Alternator Problems

Topic: Alternator Problems (Read 2068 times) previous topic - next topic

Alternator Problems

February 25, 2018, 10:34:51 pm

We have a 2002 U320 and have owned it since 2004. We have driven the MH 125,000 miles in that time. We have replaced 4 alternators in that time. This morning we were driving from Yuma to Tucson when the Check Engine light came on. I have VMSPC connected and the diagnostics read out said that the Alternator Potential was low and the voltage was reading 11.8 volts both in VMSPC and on the gauge. We started the generator and put the boost switch on and the voltage then jumped up and read 13.9 volts. After driving another hour we decided to try an experiment and turned the generator off. The voltage remained at 13.9 volts and after about 15 minutes the Check Light turned off and we proceeded on to Tucson with no adverse indications. When we arrived I checked the voltages at the battery isolator. The Alternator voltage read 14.1 volts, Battery 1 read 11.8 volts and Battery 2 read 12.0 volts. Now everything seems normal. Does anyone have any idea what happened and how we can prevent this from happening again? Is it normal to replace an alternator 4 times in 13 years? Do anyone think I should replace the alternator and/or the battery isolator as a preventative measure? Any ideas would be helpful. Alternator is a Leech Neville 2824LC and the battery isolator is a Cole/Hersee 48160.

Re: Alternator Problems

Reply #1 – February 26, 2018, 08:43:25 am

If your both battery bank voltages are as you say(read at the batteries) after driving, then they are less than 50% charged and likely the alternator must be repaired. The most common reason for killing alternators here on the forum is the practice of boondocking, living off the house batteries, then starting the coach and making the alternator re-charge them at max output. Using the generator to re-charge the house batteries before running the coach is much gentler on the alternator.

Re: Alternator Problems

Reply #2 – February 26, 2018, 09:06:29 am

Certainly could be the alternator, BUT you really need to do some troubleshooting before throwing parts at it.

A loose or corroded connection or bad battery isolator can give exactly the same symptoms.

Re: Alternator Problems

Reply #3 – February 26, 2018, 09:17:04 am

My opinion: 4 alternators in 13 years is a "higher than average" replacement rate.

My suggestions:

1. The alternator and the isolator presently fitted on your coach are both appropriate models for this application. IF they are wired correctly, and IF they are functioning correctly, they should do the job. See links to these models below.

2. Before you start replacing parts, a bit of time spent trouble shooting might save you some money.

3. Make sure all your battery post connectors are clean and tight.

4. The "IGN" terminal and the "DUVAC" terminal on this alternator are clearly marked. Be sure the "IGN" terminal is seeing a good 12V signal when the ignition key is "ON". Be sure the "DUVAC" terminal is wired to either the "START" battery post on the isolator or directly to the "POS" post on one of your start batteries. The "DUVAC" terminal on the alternator should be HOT (12V) all the time.

5. AFTER you have done steps 3 and 4 above, THEN check the function of the isolator. With the engine off, check the voltage on the center post, and on each of the outside posts. Then do the same thing with the engine running. Let us know the results, and we'll go from there.

Prestolite - Leece Neville

http://www.littelfuse.com/products/battery-management/battery-isolators/diode-battery-isolators/48160.aspx

Re: Alternator Problems

Reply #4 – February 26, 2018, 09:30:43 am

My 2 cents worth,had my Leece Nevel rebuilt by a shop that knew what they were doing,it only lasted 20K miles.Researched
and got a new Delco Remy for less money than another rebuild,also upgraded isolator at this time.What I like the most about the new setup is it charges right up there at 13.8 at idle,the old one did not.The old one was 130 amps,I got a 160 amp Delco
which suits my needs,you can get ones with more amps as some of the members have done.

Re: Alternator Problems

Reply #5 – February 26, 2018, 09:56:03 am

Quote from: John44 – February 26, 2018, 09:30:43 am

My 2 cents worth,had my Leece Nevel rebuilt by a shop that knew what they were doing,it only lasted 20K miles.Researched
and got a new Delco Remy for less money than another rebuild,also upgraded isolator at this time.What I like the most about the new setup is it charges right up there at 13.8 at idle,the old one did not.The old one was 130 amps,I got a 160 amp Delco
which suits my needs,you can get ones with more amps as some of the members have done.

If the shop knew what they were doing, it would not have lasted 20K. Too tight belts are responsible for most of the bearing failures unless the shop put in cheap bearings. There are ten different grades of bearings. Our LN has lasted over 100K and is working fine with excellent idle voltage. Our fire department was all Leece Neville and never had failures. They have an excellent reputation. Our U300 is OEM with 160 watts as most should be.

Pierce

Re: Alternator Problems

Reply #6 – February 26, 2018, 10:46:28 am

It's a brand new belt tensioner,and yes it's the correct one,all I can say is they probably used cheaper bearings.I understand
what your saying but unless a rebuild replaces every moving part it's only as good as the weakest part and if they replace
every part you are cheaper and better off with a new alternator.Some of the 270's come with 130 amp alternators,whether it
should be a 160 or not that's what it came with.
I don't doubt there are many grades of bearings,will do an expierement,I have my old generator bearing,will take it to a bearing
supply house(many here in the oilfield) and will see how many different ones they have,my point is it's hard to find quality when
everyone is pushing cheap chinese junk.

Re: Alternator Problems

Reply #7 – February 26, 2018, 11:28:27 am

John,

A problem with the isolator, internal regulator diodes, bad cell in the battery could all cause an early failure. One bad diode can can cause poor alternator output. Also, most rebuild shops are not familiar with the Duvac system and the wiring differences seen in our coaches. Some good links online on wiring, theory, troubleshooting, etc. This is another case for having the twin voltmeters on the dash, whether dedicated digital meters or plugin digital lighter receptacle voltmeters. The Leece Neville alternators have a regulator mounted on the top and can have the voltage easily adjusted with just a digital voltmeter and a screwdriver. Again, good photos on how to do it online.

Voltage spikes from either terminal corrosion, loose connections or an actual wire failure can cause the alternator to fail. Check heat buildup discoloration on the alternator and isolator connections.

Another possibility is that even though some coaches have an automatic tensioner, poor alternator to pulley alignment can cause tensioner "jump" and may shorten alternator life.

Pierce

Re: Alternator Problems

Reply #8 – February 26, 2018, 11:58:06 am

As far as starting a engine with low batteries after dry camping, I've always started up and let the alternator do it's job while we headed down the road. In the fire service, the alternators are always maxed out with all the radios, light bars and inverters hour after hour with no bad effect. One of the smaller PU sized vehicles has a telescoping high intensity area lighting array. You can hear the vehicle engine bog down when it's switched on but again, no failures even after hours of operation.

Pierce

Re: Alternator Problems

Reply #9 – February 26, 2018, 12:01:32 pm

Dan at Lewco in Costa Mesa, ca rebuilt my oem LN last year and it needed bearings and one diode out of 6. Lasted 125k miles. $300 range.

He commented that these were good quality with large heat sinks. The 160 matches 1/5thC of the battery bank in charge capacity and puts out more amps than the batteries will accept so no need for more output IMO.

Re: Alternator Problems

Reply #10 – February 26, 2018, 06:50:16 pm

We have almost never boondocked, dry camped, ran down the batteries below 50%, or otherwise damage the batteries. The batteries are new two years ago after another repair shop ruined them. Consulted with several repair shops in Tucson today and got some advice. As a result I did some more tests today (the results are as well as I can remember them but there were no readings out of whack). Both chassis and coach batteries show 12.8 - 13.00 volts when checked directly with a voltmeter. Checked the IGN terminal on the alternator with the ignition on but engine not running. It showed 12.8 volts. Checked battery isolator without engine running and got similar voltages. Started the engine and checked voltage at the alternator and got 14.3 volts on the red wire. Checked voltage at the battery isolator (three terminal isolator) and got 14.1 volts on the Alternator post and 14.0 to 14.1 on the two battery posts. Cleaned all terminals as much as I could. Ran the engine for about an hour and did not get any diagnostic codes or check engine light. I cannot detect any shorts, frayed wired, bad batteries, etc. Other than full failure of the alternator or the battery isolator I do not have any idea about single diode failures in either one. This whole thing completely baffles me and some of the techs we talked to today. We located a Delco 200 amp direct replacement alternator and had that put on hold. Also found a replacement battery isolator. I guess my plan at this point is to take the coach to the Frieghtliner dealer here and have them do some tests. Barring any big problems discovered, we will probably have then put in the new alternator and battery isolator and keep the old ones, get them checked, fix the alternator as required and keep them as spares. We cannot afford to go down the road and have the alternator die in the middle of nowhere.

Re: Alternator Problems

Reply #11 – February 26, 2018, 08:29:14 pm

Why not just replace the top mounted regulator?

Would be a whole lot cheaper and probably is all that is wrong with it. I would try that before replacing the whole alternator.

Re: Alternator Problems

Reply #12 – February 26, 2018, 09:01:25 pm

Quote from: jspunches – February 26, 2018, 06:50:16 pm

...................Started the engine and checked voltage at the alternator and got 14.3 volts on the red wire. Checked voltage at the battery isolator (three terminal isolator) and got 14.1 volts on the Alternator post and 14.0 to 14.1 on the two battery posts................................

js.........(EDITED) You have an isolator with 1 or 2 failed (shorted) diodes and/or you have the boost switch closed: This assumes that your 2002 coach has original alternator/isolator (or equal) components. If you have low voltage drop Schottky Diodes in an unusual replacement isolator, the following would not apply:

With the engine off and with the battery banks' B+ terminals at 12.8 Vdc and 13.0 Vdc, your batteries are charged and in good shape. With the engine running, producing 14.1 Vdc at the Isolator (Alternator) (center) terminal, both isolator battery posts should be showing between 13.2 and 13.5 Vdc (0.6 to 0.9 Vdc drop across conducting diodes). Because the isolator input is 14.1 Vdc and the two isolator outputs are instead showing 14.0 and 14.1 Vdc, that means the diodes are both shorted and the alternator is conducting electricity directly to the batteries through shorted diodes, OR, one diode is shorted and the isolator outputs are electrically connected through the boost switch. The alternator output at 14.1 sounds like the voltage regulator and the sense connection to the start battery B+ are operating correctly. In other words, a target B+ voltage of 14.1 Vdc at the batteries sounds reasonable and the sensing circuit and voltage regulator are working correctly.

If you turn the engine off, disconnect the isolator outputs (wires to battery terminals....be careful as they are at B+ potential because the other ends are connected to the batteries........ and check the isolator diodes resistances (red to battery terminal, black to alternator terminal), both backward and forward, and find infinite or extremely high Ohms in both directions, it will confirm that the diodes have failed open and that the isolator needs to be replaced. If you do the same test and both diodes show zero ohms front to back, they are both shorted and are passing alternator current directly to the battery banks. I have seen both situations occur. But first confirm that your boost switch is off. If it is off, it is still possible that the boost switch contacts are welded shut and are never opening.

You can still drive the coach by running the generator, ensuring that the charger is enabled and close the boost switch. That will charge your house battery bank and, through the boost switch, the start battery bank. Not the most efficient way to travel but possible for unlimited time and distance.
I attached a simplified circuit sketch for you, HTH,
Neal

Re: Alternator Problems

Reply #13 – February 26, 2018, 09:12:33 pm

"Checked voltage at the battery isolator (three terminal isolator) and got 14.1 volts on the Alternator post and 14.0 to 14.1 on the two battery posts"

That does not seem correct. The diodes in the battery isolator should show reduced voltage at the two outer posts as compared to the center post.

With engine running at high idle, on mine, center alt post is 15 volts, the two outer posts to batteries around 14.04 to 14.08.

Re: Alternator Problems

Reply #14 – February 26, 2018, 09:22:07 pm

guess I am missing something here, if 14.3 V at the alternator terminal of the isolator and 14.0 and 14.1 at the two battery post then they must be passing power to the batteries. If 14.0 and 14.1 at the isolator post that are connected to the batteries then why aren't the batteries charging?
Its late here and its been a long day so I guess I have just missed a post or memo somewhere.....

Re: Alternator Problems

Reply #15 – February 26, 2018, 09:34:23 pm

Agree - the reported voltage readings don't sound logical. We still don't know where (or if) the sense wire is connected. It sounds like the OP has already decided to replace the isolator and the alternator (again), so probably not worth suggesting any more trouble shooting ideas. Hopefully the new alternator will be wired correctly by Freightliner, and he will end up with a working electrical system.

Re: Alternator Problems

Reply #16 – February 26, 2018, 09:45:06 pm

If battery banks are reading 14.0 and 14.1 volts, and probably some load on both banks which should, even the best case, read 12.8 volts if not being charged, how is the alternator not charging, or the isolator not allowing charge to batteries?
I am confused, if I saw 14 and 14.1 on my batteries, I would say all is good.

Re: Alternator Problems

Reply #17 – February 26, 2018, 10:32:37 pm

Check the voltage at the isolator center post with the engine not running and alternator not spinning. If the diodes failed in the battery isolator, are the batteries back flowing to the alternator (which they should not)?

When you are testing the battery isolator voltages at all 3 posts, make sure your battery combiner at the dash is off.

I would recheck all 3 isolator posts voltages under the following conditions (all with dash battery combiner off)

1. no engine run, no gen run, not plugged into shore power, take surface charge off with headlights on for a couple of minutes and some DC load on the house batteries. Then turn all loads off and measure the 3 posts.

2. Plug into shore power with inverter/charger on, wait a couple of minutes, check all 3 posts.

3. Unplug from shore power, no gen run, start coach engine at high idle, check all 3 posts voltages.

Write down the voltages under all 3 tests above for all 3 posts.

I did this myself before our solar install - just to check all voltage situations and verify the isolator was working correctly.

Re: Alternator Problems

Reply #18 – February 26, 2018, 11:32:32 pm

Quote from: jcus – February 26, 2018, 09:45:06 pm

If battery banks are reading 14.0 and 14.1 volts, and probably some load on both banks which should, even the best case, read 12.8 volts if not being charged, how is the alternator not charging, or the isolator not allowing charge to batteries?
I am confused, if I saw 14 and 14.1 on my batteries, I would say all is good.

Jim,

If it is not some kind of exotic Schottky diode isolator, the Isolator diodes are not conducting in accordance with intended design if there is no voltage drop across them when the engine is running. The batteries show 12.8 at rest because they were charged by shore power and the inverter/charger.
I edited my original post to try a longer (hopefully less confusing) explanation.

HTH, Neal

Re: Alternator Problems

Reply #19 – February 26, 2018, 11:45:04 pm

Quote from: Neal Pillsbury – February 26, 2018, 11:32:32 pm

Jim,

If it is are not some kind of exotic Schottky diode isolator, the Isolator diodes are not conducting in accordance with intended design if there is no voltage drop across them when the engine is running. The batteries show 12.8 at rest because they were charged by shore power and the inverter/charger.
I edited my original post to try a longer (hopefully less confusing) explanation.

HTH, Neal

You could be right Neal, I get confused easy, so I have my alternator [set at 13.6 volts] wired to my start batteries with a ACR to connect to my house batteries, which passes the same 13.6 volts that the alternator supplies to the start batteries. [unless voltage changes]. Diode isolators were the only way to go in the 70's, but from what I understand all the newer coaches and bus conversions use relay based units. OP's case may indicate a bad isolator, but why are 14.0 and 14.1 volts not able to charge both battery banks?

Re: Alternator Problems

Reply #20 – February 27, 2018, 12:14:04 am

Quote from: jcus – February 26, 2018, 11:45:04 pm

.................OP's case may indicate a bad isolator, but why is 14.0 and 14.1 volts not able to charge both battery banks?...............

Jim,
I may be reading too much into what js.........originally posted. 14.0 to 14.1 Vdc on the isolator output terminals will definitely charge a battery that was at 12.8 Vdc, at rest, just a few moments ago.

BUT js.......stated that he started engine and found 14.1 volts at isolator (alternator) input and 14.1 and 14.0Vdc at the battery post outputs. If the engine had been running for an hour or two, the two battery banks had become fully charged, for some reason there were no dc loads in the coach (never will occur in a running coach) and the isolator diodes were back biased (no forward current at all) then that would be OK.

So, that isn't likely. If the engine is started and the voltages are taken a reasonable while later, then battery banks the size of ours do not change that rapidly on an alternator and something is wrong. The batteries should be charging, trying to reach whatever the alternator voltage regulator has been set for in target voltage at the start battery B+ terminal (which assumes the 0.6 to 0.9 Vdc drop across isolator diodes), the dc loads in an occupied, running coach should never be completely zero and any forward current through our isolators always show a drop in voltage across those diodes of 0.6 to 0.9 Vdc.
HTH,
Neal

Re: Alternator Problems

Reply #21 – February 27, 2018, 12:32:52 am

Neal, I am on 3rd wiskey tonight will respond tomorrow.

Re: Alternator Problems

Reply #22 – February 27, 2018, 09:52:00 am

I will redo all the voltage measurements today and write them down and report back. It is possible that some of the measurements were not reported properly. I used my memory which is always suspect. Thanks for all the information.

Re: Alternator Problems

Reply #23 – February 27, 2018, 10:00:25 am

Quote from: jspunches – February 26, 2018, 06:50:16 pm

We cannot afford to go down the road and have the alternator die in the middle of nowhere.

Your generator will always bail you out if necessary and if you have solar, it's also plenty to easily keep you going. I have the solar connected to the house bus but with my jumper, it will keep both up in case of an isolator failure.

Pierce

Re: Alternator Problems

Reply #24 – February 27, 2018, 10:10:44 am

Quote from: Neal Pillsbury – February 27, 2018, 12:14:04 am

Jim,
I may be reading too much into what js.........originally posted. 14.0 to 14.1 Vdc on the isolator output terminals will definitely charge a battery that was at 12.8 Vdc, at rest, just a few moments ago.

BUT js.......stated that he started engine and found 14.1 volts at isolator (alternator) input and 14.1 and 14.0Vdc at the battery post outputs. If the engine had been running for an hour or two, the two battery banks had become fully charged, for some reason there were no dc loads in the coach (never will occur in a running coach) and the isolator diodes were back biased (no forward current at all) then that would be OK.

So, that isn't likely. If the engine is started and the voltages are taken a reasonable while later, then battery banks the size of ours do not change that rapidly on an alternator and something is wrong. The batteries should be charging, trying to reach whatever the alternator voltage regulator has been set for in target voltage at the start battery B+ terminal (which assumes the 0.6 to 0.9 Vdc drop across isolator diodes), the dc loads in an occupied, running coach should never be completely zero and any forward current through our isolators always show a drop in voltage across those diodes of 0.6 to 0.9 Vdc.
HTH,
Neal

Neal, think I understand what you are saying, OP's original problem was 14.1 volts from alternator and 11.8 and 12 on batteries. This would indicate to me a giant load on either coach or start system and/or stuck boost switch or a faulty isolator. Second time he posted, same alternator output, but batteries now seem to be taking charge and are at 14 and 14.1, which you say indicates a bad isolator because of improper voltage drop across it. I think I would replace isolator [or replace with ACR]. Not sure what alternator output voltage is set at, but it appears to be constant in two different scenarios, so that would be my second choice.

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