Hey All,
I'm and Electrical Engineer with no desire to buy most new EV's and the battery in my highlander finally died. I've done extensive hands on research with toyota hybrid systems and estimate that the highlander is capable of approximately 4-500hp with the OEM inverter and transaxle. The Gen 2 prius inverter is nearly identical but rated for 80kw instead of 250kw, and will "protect" it's self by shutting down at . This means the highlander inverter should shut down around 937kw or 1250hp absolute max theoretical output(1800A @750V). This doesn't count the resistance of the wires, motor, or batteries as they heat up so we can assume a more reasonable estimate of 400hp to start.

The rear motor is capable of about 75hp and is normally only used when traction isn't available in the front. More power is certainly possible but additional cooling will be added before pushing things too far. This is achieved by plumbing in a radiator and pump for the ATF cooling the motor. I may replace this motor with something bigger.

Conversion of a toyota/lexus hybrid to all EV is as simple as removing the engine and connecting a large HVDC battery directly to the inverter. However I also tested a configuration of replacing the OEM NiMh pack with LiFePo4 lithium cells without modifying any of the stock systems. Each module normally operates from 10-14.4v and is replaced with 4-72Ah LFP cells with a voltage range of 10-14.6V when placed in series. Voltage tap points are placed every 8 cells and the systems functions perfectly fine but specific hardware is needed to fool the BMS computer into using the pack at full charge instead of preferring it to sit at a lower state of charge like it does stock.


The 30kWh of LFP weigh about 1000lbs but the additional weight doesn't seem to effect the suspension much. I'm looking into options for air suspension with the EV conversion.

120-72Ah CALB cells with oem tap points at every 8 cells. About 30kWh here.

I extended the battery connection to allow the relay block to sit next to the pack for temp testing

Obviously, this setup is incredibly dangerous and was only used to confirm point of concept, laps around the block, only. Once confirmed functional the pack was dismantled and the entire rear interior was removed.

Next steps were sound deadening and heat insulation as those are very hard to do once the vehicle is in use and you will regret not doing them with an EV.
I'm about to take the engine out to start designing the front battery box.
I have 270 for a total of 70kWh and range will be heavily dependent on speed but 100-200 miles would be expected with a few aero modifications.




Full EV control is performed by taking over the inverter from the Hybrid vehicle ECU. This will be a bit of a learning process but for the most part the highlander system shares common control systems with the Lexus GS450h and almost every other hybrid from the second generation lineup. On openinverter.org the community works on reverse engineering OEM hybrid/EV systems for DIY conversion use with custom control boards. EVBMW.com sells a board for the GS450h that is well supported on openinv and will be the basis of this conversion.

This board communicates with the inverter over 4 sets of data lines sending synchronous serial data containing commanded torque, speed, power, data to the inverter. Most of this data has been figured out but there will be some extra work for me integrating the commands for the rear motor as well.

I'm recording everything as I go and will do a 20-30min video on everything once it is to a somewhat finished state.
That being said I wanted somewhere to talk out ideas and issues with the build as we go along and this will be one of the places I do that.
Thanks everyone,
LJ

 

How is it going with this project? My engine just blew in my 2012 Highlander Hybrid, so I'm curious if this is an option. Would love to hear some costs if you have them.
thanks,

 

Curious. Modules are 8S NiMH with a nominal of 9.6V. Absolute peak is very near 13.3V and can operate as low as 8.8V, so I'm not sure where the 10-14.4V range came from. The car is expecting 16S NiMH per block ranging from 17.6V to 26.6V. A 7S block would seem to fit the bill better than 4S.

 

This is really great work. I just got an 06 because I want to do something like this. I was wondering if the inverter can take a higher input voltage and provide a higher output voltage so that the motor will spin faster. I was reading about inverter failures from early 06 vins so it seems like a bad idea. I suppose it's not an issue for your 08.

 

Why not just do what Damien did, and lock the transaxle input shaft - where the ICE crankshaft went? Then use their controller to use the full power of both MG1 and MG2... and then add the rear motor in... plenty of power. Bypass the original battery pack wiring, bypass the bidirectional boost converter, and just feed 400v to the DC buss... and use a BMW i3 charger. It may not be able to exceed 75mph (because it's not 650v like the booster allows), but it will have plenty of torque getting there... as long as your battery pack can handle it. Increase the inverter cooling capacity though... since it will be running high power 100% of the time. And as you mentioned, add a cooling system for the rear axle motor too... monitoring its temperature.

Otherwise an M3 front drive unit would be a good substitute.

 

Which engine does the 2012 have?
How many miles? My 2008 has nearly 300k miles, and going strong.

 

You say you're an EE, what is your field of work??
In electrical circuit design we know that there is the "SOA"... Safe Operating Area in Semiconductors. While the switching transistors maybe can handle 1800A maximum (not continuous or even short-term average), and maybe they can handle 750V... they would never come close to surviving anything close to those two peak values [at the same time].

Toyota boost converter can reach about 650v, so that's a reasonably safe usable voltage... but the converter would never come close to providing the same peak current used at low speed / high torque acceleration... the 650v only happens at high highway speeds... where torque is much lower. That's why the converter would have to be bypassed/removed... as Damien did.

 

I’m getting ready to open up my 06. I’m pretty apprehensive about getting killed by the high voltage. I also don’t want to tear up the car or have it down for too long.

I got a high voltage DC charger and a set of contactors. As a first step, I want to use the charger to charge the onboard pack to save gas on short trips. So I want to plug in the contactors and then plug my charger into that.

From this photo it looks like the best place to put the contactors is where I have circled in red. That way I can use the onboard battery disconnect to de-energize the high voltage circuit before I cut into it.