alternator bad or isolator

Topic: alternator bad or isolator (Read 2006 times) previous topic - next topic

alternator bad or isolator

August 21, 2013, 11:35:22 pm

Hello, last night traveling my 1999 U295 started losing voltage. It got down to the lowest reading on the gauge and the motorhome started shutting down. And did before we made it to town. I tried the boost switch but did not help for whatever reason........ Had someone come out and they took the alternator to town and the shop said they changed the brushes and it was putting out voltage. While reinstalling the alternator he had jumper cables hooked up. The motorhome started and away we went. But I noticed the volts still going down. This time I was able to us the boost switch and made it to the next town. Anyone have any thoughts? If alternator is good is it the isolator? I am not sure what the isolator does.

John

Re: altinator bad or isolator

Reply #1 – August 22, 2013, 12:03:40 am

John,

If you ever get in that situation again, start the generator, turn on the boost switch. It should provide the necessary current to keep the coach running. Others on the Forum have driven many miles using the generator and no alternator output.

Re: alternator bad or isolator

Reply #2 – August 22, 2013, 06:21:02 am

if they did not rebuilt it right and connect the exciter wire the alternator will not put out any power. You need to start the coach and go to the isolator and the battery and see what is happening iwth a multimeter. It is simple to do but you need to write it down th first time so you can understand it. Your isolater should be just under the bed. You can run your generator first and figure out the house side, usually on the drivers side then start the engine and see the if the alternator is puting out power in the back of the alternator on the stud. If not then you check the battery and see the charge. It is probably something simple but you need to know where to start looking.

Re: alternator bad or isolator

Reply #3 – August 22, 2013, 08:20:05 am

Where are you John ? Let us know, someone may be nearby that can help you out.
Gary B
Atlanta

Re: alternator bad or isolator

Reply #4 – August 22, 2013, 09:24:03 am

John
Been there recently. I ran on my generator and boost switch for two 230 mile trips to Houston recently when FOT would not look at the correct issue and instead was hung up on battery connections. Long story for another time.
After my second trip to FOT for the same problem (about 560 miles) they finally looked at the exciter wire and that was the problem. Did not need an alternator just a new wire and breaker somewhere. I hope that your problem will be as simple.
Note: I was charged for both trips, but did get an apology.

Re: alternator bad or isolator

Reply #5 – August 22, 2013, 09:31:25 am

Go to your battery isolator (front edge of engine compartment-- under bed).

It is the rectangular box with aluminum fins.

With the engine off, use a digital voltmeter to measure voltage at the two outer lugs (one connects to each battery bank).

Start engine. Measure voltage at the outer lugs and also at the center lug. If you follow the wire from the center lug, it goes to the B+ terminal of the alternator. If the center lug is not reading 14+ VDC with the engine at 1000 RPM, you have a problem.

Problem could be that the sense wire is not properly connected or that the alternator is bad. The sense wire goes from the chassis battery lug of the isolator to the alternator.

Brett

Re: alternator bad or isolator

Reply #6 – August 22, 2013, 10:49:24 am

John ---- The statement that the voltage dropped to the bottom of the scale is confusing to me. If the alternator was bad, the voltage should drop to the battery voltage (about 12 volts) and slowly follow battery voltage as it discharges. If voltage drops below battery voltage then it sounds like a bad connection that is resulting in a lower voltage. The "started shutting down" thing is confusing also. Is your coach a gasoline or diesel? If the voltage was low enough on a diesel, the fuel solenoid would just drop out and shut you down. A loose connection could cause that to happen. From what you have stated I would be looking for a bad connection somewhere as well as checking the alternator and isolator. The battery is where I would go 1st just because it is the most probable and maybe the easiest. Good luck and keep us posted for the learning curve aspect. ---- Fritz

Re: alternator bad or isolator

Reply #7 – August 22, 2013, 01:20:44 pm

everyone thank you for all the input, I've just had surgery so I won't be able to check these things right now but as soon as we get home and I heal up I will check everything you've listed and get back to all y'all.so my question right now is, is it unwise to go about a thousand miles running on the boost switch?

Re: alternator bad or isolator

Reply #8 – August 22, 2013, 01:28:21 pm

As long as you are running the generator, it shouldn't be a problem. Barry and Cindy ran there coach for a few weeks till they could get home.

Re: alternator bad or isolator

Reply #9 – August 22, 2013, 02:02:08 pm

Ok thanks again for all the input. We are in Arkansas headed to Wyoming and need to make it there before checking these things. So it sounds like we should be able to do that.

John I. Smith

Re: alternator bad or isolator

Reply #10 – August 22, 2013, 02:10:09 pm

John,

It would really be better if you can diagnose the problem-- if an isolator, a temporary fix for the trip is as easy as marking and combining the wire from the alternator B+, the large wire from chassis battery and large wire from house battery and the small sense wire that goes to the alternator (all conveniently located on the battery isolator) to ONE LUG. Now, for the trip it is wired just like your car-- no isolator. Obliviously don't dry camp long enough to deeply discharge all the batteries, but sure more reasonable than having to run the generator and boost switch cross country.

I am sure you can find someone who would be glad to help with 5 minutes of diagnostic time-- none of it requiring getting dirty.

Brett

Re: alternator bad or isolator

Reply #11 – August 22, 2013, 03:00:28 pm

Okay thanks Brett, I'll see what we can do.

John

Re: alternator bad or isolator

Reply #12 – August 22, 2013, 08:02:03 pm

I had a similar problem on our 99 U295. It turned out to be a bad circuit breaker in the 12 volt panel at the front steps. It's CB #35, 6 amp. I'm trying to attach a PDF showing the location of the CB.

Re: alternator bad or isolator

Reply #13 – August 23, 2013, 05:00:21 pm

Thanks Larry for the picture. We will have to check that, we have been running on the generator till we can stop and do some checks. Thanks again.

John I. Smith

Re: alternator bad or isolator

Reply #14 – August 23, 2013, 08:52:17 pm

John ---- Another area to consider is the ignition solenoid which feeds power to all instrumentation. I had a situation where various instruments would just go dead while driving down the road, sometimes all of them. The engine never shut down as the fuel shutoff valve is not fed from this solenoid. After much trouble shooting and voltage checks, I discovered that it was this solenoid which packs a large load of circuits that are ignition switch activated. If it turns out to be that, go to foretravel to get a new one as it is specially designed to handle the load. Have you had any problems running on the generator?? ---- Fritz

Re: alternator bad or isolator

Reply #15 – August 23, 2013, 11:50:17 pm

When we first tried to run on the generator it did not work for what ever reason. Then the second time we tried to run on the generator it worked fine. Volts up around 12 and this is where it usually runs 12 to 14. We have ran all day like this. We stopped for something to eat and now the volts are back down to 10 to 11.65 so it looks like the boost switch generator is not working at this time. Its like an intermitting problem. I think we'll stop for the night, get some rest and try and check some things in the morning.

John

Re: alternator bad or isolator

Reply #16 – August 24, 2013, 11:14:35 am

John ---- The problem is sounding more like the ignition solenoid. When you shut down the coach and restarted it again, that cycles the solenoid and they just dont pull in the same every time when they get worn. Do you have an electrical schematic on board? If so, locate that solenoid. It'll probable be some where around the ignition switch. Get a couple of voltmeters and connect one on the output (load) side of it and one on the input(line) side. When the voltage on the coach voltmeter drops out of the normal range, check and see what these two voltmeters are doing. If the solenoid is bad, The inlet side will be normal and the load side will read what the coach voltmeter reads. If you desire, you can call me on my cell phone 509 - 994 - 7117 and we can talk over a bunch of things relative to the problem that I had. Your coach is much newer than ours, but electrically they may be very similar. PS ---- If you only have one voltmeter, connect it to the input of the solenoid and check it against the coach meter when the problem arises. Have a great day ---- Fritz

Re: alternator bad or isolator

Reply #17 – August 24, 2013, 11:54:13 am

A failing ignition solenoid is VERY easy to diagnose. When it fails, everything that only works with the ignition on goes off.

So, transmission shift pad will show "snake eyes", dash HVAC fan will quit, etc.

Re: alternator bad or isolator

Reply #18 – August 24, 2013, 12:43:23 pm

We did some checks this morning before getting on the road. At the isolator this is what we found.
Engine off - chassis 12.4vdc. Alternator 0vdc. House 12.4vdc

Engine on - chassis 13vdc. Alternator 14vdc. House 13.1vdc
Boost on

Engine on - chassis 13vdc. Alternator 14vdc. House 13.1vdc
Boost off

We have been running down the road with 14 volts.

We turned the lights on and the volts dropped to 12. I thought about running like this to see if the volts continue to go down . But we are stopped now getting something to eat. Sorry I tried sending this early this morning but it looks like I lost it.

Jon

Re: alternator bad or isolator

Reply #19 – August 24, 2013, 12:52:09 pm

John,

Sounds like a failing alternator is the connections on alternator and isolator are clean and tight.

Have it pulled off (not real difficult with your side radiator coach) and tested by an alternator shop.

What brand is the alternator-- we may be able to help find an authorized repair shop where you are?

Brett

Re: alternator bad or isolator

Reply #20 – August 24, 2013, 01:30:08 pm

It doesn't sound like the alternator is picking up the load when the lights were turned on.
Is the belt ok?

Re: alternator bad or isolator

Reply #21 – August 24, 2013, 01:38:59 pm

Quote from: Dave M – August 24, 2013, 12:57:21 pm

Wolf,
What clue indicates the alternato is failing when is is showing 14 volts ?

If turning on the lights drops voltage from 14 to 12, the alternator is the second suspect-- behind checking that connections between alternator and isolator are good, clean and tight.

Brett

Re: alternator bad or isolator

Reply #22 – August 24, 2013, 02:55:31 pm

This morning before getting on the road we measured voltage at the isolator. Then once we got underway the voltage readings where coming from the meters inside. Now as we are traveling on the road the voltage is fluctuating from 13 to 14 volts......... We had the alternator off the day this started and they told me the brushes were changed and the alternator was new. They also said altrernator tested good on the bench........ so the connections on the alt. Should be good, I,ll need to check at the isolator. I have just had surgery so I am limited to what I can do right.

John

Re: alternator bad or isolator

Reply #23 – August 24, 2013, 03:05:40 pm

Sound like a voltage regulator. What brand of alternator is it?
Bill

Re: alternator bad or isolator

Reply #24 – August 24, 2013, 03:27:50 pm

Thanks for the replies, Lord willing, we'll be in Laramie WY in about 30 min. Can do more checks then.
John

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