Review - GMC Capacitor Battery Cordless Screwdrivers - www.onlinetoolreviews.com

[xcz]

[Limp Arbor]

so I can buy a GMC screwdriver for $100 (roughly 3.5 times the cost of a B&D VersaPak) and trust that the capacitor will never go bad?

$29 B&D 'll skip both and stick with a screwdriver that has a 'real' lifetime guarantee (including the battery) ?itemType=3DPRODUCT&RS=3D1&itemID=3D11255=3&keyword=3D08C03.01

[J. Clarke]

> vs $29 B&D

> I'll skip both and stick with a screwdriver that has a 'real'

or

your "lifetime guarantee" tools charge in less than a minute?

[Curran Copeland]

> or

> Do your "lifetime guarantee" tools charge in less than a minute? Mine take at least 8 hours and sometimes a cold beer to recharge

[Artemus]

I'm unimpressed.

I went to the GMC website and found their so called specifications to be nothing more than an advertisement for the product. Example: "High Shelf Life - Fully charged on it's own, the Flashcell will remain charged almost indefinitely". The phrase "almost indefinitely" is pure marketing speak. In your review you mentioned the relative self discharge rates for L-ion and NiCd but not a word about the GMC.

Fast charging is great but how long does a charge last? How many screws will it drive?

Chemical batteries have a shallow voltage discharge curve until the charge is almost depleted then it falls rapidly. A capacitors voltage immediately, and linearly, falls as charge is pulled out of it. At half charge there is half the initial voltage which will have a devastating effect on the torque produced by the driver. There is not a word about this on the GMC website. If the user has to recharge after only using 10% of the charge this would be a big negative.

Art

[Leon]

IIRC he mentioned that the battery probably has 60-70 of the capacity of a modern style rechargeable tool battery. It could be 25% and with a 90 second recharge that would be OK with me.

[J. Clarke]

Uh, what do you expect? The specifications for any product are an advertisement for the product.

What matters is how many fasteners it can drive on a charge, not what percentage of discharge is achieved before it can no longer drive a fastener with acceptable performance.

It's sold in the US under the "Coleman" brand and you can find another review at

According to them it can screw in 22 fasteners under the same conditions that a Skil IXO can screw in 37.

The thing that fascinates me about this particular tool is that capacitor technology has developed to the point that such a tool _can_ be made.

[Lee Michaels]

"J. Clarke" wrote

Same here.

I remember from electronics school, way back when the big cathode ray tube (TV's) was a field of study. And how we had to isolate them with special transformers and ground it before working. Otherwise, it would kill you. Because it was a massive capaciter that stored enough charge to zap your heart into the great beyond. And there were folks who killed themselves this way on a regular basis.

I think this technology is great though. I am just wondering when the charge gets big enough to become dangerous. And if it is enough power to do many of the jobs now done by portable tools using current battery technology. The nearly instant charge thing is really interesting. That feature is definitely different. It could easily change some work habits if it proves to work well.

I have this image in my mind of a capaciter driven car. Can you imagine the charge that thing would take? And how many people would be electrocuted if the thing got into a wreck? One bright thought on that idea is that you could easily incorporate a deadly thief deterrent into its design.

[Leon]

The instant charge thing is really not too new. Older cars with mechanical distributors had a capacitor that signaled the coil to discharge and would charge and discharge 8 times per revolution of the distributor rotor on a V8. At an idle, 600 RPM, that capcitor would charge and discharge 2400 times per minute or 40 times per second. That sorta backs up the theory that the battery in the GMC driver can go through 500,000 cycles.

That may be a feasible thought, I was thinking about that last night. The electric cars use a Lithium style battery that came on strong about the same time the Lith ion batteries became widely available for tools. Voltage should not be any more of a problem with the capacitor type battery, the current battery driven car batteries deliver in excess of 400 volts and they like tool batteries are being recharged in as little as 15 minutes. I would think that the capacitor type battery would charge even faster.

[patrick]

google eestor Pat

[Limp Arbor]

No, takes about 8 hours but can go all day and then some.

[Roger Haar]

Hi,

I suspect that these super capacitors at least in tools are low voltage, High current ( charge = number of extra electrons on one side of the capacitor). Other than arcing they should not be dangerous. Think of them like a car battery.

The capacitors in TV s are high voltage.

Thanks Roger

[J. Clarke]

Your 5.7v screwdriver goes "all day and then some"?

[krw]

The stored energy in a capacitor is 1/2C*V^2, so the higher the voltage the more the charge stored. As has been pointed out here before, the voltage will go down linearly as the capacitor discharges. The power into a load (resistor) will go down by the square of the charge pulled out. It *might* be able to be charged faster, but all that energy still has to make into the "cell". High currents aren't friendly either. Whatever you do, you're storing significant energy and it will turn to fire if let loose.

In short, ;-) count me skeptical.

[Jack Stein]

That impresses me as well. If this is like most new things, it starts off slow and progresses into a battery killer. The sooner the better I say.

My favorite drill is "almost" a B&D versa drill. It fits my hand perfectly, and is perfectly balanced and super light weight. It seems B&D quit making them. The problem is the two versa batteries suck and they don't seem to last worth diddly. I've gone through about 4 sets and have about given up on it, but still, the drill is the nicest battery powered drill I have, except for the battery problem. If they made lithium-ion replacement batteries for it I would by them. Better would be the same drill with capacitor technology, but it would have to be a little more powerful than the GM thing. Hopefully thats in our future.

I have a couple of capacitor flashlights you shake to charge up and I love them. They always work unlike the damed battery lights that never work when you need them...

[Larry W]

"And there were folks who killed themselves this way on a regular basis."

I just LOVE that line!

[Lee Michaels]

"Larry W" wrote

Well........, when you are working with high voltage and/or current, you have to be careful. And the message was pounded home by instructors, many of them ex-military, who had some gory stories to tell.

We had an expression in that school. If somebody got a shock, we said they got "bit". And often when this "biting" took place, there was some yelling and screaming. At that point all classes came to a stop for a moment. The instructor would point in the general direction of the scream and say something to the effect that another person just got bit.

I made it all the way through a year of that school without getting bit. But two days before I graduated, while working on a peice of test equipment I picked up at a garage sale, I got bit. I got bit big time. I still have a dead spot on my right index finger from that. Rumors were that that scream was heard down the block.

[Larry W]

Uhh, What I found humorous was that while it is conceivable that someone would get "bit" on a regular basis, "killed" is generally a one-time kind of experience.

[Lee Michaels]

OK, gotcha. I was making a general, big picture kinda statement. You read it as a personal, singular kinda thing. As in killing themselves over and over again.