Scion xB EV – Motor and Inverter

This page discusses the Solectria AC55 motor and UMOC445TF Inverter used in my Scion xB EV conversion.


I was able to find most of the original documentation online a while back.  Thanks to ‘metadope’ for originally hosting these documents, however their site seems to have changed hands.  I am now also making these original documents available should anyone else be using or repairing this equipment. Hopefully since Solectria and Azure are out of business and liquidated, and this is obsolete equipment, whomever has the copyright rights will not care.


Solectria / Azure Dynamics

See the Wikipedia Article regarding Azure Dynamics, formerly Solectria. Azure was active in the EV drivetrain and commercial electric vehicle market from the mid 1990’s through 2012. They designed and sold drivetrains, and also built and sold small volumes of complete vehicles, ranging from experimental cars (Solectria Sunrise) to small passenger cars that were probably their most successful (the Solectria Force) to Chevrolet S-10 models, full size box vans, and most recently, an electric version of the Ford Transit Connect. Unlike many manufacturers of this sort of equipment, Azure did sell to hobbyist converters as well and did offer some ongoing support. Unfortunately, Azure Dynamics went bankrupt and was liquidated in early 2013, ending any commercial and offical support for this equipment.

My Equipment

My AC55 and UMOC445TF inverter (and some other spare parts most notably a second inverter with good brains but a bad power section) were probably salvaged from commercially converted delivery vans or small trucks that went to a too-early grave. The parts were some of a larger lot that were being sold from an abandoned storage auction, so I got a good deal price wise, though I knew the trade off was going to be less support, likely more risk of reliability issues (so far so good…) and a somewhat less efficient and heavier system than a modern equivalent.

I was able to get all the original Solectria parts I needed for the drivetrain conversion, with the exception of the interface box for the UMOC converter. This part connected to the 25 pin data cable from the inverter through which all its control and indicator signals go and broke it out to connections that could be integrated with the vehicle systems. However, this particular part was not really necessary as it worked better to build my own equivalent part that integrated the UMOC with the Elithion BMS, Car wiring, and a Gen2 Prius gas pedal.

I did build a reasonable facsimile of a Solectria UMOC445TF benchtop breakout box, which is critical for testing and debugging the system. You can see it in action on my youtube video bench testing the motor and inverter.


The Solectria AC55 and UMOC445TF inverter are 15+ year old technology. Given the rate of progress of semiconductor technology and EV motor design, it is to be expected that they are heavier, less efficient, and less powerful than the modern equivalents.

Ac55 Motor

  • Based on a 60hz 3 phase industrial motor design; hence rugged, torquey, and heavy.
  • Air cooled aluminum body and fins.
  • one or two mounting options (base mount, face mount) depending on motor frame
  • Can be wired Wye or Delta and for several voltage ranges
  • 250lbs dry (or wet) weight.
  • 175 foot pounds torque from 0 to 2000-3000 rpm with UMOC445TF inverter depending on traction battery voltage.  From that speed, torque drops off linearly to about 60 foot pounds at 6000rpm.
  • 8000rpm maximum mechanical speed, 6000rpm maximum powered speed.
  • 85% to 93% efficiency over much of operational rpm/torque band.
  • 1.25″ splined output shaft.  Spline is a ANSI 32/4 or SAE “C” spline.  This is a 14 tooth, 30 degree pressure angle, 12/24 pitch, 1.25″ major diameter and 1.04″ minor diameter spline.    It appears to be most commonly used on agricultural pumps.  Matching spline hub adapter is Hub City 0332-00034.   There are several sources (even grainger and amazon) but shop around and check ebay, as prices vary wildly. I think I paid around $20 each new price for mine; I see some sellers wanting over $100 for the same thing.

UMOC445TF inverter

The inverter (note: same part is called the “Controller” in a DC conversion) in an AC powered EV is the equivalent of the carburetor or throttle body on a gas engine.   It regulates the amount of electricity going to the motor.   Think of it as a giant light dimmer.   The inverter consists of a computerized brain which listens to signals from the driver (throttle position, forward/reverse, etc) and from the motor (speed, direction, temperature) and uses this information to switch power from the battery in the right pattern and quantity to make the motor respond as the driver expects.

  • 70kw/95 horsepower maximum paired with the AC55 motor.
  • 150V to 360V traction battery operational range.
  • 370V maximum on-charge voltage
  • 250A maximum motor and battery amps
  • Regenerative braking capability
  • Electronic reversing of the motor
  • Air cooled with built in cooling fans
  • 97% overall electrical efficiency
  • Built-in main contactor, built-in precharge, built-in traction circuit fuse.
  • RS232 plain text computer interface for configuration and telemetry.   (38400 8N1 straight cable; use serial port isolator or do not connect computer ground to vehicle ground)
  • Many operational parameters are configurable by end users, but those parameters that would allow it to run against a different motor than the one it was originally programmed for (the AC55) are set at the factory and cannot be changed by end users.  Maybe at some point someone will (re)discover how to change those settings.

Other Systems


The only reasonably affordable AC system even available to DIY converters right now is the HPEVS family of systems. These are comparatively low voltage systems (For several years, their maximum battery voltage was 108v, though it appears they have just released a much-anticipated 144v controller). Their higher end systems are comparable in overall horsepower to the Solectria system I have though owing to the lower voltage they require much higher battery current to make that kind of power and this has some disadvantages.

I have seen several conversions using these systems and I would say they are awesome for smaller cars and conversions where budget is not unlimited, and would have worked well in the scion had I retained the transmission instead of going the direct drive route. Because I did go direct drive, the additional torque of the AC55 and UMOC are a significant benefit in comparison.

Metric Mind Corporation

Metric Mind Corporation is a reseller of OEM quality AC drive systems (motors and inverters) and other EV components, and they also perform a lot of custom design and engineering work. They are known for being very high quality, high performance, and very expensive. Due to the parts being designed for OEMs, they can be very complex to incorporate into a DIY project as well. Any of their 100kw systems or bigger would have done well in the scion, though I would have probably needed a much higher gear ratio had I wanted to go direct drive, owing to the higher RPM and lower torque of most of their systems relative to the Solectria one.

Rinehart Motion Systems

Rinehart Motion Systems makes (among many things it appears) high-end 3 phase motor inverters designed for EV use. If my UMOC445TF dies and is unrepairable, or if I decide I want to try for a substantial horsepower upgrade, I will probably try to integrate one of their inverters with the existing AC55 motor.

Restoration and Testing

Everything here is written from memory.  Please use your own judgement and consult and understand all the Solectria Documentation (above) before attempting any of this.    This motor and inverter use and generate dangerously high DC and AC voltage which can be fatal.   Do not attempt any of this unless you have a good working knowledge of electrical concepts and safety.

My AC55 and UMOC445TF came to me at about a 80% discount from their original MSRP via an abandoned storage auction.   I was fortunate to have some guidance via a small amount of underhanded skullduggery as to which Solectria components out of the many that were there were likely to be the best bet for cobbling together a running system.   I paid cash and made sure I got a receipt showing the purchase was legit, and took the parts home where they sat for a couple years before I got around to playing with them.

Test Box

As the parts were as-is, where-is I wanted to bench run the system before I did anything else like start building a car around them.   I had the Motor and Inverter and cabling.  The only other part I needed to try and run it was something to emulate the various control signals the UMOC wants.   These include throttle position, motor direction, regen enable, and several other safety signals and several indicator outputs.   Fortunately all of these signals are simple TTL level except for the analog 0-5V throttle and power limiter functions.   This means it was easy to build a test box.

The test box more or less implements the schematic shown in the appendix of the UMOC technical manual, allowing control of all the switches and putting 0-5K potentiometers on the throttle and power limiter inputs.   I designed mine to resemble the test box shown in that documentation.   LEDs in series with 1K resistors go on all the indicator outputs.   All of this is housed in an electronics project box with a 25 pin female connector such that a male-male 25 pin D-shell computer cable can connect them.  It does not require any outside power; it gets everything it needs from the UMOC.

Motor Inspection

I was fortunate that the motor required virtually no work.   The motor was used and had clearly been installed in a vehicle,  but it likely had very little mileage.   Here are the basic things I checked out/replaced:

  • Ensure the rotor turns smoothly, the bearings are in good condition and lubricated,  and the spline is not bent or damaged.   The motor has a grease fitting on the front for bearing lubrication.  If adding more grease, ensure it is compatible with what was there originally.
  • Ensure the 3 phase high voltage cable is in good condition.  It consists of four smaller wires going to each of the three large plugs for a total of 12 wires.  By rearranging these wires you can change the motor configuration (Wye or Delta) and rated run voltage, (230V or 460V) however doing this would make it incompatible with the UMOC inverter.   The wires themselves were in good shape but the outer sheathing was frayed and beat up, including the EMI sheilding.   1.5″ braided EMI sheilding is quite expensive it turns out,  but a commonly available hot rod radiator hose dress up kit (see amazon or ebay) provided just the right length of stainless braided cable to replace it.   I then added a new layer of orange heat shrink insulation over the top of that.   Orange wiring indicates high voltage danger to first responders and electrical workers.    In my installation,  I had to modify the cable housing box on the side of the motor for clearance issues to the engine compartment subframe,  but most people should not have that problem.
  • Ensure the encoder is correct for the UMOC inverter and the encoder wire is in good shape.   The encoder should look like a flat square housing on the back of the motor.  The encoder provides position/speed/temperature information to the UMOC445TF via a cable with a male 9 pin D shell plug.   Make sure the plug is clean and in good shape.   Note that some AC55 motors were made for a different manufacturer’s inverter and have a cylindrical encoder on the back.  This is not compatible with the UMOC inverter without building adapter circuitry.  I know this is possible, but it is difficult.    It is difficult to test the encoder but you will be able to tell if it works by hooking the motor encoder cable up to the UMOC inverter and simply spinning the motor by hand.  the motion indicator output on the UMOC (viewed via your test box) should come on.

UMOC inspection

Given the complexity of the UMOC445TF inverter and the fact that some of its components (especially the computer board) are now basically irreplaceable,  it is important to handle the UMOC carefully and ensure it is in good condition before using it.    Unless you know your UMOC445TF’s current operational status and trust the information of whomever provided you with it you should seriously consider disassembling it and performing some checks.    Here is what I did:

  1. If any high voltage has been applied to the inverter recently,   wait at least 10 minutes after unplugging it from all sources.  there are four very large high voltage capacitors that will take a while to discharge to safe voltage levels.
  2. Open it up.   This involves removing the fan cover (four screws and one plug; easy) and then turning the unit upside down and removing all the screws (on the heat sink on 3 sides,  and the side plate edges on the battery/motor cable side)  that hold the lower housing on.   Do not remove the screws that hold the side plate with all the battery and motor cables.   That panel will stay attached.   Then using a sharp box cutter knife, carefully pry the housing cover away from the heat sink.   It is glued on with black RTV silocone sealant.   If your inverter’s sealant is already compromised, then somebody has had it open and it should be inspected/tested even more carefully.    The computer board is attached to the lower housing via a couple of ribbon cables.   Carefully unplug these on one end and you should be able to separate the halves.    All the power section components should remain attached to the heat sink.
  3. Once open,  the first thing to do is inspect for obvious damage from failures in the high voltage system.    This can take the form of burned/deformed/melted wires, capacitors, buses, and IGBT modules.   Look for signs of overheating.   My spare inverter had one of the main battery cable lugs loose where it bolted to the main contactor.  It had clearly been getting hot and arcing.  This is likely what damaged that inverter.   Make sure that BOTH the fuses (in parallel) are good.   Make sure the main contactor is in good shape.   Make sure all the big cables are undamaged and lugs are firmly attached and clean.
  4. Inspect for excess corrosion.  Unless badly abused the inverter’s power section will probably be pretty clean, but there may be some white powdery corrosion on the power section control board or the main computer board.   This can be gently cleaned off with a dry toothbrush, compressed air and toothpicks or other nonconductive, nonmetallic scraping tools;  being careful to not bend or damage any components.
  5. Check torque on ALL the high voltage connections:   several bolts, screws, and plugs on the battery cables, motor cables, contactor, and power bus to the IGBT modules and capacitors.
  6. If there is any chance your UMOC has been disassembled before,  ensure the proper polarity on the large electrolytic capacitors and the main battery cable and the main battery connector.   If you find anything backwards (cough) look for damage and replace accordingly.
  7. Test the cooling fans.   Give them 12V and see if they run smoothly.
  8. Clean the heat sink fins if it is dirty or dusty.
  9. I noticed with some of my Solectria equipment (the DC/DC converters) that way, way too much heat sink compound was used in assembly.   Too much acts more as an insulator than a conductor of heat.   If you see evidence of this under the IGBT modules,  consider disassembling to clean out the excess.
  10. Once satisfied that the unit is physically clean and intact in and out,  reassemble it enough to contain high voltage badness, but do not add new sealant until you prove it works by bench testing it with the motor.

Bench Run

Consult the video for the end result:

Obtain power supply

You need two.   The first is a simple 12VDC power supply good for 5 amps;  this emulates the car’s 12V electrical system.  A fully charged SLA battery, car battery,  or a regulated 12V power supply can provide this.

The second is harder:  You need at least 200VDC at at least 5 amps to power the high voltage section of the inverter.   Your options are:

  1. If you already have a high voltage traction battery,  you can use that with suitable fusing and precautions.
  2. If you do not have this the next safest thing is to build a small battery using at least sixteen 5ah SLA gel batteries or equivalent such as what are used in battery backups and lanterns.   It is OK if the batteries are used and mismatched as long as they are healthy enough to put out five amps or so for a few minutes.
  3. The final option is to isolate, step up, and rectify 120VAC wall power.   This is what I demonstrate in the youtube video.   This works because the huge capacitors in the UMOC filter the voltage ripple adequately but is probably still more risky for the equipment.   In this case you must be extremely careful to ensure that you do not damage the UMOC by accidentally causing regen to occur since there is no place for the recaptured power to go except the onboard capacitors of the UMOC which could rapidly overcharge them.   You must also in this case ensure that the power supply is fully isolated from the wall power for safety.     Stepping up 120V wall power by about 10% and then rectifying it will yield a bit over 200VDC and with suitably sized components you should be able to get several amps through it.    I used a 20A 120V variac with a 10% center tap and bridge rectifier power supply to do this, but it can be done with a relatively common high wattage 120V/12V power transformer as well such as might be found in larger computer UPSes like the APC 1400.

Emulate control and indicators

This means finding (unlikely) or building and using a test box such as I describe earlier.  This box must emulate throttle position,  power saver,  forward, reverse, regen, drive disable, digital enable, and it should also break out the four indicator lights:  Motion, Fault, Rotor, and Battery warning.   All signals are TTL or 0-5V analog so creating a test box is not hard to do going from wiring diagram in the appendix of the UMOC4445TF service manual document linked to above.   Double, triple, quadruple check your pinouts are correct.

RS232 computer terminal

Set up a laptop computer running on battery power and not grounded to communicate with the UMOC.   (or use an RS232 optical isolator if using a desktop machine).    Isolation is critical to avoid damaging the irreplaceable UMOC computer board.    38400 8N1 straight cable, unless you have an older UMOC with the gray RS232 plug; this needs a null modem cable.   hyperterminal (windows) or minicom (linux) will work as the terminal emulator program.   It is best to use a hardware serial port but if not available a USB serial adapter will work as well.    Make sure to configure the terminal program to NOT SEND ANY MODEM CONFIGURATION COMMANDS.  These may confuse the UMOC.   Some modem initailzation commands I sent accidentally managed to put my UMOC into firmware update mode.  Yikes.

No Motor Power Up Attempt

Here is the basic process I came up with for powering up and talking to a UMOC.

For the first power up attempt,  do not connect the motor at all.   The goal here is only to see if the UMOC’s brain comes up and you can talk to it and it can read as many control signals and data points as you can give it.

  1. Connect the test box and ensure throttle and power saver are set to minimum, and the enable switches are OFF and forward and reverse are OUT (neutral)
  2. connect laptop with appropriate RS232 cable and isolator if needed.
  3. While powered off, Very carefully connect up the high voltage and low voltage power suppies, observing correct polarity.    Reverse polarity will probably destroy the UMOC.
  4. Attach a voltmeter and ammeter to measure the high voltage power supply.
  5. Ensure the terminal program is configured and up and running,
  6. Gradually apply high voltage to the main battery connector.l   It is best to ramp up the power gradually the first time.  This will only be possible with a variable power supply like a variac.    If you are using a battery,  put a 100W light bulb or two (depending on voltage) in series to limit current in case something goes wrong.    If it registers any measurable current over a few milliamps cut the power; something is wrong; disconnect the power, and investigate.   It should not draw any meaningful load with no motor.    There will be a small amount of current that slowly drops off as the internal capacitors precharge.
  7. Once the full high voltage is applied and no unexpected current is flowing,  apply 12V to power up the onboard computer.    The fans may run briefly.   If they do not, that does not mean anything however.
  8. If everything is connected properly,  within a second or two you should see bootup messages on the RS232 output.   Hit enter and it will start outputting telemetry.   If you get this far,   this is a very good sign as it means the UMOC brain is probably OK and this is the unrepairable part.
  9. While more primitive than the more modern embedded web server approach,  you can navigate the menus and view and alter configuration.
  10. Document the existing configuration settings (using screen capture or whatever) before changing anything.    The captures I provide in my notes above show settings I had which worked for running my AC55.
  11. Note any fault messages the UMOC is outputting, and investigate as appropriate.
  12. Check response to test box control switches and throttle and power saver, but do not move the throttle much above zero as you do not want the UMOC to try and run the motor which is not there.  there are several one/zero and ADC numeric outputs on the telemetry which read out what the UMOC is seeing for these signals.   Refer to my notes for my decoding of it all.
  13. Check ADC response to battery voltage.   One of the ADC outputs in the telemetry is battery voltage.   If this does not come up to the expected value,  this may indicate a bad or reverse polarity capacitor.  Investigate carefully.  Whatever you do,  do NOT manually push the contactor closed with power applied if you see this.  You could cause one or more of the capacitors to explode.
  14. Check that precharge completes.   This can take a few minutes with the UMOC so be patient.   You can watch the voltage coming up on the telemetry.    Once it completes, then when you close the digital enable switch you will hear a clunk as the main contactor closes.   This means the UMOC thinks it is ready to run.    If precharging does not complete,  go back to the prior step and look for problems.    I had this problem because when I reassembled my power stage I put one of the big electrolytic capacitors in backwards.  Voltage came up to about 20 volts before it started leaking through the capacitor and the precharge stopped.
  15. Turn off 12V power,  then disconnect high voltage power.   Wait several minutes before disassembling the UMOC if you need to do that again.

Motor Run Attempt

  1. Turn off all power to the UMOC and wait several minutes.
  2. Connect the motor 3 phase cables and encoder cable as shown in the Solectria documentation.
  3. ANCHOR THE MOTOR TO THE FLOOR so it cannot shift around while running.   It will easily generate enough torque to flip itself over and steamroll you or knock over a workbench.   I missed this step and the motor almost flipped the first time it took off.
  4. DISABLE REGEN using the switch on the test box.   this is especially important if you are using a variac power supply.
  5. Ensure the throttle is all the way off on the test box, and that the direction switches are in neutral and both enable switches are off (disabled)
  6. Power up the UMOC using the same process as before, except take out any current limiting devices (e.g. light bulbs) you may have used the prior time around.
  7. Once the UMOC boots and you get to the telemetry screen,   manually spin the motor shaft by hand.   the “Motion” LED should come on at a fairly low RPM.   This indicates the encoder is working.
  8. Wait for precharge to complete.
  9. close the digital enable and drive enable switches.   The main contactor should close.
  10. Select either forward or reverse with the test box.
  11. VERY VERY SLOWLY ramp up throttle.  Watch the UMOC telemetry as its throttle range moves from BRAKE to COAST.  Nothing will happen (except for building anticipation) until it moves from COAST to DRIVE mode (at ADC value “512” if the default values are still in place) when motor will start to run if everything is working.    If the motor goes, congratulations you have a working system.    Turn the throttle back down into COAST (but not BRAKE) range and let it coast down to a stop.  You can then try the opposite direction.
  12. You will not be able to safely test maximum RPM or putting any real power to the unloaded motor.   If you ramp throttle up too fast you will cause something bad to happen with your benchtop power supply.  If you are using a real traction battery you will risk overspinning the motor or causing it to break its tie down/anchor and hurt or maim you or onlookers, so be careful.
  13. If the FAULT light comes on and the UMOC shuts itself down as soon as it tries to spin the motor, check the UMOC telemetry.  You have a bad motor, bad power section, incorrect three phase motor wiring, or some other problem.   My spare UMOC throws a “desat” fault at this point, which probably means one of the IGBT modules is bad.  If this is the case,  it is repairable as these modules are available and easy to test and replace.    I have not tried to fix it yet however.

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