How Voltage Regulators work, I-VR v. E-VR

[gmcjetpilot]

There is and has been a debate about over voltage and if external voltage regulators (E-VR) are better or internal (I-VR) ones are better. Also does a I-VR need OV protection added on? What happens with an over voltage.

There is no doubt that most alternators made today for the consumer, car, truck, boat, tractor is of the I-VR kind. Basically the jest of it is E-VR's are in general frozen in time, to the 1960's or 70's. The I-VR's however have improved and advanced with integrated circuits (IC) and small digital process and control functions. Can a I-VR fail? Yes sure but the fear of failure has driven add on fixes and cures (OV relays and "crow bars") that are worse than than the probable level of risk. Old E-VR's (even today) are more likely to have an OV than modern I-VR's. So all the old band-aid fixes where made for old E-VR's. I-VR's are designed to be automatic and have internal fault monitoring. As I point out in another thread, http://www.vansairforce.com/communit...ad.php?t=14282, all ND over voltage cases that have been documented have been in the 15-16 volt range, may be 18 volts? Also most avionics are made to run on 10-32 volts with surge protection to 60 volts! The risk therefore is small. (note: old radios and not all radios are made to the 10-32/60 surge standard, check with manufacture.)

So I'll let the thumb nail pictures speak for their self.

Basic E-VR in the past and today.



Now the inside of the IC chip in a typical I-VR


Now E-VR's have an advantage they can be placed in a cooler place not subject to heat and vibration. However modern electronics design and semiconductors have MTBF (mean time between failure) in the millions of hours. Statistically that is significant and means you can count on it almost as much as your or more than your prop or crank shaft falling off.

I-VR's have the advantage of being right on-board the alternator and can monitor (and do) them of the alternator. If it gets too hot it reduces the output. You don't get that kind of control with common E-VR's. There are advance E-VR's but most of the technology has gone into the I-VR. (If you need a E-VR, I recommend the Transpo V1200, a digital E-VR with internal OV protection, cost approx $60-$80, check with local auto-electric suppliers).

The regulator is that mysterious thing. It is understandable that this could be turned into fear and worry if you don't understand how it works. There is always a chance any alternator or regulator will fail, fail passive (no output) or active and pump too much power out. When you get into BIG +100-200-400 amp generators and alternators it gets to be serious business. Now 60 amps is not total child's play. Just remember you can always lower engine RPM and add load to "pull down" a so called runaway alternator. RPM has a direct effect on output if the regulator is malfunctioning as does adding extra system load.

In mine and other's experience with I-VR alternators in home-built planes and research I did into there service in cars, the worry is not justified. You can go to NHTSA (National Highway Transportation Safety Assoc) and research the data base for alternator problems, complaints, recalls, service letters on all makes and models and see how reliable and safe they are. We are talking millions upon millions of vehicles and the reliability and safety speaks for itself. Now there are some brands of alternators that are not reliable, but not the Nippon Denso that seems to have almost **[perfect service history] and no hazards issues like fires.



Here are my favorite sites that explain electromagnetism (faraday's law) and how alternators work. If you where like me, mystified about really what is going on inside, I think you will find it interesting and informative.

Alternator Secrets
Alternator and Generator Theory
Understanding Alternators -- an Overview

Anamation of alternating current generator (our alternator has three windings-ie three phase)
Anamation DC motor/generator (note the commutator)
Faraday's Law (the physics behind alternators)

Inside a ND alternator

In the 21st century alternators will get smaller, more powerful per pound and more reliable with fail safe backup redundancy in their internal controls. Just look at modern cars. They have every much the same desire and need to protect all those computers and expensive electronics. Unfortunitly the trend is to make large output and sized units for todays auto market, which needs high capacity units to drive all the electonics in todays cars. They just don't fit as nice as those 40-55 amp units of the 80's. I don't know what the future will be, but chance is the alternator of the future will have an I-VR.


**(Why are Van's ND alternators unreliable? Well for one its a matter of poor aftermarket parts and rebuilds. OEM ND units where of a different and higher quality apparently. Unfortunately they stopped making the models we use 10-15 years ago, so aftermarket is all we have now that the salvage yard supply is dry. Not all aftermarket parts are bad, and they certainly are not all of the same quality. Van has a generous return policy, and they now have a better quality supplier I believe. Also the "Plane Power" brand of ND alternators is high quality, and they do add an OV module that cuts power to the alternator in the unlikely event of an OV, if that makes you more comfortable. The price is set right and they are nice.)

[airguy]

For those of us that don't know how to read schematics (or between the lines of Georges writing ), a voltage regulator (either type) has the basic function of sensing the output voltage (or battery voltage, should be the same), and adjusting the current sent to the field winding of the alternator either higher or lower to maintain a given output voltage. Higher field winding current produces a higher magnetic field in the alternator core where the rotor is spinning, and the alternator then puts out more current to the electrical system, which manifests itself as a higher voltage. Lower field winding current produces less magnetic field and less output, with a correspondingly lower voltage. The regulator has a set "target" voltage (usually adjustable) that it always tries to match. If the output voltage it sees is above the target, it drops the field current which drops the output of the alternator, and vice versa. When you turn on a high-draw device, like a landing light, the voltage momentarily drops quite a bit as the light filament heats up to incandescent and the battery supplies the electrons needed. After perhaps 70 to 80 milliseconds, as the light heats up and the draw starts to drop due to increased resistance from the heat of the filament, the regulator is also sensing the lowered voltage and cranking up the field current, thus supplying not only the additional needed current to run the light, but also any additional current needed to keep the battery topped off. The "target" voltage of the regulator is therefor set to be the maximum-charge voltage of the battery.

Regulators must be fast acting and relatively accurate (hopefully within 0.1 volts), since changing engine (and thus alternator) RPM as well as rapidly changing loads can really make it's job difficult. High RPM and low field current can give the same output as low RPM and high field current. At some point, a maximum magnetic field is reached in the core (saturation) and any additional field current has no effect on the output beyond heating the alternator - so at idle RPM the intelligent IVR will recognize this condition (EVR's and "dumb" IVR's cannot, since they don't know how fast the alternator is spinning) and not allow the field current to ramp beyond a certain point, regardless of system voltage. Likewise, it will recognize high RPM and prevent the field current from rising excessively and producing an over-max output, and the battery acts as an electronic "shock absorber" both to supply the needed power when the voltage is low, and absorb the unneeded power when the voltage is high, to keep the voltage stable.

The only basic difference (aside from the age of the design) between IVR and EVR is whether or not it's located inside or outside the alternator. Notice I said BASIC difference - some IVR's do have some "smarts" built into them these days to sense alternator temperature and in some cases RPM to limit field current if needed.

Personally, I'm quite happy with the newer styles of IVR's - but this is one of those areas where you get what you pay for. YMMV.

[szicree]

I'm not sure that a low failure rate in cars can be extended to aircraft application. Way more vibration, fan spinning wrong way (if there is a fan), higher temps, low humidity, rapid temp/pressure/humidity changes, etc.

[airguy]

Originally Posted by airguy

Personally, I'm quite happy with the newer styles of IVR's - but this is one of those areas where you get what you pay for. YMMV.

Hmmm, didn't say anything about cars (though George did). But in any case, you're right. Conditions are different - operating principles are the same. It's up to you (as the experimental builder) to decide if the two are compatible.

[RudiGreyling]

George,

Thanks for taking the time and effort to do this,
Now everybody can read it, learn, decided for himself.

Regards,
Rudi