I agree with James that monitoring temperature and voltage of every cell is the safest way to go.
From: "James Lambden james@electroprop.com [electricboats]" <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Monday, November 6, 2017 10:51 AM
Subject: Re: [Electric Boats] Re: Battery monitor idea
I agree with Mark that midpoint monitoring is better than no monitoring.
Thanks
Ahmet
NOTE :
Yes in a 24V bus with elements consisting of 6V or 12V batteries using midpoint monitoring with a +/- 5% window would miss 11V and 13V samples, but a +/- 4% window would detect the problem. The importance of window size was mentioned earlier.
From: "James Lambden james@electroprop.com [electricboats]" <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Monday, November 6, 2017 10:51 AM
Subject: Re: [Electric Boats] Re: Battery monitor idea
Midpoint monitoring is a fast and easy way of establishing the pack has errors but is not infallible.
A string of 4 batteries could produce an error where mid point monitoring did not work
consider 4 voltages
11, 13, 12, 12
Midpoint monitoring in this case would not work so well. If you were going the mid point monitoring route, you would need to look for the slightest deviation of the midpoint.
I have seen conditions like this.
Midpoint monitoring is not enough. The only way to guarantee safety is to monitor temperature as well as voltage.
Once you get into large currents which we all have with discharge, and more will have with charging in the future, then it becomes imperative to monitor every thermal unit.
With Lithium there are plenty of Battery Management Systems that can monitor every cell, so no need to go this route with Lithium.
Lithium is easy because any computer can monitor voltage directly up to 5 volts. Lead acid is more difficult because you need a voltage divider to monitor a 6 or 12 volt battery with a computer.
James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
On Nov 6, 2017, at 3:02 AM, Mark F mark.internet@yahoo.ca [electricboats] wrote:
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 .03VoltsI 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.CheersAhmetGND |--|--|--|--|--|--|--|--|--|--| +12V NOM
| X |
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| X |
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| X |
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| X |
|--|--|--|--|--|--|--|--|--|--|
| 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
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Posted by: sv8827 <sv8827@yahoo.com>
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