[DRIVING] Project RX8 , Prius gen2, Lexus transaxle to rwd

Tell us about the project you do with the open inverter
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Pete9008 »

Is 15R a typical value? I've no practical experience here but it just sounds a little on the low side?
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

15 ohms It’s what I measured the damaged ceramic one that is originally from a bmw phev box at with my lcr meter, the ones zero ev sell on their website are 30ohms so I guess somewhere in that range is about right, I’ve tried higher values in the the past and run into issues with the dc convertor pulling the voltage out of the dc bus faster than it could get through the precharge
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by mjc506 »

My BMW 'safety' box precharge also measures 15ohms, I've something out of a prius that measures 25ohms. Somewhere in that range should be about right.
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Pete9008 »

I've got the BMW sbox too so it looks like 15R is what I'll be using as well!

I'd just worked out the bus charge time for a 1000uF cap (think the Prius gen2 inverter main bus cap is 880uF?) and with a 15R the voltage would be up to 60% in 15ms and up to full voltage in well under 100ms. That just seemed a bit quick?


That assumes no load though, if the DC converter is taking power while the voltage comes up then using a lower value resistor makes much more sense :)
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by mjc506 »

I get about .5sec with a prius inverter, DC/DC etc etc

Surge current into the caps is the concern, but reactance becomes significant quite early on. I figure if BMW chose 15ohms, good enough for me :-)
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

Over 750 miles since July and had no issues with the main caps, and most of my journeys are 4 miles to work
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by celeron55 »

OEMs use really low precharge resistor values in order to make the precharge happen really fast, and in order to have a very low remaining voltage over the contactor to lengthen the life of the contacts.

In exchange of that low value they have to monitor the precharge very fast in real time to abort it if it's going wrong. A 5 second timeout is totally out of the question. If there's a short, a 13 ohm 50W resistor will turn into smoke in the blink of an eye.

One more known precharge resistor value for the record: Model S uses a 23 ohm 50W resistor.
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by mjc506 »

Good point. Customer satisfaction (little/no delay between pressing the button and driving away) is perhaps more important than longevity (outside warranty periods, anyway).

In my bench setup, I'm closing the main contactor when HVbus reaches 95%, timeout (0.75sec) or overvoltage results in emergency shutdown (open all the contactors, flashing lights....) haha
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

Finally made a cover up for my makeshift bargain bucket heater, it’ll do for now but I’m not really happy with the amount of space it takes up and the inefficiency of powering a pump and moving water around, so long term I want to put a ptc air element in the heater box but that’s a dashboard out job!
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by lsh3rd »

Great interview with Tom today! I really enjoyed this one and I recall the exact point in the video when I connected the build in this thread with the description of it in the video.

The one thing that really jumped out at me might deserve its own thread. We know that Toyota's motors won't give all they are capable of without utilizing the higher voltage they are designed for (See Johannes's A2 build). We all know the boost converter isn't rated at a high enough power level to drive a motor in a dedicated EV conversion, so folks bypass it.

Then you said it in the video... why not use the boost converter coupled with a stage in the inverter to do higher voltage charging? The somewhat wimpy boost converter might not source enough power for a powerful motor, but it's probably adequate to charge a battery at significantly lower currents. I do wonder if anyone has considered this before and if it is feasible why has it not been used yet?

I assume it would need to be feasible to use the higher pack voltage in a Prius inverter in the logs where the boost converter was bypassed. It would also be helpful if the DC-DC converter could handle the higher voltage. It seems like most have not used these components past 400V, so not sure if it is feasible to up this by 50%. (and then I melted my inverter too??)

I'm considering weather or not to use the gen 3 Prius transaxle in a conversion - I have one I paid only $50 US for. If a charging solution existed to allow using 9 60V BMW modules in series, it might be viable. (...and probably paralleling another 9 - it would be easy to source 3 whole batteries for 18 total modules.) I am also considering sourcing the larger transaxle you started with since these are actually quite common in USA - a quick look in local yards shows three potential donor vehicles and the price would be about $120 US. It seems like a viable solution for an ultra low-cost, yet powerful conversion.
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

Thanks, actually running the boost inverter to charge a higher voltage battery pack isn’t really an issue johannes did so in the a2 build, it required and additional recitifier, current sensor and needs to be fed the rectified ac on the side of the boost converter normally connected to the battery. But it’s certainly possible and in many ways charging a higher voltage pack 96s upwards is simple 80s like I currently run is more difficult as from a 240ac source you’d actually have to buck at start of the charge and transition to boost.
As for the dc converter the Prius gen2 one shuts down at just over 320 volts I know again johu’s a2 in this mode is utilising the boost converter to buck the dc bus voltage down to the the dc converter.

For much higher voltages the gen2 Prius inverter isn’t ideal as the main cap I think is only rated to 500v.

Bmw modules in a string of 9 series will either need a different bms system or some way of running half the bms modules on a second canbus, as there are only 6 available can addresses for the modules. I know Jamie jones has a version of simpbms code for a teensy 3.6 that will handle 2 lots of modules on 2 can bus’s but I think it’s designed to work them in parallel..
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Bigpie »

I do run the packs in parallel, but the BMS doesn't care if they are in parallel or not, as long as setup correctly. SimpBMS might already have offset setup for BMWS, but you'll need a canbus bridge between the duplicated IDs to add/subtract and offset as needed or a second can interface.

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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Pete9008 »

Bigpie wrote: Fri Jan 13, 2023 8:22 am World needs more crazy Steves
This, definitely!

Worth having a look at this viewtopic.php?t=2123, I think it is compatible with the BMW modules and can cope with more than 6.
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

Lol thanks guys and I thought I was normal!
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by lsh3rd »

Ev8 wrote: Fri Jan 13, 2023 7:43 am For much higher voltages the gen2 Prius inverter isn’t ideal as the main cap I think is only rated to 500v.
Personally, I'm using a Gen 3 inverter. I have the smaller of the 2, so I should probably look to see if these are rated at 600V or 650V. I know there is a Auris/Yaris inverter in the smaller form factor, but mine came from a '13 Prius, so I'm really unsure what's under the lid. I suspect they might be 650V parts since I believe the Prius also uses different current sensors as well, so I suspect the small Prius inverter might differ compared to the Auris/Yaris inverter.

Obviously for my proposal this would matter since 9 modules should be a tick over 600V fully charged - it's really cutting it close even for the 650V caps.
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Alibro »

Great interview on Tom's channel.
Only problem is I now have to reread this from the start again cause lots of things were mentioned in the interview I'm interested in. :lol:
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

Thanks, I probably haven’t fully documented everything I’ve done here but you get the idea,
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

Hopefully someone can help here, I’ve just been out to try and plot a coast up (downhill) so I can calculate flux linkage, however when I plot udc,Id,iq,ud,up,fstat I get ud and uq displayed in digits which are in the thousands and so the Auto ranging graph makes all other values look so small they are basically a single line! Other peoples plots look like ud and uq are in volts?
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Bigpie »

Click the button that says show data logger instead and save the csv
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by johu »

Or put ud anx uq on the right axis by selecting the "r" checkbox
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

Perfect thanks guys forgot I had the r/h axis to use, and also have taken some logs in the meantime
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

Managed to succeed in some coast down logs but done stationary with the car out of gear… opened them up in excel and added a column with the maths to calculate flux linkage, mg1 for the most part mid 60’s about 66mweber pretty close to my guess of 70 mg2 seems a bit off though almost like flux linkage decreases with speed, I get from 100 to about 160 as it slows back down, currently set at 120mwebber
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Pete9008 »

Good idea doing the coast down out of gear (although you do need to be pretty confident that it is set up right, with fw it is in theory possible to overspeed the motor if a parameter is wrong).

What was Ud doing during the coast? If it wasn't zero throughout then either syncadv or syncofs are probably slightly out and that would cause an error in the calculated flux linkage. If you want to post the log I'm happy to have a look.

Edit - curious how you solved your wifi signal problem, did the antenna do the trick?
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Ev8 »

so i firstly fine tuned syncadv and sycof just logging ud and uq in the web browser, aiming for ud to be around 0 when coasting down, seems to jitter plus or minus a couple of hundred digits, Turns out MG one needed syncadv of 26 to keep ud flat, Mg2 needing 18.

but yes it was constantly in my mind about the possibly of loosing control of the motor!

the high gain wifi usb wifi adapter has certainly helped but its still flaky, i guess the 2 boards being double stacked means the wifi adapter on mg1 board is kind of sandwiched between 2 ground planes! not ideal

logs attached, ignore the first bit of each as thats bringing the motors up to speed
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Re: Project RX8 , Prius gen2, Lexus transaxle to rwd

Post by Pete9008 »

Thanks will have a look, forgot to ask, which version code were you running for this?
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