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Old 05-24-2010, 12:32 PM   #1
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Why doesnt SMB isolate the radio/CD player?

On my 2003 SMB I have the option of using the CD player using the vans 2 starting batteries when the van is running or with the key switched to accessory OR I have a switch in the back for when the engine is not running which switches the CD player to both the vans coach battery AND the 2 starting batteries.

I have already given myself dead starting batteries when I forgot to switch it back.

Why did SMB not isolate the CD player from the starting batteries when the van is not running?
(My SMB manual explains that this is how they hooked it up but does not say why.

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Old 05-24-2010, 02:02 PM   #2
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Re: Why doesnt SMB isolate the radio/CD player?

Not sure on your year but [edit: I'm told] my 06 radio does not pull anything off the starting batteries with the ignition switch off and the rear radio switch on. It only pulls from the house system. I suspect they use a relay to do this. Relays can fail or stick closed...just throwin stuff out there.

When Randy at SMBW did my rig I did ask that the added amplifier be powered by the house system and had him add a switch to be able to disable it when needed. He could have powered the amplifier from the starting battery system. I did not want that. It's possible to wire additional equipment off the starting batteries.

Why don't you PM John Kalmbach on this site? He can give you the low down. Maybe you have a relay/isolator/separator problem or maybe the something was purposely wired to the starting system for some reason.
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Old 05-24-2010, 06:48 PM   #3
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Re: Why doesnt SMB isolate the radio/CD player?

I asked Peter to fix the "switch" because it still pulled from the starter and aux battery. I showed him that when I switched it to Aux battery, my starter battery went down .1 volt. He said that it still had to pull a little from the starter battery because it was connected to the ignition system so be sure not to forget to turn it off. Double talk if you ask me but he said it with a smile.

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Old 05-25-2010, 09:36 PM   #4
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Re: Why doesnt SMB isolate the radio/CD player?

The answer is the clock, display, and relay pull off the starting battery system when the radio switch is on, so if you leave it on for some reason there is a possibility that over a long storage, both battery banks could be drained. If the van is to be stored, the best choice is to isolate each battery system.

With the back radio switch on, most of the load is applied to the house battery but depending on the type of stereo used, I'm told it can pull up to about an amp off the starting batteries as well.

It's possible to rig the radio all on one or the other and even install a "kill" switch but you will loose all the pre-sets, audio settings, clock and even maybe have to re-sinc the phone's bluetooth each time the kill switch is opened. That would be a PITA. Most people drive their vans so the radio memory is wired directly to the starting system, but for those who camp and use the audio system, most of the load is shed to the house battery system when using the back radio switch so in the morning you can still start the vehicle. Anyway that's what I was told.
In most cases the SMB rear radio switch should run accessories such as additional amps or players but some load will always pull from the starting batteries as well.

Hope that helps.

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Old 05-26-2010, 06:55 AM   #5
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Re: Why doesnt SMB isolate the radio/CD player?

Dave pretty much nailed it, there are two power sources for the radio, one that goes to battery directly, and one that is turned on by they key. (they are both fused for 15 amps) The line that is turned on by the key is the one that sportsmobile adds their mod to. This apparently can be either a switch direct or a switch and a relay depending on build. This was a very working design years ago, the un-switched line direct to the staring battery traditionally only had to power memory circuits that drew low power ( preset, etc ) as Dave said. The problem is now many radios use that same circuit (it is fused for 15 amps) as a power source when the radio is turned on fully. It is the same as your TV drawing power while turned off, but it draws more when you actually turn it on. So now when you have your radio on while camped, you will be drawing more power directly from your starting batteries. I do not see any reason why you could not run the always on circuit directly to the house battery. Of course with all solutions there may be unintended consequences.

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