C12 battery question---

[PeterK]

My understanding and experience was that NiCads would discharge fairly fast just sitting there and I have definitely experienced that with some brand tools. But - the C12 doesn't do it. Don't know what Festool did to fix this - higher quality batteries built to their spec maybe? I have 2 of the C12s and have purchased 4 others for my electricians at work and they all hold charge extremely well and keep their power up to very near the end. I know many people look at the C12 and TDK and see the NiCads and won't consider them thinking that Festool is using very old technology. I actually would be hesitant to use a different battery technology with the Festools unless there is a significant weight savings with no power and function loss. My experience is that the C12 NiCads are every bit as good as my other tools utilizing NiMH and LiIon and in many ways better. Amazing power out of the 12 volt NiCads. You can get the NiMH in the 3.0Ah battery option for the C12 but it is quite a bit heavier - I have one. Bought it for outdoor jobs needing more run-time but have not found it needed so far.

So - what exactly did Festool do different than other companies with the NiCads? They need to explain this in the literature unless it is some secret.
Pete

 

[ireland]

Hi Peter

Its actually quite simple Festool have embraced a manufacturing technique known as

WITCHCRAFT

 

[PeterK]

;D

I'm one of those who like to know how things work. Was thinking they have found a high-end manufacturer using better tolerances in manufacturing. If so, no one else seems to use them though. Guess it was a stupid question but I am gonna die from my curiousity.
Pete

 

[DaveM]

I think it's probably a combination of factors.  I recall someone stating in a previous thread on FOG that the NiCd batteries used by Festool are manufactured by Panasonic, so they're probably about the best you can get.  Also, the brushless motor in the C12 is a much more efficient design, so the batteries will last longer.  Finally, the smart charger provides optimal charging conditions to maximize the battery life.

DaveM

 

[JayStPeter]

I've taken apart a number of different battery packs and rebuilt a few myself.  I haven't had the same experience with my TDK (same battery pack as C12) as the OP.  On my refurb TDK, my batteries have always died when sitting and have gotten worse over the few years I've owned it.  They won't hold a charge overnight anymore and even the full charge is pretty wimpy anymore.  I took apart the Festool battery pack last month and was impressed with how it's built.  I don't quite know how to rebuild this one.  There are no metal tabs or wires connecting the batteries together.  There is some sort of composite board attached to the top and bottom of each cell.  When the pack is unscrewed, the whole mass of cells comes out as one solid piece.  In PC drills, they are connected by strips of metal that are tacked to the battery and the mass of cells is taped together.  Once in the plastic case, they are held tight but outside they would fall apart without the tape.  My guess is there's some sort of adhesive that holds the batteries to the composite boards of the Festool.  They aren't going anywhere even if you use the cell mass outside the plastic case.  All the other brands I've taken apart/rebuilt would fall apart outside the plastic case if you don't handle them gently.
I'm not sure how to rebuild the festool as the plastic recharge capsule/tabs are connected to the composite boards.  I'll probably send one of them off to a rebuilder and see what I get back.
There are a variety of different quality cells that the mfr's use and the PC ones are pretty good (can't remember for sure, but IIRC they are Gates).  Festool didn't leave much visible for me to identify the mfr of their cells.  I would guess panasonic just based on the amp-hr rating numbers, but there was one other mfr that sells the same amp-hr rating in the same cell size.  Most of the other mfrs had slightly different ratings when they got close to the max available for that cell size.  I'm sure I'll be able to tell what they were replaced with when I get them back though. :

 

[markcoutinho]

Can anyone tell me the advantage of the NiMh over the NiCd? Or of the other way around? Which one should I choose?

 

[Jerry Work]

Hi Mark,

The issue with all battery operated tools is the whole system, not just the battery technology.  The efficiency of the motor and drive train, the sophistication of the electronics governing soft start, constant speed and overload protection, the quality of the cells and their interconnections, and the charging system all have a great deal to do with how the tool will perform in a variety of load and recharge profiles.  Depending on all these things a case can be made for each of the common battery technologies.  Unless you are buying some unknown brand blue light special, my suggestion is to buy a system and enjoy whichever battery technology those designers felt optimum for their tool. 

As a grossly oversimplified general statement, Li technology tends today to have the greatest energy density so is lighter for a given amp and voltage rating but can suffer heat issues in some load and recharge profiles.  NiCd tends to be very rugged and performs well over a wide range of load/recharge profiles but suffers performance hits when left unused for periods of time or if recharged constantly from only a partially discharged state.  NiMh is a bit lighter and denser than NiCd but not as energy dense as todays Li and it has greater tolerance for sitting unused or repeatedly recharged after light use. 

Each technology behaves differently at the end of its discharge cycle.  Li simply goes to a certain point and rapidly dies.  For example, don't get into a dark or dangerous space with a flash light with Li batteries or you could find yourself unexpectedly "in the dark".  NiMh and NiCd tend to taper off a bit more so the bulb will go dimmer for a period of time where the Li can simply go from on to off.

Bottom line from my POV ..... there is way too much talk about battery technology and way too little talk about all the important things that go into designing battery operated tools.  Hope this helps.

Jerry

Can anyone tell me the advantage of the NiMh over the NiCd? Or of the other way around? Which one should I choose?

 

[markcoutinho]

Phew... Got it, Jerry. Thanks for your very extensive and clear explanation!