yes Ahmet, The plan is to leave all elements connected and monitor the voltages at the same point in the series pack.
I considered a resister network to monitor at the midpoint, but was concerned about some current draw on the pack.
I decided to connect at the 3rd cell in the series pack. NIMH max voltage is approx 1.4 volts this would have a theoretical max voltage of 4.2V.
I have used an arduino Nano to monitor at these points. It has 8 ADC ports on it.
I beleive they would have minimal drain on the pack.
My test so far is with 6 strings and have connected it to the arduino.
After a charge to 14 volts for the pack, my cells are in ballance withing .03Volts
I will test with a load in the next few days to see how they respond with charge/discharge cycles.
I am able to monitor the pack and send voltage reading to my PC at this point.
I will need to do some programming on the PC to massage the data though.
I am quite positive at this point with the balance of the pack after a charge cycle.
Mark
From: "sv8827 sv8827@yahoo.com [electricboats]" <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Saturday, November 4, 2017 9:43 AM
Subject: Re: [Electric Boats] Re: Battery monitor idea
If I am not mistaken the idea is to leave all the elements of the bus connected in the circuit and sense a midpoint in all series branches. For example if a cell in the lower part of a given branch has shorted, the midpoint will sag about 10% to about 4/10 of the bus voltage instead of half (ie 5/10) of the bus voltage. Once the branch with a defective cell is determined automatically by periodic polling of voltages on the points marked with X with respect to ground and an alarm is activated, the operator could cut out the defective branch quickly before cells get overcharged and find the defective cell by measuring each cell in the branch manually and maybe repair the defective cell if possible. Very clever and practical idea.
Maybe a pair of 100k resistors in series with a 22k in the middle sets about +/- 5% window for the center point of the bus and each measurement of the points marked with X is compared to this window? Maybe connect a heavy load on one cell and measure the midpoint voltage to test the system and/or determine the optimum window. Too narrow a window is likely to results in false alarms and too wide a window will miss a failure. I would appreciate if Mark shared his findings after the project is finished.
Cheers
Ahmet
GND |--|--|--|--|--|--|--|--|--|--| +12V NOM
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| X |
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| X |
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| X |
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| X |
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| X |
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| X |
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| X |
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| X |
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| X |
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| X |
|--|--|--|--|--|--|--|--|--|--|
| X |
|--|--|--|--|--|--|--|--|--|--|
| X |
From: "boat_works@yahoo.com [electricboats]" <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Friday, November 3, 2017 10:37 PM
Subject: [Electric Boats] Re: Battery monitor idea
Maybe I'm missing something here, but since you'll need to isolate the parallel connections to be able to check voltage on an individual series string, do you have an easy way to do that? Plug-in jumpers, maybe? Otherwise monitoring would seem pretty tedious....
-Tom
-Tom
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Posted by: Mark F <mark.internet@yahoo.ca>
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