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Kevin
Dodge Dakota
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2/03/2003
19:58:02
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 Subject: AC Volts on 2001 Dakota
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I have a 2001 Dakota with the 4.7 Liter engine and towing package (heavy duty altenator). The electrical system is showing 14 Volts DC, 30 Volts AC! I measured this using a digital multimeter with 1 K Ohms across the leads on a cig. lighter adapter. The 30 Volts AC is not always there, it hangs around for a while then disappears, then comes back. I've had sporatic problems with the electrical system since I bought the truck: radio fuse blew, battery died after 2 years, auto door locks went crazy after the battery was replaced (then problem corrected itself), cell phone won't charge off truck power. The dealer says his equipment doesn't show a problem.
Anyone have any ideas? The altenator was changed out last week. I either see 30 Volts AC or zero. There's a small variation with the load on the electrical system (lights, AC, etc). It looks very likely that the large AC voltage may be the root of my problems.
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BeerHat
Dodge Dakota
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2/04/2003
00:37:51
|  RE: AC Volts on 2001 Dakota
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i bet this only happens when the truck is running.
Probably have a bad voltage regulator.
Dan
01' 4.7 4x4
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Gentleman
Dodge Dakota
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2/04/2003
16:07:46
| RE: AC Volts on 2001 Dakota
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Don't know if this helps but the fuel injectors utilize ac voltage not dc, appears that something may be crossed are you are gettting some sort of a feed back, how and where th dc is converted to ac I do not know.
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Lab Rat
GenIII
2/04/2003
18:00:27
| RE: AC Volts on 2001 Dakota
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Bad rectifier in the alternator.
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JKnPA
Dodge Dakota
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2/04/2003
18:06:02
| RE: AC Volts on 2001 Dakota
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Kevin,
I agree with Beerhat. The AC voltage in the alternator should be rectified to a DC voltage by the diodes inside the alternator. If you are not getting "full-wave" rectification, it would cause all sorts of weird stuff..me thinks.
See link below for a good explanation.
http://www.autoshop101.com/trainmodules/alternator/alt102.html
John....
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Lab Rat
GenIII
2/04/2003
19:37:18
| RE: AC Volts on 2001 Dakota
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John, diodes don't rectify; they act as "check valves" to allow current flow in only one direction. The rectifier converts AC to DC.
LR
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Kevin
Dodge Dakota
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2/04/2003
21:49:30
|  RE: AC Volts on 2001 Dakota
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Thanks to all for your suggestions. It was raining today, so the scope comes tomorrow. Anyway, I think I may know what's going on. I need someone a little smarter (or at least with better sources) to check it out. Does anyone know if Dodge uses switching regulators on their trucks? Switchers, as the name implies, acts as a super fast switch cutting on and off to regulate the voltage level. Switching regulators are used in almost all home elctronics because they're cheap and give a lot of power for the size. If this is the case with my truck, it would explain the AC I'm seeing (the switching action of the regulator).
If anyone knows, let me know. Specs on the regulating frequency and voltage ranges would be great.
Kevin
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Demon-Xanth
Dodge Dakota
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2/05/2003
01:20:53
| RE: AC Volts on 2001 Dakota
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Lab Rat: a full wave bridge rectifier is nothing but 4 diodes. A singe diode would be a half wave rectifier.
What DMM are you using to measure with? Some DMMs are more sensitive to spiking and others are downright blind to it. If you can, hook up an oscilliscope and see what the waveform looks like.
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JKnPA
Dodge Dakota
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2/05/2003
09:05:25
| RE: AC Volts on 2001 Dakota
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DX.......... Thank you. Yes you need the 6 diodes ( as shown in the link) to get "full-wave rectification". I suspect Kevin has one/more bad diodes causing his problem. If you look at the alternator output with a scope, you probably would see "pulsing DC"......meaning 1 or more phases of the 3-phase AC is not being rectified.
Lab Rat..... You are correct.....diodes permit current to pass in one direction, but when you have a 6 diode setup as shown in the link, I posted, its called "full-wave rectification"
***** AC to DC conversion ******
http://www.autoshop101.com/trainmodules/alternator/alt128.html
John......
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BeerHat
Dodge Dakota
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2/05/2003
12:14:15
| RE: AC Volts on 2001 Dakota
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well then... the rectifier is typically located and integrated within the regulator right? Simple replacement of the regulator should fix his problem. no?
Dan
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JKnPA
Dodge Dakota
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2/05/2003
17:30:53
| RE: AC Volts on 2001 Dakota
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BeerHat & others......
The link can explain the operation of the alternator. I like to provide links because they can explain things better than I can, plus you get pictures.
The "regulator" and the 'rectifier" are seperate parts within the alternator. The regulator is a transistor( current device) in the rotor circuit, and the rectifier ( 6 diodes) are in the stator circuit. The problem could be any unit within the alternator. You can troubleshoot the problem with an "O-scope" or a " multimeter'. Since most people don't have an "O-scope", you s/b able to isolate the problem with a M/M.
http://www.autoshop101.com/trainmodules/alternator/alt131.html
John......
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mddak
Dodge Dakota
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2/05/2003
18:28:08
| RE: AC Volts on 2001 Dakota
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my $.02 worth.....
diodes and rectifiers - we had a big argument on this at work a while back. Bottom line we came up with is the terms are interchangable but usually the term diode is used for small components low wattage and rectifiers are high current items.
One guy said - Diodes are sold in six packs at radio shack and rectifiers are sold individually.
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JKnPA
Dodge Dakota
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2/05/2003
19:00:22
| RE: AC Volts on 2001 Dakota
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mddak,
Very good........good ole Radio Shack.
My main point to Beerhat was the "regulator" and the "diodes" are different parts of the alternator. I'll try to "paste" the page of the link I'm talking about. When i said "rectifier' I was talking about the "diode bridge' which converts the AC to DC. The "6- diode bridge" performs the rectification........see explanation.
The main point is fixing Kevin's problem, so i won't argue the diode/rectifier point.
John.......
Understanding the Alternator
--------------------------------------------------------------------------------
Rectifier Operation
The Diode Rectifier Bridge is responsible for for the conversion or rectification the AC voltage into DC voltage.
Two diodes are connected to each stator lead. One positive the other negative.
Because a single diode will only block half the the AC voltage.
Six or eight diodes are used to rectify the AC stator voltage to DC voltage.
Diodes used in this configuration will redirect both the positive and negative polarity signals of the AC voltage to produce DC voltage. This process is called 'Full - Wave Rectification'.
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Demon-Xanth
Dodge Dakota
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2/05/2003
19:53:12
| RE: AC Volts on 2001 Dakota
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Bridge rectifiers are a quartet of diodes, the rectifier arrangement in that picture was make for a 3 phase power source. (which you can see by the three coil arrangement). A diode and rectifier are NOT interchangable terms. A rectifier is a description of an arragement of diodes, a diode is just a device. There are "rectifier diodes" that are specially made for high power, high current operation, but we've also used very low power, low current diodes for a power supply section on our boards. It all depends on the amount of power that needs to be disappated. Concivably it's possible to make a special rectifier IC, which is probably done, but that would be the equivilent of 4 diodes, or in the case linked above, six. It's kind of like not all coils being transformers.
Basically, a rectifier is something that a diode is part of.
<-- Electronics tech in an electronics enginnering dept.
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BeerHat
Dodge Dakota
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2/05/2003
20:03:15
| RE: AC Volts on 2001 Dakota
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typically the rectifier is integrated within the regulator unit... at least all alternators that i've seen thusfar. if it turns out that they ARE separate on our dodges, then replace BOTH. should be cheap enough... don't half@$$ or monkey around with your charging system. do it right, cover all bases or it'll leave you stranded.
Dan
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mddak
Dodge Dakota
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2/05/2003
20:39:41
| RE: AC Volts on 2001 Dakota
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more $.02 worth.. this is why we had a big argument at work. This is from American Semiconductor.....
Diode - Rectifier
In this discussion the term diode and rectifier will be used interchangeably; however, the term diode usually implies a small signal device with current typically in the milliamp range; and a rectifier, a power device, conducting from 1 to 1000 amps or even higher. Many diodes or rectifiers are identified as 1NXXXX . A semiconductor diode consists of a PN junction and has two(2) terminals, an anode(+) and a cathode(-). Current flows from anode to cathode within the diode. A diode and schematic representation are shown below.
http://www.americanmicrosemi.com/tutorials/diode.htm
Electrical engineer :) we did some really neat things
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mpil1
GenIII
2/05/2003
22:01:22
| RE: AC Volts on 2001 Dakota
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Yep, sounds like a bad diode in the alternator.
This part is off-topic of the original post, but here goes...... :)
To settle all arguments, the words diode and rectifier are technially not interchangeable as not all diodes are used for rectification. However in the industry if a diode is rectifying we usually just call it a "rectifier." Rectification is what a diode will do to an AC waveform. Someone mentioned above, "they act as "check valves" to allow current flow in only one direction." This process of allowing current to flow in only one direction is known as rectification. A rectifer can be as simple as a single diode inline with an AC signal or a more complex arrangement of diodes such as those in full-wave and three-phase power applications.
Now the way off topic part....LOL sorry!!
"Current flows from anode to cathode within the diode." This is known as Conventional Current Flow. Another school of thought we use in engineering is that current actually flows cathode to anode (negative to positive). This is called Electron Flow. Engineers (most of them) and technicians are taught this. Either way you look at it, the numbers all come out the same. Sorry I had to blab on, but we argue this with my boss at work all the time. Damn conventional-flow junkie!!! :)
Mpil1
'02 SXT CC, 3.9L, 5-spd, 4x4, Trac-Loc...Not enough Mods Yet!!!
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