 inches to the right o' me ghoolies?

texaspyro said:

liveforphysics said:

There is a very dangerous type of lithium battery, which is the non-rechargeable little 123 size flashlight cells.

Click to expand...

You mean like the little 4Sevens Quark Mini 123 S2 flashlight that hangs out about 2 inches to the right o' me ghoolies?

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Exactly.

For a fun trick, take a stupid flashlight design, like a surefire product, something with pointlessly thick aluminum walls, long deep threads on the cap and head that are able to handle thousands of pounds, and a nice thick quartz glass lens in the front, and good fitting viton-o-rings sealing each section together.

Take one half-empty 123 cell, and one full 123 cell, load them up, screw it together nice and tight, turn it on and walk away. The empty cell drains first, then starts getting reverse charged by the good cell... off gassing happens, the metalic lithium is no longer stable in the solvent, it goes into a rapid exothermic event that can easily build thousands of PSI in a few seconds. Then BAM!!! You have a little grenade of quartz glass and fire blast forward if you're lucky, and if you're unlucky, the whole thing explodes.

Flashlights with thin cases and thin lenses are of course much less dangerous, as they tend to deform in a manor that causes them to safely leak down the pressure inside.

If you use a single-cell 123 flashlight, you're also perfectly safe, as it can't be reverse charged by another cell in the string.

Ypedal said:

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=23105

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Yes, that was truly informative and entertaining!

The only reason I'm messing with NiMH at all is because I had high quality high rate Japanese cells for $0.08/Wh from a different project lying around. And even then, it is with trepidation and numerous precautions. Plus, the low cell voltage means *lots* of cells to keep track of.

My calculations come out more like $1.21/wh. I bought a bunch of surplus 4/3 AA 3800 mah 7s packs, and assembled them into 21s bricks, with the idea of using 42s x 4p to replace the 36v SLA's I had been using. I tried a trial run with 2p, and couldn't even get the bike to speed before the voltage dropped. Unfortunately many cells were bad. As I was trying to identify good/bad packs by cycling them, then reconfiguring them and cycling/testing again, it became obvious that even if i got enough packs built and tested, daily charging would be a problem. I can only charge a single 21s brick at a time with my charger, an Electrifly Triton2EQ (Ditto for my 2 Hewlitt Packard bench supplies in series). So charging 8 bricks at, say a C/4 charge rate means that I could ride only every 2 or 3 days.
So these batteries are now collecting dust on my bench, as I ride with my new Lipo! Save your money for something that's decent

I just for back from the post office 5 minutes ago... got 30 cells on hand for testing/abusing !!.. 8)