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Old 10-16-2015, 02:04 PM   #1
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Electrical problem

I'm having an issue with my engine batteries not charging while driving. At face value it appears to be a bad/failing alternator but there's another symptom that's baffling me. Here are some details:

Measuring the voltage of the engine batteries:
Plugged into shore power, engine off: 13.8V
After driving 2 miles, engine running: 12.8V
After driving 5 1/2 hrs, engine running: 12.3V

Here's the puzzling (to me) symptom: The house batteries are full when I unplug but after the 5 1/2 hr trip they are at about 90% charge. That's the same drop as when we dry camp over an entire night.

The drop in engine batteries I'd say its the alternator but why would house batteries drain faster than usual?

Is it possible the battery separator is engaged, draining the house and engine batteries at the same time? I'm talking out of total ignorance on this point...

I'm taking it in for service next week but wanted advice from the forum so I can discuss it intelligently with the tech.

Thanks!
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Old 10-16-2015, 02:22 PM   #2
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If the engine is running, the idolator solenoid should be energized, so yes, the coach battery and the chassis battery are effectively tied together.

Thats probably why you are able to drive 5 1/2 hours.
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Old 10-16-2015, 02:27 PM   #3
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What does your voltmeter on the dash say when the engine is running? Should read around 14 volts. If less, the alternator is not charging. This is likely due to a failed alternator.
If the alternator is not charging, the BIRD solenoid will stay switched to the chassis batteries because it cannot see sufficient voltage to switch to the house batteries.
The house batteries are now isolated and subject to whatever draw you have turned on without any charge current from the alternator.
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Old 10-16-2015, 05:33 PM   #4
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There are basically two types of isolator systems.

The older and still most common one when you crank her up the solenoid engages and the batteries are connected.. Sounds like yours is working as designed.

There is one version that measures voltage and connects when it's over a set point, likely in the 13 volt range. But I DO NOT KNOW if that works both ways or only house to chassis.

It is possible to make House to chassis work on voltage but chassis to house on the ignition switch and if that's the case yours is still working as designed.

I'd have the charging system (Engine) tested.

NOTE: on vehicles with old fashion "V" belt fan belts.. I've seen belt tension kill the alternator.. Like 5 different cars including a couple dead in the middle of the road.
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Old 10-16-2015, 06:44 PM   #5
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Quote:
Originally Posted by dennis45 View Post
What does your voltmeter on the dash say when the engine is running? Should read around 14 volts. If less, the alternator is not charging. This is likely due to a failed alternator.
If the alternator is not charging, the BIRD solenoid will stay switched to the chassis batteries because it cannot see sufficient voltage to switch to the house batteries.
The house batteries are now isolated and subject to whatever draw you have turned on without any charge current from the alternator.
The gauge is needle is just over the 12 and is confirmed by my voltmeter reading after the 5 1/2 hr drive showing 12.3V.

Might be showing my ignorance here but I don't think I have a BIRD solenoid. I have a Sure Power Industry battery separator. Would they work the same and stay switched?

Thanks for the reply.
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Old 10-16-2015, 10:23 PM   #6
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Quote:
Originally Posted by kjackson View Post
The gauge is needle is just over the 12 and is confirmed by my voltmeter reading after the 5 1/2 hr drive showing 12.3V.

Might be showing my ignorance here but I don't think I have a BIRD solenoid. I have a Sure Power Industry battery separator. Would they work the same and stay switched?

Thanks for the reply.

Still betting on the failed alternator. Not familiar with the Sure Power system but from the symptoms you describe, I believe it works the same way and that is why you are seeing the run down on your house batteries.
I think once you replace the alternator and get 14 volt charging, it will take care of both sets of batteries.
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Old 10-17-2015, 04:17 AM   #7
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It looks like some Sure Power Separators are a simple key activated battery combiner.

Others have voltage sensing circuits, like BIRDs and BIMs.

Research the model #

If It is not voltage sensing and your alt. is bad, you will be running down house and chassis batteries, while driving.
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Old 10-19-2015, 08:01 AM   #8
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Quote:
Originally Posted by twinboat View Post
It looks like some Sure Power Separators are a simple key activated battery combiner.

Others have voltage sensing circuits, like BIRDs and BIMs.

Research the model #

If It is not voltage sensing and your alt. is bad, you will be running down house and chassis batteries, while driving.
It's a Sure Power 1315-200. According to a description I found:
Once the engine has started, the Battery Separator monitors the chassis battery and charging system. When the charging system reaches 13.2 Volts, indicating a charged main battery and functioning charging system, the Battery Separator will engage, connecting the auxiliary battery bank to the vehicle charging system. If the drain on the charging system by the auxiliary battery bank reduces the system voltage below 12.8 volts, the Battery Separator will disconnect the auxiliary battery bank, thus protecting the chassis charging system. The process is repeated until the charging system is turned off.

With a bad alternator, the charging system never gets above 13.2V. The battery separator will not engage. Could this point to a bad battery separator also?

Thanks for you help!
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Old 10-19-2015, 07:28 PM   #9
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There are 2 things to check.

1 Make sure the "Boost Switch" is momentary and funtioning properly.

2 Make sure that if the "Auxiliary Start" funtion is wired in, it is connected to the start terminal of the key switch and not the run position. If wrong, it will stay engaged, when the key is on, no matter what the volts are.
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