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Old 11-19-2012, 04:06 PM   #1
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1989 32' Excella
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Radio hum

I managed to get the radio in my 89 Excella working. It's just a car stereo that isn't stock. The past owner said he installed it but it never worked. So while looking at it I discovered some kind of Kentucky fried in line noise suppressor [12 v] and a blown fuse. The radio works now but I'm getting some pretty bad AC hum from the trailers transformer [original]. Just need to get rid of the hum.
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Old 11-19-2012, 04:30 PM   #2
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Sounds like a crossed wire, check the ground wire. Remember, on a car radio, the black wire is usually the ground wire and in the AS (or any RV) the black is the hot wire.
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Old 11-19-2012, 06:01 PM   #3
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Turn off the Univolt and see if the hum goes away. Of course you will need a battery in the trailer.
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Old 11-19-2012, 07:06 PM   #4
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If it is 60 cycle hum it is usually caused by poor quality 12 VC power ripple. If you have a DVM turn it to ac volts and measure the ripple. You might be able to reinstall a filter to prevent the ripple getting to the radio. There can also be a problem that the radio or the power supply is not properly grounded to the trailer chassis. lastly you could be getting airborne hum because you do not have a proper outdoor antenna or it improperly shielded as it comes inside the trailer.
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Old 11-19-2012, 08:35 PM   #5
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Radio Shack has some dc hum eliminators. You put it in line with the power source. That's a fancy name for a filter. I put one on my subwoofer in my 06 Safari. That's not to say there are other problems as noted above but the Shack has a fix for hummmmm.
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Old 11-20-2012, 09:57 AM   #6
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I've been to the local Radio Shack here in Montrose Colorado and was disappointed. But the stores are all different. This one seems like more of a cell phone store. I think the DC isn't clean because the hum sounds like 60 cycle. The noise is not there when the AC is unplugged from the trailer. The radio sounds good even with the heater motor running etc.So it's only when the Univolt is working that the dirty DC is giving it a hard time. I thought a inline filter would be an easy thing to find off the shelf. The old filter was still there when I was working on the trailer. It was fried and melted pretty bad. The fuse was blown also. This radio is a new one that the past owner installed with the melted filter and blown fuse. He said the new radio never worked [wonder why ?]. I hope that all I need now is a new filter to smooth out the dirty DC hum from the Univolt. The Univolt does make a slight bit of noise but it's not bad and seems to be working well. The radio noise is just bad enough that it's irritating to listen to.
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Old 11-20-2012, 12:16 PM   #7
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AC Hum in radio

Hello Mark Lee. If you have the same converter in your 89 excella as I have in my 88 excella here is the fix. I put a .47uf 200V cap in parallel with the diodes in the converter. That cleaned up the hum completely,
There are 2 diodes in the converter so 2 caps are needed, one in parallel with each diode.
Happy camping nm1oqrz
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Old 11-20-2012, 03:43 PM   #8
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Mark, if you get over to Grand Junction there's a US Tech store on Patterson just east of Barnes and Noble. They should have what you need.

Gene
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Old 11-22-2012, 06:02 PM   #9
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I did finally find a filter here in Montrose Colorado at a custom car shop. It helped some but there is still noise. I'm very interested in the .47uf 200v caps being installed in the Univolt. I don't have any idea of what your talking about but I'll soon be in AZ and a friend down there will. Thanks guys.
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Old 11-22-2012, 11:31 PM   #10
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Mark,

Do you have a functioning battery in the trailer?
In an RV 12 volt systems, the battery does a share of the filtering.

Also I am guessing you have an older converter. A new converter with up to date technology will improve a lot of things besides the hum problem.
Those things include longer battery life as well as better performance of 12 volt appliances.

If you intend to keep the trailer for more than a year or two, it would be worth the investment.

Ken
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Old 11-24-2012, 07:10 AM   #11
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I have two new batteries and I think it is the original 1989 converter. If I'm drawing much power on the 12v the hum becomes much more noticeable. I'm not running anything that should cause a hum in the trailer,just basic 12v regular bulb lights etc. The lights don't seem to cause any problems till the Univolt starts recharging the batteries. Like right now. I got up a few min ago and had the radio on AM. Just a very slight hum and turned on some lights. Now the hum is getting worse after there has been a draw on the batteries with lights and I turned the heater up a bit. I do intend on keeping this trailer for many years. Ken when you say"New Converter"are you talking new Univolt or another brand?
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Old 11-24-2012, 08:58 AM   #12
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I just bought a Progressive Dynamics 9245 on eBay for $120.00 including shipping.
I'd bet money the old Univolt is the problem. Do you have an external antenna?
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Old 11-24-2012, 10:19 AM   #13
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Quote:
Originally Posted by Mark Lee View Post
I have two new batteries and I think it is the original 1989 converter. If I'm drawing much power on the 12v the hum becomes much more noticeable. I'm not running anything that should cause a hum in the trailer,just basic 12v regular bulb lights etc. The lights don't seem to cause any problems till the Univolt starts recharging the batteries. Like right now. I got up a few min ago and had the radio on AM. Just a very slight hum and turned on some lights. Now the hum is getting worse after there has been a draw on the batteries with lights and I turned the heater up a bit. I do intend on keeping this trailer for many years. Ken when you say"New Converter"are you talking new Univolt or another brand?
It sounds to me very much like the converter is not filtering enough of the AC that is present on the DC output. The AC will always be there to some extent. However, there is supposed to be circuitry in a RV converter that will shunt nearly all of the AC component to ground so it does not appear on the DC output. My assumption is that some component or components in the converter have gone bad, and too much of the AC is present on the DC output. It is my opinion that is is not worth the trouble to repair the older converter. This is based on the fact the newer converters are much better designed to eliminate both noise problems and battery charging problems. A filter can be added to the power leads to the radio, but that is only a band aid solution. It will not clean up the power to the other 12 volt appliances.

Unfortunately, unless they have changed very recently, Airstream installs the very minimum quality converter that they can get away with in the new trailers. These converters will basically overcharge and ruin a battery if left plugged into AC with minimal load for anymore than a few weeks at a time. After market converters are available that are 3 or 4 stage chargers rather than the 2 stage charger installed in Airstreams. These converters will protect and condition the batteries to the point that the trailer can be left over the winter plugged into shore power.

I feel strongly enough about this problem, that I replaced the converter in my trailer before it was a year old. I installed a converter from this company:

IOTA Engineering DLS Series AC/DC Power Converters and Battery Chargers for 12VDC Systems

However it is not the only company making quality converters. If you decided you want to do this, there are many threads here discussing the options.

Ken
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Old 11-24-2012, 12:00 PM   #14
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Ken has it right. We also put in an Iota converter and also replaced the old batteries with AGM's.

The Univolt is old technology and sounds like it's lifespan is coming to an end, so euthanasia is a reasonable approach. Even if the hum is still there after a new converter is installed, it sounds like time to replace the converter. Your batteries will be much happier.

Gene
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