TOOLS REQUIRED
This process requires a voltmeter and a leaded resistor to perform (~300-330 ohms for a V1 Motion Sensor Battery).
STORY
I had a V1 Motion Sensor I needed to reactivate, and a batch of used CR2450 batteries. I did a quick no load-voltmeter only test on them and picked the top performer to use (3.119V on a 3V battery). Sounds perfect, right?
Well, the motion sensor wouldnât even light up (it should blink once when activated). So it was completely inoperative.
Now obviously, I didnât need to measure the batteries to find the highest-voltage unit. All I really had to do was pop them into the motion sensor one at a time until one flashed the light. But this article is about selecting a battery from several used units to find the one that will last the longest, and to illustrate why testing them unloaded does not tell you that (or much of anything, actually).
So I called up the CR2450 battery spec, and it said in order to test the âpulseâ condition (a high short-term load the battery should be capable of) to use a 300-ohm resistor and a test goal of 2.7V.
So thatâs what I did. This simulates the motion sensor going from its quiescent state when the sensor is in standby, to a pulse current when the sensor wakes up and transmits.
My sensor was not waking up and transmitting, which is indicated by the light blinking when you install the battery (it is trying to report motion â your body installing the battery).
I didnât have a 300-ohm resistor, so I used a more common 330-ohm size.
The pulse load is a high load, so you really donât want to leave it on the battery long. It is not a heat risk; the 300-ohm resistor will only draw 9mA at 2.7V, which would be less than 1/40th of a watt. The voltage will move as the load is measured, so what you want to do is just apply it and a few seconds later take the âgistâ of the measurement (for me that was to 2 decimal places). The highest voltage battery under that condition will last the longest.
The result on the battery I used above was that the output was less than 2.7V when loaded, a red flag.
So I tested all 9 of my used batteries, and 2 new ones. The results are in the table below.
RESULTS
You will notice ALL batteries measured above 3V unloaded, so all might otherwise be considered good (they all actually all measured above 3.1V)! Even loaded with what the battery manufacturer considers a constant load (7500-ohms), they all were still above 3V.
However when pulse-loaded, the 3 batteries that failed to light the light on the sensors were clearly below the ones that worked. They were all also the only batteries below the 2.7V target voltage.
As an example of âunloaded measurements donât workâ, notice that battery #3 had the HIGHEST voltage of the used batteries unloaded (this is the one I started with), but failed to run a sensor and measured below 2.7V when pulse-loaded.
Also, battery #1 was the LOWEST voltage of all batteries when unloaded, but still ran a sensor and had a greater than 2.7V measurement when pulse-loaded.
So unloaded doesnât work as a way to test batteries for a V1 Motion Sensor. Or for many other devices.
This process can apply to most any battery-operated device. Just do an Internet search for the batteryâs spec sheet, load the battery with the heavier load, and pick the battery that has the highest voltage in that condition.
Caveat: Donât use this process for 2-battery configurations â those should always be replaced in pairs with new batteries. Single-battery configurations only.
RAW DATA
NO LOAD (Voltmeter Only) (this test did not find the bad batteries)
âBadâ indicates a battery that wouldnât operate a sensor
Test goal = 3V
Bat# | Condition | No Load |
---|---|---|
1 | Used/Good | 3.101 |
2 | Used/Good | 3.108 |
3 | Used/Bad | 3.119 |
4 | Used/Good | 3.118 |
5 | Used/Bad | 3.109 |
6 | Used/Bad | 3.114 |
7 | Used/Good | 3.116 |
8 | Used/Good | 3.118 |
9 | Used/Good | 3.117 |
10 | New/Good | 3.185 |
11 | New/Good | 3.233 |
7500-ohm âConstantâ Load (this test did not find the bad batteries)
âBadâ indicates a battery that wouldnât operate a sensor
Test goal = 3V
Bat# | Condition | 7500 ohms |
---|---|---|
1 | Used/Good | 3.066 |
2 | Used/Good | 3.097 |
3 | Used/Bad | 3.087 |
4 | Used/Good | 3.094 |
5 | Used/Bad | 3.049 |
6 | Used/Bad | 3.091 |
7 | Used/Good | 3.065 |
8 | Used/Good | 3.093 |
9 | Used/Good | 3.103 |
10 | New/Good | 3.180 |
11 | New/Good | 3.226 |
330-ohm âPulseâ Load (this test DID find the bad batteries)
âBadâ indicates a battery that wouldnât operate a sensor
Test goal = 2.7V
Bat# | Condition | 330 ohms |
---|---|---|
1 | Used/Good | 2.82 |
2 | Used/Good | 2.94 |
3 | Used/Bad | 2.62 |
4 | Used/Good | 2.87 |
5 | Used/Bad | 2.2 |
6 | Used/Bad | 2.61 |
7 | Used/Good | 2.80 |
8 | Used/Good | 2.85 |
9 | Used/Good | 2.91 |
10 | New/Good | 3.08 |
11 | New/Good | 3.10 |
So the longest lasting batteries will be in the order of:
11, 10, 2, 9, 4, 8, 1, 7 â with 3, 5, and 6 going to the trash.