Why did power tools skip over NiMh batteries?

[BatteryCharger]

I have quite a few older power tools with aging NiCd batteries - batteries that were crap even when they were new. I know that many tool manufacturers are now using lithium instead....but how come they never started using NiMh when it was the king?

Or to put the question a different way - I bought an 18v drill about 2 years ago that came with a 1300mah NiCd pack. Way, way outdated before I even bought it. At this time lithium tools were just coming out and really expensive, but still, I have never noticed any that used NiMh batteries before that. The tool uses standard sub C cells...why didn't they use a more modern ~3ah NiMh battery? Is it just economics...or is there a reason? Or rather, is there a reason I shouldn't trash the NiCds and replace them with these? http://www.batteryjunction.com/tenergy-propel-4200-sc.html for ~4x the run time?!oo:

How would the self discharge for a 4.2ah NiMh sub C compare to a 1.3ah NiCd sub C? I know the NiCds are dead after about a month or two.

I use a multi voltage NiCd/NiMh "hobby" charger to charge up all my cordless tools.

 

[Beamhead]

I bought a makita drill when they first introduced NiMh packs, I even bought 4 extra packs. They are garbage, I use the old Ni Cad pack if /when I use that drill. I recently picked up 2 hitachi 18v LiIon and they kick butt.

 

[bulbman]

Nimh cells are more expensive and don't take as many charge/discharge cycles

 

[Light Sabre]

The answer is plain and simple: NiCads and Li-Ion batteries can deliver more current than NMH's can which means more powerful cordless tools.

 

[BatteryCharger]

The answer is plain and simple: NiCads and Li-Ion batteries can deliver more current than NMH's can which means more powerful cordless tools.

Forget about lithiums. I'm talking about before they started using them in tools. How can a 1.3ah (nominal, more like .9ah real life) NiCd deliver more current than a 3-4ah NiMh?

 

[Light Sabre]

More current as in for example: NiCad 3 amps versus NMH 1.5 amp. (I have no idea what the real numbers are.) Has nothing to do with amp hours. It's about battery chemistry and how much instanteous current it can deliver. NiCads and Lithiums can deliver more instanteous current than NMH's can. I think it is explained at Battery University if I remember correctly.

 

[Ray_of_Light]

Until the introduction of Ni-MH LSD batteries, traditional Ni-MH were known to develop an increasing internal resistance over time, starting from a resistance already higher then Ni-CD battery.
For this reason, Ni-MH wasn't initially deemed appropriate for power tools.
Nowadays high current lithium battery have all the necessary requisite to replace old Ni-CD.
This notwithstanding, I have installed LSD Ni-MH in my two drills. With some simple precautions, I believe them to be more appropriate and long lasting than lithium-ion in power tools. As longs as they are not overcharged, LSD Ni-MH have the innate tendency to keep their capacity balance - and therefore packs made of them, don't self-destroy under heavy load.

Anthony

 

[Bullzeyebill]

Ray_of_Light, what amp draw are your power tools pulling using your LSD's?

Bill

 

[Ray_of_Light]

I have a 4.8 V power drill, using four sub-C 1,2 Ah nicads. Average current draw was 5 Amps under load, and about 15 A when the chuck was stalled.

The other drill is a 7.2 V with electronic speed control. It used six sub-C Ni-Cd of better quality, around 2 Ah capacity. I measured 7 A under load, and the electronic circuit limits the current draw when the drill is stalled.

I used Duraloops in both drills, with excellent results. I don't use anymore the original charger for the 4.8 V drill (a wall wart with transformer and full bridge rectifier, no smoothing cap) but a dedicated multicell NimH charger.

For the 7.2 Volt drill, the table charger with the charge controller is still effective.

Both drills have a much better torque now, and are available for use anytime.

Regards

Anthony

 

[Ragiska]

charging nimh packs in power tools leads to dead packs in a hurry. they cannot be trickle charged like nicads, or terminated off voltage as easily as li-ion.

 

[n3eg]

What size Li-ion batteries are they using in power tool batteries? Are they all 18650?

 

[BatteryCharger]

charging nimh packs in power tools leads to dead packs in a hurry. they cannot be trickle charged like nicads, or terminated off voltage as easily as li-ion.

Well, the tool MFG could provide a proper NiMh charger. Power tool chargers are notoriously horrible, and people always complain about how much replacement batteries cost....coincidence? Everybody with a few power tools should get themselves a nice universal smart charger....

I guess it's kind of like the $40 printer that comes with a $30 ink cartridge - it's not the printer they're trying to sell you...

 

[ampdude]

NiCads have low self discharge and can take a whole lot of abuse. I have some NiCad devices dating back to the 90's that still work fine, noteably a flashlight and an electric shaver. They have both been run dead and left that way countless times, but they always come back for more.

 

[45/70]

....but how come they never started using NiMh when it was the king?

I think there are two primary reasons. First, NiCd cells have a sturdier construction than NiMH cells. NiMH cells are fragile. In power tools that are used every day, as in the workplace, NiCd's hold up better to being dropped, the tool receiving impacts, and so on.

Secondly NiCd cells hold up much better to being run down and cells within packs being subjected to reverse charging. While this is not really good for NiCd cells, it pretty much kills NiMH cells in short order.

A third reason to consider, is the fact that NiCd cells generally last between 1000 and 2000 charges, as opposed to NiMH cell's 300-500. This is offset to a large degree though by the need to recharge NiCd's more often, having to more or less completely run them down each time before recharging, as opposed to being able to "top off" NiMH's, and the NiMH cell's superior capacity. Still, in the end NiCd cells will generally achieve about twice as many Watt Hours, or more, than NiMH cells, during their lifetime.

Dave

 

[Battery Guy]

This journal article has a good summary of the issues with Ni-MH cells:

Journal of Power Sources
Volume 176, Issue 2, 1 February 2008, Pages 547-554

Progress in high-power nickel–metal hydride batteries
Peter Bäuerlein, a, , Christina Antoniusa, Jens Löfflera and Jörg Kümpersa

aVARTA Automotive Systems GmbH, Am Leineufer 51, D-30419 Hannover, Germany

Abstract
High demands to power performance, high cycle and calendar life as well can be met by NiMH batteries, making this battery system very suitable for HEV applications. The hydrogen storage alloy plays an important role with respect to power performance and life duration. Power performance and cycle life behaviour are related to each other by the electrochemical and mechanical properties of the alloy, via a more or less reciprocal relationship. In terms of power performance at medium-discharge rates, the charge transfer reaction at the hydrogen storage alloy interface was found to be crucial for the temperature-dependent behaviour of the cell, whereas at discharge rates above about 15C diffusion limitation was found especially at the negative electrode. The alloy corrosion is taking place in alkaline media, leading to the formation of surface films and a change of the chemical composition, especially in near surface regions of the alloy particles. Consecutive electrochemical cycles lead to mechanical stress and finally cracking of the alloy particles. Stability against corrosion and pulverisation on one hand and good electrochemical performance on the other hand both depend on the chemical composition of the alloy, its morphological properties and the cycling regime used.

Unfortunately, I can't attach the full article for copy write reasons.

Bottom line is that both NiCd and NiMH use essentially the exact same cathode: NiOOH. The big difference is the anode. NiCd uses cadmium (metallic cadmium in the charged state and cadmium hydroxide in the discharged state). NiMH uses an alloy that is capable of absorbing large amounts of atomic hydrogen into its crystal lattice.

The cadmium anode is extremely stable, and can be charged and discharged thousands of times with little or no degradation. Even driving the cell into reversal does little to hurt the cadmium anode (although you lose electrolyte via electrolysis when you do this, so it is not good for the cell). So for NiCd batteries, the cycle life is typically limited by the NiOOH cathode and/or loss of electrolyte over time due to electrolysis.

Metal hydride anodes are another story. The alloy slowly corrode in alkaline electrolytes, and layer of corrosion product forms on the surface, reducing the rate capability of the alloy. Also, as the alloy is cycled and hydrogen diffuses into and out off the crystal lattice, the brittle alloy is strained and eventually begins to crack. This process is commonly referred to as "pulverization". The freshly exposed surfaces of the pulverized particles begin corroding, further reducing the amount active material and the drain rate capability.

When a NiMH cell is driven into full reversal (sometimes called Stage 3 discharge), oxygen is evolved at the metal hydride electrode, and the alloy rapidly corrodes.

Corrosion of the metal hydride alloy also releases metal ions into the electrolyte. One of these metal ions, manganese, will diffuse to the separator and form a compound with potassium. This manganese/potassium compound is conductive enough to cause short circuits within the separator. This is why older NiMH cells have terribly high self discharge rates.

So the cycle life of a NiMH cell is typically limited by the metal hydride anode, which slowly corrodes and pulverizes during use.

While a brand new NiMH cell has a high energy density and may even be able to supply more power than a comparable NiCd cell, both the power capability, energy density and self discharge characteristics of the NiMH cell degrades faster than the NiCd cell.

Cheers,
Battery Guy

 

[bob_ninja]

Even NiCd die far too quickly due to 2 major problems:

- neglect = for a commercial use this is not a problem, but most of us use drills and saws once in a while. In between projects pack may sit unused for a year or more and we all know what happens then. My 1st pack I actually left in garage during winter and it didn't survive.

- cell count = for a typical pack of around 20V you need around 15 cells. I find some packs have a very good quality cells that are well balanced. Nevertheless, such a high cell count guarantees that soon some of them will reverse. Since it is extremely difficult to replace one or two cells alone, entire pack is useless.

Therefore the new Lithium cells are now replacing NiCd as they solve both problems. Especially about 3x lower cell count means less cells to go out of balance.

I actually use one of the few NiMH packs for iRobot Roomba robots (around 24V I think). They actually perform reasonably well, but all fail around the 200-400 cycle mark (rough estimate). Robot is actually programmed to seek charging base when low power. I noticed that when robot is stuck and unable to return to the base thus taking pack down to near zero SOC, then packs starts to degrade very quickly.

So NiMH work sort of Ok, but don't provide a lot of power and don't last.

The new Lithium packs should address most problems. However for now they are expensive and sold as premium product, at 2x to 4x price of NiCds.

 

[John_Galt]

Huh, I had always thought that Ni-MH was more durable than Ni-Cd, and didn't suffer from the same problems.

I thought you always had to completely discharge a Ni-Cd battery pack, or it would develop a "memory" and only retain that capacity from then on.

Shows me what I know...

 

[Chauncey Gardner]

I bought a makita drill when they first introduced NiMh packs, I even bought 4 extra packs. They are garbage, I use the old Ni Cad pack if /when I use that drill. I recently picked up 2 hitachi 18v LiIon and they kick butt.

I didn't have a good experience with the Makita nimh stuff either. Combo pack, saw & drill, not cheap.

Went to nicad Ryobi & had no issues. None with the DeWalt liion combo I have either.
But yeah, the nimh stuff from Makita was a joke. Couple strips of trim & the saw was toast, the drill would require both battery packs just to mix up a pail of paint & just barely accomplish that.

Battery Guy & Bob ninja both had good posts. Appreciate the info above & have had similar experiences like Bob's.
The newest cordless combo I just picked up should last much longer & will not spend winter in the garage.

Good thread.

 

[alpg88]

Forget about lithiums. I'm talking about before they started using them in tools. How can a 1.3ah (nominal, more like .9ah real life) NiCd deliver more current than a 3-4ah NiMh?

i took apart many cordless drills batteries.
not once i,ve seen 4ah nimh, the biggest nimh i,ve seen , that was btw total garbage, was 3ah.
good tool makers, like dewalt milwaukee, makita, use sub c, sanyo nicd, rated 2 -2,4ah, other cheap knock off tools use, 4\5 sub c 1,2-1,9ah. usually no name crappy cells.

 

[Battery Guy]

Huh, I had always thought that Ni-MH was more durable than Ni-Cd, and didn't suffer from the same problems.

I thought you always had to completely discharge a Ni-Cd battery pack, or it would develop a "memory" and only retain that capacity from then on.

Shows me what I know...

The infamous "memory" or voltage depression effect is caused by the cathode (positive electrode), which is the same in both Ni-Cd and Ni-MH cells.

In general, Ni-Cd is a more robust chemistry than Ni-MH.

Cheers,
Battery Guy