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Old 08-29-2009, 05:13 PM   #1
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Radio Switch Drains Batteries?

I had two battery drain problems on my last trip, and they both seem to have a common element. I have a single 4D (I have 2 but disconnected the old one), the whole trip was in hot weather and the fridge ran a LOT... it always runs a lot. The only thing really different from other trips is I almost never use my radio switch in the house, to run the radio off the house battery.

The first problem was after driving for 3 days I spent the day loafing and reading a book. Between a small 12v fan, the fantastic fan and fridge, a few hours should not have drained the house battery. However I left the radio switch on, since I wasn't moving around so well, so I could turn the radio on and off without moving or using the keys. After 4 or 5 hours, mostly with the radio off (like maybe an hour of radio off and on) the low battery alarm on my CO monitor starts going off, and when I looked at the panel I was down to 9.44 volts. I turned everything but the fridge off (which includes the radio switch) and ran the van for an hour.

The next morning I had plenty of voltage, so I put the radio switch back on and headed out. I figured it would be nice to just leave the radio on as I hobbled around from one side of the van to the other, but that led to my second problem. About 5 hours into my drive the low battery monitor starts going off again. I didn't want to stop so I kept driving, and after a while I found someone I could drive up to and ask for help (e.g. read the panel so I didn't have to get out). He was having problems of his own (another story) but relayed that it was 8.40 by that time.

After another leg of driving I got out and overrode the separator (BlueSea not a PowerSure) and when the batteries locked the panel jumped to 12.46 volts with the van off. I probably should have done it with the van running, but it started anyway and charged the battery. After a few more hours of driving I had plenty of power for the night, and when I stopped I turned the radio switch off again and also put the separator back on auto.

The next two days were spent driving, exactly the same as during the second battery drain, except without the radio switch being on. Everything was normal, the batteries charged and I had plenty of power all around.

I remember discussions of the van radio switch being used to keep the clock on in the dash, and then having problems with battery drain. Because of this I have come to two tentative conclusions:

1. The van radio switch (or the radio itself) somehow eats a fair amount of power, whether on or off.
2. The van radio switch somehow keeps my separator from automatically engaging while driving, keeping the house battery from receiving a charge.
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Old 08-30-2009, 12:40 PM   #2
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Re: Radio Switch Drains Batteries?

I guess I would have to go with conclusion #2. I don't know much about the Bluesea separator but from what I can tell if the RelayOn (manual) switch was below a volt, then it would remain separated. If it was floating it would go into auto mode, and above 9.0 volt it would connect together. That said, I don't see where switching the radio switch would cause it to go below a volt.
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Old 09-04-2009, 10:50 PM   #3
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Re: Radio Switch Drains Batteries?

I had a similar problem, still unclear what happened just know that I used the radio switch thinking that it would drain my aux. batteries (4D) but could not get the van started the next day. actually had to switch a battery out to get it stated???? puzzling the only thing that I might have done, but still denying it was leaving a door ajar with interior light on. But when I blamed Captain Morgan the next day he denied it. "Thats my story and I'm stickin to it"
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Old 11-20-2009, 11:50 AM   #4
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Re: Radio Switch Drains Batteries?

yeah a similar mystery has had me combing the forum. It's common for me to not drive my 04 RB-350 Diesel SB for a week at a time. When I was out working on it on a Sunday I turned on the cabin radio switch. I left the switch on but turn off the radio. Five days later I have zero van power even though the cabin battery is relavitvely full. After trial and error and much cursing, I found that this DOES NOT happen if the radio switch is left on the van battery option,,,and of course the ignition is off.

So there is something about the radio wiring that draws down even two large (new) batteries in a few days. Hard to believe, but that's the only conclusion I could come to after checking other variables.

My next step is to check out the separator.
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Old 11-20-2009, 06:46 PM   #5
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Re: Radio Switch Drains Batteries?

We talked about the Radio Switch quite a bit several years ago on the Yahoo list but the search engine on the Yahoo site isn't showing more than 10 messages. Basically, the Radio Switch should be turned off at all times that you aren't listening to the van radio/CD system. What it basically does is to switch the energy draw of the radio system from the van starter battery to the house battery. But to do that apparently (as I recall) requires a relay which is powered by the starter battery ALL of the time that the Radio Switch is turned on, whether the radio is turned on or not. The solution is 1) if not already installed, add a red LED to indicate when the Radio Switch is turned on; and 2) never turn off the radio after listening to it with the engine turned off....that is a good way to forget and leave the Radio Switch on all of the time. If you want to turn off the radio while parked, turn off the Radio Switch instead.

It would seem that a system could be designed which doesn't require a relay powered by the starter battery. But maybe the problem is in how the radio can be operated both while a van is running and while the ignition is in the Acc position. If one listens to the radio a lot while camping, maybe the power to the radio could be intercepted and run through a DPST switch mounted in the dash which would eliminate the relay...
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Old 11-20-2009, 07:38 PM   #6
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Re: Radio Switch Drains Batteries?

I check again and this is totally counterintuitive. My SMB switch has two positions "radio Van battery" and "radio extra battery" If I leave it on "radio extra battery" it completely drains the two starter batteries even when it appears to be off just sitting in the driveway. If I leave it on "radio van battery" it's fine and of course plays when I start the engine or turn the key to AC.

Did something get cross wired or is this just a quirk of SMB?
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Old 11-22-2009, 01:26 AM   #7
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Re: Radio Switch Drains Batteries?

The factory Ford radio has two power sources going to it. One is controlled by the position of the ignition switch, the other is a constant source from the starting batteries.

The SMB radio switch is connected to the wire from the ignition switch using a SPDT switch. This switch allows the radio to operate either from the starting battery or from the house battery, depending on how it is set.

Once the radio has power to operate, whether it is turned "on" or not, a couple things happen. First, the clock display will come on. Second, the constant power source from the starting batteries energizes the amplifier built into the radio, which then draws about 2 amps. This constant 2 amp draw will drain the starting batteries as being experienced.

The LED light at the switch is a good option that became standard on SMB's. You can also rely on the radio clock display, if the display is "on" with the ignition off, your starting batteries are being discharged.

I hope this helps!

John K.
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Old 11-22-2009, 08:41 AM   #8
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Re: Radio Switch Drains Batteries?

Thanks John --

I guess I will just have to remember or get some rewiring done. I'm not the first owner and the previous owner installed a fancy touch screen radio/DVD player/XM/iPod and all that and I had wondered too if something got wired wrong on that. Sound like not.
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Old 11-26-2009, 03:08 PM   #9
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Re: Radio Switch Drains Batteries?

John - some questions please:
Quote:
Originally Posted by John Kalmbach
The factory Ford radio has two power sources going to it. One is controlled by the position of the ignition switch, the other is a constant source from the starting batteries.

The SMB radio switch is connected to the wire from the ignition switch using a SPDT switch. This switch allows the radio to operate either from the starting battery or from the house battery, depending on how it is set.

Once the radio has power to operate, whether it is turned "on" or not, a couple things happen. First, the clock display will come on. Second, the constant power source from the starting batteries energizes the amplifier built into the radio, which then draws about 2 amps. This constant 2 amp draw will drain the starting batteries as being experienced.
But I think you are saying that effectively the radio is drawing power all the time. Its just a question of whether it comes from the Starter battery or the House one?

The LED light at the switch is a good option that became standard on SMB's. You can also rely on the radio clock display, if the display is "on" with the ignition off, your starting batteries are being discharged.
I do not have the stock radio any longer and the head unit has no display. i cannot get it to operate without the ignition switch when the radio switch is set to Van. When its set to House it will start operating without being switched at the radio. This seems to support my earlier statement that its drawing power all the time for its clock and memory. Its just a question of which battery set it draws from.


I hope this helps!

John K.
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Old 11-28-2009, 10:16 PM   #10
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Re: Radio Switch Drains Batteries?

The radio memory circuit constantly uses very little power from the starting battery. Once the ignition is "on", or the radio switch is set to "extra" battery, the constant power circuit then draws additional power from the starting battery for the amplifier. The switchable power circuit draws power from either the starting battery or the house battery to power the clock display and other radio functions.

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