Product Review: Bluetooth Multimeter
In Product Review: Automotive Battery Load Tester, I wrote about troubleshooting a difficult to diagnose battery drain on my ’02 Mustang GT. The preliminary diagnostics ruled out an obvious problem with the battery, alternator, starter, or parasitic battery drain.
To conclusively rule out an intermittent parasitic battery drain, I needed to use an electrical multimeter to continuously take readings over a period of 24 hours and provide an exported data file to load into a spreadsheet to look for intermittent data spikes.
The standard procedure for measuring parasitic battery drain is to connect a multimeter in series with the negative battery cable to measure electrical current. That means leaving the hood open for the duration of the test because my vehicle has a low hoodline. But I park overnight in a lot and not a garage, so this isn’t a great option for me. Instead, I created a simple custom 12V test cord to plug a multimeter into the 12V auxiliary outlet inside the vehicle. This will measure voltage instead of current, but that will supply the information I need. I’ll be looking for any intermittent drops in battery voltage over a 24-hour period. If I find any, that implies a parasitic battery drain.
I created a custom 12V test cord using two inexpensive items from Amazon:
2 ft. cigarette lighter extension cord ($6)
Insulated Multimeter Test Leads 4mm Banana Plugs ($12)
I also purchased the ANENG AN9002 Bluetooth multimeter with an Android app, from Amazon ($35). Reading and recording continuous data from the AN9002 multimeter involves connecting the Android app to the meter using Bluetooth, and then configuring the meter to continuously send the voltage readings to the app. With that set up, I plugged the meter into the 12V outlet inside the center console, locked the car, and then took my phone running the Android app with me into the house and left the phone near a window.
That worked well for several hours, but without any error message the app locked up sometime after 10 hours of data collection and I was unable to save the data to the phone at that point. All I could do was restart the phone, reconnect the app, and start all over. I tried the experiment several times, but every time app locked up sometime after 10 hours and I lost all the data. So, I packed up the AN9002 and sent it back to Amazon for a refund.
Next, I purchased the OWON OW18E Bluetooth multimeter from Amazon ($55). A little more expensive but it had a much better data collection feature. After you connect to the meter with their Bluetooth Android App, you send a command to the meter to begin data collection to the meter’s internal memory, and then the app automatically disconnects. After 24 hours, I started the Android App again, reconnected to the meter, and downloaded the collected data to a file on my phone. Simple, effortless, and reliable. Although, sometimes it would take me several attempts to get the App to connect to the meter. I also bought two rechargeable 9V batteries ($14) for the multimeter since I didn’t know how long the 9V battery in the meter would last when leaving the meter on continuously.
Next, I connected the phone to my PC to examine the data file. The battery voltage slowly and smoothly decreased from 12.7V after parking it to about 12.4V (80% capacity) in the first 24 hours. (Technical note: before I started the 24-hour data collection, I drove the vehicle on the interstate for 45 minutes to make sure the battery was fully recharged.)
That’s not good. The battery is less than six months old. In my previous article I confirmed that the battery draw when the car is parked is a very small 10mA. The battery capacity should have remained well above 90% after 24 hours. A close inspection of the voltage readings over 24 hours shows a steady, slow, decrease from 100% to 80%. There are no inconsistent, larger, intermittent, voltage drops in the data indicating a parasitic draw. Technical note: the meter reliably measures hundredths of a volt, and the battery voltage did slightly increase and decrease in sync with an outdoor temperature swing of about 20F over 24 hours, but this is expected and normal.
The test is easy to set up again, and I only drive this vehicle about once a week, so I ran a second test for a continuous duration of six additional days. In the next six days the battery slowly and smoothly decreased an additional 10%. This is acceptable. But the initial loss of 20% capacity in the first 24 hours is not.
At this point I suspect I just have a permanently weak battery that isn’t going to hold a charge over 80%. But I also discovered that the battery is dipping to 9.5V during starting/cranking which is generally considered the minimum value that can be considered OK. The battery load tester I used in my initial diagnostics did not flag this as a problem, but research on the internet is telling me that it is.
To sum up, I probably have a battery that is going to need to be replaced again within a year or two. And I don’t really know why. So, my next step is to confirm that starter cranking current is in an acceptable range and also perform a more thorough analysis of alternator output current under different conditions. For that I ordered the BTMETER-BT-605A current clamp to plug into the multimeter.
The OWON OW18E Bluetooth multimeter with an Android app and data recording capability worked very well. However, it usually took several attempts to get the App to connect to the meter. With a little more effort, their software developer should be able to automatically smooth out this rough edge with some intelligent reset/reconnect Bluetooth logic so that the the App automatically retries the connection instead of making the user do it manually. An additional concern I have is the 9V battery connection. Instead of a standard 9V PP3 snap-on connector, a poorly designed proprietary battery dock is used. After replacing the battery about 4 times, the foam-spacer in this dock was already losing its ability to tightly hold the battery up against the internal contacts. But overall, I really like this product and give it a rating of 4.5 stars.
Stay tuned for a follow-up article on measuring starter and alternator current…
