Replies

1. 
   webby | Jul 27, 2008 07:51pm | #1

   Batteries for cordless tools are given an Amp/hour rating (Ah) So a twelve volt battery with 1.2 Ah would be less gutsy so to speak than a 12 volt battery with 2.4 Ah.

   But these ratings are often not really given much attention thusly it is often hard to find them in the literature or printed on the box.

   Generally the higher voltage tools are more powerful and that is what people go for naturally. So the manufacturers use the voltage to advertise with. This satisfies most persons. Ocasionally you run into the amp hour deal with lighter duty tools.

   On the down side the higher the voltage the heavier the tool. Until recently.

   For years nickel cadmium or nicad batteries were the tried and true standard. light and powerful they held their charge reasonably well, and were relatively unaffected by cold and heat.

   NiMh or Nickel Metal Hydride, was next they were about the same size as Nicad batteries but held their charge much longer and acheived a higher amp hour rating due to the battery material.

   Lithium Ion is the newest technology. It has been used in batteries for phones and laptops, and most recently cordless tool batteriss.

   Its advantages are the same voltage rating and increased power in a smaller package. An 18 volt LI battery is the same size as a 12 volt nicad battery. The LI batteries hold their charge even longer than the NiMh batteries.

   In construction situations, or for outdoor projects,the LI batteries don't like extremes of temperature though. 

   The enemy of any cordless tool battery is heat. Rapidly dischargng a battery builds up heat in the cells of the battery and lessens battery life. This often results because people are in a hurry and use their cordless drill for things that it wasn't intended. It may work, but it is not good for the batteries. An exaple would be to use a cordless drill for drilling a lot of large holes rapidly one after the other.

   Just my 2 cents worth that I have picked up here and there. Hope it helps.

   Webby 

    

1. 
   willy | Jul 27, 2008 09:57pm | #2

   Much appreciated, Webby. I'll follow your info when it's time to replace my old 9 volt mastercraft.

2. 
   BrianDerr | Jul 30, 2008 07:14am | #8

   My impression is that the voltage of cordless tools generally spells their power, while the amp/hour means how long they can deliver that power before recharging. Something tells me it's not like in AC systems where the voltage is a given and the motor amperage determines power. I have a 18v makita 1.5 ah, and though it needs to be charged fairly often, I think it must be more powerful than the tiny 14.4v 3 ah with a huge battery that I see advertised. Sure I wish I had an 18v 3ah, but if it were as light as the 1.5ah, but it wouldn't be. And I think the tool would perform the same except for the charging frequency. Look at the max torque of impact drivers at 18v, 14v, 9v, etc., and I think you'll see that it's voltage that determines power in cordless tools, not amp/hours. These are not the same as amps not qualified by hours. Just my experience, would love to know more.Brian

1. 
   webby | Jul 31, 2008 12:48am | #11

   I think you are  correct.

   I think much of my opinnion admittedly is based on an an experience when shopping for a cordelss impact.  

   I couldn't afford the one I wanted so I was trying to talk myself into a hitachi 12 volt at Lowes for 169.

   It was okay, light and small. but the batteries looked really small for a twelve volt.

   I got online and read the owners manual paying close attention to the battery. The impact came supplied with two 12 volt 1.2 (I think) amp hour batteries. Knowing that higher Ah translates roughly into a longer run time between charges for intermittent use, I wasn't nuts about the low Ah.

   I also noticed somewhere in the literature that on average the user could expect about three  hundred recharges from the particular battery I suspected that I would use the tool alot so I passed on the Hitachi on that criteria.  Purely a personal decision.

   I recently use a hitachi at work and it is fine.

   I just prefer a combination of low tool weight, reasonable power, read as voltage, and a high Ah.

   I also should have been more clear in my original reply to indicate that voltage is the predominate criteria for determining the power of a cordless tool. I tried to inform the OP that there are other factors in battery technology that are resultant and factor into the volatage that help determine power.

   As important as power is to me, run time is equally important. I am probably a little slanted due to using an  impact for a while. 900 inch pounds of torque in a 12 volt vs. 350 in a cordless drill of the same voltage results in a lighter smaller tool capable of doing what I ask in a surprisingly controllable package. I use them for remodeling as well as driving almost all but the tiniest hinge screws when woodworking.

   Webby 

    

   Edited 7/30/2008 5:56 pm ET by webby

   Edited 7/30/2008 5:57 pm ET by webby

   Edited 7/30/2008 6:00 pm ET by webby

2. 
   highfigh | Jul 28, 2008 12:53am | #3

   It's volts AND amps (P=I x E). Volts are like water pressure and current (amps) is like flow rate. A motor uses a magnetic field to rotate, and the stronger the field, the harder it will try to turn. Use high voltage and the current decreases when the power is calculated, but use high voltage and dump a bunch of current, you have a torque monster. Add some batteries that have a fast recovery time and you have a winner.

   "I cut this piece four times and it's still too short."
3. 
   Henley | Jul 30, 2008 02:57am | #4

   I make a point of not directly contradicting people but

   I feel someone is mislead, so no disrespect intended to other poster.

   Amp hour is a rating of the longevity of the battery not power out put.
   The voltage is a much better indicator of that. Better yet is the specs. regarding torque etc.
   18V is very similar brand to brand as far as power, the gearing has far more impact then the amp hour.
   If your in the shop amp hour probably doesnt mean all that much, as changing batteries isn't all that big of a problem. If your on a ladder
   it would mean much more.

1. 
   willy | Jul 30, 2008 03:32am | #5

   Thanks Henley; I appreciate all comments. I have been shopping major outlets in my area and I'm leaning toward a Hitachi 14.4 volt lithium and its rated as 1.5 ah. I'm not in the contracting business; it's for home shop use. The Hitachi is a nice fit for my hand, o.k. weight and I got a price break from a local store. Last week I bought an 18 v ni cad that was marked down from $200 to $100. When I unboxed it, it was way to heavy for me so returned it.

1. 
   Henley | Jul 30, 2008 04:04am | #6

   I can't speak for the Hitachi but I am using
   a 18V lithium ion Milwaukee 1.5 amp. hour and am very pleased.
   The lithium lasts a good while and the 18v is plenty powerful.
   To me run time is a bit over rated. Balance and fit are crucial.

2. 
   webby | Jul 30, 2008 04:33am | #7

   Good point Henley. I did not mean to imply that a tool should be chosen based on amp hours. I really couldn't tell you the amp hours af all my batteries.

   I feel like you that a tool shoule be chosen based on the jobs it will perform, the voltage or power needed. And the overall comfort level.

   I did not mean to imply that Ah was better than the voltage to pick a tool by simply to inform the OP that as he had experienced all batteries are not created equal. And that the original question what determines power is more  than just voltage. A battery with a higher amp hour rating will run longer than a battery with a lower rating.

   Amp hours is the maximum sustained amperage drawn from a fully charged battery over a certain period of time. then multiplied by the discharge period to give the Ah rating.

   So a bargain basement 18 volt batt. with 1 Ah rating, will go dead faster than a 14.4 volt battery with 2.4 Ah under identical lab type testing. Imho

   But as I said Ah is rarely used to advertise with, leading most people to use voltage to make their choice which is one of the better criteria for most users as you pointed out. Webby 

    

1. 
   Henley | Jul 30, 2008 09:18am | #9

   Yeah it gets to be a convoluted question.
   Then you have to figure in the gearing.
   Speed vs. torque

   To me as long as it charges faster then you
   can kill it, run time means little. As far as power, I'm actually using low gear! Most
   any drill is strong enough if you flip the switch.

   Edited 7/30/2008 2:19 am ET by Henley

1. 
   webby | Jul 31, 2008 12:37am | #10

   I agree.

   I have switched over basically to impacts. for the speed and power. I don't have a LI kit but I have a dewalt 12v impact and a makita 14.4 impact. I use them for almost everything now. Their small size spoiled me for other drills. When I need a three jaw chuck I use the ones with the adapter in the impact dewalt and makita both make them.

   Most bits I have are hex shank, go right in the driver. For larger drilling or rough work I use a corded drill.Webby