Subaru Legacy + Tesla SDU Conversion

Tell us about the project you do with the open inverter
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elShankos
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Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

Hi All,

So.. I started out on the DIY Electric Car forum but it occurred to me that it would actually be better to put my build here as it's based around the OI conversion route. I had a bit of a thread here: https://www.diyelectriccar.com/threads/ ... on.208076/

But anyway, here goes! I have been planning / dreaming of this EV conversion for quite a few years and have now finally started here in Cape Town, sunny South Africa:
- Donor : 3rd Gen Subaru Legacy GT Wagon - AWD > will become rear wheel drive...
image.png
- Motor: Tesla rear Small Drive Unit (SDU) + Damien Maguire OpenInverter Control board
image.png
I recon this should fit OK in the back as I printed out a 1:1 cardboard version and stuck it under the car at my local tyre shop recently (they thought I was nuts):
image.png
- Battery: 16 X 6s1p CATL units (400V pack) out of China - still need to buy these but they are pretty much the only thing I can import into South Africa:
https://www.alibaba.com/product-detail/ ... 08616.html

- BMS: EVS BMS (previous idea was SimpBMS but this isn't really available anymore) + 16 x Tesla Rev B boards - my idea is to hook up each of the boards to the 6 cells in the above CATL batteries

- Charger: Tesla GEN 2 onboard 10kW charger + Damien Maguire OpenInverter Control board
- Tesla model 3 brake and accelerator pedal + GEN 1 iBosch iBooster
- Nissan Versa EPAS steering unit
- Tesla 2014 AC compressor - apparently these can be PWM controlled
- Tesla DC>DC converter
- Tesla charge port and cables (was pretty cheap)
- Tesla cooling pump - might re-use the existing radiator but not sure yet.
- Assorted bits and pieces

So far I have managed to get pretty much everything above into a crate (except batteries) in Minneapolis, USA, then shipped all the way to Cape Town (quite a nightmare) and now its in my garage so I'm slowly getting started finally:
image.png
image.png
Would be great to get some feedback, suggestions, ideas etc from the community! I'll stick in my updates below too.
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

Wiring Diagrams:
So I started with a concept diagram that looks like this to get my head around things:
image.png
And then over the past few weeks while swopping out the inverter control board (what a pain those SDU current sensors are!) I have been working on a main wiring diagram which at present looks like this (I attached the larger PDF if you want to have a look):
image.png
I still have a bunch of work to do on this so it's still in DRAFT stage but its getting there - lots of people on this forum have really helped me a lot so far to figure things out - and also hrs and hrs of trawling :) The answers are all here! You just have to find them :D
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THEV_Main Wiring Schematic - Rev3.pdf
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Re: Subaru Legacy + Tesla SDU Conversion

Post by tom91 »

Quick questions on your HV wiring.

-Why is there no contactors on the HV negative?

-You need precharge on the auxiliary components too
Founder Volt Influx https://www.voltinflux.com/
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

tom91 wrote: Sat Jan 28, 2023 12:00 pm Quick questions on your HV wiring.

-Why is there no contactors on the HV negative?

-You need precharge on the auxiliary components too
Hi, thanks for the queries. On the main -HV contactor Q, I'm kind of following aber333's advice as I can't really see the benefit of having a second contactor either - please see thread here: viewtopic.php?t=3101
It wouldn't be difficult to do with just using the same pre-charge signal from the OI but latching it on the -HV contactor. I've kind of gone back and forth on this.
I was actually going to make a post about this as there seems to be a real spread of opinions on this one - would be happy to hear your thoughts.

Mmm for the auxiliaries, I wasn't sure that pre-charge was necessary for these? I guess I could put a pre-charge resistor and relay across the contactor that feeds the aux's and switch it via the BMS when in charging state?
image.png
Definitely one to investigate - thanks for the heads up.

I've changed this wiring around a bunch of different ways and I think there are quite a number of ways to do this.
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

So I decided to make an alternative wiring diagram with the following 2 main differences to the Rev 3 above:
1) I've added a main -HV contactor (to be like an actual Tesla arrangement - must be a reason its there right? :) ) and also switching all the contactors in an OR arrangement - either from the BMS (non latched main contactors) or Inverter (latched main contactors)
2) Using a Tesla GEN2 rear junction box (got one for cheap in the US) to tie in the charger so now there is no extra line from the front of the car to the back.
image.png
So I think this will work (with lots of 12V relay wiring) and provide pre-charge to the auxiliaries as well in both driving and charging modes but my only concern is: what about in driving mode, switch on ignition and the pre-charge closes, then opens and then maybe the BMS takes a turn trying to close it... might have both the Inverter and BMS opening and closing the pre-charge contactor a bunch of times? Maybe not but I'm not sure about this one - bit hard to say.

Otherwise it seems like maybe a better solution - would be good to hear folks' thoughts :)
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THEV_Main Wiring Schematic - Rev4.pdf
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Re: Subaru Legacy + Tesla SDU Conversion

Post by Pete9008 »

Very interested in seeing how you get on with this. I have a 4th gen Legacy spec B which I've had for 16years now. Would love to convert it but the ridiculous UK rules on not changing the road tax following an EV conversion mean it doesn't make sense to.

Curious about your connection to the iBooster pedal position sensor, is this piggy backing off the same sensor that is normally wired to the iBooster ECU or is there a seperate one?

Edit - BTW your proposed HV wiring diagram now matches my plans (different hardware but functionally the same).
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

Pete9008 wrote: Sun Jan 29, 2023 7:44 pm Very interested in seeing how you get on with this. I have a 4th gen Legacy spec B which I've had for 16years now. Would love to convert it but the ridiculous UK rules on not changing the road tax following an EV conversion mean it doesn't make sense to.

Curious about your connection to the iBooster pedal position sensor, is this piggy backing off the same sensor that is normally wired to the iBooster ECU or is there a seperate one?

Edit - BTW your proposed HV wiring diagram now matches my plans (different hardware but functionally the same).
Nice one Pete - I always liked those 4th Gen Spec Bs. Mine is a 3rd Gen Legacy GT - E-Tune spec which I got in Japan and which I've had for 13 years now and I'm pretty attached to :) I actually don't know what the rules are around conversions here in South Africa - will have to find out at some point...

For the iBooster signal, I haven't actually done it yet - I'm hoping for a reply in this thread here where it seems like the guy piggy backed off one of the iBooster pedal position sensors: viewtopic.php?f=10&p=24310#p24310
Or I'm just reading it wrong...
If that doesn't work then I'll just go the set regen level + break light switch route.

Have you started your project yet or in planning stage?
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Re: Subaru Legacy + Tesla SDU Conversion

Post by Pete9008 »

The Legacy is a massively underrated car, at least in the UK, it's easily the most capable car I've ever owned; it's a great mix of practicality, performance and comfort! Mines been off the road for a couple of years now, it's just too expensive to tax for the amount I use it. Really ought to sell it but just don't want to!

Thanks, I had seen that post but at the moment it looks like an untested idea, it should be possible though. The CAN bus versions of the iBooster (Tesla, Honda and some VAG) also make the position information available in the CAN messages which can be used by OpenInverter. I'm interested in using the I-Pace version though as they are 2/3 the price here, the trouble is they are Flexray not CAN bus so I'm looking at alternatives to get at the pedal position.

My project has sort of started, got most of the bits but not started pulling the car apart yet (viewtopic.php?t=2347)
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Re: Subaru Legacy + Tesla SDU Conversion

Post by Scrappyjoe »

Jirre, elShankos, dit lyk lekker, man!

Just dropped by to say I’m also from Cape Town and will follow with interest!
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Re: Subaru Legacy + Tesla SDU Conversion

Post by Scrappyjoe »

Also, in South Africa, why not buy lithium cells from the solar suppliers? I know they are lifepo4 rather than li-ion and therefore a bit bigger, but they require way less cooling consideration, and you’d avoid all the import hassle.
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Re: Subaru Legacy + Tesla SDU Conversion

Post by paaa »

I started doing the same with a gen 4 bp5 ,the subframe needs good bit of cutting for my leaf motor, have tried both early and later model leaf motor. But also be aware of the height of the motor as I found ground clearance was an issue along with width between both side.
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

Scrappyjoe wrote: Tue Jan 31, 2023 8:20 pm Also, in South Africa, why not buy lithium cells from the solar suppliers? I know they are lifepo4 rather than li-ion and therefore a bit bigger, but they require way less cooling consideration, and you’d avoid all the import hassle.
Hi, so the lifepo4 cells are cool and also safer but they don't have great high C discharge rates as compared to the 3.7V NMC cells for example.
Importing is fine if you have the patience... and once you've gone through the pain a few times!
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

Just a mini update: so I got my bench test of the SDU done - I powered it off my Lifepo4 48V DC home battery system as a test and made this powerfully average Youtube video here:


Just a heads up: while "revving" the pedal its actually pretty easy to start pulling a lot of amps suddenly - so make sure you have a set up where this won't trip suddenly and possibly damage your inverter. Probably why the documentation says to put a kettle element in series - I didn't have one.
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Re: Subaru Legacy + Tesla SDU Conversion

Post by jetpax »

elShankos wrote: Sun Jan 29, 2023 7:00 pm So I decided to make an alternative wiring diagram with the following 2 main differences to the Rev 3 above:
1) I've added a main -HV contactor (to be like an actual Tesla arrangement - must be a reason its there right? :) ) and also switching all the contactors in an OR arrangement - either from the BMS (non latched main contactors) or Inverter (latched main contactors)
2) Using a Tesla GEN2 rear junction box (got one for cheap in the US) to tie in the charger so now there is no extra line from the front of the car to the back.

image.png

So I think this will work (with lots of 12V relay wiring) and provide pre-charge to the auxiliaries as well in both driving and charging modes but my only concern is: what about in driving mode, switch on ignition and the pre-charge closes, then opens and then maybe the BMS takes a turn trying to close it... might have both the Inverter and BMS opening and closing the pre-charge contactor a bunch of times? Maybe not but I'm not sure about this one - bit hard to say.

Otherwise it seems like maybe a better solution - would be good to hear folks' thoughts :)
Great to see a open discussion on this as I've also been agonising over all the possible ways of architecting my own system. My current layout looks basically the same as yours, but I'm using M3 DU with an as yet undetermined VCU (a bit heretical to say it on OpenInverter even as a Damien patron, and being in awe of @johu but I'd really like to crack the pairing process as T2C and Ingenext have done :twisted: ).

Anyway, my guiding principle is to leverage as much work as possible that has been done by Tesla, including architecture. So having unswitched HV outside the battery box is something I'd like to avoid. Also relays are a big source of reliability issues IMO and I'd want to eliminate those, especially in the contactor drive, and instead rely on CAN messages and MOSFETs.

My other aim is to keep the system as safe as possible, so having the BMS in control of the contactors seems worth the risk to the Inverter (rather lose the inverter than have a battery fire), and given that it is on the same CANbus as the DU, presumably it can shut down the drive before opening the contactors.

Also safety wise I'd like to see HV leakage detection, don't know if/when Tom is going to add SimpISO to his SimpBMS?

One interesting tidbit in the MS Theory of Operation is

When the vehicle is on and the contactors are closed, the DC-DC supplies the current necessary to operate the entire 12V electrical system. When the vehicle is off and the BMS is in standby mode (contactors open), if the 12V battery voltage drops below 12.3V, the gateway module requests the BMS to enter support mode. In this mode, the BMS closes contactors and supplies current to the DC-DC converter, which in turn maintains the 12V battery within its nominal SOC range.

So the BMS also would have to be looking for this notification from whichever entity is monitoring the 12V or be monitoring it directly (not sure if EVS-BMS does this autonomously?)

Final missing item for me is CCS support for which the LIM seems to provide most of the management, but that would need to be supported in the VCU.

BTW love your diagrams, what software did you use to make them?
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Re: Subaru Legacy + Tesla SDU Conversion

Post by alexbeatle »

elShankos wrote: Sun Jan 29, 2023 7:00 pm So I decided to make an alternative wiring diagram with the following 2 main differences to the Rev 3 above:
1) I've added a main -HV contactor (to be like an actual Tesla arrangement - must be a reason its there right? :) ) and also switching all the contactors in an OR arrangement - either from the BMS (non latched main contactors) or Inverter (latched main contactors)
2) Using a Tesla GEN2 rear junction box (got one for cheap in the US) to tie in the charger so now there is no extra line from the front of the car to the back.

image.png

So I think this will work (with lots of 12V relay wiring) and provide pre-charge to the auxiliaries as well in both driving and charging modes but my only concern is: what about in driving mode, switch on ignition and the pre-charge closes, then opens and then maybe the BMS takes a turn trying to close it... might have both the Inverter and BMS opening and closing the pre-charge contactor a bunch of times? Maybe not but I'm not sure about this one - bit hard to say.

Otherwise it seems like maybe a better solution - would be good to hear folks' thoughts :)
Looks great!
Small note. A/C and PTC heater (if you're gonna add one) are fused with 40A in the FHVJB.
https://www.diyelectriccar.com/threads/ ... ox.193729/

Any chance you found a reasonably priced pre-made harness for the SDU LV wiring?
I see people here mention that there's an OEM one from some other vehicle which works for LDU.
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

alexbeatle wrote: Wed Mar 29, 2023 4:19 am Looks great!
Small note. A/C and PTC heater (if you're gonna add one) are fused with 40A in the FHVJB.
https://www.diyelectriccar.com/threads/ ... ox.193729/

Any chance you found a reasonably priced pre-made harness for the SDU LV wiring?
I see people here mention that there's an OEM one from some other vehicle which works for LDU.
Thanks - I'm sort of getting there! No luck on any wiring harnesses - I will be making up my own. The guys from EV West sell the plugs for around $10.
Thanks for the heads up on the PTC heater and AC unit fuse ratings - will revise.
One thing I was thinking of is re-using the piping into the dash and rather connecting up a tesla battery heater and a pump - I think they are 5kW and we don't need much heating her in South Africa! Just an idea at this point to avoid trying to bash a different sized PTC heater into the existing vent system which looks like an almighty pain!
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

jetpax wrote: Fri Mar 24, 2023 5:58 am Great to see a open discussion on this as I've also been agonising over all the possible ways of architecting my own system. My current layout looks basically the same as yours, but I'm using M3 DU with an as yet undetermined VCU (a bit heretical to say it on OpenInverter even as a Damien patron, and being in awe of @johu but I'd really like to crack the pairing process as T2C and Ingenext have done :twisted: ).

Anyway, my guiding principle is to leverage as much work as possible that has been done by Tesla, including architecture. So having unswitched HV outside the battery box is something I'd like to avoid. Also relays are a big source of reliability issues IMO and I'd want to eliminate those, especially in the contactor drive, and instead rely on CAN messages and MOSFETs.

My other aim is to keep the system as safe as possible, so having the BMS in control of the contactors seems worth the risk to the Inverter (rather lose the inverter than have a battery fire), and given that it is on the same CANbus as the DU, presumably it can shut down the drive before opening the contactors.

Also safety wise I'd like to see HV leakage detection, don't know if/when Tom is going to add SimpISO to his SimpBMS?

One interesting tidbit in the MS Theory of Operation is

When the vehicle is on and the contactors are closed, the DC-DC supplies the current necessary to operate the entire 12V electrical system. When the vehicle is off and the BMS is in standby mode (contactors open), if the 12V battery voltage drops below 12.3V, the gateway module requests the BMS to enter support mode. In this mode, the BMS closes contactors and supplies current to the DC-DC converter, which in turn maintains the 12V battery within its nominal SOC range.

So the BMS also would have to be looking for this notification from whichever entity is monitoring the 12V or be monitoring it directly (not sure if EVS-BMS does this autonomously?)

Final missing item for me is CCS support for which the LIM seems to provide most of the management, but that would need to be supported in the VCU.

BTW love your diagrams, what software did you use to make them?
Hi, yeah there are 100s of ways to do this and I've spent quite a while on this with my main drivers being:
- as simple and analog as possible (in terms of contactor control)
- Not adding any more micro processors / CAN control / programming to my list of things to do and also to try and keep it simple (for me!)

CCS is definitely something I have been thinking about so am aiming to use that Tesla GEN2 Rear HV JB with the contactors in it but for now just charge at 230V and figure out the rest down the road. CCS stations are around in SA but not many - they will pick up in the next few years.

On the EVS-BMS I really need some batteries (not here yet) to get that system fired up so I can start figuring out what it can and can't do properly.
Seems like everyone on here with an SDU / LDU is keen on never opening contactors while driving no matter what so I have that signal to cut the drive 12V in case the battery isn't happy, then pull over, ignition off - get the hell out of the car?! That's my planned sequence of operations in an emergency while driving.
While charging, 12V to the SDU will be off and the BMS will control the contactors so if its not happy it can open them. :D

I make my diagrams in plain old AutoCAD - thanks for the compliment, I'll take it! I'll move onto a "construction" version at some point soon where I will draw out the actual positions of the relays in the main box and things like that.
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Re: Subaru Legacy + Tesla SDU Conversion

Post by elShankos »

Hi All, I thought I would post a mini update on my build:
- was overseas for a month!
- Now I finally have to refurbish and sell this original Vespa I have had in my garage for the past 6 years as its taking up space where I need to put the subaru to pull the engine etc:
image.png
Such a smelly 2 stroke mess!


- Then I had to find another car as a daily driver as I only own the Subaru - I eventually found a 94Ah BMW i3 so once that arrives in 10 days I should be able to crack on!

I guess we all have these distractions, changes, other things we have to do along the way etc :mrgreen:
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