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Old 07-19-2019, 04:14 PM   #1
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Alternator

Before I go out and access the top of the motor from the bedroom, I amjsut wondering if someone on here can tell me what alternator I might have on my 2000 Harney Coach with the 3126 B cat engine.
Started it today after sittin about 3 months and the volt meter shows 8-9 volts and goes down when I turn the headlights on. Coach has about 87,000 miles and has always worked great.
I will probable go out tomorrow and get the info I need and also check the alternator and see what is putting out.
Aways get great answers on here and really appreciate the website.
Thanks
Busyguy
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Old 07-21-2019, 01:52 PM   #2
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My preliminary research indicates you have a Delco Remy 21Si, which is only rated for 115 amps at 1600+ rpm on your engine tach.



I've written lengthy messages on this forum about the grossly underpowered Class A DP motorhome alternators from circa 1997-2008.



If you pull on your headlights, turn on your engine driven airconditioner and have your radio on, your load demand will exceed the output amperage capacity of your OEM alternator.


You should immediately consider upgrading to the Delco-Remy 40Si alternator, the 300 amp model, and discover if your OEM alternator is a pad mount or an arm mount to determine which specific model would fit your application.


I upgraded our DP from the 22Si (130 amp) to the 40Si (300 amp) and it's been the best bang-for-the-buck investment upgrade thus far.
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Old 07-21-2019, 03:27 PM   #3
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Volt meter reading 8 to 9 volts I assume you had to jump it off. If you disconnected as soon as it started the alternator may not have started charging and 8 to 9 volts may not be enough to excite the alt. I would try charging the batt. before pulling the alt.
I do agree with ret60sp, that would be a great upgrade. I'm considering it myself.
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Old 07-21-2019, 08:07 PM   #4
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alternator

Thanks guys for the reply. No I did not have to jump it off. My batteries are always fully charged by my Echo charger.
Everything is fine when running the engine,Volt meter on dash shows 13+ volts. Then when I turn on the headlights or dash AC the meter goes down to 8-9 volts. I am thinking bad ground from dash and have found some corrision on the ground terminal in the electrical bay.
Will get that corrected tomorrow and go from there. I have owned this coach since new and have never had a problem like this before.
Also thanks for the info on the bigger alternator. Will check in to that also.
Thanks
Busyguy
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Old 07-21-2019, 08:58 PM   #5
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alternator

Is the wiring on the 21SI the same as on the 41SI or is there a different wiring hookup?
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Old 07-22-2019, 07:35 AM   #6
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Quote:
Originally Posted by busyguy View Post
Is the wiring on the 21SI the same as on the 41SI or is there a different wiring hookup?



The 21Si is self-excited, so the battery state of charge has little or no effect on its ability to reach a charge voltage (13.6-14.1 VDC). Whats important to note about the 21Si and the 22Si is they both produce less than 30 amps at flat engine idle, about 50% of their rated power output at 1400 RPM (50-60 amps @ fast idle) and they don't reach 100% (100-130 amps) until the engine RPM is over 1900 RPM.


The 40Si will produce 190 amps at engine idle (700 RPM), 240 amps at a fast idle (1000-1200 RPM) and 300 amps at any speed over 1700 RPM. This means you can idle your engine and the 40Si will produce more amperage than your coach will demand - assuming the batteries are at 100% SOC.


This OEM alternator condition creates a significant problem, especially operating your RV at night. Add in rainy weather, a nice stereo system surround sound system thumping in the background, the dash A/C in operation and low highway speeds (<1900 RPM) and you WILL drain your batteries down to a voltage less than your ECU will allow without latching a SES or CEL.


If your batteries are less than 80% SOC and you are operating at night, the load demand on your OEM alternator will exceed its capacity, causing it to trip the thermal limiter in the 21Si, causing an immediate 100% load demand on your batteries. This might be the condition you are seeing - as indicated by the display of <10 VDC. The thermal limiter will trip at less than 100% of the rated ampacity if the RPM is too low to sufficiently cool the unit. If the unit is clogged with carbon and diesel engine soot, the ability to keep the 21Si cool will be compromised and thereby cause it to again thermally trip the limiter. When the unit cools off the limiter will reset and again start producing power. This on, off, on, off condition is not uncommon for RV's with severely underrated OEM alternators.



The wiring on the 21Si and the 40Si are the same. The 40Si also offers a "remote sense" wire - one you can install separately - that runs a 14-16 AWG wire directly from the remote sense port on the alternator to the main batteries to measure their voltage and SOC. What this does is measure the difference in the line voltage (demand - a function of amp draw) against the current measured voltage on the battery bank. This allows the 40Si with "remote sense" to raise the voltage incrementally from 13.9 to as high as 14.5 to ensure the voltage reaching the batteries is high enough to actually recharge the batteries while the other power consumers are drawing power from the system.


No, you do NOT need to worry about an over-voltage condition. The remote sense will NOT take it to 14.5 VDC unless your system is demanding more than 280 amps.


You DO NOT have to use the remote sense system. Leaving that wire out and off the system will render it a standard alternator. I recommend using it though, because it makes the system smarter and it keeps the voltage correct by adjusting the voltage based on line load conditions.


I'll attach the brochure for it in my next post. This model cost me $785 shipped to the door. All I needed to do to get it into operation was pull the OEM pulley from the old alternator, put it on the new one, and (because it is a larger diameter alternator) you'll need a longer drive belt (2 inches longer) and a self-fabricated pivot arm bracket to connect the bottom bolt. The OEM arm will be too short. I recommend using a piece of copper tubing, hammer it flat and fold it over to make a dogleg in it to create a template. As soon as you have a bolt pattern that will fit and not make contact with the alternator fan, transpose that pattern into a piece of 1/8" flat plate steel, drill the holes to match and bolt it on.
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Old 07-22-2019, 01:26 PM   #7
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alternator

Thank you ret6osp
You have provided me with a lot of very good info and I really appreciate it. Going out and take the engine cover off and check the alternator I have and see how much work space there is for me use. I know its never enough!
Will also make sure what alternator I have. I have all the books and wiring schematic's for the coach but, doesn't tell me the brand of alternator and I have never had a problem so never thought to check.
Thanks to all and as someone famous once said.Keep them cards and letters coming in.
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Old 07-22-2019, 07:39 PM   #8
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alternator

A little up date. Went out in the sweltering heat and cleaned all of my ground connections that I could find. After 20 years there were a few that were really needed cleaning. It was about a 6 pack job and when all was finished I cranked it up and everything worked like it has for the last 20 years.
Voltmeter shows charging at almost 14 and when I turn the lights and Dash A/C on it never moves.
So I will leave well enough alone for right now.
Headed for Abilene TX in Oct so hope all will go well. After 20 years with this coach I really enjoy the simplicity of it.
Thanks again for all the input. Is this a great site or not!
Busyguy.
Ps I think I am going to go with the 40SI when I get back from my trip.
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Old 10-14-2019, 03:41 PM   #9
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40Si Alternator

Ladies and Gents,


Anyone interested in following the thread and upgrading their lame OEM alternator to a much better option like the Delco Remy 40Si needs to note that they come in several models.


1. They are either 12 or 24 volt
2. They are either Pad Mount, J180 Long Hinge or J180 Short Hinge.
3. They come in 240, 275, 300 and 320 amp versions.


For a copy of the brochure go here.


Installing a larger alternator means it can be, or more than likely will be both a larger diameter and a longer length. Make sure you measure your engine spaces to ensure the version you are considering will fit.


On my selection, I had to move the old pulley from the OEM 22Si over to the 40 Si and install a longer 74 inch serpentine belt (up from the 70.5" OEM belt). I had to fabricate a longer lower mounting arm, out of 1/8 inch plate steel and then grind it (the new arm) to have clearance from the larger alternator fixed-fan. The OEM wiring on my application was already sufficiently sized so that needed no change. I changed the inline covered fuse block from the OEM 150 amp setup to a marine grade ANL 350 amp block terminal with a visible ANL fuse. You can install whatever size ANL fuse meets your application on the 350 rated block. Making it a clear inspection block is much easier than the OEM setup.
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