Battery Protection

High Voltage Charging Cut-off

After some good basic Electrical Engineering 101, Jane now has a charging cut-off circuit that monitors each cell individually. This involved designing and wiring a circuit (schematic will be posted soon), that takes the alarm output from the CellLog monitor and uses to turn off a high-current contactor between the charger and the batteries.  As part of this enhancement, a couple of relays have been added to only turn on the CellLog monitor board when either 220V (charger) is connected or when the key is turned on.  This should solve the slow drift that the CellLogs were causing on some of the cells, since they don't draw evenly across the sub-banks.  Also, put on push-button switch to provide a quick check option for the batteries.  Pushing the button, powers up the CellLogs.

The relay controlling the charging contactor require two special considerations:

• Latching - Wired it so that it would latch ON once the alarm triggered.  This way, even if the alarm condition clears, there is no way to resume charging without disconnecting the 220V supply.
• Delayed-On - Added a cap (4700 µF) across the coil and a resistor (50 ohm) in series with the coil to require the alarm to sound for about 2 seconds before the relay will activate.  This filters short alarms and any temporary issues that may occur at power-up.

The CellLog Monitor has a buzzer attached to alarm if a cell is out of range.  A quick connection to the original Alternator indicator on the dashboard now provides the driver a red warning light (replaced with LED bulb for extra brightness) if an alarm condition is in effect. The buzzer is audible inside the cabin but if the windows are down or music is up, it may be missed.

Also, added a heavy-duty marine-quality manual cut-off switch on the positive side of the battery pack.  This provides a quick, secure cut-off of the high-voltage pack, making it safer to work on the systems.

http://www.discountmarinesupplies.com/Blue_Seas_Battery_Switches_E_Series.html

The CellLogs are set to the following:

Voltage Range: 2.5V - 3.6V

Delta P (maximum cell variation): 100mV

Alarm Type: Normally Closed  (this provides a safety if a unit become disconnected or is not functioning, since the alarm will open up, triggering a alarm condition)

Pack Voltage:  

• 6 Cell sub-pack = 17.5V - 21.0V
• 7 Cell sub-pack = 20V - 25.2V

2 CellLogs have 6 cells connected to them, 2 have 7 cells to cover 26 total cells.

Completed one charge cycle and the system performed well.  One cell was slightly higher than the rest and hit 3.6V, shutting off the charge current.  Next is to test it while driving.  All of the cells are within 25mV of each other. 

Heat

A little warmth is a good thing...

Well since winter has arrived in full force (18" of snow this week), having a heater in Jane became a priority.  Originally the gas engine provided hot water to the heater coil but that is not possible now, so this project required a bit more invention.  The final implementation ended up being:

1. A ceramic heating coil from a 110V space heater: Warmwave 1500-Watt Ceramic Electric Portable Heater
2. A high current contactor to control the heater: Cole Hersee (24059-BP) 12V Insulated SPST Continuous Duty Solenoid  - First attempted to use a 30A 12V automotive relay but it melted with the high voltage.  The heating coil should only be pulling ~10A.
3. High-temperature cut-off Protection: Amico 5 x KSD301 250V 10A 70 Celsius Temperature Control Switch Thermostat N.C
4. Lighted toggle switch for the dashboard.  This was placed where the old heater mechanical control was located.  The old controlled connected to a valve which regulated the water flowing to the heater coil.  The lighted version will help the driver remember to turn this off when not in use since it will use the same power source as the drive motor, impacting overall range.

Connecting it all together....

Electrical

The blower's original switch controls the ground to the blower, so that was connected to one side of the contactor.  The new lighted toggle switch was wired to the 12V side of blower motor which is switch by the ignition switch.  This way the ignition must be on and the blower switch on before the contactor will activate.  The contractor was wired through a 20A fuse to the 84V battery main battery (after the main contactor, which is also activated by the ignition switch).

Heater Contactor mounted on the firewall

The High temp cut-off device was wired in series to the heating coil and mounted inside the blower housing near the coil.
The coil is rated at 1500W at 120VAC, so at 84VDC, I am not sure just how much heat will be available.

Mechanical

The ceramic coil was much smaller than the original Mini water coil so a adapter plate was cut from sheet metal and fit within the blower housing with the power wires being fed through on of the water inlet holes in the housing.

Cooling the motor -  A bit of irony

Cooling the Motenergy ME0913 has continued to be a problem.  Since the motor is running in reverse, the built-in centrifugal fan does not move any air. The hall sensor magnets are connected to the fan, so it cannot be removed or modified easily.  After attempting to utilize two 1" hoses to pull air through the motor using a 200CFM blower, the motor continued to overheat (100C) under only a slightly elevated load (driving the hills around home).  

Next idea...  

1. Cut a 4"x1" rectangular hole in the motor fan cover (black area on the right in the photo below).
2. Deform a 3" to 4" round duct adapter (shiny sheet metal with the bar-code in the picture) to act as a funnel from the 3" flexible hose from the blower to the round cover with the rectangular hole.  The adapter was screwed to the cover and sealed fairly well.  It would have been better to mount this on the end of the motor, but there is no room since the motor is right up against the inner-fender.  To avoid the cover screw shown in the photo there was very little room for the funnel.
3. Currently, the blower is set to pull air through the motor since that is direction that the built-in fan would move the air if it was functional.

ME0913 Traction Motor with cooling adapter.  The new right front coil spring is visible through the hole
in the sub-frame.

Next ideas - Can the motor heat be directed into the cabin to supplement the electric heat?

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.

Seeing is believing

LED Dashboard Lights

After an evening drive the other night, we realized that being able to see the speedometer in the dark is useful.  The tiny LLB987 bulbs, which may be 40 years old, just don't put out much light.  Well there are LED equivalents available from www.v12s.com which are perfect.  Not only do they fit well, but they produce a nice white light, much brighter than the old bulbs.

See for yourself.  This photo shows the difference.  The left side bulb was changed to the new LED version, the right is still the old incandescent type.  The fuel gauge may be a bit too bright, but that will be good once it is connected to the battery monitoring system.

Tomorrow, new springs for the suspension which means pulling out the old rubber cone-type (sometimes call donuts) springs and installing heavy duty real steel springs.  This should vastly improve the ride.  Currently, it feels like a bicycle, where every crack, bump and pebble is felt, since the rubber cones are fully compressed and there is no travel available.   No telling how old the current rubber cones are but they are only expected to last 5-7 years and given the lack of compression available, they are well past their life expectancy.

It keeps getting better

Covering some real ground

With the full battery pack and a instrumentation package up and running, we are now going for longer drives.  Yesterday, we covered over 10 miles on a single charge.

The charging system is working great.  Two charges, both tied to the 220V input.  One is the 1500W 91V Lithium Ion charger for the drive battery and the other a 120W 12V charger for the system battery.  Since both are automatic, they shutoff independently when charging is complete.  I have the 220V outlet on a timer just to be safe.

Instrumentation Pack

Here is a the roughed-out instrumentation pack.  This will be mounted behind the dashboard once it is installed.

1) On the left are 4 CellLog8M battery monitors.  These are set to alarm if any of the individual cells go out of range.  Currently I have them set tightly at [3.0V - 3.6V].  Charging is set to 91V which should be 3.5V/cell on average, so any major drift will be detected.  The cells have sagged below 3.0V on a recent hill climb, but recovered to 3.2 very quickly once the road leveled off.  

2) The top-right rectangular LCD is one Arduino Uno which is connected via the CAN Bus to the Kelly Controller.  It monitors: 

• Top Row: RPM, Battery Pack Voltage, Controller Temperature
• Bottom Row: Drive/Reverse, Calculated Speed (Assuming 2nd Gear for now), Motor Amps, Motor Temperature

3)  The lower LCD is another Arduino which is measures battery current through a 600A/75mV shunt.  It is power separately from the drive battery pack via a 12V adapter.  This keeps the battery system isolated from the rest of the car's 12V electrical system.  This Arduino is always on and maintains a running count of the amp-hours consumed.   The shunt is installed at the battery negative terminal to eliminate noise from the motor and to allow for monitoring charge going into the battery from either the charger or from the motor's regeneration braking.

In a quick experiment, after a 5 mile drive, I then connected the charger.  The Amp-Hour counter returned to within 3% of full.  Please note, I have not calibrated the system yet, so this is very promising.  The system is using an Analog Devices AD8210 Shunt monitor to measure the voltage drop across the shunt.  It is wired with a split-supply configuration, so 0 Amps = 2.5V going into the A/D on the Arduino.  This setup should yield about 1A precision on counting amp-hours.  Given the 20% DoD (depth of discharge) limit, this should provide plenty of margin.

Controller settings

Now that there is decent current monitoring, we tweaked the Kelly KHB72701 controller settings a bit to see if there is a bit more power available.  During the drives yesterday, The battery current never exceeded 200A and the motor current peaked at about 300A.  The spec on the motor is a max of 420A for 1 minute and the batteries should be capable of 400A-600A for short bursts since they are 60AH packs and there are several reports of people safely pulling 8C-10C.  Batteries are rated in terms of multiples of the AH measurement, so a 8C battery can deliver 8x60AH for a short burst. 

With motor blower providing plenty of cooling, he motor's temp peaked about 55C.

New Settings:  

• Throttle Range 5%-80% (this is a mapping to the mechanical throttle position).
• Max Motor Current 90% (this is of the controller max of 700A --> 455A)
• Max Battery Current 100% (700A)
• Undervoltage (Controller will start to cut back power draw at 110% of this value): 68V (cut-back at 74.8V, or 2.87V)
• Overvoltage (Controller will limit regeneration if voltage exceeds this): 90V
• Throttle Ramp: 4 (How fast it will ramp up acceleration)
• Regeneration: Off 

Off for another test drive to the grocery store....