Im a commercial/industrial electrician, and working in an aging hospital like I do, from time to time Variable Frequency Drives (commonly used to adjust speed on an AC 3 phase motor for exhaust fans) tend to blow up. Anywhere from 10-25 years after installation. The reason for this can be a number of problems, most commonly the fluid in the electrolytic capacitors dries out and causes problems in the inverter section. How this pertains to the Prius should pretty obvious to most of us Prius tech geeks- How long is the speed control on our Prius going to last before going out in a stunning shower of sparks (yes, they usually BLOW UP) A VFD takes a 3 phase power input, Inverts it into DC, filters it, and chops it up into pulse width modulated "simulated" AC. From what i understand this is the same operation as the Prius speed control, except it doesn't have to convert AC to DC, as it already has DC from the 200v NiMh traction battery. Though in regen, it basically is doing a similar AC to DC conversion. I realize that just saying the Prius'es complex control system is an off the shelf VFD is oversimplified, and im sure Toyota has ruggedized and tested all the components involved, but has anyone heard of a gen 1 or 2 having the inverter go out before? What does this part cost from toyota? Is there any service interval recommended for the capacitors in the inverter? Its a hell of alot easier to swap one out before it causes major damage in the rest of the system at 10 years or so. Its over-obsessing, I know, but at least its not another oil change thread!
I am working with electricity too and I am thinking same thing. I know that electric warehouse trucks inverter works easily 20 years. Those trucks inverters are usually in gas tight enclosures. Maybe that is the difference?
I'm no EE, but there are some analysis of the inverter of previous gens at Special Issue: Inside the Toyota Prius: Part 5 - Inverter/converter is Prius' power broker and Prius links. As for inverters going out, yes, people blow them by jumping the cars w/reversed polarity and I think some here have them fail due to overheating caused by inverter coolant pump failure. FWIW, one of my former coworkers w/a HyHi <2 years old, at the time, had his inverter fail on a trip from the Bay Area to Tahoe. IIRC, he was stranded and had to be towed. I know of no maintenance interval on the capacitors nor any other components in the inverter. The price tag is in the thousands.
Yes, I really like it too. I just wish there were more pictures and higher resolution. It is interesting (or maybe this is common for high current inverters) that the power transistors and diodes are mounted as bare die. I really wanted a picture of the "ultraheavy-gauge aluminum wedge bonds", and a better resolution pic of the plate where they've mounted all these bare die. Our wedge bonder can do a maximum of about 50 um. It sounds like these are much heavier gauge. BTW, here is a pdf of the same article. It is easier to read and has better quality pics: http://www.leandesign.org/pdf/under_the_hood.pdf
Wow, thanks. Now I have yet another hobbit link in my bookmarks. The wirebonds to the power transistors are numerous and wild...
I've had to replace IGBT's (Insulated Gate Bi-polar Transistors) before in 5-50hp VFD's, and while they may not explode, the adjacent electrolytic capacitors, do INDEED....spectacularly I might add! And when the capacitor(s) starts going bad, it will often effect other components in the system adversely as it stops acting like a capacitor and starts acting like a dead short. At this point, the function of the capacitor, to smooth out the pulsating DC into smooth, flat, transistor/PWM friendly DC, slows down and eventually stops. Heat is a byproduct of a crappy conductor (which the capacitor becomes at this point) and thats when the KA-F*****G-BOOM happens. The solution in the field for us is usually to replace the entire unit when the caps start going bad, because they tend to fry lots of things from the control board to the afforementioned IGBT's. From what im seeing on that page, the construction and cooling of the unit looks like it should help alot with the lifespan of all the components, including the caps. But they do have a lifespan... Although in 2025-2040 when these should start going gunnybags, Id imagine we will all be driving flying cars that run on rainbows so who cares, right? Maybe the flux capacitor will be a direct bolt in replacement!
Back in a previous life, when I was specifying large electrolytics in power supplies, their lifespan was very highly variable, depending on type and on the details of the stresses of a specific application. Without much more detail about the parts and usage, I would not even attempt to guesstimate the failure rate in one application based upon experience of different parts in a different application from different designers at a different company.
Do keep in the mind the inverter was redesigned on the 3rd gen (2010 model year and beyond) and is physically smaller. I don't know of any teardowns of the 3rd gen nor comparisons to the 2nd gen's inverter. The OP might also appreciate the videos and PDF at http://priuschat.com/forums/gen-iii-2010-prius-main-forum/60002-prius-technology-video.html. I've included a pic of the 3rd and 2nd gen inverters, side by side from the Prius Connection San Francisco event.
smaller is not always better... I would rather have it take up more space and dissipate the heat better, then being a bit hotter and still "within specs".
Many electrical parts are available in different grades: commercial (0 to 85C) - narrowest range, often the lower limit is freezing industrial (-40 to 100C) - winder temperature range than commercial automotive (-40 to 125C) - the widest range of temperatures military (-55 to 125C) - bring BIG bags of cash For example, the 120 VAC inverter in my 03 Prius is not rated below freezing. This would be a commercial grade part. In contrast, an automotive grade part would work below zero and up to nearly boiling. Bob Wilson
to add to that, there is RADspec too incase we want to fly our prius in space, or drive in a nuclear reactor... Also industrial/automotive chips generally work within their limits with a fudge factor from different batches. Military is guarenteed to work within their limits.
Terminology is a funny thing. Say VFD to a computer guy, and he thinks "Vacuum Fluorescent Display". The MFD on the dash sure looks like one, whether it actually is or not. And these things tend to use voltages higher than the 12 volts that goes into them, so yes, you have an inverter for the VFD. Needless to say, I found a different discussion here when I started reading. Maybe we're just running out of letters And, yes, I know MFD might be "microfarads" to some of us, but I'm not the one making these up!
I thought that's what the thread was talking about until I read the first post. But the thread title is definately misleading for some of us...
And, so long as we're having fun with these kinds of numbers: The numbers given are for the junction temperatures of the devices in question. That's not, quite, the ambient temperature. There's this number, usually called "theta", that's the ratio of the rise in temperature divided by the wattage going through a given material. So, theta(j-C) is the ratio for the temperature rise from the junction to the case of a device; theta(C-A) is the ratio of the temperature rise from the case to the air, and, yes, that varies and becomes lower with an increase in air speed, and so on. So, if you got a transistor dissipating 30 watts that has a maximum junction temperature of 125 C, and the outside temperature is is 50 C (122 F),then you want theta(j-ambient) to be 2.5 C/Watt or less. (That's (122-50)/30) In fact, you'd like to be far, far away from 2.5 C/Watt because, well, parts last a lot less time if they're run anywhere near their maximum temperature. At 1.5 C/Watt you're talking physically huge transistors, monster heat sinks, and, well, coolant. Of course, this is where life gets really interesting. Big MOS switching transistors don't dissipate much power when they're on or off, but when they're moving between the on and off states. So you'd like to make them switch between on and off fast. But the bigger the MOS transistor, the more capacitance it has, and the slower it switches. On the other hand, when one is looking at the inductors and transformers in and around the motor and other such places, those parts become smaller and more efficient when the switching frequencies are higher - but the higher the switching frequencies, the more often one is turning the trannies on and off and the more power gets dissipated in the things. So, tradeoffs, tradeoffs, tradeoffs, costs of this versus that, and this is why engineering is sometimes called an Art. Oh, yeah. The Military stuff. It's not just the range of temperature that makes the cost of the Military parts so high. It's the fact that they do nearly 100% testing over a wide range of parameters before components are shipped that drives the cost up, too. Not to mention the fancy packaging. Not to mention shaking, vibration, and so on. There's this thing where when you're flying a fighter jet in combat, and you really don't want that radar to fail. Or the jet engine to flame out. Commercial, industrial, and automotive are sample lot based with lots of math to prove that most parts will work. They're right, but it requires testing of the completed boxes as a rule. Don't get me started on space or human qualified parts. KBeck.
If you want a capacitor guaranteed to fail after a couple of decades of constant use, install the largest electrolytic commercial capacitor you can get that use internal gasketing for the sealing barrier. For critical applications (like aerospace/medical/etc.) the really long lasting capacitors have welded seals. Relatively expensive, but not rare. When you combine the temperature cycles with the slow aging of the seal, the electrolyte is going to get out. Hence your failures. I have not seen what capacitors are used in the Prius and where, but I bet that Toyota has an excellent handle on this.
