openinverter forum

Hi All,
After 2 1/2 years of having the cayman sitting in the garage on blocks 3 ft in the air, I finally was able to button everything down enough to take it out for it's maiden test drive. I only went around the block, but generally everything seemed to hold together.
Here's my setup:
Porsche Cayman 987S with Tesla LDU and openinverter board, Vero BMS (re-brand of SimpBMS), Chevy Volt Gen 1 batteries.

What I did notice was the following:
1. Throttle seemed to be a little touchy. Meaning, tip-in wasn't as gradual as it could be so when I was trying to inch forward and backward out of the garage, it was hard to crawl slowly. When I tried to start and stop too suddenly, it stalled out which required me to shutdown and re-start.
2. On braking, a louder noise was heard (not bang, but more of a groan) and again the car would shut down which required a re-start.

Both issues were resolved with re-starts but would happen when those situations happened again. I feel like it may be related to the regen settings, but the parameter reference page no longer works.

I'm at firmware 5.35.R-sine and my params file came from Boxster EV who posted it in 2024 saying it works great. My build is almost identical to his with the help of his many informed posts and answered questions so I'm eternally grateful to him for getting me this far.

Any feedback would be most appreciated. I've attached the file i'm using... Thanks in advance!!

A few thoughts:

Parameter descriptions are here.

If you're using 5.35, have you implemented the throttle safety mod described here? And calibrated your throttle as well?

The loud bang and shut down on regen sounds like the desaturation fault that happens at full throttle on the LDU. Basically the Tesla gate drivers shut down when they are unhappy with the current they are seeing and it takes a power cycle to reset. The bang is the drive train suddenly unloading. (unless there's a whole lot more clattering around after the bang, then it's the axle breaking, ask me how I know)

Looking at your params, I'd suggest lowering boost and raising fweak. Make small changes on fweak, you can make bigger ones on Boost.
You may also need to lower fslipmax, that's high for any LDU, but especially a base inverter.

Possibly back off a bit on offthrotregen, but you're in an ok range.

Also for the sake of your batteries, raise udcmin. It should be above your 0% SOC voltage, its currently set to 20.

Awesome. Thanks for the quick response! I did calibrate the throttle but it was probably 6 months ago so I'll double check it again.
Will follow your advice and report back.

Thanks again!

Also, forgot to ask.... Since it was probably six months since I last tried to fire up the motor (before I got it going to take it on it's first test drive), it looks like the inverter lost all the settings and resorted back to defaults so it wouldn't work at all. I had to re-upload my params file to restore everything and then it started working again. If the inverter doesn't see power (low voltage or high voltage) for a period of time, is this known to happen? After how long?

spiff wrote: ↑Wed Sep 03, 2025 1:07 am Also, forgot to ask.... Since it was probably six months since I last tried to fire up the motor (before I got it going to take it on it's first test drive), it looks like the inverter lost all the settings and resorted back to defaults so it wouldn't work at all. I had to re-upload my params file to restore everything and then it started working again. If the inverter doesn't see power (low voltage or high voltage) for a period of time, is this known to happen? After how long?

I have never seen this happen. Make sure you remember to click Save Parameters to Flash before turning the car off, otherwise any changes will be lost. Also it won't save in Run, so either make and save changes before giving a start signal, or use the manual stop before saving and then turning off.

So. I recalibrated the throttle and adjusted fslipmin as per the starting guide first and also adjusted a few other settings. It seemed to make an improvement and the inverter wasn't shutting off during breaking. Starting off felt a bit better too.

So I drove for a few more minutes and the power started reducing to the point where the inverter shutdown even at the slightest nudge of the throttle. I waited a bit and the power came a bit but quickly died out again. I checked main HV and it was fine, then I checked 12V and it is a little low (12.5V) but still okay.

So when I looked further at the spot values the temps for the heatsink were 58.5 deg C after sitting with the pump running for a bit (20 mins) and rotor temp is 31.9 deg. Setpoints for both are HS Max is 85 deg. C and rotor is 300 deg C.

Could it be the heatsink overheated? There may be air in the lines so I'll have. to flush and confirm.

spiff wrote: ↑Thu Sep 04, 2025 2:39 am So when I looked further at the spot values the temps for the heatsink were 58.5 deg C after sitting with the pump running for a bit (20 mins) and rotor temp is 31.9 deg. Setpoints for both are HS Max is 85 deg. C and rotor is 300 deg C.

Could it be the heatsink overheated? There may be air in the lines so I'll have. to flush and confirm.

That sounds like something overheated. If my car is sitting with the pump running for 20 minutes, I'd expect the inverter temp to be close to ambient.

Thanks! I’ll give it a shot tonight.
Love your Yoitube channel btw..

So I tried to purge the coolant lines and think I did a reasonable job but not totally sure.
I took the car for another run and got it up to ~20mph a few times and plotted the rotor and heatsink temps. Does the following look normal? The HS temp is closely following the throttle inputs. Not sure if it should be going that high that quickly.... Would. appreciate any feedback on this if it's just a cooling issue or could my parameters also be causing it to overheat too quickly, or is this normal? The red line is the Heatsink which tripped the max value yesterday.

How is you cooling setup plumbed?

Take pictures and describe the flow path.

You have serious issues in your cooling system.

Following throttle inputs, yes to an extent. Getting that high that quickly, no. I rarely (if ever) see hs temps above 50C

A couple questions:
What direction are you flowing water through the drive unit? Factory configuration is motor first, then inverter. I had mine backwards and actually saw cooling improvement, even though its picking up heat from the motor first, when I switched to factory, because it corrected the flow within the drive unit.

How big is your radiator, and is it getting good airflow?

What pump(s) are you using, and are you confident that it is running correctly and consistently?

Thanks. Good to hear this is not normal behaviour or I wouldn't be able to go above 20mph!
Here's my setup:
Using factor Porsche radiators (two sides and one centre), a 35 Lpm pump. The pump (from the sound at least) is running consistently.
.

I'm 90% sure there's either a blockage somewhere (pinched hose) or more likely still air in the system so I'll focus on that now that I know this isn't normal.

I'm open to any additional feedback anyone has.

Thanks,
Paul

Way too much resistance. Put motor on its own loop with charger and dcdc.

Also what pump is this?

Yeah that's way too much stuff for a single pump. I'd say give the LDU its own circuit and pump, or like Tom suggests put it on a circuit with the DC-DC and charger.

In my car, the LDU has its own circuit, the DC-DC and charger are on one together, and the battery will eventually have its own.

Hi Guys,
Sorry I was on vacation for a few weeks in the south of Spain. It's a tough life I know.

Back to the build...
I re-routed the expansion tank to feed just at the input of the pump. It's a Davies-Craig 35L/min pump, same one that Paul used on his BoxsterEV build. I first wanted to rule out any air in the system, so I drained the coolant and then vacuum filled the system.

This time, when I turned on the power and started tracking values when the inverter was not but the motor was not spinning, it slowly started rising in temperature. It was in forward and I pressed the accelerator a few times just to ensure it worked. But as I let it sit like that not turning, the heatsink temperature went from about room temp all the way up to almost 80 Deg C over the span of about 20-30 mins. I went around and felt around the rotor casing, gearbox and inverter casing and it only felt a little warm between the inverter casing and the gearbox casting on the top side. Definitely not hot, but just a little warm compared to all the other areas of the motor.

Since the batteries are directly downstream of the motor in the coolant flow, I checked the battery temps from the BMS when the motor heatsink was showing 70-75 degC and the battery temps were showing room temperature. All the hoses also felt cold.

So is there something else happening here where the heatsink coolant passages could be blocked but the main rotor passage is not?

Would it be normal for the motor heatsink to just increase like that with no current going through it just in ready state? Do I need to calibrate the heatsink temp setting? It almost seems like it may have stabilized around 70-75, but I'm not sure as it got closer to 80 degs before I turned it off.

As I mentioned before, the motor seems to spin when I test drove it (other than optimizing the parameters to avoid the jerking and cutting out).

Thanks in advance!

spiff wrote: ↑Tue Sep 30, 2025 2:05 am This time, when I turned on the power and started tracking values when the inverter was not but the motor was not spinning, it slowly started rising in temperature. It was in forward and I pressed the accelerator a few times just to ensure it worked. But as I let it sit like that not turning, the heatsink temperature went from about room temp all the way up to almost 80 Deg C over the span of about 20-30 mins.

Had you selected a direction, or was it just sitting there in "neutral"?

When I have had my inverter on but in neutral with the cooling system not running, I have seen no temp rise. When I select a direction (thus starting PWM) I will see a slight rise without the cooling system running. I don't think I've ever let it sit for 20 minutes "in gear" with the cooling system off, so I don't know how hot it can get. But it seems you've got some sort of issue, either with the temp sensors or the inverter itself.

spiff wrote: ↑Tue Sep 30, 2025 2:05 am I went around and felt around the rotor casing, gearbox and inverter casing and it only felt a little warm between the inverter casing and the gearbox casting on the top side. Definitely not hot, but just a little warm compared to all the other areas of the motor.

I've not done the same, so I can't compare, but that location would be where coolant is coming out of the stator and heading down to the inverter.

I have not seen the motor temp rise when not spinning.

I still think there's a good chance the pump is just not able to push coolant against all that resistance. If I were you, I'd strongly consider putting the LDU on its own circuit or adding additional pumps in line.

I've seen this and it turned out the inverter was damaged

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P.S.Mangelsdorf wrote: ↑Tue Sep 30, 2025 11:24 am Had you selected a direction, or was it just sitting there in "neutral"?

The power was on (pre-charge complete, main contractors on) and the direction was forward. When just 12V connected to the inverter without the HV power turned on, the HS temps went back down slowly.

So I’m assuming this isn’t normal behaviour and no easy way to check calibration on the temp readings? The rotor temp stayed at room temp during this time and barely moved if at all when I was turning the motor briefly to test function.

johu wrote: ↑Tue Sep 30, 2025 1:20 pm I've seen this and it turned out the inverter was damaged

Any way to test or confirm this? Or a specific part of the inverter I need to look at to diagnose? Or was the inverter damaged beyond repair requiring a new inverter or motor?

Not great news to hear.

The reason I’m hesitant to think it’s not enough cooling or the pump is overwhelmed (has too much resistance) is that when I feel the downstream hoses, I can feel the vibration of fluid running through the hoses. Immediately before and after the motor, the hoses also feel cool, even when the HS temp was showing close to 80 degrees C. I understand if you have no fluid moving, you’ll definitely see the rise in temps, but it would be strange that at the outlet of the motor, the hoses was still feeling cold.

spiff wrote: ↑Tue Sep 30, 2025 8:48 pm Any way to test or confirm this?

In the case I witnessed we didn't even look at tmphs but we found the inverter enclosure to be hot to touch with the car just sitting on the lift and the inverter connected to HV. I think the PWM was even off.
Strangely the motor would even spin up but the car had no power and quickly tripped over current faults. Swapping in a new inverter solved the issue.
Maybe if you can get ahold of a single phase module you could try and replace only the faulty one. Provided only one is defunct.

spiff wrote: ↑Tue Sep 30, 2025 8:48 pm The power was on (pre-charge complete, main contractors on) and the direction was forward. When just 12V connected to the inverter without the HV power turned on, the HS temps went back down slowly.

So I’m assuming this isn’t normal behaviour and no easy way to check calibration on the temp readings? The rotor temp stayed at room temp during this time and barely moved if at all when I was turning the motor briefly to test function.

Ok, so with the direction selected, PWM has started, and that's what generates heat in the inverter. In my experience, sitting idle with PWM on will cause a rise in temperature, if my cooling system isn't running. To me, this points to a cooling system fault.

spiff wrote: ↑Tue Sep 30, 2025 8:48 pm Immediately before and after the motor, the hoses also feel cool, even when the HS temp was showing close to 80 degrees C.

This is a red flag. At significantly lower temperatures, I can feel the hoses getting warm all the way up at the radiator.

spiff wrote: ↑Tue Sep 30, 2025 8:48 pm I understand if you have no fluid moving, you’ll definitely see the rise in temps, but it would be strange that at the outlet of the motor, the hoses was still feeling cold.

It sounds to me like there might be an internal blockage, preventing coolant from getting to the inverter. It might be worth pulling the inverter off and confirming if coolant is getting into the inverter cooling passages.

Before fully doing that, you might consider removing the inverter case, reconnecting power, and powering up the inverter to see if you can observe it getting hot. Because if it doesn't, then it's a sensor problem. If it does, then it's a cooling problem, or maybe a bad phase. I say this with the full caveat that applying HV with the inverter exposed is dangerous, sketchy, and needs to be done exceptionally carefully. But I've done it several times, so it is possible to do so.

Sorry for the delayed response. Life gets in the way with general busyness. So I had a chance to some more digging on the issue. I started by testing the coolant pump in the car by pulling off the coolant exit hose to see if coolant was coming out and it did, but slowly. I checked for blockages in the motor by running an external pump to push coolant through the motor and it was full flow. Then I isolated the coolant pump from the car to test it separately and found that the slightest air introduced to the pump prevents it from pumping. When it is primed properly, it does give the full 35L/min. So I realized that the system must still have air in it, even after vacuum filling.
I then went through a process of filling, then pressuring through an external hand pump at the coolant tank, running the electric pump and loosening various hose clamps at specific locations in the circuit to vent the air that was trapped.

Because it is a custom system, I’d be the first to say it wasn’t designed optimally to easily get rid of air. Using the process above, stopping frequently to refill coolant, then pressuraize, run the pump, let air escape out of several points finally seemed to work.

Now heatsink temps are stable both in idle and when the motor is spinning. So it looks like the pump is sufficient (for now, until I test further on the road).

Now, onto continuing to tweak parameters, the fun part!

Thanks again everyone!

Final comment to put this one to bed:
I didn't add a 2nd coolant pump. Had the car on the road this morning above 60 km/hr and the heatsink temp stayed flat at around 21 deg C. So my coolant flow diagram was still:
Pump ->motor ->batteries -> charger/DC-DC ->radiators (3) ->Pump on a 35 L/min Davies Craig unit, with Chevy Volt battery setup.

Now off to tweaking params to get it not to stall consistently.

So I was fiddling with parameters and seemed to be making good progress on throttle tip-in, but only when applying throttle gradually. But I realized I was using a different set of parameters from the ones I attached in my first post in this thread. The ones I posted were from Boxster EV who's been successfully running this set. for quite some time. So I uploaded those to try and now the pre-charge circuit doesn't seem to work. Is there anything obvious that could change in the parameters to cause this to happen before I start tearing into the wiring and HVJB? Unfortunately, i thought I had backed up the parameters I was running before I updated, but unfortunately don't have a copy. Here's the parameters I'm trying (and not getting out of precharge): Here's my error message:

So udcsw is 200 and udcmin is 20, what battery voltage are you running? Do you hear your contactors cycling?

Battery voltage is currently about 375V. I hear the precharge contactor going on when i put the key in, then turning off after a few seconds. During this time, i give the start signal which nornally turns on the main contactor but after the parameters upload, it doesn't close and i get the readout you see.