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Old 04-05-2017, 12:24 AM   #1
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Default Isolator, Coach Batteries Issues

This may be a long story, but here goes. I am a fairly new Class B owner. The other night, the Check Gauges light went on and the alternator gauge on my 2002 Dodge Ram Van 3500 Leisure Travel went all the way to the left. I turned off all electricity and made it to the nearest campground. The next morning AAA assisted me to a reputable car clinic. According to them my alternator was putting out 27 volts, frying my engine battery. So, I had them replace both. It tested OK for them in the shop. But in test driving the rig, the Check Gauges light came back on and they said the voltage dropped to 8 volts. I suppose they had a computer hooked to the diagnostic port. They had no knowledge of motorhomes and saw that the wiring went through the isolator. Hence, the disconnected the cables to it and tied the alternator and engine battery cables together. Problem solved in their minds.

Being a new owner of the van, I suspected that maybe the coach batteries were weak, so I asked them to load test them. They left them hooked together during testing. One tested bad and one tested good. What is surprising to me is that the "Charge Eye" on the bad one showed "Green" or Good and the "Charge Eye" on the good one showed "Red" or bad! Consequently, I began to wonder if the bad battery developed a short, making the alternator put out too much voltage, burning it out and also the engine battery. And, could a malfunctioning isolator be the cause of this? And why only 8 volt output of the alternator when the isolator and coach batteries were hooked up?

In doing studying, I found in the documentation that accompanied the coach, a sheet pertaining to the isolator in the van. It included a procedure for checking the isolator, using a voltmeter to determine if it stops current one direction and lets it pass the other direction. I only have on hand a very inexpensive voltmeter, but I conducted the test. Going from the alternator post to ground there is some resistance, but some openness. Going from the alternator to the engine battery post (I think), there is resistance one direction and openness the other direction. But going from the alternator post to the coach batteries post, there is no openness for either polarity. Again, this is an inexpensive, needle version of a voltmeter.

I am now on the road, but stranded with brake problems (not related, of course), but I have struggled to find someone familiar with motorhome wiring. They all say they know nothing about them, although I feel the situation may be fairly simple for some knowledgeable person. So, I am turning to this forum. I hope some of may off me some comments and advice.

Any thoughts! Thanks in advance!
Gregg
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Old 04-05-2017, 12:42 AM   #2
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.

How old are your house batteries?
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Old 04-05-2017, 02:34 PM   #3
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I do not know. I bought the unit last November, but I am quite sure the dealer did not put new ones in. So they are probably up for replacement. I think replacement will be my first step unless I get advised differently. If one battery is good and the other bad, I could use the good one in a pop-up camper I have. But I am also concerned about the isolator--can it cause problems?
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Old 04-05-2017, 03:19 PM   #4
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.

I doubt the dealer would be so benevolent as to give you a new battery.
They will get away with murder if they can,
which I think they just got away with murder.

There should be a date code on the battery.

If the batteries do not look new,
they are not new.
ie. you should replace them.
They are good for approx 5 yrs.
Some have luck in keeping them longer.
But if they have ever been discharged below 50% for an extended period of time, they are weakened, or maybe even toasted.

Which isolator do you have? Brand? model number?
Picture?
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Old 04-05-2017, 05:31 PM   #5
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I cannot find a manufacturing date, but the batteries are fairly dirty. I am sure they have some age on them, but I have no idea how much. Plus I have no idea how they were treated. I do know that they would at least handle my needs for overnight, but I always either drove the next day or would be on shore power, hence they were never tested for a long period.

The isolator is manufactured by Leisure Components. Model 496HT, 3 post, 135 Amp. Link to picture: [URL="http://https://1drv.ms/i/s!AtjihSWJj8H2gq02vCdjuT6ho0Spdg"]

Can a bad isolator do damage to anything other than not protecting the engine battery?

Do batteries have to be detached from each other when doing voltage testing?

Thanks for the replies. They are very much appreciated!
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Old 04-05-2017, 06:45 PM   #6
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Isolators can cause some damage from what I have heard. It appears some of them sense the voltage of one or the battery banks, and if that connection is lost the alternator can lose reference and go full voltage, which may be what happened initially to you.

Batteries that are in parallel have to be disconnected to get any useful voltage readings. In series you can check then connected, but it is still best to disconnect them and let them sit a while before checking.

You may want to just consider biting the bullet and replacing the whole works on the coach side. Two new TRUE DEEP CYCLE batteries, and a new isolator or upgrade to a solid state separator/combiner
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Old 04-05-2017, 07:02 PM   #7
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Thanks for the additional input and information.

Do you have a recommendation for the upgrade solid state separator/combiner? I found one at Robust, inexpensive 12V 150+amp smart battery isolator and smart split charge relay for RV, car, and truck applications, dual battery isolator but I was surprised how little it cost and how small it seemed. My current isolator seems much more robust, but perhaps that is due to different technology.
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Old 04-05-2017, 08:36 PM   #8
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Battery Doc® 12 Volt 150 Amp Battery Isolator - Wirthco Engineering, Inc.

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Old 04-05-2017, 10:25 PM   #9
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Quote:
Originally Posted by booster View Post
Isolators can cause some damage from what I have heard. It appears some of them sense the voltage of one or the battery banks, and if that connection is lost the alternator can lose reference and go full voltage, which may be what happened initially to you.
I'm not aware of any isolators that employ a battery voltage sensor. The sensing terminal typically was on the alternator which examined battery voltage and adjusted the alternator voltage to compensate for voltage drop across the isolator diodes + cable resistance losses.

I think hard wired alternator sensing technology has been replaced with the advent of computer control of alternator field windings which makes the report of 27 volts delivered a little puzzling because the computer is continuously monitoring battery(s) terminal voltage and if it sees no battery voltage, it clamps the alternator field current to prevent the alternator from taking off into over voltage. To deliver 27 volts from the alternator, the field windings would have to be subjected to a forced full field condition which seems unlikely if there is a physical connection to any battery.

Additionally, every appliance in the coach would be subjected to 27 volts and I am puzzled why there was't some appliance and lighting filament failures.
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Old 04-05-2017, 10:34 PM   #10
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Quote:
Originally Posted by gksmith View Post
Thanks for the additional input and information.

Do you have a recommendation for the upgrade solid state separator/combiner? I found one at Robust, inexpensive 12V 150+amp smart battery isolator and smart split charge relay for RV, car, and truck applications, dual battery isolator but I was surprised how little it cost and how small it seemed. My current isolator seems much more robust, but perhaps that is due to different technology.
When employing isolators and the alternator is turning, both engine and house batteries are charged but when shore power is hooked up, the battery charger typically will only charge the house battery. A bi-directional separator addresses this and will permit the shore power battery charger to address both batteries.

A commonly found separator for this is the Surepower 1315 bi-directional separator which is offered in both 100 and 200 watt versions. The Cadillac quality separators are ACR separators made by Blue Sea.
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