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Old 04-29-2008, 05:40 PM   #1
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1966 17' Caravel
Tualatin , Oregon
Join Date: Apr 2007
Posts: 20
Humming Transformer on 1966 Caravel


I have a transformer that's humming. Originally I thought it was a bad univolt but after reading through the treads, I have come to realize that the '66 Caravel has a transformer that coverts the 110AC to 19 and 12 VAC. The coverted AC goes to the univolt which some how converts the 12 and 19 VAC to DC feeding the lights, pump, and fan (see below for wiring diagram provided by azflycaster).

I just came from the local RV supply store and they have never seen this setup before. They said usually the 110V AC comes in and goes straight to a coverter or univolt. In the '66 Caravel case, I have the 110 AC going to the transformer, then to the univolt.

I'm not sure what to do at this point, I am thinking about pulling the transformer, use the 110V feed to feed an intellipower 9100, and hook up the 19VAC and 12VAC as the intellipower DC output. Will this work?

Thank you in advance for any responses, Cosmo9404

Usefull thread from my form research:

Wiring diagram provided by azflycaster

I have attached a picture of:
1. The Caravel transformer with the 110V input and the two outputs (12VAC and 19VAC)
2. A picture of the front face of the univolt.
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Old 04-29-2008, 05:50 PM   #2
Well Preserved

1993 21' Sovereign
Colfax , North Carolina
Join Date: Jun 2003
Posts: 20,355
How many fans do you have? What water pump do you currently have?
If 'twere me, I'd replace the 19 volt a.c. fans and water pump motor with 12 volt d.c. models.
Then I'd put a modern converter in place of the multivoltage unit you have now. One less "different" thing to worry about, and if something happens to the updated 12 volt d.c. stuff, you can go get replacement parts and supplies from any RV dealer.
If you are planning on keeping your little trailer "original", that is another can of squash.

Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
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Old 04-29-2008, 06:03 PM   #3
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1966 17' Caravel
Tualatin , Oregon
Join Date: Apr 2007
Posts: 20
My pump is a 12V DC pump so it can only benefit from the upgrade. The only fan that I have is a fan in the stove vent but it's in sorry shape so I can upgrad to a 12V DC.

Is there a way to just replace the transformer with a new intellipower unit or do I need to install an intellipower unit and a new fuse box?
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Old 04-29-2008, 06:43 PM   #4
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Valley View , Texas
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Replace it!

I had the same thing. Replaced it with a WEFCO and never looked back. If you want another one like the one you have I can send you my old one.
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Old 04-29-2008, 08:14 PM   #5
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1966 17' Caravel
Tualatin , Oregon
Join Date: Apr 2007
Posts: 20
Thanks for the replies folks. When you upgraded to the WFCO converter, how did you wire it into place? Currently, the transformer has a 110VAC input which I can wire into a new converter. The output is where I'm lost. Do I use the existing four 12 gauge wires (2 positive and 2 negative) that are currently the transfromer 12VAC and 19VAC outputs and connect them to the new converter output?
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Old 05-02-2008, 10:11 AM   #6
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1966 17' Caravel
Tualatin , Oregon
Join Date: Apr 2007
Posts: 20
Based on what I read, the helpful replies/emails, and the wiring diagram, I decided to do the following:

1. I disconnected the 110V going to the transformer and put wiring nuts on the hot and neutral wire (See pic 1)
2. I installed the intellipower converter (with the charge wizard) next to the battery. I wired the intellipower unit directly to the battery.

Based on the wiring diagram, I am cutting out the 19 and 12V AC power going to the lights, pump, and fans when the univolt is switched to "City Power." Now I keep the switch on "Battery Power." When I am unplugged from shore power, I have use of all DC components. When I am plugged into shore power, I have 110VAC at my outlets, 110VAC going to the intellipower then safely charging my battery, DC voltage from my battery feeding the DC trailer componets.

No more humming from the transformer, my battery isnt getting fried anymore with the new intellipower converter and charge wizard, and I didn't have to do much rewiring.
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Old 05-02-2008, 11:02 AM   #7
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Cambridge , Ohio
Join Date: Feb 2008
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Wink humming transformer

I once had a converter/ trans unit in an old SOB that always hummed. I tried to find the reason, not finding any bad connections, wrong voltages etc. Finally after a lot of head banging I was at the end of my rope and said to this inanimate object, "why in the world are you humming like that?". A moment later I heard......."'cause I don't know the words"

Sorry, I couldn't resist

Seriously tho, some transformers/ motors do have a hum to them, especially lower quality units. Sometimes the coil's laminations are somewhat loose causing this buzzing. I've got a cheap ceiling fan that really hums. If a unit had "always been that way" I wouldn't get too excited if all connections/ volts were acceptable. But if the device suffers from acute humming then I would be more concerned. That , and if it really annoyed me.

I don't have an Airstream yet (someday....) Right now I getting ready to start restoring a '49 Spartan Royal Mansion though. I do recall as a kid my parents giggling all the time about an Airstream camping neighbor cursing at his wife about the "@#%& Univolt" in their trailer. Every time they saw an Airstream they brought this up and had a giggle. We had a '67 Globestar SOB that was wired with two separate systems, 12v and 110v, and simply used a battery charger to keep the batt. up....Low tech but worked pretty reliably though.


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