Once the alternator heats up under load, efficiency drops by 15 to 25 percent. 5v on Idle after a few mins, Hopefully this is the end of this problem I also found out what was going on with the voltage display on the cluster :embarrass. One of the best ways to check the output of the alternator is to conduct a load test. Parasitic – Key Off – Drain. The best way to test for voltage drop in the alternator wiring is to place an artificial load on the batteries using an inverter and hairdryer or small heater. However, here is my question. 04 volts at the B+ terminal, then the battery terminals MUST read at least 14. Battery must be recharged or alternator will be damaged. Under load, however, the air gap flux is determined by the ampere-turns of the rotor and the ampere-turns of the stator. Test complete charging system including alternator, regulator, and battery. If you've run your car for a long time and while the car is running the voltage reading is in the 13-14 volt range, but then you shut the car off and the battery voltage instantly drops to well below 12 volts (10 volts or under; 9 volts or under in freezing weather conditions), it is likely that your battery needs maintenance or replaced. You might assume the transformer's output voltage is highest at no load. It does all this and still offers only a max voltage drop of less that 0. If the recovery voltage is less than 90 percent of rated voltage, a point on the voltage dip curve beyond which the voltage will not recover to should be identified …. Voltage drop over a length of wire is proportional to the amperage flowing through it. Single-phasing, which is the complete loss of a phase, is the ultimate voltage unbalance condition for a three phase circuit. Voltage drop tests are most effective with high amperage circuits, and are often used when diagnosing the starting and charging systems in automobiles. 7L with Hiniker Plow. Of course at idle, the alternator won't be working to its full portential. Voltage is how the computer determines battery condition and state of charge. When this happens, the battery cannot be charged to greater than 11. A sudden change in the load can cause the voltage to fluctuate while the regulator is trying to stabilize it. (R=E / I) Example: If the voltage drop on a circuit was 3Volts and the load drew 12 amperes then the impedance of both conductors would be 0. There is also colour coding, but it varies not only among alternators but also among car makers who use the same make of alternator. 9 depending on the voltage regulator installed on your alternator. the truck doesnt die. Revving the engine past 1k RPM doesn't cause voltage to increase past 12 once it's dropped. This voltage will be maintained when the battery is fully charged and the electrical load is low. RESPONSE TIMES For a sudden introduction of the rated load under a constant speed, the voltage returns to the rated voltage in less than 0. WEN 3100-Watt Oem Branded Alternator Gasoline Portable Generator at Lowe's. Hi Rick1999 this is lostrider, you stated the alternator is charging at 12. system voltage drops to 22 V (11 V on 14 V side). Have her towed home, get her started and running again, multimeter shows less than 12V on the battery at idle under load. The Left Side Navigation for Make Model for your vehicle might be under contstruction. It doesn't look like a belt slip, since the voltage stays constant while I drive. This is a logical assumption, but one that's not necessarily so. As an added twist, it seems that the alt will charge at warm-idle (650 RPM) under heavy load if the vehicle has just entered the warm-idle state -- which I believe is because the "desired" voltage is still 14. Now the Good News!. The voltage drop is directly proportional to the amount of current flowing in the circuit. failing that - go under the hood and check positive jumping terminal to the negative grounding block. It drives an external logic level N channel enhancement power FET for control of the alternator field current. Let us assume that you get your supply from your nearest distribution transformer- say few hundred feet away, through a distribution line having an impedance Z ohm. The load on the alternator is dependent on the load required to maintain this voltage. so, whenever I stop at a light, it goes to 12 but when at speed, 14 volts. Southwire's Voltage Drop Calculator is designed for applications using AWG and KCMIL sizes only. Disconnect the power supply wires X1,X2 and Z1,Z2 and the alternator voltage reference (terminal strip J1). 8v then it may well be that your alternator is faulty. Alternator is a <2 year old Hervey D110. At the parts store I asked for a 1986 Buick LaSabre, 8 cylinder alternator. 4 (engine off) to an average of 13. Resistors R1 through R3 provide an adjustable voltage divider. 12-Volt Alternator Installation & Operation Manual Introduction Thank you for choosing a Balmarr high-output alternator. Any large single phase load, or a number of small loads connected to only one phase cause more current to flow from that particular phase causing voltage drop on line. 4 amps (remember, the voltage drop across a diode is not linear, it is. The circuit serves as a voltage regulator that controls voltage by adding or removing load to the system. 2 V, that is, 2. With a battery load tester, apply a load equal to one-half the vehicle's CCA specification for 15 seconds. At the parts store I asked for a 1986 Buick LaSabre, 8 cylinder alternator. engine and verify that no-load voltage is 13. Battery voltage should not drop below 10 volts under starter load Engine will not turn over - Under this circumstance, we will be looking for a problem with the starter engagement circuits. I removed the yellow wire from the output terminal, extended it and ran it to the battery + terminal. The voltage at the alternator output increases to the right value, & the new. 5V as soon as I get off the gas. Experiment 57 I ' The Alternator Under Load To determine the voltage regulation characteristics of the altemator with resistive,. Precise measurement of battery voltage, including negative lead to accommodation any common ground line voltage drops. An alternator gives sinusoidal wave form of voltage at no load. My biggest concern at the moment is the voltage drop that occurs while driving. 2 volts at high currents. 11 With the same rpm with Doors open, A/C and Fan set at High and Radio voltage dropped to 13. It is common for a system’s sKVA—or its sKW and maximum allowable transient voltage drop—to determine the size of the generator. The fact that the voltage drops to 11. Discharging them lower than this will drastically reduce the life of the battery. Parasitic Drain Another common problem is Parasitic Drain. Voltage is how the computer determines battery condition and state of charge. 1960s–1970s) used a discrete device mounted elsewhere in the vehicle. As an added twist, it seems that the alt will charge at warm-idle (650 RPM) under heavy load if the vehicle has just entered the warm-idle state -- which I believe is because the "desired" voltage is still 14. As soon as the overvoltage relay opens the field drive and the alternator is turned off, the electrical voltage will drop back to about 12 volts. Since low voltage can result in increased amperage draw and higher motor temperatures, I felt it would be good to write a post on problems caused by voltage imbalance in 3-phase systems. Wholesale Supplier of AC Alternators Diesel Generator - Kirloskar AVR, Alternator Terminal, Voltage Suppressor and Power Surge Suppressor offered by Delcot Engineering Private Limited, Chennai, Tamil Nadu. drop on the cable very low. 5, and saying now after under a load they are at the same voltage they had before not under a load. Compressor clutch is new, takes 3 amps to run it (within specs) Alternator is new, puts out 55 amps clean voltage. This is because when load is disconnected, I a is zero hence there are no voltage drops and no armature flux to cause armature reaction. Loose connections can add to voltage drop. S = P - jQ). battery was factory, and figured it was about time anyway, even though it still held up under the load test. Honda's Dual Mode Charging System For many years Honda and Acura have utilized a dual mode charging system to increase fuel efficiency and to decrease the drag on the engine when starting. The magnitude of the drop depends on key factors such as the design of the alternator, its component parts, its excitation system and its AVR. Have her towed home, get her started and running again, multimeter shows less than 12V on the battery at idle under load. Voltage drops to 12. As you add electrical load by turning on more accessories, the voltage will drop. The alternator creates direct current, measured in volts, to achieve this. It does not increase with a faster engine speed. When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, and then taper off, leveling out at the specified voltage. 7 volts which would not be determental to performance or components. Check for voltage drops at the positive and negative battery cable connections, the alternator BAT+ power connection and the engine ground strap(s). Alternator manufacturers each have their own system of connecting output leads. There was a voltage drop on the dash gauge 9-10 volts. If you can't do this yourself go to an auto electrician and get them to check. If the above test looks suspect, you may have low alternator output and this certainly can cause all form of faults and system malfunctions on the later BMWs (about 2000-on). Battery a device that stores and provides electrical power for the vehicle. Your alternator may be putting out the proper voltage (at the alternator), but if your voltage is being measured back under the dash, you could be losing 0. Yes, when you connect a Lithium Battery to your alternator the charge voltage will drop to just above the battery voltage and will only rise slowly until the battery is nearly full. The value of E – V will depend upon the internal impedance of the winding which includes its resistance, R and more significantly its AC reactance X, the current and the phase angle. The device features separate color-coded volt and amp meters. ) The secondary power ground is between the back of the intake manifold and the driver's side firewall. Depending on the power factor of the load. Video coming shortly. Having the charging system amperage may give you a better diagnostic of the charging system, if necessary. My only concern with these Alternator Voltage Booster diodes is that some of them require you to replace the 7. (3 volts/12 amp. 01 ohms is too little for all but the most expensive and sophisticated ohmmeters to measure, but measurements of voltage drop will indicate. I did do a voltage drop test and got 0. 5 volts +- a little bit, and a battery thats constant at about 12. You may incur additional voltage drop(s) by adding additional loads to the system such as headlights ect. If this were a real generator system, the regulator would call for more voltage. Honda's Dual Mode Charging System For many years Honda and Acura have utilized a dual mode charging system to increase fuel efficiency and to decrease the drag on the engine when starting. Once enough load has been placed on the system, the primary alternator voltage will begin to drop. Since the energy conversion is not 100% efficient a portion of the horsepower supplied at the pulley is wasted as heat. ” (ii) In the case of leading load p. Using the alternator case as ground reference measure the voltage at the alternator output lead with a good load turned on. Put meter on it while running and watched min/max for about 45 min. The load on the alternator is dependent on the load required to maintain this voltage. of the load. To that end, you can measure the actual output of an alternator under a simulated load, which allows you get an idea of what it is capable of putting out in real-world conditions. Next load the alternator by turning on dc loads such as lights, radio, etc. At the end of the ten seconds the voltage across the terminals is measured and this voltage determines how good the battery is. If it creates too little or too much voltage,. 2V for vented lead acid batteries and 14. Is the machine beeping and the battery/alternator light coming on? Normal running voltage should be 14. here we will see about some causes of generator voltage drops. There is a very big difference when a car battery drops even a small amount of voltage. Roadi Battery tester can not only test alternator charging voltage (load/unload status), but can test the healthy status of rectifier diodes. " Conducting a Voltage Drop Test. Always err on the side of largeness and play it safe. There is an additional terminal for status information. Seen above is a factory re-manufactured alternator next to a failing unit removed from a 1998 GS400. A 30 percent voltage dip reduces starting KVA by about 50 percent (0. at the SMA shop as we revisit the 2005 Ford Explorer that we diagnosed and repaired only to find that the new alternator could not meet the electrical demands of the vehicle!. If the voltage drop exceeds 0. The motor’s NEMA code letter, which identifies the starting kVA/hp, is a representation of the starting inrush current. 6!! WARNING!!!! WARNING!! VOLTAGE DROP TEST: Perform this test under full load (all lights, fan, A/C, etc. As you add electrical load by turning on more accessories, the voltage will drop. - Harmonic levels for the current (and voltage if possible) It is important to know exactly what load the alternator is supplying and whether there is any transient load shifts near the time the problem occurs. If the alternator becomes a load at low enough speed (or you hae enough accessories on to pull down the battery), then you could get voltages that are below the battery's 'nominal' voltage. The voltage should not drop below 9. 5 volts +- a little bit, and a battery thats constant at about 12. However as for the voltage drop from the alternator, that is normal. 5 is normal depending on how much load your car is drawing. I'm running a 3 wire alternator and on idle, my voltage meter reads about 13 volts. Now if i start my car, and let it idle, it will usually stay at around 14. There is A LOT of complicated math/physics that determines the voltage output of an alternator. When idling with a heavy electrical accessory load applied, the alternator may not be able to keep up, and the voltage to the battery drops below 12 volts. At least for the first few cycles, the voltage dip is determined by the size of the load. voltage one Q)As the an alternator on an alternator implies that its voltage regulation--> any oa n power factor of the load of an alternator decreases, the magnitude of generated v age required to give rated terminal voltage--> decreases Q)Which one of the following method gives more accurate result for determination of voltage. i am using lead acid battery and it is 1 year old. When a battery has just finished charging (or when you just shut off your car after driving for a bit), the battery will typically have a "surface charge" so its voltage will be in the upper 12s or possibly even low 13s, and it takes the battery a while (couple hours, perhaps) for its voltage to drop down to its true. When this happens, you'll find yourself without a working vehicle and possibly stranded. A 65amp alternator should put out 65amps in these conditions if working properly. "A voltage drop test is a good ‘best practice’ during your scheduled preventative maintenance or before replacing the battery, starter or alternator," explains Clint Stohler, Director, Technical Service and Training. To observe the effect of unbalanced loads on the output voltage. I have an '06 with 145k miles and think I may have a bad alternator. If you don't see the recommended voltage when you check charging voltage at the battery with the engine idling, check the wiring connections at the alternator — not just visually or by wiggling the wires or connectors, but checking for excessive resistance by doing a voltage drop test. 5 Install new alternator and NEW belt. 5 amp fuse with the diode and the one I tried about 12 months ago did not blow even at 20amps. • Checks all types of alternator and regulator terminals and functions such as computer control, soft start delay, feedback, under/over voltage indication, PCM control, load response control, tachometer frequency, etc • Simulates all signals to the alternator including on-board computer functions. 6 (six tenths) of a volt, replace the diode trio. You may work ahead if you like, but do not fall behind. cause the starter to turn slowly, because of low voltage. Check for voltage drops at the positive and negative battery cable connections, the alternator BAT+ power connection and the engine ground strap(s). All it needs to do is disconnect the battery charge cable from the battery with a relay, or maybe a simple command the alternator's built in regulator to drop it's voltage down to 12V. Checking Alternator Voltage Output with a Multimeter. 5 V or less. Open circuit or No load test on Transformer Open circuit test or no load test on a transformer is performed to determine 'no load loss (core loss)' and 'no load current I 0 '. You have TWO circuits to check, "run" and "bypass" in start To check RUN Turn key to "run" with engine OFF. I have an '06 with 145k miles and think I may have a bad alternator. Rotor rpm are a factor of pulley ratio multiplied by engine speed. 2 "Sense" (Red AWG #10 or #12 wire on white molex plug) The 'Sense' wire checks the voltage output level of. Alternator output is set by field excitation. Ideal Specifications: Constant voltage = 13 volts; Current Limit = 12 Amp. 6V with zero load, fully charged. I just noticed that when I rev my engine in the blazer the voltage goes down and takes a few seconds to come back up. If the sense wire is connected at the battery, the circuit will still work, but the battery voltage will need to drop before the alternator is turned on. 5 volts d/c. A high voltage is desired to assist in “striking” the arc (getting it started), but like the discharge lamp, an arc doesn’t require as much voltage to sustain itself once the air has been heated to the point of ionization. Technically speaking, 12. 5 vdc at idle but within specs at high rpm you need to check the idle speed. This would leave nothing extra to serve the other electrical demands put on the system by lights, air. 0, there will be 75% difference. The voltage regulator does just what it says: it regulates the voltage from the alternator. When the voltage is above 13. VOLTAGE REGULATOR R 449 I NTRODUCTION TO THE R 449 LEROY-SOMER Réf. Then set their voltage to 14. Any voltage drop observed to be greater than about. Hook one probe of your meter to the ignition buss under the hood. Under the load condition, the terminal voltage of alternator is less than the induced e. Regulator bypass test- connects full battery voltage to the alternator field, leaving the regulator out of the circuit. Page 1 of 3: How to Test the Alternator (Ford 4. 4 (engine off) to an average of 13. 7L with Hiniker Plow. 5volts Under load A\C flat out and High Beam on drops to 12. C generator synchronized and coupled with the alternator on the same shaft is used for this purpose. Tacomas (2005-2015)' started by Tiddlywinks, When placed under load the voltage drops to around 13. If the regulator is external to the alternator, having volt drop on the ground side of the voltage regulator will also cause over-charging. § Voltage Drop Testing. 7v for the rest of the ride. Checking for voltage drops in a circuit is a good way to find hidden problems that may be causing a charging problem. FULL-LOAD TEST. Even if rpm were held constant, i. This page is our exhaustive list of Alternator Kits & Starter Kits Tips to help you locate a correct one would be Possibly. A voltage drop of. In addition, as the compression in the cylinder rises (under WOT), the voltage required to jump the spark gap also increases. 3 volt reading will drop down to about 10. waited for the voltage. 3V (check as in fig. The way it is suppossed to work is it only drops the voltage to 12. Alternator Voltage Regulator FET Driver The CS3361 integral alternator regulator integrated circuit provides the voltage regulation for automotive, 3−phase alternators. Without the Smart Charge an alternator should give 13. 2 when truck is off. These products are designed using the most advanced technology available to provide the fast, easy, and accurate testing procedures available for the both novice and professional technician. If speed drops of more than 5% occur, the AVR unit will automatically decrease the voltage proportional to the frequency (U/f-constant). 4v from the B+ on the alternator and 0. Often, this load test is more likely to show a bad battery when the batteries are relatively discharged than if they were full. I do not think that VW uses a remote sense lead arrangement (costs more money). 5 volts, thats not normal, here is the procedure to check the alternator, this is a no load test, the voltage should be between 13-15 volts, if the alternator isn't suppling the proper voltage then it will need to be replaced, it will take a volt meter to do the test if you have one. 25 volts or less is Ok and the alternator is bad. Then, the battery voltage goes up to 6 V, where it remains for a few seconds, before returning to the nominal voltage range within a rise time of a few seconds. The charging of the battery will place the load on the wire. Connecting at the alternator will defeat this. caused not only by the system voltage unbalance but also by the system impedance, the nature of the loads causing the unbalance, and the operating load on equipment, particularly motors. Observe both voltage values when the output drops - both should be very low (under 0. 6V, then the battery would literally never charge. • Alarm and advisory information Dash lamp: over voltage, under voltage and temperature alarms. The alternator is the primary source of electrical energy when the engine is running. Switching of three phase heavy loads results in current and voltage surges which cause unbalance in the system. It is not unusual for your system voltage to drop a bit under these conditions. It's not a bearing noise. By repositioning the voltmeter test leads, the point of high resistance (voltage drop) can easily be found. The output voltage of an alternator depends essentially upon the total flux in the air gap. Building off the above principals, corrosion or poor connections act like a load in series with the device and cause less voltage to make it to the device. (LOAD TEST) Turn on the high beam headlights and turn the heater or air conditioner blower to its highest setting. cause the starter to turn slowly, because of low voltage. A sudden change in the load can cause the voltage to fluctuate while the regulator is trying to stabilize it. With Delta you get lower voltage but more amps. 5 which seems to be just fine. * The voltage-drop spec between the alternator and the battery is thetextbook maximum. " Conducting a Voltage Drop Test. Without low voltage protection, the typical end result will be a ruined battery. Rectifier with SCRs for output voltage and current control are often used in loads such as static UPS systems. I just noticed that when I rev my engine in the blazer the voltage goes down and takes a few seconds to come back up. Voltage only drops if you hook the devices in series. Check the large battery terminal on back of the alternator. View Notes - exp 57 from EEE 360 at Arizona State University. sounds like it isn't turned on. • Checks all types of alternator and regulator terminals and functions such as computer control, soft start delay, feedback, under/over voltage indication, PCM control, load response control, tachometer frequency, etc • Simulates all signals to the alternator including on-board computer functions. Good luck, Gerry _____. VOLTAGE & CURRENT CHECKS. If you find battery voltage on one terminal and less than battery voltage on the other terminal, yet the output current or voltage are too low, suspect an open diode. I have Hervey's fancy double ground cables run to the transmission. 137,000 km. 03 Check the battery cables and alternator charge-wire for bad connections, improper cable and wire size, or corrosion. x volts to about 12. So over time the voltage drops lower and lower as the car is used over about a two month period. Wholesale Supplier of AC Alternators Diesel Generator - Kirloskar AVR, Alternator Terminal, Voltage Suppressor and Power Surge Suppressor offered by Delcot Engineering Private Limited, Chennai, Tamil Nadu. 12 volts is the standard automotive battery in today’s vehicle and each of the battery has 6 cells with a voltage of 2. The voltage regulation of an alternator is defined as “the rise in voltage when full-load is removed (field excitation and speed remaining the same) divided by the rated terminal voltage. 5 volts for a while, but then drop down again with light electrical load. A 30% voltage dip is sometimes used as a rule of thumb. Charging system -Elect. Keep the probes on the terminals for 10-15s to notice any continual voltage drops. The device features separate color-coded volt and amp meters. Some solid state isolaters use FETs and diodes in tandem to reduce voltage drop. If your battery is more than three years old, it should be load tested for proper operation. But it is also desirable, that, this voltage waveform should not be distorted under load condition. Using a voltmeter to check for voltage drops across connections can reveal bad connections that may reduce the charging voltage. make sure your charging wire from alt to battery is sufficient. A brushless alternator is composed of two alternators built end-to-end on one shaft. When full charge is approached, a diode isolator still drops from 0. New battery,belt and alt but voltage drops and squeals under load asked by Lyle on January 14, 2017 When my truck's air conditioning or heater is on, the voltage drops below or at 12v and makes a load squeal sound. Over time during a drive, the voltage steadily drops little by little until it reaches right around 13. Then, when the RPM is over 1000 to 1500 RPM, moving or not, the voltage jumps to 14+ volts. 8V when under the load of the headlights and heater on full blast. Depending on the power factor of the load. Voltage drop tests are most effective with high amperage circuits, and are often used when diagnosing the starting and charging systems in automobiles. Electrical Machines - Generators (Description and Applications) The primary supply of all the world's electrical energy is generated in three phase synchronous generators using machines with power ratings up to 1500 MW or more. But you might want to check the alternator, battery and charging circuit if it dips below battery voltage. For genset applications, this should be less than 5% in order to minimise the power dissipated during start. Remote voltage sensing is not available with the ONE-WIRE alternator, therefore the wire from the alternator to the terminal block must be sufficient in gauge size to handle all electrical system load without significant voltage drop. Regulator regains control of alternator below output voltage. Run the engine at 2000 RPM. You may incur additional voltage drop(s) by adding additional loads to the system such as headlights ect. 3 V when hot, with both fans running and lights on. Ideally, the voltage drop across any connection should be zero or less than 0. The diodes drop a little voltage, this makes the diodes get hot. The voltage regulator looks. In this manner, the system is a closed feedback loop that self-regulates. 9 - Ford Focus question. At idle with no load applied voltage was 14. Check your manufacturer suggested service schedule. Each coil set is a "phase" of the alternator so when you measure voltage,ohms or current to test one phase of the alternator you would measure the "phase". The alternator output should fall, it will need some load for this test]. This alternator will be produce an AC voltage to a load. Introduction of the rated voltage, starting from idle to rated speed, causes a temporary voltage drop lower than 9%. My numbers don't necessarily mean that the alternator is bad, just wanted to show you where my numbers are. Voltage drop tests must be done while the engine is idling with a charging load on the system. Glazed or burned streaks on the belt are an indication of slipping. This is a 'sense' wire, and under a heavy load will raise the voltage output to compensate for voltage drop in the charge wire from the alternator. Should the alternator cut-in the voltage may be up to 1V above the nominal voltage when operating in this condition. Voltage drops to just under 13v when I turn on the parking lights, then to 12 w/the lights on. 1960s–1970s) used a discrete device mounted elsewhere in the vehicle. Services – Interestingly there is no recommended voltage drop for service conductors, but this FPN reminds the Code user to consider voltage drop of the service conductors [230-31(c. This alternator is uniquely engineered to provide the finest performance and durability for your vessel. 5 Install new alternator and NEW belt. "Load dump" is a term that stands for the serious voltage spike and oscillations that occur if the load is suddenly removed from an alternator. As an added twist, it seems that the alt will charge at warm-idle (650 RPM) under heavy load if the vehicle has just entered the warm-idle state -- which I believe is because the "desired" voltage is still 14. Under a cold-cranking. So over time the voltage drops lower and lower as the car is used over about a two month period. Under heavy load, the regulator may reach its limiting capability and voltage will fall substantially as current increases. 6 volts, go to Step 04. A 30% voltage dip is sometimes used as a rule of thumb. Voltage always follows the path of least resistance, so if the circuit or connection being tested has too much resistance some of the voltage will flow through the DVM and create a voltage reading. 5 volts could indicate a failing battery. If the voltage drops a bit (but not below 12. is putting out 14. when the battery is allowed to charge for some more time the battery voltage starts reducing. If the load is then increased, the voltage out momentarily droops, so the field current is raised by the regulator. I could see the alternator voltage drop under increasing loads until it dropped below 12. Alternator Testing The alternator outputs approximately 14. Remove the alternator and bench test it to confirm or deny this as being the problem. Rotor rpm are a factor of pulley ratio multiplied by engine speed. Most winch ratings are at 12 volts. Ford f 100 engine cj pony parts f series super duty specifications ford trucks blueprint engines ford 306 c i d drop in ready long block ford f 150 reviews research f. 5 Install new alternator and NEW belt. Let us assume that you get your supply from your nearest distribution transformer- say few hundred feet away, through a distribution line having an impedance Z ohm. 5 Volts or so. 7 Volts more than in test 1. (R=E / I) Example: If the voltage drop on a circuit was 3Volts and the load drew 12 amperes then the impedance of both conductors would be 0. as illustrated. By repositioning the voltmeter test leads, the point of high resistance (voltage drop) can easily be found. Of course at idle, the alternator won't be working to its full portential. now if the voltage regulator went bad in the alternator, you would either have low voltage and the car will run like crap if it gets. Its internal cotactors get burned after awhile and increase in resistance causing a volt/amp problem.