Cord for Cordless DeWalt tools

[Leon]

I don't believe it either. They would get pretty hot. The drills get their power from gear reduction.

[B A R R Y]

[LQQK]

I don't know why you say its *understandable*.

Its damn sleazy. They should make the batteries available for a reasonable price.

[CW]

That's why he said it's understandable. "Damn sleazy" is a common business model. Free greed, it's the American way.

[N Hurst]

I have no clue, honestly! When I need to get a new battery for my drill I'll be sure and research that. :-)

-Nathan

[Oughtsix]

I think the trick setup would be to build a battery belt. This way you could put all the weight of the tool around your waist and still have the convienence and portability of battery power but use higher capicity D sized cells instead of the usual "sub C" cells. I have taken apart my dead Dewalt battery and it has thin bus bars welded between the batteries and a wire no more than 16 gauge from the last cell back to the power connector. A coiled telephone cord would be to light but if you could find a coiled 16 gauge cord this would be perfect.

I have known a couple of professional photographers that have worn battery belts or battery vests to power their cameras and get decent recycle time on their high power flashes.

[Guy Berthiaume]

I actually didn't expect this conversation to go into the design issues I might face. But, if you guys are willing to discuss this, then I am more than happy to get your help.

Part of this project will be to determine the battery specs. DeWalt has chosen not to publish specs on the batteries or the tools that use them (at least any that I can find). I can find neither current ratings nor horsepower ratings.

From my experimentation so far I have found the Equivalent Series Resistance (ESR) of my remaining battery is about 0.2 ohms. This puts the short-circuit current at about 90 Amps. Assuming a stalled motor has an impedance of 1 ohm (a big assumption right now), then the peak current under worst-case conditions is around 15 Amps.

Under normal load conditions, I would expect half that value. A switching power supply with a peak output of 15 Amps and continuous output of 8 Amps should suffice. That translates into a supply that can handle 144 W continuous, and 270 W peak. That will be a hefty supply. 270W is equal to about 1/3 HP.

The other issue is that most switching supplies have over-current protection which could cause the tool to stop/start in rapid succession if the supply can't handle the peak current demand. I would expect that to have an adverse effect on the item being worked.

I actually have several small 18 V supplies that I can parallel for combined output of 225 W max. This doesn't fit the exact requirements, but it will be good enough for an experiment.

Guy

[Guy Berthiaume]

Just so you understand, I mean that I understand their profit motive.

Myself, I wouldn't go so far as to call it sleazy because I have no way to know what issues they face in manufacturing these batteries, but I wouldn't be surprised if they have an "embarassing" profit margin.

Guy

[WoodButcher]

If used continuously under heavy load, yes, the drill would get quite hot. However under the intermittant loads usually applied this is not an issue.

Torque and power are not the same thing.

Art

[Leon]

IIRC Hitachi or Makita offered the remote battery belt 2 or 3 years ago, they may still offer it.

[WoodButcher]

I think the motor specs would be more relevant than the battery specs. Like you stated, the battery is capable of far more amps than the motor would ever draw. Your plan of testing with your existing supplies is a sound one.

A switching supply is definitely the way to go. An off line switcher running at several hundred KHz will have magnetics which are much smaller and lighter than the cells of your current battery pack. Your over-current concerns can be addressed by simply designing it to go into a constant current mode instead of shutting down and restarting. I also wouldn't bother with PFC. A non-isolated design will be more compact and less costly than an isolated one and the drill/saw/whatnots are usually insulated sufficiently to avoid shock, but this is a safety issue and is your call. And finally, given the application, the ripple spec can be relaxed or even eliminated as the motor(s) receive PWM current supplied by the VSR electronics anyway. If your design for the converter allows the voltage to fall to zero 120 times per second this would be probably be unnoticeable to the user.

Art

[Nova]

It looks like the DeWalt 18V drill currently shown on their web site is listed at "510 Unit Watts Out"??? 510W / 18V = 28.333 Amp.

[Gordon Airporte]

Guy Berthiaume wrote: > It sounds like I am going to have to design my own converter. I can

I just came across an article on the web about battery to corded conversion and immediately thought of this post. Here's the link:

heard about it through

[Guy Berthiaume]

This is not good news. If the input power to the drill is 500 W, then it will probably not be practical to do what I am planning.

DeWalt's web site is very hit/miss with the power ratings of the devices. It looks like most of the corded devices have power ratings and most of the cordless devices do not, which is why I didn't see them before. I was checking the ratings for my particular tools.

So, if I use the corded tools as a guide, and assume that the cordless versions produce at least half the output of the corded devices, then the power requirement goes way up... The corded circular saws are rated above 2 KW.

I will continue with my experiment, but I'm not encouraged at this point...

Guy

[CW]

[John]

My younger received a similar Ryobi drill/driver as a wedding gift (from someone who knew she has a "fix-it" personality).

It serves well for basic home handy-person use. I wouldn't recommend it for installing a deck or a room of drywall, but it works OK for hanging curtain hardware and the like.

John