Stranded!

[YC1]

Originally Posted by jsmmonaco

they say there are no stupid questions, hope that is true.............once you guys get "stranded" on the road home again, would someone please explain how you all learned so much about the electrical systems of your MH..............it truly amazes me how much knowledge you guys have with "wire this", "charge that".....................I understand the basics, such as unplug alternator and start genset to run on battery power only, but the rest is so confusing, to me at least.............are you all retired electrical engineers?................

Fcc 1st class license
Senior Service Center Manager Motorola 17 yrs
Owner of Telecommunications company (Motorola) 18 yrs
Senior Certified Electronic Tech
Specialty is commercial two way radio. 911 centers, command vans, anything that moves and needs communications.
Pilot, built my own airplane. Including all electronics.

Rver. Owned several rvs over 40 yrs.

It has taken me several years to become competent in the complexities of these large RV's.

This forum has taught me a tremendous amount. There is an amazing amount of expertise here. TEAM. Together Everyone Achieves Magic.

[CaymanPilot]

Thanks to all contributors! Yesterday afternoon I disabled the alternator by disconnecting the large positive cable from the output side and wrapped it good with electrical tape, then wire tied it to a bunch of wiring so it wouldn't flop around. Then disconnected the sense wire, wrapped it and wire tied it also. Bypassed the Trombetta by stacking both battery cables on one post. Reinstalled driveshaft (ugh!) and torqued bolts to 37 ft lbs per torque spec table found on Internet. Cranked 'er up and down the road we went with the generator and inverter supplying power as needed. Drove the 70 miles to a campground where we'll stay a few days before heading home about 330 miles away. Sincere appreciation for all contributions on this thread that helped us salvage the remaining days on our short spring vacation. Irv2 rocks!

PS. Myron, I am a ham, a private pilot and major motorhome tinkerer. Appears we have a few things in common.

[mel s]

Originally Posted by jsmmonaco

they say there are no stupid questions, hope that is true.............once you guys get "stranded" on the road home again, would someone please explain how you all learned so much about the electrical systems of your MH..............it truly amazes me how much knowledge you guys have with "wire this", "charge that".....................I understand the basics, such as unplug alternator and start genset to run on battery power only, but the rest is so confusing, to me at least.............are you all retired electrical engineers?................

jsmmonaco
I learned much about the various systems in my coach out of necessity.

At one time or another nearly everything in my now 20 year old coach has broken, worn out or failed to work properly in the 15 years, (127,000 miles), I've owned my coach.

If I had not learned how to fix those breakdowns/problems when and where they happened many of those breakdowns would have left me stranded...(or at the mercy of overpriced, sometimes unscrupulous, repair shops).

Mel
'96 Safari, 148k miles, (with everything currently working).

[jacwjames]

Tow truck driver not wanting to put the drive shaft back in is just an excuse. He didn't want to have to crawl under the coach and do the work.

Same thing happen to me but at least the rig was parked at a Cummins shop, the driver knew that Cummins would have to put it back in. It's usually harder to put in then take out. BTW, when Cummins did put it back in they didn't make sure it was in phase. Once I got home I had to take out and put back in phase. Not a big deal.

[mel s]

Originally Posted by jacwjames

Tow truck driver not wanting to put the drive shaft back in is just an excuse. He didn't want to have to crawl under the coach and do the work.

jacwjames
I'm not a coach towing expert but don't think that is true.

My coach has been towed to a repair shop twice. (once in MN in '02 and once in WI in 2015)....both times the tow truck driver disconnected/removed the drive shaft but the shop where the coach was towed was responsible for putting it back.

Mel
'96 Safari

[CaymanPilot]

Originally Posted by jacwjames

Tow truck driver not wanting to put the drive shaft back in is just an excuse. He didn't want to have to crawl under the coach and do the work.

Same thing happen to me but at least the rig was parked at a Cummins shop, the driver knew that Cummins would have to put it back in. It's usually harder to put in then take out. BTW, when Cummins did put it back in they didn't make sure it was in phase. Once I got home I had to take out and put back in phase. Not a big deal.

Jim, how did you determine whether or not the driveshaft was in phase? I didn't know that had to be done so will have to check mine to see if it is in phase or not.

[twinboat]

If he didn't pull the slip joint apart, and it was in phase, it still is.

Look at the U joint cross's. They should be in exactly the same alingment. Cap for cap, end for end.

Google "driveshaft phase" for pictures.

[mel s]

Originally Posted by CaymanPilot

Jim, how did you determine whether or not the driveshaft was in phase? I didn't know that had to be done so will have to check mine to see if it is in phase or not.

CaymanPilot

[CaymanPilot]

Thank you Twinboat and Mel. Wow, I am learning lots of good stuff due to this adventure! I plan on crawling under the motorhome today to check the torque on the u-joint bolts so will also check phase. I don't believe the tow truck driver separated the slip joint but you never know.

[Hit_the_Rhod]

Originally Posted by mel s

CaymanPilot

Okay, it looks from the diagram like the driveshaft pictured can be assembled 4 different ways, two of which would be "in phase" by your description, and two "out of phase". Question, of the two "in phase" possibilities, are both correct, or is one 180 degrees out?

[twinboat]

Many times in a splined shaft, there will be a suttle difference with "in phase" and 180ish degrees out.

If it looks close, try to turn it 180 degrees and see if it's perfect.

I have also seen master splined slip joints that can't be put together wrong. 1 slot is missing and one tooth is wide.

[CaymanPilot]

Just checked u-joint bolt torque and phase. Both good. I didn't feel any vibration while driving the 70 miles after installing the driveshaft so I think it's safe to assume it is correctly in phase and not 90 or 180 degrees out.

[CaymanPilot]

Arrived safely home yesterday with alternator disconnected, Trombetta bypassed and generator running the entire 400 mile trip. Thanks again to all contributors who supplied information for the workaround.
Now I am faced with correcting the problem. At this point I am not sure whether it is the alternator itself or an intermittent problem with the "sense" wire that connects to the alternator. It was suggested in this thread that the sense wire is connected to the alternator on one end and to the positive chassis battery terminal at the other end. I looked over my wiring schematics and can say that it "appears" to be true although I couldn't find a direct connection as the wire passes through several multi connector chassis connectors and it was impossible to trace it all the way through. So, I decided to test for battery voltage at the alternator end of the disconnected sense wire. Test results: With battery switches in the on position and the ignition switch in the off position there was zero volts between the sense wire and ground. With the battery switches in the on position and the ignition switch in the on position there was zero volts between the sense wire and ground. This tells me that either the sense wire is not connected to the positive terminal of the chassis battery or there is an open somewhere in that circuit. If the sense wire should be connected to the positive terminal of the chassis battery, then the next step should be to run a fused (external to the wiring loom) wire of the same gauge from the positive terminal of the chassis battery to the sense wire post on the alternator, start the engine and see if the over-voltage condition disappears.
Would appreciate any comments on my logic, suggestions for improving the procedure or confirmation on whether or not I am on the right track.
Would be very cool to have one thread that shows the issue, how to limp home and how to fix the problem when you get home for any future unfortunate motorhomers that experience the same issue I am experiencing.

[twinboat]

That is one way to test it.


You could also jump battery voltage from the alternator output post to the sense wire, if your alt output wire is hot all the time.


It may undercharge slightly but that will tell if its the problem.


Most " always hot " wires are fused near the battery, for safety against shorts. It could be a fuseable link built into the wire.


If the end of the sense wire is not on the battery, follow the cable towards the starter and components in between. The closer it is to the batteries the more accurate it is.