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Old 10-16-2010, 04:04 PM   #1
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Gas coach charging problem

I have a '99 Newmar Mountain Aire gas 3767... Normally when the engine is running and I check the coach battery voltage at the main control panel it displays 13.6v. I'm now showing only 12.2 with the engine running or not running... The voltmeter on the dashboard is showing normal charging.

Also, I'm not sure shore power is charging the coach batteries, don't know... I returned home after 2 weeks camping plus the trip home and the batteries showed only 12.2v at the control panel. ????

Can anyone tell me what the problem may be or where to start looking for the problem.. My coach is stored in a storage lot so I can't check shore power till I get back to a CG.

Thanks... Bill...
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Old 10-16-2010, 05:44 PM   #2
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Can anyone tell me what the problem may be or where to start looking for the problem.. My coach is stored in a storage lot so I can't check shore power till I get back to a CG....
wilythek, You may have to look at getting a new battery if the existing battery is failing to hold a charge.
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Old 10-16-2010, 05:56 PM   #3
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Sounds to me like it is possible your battery isolator is not operational for some reason or dirty terminals. The alternator goes to the center terminal and the coach and engine battery to the other two. Check the voltage at the two end terminals and the center terminal with the power off. Start the engine and wait a few minutes for everything to stabilize. Then measure the voltages. The alternator terminal will measure a bit higher than the other two and they should be at a higher voltage than with the engine off. Also, measure the voltages for your coach batteries directly on the battery terminal and then the cable connection. If there is a difference, you have built up crud and should remove the cables and clean them and the battery posts.

This should at least be a start. Good luck.
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Old 10-19-2010, 01:01 AM   #4
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Alternator is not charging, bad isolator or wire

You stated key information when you listed 12.2 volts running or not.

When the engine is running and if the alternator is working the voltage WILL be different and SHOULD be higher.

So wherever this measurement is taking place, the alternator is not connected to it or not working.

First locate your engine battery and measure the voltage there to be certian the main battery is getting a charge and if your alternator is working, if this is failed you need ot worry or get a portable charger if you are on the road as you will need to charge the battery to avoid being stuck someplace.

Depending on the size and state of your batteries, the amount of current that is drawn by the batteries as a percentage of the capacity of the alternator will determine the actual voltage.

So if engine at idle, low batteries (about 25 % LEFT) as indicated by 12.2 VDC the charging voltage may only come up to 13 volts or so until the engine is at higher speed or the batteries gain some charge.

Check at each battery, check both the post to post and post to ground, a bad ground connection will be a concern.

Also check while the engine is running or with inverter on and engine off the voltage across the connection.

One probe is scratched into the center of the post while the other is scratched into the wire where it goes into the connector, if there is corosion inside the interface between the post to connector or connector to wire it will show up as a voltage here, this measurement needs to be zero.

Depending on the type of battery isolator, if diode type you add 0.6 volts to all measurements on the alternator side of the isolator, if seledoid then no change.

Voltage at alternator output should be more than it was with engine not running, and not exceed 14 volts, it may vary with engine speed, and usually will be between 13 and 13.6.

If you cannot get to the alternator then locate your isolator, it will have 3 large wires, the center is usually the alternator input and the other 2 go to the batteries.

Check voltage on all 3 posts.

Then work towards all batteries checking wires and connections.

Work until you find something not correct, then determine why it is not correct and make a repair.

You are not finished until all batteries are getting correct charging voltage when the engine is running, you could have multiple problems or a single one, just take your time and you will get it.
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Old 10-19-2010, 01:13 AM   #5
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Bill:
I would start with the voltage @ the MAIN ENGINE BATTERY with the engine @ idle speed. If it's not around 14.2 volts, you have a charging problem. I would start with having the alternator checked. Batteries will only retain what the charging system can put in to them. Good Luck, Happy trails & travel safe.
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Old 10-20-2010, 11:01 AM   #6
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Gas coach charging problem

Thanks to all for the helpful suggestions. Here is what I've found so far...

For some reason (one time only ??) it appeared that I was not charging the house batteries as I mentioned in my first post, when I said that the house batts were 12.2 v engine running or not. The volt meter on the dash indicated the alternator was working ok.. It has been working as it should since then... but I have found this out;

With all batteries at rest for 24 hours the engine battery was at 12.6v, the house batteries at 12.2v..With the engine running at idle speed the engine battery was reading 14.6v and the house batteries 14v... does this sound normal???

I've not figured out yet if the house batteries are holding a charge or not... I replaced the house batteries 5 years ago with (2) 6v golf cart batteries... The previous owner said he replaced the engine battery. He owned the coach for 3 years. I'm guessing it's about 6-7 years old. I'll bring them home later today and put them on my portable charger and find out. Any other thoughts will be appreciated.
Thanks guys. Bill....
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Old 10-20-2010, 02:19 PM   #7
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If both sets of batteries are reading 14+ volts at idle then your charging system is just fine or both the chassis and house batteries. This does NOT count out the fact that the battery cables may not be making good connection to the battery posts because of oxidation or corrosion. They can look fine from the outside. I would take both the positive and neg cables and wire brush the inside area of the cables and the battery posts until they are shinning. You can buy a special wire brush that will make the job a lot easier from most auto parts stores. In my younger days I have been fooled a couple of times by bad connections to the battery posts that I thought looked just great on the surface.
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Old 10-21-2010, 01:03 AM   #8
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Normal and broken...

OK, 14.6 VDC on starting battery and 14.0 VDC on coach battteries indicate the following.

Alternator is working
0.6 VDC difference between starting and coach batteries indicates a diode between the 2, so a diode type isolator must be installed someplace.

THE BROKEN part
You need to locate the isolator to confirm how it is connected and measure all of the posts, I suspect it may have been blown out on the starting battery side or someone who hod no clue bypassed it.

The alternator seems to be adjusted to compensate for a diode based isolator, thus the 14.6 VDC reading.

This voltage is TOO HIGH and will over time fry the starting battery.

Given the voltage on the coach batteries was at 14.0 the alternator is STILL a little too high and the coach batteries will not like this too much either.

If your alternator is a decent sized one then the batteries have little chance against it, they will just give up the goast and leave you stranded.

Your to do list.
Find and repair the isolator
Confirm process to adjust voltage on alternator.
Adjust for 13.6 VDC at idle measured at the batteries.
Confirm high idle maintains less than 14 VDC.

Mike advised cleaning the cables, I second that, except while at the store get the reamer/scraper for battery posts, it will remove metal and make the shapes the same. way better than the brush.

Get a can of the cleaner and clean everything

Get a can of the cheapest spray paint.
After everything is clean and the wires reattached and all is dry, spray the posts, connectors and the wires with the paint, goop it on thick, runny is fine, you want it flowing wet, this is an old radioman trick I have been doing for years.

The acid does not attack the paint so where there is paint the acid tends to be fine for a good long time.
So if you use the scraper/reamer tool you will have a great fit on the posts, then the paint will fill any gap that is not touching and seal it off from the acid.

It will creep into the wires and any open spot that you soak it into, so sloppy is better...within reason.

You may want to clean the battery bay and repaint it too while you are at it.
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Old 10-21-2010, 09:10 AM   #9
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Let me ask some questions because I am easily confused. Would the isolator have to be hooked up and working correctly or if when dry camping you would run down both the chassis and the house batteries together? If I remember correctly from my engineering daze a diode has two failure modes... an open usually have a crispy critter or it can be shorted. If crispy critter then the house batteries would never have charged up and reading of 14+ volts so that is out. If shorted, which is very unusual, then it would be the same as jumping around the diode and you would see exactly the same voltage on both sets of batteries plus you would run them both down together.

The alternator output voltage depends on the load placed on it. Right after you start a motor it will jump up above 14 volts to replace the power used to start the motor. If the batteries are low in voltage then the alternator will put out a high voltage until they charge up. The question here would be if the alternator output voltage correctly drops down when the batteries charge up. In the first post it was stated that the voltage was down at 13.6 V so the regulator is working. I don't know of a standard alternator that has adjustable voltage out. I have a special application alternator with a built in regulator that I can adjust but that is very unusual.

By all that is said it appears to me that the actual charging system is working just fine and the problem may be just dirty battery cable connections or just one battery that has failed and is pulling down the rest after a short period of time or there is nothing wrong. Like I said clean all the connections inside and out and while they are disconnected take the batteries in and have them checked under load. Most car parts stores will do this free of charge..
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Old 10-21-2010, 10:47 AM   #10
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Lots of discussion going on here. I'll see if I can find out more info... Buuuut, just for comparison I checked the charging voltage on my Ford car and the alternator is putting out 14.4v... I checked the output on my S10 pickup and the alternator is putting out 14.8v. The MH is putting out 14.6v smack in the middle..

Also I have absolutely no acid corrosion on my coach batteries... I topped off each cell with 1 1/2 ounces of Mineral Oil the day I bought the batteries 5 years ago..
Thanks.
BIll...
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Old 10-21-2010, 11:22 AM   #11
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Bill, I am not talking about acid corrosion which is easily visible on the terminals. What I am talking about happens between the inside of the battery cable hole and the outside of the battery post where they make contact with each other when they are put together. After a period of time it builds up a coating that is dark gray in color and increase the resistance of the connection and prevents the battery from being charged up. The battery cables should be taken off the battery and the inside of the battery cable hole and the battery post should be scrubbed with a wire brush until shiney. That is why they back the special battery cleaning brush.
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Old 10-21-2010, 11:34 AM   #12
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Thanks Mike.... I'll do it... I brought my batteries home and they are now on my charger running a desulfating process, then I'll recharge them.
Thanks. Bill
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Old 10-22-2010, 01:13 PM   #13
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Isolator statement

Above I mention concerns with the isolator and the possibility of it being broken.

Mike has a good question that I may not have properly explained, here we go.

The isolator has 2 diodes both pointing towards the center, thus corrent cannot go from end to end, only from center out, or from outside in to center, depending on how you deal with current flow.

So the alternator connects to the center pin, the 2 different battery systems connect to the outside connections, both batteries can charge, but loads on one battery system are isolated from the other due the the one-way function of the diodes.

What I was indicating above was the possibility of a problem on the starting battery side.

Given the 0.6 VDC difference in measurements posted, and with that being the junction voltage of a diode, this indicated one battery had a diode's worth of voltage added to it, so there was a possibility of problem.

Either the diode on the starting battery side was shorted, or someone in the past in trying to repair a problem with the charging system may have moved the wire for the starting battery to the center pin and connected it directly to the alternator.

Whatever is actually going on, the difference in voltages between the 2 batteries indicate something is not correct, this needs to be discovered and repaired.

The charging voltage may be allowed to run higher as other posters have advised, automotive use is typical of short drives that have little time on average to recharge the battery after starting, and the design of the battery may allow the higher charge for short periods of time.

But when one conciders the larger expense of the batteries in the MH, and the longer time that the engine may be running, one should try to have the charging system operating in a manner to optimize the battery, not punish it.

Charging current more than the maximum allowed can damage the battery, 1% of capacity is best for floating and usually 25 amp maximum charge to recharging, a 160 amp alternator set with a voltage too high will certianly toast a battery.
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Old 10-22-2010, 09:11 PM   #14
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Quote:
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With all batteries at rest for 24 hours the engine battery was at 12.6v, the house batteries at 12.2v..With the engine running at idle speed the engine battery was reading 14.6v and the house batteries 14v... does this sound normal???
First thing that comes to mind is... Have you performed a hydrometer reading on the house batteries yet?
If one cell is lower than all the others it would indicate a faulty battery. This may also cause erroneous voltage readings while the charging system is operating.
If you don't have a hydrometer you can find one cheap at most auto parts stores.
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