Power Supply

[IowaCamper]

Hello:
First time posting in a while, but have been here reading a lot.
Question: I am in the process of De-winterizing the old Travel Trailer.
I have it plugged into the house at the present time checking everything out
and have noticed a pretty loud humming noise coming from the power supply.
I know they make a noise but this seems louder than I have ever noticed before.

Any ideals on what would be causing this?????

Thanks in advance for your help.

John

 

[John From Detroit]

There are two things that cause power supplies to "HUMM"

Loose laminations on the transformer, normally not an issue if they were not loose last year but who knows

Short curcuit... A battery that is completly dead, or shorted, would account tihs

Trouble shoot procedure... Disconnect 12 volt lead from the converter (what it's called) and see if it quiets down

If it does not, replace, if it does, well, disconnect the batteries and re-connect converter.  Quite, have batteries looked at (They may just need charging)
and act accordingly.  If batteries are dead and converter still is too loud with them disconnected,  look for short elsewhere

 

[IowaCamper]

Thanks for your suggestions, John In Detroit . I unhooked the lead to the batteries it did not make a difference. The batteries are fully charged hooked everything back up and still has the loud "HUMM". Where does one start in trying to find a short?  I don't know much about electricity so I'll need to know what type of meter to use and how.

I know, I'm not asking for much lol .    I might be further ahead to just go buy a new converter.

Thanks again,
John

 

[Gary RV_Wizard]

You didn't mention the year & model of Rv or the brand of converter, but it sounds like it might be one of the older Magnatechs. They are quite noisy and seem to get noisier with age.  Models from the late 90's and earlier are pretty crummy chargers too, so replacing it might be a good idea anyway. I recommend either Progressive Dynamics or Iota, with the Smart Charger feature.

But I would usually suspect your batteries are causing this sort of problem. An increased hum generally means the converter/charger is putting out more current (amps).  That can happen even if a battery appears fully charged via a voltage check. A bad cell will still draw power from the charger. Did you remove all the cables directly from the positive post of the battery when you tested that?  You may have a separate charge line, different from the big cable that pulls power out of the battery(s).

If you aren't a skilled electrician, I wouldn't bother looking for internal shorts in a converter. If you don't find a loose mounting screw or similar mechanical problem that lets it vibrate, I wouldn't bother removing the cover. There is probably a sticker that says no user serviceable parts on it anyway.  That doesn't mean John in Detroit couldn't fix it, but it does mean some fairly arcane knowledge is required.

 

[John From Detroit]

Thanks for your suggestions, John In Detroit . I unhooked the lead to the batteries it did not make a difference. The batteries are fully charged hooked everything back up and still has the loud "HUMM". Where does one start in trying to find a short?  I don't know much about electricity so I'll need to know what type of meter to use and how.

Trust me, We don't mind answering questions,  Heck, we often learn as much as you do from your questions.

You have only done half the test,  The other half is disconnect the 12vdc lines from the CONVERTER and see if the noise goes away....  This is also where you start to test for shorth, Here is how.


Unhook batteries, Unhook JUST the positive (normally red) wire from the converter, TURN OFF everything and I mean everything, in the trailer.  Plug in converter. If the humm is still there..  Replace converter to quite it down
If you are using flooded wet cells, a Progressive Dynamics Intella-charger with charge wizard is hard to beat

Of course if you are planing on installing an inverter to power your 120Volt toys from the 12 volt batteries.  Well, the better ones often have chargers built in.  (I kind of like my xantrex)

Now, for the short test,  As I said TURN OFF EVERYTHIGN, PULL FUSES if you have to (remember where to put them back please, WRITE it down)

If you have a 12 VOLT drop lamp it's easier but any 12 volt lamp with leads will work,  The tubular ones often used for dome lights in cars (with wires on both ends) are often best , with this type of bulb you need two jumpers (Wires with alagator clips on both ends)

Test lamp method,  one end of one jumper to one end of the lamp, and one end of the other jumper to the other end of the lamp.... 12 volt drop cord method skip this step

WITH CONVERTER UNPLUGGED!
Hook one lead (either drop cord lead or test lamp lead) to the 12 volt wire disconnected from the converter,  Hook the other lead to the converter terminal from which you disconnected the 12 volt lead.  Plug in converter

Does lamp light,,  IF NO, then no short. Start replacing fuses one at a time.

When lamp lights suspect that circuit, however remove it's fuse and continue replacing untill all fuses have been replaced (Save the ones that lit the lamp)

Now, make sure whatever is down stream from those fuses is truly turned off

 

[Tom]

...we often learn as much as you do from your questions.

Make that a capital WE.

 

[IowaCamper]

Thank you so much for the step by step directions. I will print this out and Give it a shot this coming weekend. Again thank you for the help.

John