PicoScope 7 Automotive
Available for Windows, Mac, and Linux, the next evolution of our diagnostic scope software is now available.
Dual 12V Batteries
Dual 12V Batteries
When performing the battery test on a 12V system equipped with "dual" batteries (two 12V batteries in parallel). Should I connect my scope as directed in the proceedure and simply double the CCA then proceed with the test as normal? Is this still going to be a valid test for both batteries?
Thanks.
Thanks.
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Steve Smith
- Pico Staff Member
- Posts: 1594
- Joined: Sun Aug 25, 2013 7:22 am
Re: Dual 12V Batteries
Hello and thank you for the post
Using the Pico Diagnostics (PD) battery test for testing dual 12 V batteries in parallel would only return a “collective” result for both batteries based on total voltage drop and current draw
The following link describes how the PD battery test calculates the displayed test results viewtopic.php?p=77701#p77701 which are dependent upon the load placed across the battery via the starter motor
I am not sure if the engine/starter motor you are testing has huge current demand sufficient to require both batteries or, if dual batteries are installed purely to provide additional current as and when required combined with additional capacity for vehicle duties (E.g., ambulances with tail lifts etc.)
With dual batteries in parallel there is a tendency for an underperforming battery to be “masked” and balanced by one exceptional battery and therefore it is better to test them separately
I.e., disconnect one battery and carry out the PD battery test, then repeat this process for the other battery.
If this is possible it is an option but clunky at best and if your engine/starter motor demand high current (i.e., using one battery would be unfair load) then testing both batteries in situ using PicoScope is the better solution
The image below (Thank you Ben) describes how you can monitor the performance of both batteries (voltage) and the individual current flow (contribution) from each battery during discharge (cranking) and absorption/charge (engine running with alternator active)
Note: The current flow will be reversed between cranking and charging as can be seen in the graph view of the PD Battery test
You may have to modify your connection technique (from image 1 above) if the battery lead arrangement differs, if access is limited (or impractical) or if you have only one high current clamp
Remember one current clamp will return the total current from both batteries when placed in the appropriate position in the circuit above (I.e. main positive cable to both Starter and Alternator)
If using the connection method in the image above..........
1. Using a math channel A - B will determine the difference in voltage between both these measure points (Subtracting each battery voltage from one another)
This should be very low indeed if your batteries are balanced and the volt drop in the connecting cables are at a minimum
2. For total current from both clamps you can create the math channel C + D
I hope this helps, take care…….Steve
Using the Pico Diagnostics (PD) battery test for testing dual 12 V batteries in parallel would only return a “collective” result for both batteries based on total voltage drop and current draw
The following link describes how the PD battery test calculates the displayed test results viewtopic.php?p=77701#p77701 which are dependent upon the load placed across the battery via the starter motor
I am not sure if the engine/starter motor you are testing has huge current demand sufficient to require both batteries or, if dual batteries are installed purely to provide additional current as and when required combined with additional capacity for vehicle duties (E.g., ambulances with tail lifts etc.)
With dual batteries in parallel there is a tendency for an underperforming battery to be “masked” and balanced by one exceptional battery and therefore it is better to test them separately
I.e., disconnect one battery and carry out the PD battery test, then repeat this process for the other battery.
If this is possible it is an option but clunky at best and if your engine/starter motor demand high current (i.e., using one battery would be unfair load) then testing both batteries in situ using PicoScope is the better solution
The image below (Thank you Ben) describes how you can monitor the performance of both batteries (voltage) and the individual current flow (contribution) from each battery during discharge (cranking) and absorption/charge (engine running with alternator active)
- Image 1
You may have to modify your connection technique (from image 1 above) if the battery lead arrangement differs, if access is limited (or impractical) or if you have only one high current clamp
Remember one current clamp will return the total current from both batteries when placed in the appropriate position in the circuit above (I.e. main positive cable to both Starter and Alternator)
If using the connection method in the image above..........
1. Using a math channel A - B will determine the difference in voltage between both these measure points (Subtracting each battery voltage from one another)
This should be very low indeed if your batteries are balanced and the volt drop in the connecting cables are at a minimum
2. For total current from both clamps you can create the math channel C + D
I hope this helps, take care…….Steve
Re: Dual 12V Batteries
Thank you, great information. I like the image 1 setup and will give that a go. I appreciate your help and time spent to give me more options and a better understanding of the battery test. This information will help others also.
Thanks.....Bob
Thanks.....Bob