elecric motor humming

I haven't yet but probably will take the top off and with the car on Jack stands see what the voltage is to the motor terminals. I know they say the bi-polar transistors they use in the inverter boost the voltage up but I'm almost willing to bet that the main boost in voltage comes from MG1 and a 150%boost from the transistors is just on the cusp of unbeliveable especially at the amperage needed by MG2. Your right that the inverter is inactive till the ready light comes on. Same with the first generation. Even with the car in Acc. mode the OBD11 side is dead.

 

In ACC, yes it will be dead, but not in Ig-On. Just about the only thing dead in that mode is high voltage and the items that need it.

Remember, the motors/generators are 3 phase AC.

You can easily boost voltage electronically. It's done all the time when high voltage is needed with a low voltage power supply. I believe LCDs are or were such a case. All you need is a capacitor or inductor, and a switching circuit. I do grant you, that you lose current as you can't create power. That is why running the car on pure battery gets little performace, certainly not what MG2 is capable of. The point of raising the voltage was to minimize resistance losses in the circuitry.

If I remember correctly, the AC compressor is 207V.

 

Well, I became curious about this "hum" so I drafted my nice neighbor to help me. We went for a short drive to warm the car up, then returned to the condo and as I backed into my parking stall, I popped the hood.

The neighbor then lifted and supported the hood while I cycled from Off-Acc-IgOn. With the hood up, the hum is VERY noticeable! The neighbor pointed to where he thought the hum was coming from.

The location appears to be below and to the right of the plastic cover "Hybrid Synergy Drive." I'm guessing either inverter coolant pump or thermos coolant pump?

There is nothing magic about AC-DC-AC or DC-AC-DC conversion, especially when you keep in mind that a 3 phase generator/alternator is the most efficient and easiest to convert. That is, you don't have to "make up" the missing phase, which is wasteful.

Industrial VSD (Variable Speed Drives) help increase the efficiency of 3 phase electric motors running pumps or fans. They use IGBT (Insulated Gate Bipolar Transistors) now instead of regular Bipolar transistors, due to much improved performance and efficiency, in a much smaller package.

For most industrial motors, PWM (Pulsed Wave Modulation) is ideal to control a 3 phase motor, as you minimize heat buildup and most of the noise associated with regular VFD harmonics. Older VFD's would use capacitor banks and Bipolar transistors to dramatically vary the frequency and voltage applied to the motor, which would create a noticeable buzz or humming sound at the motor.

The IGBT VSD with PWM much quieter and more efficient than old VFD, with some tradeoffs: the winding insulation must be much heavier or you will get corona at the pulse-width peaks, as the frequency makes the rapid transition back. The motor lead lengths must be carefully calculated - with lots of nasty calculus - or you will not get expected performance. Also, the VSD itself can give off a whine or hum.

The IGBT VSD is heavily heatsinked and usually liquid cooled. If you don't keep the heat buildup below threshold, the IGBT will run wild and self-destruct. The advantage of using computers is that we can carefully monitor, with thermistors or RTD's, heating in the motor and the inverter, to either apply more cooling or to reduce power output.

I don't think the hum is anything to worry about, and in normal driving you probably wouldn't even notice it. Toyota appears to have done a good job with sound insulation, and I bet they had to deal with odd harmonics during their prototyping.

 

If weather permits, remain in ACC mode when sitting. If weather doesn't permit, remain in Ready so A: you have AC in hot weather, B: you have heat in cold weather (heat derived mostly by engine coolant, supplemented by 360W 2x15A) of resistive heating. If your HV battery gets low, the engine will charge it, which is not an option in IG-On or ACC mode, though not much that can run in ACC will drain the 12V battery that quickly.

 

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No problem - it was a fun experiment and my neighbor actually owes me. He's the one with the BMW 745iL that is always in the shop.

A quick comment as there have been posts about using a voltmeter to actually check voltages at MG1 or MG2.

UNDER NO CIRCUMSTANCES DO THIS. EVER.

Unless you use a very high impedance meter, say a Fluke 434 Power Quality Analyser or a Fluke 88V Automotive Tester, you can introduce electrical noise that may very well confuse the CANbus and set the Master Warning triangle.

A slight bit of electrical leakage could also degrade or damage the IGBT's in the inverter. I have been sent repeatedly on call to plants that have had issues with their VSD's, only to find that noise inductors had been left off, feeding catastrophic electrical noise back into the IGBT and ruining it.

You may also introduce a short on the DC bus that could prove quite dangerous, possibly fatal. Unless you've had specific industrial training to work on high-potential DC systems, stay away.

At a pulp mill about 15 years ago, I saw the end result of a crew being kind to a stray cat. Instead of taking it to a local Humane Society shelter, they kept kitty around and fed him. One day he went snooping around the DC breaker room looking for mice.

Kitty then snuck past a barrier and landed on the high-potential DC busbars. The resultant explosion of 600 VDC blew out a wall and shut down a paper machine for over a month. They found parts of kitty here and there.

I'm not saying a Prius has the same potential, but with any chemical battery system, there is potential for very high short-circuit currents before the protective device(s) open. There is no way in h*** I would pull the isolation cover off MG1/2.

 

I'm an auto electician by trade that has moved to the forklift side of things. We deal with A/C to 575 and DC-AC to 80 volts on the Toyota electric forklifts, which use essentially the first gen system and thier IGBT's and associated swithching. Rather a cool system that will easily do an 8 hour shift without a battery change. We've only had a very few problems with the DC/AC inverter system on the ones we've sold/leased. There isn't much on this car that I wouldn't be afaid to repair. Air bag system comes to mind as they tend to be flaky. The other stuff is just stuff that you have to pay attention to detail, or get killed, just like a lot of things I get to work on. I agree on the high impedance meters for anything over 118 AC.