Today I was trying to figure out why power windows work slow and this is what happened. I connected vehicle to battery charger set at 40 amps to see if windows would go faster. (trying to determain if it was battery issues) I observed no change in speed so I tried it on I think it was 150 or 200 amps. It was at this time the windows and radio stopped working. (possibly other things just not sure) I disconnected the charger and returned to the drivers door and the radio came back on (clock was wrong time) and the windows began to work again. (still very slow) So I was wondering 1) is there some sort of auto rest breaker that tripped and reset and or could I have damage something even though everything works again. 2) any ideas about the slow power windows??? Any help or ideas would be great

jim

 

Are you aware that a battery charger that is capable of 200 amps puts out MUCH more voltage than 12.5 VDC?. I mentioned this in another thread. In order to push 200 amps through a charged 12 V battery and a 12V system, the voltage would have to be (just a guess, but your charger info should tell you) considerable, like maybe 30-50 or more VDC. Voltage is what drives amperage. You cannot get an increase of amperage in any given system unless you increase voltage or decrease resistance. That is part of the Ohms Law formulas.

Given that, you may well have damaged some electrical components. For example, some cheap diodes may have a PIV (peak inverse voltage) threshold that you exceeded, which would probably blow them. Not saying thats what happened, but it is clear to me that you did something to the electronics. No doubt about it, the excess voltage caused excess current flow through the breakers/fuses and tripped them. I am curious why you didnt blow and fuses----maybe you did.

Reasons like this are why they tell you to disconnect the ground cable when welding on vehicles.

 

I would say your wrong with your example. We run 200 amp alternators on tractors with 12 volt systems all the time. These alternators don't go over 14.5 volts to induce 200 amps of current under a heavy electrical load. These tractors will use up to 14 onboard computers depending on attached options, so they closely monitor system voltage and have protection parameters to guard against voltage spikes. The automotive industry uses the same protection systems.

Just because you set the charger to a 200 amp setting doesn't mean it will automatically put out 200 amps. You would need to be cranking the engine with a dead battery to get the full 200 amps out of the charger.

The over voltage protection system on the vehicle probably shut power off to the computer which has the drivers in it that controls the windows. The same thing would happen if your alternator regulator failed allowing the alternator to overcharge.

 

Yes, I agree that under a heavy load an alternator might need might to put out higher amperage. A popular upgrade on cars and trucks is the 130 amp alt, but that is for extra load, not normal operating system functions. Thats not what you said. Your example of your vehicle was only loaded to test window motors, which is a normal OEM system function.

If you checked your amp guage on the 40 amp output scale, it may have only put out ~15 A (example) At that point there would have been no need to go to 200 because it had regulated. All that will depend upon the condition of the battery which you have not confirmed. When you went to the 40/200 amps output, it did output more voltage. If you have some battery internal problem, the regulator can be fooled.

The electrical system is protected by fuses, breakers and fuseable links. All are current sensitive. The computer (PCM) does not control the windows. The window motors are stand alone as is all the 12 V equiptment. The PCM does not operate or pass 12 V. Functions requiring 12V are operated by relays, which the PCM operates the winding. You described 2 possibles, a tripped breaker, which reset and possible guage problems caused by the extra voltage. I am quite sure the clock is not controlled by the PCM, at least it never was before. I am still surprised that it quit and came back on---sounds like a fuse, but they dont reset.

I dont know the condition of your battery, but from experience I can tell you one condition that will cause your symptoms and also cause that large voltage spike from a big charger. It is a common condition.

A bad battery will sometimes read the rated voltage, but will drop voltage to almost 0 V when any load is applied. soon as the key is released, they will read 12.5 volts again. What you are reading is a surface charge. A charger hooked to it will regulate to 0 in a minute or less. If you have a 200 amp charger hooked to it, it may be sitting at low amps. But, when you hit the battery with a load, the voltage will drop significantly, and the charger will see that change and ramp up to a high rate to compensate. Thats where you may get a momentary high voltage condition. Maybe you were lucky you did not get any blown links or fuses, only tripped breakers.

Maybe it didnt go to the max rated amperage, but it, no doubt, went up. The only way to know for sure is to hook up the Fluke to capture the max readings. I am thinking the battery is bad. Anyway, sounds like you are aware of how chargers work, but consider the other things. LOL

I stick to my statement earlier. Any time you hook up a 200 amp charger, you have to account for the fact that it may well go to 200 amps. I wouldnt even hook up a charger like that to anything but an isolated battery and then for safety, stand back.

 

Your earlier post stated that in order for a charger to put out 200 amps the voltage would have to go to 30 - 50 or more VDC. That statement is incorrect, an automotive system will not handle voltages of that level.

You also stated "You cannot get an increase of amperage in any given system unless you increase voltage or decrease resistance." This is also wrong, by decreasing the resistance the amperage will also decrease. The resistance is providing the load that the amperage is trying to overcome, if you have enough resistance in the circuit (such as cranking the engine), the amperage will go up to the limits of the charger to try to overcome the load. But it will not put out 50+ volts.

Also, I am not the one with the original post or problem, I am just not agreeing with all your electrical theories.

 

Thats the point I am trying to make----automotive systems will not handle that kind of voltage. Seems we are not in agreement on how, with a 200 A charger, can put that kind of voltage into a system. I have given one senario.

Increasing resistance in a circuit decreases current flow. I didnt make that law----it is ohms law, very basic. lets see if I can remember the formula--

I=P / R current (I) = power (P) divided by resistance (R)

Power is ~12.5V in this case. Resistance is the resistance of the whole load or a specific load (ie: window motor). if you increase resistance, without increasing power, the current flow is less. If you increase power (P) without increasing R, I will increase.

Cranking an engine will not increase voltage, I never said it would, read my post closely. The only way you might increase voltage to those amounts, is if you have a charger capable of 200 A hooked up at the same time and have a battery thats not capable of delivering its rated amperage. Even a good battery will drop some voltage when the starter hits it. That will trigger a charger to increase voltage to regain the 12.5 VDC. The amount will depend upon the state of the battery and the capabilities of the charger.

If the limits of the charger are 200 amps, and the battery voltage drops enough, it will put out considerable voltage to get to its rated output. I believe I said maybe 30-50 volts---amount not exactly specified. I am pretty sure I have seem chargers that put ~90 volts to pump the amperage through a dead battery for a quick charge. Again, put a Fluke multimeter on it----.

Is O.K. to not agree with my "theories". What you need to do is disprove my interpretations of Ohms Law. Thats where my "theories' come from. I sat through many a class with instructors trying to pump this stuff into my head and I worked with this stuff for 34 years. Had to refer to "Mr. Ohm" lots of times, even had to design some circuits.

 

Ok just had time to read the posts. I did check the charger , while on 40 amps puts out 12.5 volts. Then when I switch to 200 amps voltage goes to 17.2 volts. This is using voltage meter with no load on charger. So I what I am wondering is by hitting the battery with that 17.2 volts, did or could I have damaged any key electronic components? Like I had posted everything now seems to be working fine. (although windows are still very slow!!!!!). Thanks again Jim

 

I think with a dead battery in circuit, the voltage would be considerably higher to push even the full 40 amps to the battery. I guess we really need someone to get a really dead battery and measure.

I dont think that 17 volts would do much damage because that wont push a tremendous amount of amperage. I guess you have checked all the connections and grounds to the frame/body. Have you had that battery load tested? Maybe you have already thought of that, those batterys will not accept charge but will read ~12.5 without any draw.

 

Well, I depended on memory and misquoted the Ohms Law formula for determining current flow. The method and figures would have been correct, but the symbol I used for voltage (actually electromotive force) was not correct. "P" is the formula symbol for "power" which is rated in watts (volts X current). The formula should read: I (current)=E (volts) divided by R (resistance).

2008 isnt even over and I have already made 2 mistakes, actually 3 counting the time I told the wife to get back in the kitchen.

 

So you are saying voltage will not increase to a point to damage parts at 200 amps?????? Or are you just correcting your fomula???? thanks

 

Just correcting the formula