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Old 09-09-2011, 02:50 PM   #1
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Benefit of Battery Disconnect

If constantly plugged into shore power, is there any benefit to shutting off all 12v breakers, or using one of these battery disconnect switches?

Battery Disconnect Switch 511655-01 [511655-01] - $38.95 : Out-of-Doors Mart!, More Airstream Parts on-line than anyone!
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Old 09-09-2011, 03:15 PM   #2
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IMO, not much...
There is no reason to turn off the 12 volt devices is you are on shore power. If you have the original converter, you would benefit by shutting it off as they can overcharge your battery(s). A better solution would be to install a 3 stage converter that will be quiet and maintain you battery(s).
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Old 09-09-2011, 03:36 PM   #3
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if you have the original buzz box converter charger two things you might consider.

1. plugged in, the buzz box takes 55 to 85 watts doing absolutely nothing, which over time costs considerable money. I have measured this with a "Kill O Watt" meter. 55 watts x 730 hours per month = 40 kwh a month and at 11 cents a kwh that alone is $4.40 a month. $50 a year in electric power to do nothing but hum. The newer converter/chargers, such as the Progressive Dynamics PD 9200 series only take a watt or two siting idle.

2. There is evidence that using the original buzz box, constantly hooked to the battery, will cause the acid/water in the battery to "boil off" and eventually, if not replaced, ruin the battery. Although I have not had this happen personally, others report it as a problem.

Using the battery disconnect switch would prevent #2, but the ongoing cost from #1 would not be eliminated, with the original buzz box.

There are no benefits from shutting off the 12 volt breakers (but only fuses that I know of in your '79 Soverign) that I can think of.

To sum: original buzz box, shut it off. Modern 3 stage converter charger, leave it alone.


By the way, some leave their refrigerator on when not using the rigs. The type of refrigerator in RV's are very large energy users compared to the normal compressor type in your house. They probably average over 200 watts an hour of energy consumption, depending on outside temps. That can set you back over $190 a year at 11 cents a kwh.
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Old 09-09-2011, 05:19 PM   #4
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IMO, not much...
A better solution would be to install a 3 stage converter that will be quiet and maintain your battery(s).
The newest version of the Progressive Dynamics Intelli-Power 4600 series converters now has 4-stages: The Intelli-Power 4600 Series Upgrade or Replacement RV Converter/Charger with built-in Charge Wizard is the Brand of choice by leading RV manufacturers. I'm still using the OEM Magnetec 55-amp converter, which is doing fine for me at this point. I know I'll replace it with a Progressive Dynamic converter when/if I start having problems.
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Old 09-09-2011, 06:29 PM   #5
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The PD converter/charger 9200 series that has been around for a long time has the same 4 stages but they are called out differently. Boost, normal, storage and "equalize" was the old system, now it is boost, normal, storage and "desulfation". Same voltages and times on the equalize and desulfation from the specs I see. Ah, marketing. So, nothing has really been added, just stated differently.
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Old 09-09-2011, 07:42 PM   #6
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IMO, not much...
There is no reason to turn off the 12 volt devices is you are on shore power. If you have the original converter, you would benefit by shutting it off as they can overcharge your battery(s). A better solution would be to install a 3 stage converter that will be quiet and maintain you battery(s).
Yep....up-grade you won't regret it. Did this 3 years ago, great unit, great customer service!!!! Call Randy.

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Old 09-10-2011, 08:55 AM   #7
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Thanks for the replies anyone. I do have one of those intellipower converters, so I guess there are no concerns. My fuses have also been upgraded to breakers, which are located are now located in the upper left tambour cabinet in the front of the Airstream. In the past I've shut off the 12volt main switch, which can be hard to find if it is pitch black outside. So I'd thought about putting in one of those battery disconnects by the door, but since we are at a place with constant shore power (unless the shore power GFCI trips), I guess there is no need.

BTW, what is it that is different about the RV refrigerators that causes them to draw more juice? We have an older Norcold that was set-up for 110/12v, and I've had problems with the 110 as of a few months ago. I've unplugged it and have just been running it on 12volt and all seems to be fine. Cools real well.

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There are no benefits from shutting off the 12 volt breakers (but only fuses that I know of in your '79 Soverign) that I can think of.

To sum: original buzz box, shut it off. Modern 3 stage converter charger, leave it alone.


By the way, some leave their refrigerator on when not using the rigs. The type of refrigerator in RV's are very large energy users compared to the normal compressor type in your house. They probably average over 200 watts an hour of energy consumption, depending on outside temps. That can set you back over $190 a year at 11 cents a kwh.
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Old 09-11-2011, 11:32 AM   #8
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Originally Posted by KYAirstream View Post

BTW, what is it that is different about the RV refrigerators that causes them to draw more juice? We have an older Norcold that was set-up for 110/12v, and I've had problems with the 110 as of a few months ago. I've unplugged it and have just been running it on 12volt and all seems to be fine. Cools real well.
The RV refrigerator is thermally very different from a home refrigerator. It uses a heater to make cold (or a propane flame). It is kind of hard to explain how that happens, but the bottom line is that it is a lot less efficient in energy use. The heater in most RV refrigerators is in the range of 300 to 350 watts, and it runs a good deal of the time, making the refrigerator an energy hog vs. a home unit. (home units might average 100 watts).

That said, there are a very few 120/12 volt only refrigerators which actually are compressor units, like those in your home. The way you can tell is if they Hum when operating, and have NO way to run on propane. They are fairly unusual though. Since Norcold did make those at one time, yours could possibly be one of them, but I rather doubt it.

If your Norcold is a conventional RV type refrigerator, which has a propane connection, and you are using it on 12 volts, what you are doing is to substitue a 12 volt electric heater for the 120 volt one to operate it. Two things here: One is that the 12 volt heater is of lower wattage, and in very hot weather will not cool the refrigerator as well. If you are happy with it now you may not have that issue. Second thing, the 12 volts has to be supplied from somewhere, and that is your converter/charger. Since the 12 volt heater takes in the range of 240 watts that is 20 amps at 12 volts. So, your converter takes 120 volts, drops it to 12, and then the 20 amps or so feeds your refrigerator. Not easy on your converter/charger to do that. BTW, on battery power only (no hookups), your batteries will die very quickly, in a couple of hours.

In the rare case you have a Norcold compressor type refrigerator with no propane hookup, there is no problem running it on the 12 volts, the compressor load is probably 4 to 5 amps at 12 volts. If it is a conventional electric heater type refrigerator though, I would have it repaired so it runs on the 120 volt heater as designed.

Sorry to be so long winded, but the question is just not easy to cover in a few words. As an ex professor, we also tend to go on and on and on...
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Old 09-11-2011, 07:43 PM   #9
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Thanks a lot for the reply. I appreciate the length you went to explain the situation. My Norcold must have a compressor, because one thing that has bugged me about it is the vibrations it can cause to the surrounding cabinets. Also, I have heard what sounds like a regular compressor kicking on, so that must in fact be what it is. I guess given the 110 isn't working right, it's a good thing that it is a 12v compressor fridge. Last time I was down it was about 98 degrees out and the thing cooled down fast and maintained temp without any problem. It's an old fridge, but works fine. Just wish it didn't make so much noise...
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Old 09-11-2011, 08:02 PM   #10
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That's odd, my compressor refrigerator automatically switches from 12V to 110V, if available, it actually runs on 12V with a converter to reduce the voltage to 12V. Look in the back, through the inspection hatch on the outside and see if there is propane.

Bill

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Originally Posted by KYAirstream View Post
Thanks a lot for the reply. I appreciate the length you went to explain the situation. My Norcold must have a compressor, because one thing that has bugged me about it is the vibrations it can cause to the surrounding cabinets. Also, I have heard what sounds like a regular compressor kicking on, so that must in fact be what it is. I guess given the 110 isn't working right, it's a good thing that it is a 12v compressor fridge. Last time I was down it was about 98 degrees out and the thing cooled down fast and maintained temp without any problem. It's an old fridge, but works fine. Just wish it didn't make so much noise...
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Old 09-11-2011, 08:11 PM   #11
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http://www.bdub.net/Refrigeration_in_the_GMC.pdf

That link will tell you more than you really care to know about your Norcold refrigerator. I expect some simple issue with the original inverter/transformer system in your Norcold which is why it will not run on 120 volts. Usually it is the other way around, fine on 120, nothing on 12V. The noise may be just hard rubber in the compressor mounting supports, or something touching the compressor and transmitting the vibrations. It is called a swing motor compressor, and operates somewhat like a slinkey, at a resonant frequency so they do make noise. The original chopper inverter in the power system also provided a crude approximation of 60 hz, and made the noise worse.

It is unusual to have one in an Airstream, someone must have replaced the original propane refrigerator at some point, but still long ago. The swing motor Norcold was the standard refrigerator in the GMC motorhomes of 1973 to 1978. I had one, and learned about it and wrote the article above.
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Old 09-11-2011, 08:40 PM   #12
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Definitely no propane - this is a 12v/110v unit.

Thanks for the article. I will definitely read that to learn more about my fridge.
I probably should have given a little more background on the unit. It was not in the Airstream when I purchased it. The original unit didn't work, so my father installed a unit that he had from a prior motorhome. Actually, he had given it to someone else and it had remained sitting in an old barn for years. Since this person had no plans for it, I was able to use it. Fortunately, it still worked, and worked fine for several months in my Airstream, but just recently started tripping the shore power GFCI. I realized that even with the fridge in the off position, the GFCI would trip the second the fridge was plugged in. Consequently, I've just left it unplugged for now and it has worked fine. Any idea what might be going on with it?
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Old 09-12-2011, 11:28 AM   #13
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GFIC issues can be difficult to diagnose, especially over distance via the forum. Somehow current of more than 5 mA is traveling from the hot line to ground, without going through the neutral. One thing I would try first is to run an extension cord directly to the refrigerator, and plug it into a known good GFIC in the house and see if it trips the GFIC. If it does not, you may have a bad GFIC serving the trailer itself. Also, the fault current can be distributed, and a little leak here and there can all add up to the 5 mA needed to trip out the GFIC. When you plug the refrigerator in, it may just push things over the top.

Those are my best guesses. Let us know what happens.
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Old 09-12-2011, 11:59 AM   #14
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IMO, not much...
There is no reason to turn off the 12 volt devices is you are on shore power. If you have the original converter, you would benefit by shutting it off as they can overcharge your battery(s). A better solution would be to install a 3 stage converter that will be quiet and maintain you battery(s).
My 2005 came with a Paralax Converter - I believe it has several stages of charging, but no doubt not as sophisticated as some.

Of course if I ever need to replace it I will go with one of the recommended units.

In the meanwhile - I'm not sure if it is really necessary or not - but I have replaced the positive battery connectors on both batteries with teh type of connector having a knob that allows you to break teh connection with a turn or so of the knob. if we are camped and plugged in to 110v for more than a couple of days, I will disconnect the batteries using these quick disconnects, and then reconnect them when we are ready to hook up and leave.

Perhaps the built in battery switch would do the same thing, I didn't check that so I'm not sure. I don't recall if I looked at teh wiring diagram or just assumed that it would should off all 12v to the trailer which would not have been what I wanted to do of course.

Brian.
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