Cordless Reciprocating Saws - Part 4

Conduct endurance tests of 18-volt cordless reciprocating saws to determine work that can be anticipated at fire/rescue incidents.

Subject:  Cordless Reciprocating Saws, Part 4

Topic:  Endurance Testing of 18-Volt Cordless Reciprocating Saws

Objective:  Conduct endurance tests of 18-volt cordless reciprocating saws to determine work that can be anticipated at fire/rescue incidents.

Task:  Measure the capability of reciprocating saw batteries and saw blades to perform typical vehicle rescue tasks.

It seems no one really knows what the endurance capability of an 18-volt reciprocating saw is when used by firefighters. I therefore set out to determine just how many cuts can be made with an 18-volt saw and one battery.

To accomplish my mission, I designed a series of endurance tests to determine the work output of two different 18-volt batteries from DeWalt and one type from Milwaukee under various rescue situations. The endurance tests began in November 1998 and have progressed continually since then. Each test simulates a real-world situation or condition that firefighters may encounter with a reciprocating saw.

The No-Load Test

To determine the maximum run time of an 18-volt battery, I secured the trigger of an 18-volt Milwaukee and a DeWalt reciprocating saw in the "on" position. I then snapped on a fully charged 18-volt battery, letting the saw run unloaded. I recorded the running time of the saw until the 18-volt battery discharged and the saw action stopped. This elapsed time was my baseline run time. All other tests, in which the saw had to operate under a load and actually cut material, were compared to this maximum no-load run time.

Milwaukee’s 18-volt batteries powered its saw from 11 minutes, 50 seconds to over 15 minutes. Milwaukee’s average no-load run time was 13 minutes, 24 seconds. DeWalt’s original XR2 batteries powered its saw almost twice as long, a remarkable 23 minutes on average. In 1999, DeWalt introduced a 2.4-amp hour NiCad battery called the XR+. This battery, advertised as having 40% more power than its original XR2 battery, represents the maximum capacity available in NiCad battery technology today. In no-load tests with the new XR+ battery, the DeWalt saw increased its run time from 23 to 30 minutes.

The "Aged 60 Days" Battery Test

Both DeWalt and Milwaukee claim that their batteries experience a 5% loss of energy per day when not on a charger. To determine how battery deterioration could impact fire service users, I designed an "aged 60 days" battery test. Three Milwaukee batteries were fully charged, then left to sit alone on a shelf at normal room temperature for more than 60 days. After this aging period, I repeated the no-load test with these batteries. Whereas a fully charged Milwaukee battery ran in excess of 13 minutes, the two-month-old batteries averaged a little over eight minutes. This represents a loss of almost 40%, a significant loss of energy. This reinforces the recommendation that all cordless tool batteries be left on a charger at all times to maintain their fully ready state.

The 2x4 Lumber Test

The next series of tests was designed to evaluate the saws on a material that any fire department could readily have to cut through. Common 2x4 dimensional lumber was selected and placed in a workbench clamp. With the stopwatch running, inch-thick slices were cut off until the useful power of the battery diminished. A record was made of when each cut was completed as well as the total number of cuts and the total battery operating time.

For all wood-cutting tests, each saw used a Milwaukee AX 10-tpi (tooth per inch) wood-cutting blade. A new blade was used for each test. During the DeWalt tests, the blade came loose in their old-style key chuck system twice and the handle design hurt the operator’s gloved hand at the base of the thumb upon conclusion of the rugged tests. During the Milwaukee tests, saw vibration caused the battery to disconnect from the handle of the saw.

The Milwaukee recip saw was able to cut 27 to 35 cuts with the battery cutting from four minutes, 52 seconds to a maximum of six minutes, five seconds. Under the conditions of this aggressive cutting test, the Milwaukee batteries lasted 37% as long as during their initial no-load test.

Since the DeWALT saw ran nearly twice as long as the Milwaukee in the initial no-load test, I anticipated twice the performance cutting wood. That theory, however, did not hold true. The DeWalt saw with the original XR2 battery was able to complete from 16 to a maximum of 27 cuts through the 2x4 lumber, operating for an average of five minutes, 40 seconds. This work output matched that of the Milwaukee saw. The DeWalt batteries powered the saw under load for approximately 25% of their no-load run time.

The A-Pillar Metal-Cutting Test

To simulate a typical vehicle rescue scenario, I developed an A-pillar test. In this evaluation, one firefighter used the same reciprocating saw to cut through the same front A-pillar of a car. As cuts were made, times were recorded at the completion of each cut. Each test stopped when the saw’s cutting action stopped.

The Milwaukee reciprocating saw made 10 to 12 cuts through a typical A-pillar. The battery lasted from six minutes, 37 seconds to seven minutes, 43 seconds of operating time.

For the DeWalt A-pillar test, I used both an original XR2 battery and the upgraded XR+. With the XR2, the DeWalt saw typically operated for seven minutes and cut approximately 12 slices off an A-pillar. Fitted with the new-generation XR+ battery, in excess of 20 A-pillar cuts were completed with the saw running from eight minutes, 20 seconds to almost 121?2 minutes.

The Power Hawk 12-Volt Battery Test

Curtiss-Wright manufactures the Power Hawk line of extrication equipment. Its system operates all its components off 12-volt DC electrical current. In a cooperative venture with Milwaukee, the Power Hawk product line now includes a kit to power a Milwaukee 18-volt reciprocating saw off the system’s 12-volt power pack. This 12-volt battery is huge compared to the small 18-volt batteries used on the cordless saw and gives the saw a remarkable run time.

The adapter fits only the Milwaukee cordless reciprocating saw and retails for approximately $416. This includes the power cable and the 12-volt adapter that fits on the saw handle.

I conducted tests to measure the work-output difference between a Milwaukee recip saw with the Power Hawk 12 battery pack and one connected to only a single 18-volt battery. One firefighter with the Milwaukee saw and the Power Hawk battery pack cut through the B-pillar of an automobile seven to 10 times, simulating the average work capability of a single 18-volt battery. B-pillar cuts require more effort than A-pillar cuts because of the thicker materials that comprise the pillar. In addition in this test, one of the cuts not only went through the B-pillar, but also sliced through a Grade 8 backing plate of the seatbelt assembly. Milwaukee Torch blades were used.

Seven B-pillar cuts required five minutes, 20 seconds to complete. Upon completion, the Power Hawk battery pack indicated that 76% of its energy remained after all cuts were completed. At that rate, it is estimated that use of Power Hawk’s 12-volt power unit lets the reciprocating saw operator cut for at least 22 minutes, four or more times the work possible with a single 18-volt battery.

The Nomad Battery Pack Test

To answer objections of short run times for individual 18-volt batteries, the Fiskars Energy Systems Co. of Wausau, WI, introduced the Nomad 7000 Energy System. The Nomad unit lets the user connect three DeWalt 18-volt batteries in a parallel circuit and store them in a portable backpack-style carry pouch. All three batteries are fitted with end caps inside the pouch, connecting them into one electrical circuit.

Extending from the pack is a thick coiled cord with an end piece that resembles a DeWalt battery. This attachment is the power conversion unit microprocessor, which converts the energy from the three batteries to sufficient voltage to power the reciprocating saw. Another feature of the new Nomad unit is that it comes with a built-in trickle charger. Connecting the Nomad to a 110-volt power source will let all three DeWalt batteries charge while inside the Nomad pouch. Because it is a trickle charger, however, it takes 12 to 14 hours for all batteries to fully recharge.

Using DeWalt’s original XR2 batteries in the Nomad battery pack, saw operators were able to complete the following evolutions:

• Seven A-pillar cuts
• Two B-pillar cuts
• Five C-pillar cuts
• Seven Nader pin cuts
• Four hinge leaf cuts
• One brake pedal shaft cut
• Four steering wheel ring cuts
• One steering column cut.

This test exhausted several saw operators and consumed six DeWalt nine-inch/14-tpi blades. In two other tests, the Nomad powered the saw through 12 minutes, 13 seconds of actual cutting time and 12 minutes, 43 seconds of aggressive cutting. The last test wore out three Torch blades and let me complete the following:

• Eight A-pillar cuts
• Four B-pillar cuts
• Four Nader pin cuts
• Four hinge leaf cuts
• Two steering wheel ring cuts

When the Nomad pack was equipped with fully charged DeWalt XR+ batteries, cutting time increased to a remarkable 18 minutes, 36 seconds.

Ron Moore, a Firehouse contributing editor, is a battalion chief and the training officer for the McKinney, TX, Fire Department. He also authors a monthly online article in the Firehouse.com “MembersZone” and serves as the Forum Moderator for the extrication section of the Firehouse.com website. Moore can be contacted directly at [email protected].