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Old 08-22-2012, 08:07 AM   #1
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Interstate Battery Isolator

This post is primarly directed towards those knowledgable about the charging system on late model Interstate coaches.

As I mentioned in another post, the 220 amp alternator does not appear to be charging the house batteries in a new just delivered from the dealer 2013 Interstate Lounge.

Battery voltage measurments taken from the electrical info panel with all consummers turned off:

Engine OFF - Chassis 12.64v, House 12.70v
Engine @ idle - Chassis 14.20v, House 12.70v
Gen ON - Chassis 12.65v, House 13.83v
Shore 20 Amp - Chassis 12.66v, House 14.05v

I'd like to troubleshoot this myself so that I can learn how the system works and avoid the 100+ mile drive to the dealer.

Any advice on how to troubleshoot this and a description of where the battery isolator is located in my coach would be apreciated.
Thanks.
Glenn
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Old 08-22-2012, 09:11 AM   #2
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There is battery disconnect button on ours, which says "use" or "storage".

It has to be set to "use" to charge, also to use the battery power internally when not connected to shore power.

Ours is right inside the side door. If you can't find yours, the owners manual should tell you.

If you aren't able to figure this out with help from here, I would just call your dealer, ask for the service department and get your info that way. We had the mechanic from our dealer on speed dial the first few months. There are just so many little things.


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Old 08-22-2012, 11:31 AM   #3
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Quote:
Originally Posted by gastockman View Post
As I mentioned in another post, the 220 amp alternator does not appear to be charging the house batteries in a new just delivered from the dealer 2013 Interstate Lounge.

Battery voltage measurments taken from the electrical info panel with all consummers turned off:

Engine OFF - Chassis 12.64v, House 12.70v
Engine @ idle - Chassis 14.20v, House 12.70v
Gen ON - Chassis 12.65v, House 13.83v
Shore 20 Amp - Chassis 12.66v, House 14.05v

I'd like to troubleshoot this myself so that I can learn how the system works and avoid the 100+ mile drive to the dealer.

Any advice on how to troubleshoot this and a description of where the battery isolator is located in my coach would be apreciated.
Thanks.
Glenn
I know where the house battery disconnect switch is on late-model Interstates. That's easy and shown in the owner's manual. As for the isolator that bridges the chassis and house systems and allows the house batteries to charge off the engine alternator, I have no bloody clue, and the manual doesn't say. I'd really like to know that one myself. There are no settings for the user to change— it's all automatic— so the isolator is probably tucked up somewhere relatively inaccessible.

Before you try a 100+ mile drive, try a 100+ mile phone call. A phone call to the service department of the dealer you bought it from can help immensely for solving "Where is it?" and "Is it supposed to do that?" questions. Speaking of which, once my cell phone recharges, I'll have to call my dealer and ask that question about the battery isolator. You've got me curious.

By the way, when the motorhome's batteries are charging, you're not measuring the battery voltage, you're measuring the charging voltage. You only measure true battery voltage when you turn off the source that's charging the battery, then let the battery sit a few minutes to stabilize. That means your readings while charging on shore power, charging on the alternator, or charging on the generator, are all misleading numbers and don't indicate your battery's state of charge.
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Old 08-22-2012, 11:41 AM   #4
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From page H-13 of the 2012 manual:
Battery Separator
The Battery Separator is located under the center lounge on the rear lounge model and the roadside bed on the twin bed model and is accessed by opening the rear cargo doors. It is designed as a solenoid priority system to protect the chassis charging system from excessive loading while allowing house batteries to be charged. The Battery Separator has two basic uses:
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Old 08-22-2012, 11:49 AM   #5
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Originally Posted by wayneskid View Post
From page H-13 of the 2012 manual:
Battery Separator
The Battery Separator is located under the center lounge on the rear lounge model and the roadside bed on the twin bed model and is accessed by opening the rear cargo doors. It is designed as a solenoid priority system to protect the chassis charging system from excessive loading while allowing house batteries to be charged. The Battery Separator has two basic uses:
Thanks. That helps.
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Old 08-22-2012, 12:24 PM   #6
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Thanks for the replies.

Seems like the "seperator" in my coach is not functioning as designed - not joining the engine and house battery banks during charging.

Manual states on page H-13: "When the engine battery or house batteries are charging, the battery seperator will engage, joining the two battery banks."

So correct me if I'm misinterpreting this, in theory when joining the two battery banks together during charging I should see an increase in voltage (which represents the charging voltage) for both the engine and house battery banks.

However, this is not the case with my charging system. The alternator only shows a charging voltage increase for the engine battery and both the generator and shore power show a charging voltage increase for only the house batteries.

Bottom line - I'll call the dealer to see if they can help me sort this thing out. Good advice.

I'm hoping it's a simple fix, like resetting something or securing a loose wire.

Thanks again for responding - very helpfull.
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Old 08-22-2012, 01:45 PM   #7
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You could have a bad separator or a bad connection. If you have a Twin Bed model, it's very easy to access the separator and you could check for a loose connection yourself. On the lounge models it may be harder to get at the separator.

Do let us know what the fix was.
Good Luck,
Wayne
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Old 03-25-2013, 10:32 AM   #8
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I have a 2012 Interstate with the same problem as Glenn (Gastockman) had.
last season, the alternator charged the house batteries but no longer does. We now must run the generator from time to time while on the road.
Anyone know how this was resolved?
My dealer tells me that's how it should work but I believe he's wrong.
Thanks for any input,
Duane
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Old 03-26-2013, 03:31 AM   #9
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Originally Posted by Dosno View Post
I have a 2012 Interstate with the same problem as Glenn (Gastockman) had.
last season, the alternator charged the house batteries but no longer does. We now must run the generator from time to time while on the road.
Anyone know how this was resolved?
My dealer tells me that's how it should work but I believe he's wrong.
Thanks for any input,
Duane
Your dealer is WRONG! Right now I'm in the process of working with a dealer and the AS national service manager trying to determine why mine won't charge from the Sprinter alternator. I'll post results if we figure it out.

Wayne
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Old 03-26-2013, 05:15 AM   #10
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gastockman,

Did you ever get this problem solved? We'd sure like to hear the outcome!

Wayne
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Old 03-26-2013, 05:18 AM   #11
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There's a trick to it. If the house batteries are badly depleted, the engine alternator won't charge them. Apparently there is a relay that disconnects to two systems to prevent a draw on one system from depleting the other battery.

But, if the house batteries aren't too dead, the engine alternator will top them up.

I don't know exactly what house battery voltage trips the relay. But I found out about that relay the hard way, when I accidentally let my house batteries get badly depleted (down to below 50% charge), to the point that all on-board charging systems were ineffective, and I had no choice but to remove the batteries to bench-charge them.

After that once, I've had no problem, Even if the house batteries are down to about 80% or so, I've had no problem charging them back up from the engine alternator as I drive. I take advantage of this when loading up for a trip, by starting the fridge a couple of days early to get it good and cold before I put the food in. By the time I arrive at the campground, the battery drain from the fridge has been replaced from the alternator and the batteries are back up to 100%.
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Old 03-26-2013, 05:37 AM   #12
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Originally Posted by Protagonist View Post
There's a trick to it. If the house batteries are badly depleted, the engine alternator won't charge them. Apparently there is a relay that disconnects to two systems to prevent a draw on one system from depleting the other battery.

But, if the house batteries aren't too dead, the engine alternator will top them up.

I don't know exactly what house battery voltage trips the relay. But I found out about that relay the hard way, when I accidentally let my house batteries get badly depleted (down to below 50% charge), to the point that all on-board charging systems were ineffective, and I had no choice but to remove the batteries to bench-charge them.

After that once, I've had no problem, Even if the house batteries are down to about 80% or so, I've had no problem charging them back up from the engine alternator as I drive. I take advantage of this when loading up for a trip, by starting the fridge a couple of days early to get it good and cold before I put the food in. By the time I arrive at the campground, the battery drain from the fridge has been replaced from the alternator and the batteries are back up to 100%.
I hope it's a rare event for you to draw your batts to below 50% SOC. I try to never do that as it is harmful to the battery.

This from the Trojan Battery User Guide even suggests 80% minimum SOC.
5. How To Maximize the Performance of Your Trojan Battery
Follow all the procedures in this User’s Guide for proper installation, maintenance and
storage

Do not discharge your battery more than 80%. This safety factor will eliminate the chance

of over-discharging and damaging your battery

The problem of course is that voltage is an imperfect measure of SOC. I just installed a Trimetric TM-2025-RV battery monitor that will give me a pretty accurate measure of SOC. It's also neat to be able to see exactly how much current is flowing into and out of the coach batts. It measures down to .01A.

Wayne
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Old 03-26-2013, 05:54 AM   #13
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I hope it's a rare event for you to draw your batts to below 50% SOC. I try to never do that as it is harmful to the battery.
I try never to do it, either, but back in my early days of Airstream ownership, I wasn't aware of just how much current that danged propane solenoid switch draws, and I accidentally left it on for an extended period of time. I figure I probably took a whole year off the life of my house batteries that time.

Nowadays I'm meticulous about shutting off everything when I put my Interstate to bed in between trips. Everything except the alarm system, that is, but that runs off the main battery. I even added a small dashboard solar panel that plugs into a power outlet, to help the main battery keep up with the draw of the alarm system.

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Old 03-26-2013, 10:27 AM   #14
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Thanks for your responses. I'm encouraged, as a newbie Airstream owner, that there is help out there.
I didn't know that the propane solenoid switch draws power even when the house disconnect is off. Thanks.
I called a different dealer and the service manager there told me that the alternator SHOULD charge the house batteries.
Please let us know once someone finds the issue.
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