:) Actually, I went to school for electrical design, and I never pursued the field because the math was way over my head. My "gift" is the ability to figure which part has failed in a circuit that someone else already designed and built. All I have to do is solve the cause, then put back the same part that was there before. That's similar to the difference between a mechanic and a car designer.
I was referring to your van when talking about something being damaged. As I mentioned, your generator cannot put out more current than it was designed for. Another way to think of this is the other guy connected a battery to his vehicle, but with jumper cables in between, and that battery also happened to be connected to your van too.
There was a TV commercial a few years ago that showed five cars hooked to one battery, and they all started in winter weather. I was skeptical about some of their claims, but one car would not be damaged by having the other cars connected to the same battery.
If any damage would occur in your story, it would likely be to the other vehicle, but only if he managed to get the engine started, and he removed either of the jumper cables while the engine was running. Many years ago, uneducated mechanics would remove a battery cable while the engine was running. Their thinking was if it stayed running, the generator must be working. There is a real lot wrong with doing that today, including the engine may stall even when the charging system is working just fine, or more commonly system voltage will go much too high and destroy multiple computers. The battery is the main component that helps the voltage regulator maintain system voltage to a safe level, (13.75 to 14.75 volts). With one battery cable disconnected, system voltage can go as high as over thirty volts, especially if engine speed is increased. That will destroy any light bulbs that are turned on, and will damage numerous computers.
We hook jumper wires to batteries in cars to test light bulbs and fan motors all the time. Your friend did the same thing to run the window motors. Those motors were just on a vehicle, not sitting on a workbench.
If you want further verification your van is okay, have the charging system tested. It takes longer to connect the three cables than it does to do the tests. The generators that were available for your van include a 75-amp, 95-amp, and a 130-amp. During the "full-load output current" test, you will find one of three values. If there is no defect, output current will be within a few amps of the unit's rated current, exactly one third of that current, or 0 amps.
Every AC generator has six diodes built in. Those are one-way valves for electrical current flow. If one of them shorts, you will lose two thirds of the generator's current-producing capacity. You would only get close to 25 amps from a 75-amp generator. It is possible there would be no symptoms, but typically the electrical system needs more than that, so the battery would have to make up the difference until it slowly runs down over days or weeks. One potential symptom is increased whine from AM radio.
If the test shows 0 amps, by far the most common cause is worn brushes. That is due strictly to mileage and how hard the generator has had to work on a daily basis. Drawing high current to run the heater fan on the highest speed, with the wipers and head lights on, will have no effect on those brushes. Doing that almost every day for a few years will make those brushes wear faster. You would notice this right away. If the engine was able to be started, it would stall within a half hour to an hour from a dead electrical system.
Other than those three conditions, it is physical not possible for a generator to be weak. If you have a 95-amp generator, testing will show it is able to produce 95 amps, (typically 90 - 100), 30 - 35 amps if it has a bad diode, or 0 amps. Be aware though, there are other things that can cause it to produce 0 amps besides the worn brushes. There's wiring, a fuse, and the voltage regulator we need to look at too.
The rest of the testing includes charging voltage and "ripple" voltage. Charging voltage must remain between 13.75 and 14.75 volts to prevent over-charging the battery. Your voltage regulator is capable of detecting a no-charge condition, which is typical, but also an under-charge and an over-charge condition. Any of those defects will cause it to turn on the dash warning light.
Ripple voltage is the variation in charging voltage that is characteristic of all AC generators. It is what AM radio picks up as that irritating whine. Most professional load testers only show ripple voltage as somewhere between "low" and "high" on a bar graph. It will be low most of the time. High ripple voltage is a result of one of those diodes has failed.
If you find ripple voltage is low, output current is close to one of those three values I listed, and charging voltage is within specs, your charging system is working properly, and you can sleep well. If testing shows a diode has failed, I would be suspicious that happened a long time ago and there were never any symptoms. I've driven cars like that in the past. I just avoided using the higher heater fan speeds, and did not use other electrical devices that weren't needed. As I mentioned already, your generator can't produce more current than it was designed for, and the diodes are capable of withstanding that much current for longer periods of time than normally occurs. The other characteristic I have not mentioned is all generators produce exactly the amount of current needed to run the electrical system and recharge the battery, and no more. The only time the maximum current will be produced is during the full-load output current test, and that lasts about three seconds.
Saturday, June 3rd, 2017 AT 1:56 PM