26 Batteries and Balancing

Balancing Saga

Went out for a Sunday drive this weekend and about 3 miles in the drive the battery alarms starting going off whenever more than 60 amps (1C) were being pulled from the pack.  Seemed strange since the pack was just charged.  The battery monitors showed several cells with large differences (DIFF Error). The alarms was set to ring at 150mV difference across the sub-packs (6 or 7 cells).  After  the 100A draw, the monitors were showing 250mV differences for several cells.

Well this is what all of the posts on the web about balancing tried to say.  If the cells are not balanced, they will drift and eventually some the charge difference between cells will be enough to be noticed.

Well, we limped home from the Sunday Drive and the cells are returned to a nominal voltage of ~3.2V after a few minutes of rest so I know they were not too discharged, just getting low.

Nonetheless, this has prompted a full manual balancing process.  Picked up a Onxy 235 cell charger and balancer that can charge and balance 4 cells at a time at about 8 amps.  Tried it on one cell, it worked like a champ, tapering off current as the cell approached 3.6V.  Wired up the 4 cell balancing cable and one of the 4 cells had enough difference in charge that it hit the Upper Voltage Limit of 3.6V well before the rest, triggering the alarm.



So now, the charging process is down to trying to charge 4 at a time but if there is too much variance, resorting to single cell charging to get them all within a few percent of each other.  LiFePO4 batteries have very flat discharge curves, so a tiny voltage variation could equate to several AH of charge.  It seems the only real way to know is to top off each cell until the current draw from charging is quite low (<1A) and  the same cell-to-cell.



Near the end of the charge process, the cell voltage will spike up 0.2V to 3.6V. The charger is set to 3.6V so as soon as the cell hits that, the charging will safely stop.

Springs

Finally completed the Hi-Lo installs.  The fronts and rears are in and set.  Final right height, based on the factory spec of 53 inches at the roof, is 9.75" at the lower sill seam near the rear wheel.  The back is about 0.5" higher than the front which is normal for Classic Minis.  Looks good, handles well, and the ride is quite smooth now.  At this height there is sufficient compression at the springs when the wheels are off the ground to keep the springs in place.  Much lower and larger upper bump-stops would be needed.

Blower

A new blower was installed to cool the motor.   The leaf-blower, though effective was just too loud.  The new blower is Jabsco, 3" Blower, Flexmount, 105 CFM,   Much quieter and about the same CFM as the leaf blower.  Mounted much nicer also.

Computer Work

The work continues to refine the software running on the Arduinos.  Was able to connect the battery monitor Arduino to the Mini's fuel gauge so the gauge shows charge level now.   Used one of the PWM outputs on the Arduino (Pin 9) to drive the following circuit.

The PWM was set to a range of 0-205 to map from 0%-100% of the charge.  100% is still set to 48AH even though the batteries are 60AH cells.  This leaves 20% of margin.

Also added some more error messages to the Motor monitor to indicate different situations like over temp or low voltage or over current.

Wash and Wear

Wipers and Washers

For a bit of a distraction this weekend, I dove into the windscreen wipers and washers.  The wipers were operational, but very slow.  The washer was an unknown situation.

First was the washer motor.  It is shown below behind the washer bottle.  The motor was pulling current but would not spin.   It was simple to disassemble, just a few tabs to bend back.  It didn't look too bad inside for a 40 year electric motor that has been exposed to moisture its whole life.  The motor was frozen but a little persuasion and it spun free.  A few drops of lithium grease on the shaft and it was humming away.  The pump is in decent shape and just needed a little cleanup of the o-ring.

The washer bottle was another story.  It had a 4" crack on the back side where it slides into the mounting bracket.  Well, a little fiber-glass patch work and it was water tight and probably stronger than the original plastic.  Reasssembled the system system and water sprayed out of both nozzles.  Two issues still:

• The spray jets are positioned right under the wiper arms and thus very little water gets to the windscreen unless the wipers are going.    
• There is no switch to activate the washers.  The wire is behind the dash, but it is not clear where the switch is or was.  Some Minis have the washer switch on the turn-indicator stalk, but Jane's stalk is already full with high-beams and the horn.  A new switch will have to be added to the dash

Black Washer Motor behind yellowish washer reservoir. 

The Wiper motor shown here was mostly just gummed up.  After opening it, cleaning out the 40 year old grease (it wasn't very greasy anymore) and trying to clean-off as much exterior grime as possible, it now spins great with two speeds and automatic parking.  The park switch was a bit sensitive to how the connectors were attached, but after a small adjustment of the inner switch connection, the parking function works as expected.  There is a plunger that is pushed from the motor shaft that separates a contact in park-switch when the motor is in the parked position, stopping its rotation.  One interesting observation about the wiper motor.  The cover holds the permanent magnets and is not marked.  It has two possible orientations, 180 degrees apart.  In one orientation, the motor would spin the drive gear counter-clockwise.  In the other, clockwise (the proper direction).  Of course, it took two tries to figure this out.

Battery Monitoring

The battery monitor has advanced quite a bit.  Shown here is the four CellLog 8M based monitor.  The CellLogs are mounted on a board from ElectricPorsche.ca.  Robin at Electric Porsche has designed this board which was a perfect fit for Jane's needs.  It now monitors all 26 cells and activates a loud piezo buzzer if any of the cells are out of range.  I currently have them set at 2.50V - 3.55V as the normal range.  The looping wiring on the right side is setup to assure that if a CellLog fails or a wire comes loose, the alarm will sound.  The CellLogs keep the 4 relays closed when on and not-alarming.  If a CellLog goes off or alarms, it ceases to maintain the closed relay and the buzzer is sounded.    This system mounted in the boot, on the boot lid, so it folds down quite nicely for easy viewing.  Also, I moved the 600A contactor back to the boot today so that it would not be exposed to the elements under the hood.  Was able to use the electric fuel-pumps power to activate the contactor when the 12V system is turned on with the ignition key.  Just one of the many clean-up things that needed to be taken care of.

Charging update:  With the CellLogs operating now, I have turned down the charger to an 86V terminating voltage, which is 3.3V per cell.  The charger is designed to switch to constant voltage at that point until the current drops to about 1 amp.  This is not the fastest way to charge.  When the charger was set to 91V, a few of the cells would exceed the 3.55V alarm voltage before the pack reach 91V (26 x 3.5V).  Wanting to be conservative, I opted for a slower charge at a lower constant voltage, which should be easier on the cells.  After a couple of charge cycles with this new setup, all of the cells are staying within 30 mV of each other.  LiFePO4 batteries have very steep voltage curves when they near the end of the charge cycle, so as the few slightly fuller cells got near the end of the charge, they would shoot up the voltage curve triggering the out-of-range alarm while the rest were still taking in the last few amp-hours.

Springs

New Springs on the rear

Replaced the rear, very dead rubber cones with new springs today.  The springs are called the SRP-200 (Red, firm).  I started in the back, since most say it is simpler.  However, removing the old springs from the struts turned into a 2 hour job of cutting, chopping, heating, grinding, sawing and a few other choice actions.

This is what Jane's struts looked like.  The top one has the remnants of the old rubber spring.  The bottom one has had it cut away with a angle grinder.

Here are the new springs.  (C-SRP200 from SRacer).


Also, realized that the knuckle joints on the structs were in need to new protective covers during all of this.  The knuckle joint provides rotational flexibility for the strut. Shown here, the top seats in the frame and the strut slides on the post at the bottom.



The front left spring was rather easy to replace.  It required just one trip to Home Depot to get the parts to build a spring compressor.  A 2' piece of 1/2" all-thread, some nuts, a few washers, and for $7, a Mini spring compressor was born.  Worked like a champ.  Removing the upper suspension arm was easy by simple removing the cover plate from the shaft for the arm, taking off the two 3/4 nuts on each end and simply pulling the shaft out.  Took all of 10 minutes.  Once the new spring were compressed, the arm went right back in place.   The front knuckle joints were in good shape, so they just got repacked with grease and sealed-up.

The old rubber spring was a mess but it did separate from the trumpet much better than the rear ones.  A few hits with an old chisel and the spring separated from the trumpet strut.

The right side is going to be trickier since the new electric motor sits right in front of the upper suspension arms shaft cover plate.  Looks like the motor is going to have to be raised out of the way.  

With the new springs in, the front-end sits about 2 inches higher than the rear now.  Makes for an interesting look.  Hi-Los are on order to bring down the front and level the whole car.  A Hi-Lo is just a adjustable strut that can be extended or retracted to raise or lower the suspension.  I guess the reduced weight of the engine missing, does not compress the springs enough to keep things level.