Alternator Problems

Topic: Alternator Problems (Read 2067 times) previous topic - next topic

Re: Alternator Problems

Reply #25 – February 28, 2018, 11:18:49 am

Sorry, I was unable to do voltage checks yesterday due to weather, but will try today if rain lets up. Called MOT yesterday and they suggested that the symptoms I had would be consistent with a failed automatic resetting circuit breaker on the line that feeds the Cummins engine computer. They also said that the engine computer only looks at the battery voltage periodically and that explains the delay between the alternator voltage resuming 13.9 volt output and the extinguishing of the check engine light. I am replacing the circuit breaker (15 amps, $4.75). Will check in later with voltage readings.

Re: Alternator Problems

Reply #26 – February 28, 2018, 11:55:07 am

Quote from: jspunches – February 28, 2018, 11:18:49 am

Sorry, I was unable to do voltage checks yesterday due to weather, but will try today if rain lets up. Called MOT yesterday and they suggested that the symptoms I had would be consistent with a failed automatic resetting circuit breaker on the line that feeds the Cummins engine computer. They also said that the engine computer only looks at the battery voltage periodically and that explains the delay between the alternator voltage resuming 13.9 volt output and the extinguishing of the check engine light. I am replacing the circuit breaker (15 amps, $4.75). Will check in later with voltage readings.

Please keep us informed, have a hard time seeing how a circuit breaker feeding the engine computer can cause low voltages at the battery isolator, so let us know if this cures it.

Re: Alternator Problems

Reply #27 – February 28, 2018, 11:31:12 pm

Still did not get to doing voltage measurements due to weather. As I said I contacted MOT about our problem and they thought that the automatically resetting circuit breaker in the line between the isolator and the engine computer maybe be defective in that it opens prematurely and does not close very quickly. They thought that this would cause the symptoms that I described. I will replace that cb, 15 amps, $4.50 and see what happens. I will do the voltage measurements when the weather improves. Thanks to all who made suggestions.

Re: Alternator Problems

Reply #28 – February 28, 2018, 11:37:06 pm

Quote from: jspunches – February 28, 2018, 11:31:12 pm

Still did not get to doing voltage measurements due to weather. As I said I contacted MOT about our problem and they thought that the automatically resetting circuit breaker in the line between the isolator and the engine computer maybe be defective in that it opens prematurely and does not close very quickly. They thought that this would cause the symptoms that I described. I will replace that cb, 15 amps, $4.50 and see what happens. I will do the voltage measurements when the weather improves. Thanks to all who made suggestions.

Thanks JS, you posting problems and cures, helps everyone learn about their coaches.

Re: Alternator Problems

Reply #29 – March 02, 2018, 01:16:51 pm

I was finally able to do voltage readings and actually we wrote them down instead of relying on my memory..

Conditions: Boost switch off, ignition off, shore power disconnected, engine off.
VMSPC = 0.00 (Does not read with ignition off)
Power Line Monitor/Pro Sine = 13.0
Alternator Ignition post = 13.0
Alternator Hot Post = 13.0
Alternator post on Isolator = 12.9
Batt #1 on Isolator = 12.9
Batt #2 on Isolator = 12.4
Dash Reading = 13.3

Conditions: Boost Switch off, Ignition on, Shoreline power off, engine off
VMSPC = 12.1
Power Line Monitor/Pro Sine = 12.25
Alternator Ignition post = 12.0
Alternator Hot Post = 12.1
Alternator post on Isolator = 12.3
Batt #1 on Isolator = 12.3
Batt #2 on Isolator = 12.2
Dash Reading = 12.4

Conditions: Boost Switch off, Ignition on, Engine on, Shoreline power off (engine started fine without boost switch on)
VMSPC = 14.1
Power Line Monitor/Pro Sine = 13.75
Alternator Ignition post = 0.00
Alternator Hot Post = 15.0
Alternator post on Isolator = 15.0
Batt #1 on Isolator = 14.1
Batt #2 on Isolator = 14.2
Dash Reading = 14.3

Seems to me that everything is reading okay. I think what MOT was talking about regarding the self-resetting 15 Amp circuit breaker (schematic B-2126, wire E59, connects engine battery isolator post to Batt Volt Sensor ALT) was the original set of symptoms, ie check engine light, low battery reading on VMSPC, after shutting off generator, voltage recovery on VMSPC, and after 15 minutes the check engine light turning off. MOT was not talking about any voltage readings taken while we were parked. I will receive the cb today and will install tomorrow and I will report. We have been running the engine occasionally while parked and have not had the check engine light, however we have not been on the road. Thanks again to all those who are helping, I am learning more about the charging system than I ever wanted to know.

Re: Alternator Problems

Reply #30 – March 02, 2018, 01:53:17 pm

Quote from: jspunches – March 02, 2018, 01:16:51 pm

I was finally able to do voltage readings and actually we wrote them down instead of relying on my memory..

Conditions: Boost switch off, ignition off, shore power disconnected, engine off.
VMSPC = 0.00 (Does not read with ignition off)
Power Line Monitor/Pro Sine = 13.0
Alternator Ignition post = 13.0
Alternator Hot Post = 13.0
Alternator post on Isolator = 12.9
Batt #1 on Isolator = 12.9
Batt #2 on Isolator = 12.4
Dash Reading = 13.3

Conditions: Boost Switch off, Ignition on, Shoreline power off, engine off
VMSPC = 12.1
Power Line Monitor/Pro Sine = 12.25
Alternator Ignition post = 12.0
Alternator Hot Post = 12.1
Alternator post on Isolator = 12.3
Batt #1 on Isolator = 12.3
Batt #2 on Isolator = 12.2
Dash Reading = 12.4

Conditions: Boost Switch off, Ignition on, Engine on, Shoreline power off (engine started fine without boost switch on)
VMSPC = 14.1
Power Line Monitor/Pro Sine = 13.75
Alternator Ignition post = 0.00
Alternator Hot Post = 15.0
Alternator post on Isolator = 15.0
Batt #1 on Isolator = 14.1
Batt #2 on Isolator = 14.2
Dash Reading = 14.3

Seems to me that everything is reading okay. I think what MOT was talking about regarding the self-resetting 15 Amp circuit breaker (schematic B-2126, wire E59, connects engine battery isolator post to Batt Volt Sensor ALT) was the original set of symptoms, ie check engine light, low battery reading on VMSPC, after shutting off generator, voltage recovery on VMSPC, and after 15 minutes the check engine light turning off. MOT was not talking about any voltage readings taken while we were parked. I will receive the cb today and will install tomorrow and I will report. We have been running the engine occasionally while parked and have not had the check engine light, however we have not been on the road. Thanks again to all those who are helping, I am learning more about the charging system than I ever wanted to know.

That makes sense and could be your problem. That learning too much part, may help you down the road someday.

Re: Alternator Problems

Reply #31 – March 02, 2018, 03:45:36 pm

Quote from: jspunches – March 02, 2018, 01:16:51 pm

Conditions: Boost switch off, ignition off, shore power disconnected, engine off.
VMSPC = 0.00 (Does not read with ignition off)
Power Line Monitor/Pro Sine = 13.0
Alternator Ignition post = 13.0
Alternator Hot Post = 13.0
Alternator post on Isolator = 12.9
Batt #1 on Isolator = 12.9
Batt #2 on Isolator = 12.4
Dash Reading = 13.3

Conditions: Boost Switch off, Ignition on, Shoreline power off, engine off
VMSPC = 12.1
Power Line Monitor/Pro Sine = 12.25
Alternator Ignition post = 12.0
Alternator Hot Post = 12.1
Alternator post on Isolator = 12.3
Batt #1 on Isolator = 12.3
Batt #2 on Isolator = 12.2
Dash Reading = 12.4

Conditions: Boost Switch off, Ignition on, Engine on, Shoreline power off (engine started fine without boost switch on)
VMSPC = 14.1
Power Line Monitor/Pro Sine = 13.75
Alternator Ignition post = 0.00
Alternator Hot Post = 15.0
Alternator post on Isolator = 15.0
Batt #1 on Isolator = 14.1
Batt #2 on Isolator = 14.2
Dash Reading = 14.3

Something is not right with the IGN (hot with ignition) excite connection on the alternator.

Re: Alternator Problems

Reply #32 – March 02, 2018, 05:30:34 pm

Quote from: Chuck & Jeannie – March 02, 2018, 03:45:36 pm

Something is not right with the IGN (hot with ignition) excite connection on the alternator.

Chuck, according to my wiring diagram , the possible faulty breaker js is talking about, is between voltage sensor on the alternator, and the start battery side of the isolator. if breaker open that might cause it to show 0 volts.

Re: Alternator Problems

Reply #33 – March 02, 2018, 06:13:12 pm

I had the same problem. The alternator was rebuilt put back on and no voltage. Finally found the resettable breaker mounted on the wall at the end of the bed (engine side) was bad. $3.69 later all was good. It was by luck that I found the problem...I was playing around with the tester and when I tested the back side of the breaker I heard it click. I checked and sure enough, over 14 volts. Replaced and no problems since.

Re: Alternator Problems

Reply #34 – March 02, 2018, 06:42:53 pm

Can't seem to keep two different things straight here. The alternator has a SENSE wire, and it has a IGNITION (excite) wire.

The SENSE wire connection on the alternator should read voltage from the engine start battery bank. I believe this is what JS is referring to as the "Batt Volt Sensor ALT". This wire should be hot all the time. If the faulty breaker under discussion is in this circuit, whether it is open or closed should have no affect on the IGNITION (excite) wire.

The IGNITION (IGN) excite wire is only supposed to be hot when the ignition switch is turned to ON position. When the ignition switch is OFF, this wire should see ZERO voltage.

JS is reporting the exact opposite condition in his readings. Hence my opinion that "Something is not right..."

Re: Alternator Problems

Reply #35 – March 02, 2018, 07:11:40 pm

Quote from: Chuck & Jeannie – March 02, 2018, 06:42:53 pm

Can't seem to keep two different things straight here. The alternator has a SENSE wire, and it has a IGNITION (excite) wire.

The SENSE wire connection on the alternator should read voltage from the engine start battery bank. I believe this is what Jim is referring to as the "Batt Volt Sensor ALT". This wire should be hot all the time. If the faulty breaker under discussion is in this circuit, whether it is open or closed should have no affect on the IGNITION (excite) wire.

The IGNITION (IGN) excite wire is only supposed to be hot when the ignition switch is turned to ON position. When the ignition switch is OFF, this wire should see ZERO voltage.

JS is reporting the exact opposite condition in his readings. Hence my opinion that "Something is not right..."

Chuck, on his coach hard to see back of alternator, possible he put voltmeter probe on sense terminal which will read 0 if breaker is open. Agree ignition terminal should be hot when key is on. We should wait till he replaces breaker and retests. But I agree , present readings, if correct, are strange.

Re: Alternator Problems

Reply #36 – March 02, 2018, 07:37:16 pm

On this test:

"
Conditions: Boost switch off, ignition off, shore power disconnected, engine off.
VMSPC = 0.00 (Does not read with ignition off)
Power Line Monitor/Pro Sine = 13.0
Alternator Ignition post = 13.0
Alternator Hot Post = 13.0
Alternator post on Isolator = 12.9
Batt #1 on Isolator = 12.9
Batt #2 on Isolator = 12.4
Dash Reading = 13.3

On this test, with engine off, alternator post on isolator should read only a little leakage, like .15.

You are getting voltage back to the alternator (and center post on the isolator) when you should not.

My best guess is a bad isolator (or mis-wired), but replacing the cheaper breaker first then repeating the test could not hurt. This "could" be damaging your alternator over time by constantly having voltage to it when that should not occur.

Re: Alternator Problems

Reply #37 – March 03, 2018, 01:32:35 pm

Jim C is absolutely correct I was reading the wrong post as the IGN post.

So here are updated readings.

Conditions: Boost switch off, ignition off, shore power disconnected, engine off.
Power Line Monitor/Pro Sine = 12.25
Alternator Ignition post = 0.00
Battery Sense Post = 13.5
Alternator Hot + Post = 13.4
Dash Reading = 12.6

Conditions: Boost Switch off, Ignition on, Shoreline power off, engine off
VMSPC = 12.1
Power Line Monitor/Pro Sine = 12.25
Alternator Ignition Post = 12.6
Battery Sense Post = 12.4
Alternator Hot + Post = 12.7
Dash Reading = 12.3

I tried to change the CB but found that FT has cleverly hidden the nuts to the screws holding the CB behind the metal plate holding everything. I would have to remove the plate to just change the CB. So I am not going to change the CB unless the problem reoccurs as it seems that the change will be a major undertaking. If the problem reoccurs I will then change the CB. We have run the engine at high idle for about 45 minutes now without a Check Engine light.

Re: Alternator Problems

Reply #38 – March 03, 2018, 01:39:38 pm

Mind reached a blank,what's a CB besides a coach buck?

Re: Alternator Problems

Reply #39 – March 03, 2018, 01:47:37 pm

Quote from: John44 – March 03, 2018, 01:39:38 pm

Mind reached a blank,what's a CB besides a coach buck?

circuit breaker. Do not know if JS has rear slide and east-west bed, but if you do, you only have a small compartment door, [as opposed to opening bed and seeing the whole engine] A real PITA to work on engine.

Re: Alternator Problems

Reply #40 – March 03, 2018, 02:38:34 pm

Conditions: Boost switch off, ignition off, shore power disconnected, engine off.
Power Line Monitor/Pro Sine = 12.25
Alternator Ignition post = 0.00
Battery Sense Post = 13.5
Alternator Hot + Post = 13.4 That is an issue. On the 3 coaches I have owned, the alternator and the alt post on the battery isolator should read near zero when engine is off and alternator not spinning.
Dash Reading = 12.6

Re: Alternator Problems

Reply #41 – March 03, 2018, 03:08:55 pm

I know I am slow but let me see if I understand. Boost Switch Off, Engine Off, Shorepower Off, I should read basically zero volts at the Alternator post on the isolator. Correct? Boost switch on or off should not make a difference because that ties the batteries together but does nothing to the alternator post on the isolator. It sounds like I need to change the isolator. Correct?

Re: Alternator Problems

Reply #42 – March 03, 2018, 03:48:59 pm

Quote from: jspunches – March 03, 2018, 03:08:55 pm

I know I am slow but let me see if I understand. Boost Switch Off, Engine Off, Shorepower Off, I should read basically zero volts at the Alternator post on the isolator. Correct? Boost switch on or off should not make a difference because that ties the batteries together but does nothing to the alternator post on the isolator. It sounds like I need to change the isolator. Correct?

As Dan says, current should only flow from center post of isolator to each outer terminal, house and start batteries.
Should not flow from batteries to alt. When alt. not turning should be 0 volts at center post. Does seem like one or more diodes are bad.

Re: Alternator Problems

Reply #43 – March 03, 2018, 03:53:18 pm

" I should read basically zero volts at the Alternator post on the isolator. " (with engine not running and alternator not spinning)

Correct. If the engine is not running, the center alternator post on the isolator should be basically zero. It's my opinion that the diodes have failed in the isolator. It could be "possible" than some form of mis-wiring from alternator to coach could create the same symptom.

Re: Alternator Problems

Reply #44 – March 03, 2018, 04:33:52 pm

Quote from: AC7880 – March 02, 2018, 07:37:16 pm

On this test:

"
Conditions: Boost switch off, ignition off, shore power disconnected, engine off.
VMSPC = 0.00 (Does not read with ignition off)
Power Line Monitor/Pro Sine = 13.0
Alternator Ignition post = 13.0
Alternator Hot Post = 13.0
Alternator post on Isolator = 12.9
Batt #1 on Isolator = 12.9
Batt #2 on Isolator = 12.4
Dash Reading = 13.3

On this test, with engine off, alternator post on isolator should read only a little leakage, like .15.

You are getting voltage back to the alternator (and center post on the isolator) when you should not.

My best guess is a bad isolator (or mis-wired), but replacing the cheaper breaker first then repeating the test could not hurt. This "could" be damaging your alternator over time by constantly having voltage to it when that should not occur.

Dan, why do think alternator will be damaged? On most vehicles that do not have isolators, hot lead from alternator is directly attached to battery and is hot all the time. Maybe Duvac type alternators have different internal wiring that may cause problems, but on all my coaches I have removed isolator and wired alternator output direct to start batteries and use a ACR to connect start to house batteries and have not seen a problem yet. JS probably needs to replace isolator because both banks may be combined and if some unseen load, discharge both banks.

Re: Alternator Problems

Reply #45 – March 03, 2018, 06:04:30 pm

Quote from: jcus – March 03, 2018, 04:33:52 pm

Dan, why do think alternator will be damaged?

He said in post one he has replaced the alternator 4 times over 125,000 miles. That seemed a excessive failure rate.

I'm simply unsure of the effect of having 13 plus volts at the alternator constantly while plugged into shore power. If you have done so with no ill effects I may have been wrong on that point.

I am still sure that when parked his center post on the isolator should have no or very minor (leakage) voltage.

Re: Alternator Problems

Reply #46 – March 04, 2018, 02:26:18 pm

We changed the Isolator and somehow managed to change the 15amp circuit breaker today (what a struggle with all the corrosion on the bolt and nut). The voltage at the alternator post, boost off, shore power disconnected, ignition off, engine off is now about .8 volts fluctuating to zero. Ran tests and it seems to be working. Ran engine at high idle for 30 minutes no check engine light. We are parked here until the 12th of March so we won't be road testing it until then. Will report after parking on the 12th. Thanks to all that contributed to this post.

Re: Alternator Problems

Reply #47 – March 04, 2018, 02:44:34 pm

For our info,what isolator did you go with?

Re: Alternator Problems

Reply #48 – March 04, 2018, 04:10:28 pm

I just used a Cole/Hersee 48160 isolator that is the same as was in the MH. It seems to be working as advertised.

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