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Old 03-20-2008, 03:04 PM   #1
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SMB Battery Isolator/Separator

I thought this would be good to have availiable for basic information as I have had problems in the past with my isolator/separator operation. This may be somewhere else on the forum but seems this is the best place to post about it. Note that this is what is offered as of 2006, older model SMB's could have a different unit.

This was my responce from SMB about Basic operation:

I have replied below in all CAPS.

-----Original Message-----
From: Dave Boyer []
Sent: Monday, March 17, 2008 12:18 PM
Subject: 12 VDC plugs/isolator
Peter I have had some people ask how the isolator operates and I think this is how it works. (This is from Sure Power). I would like to verify this for for future troubleshooting. I also need to know how the plugs are wired.

According to Sure Power:
The battery separator is designed for use in multi-battery applications as a solenoid priority system to protect the chassis charging system from excessive loading while allowing auxiliary batteries to be charged. The battery Separator has two basic operational characteristics:

1. Assist in engine starting.
When the starter is activated, the battery separator compares the voltage of both banks. If the chassis battery is lower than the auxiliary battery bank, the battery separator will engage allowing the auxiliary battery bank to aid in vehicle starting. (The start signal must be at least three volts for this operation to occur.

2. Protecting the charging system.
Once the engine has been started, the separator monitors the chassis battery (twin starting batteries in the case of a Ford diesel) 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 separator will disconnect the auxiliary battery bank, thus protecting the chassis charging system. The process is repeated until the charging system is turned off. A delay function has been incorporated in the circuit to prevent the separator from reacting to momentary voltage fluctuations and chattering. The priorities are to assist in starting, if required, and to protect the charging system from excessive drain.

I assume the types we have in our vans are the bi-directional type units because if you were to leave something on in the van you would want to protect one bank or the other depending where the draw is coming from. Of course if you leave one item on pulling off the starting batteries and one item on pulling off the house battery the isolator can’t do much for that. I do know that SMB upgraded to a 200 amp model in my van and I think it is made by Sure Power. YOU HAVE THE 200 AMP MODEL1315-200


Does it work off the key or ignition? IT ENGAGES AFTER THE KEY IS TURNED TO THE ON POSITION

Will the battery banks, (the starting and house) stayed tied together until one or the other drops to 12.8 wherein the isolator will open and separate? YES

Do the 12v accessory plugs in back come off the house system? YES, THEY DRAW FROM THE HOUSE BATTERY

I’m sure that the dash 12 plugs come off the starting batteries, correct? CORRECT

Dave Boyer

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Old 03-20-2008, 04:36 PM   #2
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"Will the battery banks, (the starting and house) stayed tied together until one or the other drops to 12.8 wherein the isolator will open and separate? YES "

OK, so if I understand this correctly, is the following scenario possible:

Say I want to park my van for an extended time, as in months. Say also that I have solar panels on the roof, and I'm expecting those to keep everything topped off while I'm away. While this is happening, assuming both batteries start above 12.8V, the solar will keep BOTH sets of batteries topped off as they'll be connected.

BUT, say one night (while the solar panels aren't doing their magic solar thing) the overall system voltage drops below 12.8V; very possible actually. Then the isolator kicks in to isolate mode, and the next day when the sun comes out, and from that point forward until I return, the solar panels will ONLY keep the house battery topped off. This would happen because the isolator would be trying to "protect" my house batteries from any parasitic load on the starter batteries. Correct?

And, is my assumption correct that if I want to avoid this while having it parked, that I should probably bypass the isolator with dedicated wiring.

This is actually a possible usage scenario for me coming up, so I want to make sure I understand this correctly.

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Old 03-20-2008, 05:41 PM   #3
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That is correct, up to a point.

And that point is:

When the house batteries are charged to 13.2V, the system will start to charge the starting batteries. If the starting batteries are low enough that they pull the house system below 12.8V, the charging will stop (after a delay period - so some charging does take place). When the house batteries again reach 13.2V, charging will resume. This cycle will repeat until either the starting batteries are charging and the system stays above 12.8V or until the sun goes down.

Unless the starting batteries are nearly completely discharged, they shouldn't pull the house batteries down below 12.8V.

I have a 125W solar panel and it works just like the above. I can tell when the system switches to charging the starting batteries, because if the starting system voltage changes more than 0.3V the ScanGuage will see that as a KEY ON condition and start running. The ScanGuage will not turn off until I shut down the engine. I don't fully understand the conditions that cause a 0.3V rise in the starting system, but I know when it has happened - when I get in the van and the ScanGuage is on trying to connect to the non-running engine.

There is no need to disconnect the battery separator. The system will keep all the batteries charged - if the solar panel has enough capacity to overcome the self discharge from all the batteries as well as any parasitic loads.

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Old 03-20-2008, 05:53 PM   #4
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Awesome, thanks. That makes my life a lot easier.
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Old 03-20-2008, 07:46 PM   #5
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battery isolator

Very interesting post. I know Greg tried to explain all this to me, but I was experiencing brain overload at the time. When my SMB is under the carport, i have it plugged into shorepower. I just checked the house & chassis voltage, both 13.2, so I assume the system is working as designed. Thanks for the info.


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