This was also posted to the Prius_Technical_Stuff yahoogroup. . I've been investigating some inverter temperature stuff. I don't think anyone's determined the right incantation to make a Scangauge display inverter or motor temps yet, so I've brought out taps from the GIVT and MIVT temperature-monitor ECU leads for the MG1 and MG2 inverters respectively which produce a voltage somewhere between 4.5 at "cold" and 2.something at "fairly hot". Similar inverse indication as a NTC thermistor with a pullup, but linear rather than having the odd curve that the ECT lead does, and it's an actual electronically-driven output rather than a raw sensor. I assume they're derived from those extra leads right into the transistor dies that sense heat. I can't really tell where either xIVT lead goes on the inverter board as they come off the connector and quickly dive into the inner layers. . I divide them by 3 and switch them into the same ECT linearizer nonetheless, figuring it's a convenient way to just get a relative reading even if it's not dead accurate. I want something I can check as an overheat warning on hot drives. But I thought it would have slightly better range than I've been seeing so I went to investigate more closely this evening. I set up to monitor temps about three different ways: the AE laptop doing active queries to the hybrid ECU, a voltmeter hung straight off the outputs, and my little panel circuit. I wanted to see a larger range, and thought okay, how does one get the inverter decently warm fairly quickly? Obvious thing to try: pull the coolant pump power and then carefully send some current through the transistors. . We've heard plenty of stories of peoples' Priuses dying on the side of the road after losing the inverter pump. Well, a careful listen to my five year and 100K-plus old unit tells me that my own pump is starting to get a bit of bearing noise and probably won't last forever either, and it's time to spring for a new one to keep ready to swap in. But in the meantime, there's some playing to be done. After pulling the power and hearing it go silent, I tried a very careful little bit of force-charging while hawking GIVT. From a little more than 40C, mostly coming from existing underhood temps, it bounced up a little but still settled back down quickly after I stopped. I tried a little more. I tried watching MG2 and dragging the car back and forth a bit against the parking brake, sending 20 amps through the big guns for the length of the driveway, back and forth. Those temps crawled up a little but even with the coolant loop still *not* running, it was clear that transistor heat was rapidly dissipating into the big surrounding block of metal inverter case. In fact the rear brake drums were getting considerably warmer than the inverter from all that. . I went for a drive. MG1 works the hardest under normal street travel if you aren't demanding a lot of electric, and MG2 gets occasional bursts on braking events, but while both were pushing 70 C after a while [with the engine right next to it up at full running 85 C temp by now], neither figure seemed to be getting to truly dangerous levels. Under normal driving in ~ 70F ambient temps, it seems that the coolant pump is less important than any of us thought. Not to the nonessential level -- it's still important to have the cooling capacity for those switching elements... but having it fail does *not* spell instant inverter death and crispy-fried transistors, and one could probably tool along in not-too-hot ambient weather for quite a while without ever realizing the thing wasn't running. . I wound up stopping by a local cruise-in, whose organizers reassured me that there was certainly a place for a new and interesting car among the old and loud ones [phrased as: "if it's got four wheels and rolls, bring it in!"] ... so I pulled in and entertained people with tours of the ripped-apart dash and such. Lots of interest, in fact, which I found sort of surprising from folks who had come out to celebrate muscle-car mystique. Left the system powered up the whole time I was there, inverter pump still disconnected, with the hood up so people could see the stuff and ask questions if they'd never really looked at a Prius before. Even with periodic HV-battery topoffs by the engine, the inverter temps drifted down to around 50C and stayed. The inverter case was only mildly warm to the touch. . And to think of all those car and energy shows and other events I've been to where I had the system powered up all day, putting needless hours on the inverter pump when really, I didn't need it just to run the DC/DC converter for my power feed. The metal case can radiate quite a few watts on its own without help, and that's apparently sufficient to keep it in safe temp ranges in powered-up-but-quiescent operation. It's probably time to put in a switch for the pump, since its connector is actually not that easy to reach in and unhook. . I did get a few funny stares as I silently slid my way along the rows at the cruise-in, at less than a walking pace, looking for a spot. I looked back at some of these folks and said "vroom, vroom!" and they thought that was hilarious. It's especially appropriate because I'm intending to get into Madison early and make the pre-Hybridfest cruise-in next Thursday. Wires hanging out of the dash and a laptop with bargraphs in the shotgun seat does attract a certain interest. . _H*
Hi Hobbit, I am also starting to worry about the inverter pump on my 2004 with 81K miles and just bought a replacement for $88 plus shipping from Champion Toyota, Houston. (MSRP is $116.) The part number is G9020-47031, it had to be special ordered. Consider that most inverter pump failures have been reported in the hot summer months. This supports your observation that you can drive a reasonable distance in moderate ambient temps without the inverter pump running, and suffer no ill effects.
An additional piece of info: Toyota's "operation history data" logging facility of the HV ECU flags occurrences of either inverter temp rising above 111 deg C. That's quite hot, and possibly also the point at which the triangle goes on and the car takes steps to protects itself. The 80 C I was able to only momentarily achieve through various forms of abuse yesterday was still well under that. . I also observed in the "driveway tests" that when MG2 is pulling hard against a load but going VERY slowly, its inverter temp actually jiggles upward a little, maybe about 5C worth, about 1/3 of the time. Apparently some source for the temp readings is actually affected by whether its associated transistor is actively passing current at the time or not. That's fascinating. I'm not sure if that really means the die's temp is really going up and down on such a fractions-of-a-second basis, or the presence of all that current simply affects the sensing element directly. Maybe some combination of both. . _H*
Thats cool Hobbitt. Good work. My warranty status prevents me from tearing into the car for things like that. I was always surprised at how cool the inverter ran. Always thought it was because of a very efficent pump system. Guess not. Here in Tampa in the dead of cruel summer never saw more than 130-140F inverter case temp. It would spike substanstantially from heat soak after you shut it off. The total underhood heat would get it where I guess the inverter mass would work against it with no air moving around it. But your study shows that in cooler parts of the country you can drive quite a while with a failed pump and not have any problems. Thats scary.
I think they appreciate anybody who understands the details of how their car works, and one of the reasons many car hobbyists stay with older cars is because they're easier to understand. So having somebody demystify the electronics of a new car, particularly something as complex as the Prius, is an interesting, and probably rare, treat for them. Especially from somebody who understands it simply because it's their interest to do so, and not because a car manufacturer is paying them to promote a vehicle or technology.
Great analysis. Why wouldn't Toyota put a thermostat on the pump and only run the system when the inverter temp exceeded a certain point? That would probably make the pump last longer than the car. As for the Prius fitting in at the cruise, the pics of my car below were taken at a cruise. Around here the car guys are pretty liberal, and seem to like just about anything (especially if it isn't stock - any personalization gets respect, as it shows you are into mods and not just a "driver"). I've had over 60 cars, including muscle cars, and hang out with the hot rod crowd here in Denver. The only dissing I get is from our oldest daughter, who loves to laugh at my "toy" car, giving me left-over batteries to keep it going, etc.
I've posted my recent experience replacing the inverter coolant pump here: http://priuschat.com/forums/gen-ii-.../65173-how-replace-inverter-coolant-pump.html
I ordered a replacement pump as I have over 101k miles. I am not so sure if I should replace the pump when I replace the inverter coolant.
It seems a good preventive measure to replace it, especially since you have already ordered one why not do it? Good luck!
Thanks guys. I ordered it to replace the pump along with the coolant. It seems wasteful because the pump is working fine. I looked under the cap and I can see the waves. But then I wouldn't want to change the pump later when it fails, say at 120k or 150k.
Yes, it appears that you log many miles per year on your Prius. Is it wasteful to replace the pump at a time and place convenient to you; or is it better to wait for the pump to fail and cause the inverter to overheat, usually at a time or place that is not convenient - maybe on the Long Island Expressway during rush hour traffic? Then you have to pay for a tow, pay premium prices for the dealer to replace, etc. That seems more wasteful to me.
Patrick, you make a good point. I will be replacing the coolant because I do not want to void the warranty on the inverter. If I remember correctly, it goes up to 10 years / 150k miles since NY is one of the CARB emission state. You point persuade me to replace the pump as well. I hesitated because Hobbit's finding indicates that the pump is not critical (no damage) and another user reported the car can operate after cooling it down (shut off). My car is a little over 3 years old and changing the coolant and the pump every 3 years seems too frequent. I guess that's because my commute is twice longer than an average American. The new and improved pump should last longer. $100 pump every 100-150k miles is not bad. The coolant is still red pink. Is there a way to tell the life left in it?
Stop ordering backup pumps for future repairs! I am in desperate need of one and the dealership can't even give me an ETA on when it will eb available because they are backordered nationwide! I'm stuck with a rental and Toyota will only cover half the cost. Does anyone know of a source to obtain this part other than through the dealership? It's been almost a week already without even an ETA ont he part, let alone an estimate of when it would actually be shipped and the repair completed.
