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Old 04-18-2015, 05:55 PM   #1
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Identify this little box?

I have a little "issue" with the 30' Airstream Land Yacht. When I have shore power, there is power to the converter under the dash. When I unplug shore power, the converter outlet has no power. (this has been an issue for some time)

I had an alternator go bad, had a mechanic replace both it and the battery at the same time. He told me that the new alternator was producing 14+v at the alternator, but at the battery it was only getting 12.7v. He said the alternator went into this little box, and on the output side of the box it was reducing the power to 12.7v?



Is this some sort of AC/DC power box that will resolve the issue of no power to the converter outlet?

If someone can tell me what this box is, who makes it, where to find a replacement, (without me taking the box off, and looking for numbers) I would certainly appreciate it...

Thanks in advance

Steve
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Old 04-18-2015, 06:29 PM   #2
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Little Box

To me it looks like a battery isolator. It is used to isolate 2 batteries from each other when they are being charged from the same source ( so they can't run each other down). I think there are 2 big rectifiers in there and the box is just a heat sink as the diodes can get hot.
Just my guess.
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Old 04-18-2015, 06:36 PM   #3
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Quote:
Originally Posted by nm1oqrz View Post
To me it looks like a battery isolator. It is used to isolate 2 batteries from each other when they are being charged from the same source ( so they can't run each other down). I think there are 2 big rectifiers in there and the box is just a heat sink as the diodes can get hot.
Just my guess.
Happy camping nm1oqrz
What 2 batteries would be charging from the alternator? There is only 1 battery that is charged from the alternator and 2 house batteries. Why would this bring the voltage down from 13.9v from the alternator to 12.7v getting to the battery?

Thanks for the input..

Steve
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Old 04-18-2015, 07:10 PM   #4
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I really don't know anything about these but I did find this article that you might find interesting. It seems it is typical for a diode based isolater to provide a voltage drop. This article is about boats but they are commonly used on RV's too Marine Battery Isolators: Old Types Versus New
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Old 04-18-2015, 07:34 PM   #5
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It is a battery isolator. When you have 2 different 12-volt systems (e.g., a chassis system and a house system), you want to prevent the house system from drawing down the chassis system. This is necessary so that there will always be enough power in the chassis system to start your coach. Sadly, this isn't always the case, as there are some things that will run off both systems (such as the power steps - when I had a 1994 AS Land Yacht moho).
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Old 04-18-2015, 07:50 PM   #6
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Originally Posted by blkmagikca View Post
It is a battery isolator. When you have 2 different 12-volt systems (e.g., a chassis system and a house system), you want to prevent the house system from drawing down the chassis system. This is necessary so that there will always be enough power in the chassis system to start your coach. Sadly, this isn't always the case, as there are some things that will run off both systems (such as the power steps - when I had a 1994 AS Land Yacht moho).
Is there any updated "solid state" replacement that I might be able to install? If so, where would one go to find it?

Steve
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Old 04-18-2015, 07:59 PM   #7
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This is the one in my boat. They are available at most marine stores and on line.

Quick Cable | Battery Isolater Switch rated up to 100 amps
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Old 04-18-2015, 09:11 PM   #8
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Originally Posted by AWCHIEF View Post
This is the one in my boat. They are available at most marine stores and on line.

Quick Cable | Battery Isolater Switch rated up to 100 amps
Is this the typical set-up for the RV? Because my fridge does not get power once I disconnect from shore power.



If the system is set up for this, then this device may end up working for me.

How do I tell if there are enough amps? volts? protected by this device?
see it on this page...

Steve
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Old 04-19-2015, 02:48 PM   #9
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Quote:
Originally Posted by Woodyacme View Post
Is this the typical set-up for the RV? Because my fridge does not get power once I disconnect from shore power.



If the system is set up for this, then this device may end up working for me.

How do I tell if there are enough amps? volts? protected by this device?
see it on this page...

Steve
It is a battery isolator Steve and allows your alternator to charge both the engine battery and the coach batteries. The fourth wire (little terminal) is a control signal to the alternator which reduces the charging voltage level when the engine battery reaches a full charge. There are two large diodes in the box. You can read about them here:
https://www.google.com/search?q=batt...17%3B564%3B421

With the engine off you can check the voltage of each battery system (the two outside terminals). The alternator output is on the center terminal. The box isolates the two batteries while still providing a charge voltage when the engine is running. It has nothing to do with the shore power charge system. The amp rating of the isolator depends on the alternator output current capability. (100 amp alternator get 100 amp isolator)

There is a voltage drop across the diodes which is normal. It is dependent on the current being drawn. The isolator favors the engine battery and to make sure you can always start the engine.

Howard
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Old 04-19-2015, 03:48 PM   #10
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Everybody id'ed it right but you would need to test which wires are going where and if the input from the alternator is on the right post. Using a multimeter you should be able to disconnect all wires and see if your diodes are working. In the past I have found isolators can cause problems as well as stopping problems. It is supposed to keep systems separated from each other, if a diode breaks down you will not get needed current even if alternator is providing it.
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