2 12 volt batteries, 24 volt battery test

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2 12 volt batteries, 24 volt battery test

Postby imcgyver » Thu Jan 20, 2011 6:59 pm

Hello, I was wondering on the battery test for a 24 volt system the instructions say to test battery seperatly, question do I set the program to 12 volt or 24 volt for 2 12 volt battery 24 volt system?
Thank you for your time and response.

Re: 2 12 volt batteries, 24 volt battery test

Postby ziko » Wed Jan 26, 2011 2:34 pm

Hi you may have to do the test twice, once for each battery.

Kind regards

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Re: 2 12 volt batteries, 24 volt battery test

Postby Pinpoint » Fri Dec 21, 2012 11:04 pm

So what's the point of having a 24v option in the first place?.?.?.?.
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Re: 2 12 volt batteries, 24 volt battery test

Postby Robski » Sat Dec 22, 2012 7:14 pm

So what's the point of having a 24v option in the first place?.?.?.?.

What would you do if you wanted to load test with lets say a Midtronics battery tester ?

One at a time or both together ?
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Re: 2 12 volt batteries, 24 volt battery test

Postby antthecat » Sun Dec 23, 2012 12:10 am

I'm guessing 24v is for the heavy goods market.
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Re: 2 12 volt batteries, 24 volt battery test

Postby FioranoCars » Mon Dec 24, 2012 2:36 am

i will admit that as we not longer have a lorry with 24v i have not done this test, but the theory is...

i assume the batteries are wired in series right next to each other ? Therefore producing 24volts ...

Then the test should be using the 24v option not 12v, but testing both batteries together ie putting the probes across the terminals where the vehicles supply leads leave the battery area (one to chassis and one for positive to where ever it goes) ... did you look at the graph to see what you did capture? can you post you data file?

if you were to test each battery individually then use 12v and put the probes on to the terminals of only one battery at a time. however i am not sure this will give a true reading and have never tried it. you could not do the extended tests as volt drop calculations would be wrong.

if unsure, use a multimeter set to volts in the same position you plan to use the pico probes, the dmm will show how many volts you have at that point in the battery config. if you have your probes in the wrong places the program will not give useable results.

if you still struggle to get good results try a known good vehicle with similar battery setup, or try to just take a battery voltage vs amp clamp reading in picoscope over an 8second timeframe while cranking the engine to start ... you should see the volt dip as it cranks with amps peaking ... basically seeing the compression cycles of the engine.

hope you get to the bottom of it!
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Re: 2 12 volt batteries, 24 volt battery test

Postby Alan » Mon Dec 24, 2012 8:59 am

The problem with testing 2 x 12V batteries at the same time (as if a single 24V battery) is that if one is "good" and one is "bad" then the results are inconclusive / misleading.

To deal with the 2 x 12V situation we will be adding an improved 24V test during 2013 that can only be done with a 4 channel scope. This will give independent results for both batteries.

For now its best to test the 2 batteries separately but a word of caution when you do this. There is no issue in testing the first battery (the one that goes to chassis ground) but if you measure across the second battery you are measuring (with respect to chassis GND) 12V to 24V. This breaks the "golden rule" where the black lead should never be connected to anything other than 0V. If you do use this method make sure there are no other ground connections between the vehicle and the scope / laptop. Just use one channel for the current clamp and the other for the battery. Do not connect up any more channels. Do not charge the laptop from the vehicle, do not use a scan tool connected to the PC etc. If the scope or laptop gets grounded to the vehicle when you do this test then the readings will be wrong and you may trip the self resetting fuses inside the scope.
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