Delay Wipers = weird

[DavidC]

Ok I am going to post everything I found.
The test is from the positive post to ground (alternator case). Meter set on AC volts and the lowest setting since you are measuring millivolts.

Katoom posted this
Using a basic volt meter which will read in AC as well as DC...

Switch the tester to AC and set to 0.000v. You test by connecting the red positive line of the tester to the alternator output main on the back, and touch the black negative line of the tester to the alternator housing.

Have someone help you by starting the engine and turning on EVERY electrical component, lights, radio, AC, etc... Then ramp the throttle up to 2000 rpm and see what the tester tells you.

I would only use the AC compressor if you can keep it running as on/off loads may skew the readings, same with turn signals flashers. Blower motor on high should be good.

Mopar1973man.com
Originally I post 0.1 VAC would be a fail but under different circumstances, some people were getting issues below that number. So the 0.05 marginal number pops. Basically, if you can test and reach or pass the 0.05 (50 mv AC) I suggest having the alternator bench tested to verify if it bad or not. Because ever truck has different loads during the test and there is no way to accurately load the alternator from test to test so that why I suggest all load off hoping to even out the loads and get a test number we can all play by.



10 to 30 mV (0.01 to 0.03) is a normally good alternator.

50 mV (0.05) is getting marginal bench testing is advised.

100 mV (0.1) is failing. Bench testing is still strongly advised to verify the alternator.

 

[PBJ2500CTD]

You really need to get the electrical working right, less voltage = more amperage and more of a chance of arcing contacts causing pitting etc.. This includes relays, switches (headlight for example),AC/heat motors the list goes on and on. I believe you can buy new replacement Denso (foster truck ?). Not to mention the havoc on electronics, PCM, ECM etc. It's just a time bomb ticking.

Dave

^^^^^^^What Dave said^^^^^^^Both posts 40 & 41^^^^^^^

 

[fest3er]

The intake heaters draw 200A; the stock alternator puts out only 136A.

Since you have other electrical problems, you should minimize them first. A visual inspection of the back of the alternator might be enough; if two or three things back there look 'burned', you'll almost certainly find two or four lobes of the alternator output missing or weak. Once you're fairly certain of charging, check all (and I do mean *ALL*) ground points; corroded grounds do cause weird electrical problems. *Then* take the wiper motor apart and fix the eletrical innards.

 

[PBJ2500CTD]

For those who like a visual of the waveforms for good and bad diodes check these links for a description. You can readily see the AC component riding on the DC output with the bad diode.

https://www.circuitspecialists.com/blog/testing-an-alternator-with-an-oscilloscope/

https://www.brighthubengineering.co...w-to-test-an-alternator-with-an-oscilloscope/

Testing alternators:

https://axleaddict.com/auto-repair/Alternator-Problems-and-Automotive-Charging-System-Tests

 

[PBJ2500CTD]

The intake heaters draw 200A; the stock alternator puts out only 136A.

Since you have other electrical problems, you should minimize them first. A visual inspection of the back of the alternator might be enough; if two or three things back there look 'burned', you'll almost certainly find two or four lobes of the alternator output missing or weak. Once you're fairly certain of charging, check all (and I do mean *ALL*) ground points; corroded grounds do cause weird electrical problems. *Then* take the wiper motor apart and fix the eletrical innards.

Good point on checking the grounds, especially with so many electrical issues.

 

[DavidC]

Yes an oscilloscope is invaluable especially for finding noise on a circuit. I have one in storage but is a little large to keep in the RV as it is a 2 screen dual channel that is approx. 6" tall, 14" wide and 20" deep. Next time I am there I will have to check it out. I have not seen much on it but it would probably be great on crank position sensors and the ABS/speed sensors as yo could watch the pulse signal.

Dave

 

[fest3er]

You can get USB-based 25MHz sillyscope devices for less than $100:

• https://www.sainsmart.com/products/...efSrc=11091818452&nosto=customers-also-bought
• https://www.sainsmart.com/products/owon-vds1022-25mhz-2-1-channel-pc-usb-oscilloscope

Or you can buy some parts and make a 20kHz scope using your laptop's mic/line input: https://www.instructables.com/id/Use-Your-Laptop-as-Oscilloscope/.

 

[PBJ2500CTD]

You can get USB-based 25MHz sillyscope devices for less than $100:

• https://www.sainsmart.com/products/...efSrc=11091818452&nosto=customers-also-bought
• https://www.sainsmart.com/products/owon-vds1022-25mhz-2-1-channel-pc-usb-oscilloscope

Or you can buy some parts and make a 20kHz scope using your laptop's mic/line input: https://www.instructables.com/id/Use-Your-Laptop-as-Oscilloscope/.

Thanks for the links. May have to look into these. My Tektronix 453 ain't happy balancing on the fender...or, was the fender not happy with the Tek 453 balancing on it???

 

[fest3er]

Tektronix equipment has always had a problem with vertigo. I've been known to tie my 465B to the hood to prevent unepected falls.

 

[PBJ2500CTD]

Tektronix equipment has always had a problem with vertigo. I've been known to tie my 465B to the hood to prevent unepected falls.

Put antlers on it and nobody will ask questions...

 

[Joe Mc]

You guys crack me up = thanks. Good info BTW, appreciated. I'll give testing the alternator a go with my trusty Fluke Clamp Multi-meter and see what that yields. Interesting that the alternator would read AC Vs. DC volts. But as mentioned earlier Electrical is my weaker point. Have a good night all.

 

[DavidC]

The alternator actually generates AC voltage then the Diodes allow one way flow = DC voltage although it is not truly pure DC because of the lack of filtering. When one or more diodes fail it will lower the output and can bleed AC. All of which is not good. FYI, my 99 has a Bosch alternator but I understand can interchange with Denso. The only difference is the location of wiring terminals but there is enough wire for the locations which makes sense as I do not think Dodge would put different wire harnesses on trucks for alternators.

 

[PBJ2500CTD]

You guys crack me up = thanks. Good info BTW, appreciated. I'll give testing the alternator a go with my trusty Fluke Clamp Multi-meter and see what that yields. Interesting that the alternator would read AC Vs. DC volts. But as mentioned earlier Electrical is my weaker point. Have a good night all.

Only significant AC when something broke...
The alternator produces AC voltage (alternating current) which is converted to a pulsed DC signal via the diode bridge circuit where the negative part of the sine wave is applied as a positive voltage. In the website example photos you will see a ripple wave looking like a bunch of little m's connected together. The faster the alternator turns the higher the frequency of the ripple wave and the more stable the output DC voltage becomes (appears as a straight line).

 

[PBJ2500CTD]

Ya beat me to it Dave!

 

[PBJ2500CTD]

Only significant AC when something broke...
The alternator produces AC voltage (alternating current) which is converted to a pulsed DC signal via the diode bridge circuit where the negative part of the sine wave is applied as a positive voltage. In the website example photos you will see a ripple wave looking like a bunch of little m's connected together. The faster the alternator turns the higher the frequency of the ripple wave and the more stable the output DC voltage becomes (appears as a straight line).

And when a diode croaks the signal looks like a heart attack trace...

 

[PBJ2500CTD]

When the alternator works correctly it "appears" like a flatline EKG. Unless you expand the signal to see a bunny having an intimate moment. Gosh. I gotta watch my analogies...
Think I'll take a break and go check my mail....

 

[DavidC]

Can't have enough Easter Bunnies

Dave

 

[fest3er]

If I recall correctly, alternators are three-phase generators; they generate three 'sine waves' of output. The current alternates between flowing forward and flowing in reverse (the voltage alternates between +14V and -14V. The output is fed through diodes that, in essence, reverse (rectify) the negative voltage to positive; they also prevent the alternator from draining the battery when not running. So one rotation of the alternator should produce three complete sine waves. Rectified, the negative parts are 'reflected' to the positive side, so you should see 6 half-waves, all on the +V side, all at (very near) the same +14V level. If a diode becomes weak (doesn't block reverse voltage as well when it gets hot), you'll see one half-wave at a lower voltage than the others; the max output current of the alternator will be a little lower, and the alternator will drain the battery a little when off. If a diode fails shorted, one half-wave will be flat; the max output current will be 1/6 lower, and the alternator will drain the battery when the engine is off.

So. If you see a spark between the B+ cable and the alternator when you (dis)connect them, the alternator allows reverse current flow and you should rebuild/replace the alternator. If your sillyscope shows a weak half-wave or one or more flatlined half-waves, rebuild the alternator. And, as I said before, if you see 'burnt' spots at/near the diodes on the back of the alternator, it's almost guaranteed that the diodes are almost dead. And, no, you probably shouldn't ask the cart pusher to hasten their demise (http://www.intriguing.com/mp/_scripts/dead.php).

Rebuilding the alternator is usually less expensive than buying a new one. But the one in my '98 is built such that it's a Royal PITA to take it apart to rebuild (don't remember which mfr made it). Usually bearings, diodes and a couple other parts are all that need to be replaced; but the shop will bench-test the various pieces to verify.

 

[PBJ2500CTD]

If I recall correctly, alternators are three-phase generators; they generate three 'sine waves' of output. The current alternates between flowing forward and flowing in reverse (the voltage alternates between +14V and -14V. The output is fed through diodes that, in essence, reverse (rectify) the negative voltage to positive; they also prevent the alternator from draining the battery when not running. So one rotation of the alternator should produce three complete sine waves. Rectified, the negative parts are 'reflected' to the positive side, so you should see 6 half-waves, all on the +V side, all at (very near) the same +14V level. If a diode becomes weak (doesn't block reverse voltage as well when it gets hot), you'll see one half-wave at a lower voltage than the others; the max output current of the alternator will be a little lower, and the alternator will drain the battery a little when off. If a diode fails shorted, one half-wave will be flat; the max output current will be 1/6 lower, and the alternator will drain the battery when the engine is off.

So. If you see a spark between the B+ cable and the alternator when you (dis)connect them, the alternator allows reverse current flow and you should rebuild/replace the alternator. If your sillyscope shows a weak half-wave or one or more flatlined half-waves, rebuild the alternator. And, as I said before, if you see 'burnt' spots at/near the diodes on the back of the alternator, it's almost guaranteed that the diodes are almost dead. And, no, you probably shouldn't ask the cart pusher to hasten their demise (http://www.intriguing.com/mp/_scripts/dead.php).

Rebuilding the alternator is usually less expensive than buying a new one. But the one in my '98 is built such that it's a Royal PITA to take it apart to rebuild (don't remember which mfr made it). Usually bearings, diodes and a couple other parts are all that need to be replaced; but the shop will bench-test the various pieces to verify.

Good description. The varying voltage created by the defective diodes would generate a small, perceptible AC signal if you were to read the meter set to low range AC.

I was going to post some educational information on the differences between a generator and an alternator, BUT out of three websites I was going to use for reference I found all three had grossly conflicting or erroneous information...it caused a significant additional flicker of the flickering cell of my two remaining brain cells. So, I deleted it.
I either need to go back to school to bone up on my ancient electronics degree (electron tubes rule; and they're pretty much EMP/ESD proof !!!), or join the "we're doomed" crowd.

 

[Joe Mc]

OMG Bruce = join the “we’re doomed” crowd... When it comes to electrical I’ve been part of “that” crowd “for-everrrrr”. LMAO