TOP BALANCING THE BOTTOM

When I started bottom balancing the second battery module, readings were taken on each 1/2 cell. There are two individual groups of pouch cells within each cell that are hooked in series, with each side reading around 3.85 volts to the center terminal or 7.7 volts across the entire cell.

POUCH CELL

ASSEMBLED CELL CUT AWAY

CELL SHOWING THE TERMINALS

SIXTEEN CELL MODULES

When initial readings were take across the entire 16 cell module, it measured 124.5 volts and each of the half cells were within a couple hundredths of a volt of each other, so I assume the Better Place Battery Management System (BMS) was top balancing the individual cells. After draining the entire module down until the lowest cell was 2.6 volts, I let the pack sit for a couple days and took readings on each half cell again, this time trying to identify the highest half cell. The lowest had come up to 2.85 volts and the highest was up to 2.95. By the end of the day the highest cell had come up to 3.04 volts, so I hooked the two 150 watt quartz lights up and drained the pack down until the highest cell was at 2.6 volts. The lowest cell had gone down to 2.45 volts. Then I hooked up the 40 watt bulb and let the voltage start climbing back up at a lower amp draw. Once the voltage climb stopped, I turned off the 40 watt bulb and turned on a 15 watt night light. I always put a note on my computer that the batteries are discharging so I will not forget to stop the drain before going to bed. 

I may need to repeat this process several times before the half cells finally stabilize below 3 volts. Once they have set for several days and are all under 3 volts, I will use the Powerlab6 to bring them all up to 3 volts. Kind of like top balancing the bottom, as the Powerlab6 will not automatically shut off at a voltage under 3 volts when charging and if you try and discharge them below 3 volts, they just keep drifting back up. It seems that charging to bring them all to the same level at the bottom works better and gets them all to a more uniform voltage.

The LiMn2O4 cells operate at a higher voltage range that the LiFePo4 cells at at around 3.9 resting voltage (give or take) as opposed the the 3.36 volts of the Lithium Iron Phosphate cells and there isn't a lot of information on bottom balancing LiMn204 cells yet. Jack Rickard of EVTV reported that they just did not want to stabilize below 3 volts and said that is now the voltage he is using, so that is where I came up with using 3 volts.

After an hour or so with the 15 watt night light hooked up the highest cell stabilized at 3.809 volts, so the light was shut off and I will wait until Wednesday night to check all of the individual cells again. By next weekend, if they are all below 3 volts, I will start bringing them all up to 3 volts with the Powerlab6, if not, I will drain the module down until the highest cell is 2.6 volts and wait another week to see if it stabilizes below 3 volts.

Until next time,

Randy

PS. Still searching for the lost connectors!

WIRING COMPLETION IS LOOMING AHEAD!

Saturday the MC4 Cable Connectors arrived, so the connection was made through the fuse to the positive side of the battery pack for the heater. The diodes for 12 volt positive power, that I had originally thought were needed, arrived also but upon closer inspection of the correct schematic, found that there is a relay that puts power to the fan switch when the heater button is in any position but off. This circuit will make sure the fan is always running when the heater is turned on.

HEATER SCHEMATIC

After the MC4 connectors were made up and the fuse installed in the circuit, the final connection to the traction pack was made.  Then work moved to the inside of the car to make up the control wiring to 12 volts. All of the circuit is completed and ready to connect to the heater control unit when the center console goes back in.

FUSE INSTALLED HEATER CONNECTED

12 VOLT HEATER CONTROL CONNECTIONS

Earlier Saturday morning, I made a trip to Jo Ann fabric and picked up some grained vinyl to cover the top plate on the center console, where the Dell Venue 8 will be mounted. The vinyl was cut and adhesive was used to attach it to the wooden top cover plate. Part of the vinyl was clamped in place and while the adhisive was drying, work was done on other projects. Getting the vinyl attached was a little bit of a challenge, but it ended up working out nicely.

CENTER CONSOLE TOP COVER CLAMPED

TOP COVER AND VENUE 8 MOUNTED

CONSOLE COVER BACK VIEW

Then to the motor compartment, where the wiring was run around the firewall, to determine how much wire will remain inside the car. The project was started on Saturday, so Sunday Morning, I continued by getting out my box of loom and installing it over the new wiring harness run. After the loom was installed, I made up the speedometer plug and started fastening the loom to the firewall. The run from the controller and pot box have not been fastened down yet, so now that all of the wiring is complete, can be attached.

WIRING HARNESS LOOMED

SPEEDOMETER CONNECTION 

The Better Place module was connected to a 40 watt light bulb and readings were taken on each cell to determine the lowest one. As expected, the voltages went down as measurements were taken from the first cells bottom balanced to the last ones. The first few cells were back up to over 2.9 volts and tapered down to the 2.7 range on the other end of the module. The JLD404 is connected to the lowest cell and will be drained down until it reaches 2.5 volts, which is actually around 2.595 volts when measured with the volt meter. Then the pack be allowed to sit for a week or so and try and the low cells will be charged back up to 2.7 volts with the Powerlab 6. I am not sure this will work but it is worth a try, as trying to bottom balance all of them to 2.7 volts through discharging is not working.   

BOTTOM BALANCING CONTINUES

I needed to get a piece of aluminum bar, more loom clamps, and some screws to mount the clamps, so it was time to make a run to Millersport Hardware. Do It Best Hardware seems to be a bit less expensive than the Ace Hardware in Baltimore, OH but the Ace has a better selection of stainless steel fasteners. When I left the hardware store is was just about Beer:30, so I stopped at Valero and picked up a 6 pack of Sam Adams  Rebel IPA. After enjoying a couple if them, it was time for a little NAPcar along with the EVTV Weekley Show. It was getting rather warm outside, so thought it was a good time to take a break before continuing work on the Fiero this evening.

So entertained and refreshed, I went back out and made brackets for the wiring harness runs, while continuing to monitor the Better Place battery module discharge. When I came in around dark, the lowest cell was at 2.58 volts and the highest cell was around 2.75. I am hoping to bring the pack down enough that the highest cell is around 2.7 volts. I have a small night light hooked up and I am hoping that by discharging at a low amp level, the cells will not drift back up as much.

Anyway, that's it for this week, 

Randy