by Dave Conklin
The website theprepared.com challenged DayZero to pull 5 of our hand-cranked generator water boxes off the shelf and turn the crank 10,000 times on each one.
The Test Rig
We built a test stand that uses an electric motor to turn a wooden disk. The handle of the generator crank fits loosely through a rectangular hole in the disk. We added a timing circuit and two counters. The timing circuit runs the motor for 68 seconds and then turns it off for 22 seconds, and repeats the cycle until power is switched off. The 68-second ON time accounts for the 8-10 turns it takes to get the UV light fully on, followed by one minute to achieve the required 40 mJ/cm2 dose. The short 22-second OFF time permits the test to be completed in about 3 hours. One counter records the number of revolutions of the wooden disk, and the other counter records the number of 68-secs-on-22-secs-off cycles.
Testing… Testing… Testing…
We tested five WB-GX units from our inventory, serial numbers 021, 040, 039, 022, and 017. All 5 passed the test successfully. In each case, the UV bulb still burned brightly after more than 10,000 cranks. Details for each of the 5 units are given below.
Test 1 – (and some problems)
Unit 021 was tested on 5/22 with the test stand set up at David Holman’s shop. The test ran from 1:55 to 4:30 pm, completing 10,158 crank revolutions and 120 cycles. David H continued running the same unit in 2 more sessions. From 6:54 pm to midnight, 17,877 revolutions and 172 cycles were completed. From 5:33 am to 9:42 am on the morning of 5/23, an additional 14,336 revolutions and 172 cycles were completed. The test was stopped when it became clear that the test stand had gotten out of alignment.
The test stand was moved to Dave Conklin’s shop on 5/23. A 12 mm hole was drilled in the wooden disk at the axis point to allow aligning the drive shaft and the generator shaft with the wooden disk in place. Operation with unit 021 revealed that drilling the hole in the disk had introduced some wobble in the connection between the disk and the drive shaft. The wobble increased the amount of power required to turn the disk and generator, overloading the drive motor.
The Test Rig Revisited
On 5/26, a metal plate was inserted between the wooden disk and the aluminum bar turned by the drive shaft, to stabilize the connection between the disk and the drive shaft. The metal plate has a 6 mm hole at the axis of the disk to allow for alignment while the disk is in place on the drive shaft. In this new configuration, supplying 21 V to the drive motor results in a current draw of about 2.5 A, within the nominal 2.85 A rating for the motor.
Tests 2-5 – Smooth sailing
Unit 040 was run successfully on the test stand from 12:24 pm to 3:21 pm, completing 10,046 crank revolutions in 117 cycles. At the end of the test, the drive motor was quite warm, while the electronics enclosure on unit 040 was slightly warm. The drive motor was run at 20.9 V and generally drew about 2.5 A.
Unit 039 was placed on the test stand later that same day, 5/26. It was run successfully from 5:33 pm to 9:10 pm, completing 11,401 crank revolutions in 131 cycles. The drive motor ran at 20.9 V and generally drew about 2.1 A. At the end of the test the drive motor was hot, while the electronics enclosure on unit 039 was only slightly warm.
The next day, 5/27, two more units were tested. Unit 022 was run successfully from 8:02 am to 10:58 am, completing 10,129 crank revolutions in 117 cycles. The drive motor ran at 20.9 V and drew 2.4 A.
The fifth unit, unit 017, was run successfully from 1:16 pm to 4:11 pm, completing 10,005 crank revolutions in 115 cycles. The drive motor ran at 21.0 V and drew 2.7 A.