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Conversion Question.

 
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Old 04-29-2011, 04:37 PM   #1
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Conversion Question.


I know enough about electricity to do minor jobs from the wall out & a little more. I know whether I'm looking for DC, AC, Continuity, Resistance, Voltage, Current...basically set & read my multimeter. I know Ohm's law & the "EIR" triangle. But for the life of me I can't figure something out that's probably right in front of me.

I want to be able to read a corded tool's amperage from the manual or description & be able to choose a cordless counterpart that will have roughly the same amount of power at nominal or even at peak voltage.

Example: Let's say I have a 7Amp 1/2" hammer drill, will an 18 volt cordless 1/2" hammer drill have the same "ba!!$" as the corded or will it take a 28 volt cordless drill ? The question applies to all tools 12 Amp Sawzall/28v Sawzall or 36?

Is there a table somewhere that outlines this?
I'll probably feel like a num-nuts for not figuring the right equatiuon but whatever... lol
Thanks...
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Old 04-29-2011, 05:24 PM   #2
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Re: Conversion Question.


That's a good question. I've thought about that one myself. I think that looking at torque, for a drill motor, for example, is the best way. The amp hour rating would be best, but I have yet to see that on a cordless tool.
I do happen to have alot of experience with the Milwaukee v28 tools, and they are THE BEST. The sawzall is much more powerful than the 6.5 amp corded, and just slightly less than the 13 amp corded. The hammer drill is hands down the best. Very powerful, but also heavy. The circ saw is handy for a quick cut or working on a ladder (cuttting out siding for replacement windows comes to mind), but it can't even come close to replacing a 15amp worm drive.
Hopefully a REAL Sparky will be along to straighten us both out.
I've terminated 15,000 volt lines in a vault and wired up three phase, high voltage industrial motors, but I can't figure this one out!!

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Old 04-29-2011, 05:36 PM   #3
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Re: Conversion Question.


Comparing RPMs, torque, stroke length, IPMs etc tells us about performance but man, there's that "umph", balls to the wall factor. I'm trying to go as cordless as possible & this is a PITA. You're right Amp/Hr on the tool would help but they just rate the batteries.
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Old 04-29-2011, 05:55 PM   #4
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Re: Conversion Question.




Yeah, I hear ya. All I can offer is my personal experience. Milwaukee is the only brand I use for cordless. I can't remember the last time I broke out the corded sawzall (I think it was a plumbing job with a cut station for galvanized pipe). I use the v28 for EVERYTHING. Ditto on the hammerdrill. It wont replace a 1 1/8" spline drive demo hammer, (obviously) but drilling/driving/ hammerdrill work it's better than my 1/2" corded.
The saw, just an accessory. Can't replace a plug-in.
Now the down side. Batteries have a finite life. They cost $125 to replace.
The hammerdrill is heavy. I have a m18 for all my light duty screwdriving.
But the v28 will drive 3" plus lag bolts, and attach holdown anchors. I was on a job with this kid, we didn't have power yet so everyone was using cordless, and he'd just got the new Makita impact driver and was bragging about it. Well I was installing holddowns and he says "hey, try this". The damn thing stalled with the bolts halfway in. I gave his Makita back and said "watch this". I had to be careful not to strip the bolts out with my v28.
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Old 04-29-2011, 06:21 PM   #5
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Re: Conversion Question.


The tool manufacturer's won't supply you with the information you need to make an apple-to-apple comparison. They want to keep you in the dark, and so far they've done one damn fine job of it. As soon as Brand A figures out a way to compare themselves to Brand B, Brand B uses another obscure Unit Of Measure to apply to their stuff.

Just the other day, I say lawn mowers measured in torque. 6.75..... 7.00..... 6.25...... No other information, just a number followed by 'torque'. "6.75 What?", I asked. The salesperson had no freaking clue. The entire tool industry operates this way.
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Old 04-29-2011, 07:29 PM   #6
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Re: Conversion Question.


Quote:
Originally Posted by MilwaukeeMike View Post
Comparing RPMs, torque, stroke length, IPMs etc tells us about performance but man, there's that "umph", balls to the wall factor. I'm trying to go as cordless as possible & this is a PITA. You're right Amp/Hr on the tool would help but they just rate the batteries.
funny thing is i just decided im going CORDED!!!
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Old 04-29-2011, 07:42 PM   #7
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Re: Conversion Question.


Quote:
Originally Posted by 480sparky View Post
The entire tool industry operates this way.
I hear `ya but there has to be a way to figure: "Tool A" motor operates on 18 (+/-) volts DC = "Tool B" motor operates on X Amperage (+/-) @ 120 Volts AC. Solve for X

They tell you mA/hr for the battery, what exactly does THAT mean ?
Does it mean the battery produces 3 Amps of current for every hour of discharge ?

I've combed the few electrical books I have, the web and asked the electrical instructor at the tech school (the guy was an encyclopedia of electrical knowledge it seemed) for the answer & nothing...LMAO

Really?

Last edited by MilwaukeeMike; 04-29-2011 at 10:52 PM.
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Old 04-29-2011, 07:48 PM   #8
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Re: Conversion Question.


Quote:
Originally Posted by POOLMANinCT View Post
funny thing is i just decided im going CORDED!!!
Why?

Last edited by MilwaukeeMike; 04-29-2011 at 10:53 PM.
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Old 04-29-2011, 07:56 PM   #9
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Re: Conversion Question.


Quote:
Originally Posted by A.T.C. View Post

The saw, just an accessory. Can't replace a plug-in.
We're a bit off topic but.... No cordless will replace a Worm Drive Circ or 13-15 Amp Super Sawzall or any heavy Recipro anytime soon. Dewalt's 7-1/4 36V circ might replace a corded sidewinder but not the Worm.
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Old 04-29-2011, 08:10 PM   #10
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Re: Conversion Question.


Quote:
Originally Posted by MilwaukeeMike View Post
...........They tell you mA/hr for the battery, what exactly does THAT mean ?
Does it mean the battery produces 3 Amps of current for every hour of discharge ? ..........
It means that at the current state, the battery is producing 3 miliamps over the course of one hour.
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Old 04-29-2011, 08:32 PM   #11
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Re: Conversion Question.


Quote:
Originally Posted by 480sparky View Post
It means that at the current state, the battery is producing 3 miliamps over the course of one hour.
The tool is running on 3 Amps then?
So the C in DC is measured in Amp/hr ?


freakin Edison...

Last edited by MilwaukeeMike; 04-29-2011 at 08:39 PM.
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Old 04-29-2011, 08:47 PM   #12
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Re: Conversion Question.


C in DC is Direct CURRENT. Meaning there's electrons flowing. DC means they're flowing in one direction only... from one terminal of the battery to the other.

mA is milliAmperes, or 1/1000 of an Ampere, the rate at which said current is flowing.
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Old 04-29-2011, 09:43 PM   #13
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Re: Conversion Question.


Quote:
Originally Posted by 480sparky View Post
C in DC is Direct CURRENT. Meaning there's electrons flowing. DC means they're flowing in one direction only....
I know, when I said "C in DC", C meant amperage/current (same thing right?) and AC flows into the "load" and returns, got it.

Quote:
Originally Posted by 480sparky View Post
mA is milliAmperes, or 1/1000 of an Ampere, the rate at which said current is flowing.
I know this also but...
Quote:
Originally Posted by 480sparky View Post
, the battery is producing 3 miliamps over the course of one hour.
...sorry, I thought it was a typo but figured I'd ask you anyway champ.

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Old 04-29-2011, 09:57 PM   #14
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Re: Conversion Question.


Quote:
Originally Posted by MilwaukeeMike View Post
I know, when I said "C in DC", C meant amperage/current (same thing right?) and AC flows into the "load" and returns, got it.
C=Current, simply meaning electrons are being moved. It is not a Unit of Measure any more than 'red' or 'blue' can tell you how much paint you have. It could be AC (alternating current) or DC (direct current). The C in AC or DC merely implies the driving force, not a specific amount. It could be a mathematically tiny amount, a terrifyingly large number, or anywhere in between.

How many electrons are being moved is measured in A=Amperes. 1 Amp is a one coulomb (unit of charge) per second. The charge of an electron is 1.6 x10^-19 so the number of electrons in one coulomb is 1/1.6x10^-19 = 6.25x10^18 electrons.

So for one Amp that would be 6.25x10^18 electrons per second flowing through a given point the circuit.
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Old 04-29-2011, 10:48 PM   #15
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Re: Conversion Question.


Ohhh... Sorry, I'm an electrical layman, if that, but I get the "paint color" analogy (good one btw)... OK, you obviously know your trade inside & out, please help me figure out the original question. How can I mathematically compare a corded tool to it's cordless counterpart ? Is it even possible with the information provided ? Don't give up on me yet Sparky!!!

Last edited by MilwaukeeMike; 04-29-2011 at 10:51 PM.
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Old 04-29-2011, 10:56 PM   #16
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Re: Conversion Question.


Like I said, I doubt you'll find the information needed to make an apples-to-apples comparison. One the whole, though, I'd say battery tools are far far behind corded ones in terms of sheer power. Yea, you can find a $400 cordless drill that will outperform a $25 corded one, but that's like comparing a older Lambourghini to and new pickup. The Lamb is nice, but I'd rather drive a truck since it does what I need it to do.

Some day, I'm sure we'll see tools advertised with thread counts and transfat content just to keep us in the dark.
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Old 04-29-2011, 11:22 PM   #17
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Re: Conversion Question.


Quote:
Originally Posted by MilwaukeeMike View Post
I hear `ya but there has to be a way to figure: "Tool A" motor operates on 18 (+/-) volts DC = "Tool B" motor operates on X Amperage (+/-) @ 120 Volts AC. Solve for X
If you want to solve for current using ohms law, then you need to know resistance, but you don't have that. The only way I can see finding the amount of power dissipated in your cordless drill is to break open the drill and measure the current going to the motor. Then solve using W = IV.

Quote:
They tell you mA/hr for the battery, what exactly does THAT mean ?
Does it mean the battery produces 3 Amps of current for every hour of discharge ?
Average milliamps per hour, that's what I always thought it meant. But I don't think it will tell you the current being drawn at a particular time.

Quote:
I've combed the few electrical books I have, the web and asked the electrical instructor at the tech school (the guy was an encyclopedia of electrical knowledge it seemed) for the answer & nothing...LMAO

Really?
They get a lot of weird questions like that, you'll just have to try it. You won't find the answer to every scenario in a text book. But if you understand electricity then you can figure anything out.
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Old 04-30-2011, 10:23 AM   #18
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Re: Conversion Question.


For battery capacity rating, the concept is that at X voltage, the battery will provide (for example) 100 amps for one hour. That would be a 100 amp hour battery.

By extension, that battery would provide 50 amps for two hours, 25 amps for four hours and so forth.

Part of the problem with comparing corded tools with cordless is that batteries have an internal resistance that limits the peak current draw (meaning usable power), whereas AC tools are limited only by the motor's internal impedance and what the circuit is fused for. All else being equal, the AC motor will always have a higher capacity.
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Old 04-30-2011, 11:03 AM   #19
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Re: Conversion Question.


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Originally Posted by Tinstaafl View Post
For battery capacity rating, the concept is that at X voltage, the battery will provide (for example) 100 amps for one hour. That would be a 100 amp hour battery.

By extension, that battery would provide 50 amps for two hours, 25 amps for four hours and so forth.

Part of the problem with comparing corded tools with cordless is that batteries have an internal resistance that limits the peak current draw (meaning usable power), whereas AC tools are limited only by the motor's internal impedance and what the circuit is fused for. All else being equal, the AC motor will always have a higher capacity.
That is partially correct. Most batteries have a 20 hour rating. this means that a 100 amp/hour battery will give you 100 amps over 20 hours or 5 amps per hour. If you discharge the battery at a 1 hour rate, you will get less, somewhere around 93 total amps.
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Old 04-30-2011, 11:49 AM   #20
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Re: Conversion Question.


Quote:
Originally Posted by A.T.C. View Post
That is partially correct. Most batteries have a 20 hour rating. this means that a 100 amp/hour battery will give you 100 amps over 20 hours or 5 amps per hour. If you discharge the battery at a 1 hour rate, you will get less, somewhere around 93 total amps.
I read that a while back & forgot all about it, if my battery is "3.0 Amp/Hr" it would run at 3 amps for 1 hour. So if my tool's motor carries a load of 6 Amps this battery would last approximately 1/2 hr. so Tin's right. This a good "indicator" of the tool's power, but I wanted a more "scientific" way of finding the answer.

If you've ever run an 18, 28 or 36 volt tool JUST for the battery to drain in order to time a fully charged battery's run time on that tool you'll see the tool run (NO LOAD) anywhere from 20-40 minutes depending on the tool AND the battery type NiCad or Lithium & age. The NiCad, I've found, run for a longer period of time but "taper off" making it a slower more "painful" death. I've found that Lithium batteries run for a shorter period of time overall but give you "close" to full power all the way through the charge.

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