Did I damage my electrical system

Tiny
PAT DILLON
  • MEMBER
  • 1993 FORD E-SERIES VAN
  • 4.9L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
I worry that I damaged my electrical system by helping my neighbor. He has a Dodge Nitro, and on his way home the battery light came on, and the truck started acting funny. Once he got home, and turned off the truck, it would not restart. There was no power. When I came outside, he had the battery out of the truck. Apparently he had tested the battery and determined it was shot. But the electric windows were still down on his car so he needed power to get them to go up so he could secure his car. He direct-connected from my old van to his Dodge. That is to say, he tried to power up his Dodge without having a battery in his Dodge by running jumper cables from my battery (with my engine running) to his Dodge. I am not sure how he hooked up the cables. It looked like he was hooking the positive cable to the fuse box in the Dodge. I have never heard of doing this. The direct connection did give some power to the Dodge but it was not enough to power up the windows. It was only enough to make some interior lights go on. It caused a huge draw down on my poor old van. My van is a 1992. It runs good, but I treat it with kid gloves because it is so fragile. I am very worried that this procedure might have damaged something in my own electrical system.
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Friday, June 2nd, 2017 AT 9:20 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
You did not list any symptoms or reasons to suspect there is a problem with your van. As for how the jumper cables were connected, the battery's positive cable has a smaller wire that goes right to the under-hood fuse box, so the positive jumper cable can be connected there too if it's more convenient. In fact, it was probably smart to do so. That way it is not likely to flop around and touch the body, which would cause a huge shower of sparks.

It is important to understand that while his battery might indeed be defective, that is not what the "battery" warning light is for. That light means the alternator is not charging the battery while driving. The electrical system will go dead within about a half hour, and even less if the head lights or heater fan are on.
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Friday, June 2nd, 2017 AT 9:48 PM
Tiny
PAT DILLON
  • MEMBER
Thank you so much for your reply. There is nothing about my van to indicate that it was damaged. It is just that I worry I did damage to it. Damage that I cannot see. But it sounds to me as if his method of trying to provide power to his truck. That is hooking the cables from my van directly to his fuse box while his battery was completely disconnected is not going to cause damage? Is doing it this way as opposed to having his battery in his truck basically the same thing? I have never heard of anyone disconnecting their battery and trying to provide power to the car by direct connecting the cables to his fuse box. Thank you again for your help.
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Friday, June 2nd, 2017 AT 10:17 PM
Tiny
CARADIODOC
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As an electrical specialist, I do all kinds of things most people would never think of. It helps that I was also a TV/VCR repairman for over thirty five years. You will never get enough current through any jumper cables to run a starter motor, but lights and windows draw very little current. Jumper cables are much beefier than what is needed for that.

The issue with his old battery is the most common way for one to fail is when one of its six cells shorts. That, in effect, turns it into a ten volt battery. If the jumper cables were connected to that, it would act similar to a dead short, and your generator would work really hard to try to get it up to twelve volts. It would never be able to do that, but it would try.

You should also understand that AC generator's, (to use correct terminology, "alternator" is a Chrysler term), are physically incapable of developing more current than what they were designed to deliver. It can not develop so much that its fuse wire will burn out, and it can't overheat any internal parts unless its maximum current is being requested for a long period of time. The only time we do that is when testing the system, and that part takes all of two to three seconds.

The way this was done, your electrical system had no idea where the power windows or lights were. It does not care if they were on your van or on the other vehicle. All your battery and generator know is they were running some windows and lights. This is no different than plugging a spot light into your cigarette lighter.
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Saturday, June 3rd, 2017 AT 12:17 AM
Tiny
PAT DILLON
  • MEMBER
Thank you, your reply was very well-written. I had to read it very slowly because it was dense with information, but I understood everything you said. It seems, though, that you confused my worry about my van's electrical system with that of my neighbor's Dodge's electrical system. I am not concerned with whether he did any damage to his vehicle. I am concerned with whether hooking up the cables the way he did could have damaged my van. First there is the general way they were hooked up (through his truck's fuse box with the battery disconnected), second there were sparks flying everywhere around his fuse box when he was attempting to attach the clamp, and lastly there was a big drawn down on my van's engine. So that is really my only concern. I think I suffer from a bit of OCD. It bothers me that damage might have been done; damage that I cannot see, but which may have weakened or shortened the life of my van's system. I am fascinated by your knowledge of voltages and engines. You must have a gift for it. I have tried to learn about it, and I always walk around with a puff of smoke billowing from my head.
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Saturday, June 3rd, 2017 AT 8:29 AM
Tiny
CARADIODOC
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:) 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.
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Saturday, June 3rd, 2017 AT 1:56 PM

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