Do modern car/boat alternators use PFC circuits? - Page 1
Forum section: electronics / projects

author: e100
author_rank: Frequent Contributor
timestamp: July 23, 2019, 03:44:12 am
content: PFC cicuits are common on mains powered DC power supplies but I couldn't find much information about their use in low voltage systems such as the car alternators or wind turbine generators used on boats.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 23, 2019, 04:45:42 am
content: An increasing number of cars are using switching power supplies for the 12V.http://techno-fandom.org/~hobbit/cars/ginv/i1mech.html

author: MosherIV
author_rank: Super Contributor
timestamp: July 23, 2019, 06:56:54 am
content: I doubt it.Why (how) would you power factor correct dc voltage/current?Car alternators are internally rectified to produce 13-14V dc to charge the car battery.It is very difficult to get to the raw ac in a car alternator.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 23, 2019, 07:10:43 am
content: The raw output of the alternator is usually AC and I understand the questing in the way weather the generators internally use a kind of PFC circuit instead of the a normal simple rectifier.An extra PFC circuit in theory could increase the power rating by a little, however I don't think it is worth the trouble. A simple rectifier is just more reliable. Using a little more copper in the alternator may still be more cost effective than the extra electronics. So I don't think they use active PFC.

author: tautech
author_rank: Super Contributor
timestamp: July 23, 2019, 07:24:27 am
content: Quote from: e100 on July 23, 2019, 03:44:12 amBecause there is zero need for it.For a PSU especially SMPS one must limit its effects in the mains supply whereas power from an alternator originates from within it and it’s three phases are each full wave rectified for a HF ripple output where the R of the load (battery) further absorbs ripple. Other DC loads are always sourced from close to the battery so to source cleaner DC than directly from the alternator.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 23, 2019, 10:30:33 am
content: Given that the typical claw-pole rotor alternator is around 55%-60% efficient, it makes absolutely no sense to spend lots of money (relatively speaking) adding PFC to it when it would cost far less to simply change to a more efficient rotor design (the claw pole rotor does a very poor job of concentrating the flux from its field winding).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 23, 2019, 06:01:40 pm
content: It could be used, but it would greatly complicate a component that is otherwise very simple, not very efficient, and heavily stressed. Engine bay components get very hot indeed. It could be done with some difficulty with silicon parts, or perhaps less difficulty with GaN parts (or SiC if this were a high voltage system). Nevermind the commercial availability (currently ~boutique) and cost of packaging those devices (200°C+, usually gold and ceramic), of course.In short, all you gain is slightly less heating in the winding -- reduced harmonic currents. Actually hmm, how much of that even is true, because, if the voltage ends up flat-topped, that's not instantly causing huge current spikes. The output impedance isn't nearly as low as a proper generator is. So that leaves slightly increased core heating due to the voltage harmonics, but that's really a small part of an already very toasty core -- due to the relatively high operating frequency and laminated iron construction.Probably, significantly more efficiency would be saved through using thinner laminations, of higher quality material (lower losses, and maybe higher Bmax, though Bmax really only affects volts/turn at idle speeds), and tighter tolerances probably with a better salient-pole rotor configuration (as mentioned above). All of which increase the cost, for a low ranking system (that is to say, the electrical power in an average ICE vehicle is a tiny fraction of the total available power).This would be applicable to hybrids and electrics, but I'm guessing they usually use direct-drive inverters, so regenerative braking, and generation from the APU where applicable, is trivial in the sense that the power train (both electrical and mechanical), is all there. (The control may be nontrivial, to get a controlled-power polyphase inverter system running, but that's just 1's and 0's; a solutionexists, it's just engineering to find it.)Tim

author: David Hess
author_rank: Super Contributor
timestamp: July 23, 2019, 06:42:11 pm
content: The output from the alternator is controlled by the field current so the output is high impedance; it operates like a current transformer with gain instead of a low impedance voltage source like with a power line.So the conduction angle of the output rectifiers is much higher and the power factor is better than a line power operated rectifier and capacitor filter. I am not sure there would be any improvement to be had by adding active power factor correction and given the currents involved, construction would be difficult.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 24, 2019, 04:49:43 am
content: Quote from: MagicSmoker on July 23, 2019, 10:30:33 amThe move is towards permanent magnet rotors, then stepping down the voltage with a switching power supply.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 24, 2019, 11:44:14 am
content: Quote from: NiHaoMike on July 24, 2019, 04:49:43 amReally? That's exceptionally stupid, even for an automotive OEM, which can usually be counted on to do things too cheaply, rather than the other way around. PM rotors are much more expensive and can't withstand even moderately high temperatures (some types of rare earth magnets start to suffer demagnetization at less than 100C), to say nothing of then needing an SMPS to provide voltage regulation and current-limiting. It would make far more sense to simply replace the crappy claw-pole rotor with a salient pole wound-field rotor as found on larger synchronous machines since it could use the same field current regulator design and 3-ph. bridge rectifier.

author: duak
author_rank: Super Contributor
timestamp: July 24, 2019, 06:30:53 pm
content: An AC generator (alternator) equivalent circuit includes a series inductance Ls. This can be a good thing for limiting peak currents such as those using rectifiers to convert to DC or should it be overloaded. Automotive DC generators have current limit relays, but alternators don't. I don't know what the value of Ls is for a typical alternator. I used an old alternator to test a PWM driver I was developing. I recall Ls was in the low mH range but definitely not more than 10 mH. Ls provides a measure of PFC and I think you won't see the extreme current pulses that occur in a capacitor input offline supply.

author: David Hess
author_rank: Super Contributor
timestamp: July 24, 2019, 09:27:52 pm
content: Low millihenries is what I remember for car alternators and about 3 or 4 ohms so 3 or 4 amps at 12 volts of excitation.I once built a PWM switching regulator based control circuit for my car charging system and measured the alternator characteristics with an impedance bridge for modeling purposes which allowed me to get the pole-zero frequency compensation close on the first try. Load regulation at the battery terminals was better than 10 microvolts for a 30 amp change in load current where the stock regulator was 100s of millivolts under the same conditions.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 25, 2019, 01:06:39 am
content: Quote from: MagicSmoker on July 24, 2019, 11:44:14 amThe added cost is offset by removing the need for a separate starter motor. Then add auto start/stop, to boost MPG and help otherwise conventional cars stay competitive with hybrids and EVs.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: July 25, 2019, 05:44:15 am
content: Quote from: NiHaoMike on July 24, 2019, 04:49:43 amI thought the general push was to a much higher voltage. I know this is already electric cars, but I think there is a big push to 48 volts for internal stuff. Now with better on-chip DC-DC capabilities, the reduced cost of wires (esp the weight gains) easily outweighs the cost of fancier DC/DC.12 V used to just be nice with lead-acid (I think, don't know why you wouldn't want to put more lead-acid cells in series?). I think some bigger vehicles, like trucks use 24 V? .SMPS technologies are really becoming cheaper, and the increase in EV stuff is only helping their price go down further (lots of research going into that). Same with GaN and SiC - their cost is coming down to the point where their increased cost can be justified for the benefits they offer in system design.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 25, 2019, 01:55:45 pm
content: Quote from: NiHaoMike on July 25, 2019, 01:06:39 amAhh, yes. The mild hybrid/belted-alternator-starter thing. I was so fixated on conventional ICE vehicles changing their alternator design over to PM that I totally forgot about mild hybrid systems. I'm still not sure this makes any economical sense, but it is definitely true that mating a PM rotor alternator - that is, a PM synchronous motor/generator - to a 6-switch inverter with field-oriented ("vector") control allows the alternator to act as a motor or generator and with ideal power factor at all times. Whether the higher efficiency of the mild hybrid system offsets the vastly higher cost over the lifetime of the vehicle is another question altogether, though.

author: Zbig
author_rank: Frequent Contributor
timestamp: July 25, 2019, 02:17:40 pm
content: Quote from: NiHaoMike on July 23, 2019, 04:45:42 amNot saying they aren't (don't know) but the page you've linked talks about Toyota Prius (hybrid) specifically. Toyota Hybrid Synergy Drive uses completely different electrical system topology. You don't have a conventional alternator there: the 12V system and the 12V lead-acid battery (yes, there still is one) are powered from high voltage (c.a. 400V IIRC) DC coming from the High Voltage Battery or either of the two Motor-Generators via the Inverter-Converter.

author: james_s
author_rank: Super Contributor
timestamp: July 25, 2019, 03:57:09 pm
content: Quote from: NiHaoMike on July 25, 2019, 01:06:39 amThose silly auto stop-start systems exist to exploit a loophole in the way idle emissions are calculated. They have a negligible impact on real world fuel economy and anecdotally they seem to have a very real impact on battery life. They certainly are annoying to drive a vehicle that has one too, especially the cheap ones that have an ordinary noisy starter that engages.

author: soldar
author_rank: Super Contributor
timestamp: July 25, 2019, 04:06:10 pm
content: PFC circuits exist in devices connected to the mains because the energy (current) has to be transported hundreds or thousands of Km from generation to consumption and PFC provides a reduction in power wasted in transmission.In a car it makes no sense.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2019, 04:45:29 pm
content: Quote from: Zbig on July 25, 2019, 02:17:40 pmWe picked up our nice Kia Niro Hybrid earlier this week. Kia phased out (no pun intended) the 12V lead-acid battery in 2018 - It was there when the car was first released in 2016. It uses both the 32kW drive motor and the Engine belt coupled Hybrid Starter Generator (8kW) for regeneration. Both are hooked up to the high voltage battery (240-270V).Apparently there is now a separate 12V auxiliary section in the main (LIPo) high voltage battery (there's a regenerate button to recharge it from the main battery if it gets low), but both of the motors, and the Aircon compressor too are 3-phase permanent magnet type, driven by the inverter module from high voltage battery.It took me a while searching around the boot for the Aux battery compartment before I found a reference on the web to it being phased out. The earlier service manual reference that I have still had it included.I can't get my head around these new 48V 'mild' hybrids! A tax / congestion area get-around?I do like the belt drive starter generator though, pinion drive 12V starters are a really weak link for stop-start operation.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 25, 2019, 05:56:00 pm
content: Quote from: Gyro on July 25, 2019, 04:45:29 pm48 V mild hybrid is basically start-stop++. You get a more powerful combined starter/generator that is attached directly to the drive shaft and replaces the starter and alternator. It can restart the engine faster than a crappy 12V starter motor and also start to move the car forward while starting for impatient people who need to move *now* when the light turns green. The 48 V system is also enough to power an electric AC compressor which means the compressor doesn't have to deal with the huge RPM range of the engine and also doesn't shut off when the engine stops at a traffic light. The electric motor costs more than a pulley, but also gives the manufacturer more freedom in placement, and may allow complete elimination of the serpentine belt. You get a small amount of regenerative braking which still helps for stop/go city driving and if you can put some of the other higher power accessories on 48V you save a bit on copper costs. Since 48V is still considered "safe" you don't have to implement the same emergency cutoff and auxillary battery systems that traditional hybrids have.

author: oPossum
author_rank: Super Contributor
timestamp: July 25, 2019, 08:05:48 pm
content: The latest Mercedes I6 has no serpentine belt and uses a 48 volt electrical system.Some of the benefits explained...https://youtu.be/7PkX-NH6bE0?t=263

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 25, 2019, 08:06:31 pm
content: Quote from: soldar on July 25, 2019, 04:06:10 pmYeah, excellent point... /discussion.

author: schmitt trigger
author_rank: Super Contributor
timestamp: July 25, 2019, 08:37:01 pm
content: I drove for 8 years a 2005 Honda Civic Hybrid.The main electrical motor (BLDC) was sandwiched between the CVT transmission and the gas engine.The vehicle had a start/stop function, and since the HP rating of the electrical motor was a significant portion of the engine's HP rating, it would start immediately and effortlessly.Even so, the start/stop function could become annoying. Fortunately, it could be disabled. And the MPG loss, to the best of my recollection, was negligible.Thus, I agree with previous posters that start/stop function is only a gimmick that auto manufacturers employ to game the economy ratings.

author: james_s
author_rank: Super Contributor
timestamp: July 26, 2019, 12:21:24 am
content: My partner has a Prius which shuts off the ICE when the car is stopped but it doesn't bother me too much on those. The electric motor is sufficient on its own to get the car rolling which gives the ICE plenty of time to fire up. I'm still not convinced that all that complexity is worth the gains however it's a 2002 model still running the original traction battery and it has surpassed my expectations, being impeccably reliable.On a non-hybrid the stop-start system exists only to game the system. I hope that eventually the rating system catches up and closes these loopholes because driving a car that has one of those is a terrible experience. Especially the more primitive ones that don't disable stop-start when the AC is running, every time you stop at a light the vents start blowing warm muggy air until the thing chugs and lurches forward when you step on the gas.

author: duak
author_rank: Super Contributor
timestamp: July 26, 2019, 04:17:47 am
content: Which vehicles have belt start engines? Do they have a conventional starter too?

author: Circlotron
author_rank: Super Contributor
timestamp: July 26, 2019, 07:34:36 am
content: Quote from: soldar on July 25, 2019, 04:06:10 pmWith a transformer driving a bridge rectifier and capacitive input filter you can only get about 60% of the transformer VA rating as DC Watts. Might be the same situation with a sine wave output alternator. PFC= more DC watts for the same AC VAs.

author: Circlotron
author_rank: Super Contributor
timestamp: July 26, 2019, 07:44:17 am
content: Some time ago I put a scope on a car alternator winding. Was completely unloaded and on a test bench. The winding voltage was a sine wave of sorts but with fairly flattened peaks. This would broaden the conduction angle and reduce the current peaks, presumably with a better power factor than if it were a normal peaky sine wave.The claws on the rotor are triangular and the air gaps between the claws are as a consequence skewed. Maybe these skewed air gaps introduce the flux into the stator in a more gradual and constant manner and that way produce the flattened top sine wave?

author: soldar
author_rank: Super Contributor
timestamp: July 26, 2019, 08:59:41 am
content: Quote from: Circlotron on July 26, 2019, 07:34:36 amThat's my point. With transmission lines being hundreds of Km long and including transformers along the way you want to optimize the power factor of the load.With a car alternator it seems more simple and reliable to oversize it than to include electronics which are more prone to problems. If my car has a 100 amp alternator and I need more it is simpler to install a bigger alternator than to add a bunch of electronics which will still waste some energy in the form of heat.

author: mikerj
author_rank: Super Contributor
timestamp: July 26, 2019, 11:20:43 am
content: Quote from: duak on July 26, 2019, 04:17:47 amThe second generation Smart ForTwo (451) had a belt drive starter/alternator and no conventional starter motor. It is very problematic on this model, the belt is quite narrow and under a lot of tension and the high forces on the alternator/starter mountings cause the holes to elongate and the resulting misalignment causes the belt to wear and snap. The same belt drives the coolant pump, so plenty of these cars have died with badly overheated engines.

author: Circlotron
author_rank: Super Contributor
timestamp: July 26, 2019, 12:37:38 pm
content: Quote from: duak on July 26, 2019, 04:17:47 amHaflingers had a combined generator/starter/cooling fan that started the engine through the belt. Called a dynastarter. My uncle had one back in '69-'70.

author: David Hess
author_rank: Super Contributor
timestamp: July 26, 2019, 02:03:36 pm
content: Quote from: Circlotron on July 26, 2019, 07:34:36 amIn the past under those circumstances, they added a series inductor for passive power factor correction.I have seen some old off-line switching power supplies which used a 60 Hz transformer for isolation followed by a low voltage non-isolated switching regulator but none of them included power factor correction. It seems like it would be easy to add though.Quote from: Circlotron on July 26, 2019, 07:44:17 amThe alternator is designed to operate into a constant voltage load and roughly current excitation so an output current measurement would be more meaningful.QuoteCar manufacturers are nothing if not economical to the point of being cheap so rotor construction which increases the power factor so that less copper and cheaper diodes can be used makes sense.

author: Miyuki
author_rank: Frequent Contributor
timestamp: July 26, 2019, 03:36:19 pm
content: Also is here a frequency problemCar alternator turn at 4-6 000 rpm at cruise speed with 12 or so pole rotor it makes more than 1000 Hz and even distorted by slow diodes in alternatorI dont think there is any control circuit that can track PFC at this speed and non sinusoidal shape

author: calexanian
author_rank: Super Contributor
timestamp: July 26, 2019, 08:33:14 pm
content: Baring new fancy, electric, or hybrids......No. The typical automotive alternator is Typically a 3 phase, half wave rectified output and the output power is controlled by having a couple of different level field strengths controlled by either taps, or a large external resistor. Some are called one wire alternators, which are fairly common today, have this switching internal where only a single lead comes out to the positive terminal of the battery and everything else is controlled internally, but the mode of action is the same. When the RPM is low or the battery is nearly fully charged the field strength is low therefore not either loading the motor at idle down too much as to stall it, or not overcharge a battery at high RPM. All alternators use the metal housing as ground.

author: David Hess
author_rank: Super Contributor
timestamp: July 26, 2019, 08:45:35 pm
content: Quote from: Miyuki on July 26, 2019, 03:36:19 pmIf there was a real need for it, adapting an active PFC circuit to operate with a higher input frequency would not be a problem. I checked a couple PFC controllers and did not see any issue operating them into the kHz range.

author: Circlotron
author_rank: Super Contributor
timestamp: July 26, 2019, 11:14:31 pm
content: Quote from: calexanian on July 26, 2019, 08:33:14 pmNope. Automotive alternators have a full wave rectified output with six diodes. At low rpm sometimes as much output as possible is required from the alternator, e.g. on a hot night in stop start traffic, as well as all the usual electrical stuff that is always demanding power, there is the headlights, radiator fan, aircon compressor clutch, aircon blower, and brake lights when stationary. To have the alternator field strength low at low rpm is not a good thing, especially if the battery is not in perfect shape. In any case, all cars with EFI for the last 30 years or so have idle speed control to keep engine idle speed within an acceptable range regardless of the parasitic load of accessories. With my car idling in neutral I can pull the steering wheel a bit and the idle speed comes up slightly to counter the extra load the power steering pump puts on the engine. Same thing happens when the aircon compressor cuts in. A pressure sensor in the ps pump tells the computer there is more load, or a temp sensor tells the computer to engage the aircon compressor. In both cases the computer also tells the IAC stepper motor to open up a few clicks to maintain or slightly increase the idle speed.

author: calexanian
author_rank: Super Contributor
timestamp: November 18, 2019, 09:15:22 pm
content: Just pulled a alternator from a 97 ford apart. Still just three rectifiers.

author: Circlotron
author_rank: Super Contributor
timestamp: November 18, 2019, 10:47:02 pm
content: Quote from: calexanian on November 18, 2019, 09:15:22 pmAre you looking at the three small diodes that feed the rotor with excitation current? There should also be six big diodes on two separate heatsinks.Something like this: