Voltage drop driving in rain

[Karl Welhart]

I get a voltage drop, down to 11.5-12.2, while driving in heavy rain storms.  Called Monaco tech support and they told me it was a bad voltage regulator.  Replaced the voltage regulator and still have the same issue.  Just the other day someone suggested that I need a direct ground wire from chassis to alternator.  Does anyone have an idea on how to fix this problem?

Thanks,

Karl

[Tom and Pam Brown]

Karl,
Have you inspected your belt?  Sounds like it could be slipping when it is wet, indicating it needs to be replaced.

Just a thought.

[Edward Buker]

Karl,

In order to get a voltage drop there has to be a connection that with moisture gets more resistive. That would mean a connection that gets wet, is loose, or has minimal contact area due to corrosion or oxidation. That is what you are looking for given you have had the regulator changed and that did not solve your problem. The internal alternator connections are not very exposed to moisture so in my mind they are not likely candidates. Regulators go bad but they do not heal themselves with the weather.

It would be good to get some voltage reference values when things are dry under idle conditions. The terminals that are likely measurement candidates relate to where the current flow travels and what are voltage reference connection points to regulate the alternator output. You will be measuring all of the positive terminal points mentioned with the minus meter lead connected to ground. The alternator ground leads should have zero volts at the alternator when measured to another good chassis ground point. If it doesn't measure zero, that voltage difference is telling the alternator to shift voltage output to compensate.  The alternator does require a good wire ground connection to the chassis and battery bank to regulate properly.  Check in all cases to see that the wire within the crimp connectors involved is not corroded.

The terminals that you want to clean and in some cases seal with a corrosion preventer are the ground wire to the alternator. The positive lead to the isolator, the isolator feeds to each of the battery banks. The battery grounds to the chassis and the positive battery terminals. All of these connections should be clean and corrosion free. As a minimum I would sand/wire brush the main ground connections to the chassis, sand and clean the alternator connection wire to ground. I choose the grounds to the chassis given they are more prone to rust and corrosion. Be sure that the inverter charger is off and the batteries are disconnected when you are lifting and cleaning connections.

When you are satisfied that the connections are good and you have the reference values recorded you can repeat those measurements when the problem occurs and see where the voltage drop or change occurs. You could also wet the ground connections and see if the voltage changes as a response. There is a smaller chance that a battery switch terminal or the switch itself could be involved so you may want to peek at those also.  Hope this helps.

Later Ed

[Karl Welhart]

Ed,

Thanks very much for the message.  I have checked most connections including the main ground wire and all the connections on the alternator.  No voltage measured on the ground to ground leads at idle.  I have not checked the isolator connections.  The drive belt was replaced just before I replaced the voltage regulator.  This problem is driving me CRAZY.  This drop in voltage only happens during a very hard rain on a road that is dished badly (like most interstate highways).  The voltage drops for 5-10 seconds, then comes back to normal and repeats...  

Do you know where the negitive wire on the alternator attaches to the chassis?  I cannot tell because of the wire bundle it goes through.  Also, my alternator connections are facing forward just behind the left (driver's side) rear tires.  Needless to say, they are getting direct water spray from the tires going down a road during wet conditions.  Originally, these connects (for that matter, all my 12v connections) were covered with liquid plastic tape.  Most of them have been cleaned, brushed and sprayed with anti-corrision grease.

Karl

[Paul Schwalen]

Karl,

I had the same issue with a Diplomat.  It turned out that the battery connection at the starter was loose.  After tightening it the problem was solved.

Good luck.

Paul

[Steve Jewell]

Karl,

I would bet on the belt tensioner or the belt. On a dry day start and let idle. Make sure it is charging ok. Then get the hose and wet the belt.


Steve J

[Karl Welhart]

Paul,

I will check the connections on the starter.  It makes sense because the starter is also in the spray zone of the right side rear tires.

Thanks...

Steve J,

I have replaced the belt and tensioner.  Still have the problem.  Could never duplicate the problem with water from a hose.  This has only happened with major down pours and dished road conditions.  Does not happen under normal (even in Florida) type of rain condistions with the water running off a flat or crowned road.  Got to be just the right amount of water hitting something...

Thanks to all,

Karl

[Edward Buker]

Karl,

Intermittent problems are tough to figure out and I can see why this is driving you crazy.

The comment from Paul about the starter is a good one. On cars, the battery lead can go right to the starter and that lug can also be used as a terminal point for the alternator output. For our case I belive the alternator output goes directly to the center terminal of the isolator only. There may be a ground lug to the starter frame involved. Good to check them all and be sure they are tight, clean, and if very exposed to water, perhaps it would be worth a try to apply some liquid tape there also.

Usually the ground lead from the alternator is terminated close by on the top region of the engine. Look for a single wire or a small bundle of wires to a ground lug. Given this problem only occurs under the most severe conditions, maybe water is getting into the alternator brushes or internal connections until airflow and spinning forces intermittently clears them. I have not heard of this, and given it would be an uncontrolled current path situation, I would expect some components within the alternator to fail if this was happening. Things like the diode pack or regulator.

You could also have good clean corrosion free connections in all cases and rather than a series voltage drop in one of the normal current paths you could have a parallel current path (short) created by the water connecting a plus lug to a nearby metal ground. This load, like a short or near short pulls the alternator output voltage down until enough of the water is cleared and the short is removed.

 I'm not sure if this is possible but there are some clamp on DC voltmeters today. I think I saw one at Sears for around $60. Seems like if you could put the clamp on the alternator ouput wire and tape it/tie wrap it safely in place. Run the wire leads into the coach and set up the meter in the closet or bedroom to get some diagnostics while the problem is occuring.

What would be good to know is if there is a very significant current flow that coincides with the low voltage readings that you are seeing, or if the voltage drops without a high current output. The high current out would indicate that all is well with the belt drive, the alternator internal components under wet conditions, and that an external short is drawing current. If the voltage drop occurs without a high current output I would look at the ground lead or the possibility that water is intermittently causing regulator problems within the alternator. If it is the high current case you could then begin to move the voltmeter clamp to various positive wire locations over time to see where the current flow is going.

Tough problem to sort out.....hope this helps.

Later Ed

[Karl Welhart]

Ed,

GREAT suggestions.  Yes, the current load is high during this condition.  This may indicate a short somewhere in the system.  Finding this may be difficult...  Even though I have owned this coach since new (2002), this problem has only been something that I have noticed with in the last couple of years.  Nothing may be different, but my recent circumstances to drive under these conditions.  Anyway, thanks again for all the input.

Karl

[Bill Sprague]

I had some strange electrical issues driving in the rain caused by the electrical bay below the driver getting wet.  The water spun off the left front wheel and through a wire bundle hole that was not sealed very well.  The key to finding it was seeing a little dried mud in the bay!