Comments by "SeanBZA" (@SeanBZA) on "Royalty Auto Service" channel.

  1. New subscriber, and all great points people overlook. Especially about testing diodes, which people almost always, even experienced mechanics, overlook. Depending on the multimeter you can switch to AC volts, and some have a dual display, which will show both DC volts and the AC voltage on it, so that you can diagnose a failed diode pack without a scope. Others when in AC volts disregard the DC, so you get the AC voltage only. As well remember that there are 9 diodes in the alternator, 6 high current ones that feed the output, and 3 lower current ones that provide the excitation to the rotor, and those 3 also can have a diode fail. Most voltage regulators will have a terminal, or a place you can put a probe, to measure that field voltage as well, so your scope can test those diodes as well.
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  2. Very likely alternator died, and they disconnected it without disconnecting battery, and blew the fusible link when the alternator output lead shorted to the engine block. Then never thought the fusible link was blown. Plus likely battery acid had corroded the wires by the battery, so them twisting the wires together, after finding the link was faulty, still did not give good contact. Thus new alternator, new battery and still a problem so put in a used ECM, thinking that was the issue. Been down that road.....
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  3. No, that is a full wave 3 phase rectifier, as diodes are a lot cheaper than copper, so putting in 6 diodes, and only half the number of turns of thick copper (or for the cheap alternators the thicker CCA wire) to get the rated current output, is a lot cheaper than having to put in double the number of wire. Then make a larger case to fit them, and having to get much more expensive diodes, rated at 200V, as opposed to the regular diodes that are rated at 30V, and are designed to break over at around 40V, to handle the case of a load dump transient (which is part of the job of the alternator now, as electronics in a vehicle is so much more than when a generator was around to drive only a few lights and a coil with points), or a regulator failing and causing the alternator to go to full output. Ripple you see there 6 peaks per revolution of the alternator field past the pole pieces, because of the 2 phases, and at any time 2 diodes are conducting at the peak. The larger lower ripple is because of the rotor turning once in the housing, and also the slower response of the voltage regulator modulating the average output voltage, as it is being aimed at a particular set voltage by the internal regulator module. Typically 14V4 when cold, and dropping to 13V8 as the regulator heats up, to closely track the actual battery temperature, but still provide a high initial current to charge the battery from cold, tapering off with time. With modern alternators getting controlled from the ECU the initial voltage set is zero for a few second,s to allow the ECU to gain control of idle RPM correctly, and start the cold start warm up and keep emissions down, then it is ramped up to get voltage to 14V4 for a few minutes, to provide a full charge to the battery. Maintained till the ECU sees the battery current start to taper off, as the battery approached full charge, sensed by the sensor on the ground lead. Then it will depending on the model, either switch to a 15V charge for a few minutes, to desuplhate the battery, set by a counter programmed per the OEM battery manufacturer as to best profile for this, or will drop the battery voltage to a set voltage as determined by ambient inlet air temperature, and engine compartment temperature (coolant return temperature) so as to not overcharge the battery, and all the time monitoring, so that the sensed ground current in the battery is close to zero, so the alternator provides all the engine and vehicle current draw. this means that your alternator warning light comes on when the ECU detects the battery is being forced to provide current for more than 5 seconds, either due to the engine not running, or that the load exceeds the output 5 seconds after it has been commanded past 95% duty cycle on, and the alternator is not supplying this current.
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  4. Should be in total under 0.5V, if more check for good connections and corrosion. Remember this includes both battery to alternator, and starter, plus the fusible links that are typically used, plus the ground cable from engine to frame, and the ground cable from frame to battery. most often engine ground, and battery to frame, is the one neglected, and often one is poor contact. Remove the chassis connection, clean the terminal lug, the bodywork there, and apply a thin film of grease ( white grease, dielectric grease, Vaseline, wheel bearing grease, or even gear oil or engine oil at last resort), and put the connection back, and make sure the nut is clean on the contact face as well. There are often TSB's about this, famous on GM products as they age, and covering multiple models and years. Same for the fusible links and multifuse units, undo, clean the contacts, retension for the plug in ones, and clean and reconnect both with a thin film of grease on all mating surfaces.
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  5. But a multimeter is cheap, or even free at Horror Fraught, and well worth keeping in the vehicle, the free Harbour Freight one is good enough to use here, and accurate enough. Blow it up, get another.
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  6.  @abdul-kabiralegbe5660  12V8 with high engine compartment temperature is correct with a fully charged lead acid battery, as the terminal voltage, which with a fully charged battery is 13V8 at 25C, is going to drop as the temperature rises. Older alternators that charged at a fixed voltage, 14V4, or 13V8, irrespective of temperature, thus would overcharge the battery, causing it to lose electrolyte due to it being split into hydrogen and oxygen. Some sealed batteries, and some more expensive refillable ones, have a palladium catalyst in the vents to recombine this to water, slowing down the loss, but you always had to add pure water to the battery to give it a long life. Thus checking the battery water, and filling up at each service. Sealed batteries are the exact same now, just there is often a cover over the screw off caps, and they say sealed for life, as they know there is enough water there to get you out of warranty before a cell boils dry, and you buy a new battery. Pull off the label, see the caps, and check the water, and you get many years more service out of them, and check the water monthly as well, even if it means you have to remove the hold down and the terminals to get to the caps. Done that to all mine, and got to see that they would last 5 years just filling up every 6 months or so, all cells taking around 100ml of water to fill up again. Otherwise would have had the battery fail around 25 months after buying, just outside the 24 month warranty. OEM battery had caps, but was never checked, despite it being part of the OEM service routine.
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