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Old 01-28-2016, 07:10 PM   #1
gte
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Default Coach Battery Charging

I have a 2008 RS and am concerned the coach batteries are not being charged when the engine is running.
When I measure the voltage to ground out of the isolator I get 14.2 volts. I also get 14.2 volts on the engine battery. On the coach battery I get 12.5 volts. I also get a 1.75 volt drop from the isolator to the positive terminal of the coach battery. I would have thought the voltage drop across this wire would be zero. Could it be there is sometbig wrong with the battery causing this drop, like a large current from the isolator or could the wire be bad? My batteries are 7-8 years old and I have an appointment to replace them but want to make certain the charging system is working. Thoughts?
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Old 01-29-2016, 12:44 PM   #2
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Default Re: Coach Battery Charging

Keep checking voltage at all points along that wire untill you find the source of the problem. There are several connections, so you can isolate the spot. Very high probability that it is at an interconnection. Corrosion causing a high resistance?
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Old 01-29-2016, 01:59 PM   #3
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Default Re: Coach Battery Charging

Thanks Trekker. I measured the voltage to ground at all the points in the picture and got 14.2 volts. One of the wires goes to the positive terminal of the battery so when I checked there I got 12.5 volts so there is a loss across that wire it seems.
I made additional voltage measurements and found that
Engine Off Engine on Generator On Connected to Shore power
Coach 12.45 12.45 14.6 13.7 volts

Engine 12.76 14.2 12.7 12.7 volts
I think the generator current passes through the isolator and thus the wire in question too. Weird. I am having new batteries installed today so will check after that.

Sorry about the formating but I think you can read it.
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Last edited by gte; 01-29-2016 at 02:02 PM.
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Old 01-29-2016, 03:03 PM   #4
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Default Re: Coach Battery Charging

When charging the house batteries from the generator or on shore power, the battery separator under the hood is not involved. The Tripp-Lite inverter/charger is connected directly to the batteries and does not go through the seperator. Charging with shore power or with the generator on should be the same. With the generator running or plugged into shore power and the van engine off you should also see the starter battery getting charged.

The differences in charge voltage on the house battery between generator and shore power could be due to moving from from absorption to float by the Tripp-Lite.

Sure looks like there is a bad connection between the seperator and the battery, you could jump it with a jumper cable to see what happens to the voltage at the battery. This would explain the symptoms you are seeing since you also get no charging of the engine battery when you are on generator or plugged in. This same connection would handle the charging current from the Tripp-Lite to the engine battery.

Do you currently have wet cell house batteries? You may know already that you don't need to change the Tripp-Lite settings if you switch from wet cell to AGM, no matter what you get told by Roadtrek or Tripp-Lite support.

Last edited by gregmchugh; 01-29-2016 at 03:40 PM.
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Old 01-29-2016, 06:40 PM   #5
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Default Re: Coach Battery Charging

Hi Gary,
Correct me if I misunderstood, with the engine running, you’re saying you are getting same 14.2 volts on the battery separator 2 terminal posts and only 12.5 volts to the coach battery post? If that’s the case did you check the circuit breaker between the separator and coach battery? It could have failed or failed to reset after it has been tripped, check its continuity. You can try to manually reset it by momentarily disconnecting the + cable that leads to the battery.

If there is a voltage difference between the 2 separator terminal posts with the engine running and alternator is providing the charge voltage, 2 things that could go wrong…either your separator has failed or the coach battery is causing the system voltage to dip below 12.4-12.9 volts while separator is active, at this point the Sure Power battery separator will disconnect both batteries to protect them from excessive drain.
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Old 01-29-2016, 07:44 PM   #6
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Default Re: Coach Battery Charging

Greg and RT
Thanks for your comments, they are helpful. I had also sent a note to Peter Lange and he suggested the breakers.
Today I had new AGM engine and coach batteries installed and now with the engine running I get 13.4-13.5 volts to ground on everything; isolator, breakers, coach and engine. I hope this suggests the isolator and breakers are okay, but I do wonder why it is not 14.2 volts. Maybe the "Y" cable or the fact that the batteries are new and fully charged? Thoughts?
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Old 01-30-2016, 12:39 AM   #7
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Default Re: Coach Battery Charging

The Y cable is always a potential cause of electrical issues so it might be good to check it out.

The 13.5v vs 14.2v alternator output could be due to a large load, one that is mentioned in cases like this is the electric heating element in the HVAC system that heats up the air until the engine heats up. Not sure if this item is in all vans or if it is an option. I guess you could turn off the heat and see if the voltage rises.
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Old 01-30-2016, 09:27 PM   #8
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Default Re: Coach Battery Charging

It was warmer today so I could make more consistent voltage measurements with my new coach and engine AGM batteries. I did not get under the RV to measure the alternator output directly but will when warmer weather arrives. I was surprised that the engine and isolator values with the generator running were a volt lower than the coach reading but the generator must not connect to the engine battery.
I still wonder about the "Y" cable.

Engine off, no shore power or generator
Coach - 12.7 volts
Engine - 12.7
Isolator and breakers - 12.7

Engine running
Coach - 13.6
Engine - 13.6
Isolator - 13.3-13.6

Shore power connected and coach power switch on
Coach - 13.7
Engine - 13.7
Isolator - 13.6-13.7

Generator running
Coach - 13.75
Engine - 12.75
Isolator - 12.75
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Old 01-31-2016, 12:55 AM   #9
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Default Re: Coach Battery Charging

120v AC comes into a transfer switch, inside the rear driver's side seat base in our 08 RS, from the shore power plug and from the Onan generator. The 120v output is selected with the generator having priority if both are present. The transfer switch also provides the delay you see before power is active in the van. The 120v AC output from the transfer switch goes to the Tripp-Lite powering the battery charger that connects to the house batteries without going through the seperator. The charge level voltage on the house battery connection at the seperator should trigger the connection to the starter battery. The last two sets of readings are showing different results between shore power and the generator which needs to be investigated.
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Old 01-31-2016, 02:54 AM   #10
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Default Re: Coach Battery Charging

Quote:
Originally Posted by gregmchugh View Post
120v AC comes into a transfer switch, inside the rear driver's side seat base in our 08 RS, from the shore power plug and from the Onan generator. The 120v output is selected with the generator having priority if both are present. The transfer switch also provides the delay you see before power is active in the van. The 120v AC output from the transfer switch goes to the Tripp-Lite powering the battery charger that connects to the house batteries without going through the seperator. The charge level voltage on the house battery connection at the seperator should trigger the connection to the starter battery. The last two sets of readings are showing different results between shore power and the generator which needs to be investigated.
Thanks Greg. I thought it odd too. My first thing to do is to verify these measurements tomorrow. I thought the charging voltage should be around 14.1 volts and it was not. Should it be 14.1 or so? I do notice the delay you mention and hear the relay click on after a delay so that seems to be working.

If my measurements were incorrect and the voltages are the same I still wonder about the fact they are not higher.

If my measurements are correct could the problem still be with the isolator or the breakers or the "Y" cable and how do I check this out?

Also I should mention that I have a Progressive Industries surge protector on the shore power input but not on the generator. I believe it could be wired for both but I chose to only protect the shore power input.

Another measurement I made was from the breaker to the positive of the coach battery (basically across the connecting cable)and I saw 0.1 volts or so.

Later edit.
I have read your response a number of times and now wonder if my readings are correct if the isolator is not being activated and that is why the voltage to the engine battery is basically the battery voltage alone not the charging voltage.
With the engine running are both the coach batteries and the engine battery fed voltage from the alternator directly and not through the isolator? If so this may mean the isolator is bad or possibly the breakers.
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Last edited by gte; 01-31-2016 at 03:07 AM.
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