Cordless Impact Wrench Performance vs Battery (Max Current vs. Capacity)

[YoshiMoshi]

Milwaukee makes a cordless right angle impact wrench, 2565-20. As part of their M12 line of power tools. A YouTube channel tested the performance of the tool, with their different batteries. I'm having difficulty in understanding the observations. It seems that higher output current batteries do not necessarily mean higher performance.

The Data collected from the video:

• CP 1.0 peak torque 131 ft lb
• CP 2.0 peak torque 144 ft lb
• XC 4.0 peak torque 159 ft lb
• XC 6.0 peak torque 182 ft lb

Now the internals of the batteries:

Combining the data

1. CP 1.0, 1 Ah, Peak Torque 131 ft lb
   1. 3x Samsung 13Q, Total Max Continuous Discharge Current From Battery Pack = 15 A
   2. 3x Moli IMR-18650E, Total Max Continuous Discharge Current From Battery Pack = 20 A
   3. 3x Samsung 15M, Total Max Continuous Discharge Current From Battery Pack = 23 A
2. CP 2.0, 2 Ah, peak torque 144 ft lb
   1. 3x Samsung 20R, Total Max Continuous Discharge Current From Battery Pack = 22 A
   2. 3x LG HG2LGDAHD41865, Total Continuous Discharge Current From Battery Pack = 20 A
3. XC 4.0, 4 Ah, Peak Torque 159 ft lb
   1. 6x LG HG2LGDAHD41865, Total Continuous Discharge Current From Battery Pack = 40 A
4. XC 6.0, 6 Ah, Peak Torque 182 ft lb
   1. 6x Samsung 30Q, Total Continuous Discharge Current From Battery Pack = 30 A

Taking the best configuration for each battery (the video didn't specify):

1. CP 1.0, 1 Ah, 23 A, Peak Torque 131 ft lb
2. CP 2.0, 2 Ah, 22 A, Peak Torque 144 ft lb
3. XC 4.0, 4 Ah, 40 A, Peak Torque 159 ft lb
4. XC 6.0, 6 Ah, 30 A, Peak Torque 182 ft lb

Well I don't get this:

• CP 2.0 had better performance than the CP 1.0, despite delivering less current to the tool of 1 A. The difference is that the 2.0 has a larger capacity of 1 Ah. But why does the increase capacity result in better performance?
• XC 6.0 had better performance than the XC 4.0, despite delivering less current to the tool of 10 A. The difference is that the XC 6.0 has a larger capacity of 2 Ah. But why does the increase capacity result in better performance?

I would presume that a battery pack that is able to discharge more current, would result in better performance. But that doesn't seem to be the case here. It seems that larger capacity battery pack increases performance more than a battery pack that draws more current. I don't really understand why. Thanks for any help!

Also, I was looking into custom battery packs. Am I right that say for example the XC 5.0 has a maximum continuous discharge current of 50 A, but the power tool will only consume the maximum amount of current it needs. So while the battery pack may support a maximum of 50 A, the power tool may not necessairly consume 50 A. There is some sort of maximum, at which a battery pack that can output more current won't result in any difference in performance?

 

[Baluncore]

Energy usage is also dependent on the number of impacts per second. Where is that in your analysis?

Be aware that impact drivers may destroy some low-cost or generic battery packs, by fracturing the internal connections.

 

[YoshiMoshi]

I don't have that data. But if the same tool is used, is it safe to assume it's the same?

These are official battery packs from the manufacture and not the cheap knock offs.

I just find it interesting, battery packs whose cells that can output less current, but have a higher capacity, result in better performance in the tool.

I would have thought battery capacity would just have longer run time, and not better performance, and that batteries that can output more current, would result in better performance.

I don't really understand it. Unless, batteries with a higher capacity can have more impacts pet second? But I don't know why this would be the case.

 

[YoshiMoshi]

In case anybody else finds this. Torque test channel did a video on this. An impact wrench, there's a spring that the hammering mechanism has to overcome. You only need so much current to overcome the spring. There is an optimal current. Upping the current to the motor of an impact wrench won't have the same impact as such a drill. A bigger power source supplying more current might make the motor spin faster in an impact, but it's still the same hammering mechanism over the same size. Spinning the motor faster won't have an increase on the torque.

A higher capacity battery will have less voltage drop over a smaller capacity battery. So a higher capacity battery might have a higher torque in the first few seconds over a smaller capacity battery with a higher current. If you hold the trigger long enough, eventually the higher current battery may have an insignificantly higher torque.

Essentially, there's a cost optimization, where adding more current will have marginal, likely unnoticeable (unless your measuring it) increase in torque. If your trying to bust free a fastener, a higher capacity battery will be better, because you will get more torque quicker in the first few seconds.

 

[Baluncore]

A force, or a torque, is not work done. Productive work is only being done when the impact torque causes a rotation against friction.

If rotation does not occur, the impact wrench forms a resonant oscillator, with circulating energy, which has a lower power consumption.

When the fastener begins to rotate, the energy balance of the hammer mechanism changes, and you can hear a change in the impact oscillator.

Brushless motors, with switching electronic controllers, efficiently limit the current to the motor. That regulates the torque, prevents overheating of the motor windings, while also limiting injury to the tool and operator. The maximum available battery current, needs only be sufficient for the tool. Increased current capacity is of no immediate advantage.

 

[Tom.G]

Increased current capacity is of no immediate advantage.

Just means you get more "bangs" for a buck!