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Acceptable AC voltage with grid heaters on


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Hey guys, 

After a long saga of chasing my tail, I figured out that my alternator was shot. I had previously measured it with cheapy multimeter and it was holding a .02vac so I sort of put it at the back of my mind and kept on going. Anyway, I realized that my power probe had a true rms setting and remeasured and saw some pretty bad numbers.

 

I picked up a 02 Durango 160 amp hairpin alternator from O'Reilly today. I had them test it before I took it and it tested at .36. They couldn't get another until next Tues so I took it.  I installed it, and at idle its pretty much what it tested on the bench at the store. When the grids cycle on, Im seeing about 1.65vac. I couldn't find a reference for what is acceptable. It settles back around .03vac once the grids turn off.

Id love some input to whether that's normal and acceptable.

Here's a quick vid you can see the spike near the beginning when the grids turn on.

John

Edited by JHFIII
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Normal to see the spike but the amount is the problem. Since there is no way to evenly load the system there is no way to test the alternator at home. Like if I turned on everything in my truck with LED lights and HID headlights will have lower load vs your truck. So of course my ac noise voltage is much lower. I can't say only my values work. This where you need to bench test the alternator before leaving the store if it passing then your fine. But yes its normal for AC noise to rise with grid heaters. This is another reason why I unhook mine in the summer no need to add stress to the alternator diodes. 

 

This is why we made the home test unloaded so there is just resting alternator and measure the AC voltage. Since there is no way to even load evbery truck and get the same results to the same test. Even grid heaters could fire 1 or 2 elements depending on the temp at start time. IAT controls pre-heat. Then Battery Temp controls post heat.

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I did have them test it at the store. It "passed" with .36vac. For reference, there were no accessories on in the vehicle during the test in the video. Only the grids cycling.

In the vid, I think it was down to 1 grid cycling at that point bc with 2 cycling it was at 1.65vac vs the 1.0 seen in the vid.

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Go warm up the truck and drive it. Once full warmed up now test.

 

Again with grid heater running and engine is cold the batteries are cold so high numbers are seen. Drive it and warm it up and leave it run now test your AC noise again. At this point the grid heater are disabled and batteries should be charged and engine is warmed. 

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Not sure about the alternating grid heaters either you could test for that by using a test light and probe the two trigger posts on the solenoids to see what is going one. 

 

Still in all the testing should be done on a fully warmed truck that has been driven till full operation temperature. Regardless the first start up the batteries are drawn down deeply between the pre heat grid heaters and the cranking over. This is not a fair test. Again make sure to drive the truck till completely warm and then leave it run and do your test again. This should be unloaded alternator with everything turned off.

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Understood on the fully warmed up truck. Ive been dealing with some other issues, but it should be ready to test drive now. The alternator should be the last piece of that puzzle. The old alternator was causing some wicked tcc cycling issues and simultaneous apps issues. Ill test it on a warm truck no acc and update.

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2 minutes ago, JHFIII said:

The old alternator was causing some wicked tcc cycling issues and simultaneous apps issues.

 

Easy pull the alternator field lead (blue and green wires) and see if the problem goes away.

 

APPS being weird the only thing I can suggest is replacement. 

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On 11/14/2020 at 6:05 AM, Mopar1973Man said:

 

Easy pull the alternator field lead (blue and green wires) and see if the problem goes away.

 

APPS being weird the only thing I can suggest is replacement. 

I wouldn't replace it I would change it and go to the Timbo APPS.

 

The spike in volts AC cannot really be properly seen on a voltmeter, you would need a scope to see it clearly. My source tells me it occurs only for a millisecond and is when the grid heater relays first make contact. I have been told this is a negligible AC spike and is common on most our trucks. On a scope you would mostly see a flat line with just a small short spike each time the solenoid first touches contacts.

 

I am wondering about the condition of your batteries and post clamps.  Is everything very clean and bright including all other electrical connectors and terminals for good Positive / negative connections for a well balanced system?

Edited by JAG1
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Difference... Solenoid spike is true it does make a sudden spike but... That's not the one I worry about it the the constant generation of high AC noise from the alternator as long as the grid heater is running. This is due the high current load on the alternator the load is typically higher than what the alternator can produce at an idle so the diode heat up and AC noise streams forth in to the rest of the truck. 

 

I understand that spike too being if I hook up the lighted switch on my exhaust brake it will blow the LED light out in fraction of a second being the spike from the exhaust brake solenoid for the vacuum control is big enough to blow the LED out. But after 423k miles I realize the fraction of a second spike is nothing its the constant generation of the AC from the diodes that is more damaging. If solenoids were the true downfall it would of wipe out way more than Dodge. Ford uses the same solenoids for glow plugs, starter solenoid, etc. Even our Starter is a huge solenoid that pulled the contact plunger into the battery contacts to spin the starter. 

 

Like being exposed to a single gun shot (the single BANG) vs. a full automatic just rattling for hours (BANG, BANG, BANG, etc.) the single bang you recover pretty quick but listening to hours of it will most likely ruin your hearing. Just like the ECM and PCM a single shot pulse is nothing it will absorb the single hit. But hours of rattling AC noise will kill any computer. 

 

I could pull this sideways a bit. My home inverter is called a Modifed Sine AC inverter. It is not a pure sine wave. It a stepped up and down. Tons of people told me don't use it it will destroy your electronics in your house. Nope not true. The sinewave even though its noisy its clean enough to be used. I'm still running the entire house on this inverter over 25 years. So how much noise is allowed is hard one to place a limit on but cleaner power is always better. But some ripple and noise isn't the end of the world either being like I just showed after 25 year I've never lost an device in my house. Even my PC is older than dirt and needs replacement still using every day and working the site.  

 

Little info on my Trace Inverter...

http://nooutage.com/tr.htm#:~:text=The Trace series Inverter%2FCharger,in an off-grid application.

image.jpeg

 

Solar Powered RV - Recreational Vehicle (RV) - Mopar1973Man's Dodge Cummins  Forum

 

Take it even farther... I've installed a Harbor Freight 1,200W inverter in my RV. Another case where everyone state don't use on electronics because it will kill it short order with dirty power. It been installed for better than 5 years and used every camping trip and still have the same TV in the RV 5 years later no issues. Charged my cellphones and other devices on that power too. 

 

Just food for thought... 

Edited by Mopar1973Man
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17 minutes ago, Doubletrouble said:

Interesting.......

 I now want to check my ac noise again. Refresh memory please, the DVM gets hooked to the charge lead from alt to engine ground correct? It's been minute since I did this, I searched but couldn't locate it.

 

Requirement. DVM able to measure any AC frequency below 2 volts. 

 

Black probe goes to the passenger battery. Then the red probe on the alternator charge post. Engine fully warmed up and batteriescharged up and no loads running. 

 

0.05 AC Volts seems to be the top limit for most.

Edited by Mopar1973Man
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URGENT - WINTER WEATHER MESSAGE
National Weather Service Boise ID
248 AM MST Sun Nov 15 2020

IDZ011-013-016-028-033-ORZ062-151800-
/O.CON.KBOI.WW.Y.0012.000000T0000Z-201115T1800Z/
West Central Mountains-Boise Mountains-Western Magic Valley-
Camas Prairie-Upper Weiser River-Baker County-
248 AM MST Sun Nov 15 2020 /148 AM PST Sun Nov 15 2020/

...WINTER WEATHER ADVISORY REMAINS IN EFFECT UNTIL 11 AM MST
/10 AM PST/ THIS MORNING...

* WHAT...Snow expected. Total snowfall amounts of 1 to 4 inches
  are forecast at elevations between 3000 and 4500 ft, with 4 to 8
  inches from 4500 ft to 6000 ft, and 8 to 14 inches above 6000
  ft MSL.

* WHERE...Portions of eastern Oregon, west-central Idaho, and
  southwest-central Idaho.

* WHEN...Until 11 AM MST /10 AM PST/ this morning.

* IMPACTS...Travel could become very difficult.

* ADDITIONAL DETAILS...Breezy conditions will result in areas of
  blowing snow above around 7000 ft.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Slow down and use caution while traveling.

The latest road conditions can be obtained by calling 5 1 1.
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It's great, finally a real November weather pattern. Ski lifts, lodges and restaurants won't be suffering like the last couple years. This a real good thing and on this Sunday like everyday we need to be very thankful :thumb1: . Like Mike Nelson when he needs some work and wants to see a broken truck come in his road :pray:

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