Monitor cell balance / status three by three $50-solution
Just ordered 6 pcs of "Lipo Battery Low Voltage LED Tester Meter 1S-8S Buzzer Alarm Indicator" sold on Ebay for about 3 USD each including shipment.
(a cut and paste from the product description)
Use for 1-8s Lipl/Li-ion/LiMn/Li-Fe
Voltage detection pricision: 0.01V
Unit voltage display range: 0.5V-4.5V
Total voltage display range: 0.5V-36V
1S test mode voltage range: 4v-15v
Low voltage alarm mode for 2-8S
Alarm set value range: OFF-2.7V-3.8V
When the voltage is below the set value,it will buzzer with red LED light,pre-set value 3.3V.
Push key which can change the voltage settings and save.
I plan to use three Ethernet patch-cables for each battery-box because it's cheap and available.
Those modules fits in to a old IDE hard drive cables or any other socket with 2,54 (?) split.
A connection on every third cell would give proper input to this LiPo-device, and since the alarm can be set to trigger between 2.7V-3.8V I assume this will work pretty good to find the worst cells in the package.
Together with 35pcs of ring terminals and 35pcs of 3A car fuses (spade fuses?) it would be possible to find week cells both visual and audibly during riding.
This solution would cost about 50 USD and some work effort.
I do not know how to disconnect them, it might be possible to add a tiny relay on the ground of each module. But I do not know if the module will continue to draw current. But I will add this info as soon.
I will post any progress as soon as the parts arrives.
Very interesting, please keep us posted with your progress.
How's the accuracy/precision on these modules? I bought two of those and a cell-log to monitor my 24 cells, but until I resolve how best to add a 30A charger, I'm holding off on modifications.
The folks over at ES, had hinted to putting a switch on the NEG pin to reduce current draw. Hoping same holds for these devices. Amazing how puny these RC devices are. I was expecting something much bigger.
So far so good.
Just ran a quick test over 9 cells, 3+3+3.
Did set the alarm level to 3,6V and connected a 12V 100W bulb.
After 30sec the "thing" started beeping and flashing indicating an issue in the cell 1-3 area.
Measuring with a mutimeter confirmed that one cell was dropping, while the other 8 stayed a little above 1,2V.
So it looks very promising, and I will continue with at modification of the whole pack.
Now my modified packs are mounted on the bike, and it works very well!
It turned out to be pretty noisy when the battery had low charge, and the "gizmo's" was set to 3,6V.
It also tock two Y-connectors to join the front and back pack, since two of the modules measures cells in both packs.
I regret not buying TP-cables of higher quality, since the cheap ones on Ebay had extremely thin wires, insulations was party missing, and the metal (not cupper) in the leaders was not possible to solder.
The red and black 1,5mm2 cables will be used for handlebar heating, and external EQ-charging, all secured with 10A fuses.
What's left is to do some kind of mounting of the monitoring-buzzers.
I have used 2A car fuses, and soldered a ring-terminal directly on to it. Squeezed a flat-isolated-female-terminal to the network cables.
It took a spread cheat to be able to get all the connections in the right place.
Now there is a video available on Youtube, showing monitoring of 2/5 of the cells.
It works well, and a solution I can recommend to implement if you tear down your battery pack.
I do not (yet) have the device connected constantly, only from time to time to make a "health check".
I can recommend useing high quality Ethernet cables, an not the low cost ones I bought, which I now regret.
I'm planning to search for the lowest cells and replace them, without spending too many hours.
I've just bought 2 voltage monitors of 8s, like the ones in the video. An Imax b8 is heading for home and it will soon arrive.
Each voltage monitor can check 24 cells. The imax b8 can charge: NiCd/NiMH battery cell count: 1-27cells
I can Charge and discharge 3 groups in series of 9(8) cells each time, totaling 27 (24) cells. With 4 tests I can check all 102 cells of the pack. During discharge, as soon as an alarm beeps, I will have found the weakest cell. I may carry further discharge in smaller groups to find the second weakest cell. If the discharge amount of the entire serie is above 26 Ah, i won't replace any cell at all.
I have tested this monitoring solution in My LI conversion. 40S 40Ah, with the MINIBMS setup to beep an alarm if any cell goes under 2.5V. And it never gave any beep signal during the entire recording.
The monitoring devices do not work properly under hi-discharge conditions. They are affected by some kind of electric noise, because displayed readings tend to be inaccurate: they can show a dying cell at 1.99V and immediately an overcharged cell at 4,02V under same discharge conditions, which is impossible.
The video is composed of 4 parts:
1- voltages 1h after a full charge, battery at 135V
2- voltages when full charge is ending, 137V
3- voltages under light load, 128V
4- the interesting part: voltages under hi load, 120V
Monitoring devices are set to beep under 2.7 Volts
The battery was at 12Cº
Anybody tried this cell loggers?:
Do they work?
Yes, used 3pcs on my old 24 cell scooter:
Worked quite well and with the "S-version" you can record and read (via computer) the voltage of each cell after a ride.
This is a very good way to check the status of the cells because you see how they perform under different loads.
Take some work though with 5 cellogs.
R, I'm using one of them also with my xm3500li.
I have my pack wired for balance charging 4x 5cell, so I just use that logger on 4 days of commuting over the same general route, monitoring 5 cells at a time. Then look for the cells that drop lower than the rest.
thanks Johnny J and TeamSlacker.
I've just tested one logger device on 7 cells. The logger works perfectly. However The results are quite scary: accelerating to 120V, some cells drop to 3.1v, some other to 2.9!
I'm going to need five of them, like this: