Do Ah Have Any Effect Other Than Runtime?

[freudianfloyd]

I have been looking at getting an M18 impact, so I have been trying to figure out how to get the most bang for my buck.

I found d a pretty good deal on the bare tool, but also on the drill/driver combo with 2 1.5 Ah batteries for not much more than I can buy a charger and 1 5 Ah battery.

My question is, does a 5 Ah battery have any benefit other than runtime? Or would it be just as powerful with the 1.5 Ah battery but just for a shorter amount of time?

 

[reptilezs]

with a smaller pack you get slightly reduced power especially with the high demand tools and limited run time

 

[M6erfan]

A year or so ago I did a bit of research because I had the same question. I found nothing besides anecdotal evidence that supports higher Ah equate to more "oomph". Doesn't mean it's not true, just that I couldn't find anything...

 

[jd_1138]

I can't feel a difference other than the obvious difference of having a longer run time. I would think that the maker would have to engineer in more current draw to get more ooompth if it detects a larger capacity battery has been plugged in. I have Makita and Ryobi and used to have DeWalt.

If the price isn't much more, I'd pick up the combo even with the small batteries, though I'd also pick up at least some 3.0 batteries soon.

 

[MattT]

A year or so ago I did a bit of research because I had the same question. I found nothing besides anecdotal evidence that supports higher Ah equate to more "oomph". Doesn't mean it's not true, just that I couldn't find anything...

I've seen published Ingersoll Rand numbers that showed a lower torque for smaller batteries. Was for one of the IQV20 impacts IIRC.

 

[ChrisLS8]

In my seat of the pants experience the larger batteries give a bit more power.

The other day I was using my impact to tighten down anchors and with a 5ah DeWalt I barely ran em down. Slapped the 9ah flexvolt on and it finished em off. I had identical results about 10 times

Take it with a grain of salt cause it's not a controlled environment and there are a lot of variables.

 

[KnurledNut]

A Makita 5 vs 3 is slightly more powerful.

 

[freudianfloyd]

I appreciate all the info. I went ahead and bought the impact bare tool and the combo. The combo I found did have 2.0 Ah batteries, so that's a slight improvement over the ones I originally was looking at.

 

[Ign]

Yes it absolutely does. If amp hours didn't matter you could crank your truck with an M12 pack. After all, 12V is 12V, right?

Seriously, see this, you get more power and RPM from more amp hours. This question pops up every 6 months and I don't understand why it's a difficult concept - especially when a tool has to "dig deep" it's got a deeper well from which to drink when it needs it most.

http://www.realtoolreviews.com/does-size-matter-dewalt-flexvolt/

 

[kctyphoon]

You can HEAR a clear and noticeable difference just in the rpms. Tests have been done on video that prove bigger packs produce more power. I cant even place a 9.0 pack in my compact blower and just gun in to full throttle - the tool with just shut off.. i have to start it at a slower speed first and then gun the throttle.

 

[Brian Puccio]

And not just higher amp hours, but also the types of cells in the batteries and their peak discharge rates.

 

[Dingleburry]

This what happened to me
Hi torque impact didnt run long on 1.5 ah batteries. About 10to 15 seconds of impacting
The current draw was so high, the smaller batteries have too much voltage drop.
Put in a 5.0 battery and it tore through the job no problem.

Series up batteries the voltage goes up, current stays same.
Parallel up batteries voltage stays same, current goes up.
Since the battery packs are the same voltage, theres more paralleled cells, providing more amps.

 

[freudianfloyd]

No biggie, I will just pick up a 5.0 Ah battery in the near future.

 

[Citation]

with a smaller pack you get slightly reduced power especially with the high demand tools and limited run time

A year or so ago I did a bit of research because I had the same question. I found nothing besides anecdotal evidence that supports higher Ah equate to more "oomph". Doesn't mean it's not true, just that I couldn't find anything...

The first is theoretically true and the second is probably true in many real life cases. A higher Ah battery, all else equal, can support a higher drain. This is why the fastest accelerating Tesla cars are the ones with the biggest, heaviest batteries. But if the tool isn't designed to take advantage of the extra potential current capabilities of the battery then it's just extra run time.

 

[Negen]

Here are some discharge rate charts for some 18650 cells which are mostly what are used in battery packs. Notice the tests stop at 2.5v after that damage will occur. Not all battery packs are the same and with these things getting what you pay for is just that. High end new tech cells even if secured by the 100,000s will run about 4-8$ per cell. Depending on your place in line. With the manufacturer. These have fairly finite production rates. Not all 4ah cells discharge the same. Some are designed to discharge at fast rates and some designed for long run times.

https://www.houseofbatteries.com/custom-batteries-custom-lithium-ion-polymer.html

https://www.powerstream.com/18650-high-discharge-rate.htm

https://marsen.com.au/products/batteries/panasonic-ncr18650b-3-6v-3400mah-protected/

http://budgetlightforum.com/node/42074

Sent from my G8141 using The Garage Journal mobile app

 

[ddawg16]

For the same given voltage, the 'umph' will be about the same for both a small or large pack

I said 'about'.

If we assume an 18v pack using typical Li cells (18650's or 21700's), you are looking at 5 cells in series to get you 18volts.

The Ah rating is based on the Ah rating of each cell. You can assume the typical Ah of an 18650 cell is going to be around 2500 mAh. So if they are saying that pack has an Ah rating of 1.5 Ah, it sounds like they are using derated cells and there is only 5 of them. The 5 Ah pack is most likely 10 cells (2 cells in parallel for each bank)

Each cell has a fixed internal resistance. What this really means, while the Ah rating might be ** amount, under high current draws, the cell can produce a lot more juice. Using Ohms law, it's easy to understand that if you put two cells in parallel, the internal resistance will be less. Hence, a pack with a higher Ah rating (2 or more cells in parallel) will be able to deliver more current.

So...yes, the higher Ah rating pack will be able to deliver a bit more 'umph' under high load conditions.

So....back to the original question......unless you expect to run the tool at max loads...and need the run time....take the deal. You can always buy the larger pack if you need it.

Side note.

One of the main reasons for Li battery pack failures is for guys to not put them on the charger after they are drained.

Li cells literally die if the cell voltage drops below 2 Vdc. The Li battery pack has a BMB (Battery Management Board) that shuts off the output when the cells get close to the bottom end. But, if you toss the pack to the side and wait a couple of months before you toss it on the charger, there is a chance one or more cells may have dropped below the 2 Vdc level. In most cases, there is NO recovery from this point.

 

[mudflap]

For the same given voltage, the 'umph' will be about the same for both a small or large pack

I said 'about'.

If we assume an 18v pack using typical Li cells (18650's or 21700's), you are looking at 5 cells in series to get you 18volts.

The Ah rating is based on the Ah rating of each cell. You can assume the typical Ah of an 18650 cell is going to be around 2500 mAh. So if they are saying that pack has an Ah rating of 1.5 Ah, it sounds like they are using derated cells and there is only 5 of them. The 5 Ah pack is most likely 10 cells (2 cells in parallel for each bank)

Each cell has a fixed internal resistance. What this really means, while the Ah rating might be ** amount, under high current draws, the cell can produce a lot more juice. Using Ohms law, it's easy to understand that if you put two cells in parallel, the internal resistance will be less. Hence, a pack with a higher Ah rating (2 or more cells in parallel) will be able to deliver more current.

So...yes, the higher Ah rating pack will be able to deliver a bit more 'umph' under high load conditions.

So....back to the original question......unless you expect to run the tool at max loads...and need the run time....take the deal. You can always buy the larger pack if you need it.

Side note.

One of the main reasons for Li battery pack failures is for guys to not put them on the charger after they are drained.

Li cells literally die if the cell voltage drops below 2 Vdc. The Li battery pack has a BMB (Battery Management Board) that shuts off the output when the cells get close to the bottom end. But, if you toss the pack to the side and wait a couple of months before you toss it on the charger, there is a chance one or more cells may have dropped below the 2 Vdc level. In most cases, there is NO recovery from this point.

I think a very low draw tool can kill a battery too. I have a PC combo kit we use for camping. If the single LED flashlight drains the battery, its hard to get it to take a charge after that. Sometimes i have to get a couple volts in it with my jumper box before the charger will even try.

 

[kctyphoon]

No biggie, I will just pick up a 5.0 Ah battery in the near future.

Best place is eBay.

 

[ddawg16]

I think a very low draw tool can kill a battery too. I have a PC combo kit we use for camping. If the single LED flashlight drains the battery, its hard to get it to take a charge after that. Sometimes i have to get a couple volts in it with my jumper box before the charger will even try.

I suspect those are not Li batteries.....or it has a piss poor BMB

 

[mudflap]

I suspect those are not Li batteries.....or it has a piss poor BMB

They are LI, Porter cable 20 Volt series. It dosnt happen with the big flashlight, or any of the other tools. Just the little flashlight with the single LED.. The battery will power that thing forever, but if it dies on there.. will show less than 1 volt on a meter, and the caharger will flash bad battery until i get over 2 volts in it. Then it charges fine.

 

[u3b3rg33k]

I have been looking at getting an M18 impact, so I have been trying to figure out how to get the most bang for my buck.

I found d a pretty good deal on the bare tool, but also on the drill/driver combo with 2 1.5 Ah batteries for not much more than I can buy a charger and 1 5 Ah battery.

My question is, does a 5 Ah battery have any benefit other than runtime? Or would it be just as powerful with the 1.5 Ah battery but just for a shorter amount of time?

when you go to the bigger M18 packs, they add capacity by adding another parallel string of batteries. so going from a 2Ah (1 string) to a 5Ah (2 parallel strings) to a 9Ah (3 parallel strings) battery means there's 33% more "ampacity" in addition to the added stored energy. this is what they mean when they say "high demand" on the side of the pack. not so important for regular drills, much more important for bigger saws/whole hawgs. it's also why the smaller batteries run hotter on high power tools than the bigger batteries. more amps pulled out of each string on the smaller batteries.

 

[6PTsocket]

Yes it absolutely does. If amp hours didn't matter you could crank your truck with an M12 pack. After all, 12V is 12V, right?

Seriously, see this, you get more power and RPM from more amp hours. This question pops up every 6 months and I don't understand why it's a difficult concept - especially when a tool has to "dig deep" it's got a deeper well from which to drink when it needs it most.

http://www.realtoolreviews.com/does-size-matter-dewalt-flexvolt/

The analogy doesn't work. Another factor is the maximum current a battery can supply. I am talking about Amps, not A/hr. That depends on the chemistry and construction. Even big 12 volt batteries that are made for deep discharge are not made to supply high starter current. However a battery that can only supply current at a low rate can recharge a high current battery. There is a video of somebody recharging a car battery with a string of AA's and stating the car.

Sent from my SM-G900V using Tapatalk

 

[DFB]

My own experiments with a non contact tach taking readings from several different Milwaukee drills and impacts most often shows a slight NO LOAD peak rpm increase with XC packs installed verse the smaller compacts batteries. And the that level also stays pretty consistent across the batteries discharge.

On a personal level it really depends on the job at hand...I use compacts in low volume use, low amperage draw situations they can make a tool lighter and possibly be more manageable with certain situations like shop, belt hook, tool pouch, ladder use.

Under any real demand they can quickly run out though, and XC shine.

That's all I got

 

[ddawg16]

They are LI, Porter cable 20 Volt series. It dosnt happen with the big flashlight, or any of the other tools. Just the little flashlight with the single LED.. The battery will power that thing forever, but if it dies on there.. will show less than 1 volt on a meter, and the caharger will flash bad battery until i get over 2 volts in it. Then it charges fine.

When you let a Li go below 2 Vdc, that battery is basically done. The light should have a BMB that shuts off the light when the voltage gets below 3 v

Li's are very well characterized....i.e., 3.5 Vdc = 30% charge.

 

[Ign]

The analogy doesn't work. Another factor is the maximum current a battery can supply. I am talking about Amps, not A/hr. That depends on the chemistry and construction. Even big 12 volt batteries that are made for deep discharge are not made to supply high starter current. However a battery that can only supply current at a low rate can recharge a high current battery. There is a video of somebody recharging a car battery with a string of AA's and stating the car.

Sent from my SM-G900V using Tapatalk

It doesn't matter - unless a GJ member here is going to run a test as scientific or more scientific than the RTR link I provided and document and present it well, anecdotal evidence of "gee it doesn't seem to make a difference" can't stand up.

Analogies are, by definition, rarely perfect or it wouldn't be an analogy

 

[mudflap]

When you let a Li go below 2 Vdc, that battery is basically done. The light should have a BMB that shuts off the light when the voltage gets below 3 v

Li's are very well characterized....i.e., 3.5 Vdc = 30% charge.

Once i can get a couple of volts in them..they charge fine, and seem to suffer no ill effects..But we just use them on flashlights. There is no charge indicator, so i just have to fully charge them once in a while to keep it from happening.

 

[MikeF2316]

Yes it absolutely does. If amp hours didn't matter you could crank your truck with an M12 pack. After all, 12V is 12V, right?

Seriously, see this, you get more power and RPM from more amp hours. This question pops up every 6 months and I don't understand why it's a difficult concept - especially when a tool has to "dig deep" it's got a deeper well from which to drink when it needs it most.

http://www.realtoolreviews.com/does-size-matter-dewalt-flexvolt/

200 amps for 1 second is only 1/3 amp-hour. So a 2 ah battery has enough energy for 6 seconds of cranking. So all you need is a honking big capacitor and a circuit to charge it, and a little time. You might want to use one of the new 6.0s for a little reserve.

 

[kctyphoon]

I’m by far no expert on batteries - but a long time ago when i said i wish they made an m18 powered jump pack - people laughed- yet here we are with lithium jump packs twice the size of a cell phone sold at every home store.

 

[plinker]

I’m by far no expert on batteries - but a long time ago when i said i wish they made an m18 powered jump pack - people laughed- yet here we are with lithium jump packs twice the size of a cell phone sold at every home store.

That's not a bad idea at all. I think it'd work pretty well.