First time posting but have been reading alot of great information.
I believe I am having a problem with my converter. (TU-775-2) Plugged into shore power converter is buzzing, then interior lights stop working and I go out to check converter and it is no longer buzzing. It is located in an outside compartment, most rear on driver side. This compartment is enclosed except for 2 grate type sections that I assume allow air to circulate, looking in the compartment converter is mounted to left wall. Right wall has mesh or grating section and straight back is the other compartment wall that has the mesh.
I was looking at replacing the converter, and seems like PD9280 is the one many recommend here. My problem is the PD9280 says it is not sealed for moisture, I worry about placing this in the "original" location and killing it when moisture gets to it. Any thoughts?

I had the same buzz-box that you refer-to in this post.

Was also mounted in the engine compartment and began to fail.

I replaced mine with a PD9280 and mounted it under the bed (in an interior space), which was located within a foot of the TU-775-2 had been mounted.

Installed an outlet box for a 120vac power supply and drilled thru the bulkhead to make DC connections in relatively the same location of the previous converter/charger.

Was a fairly easy job, but really depends on the configuration of your coach, adjacent to the engine compartment.

Thank You for the reply. I will look into the option of moving it inside.

Hey bbbv4711...

Were you able to determine a way of installing a new converter???

Death to the old BUZZ-BOX!

Mine is in same compartment as the generator. Replaced last year and seem to work well in that area.

Not that a new charger system wouldn't be nice. the TU-775 converter will thermal off if air flow is blocked or the fan is not running. The fan in our wasn't running. I had a small fan that I ducted into it. Has been working fine since. Our is mounted under rear closet floor inside coach.

quote:

Originally posted by ~Mac~:
Hey bbbv4711...

Were you able to determine a way of installing a new converter???

Death to the old BUZZ-BOX!

Have not actually looked at it have been busy the last week, but thinking I could mount in closet that would put right above current location.

quote:

Originally posted by Sloop John B:
Mine is in same compartment as the generator. Replaced last year and seem to work well in that area.

Mine is the compartment next to the generator, good to hear yours is working well. I was worried that some of the units I was looking at were not sealed like the TU-775. But then I know nothing about any of them and was assuming.

quote:

Originally posted by Doorman:
Not that a new charger system wouldn't be nice. the TU-775 converter will thermal off if air flow is blocked or the fan is not running. The fan in our wasn't running. I had a small fan that I ducted into it. Has been working fine since. Our is mounted under rear closet floor inside coach.

I have not even checked the fan. I should look into that, but I am thinking I have another problem. I use to have 12v when not hooked to shore power or generator, but do not now that I have had the converter problem. The only time I have 12v is when hooked to shore power until the TU-775 kicks off then nothing until it comes back on. Batteries charged and no 12v unless hooked to shore or generator.

Sounds like a problem which totally involves the potential slow death of your converter/charger.

Search the archives regarding these issues.

Plenty of information out there.

Rusty had been quite helpful when I was experiencing problems of this nature.

It appears the converter is a dual-output, common in coaches of that vintage. Contemporary converters are single-output.

Dual-output converters have a house 12VDC output and a second to charge the battery. A cutover relay disconnects the house battery from the house 12VDC when shore power is connected; house 12VDC is supplied by the converter.

Single-output converters are connected solely to the house battery, and the house battery (now kept charged by the converter) supplies house 12VDC directly at all times.

Your symptoms are that of a failed cutover relay in the converter, in that it isn't transferring house 12VDC supply to the converter but is disconnecting the battery. The buzzing you hear could be relay chatter.

Should you replace the converter with a single-output (dual-output units are pretty much obsolete), you'll have to bridge the two original output connections from the converter.

This guy always knows exactly what to say...

I kinda knew this stuff, but was in no way able to explain-it as Rusty can.

I would concur that this is what is wrong with your charger/converter and this is nearly exactly what Rusty posted, regarding my problem, about 7-8 years ago.

The new converter/charger is a minimal investment considering what it does.

You will be happy with the decision to replace the dying buzz-box...

I have finally started this little project.....guess I was waiting for it to get too hot to do anything before tackling this.
I pulled the TU-775-2 out, the problem I am having is there were 2 wires in the compartment that were hooked to the converter. They appear to run out of the compartment and in to the generator compartment. There is a RED and a GREEN. The converter has 2 wires coming out of the box a Red that was connected to the RED in the compartment and a White that was connected to the GREEN, this connection also had a green wire from the lug on the side of the box.
I was under the impression this buzz box was dual output, do they typically separate out somewhere else?

That's an old Magnetek, and dual-output, IIRC.

It's time to replace the converter (it's 29 years old) and to trace the former output wires. It's possible that the PO wired the converter's house output to the batteries; this is bad, because there is no protection for the batteries like there is on the battery charger output.

The wiring diagram I have on my Triad Converter shows the red going to a 50a breaker or fuse and the 12v breaker box. The output of the breaker to the (+) house batteries and generator. The White or Black to the (-) house batteries. From you description of the problem I would say you have a open or blown fuse or bad breaker. Ours has a 50 amp breaker. Make sure the (-) has a good ground and the house batteries have a good ground. Our model is a TU 470-2t 70a charger. Your TU-775-2 might be different.

Good morning, bbbv4711, Rusty, and Doorman;

While the topic of replacing a 29 year old "RV 12 VDC power converter" has come up, there is another consideration for thought on why you should do this:

There is a real reason why those old "power converters" were referred to as "buzz boxes." Often they did buzz in synchrony with the 120 VAC powerline feeding them. The old "power converters" are merely the first half of a power supply with no filtering nor regulation. That buzzing is probably loose laminations in the transformer core. While it is annoying, it may not indicate the eminent death of the "power converter."

However, that point about " . . . no filtering nor regulation" is still there. Changing to one of the modern real full power supply type 12 VDC electrical power units will make a real difference in the quality of the 12 VDC electrical system in the coach. Those old "buzz boxes," such as my original B-W 6345 (so-called Magnetek type) was actually putting out only a full wave rectified AC sine wave on the "RV 12 VDC electrical system" in the coach. They could legally say that it was "12 VDC" (sort of) because the average voltage was about 13 VDC, but the peak voltage on the top of the pulsating DC waveform was actually about 18 volts.

When I started the conversion from the old incandescent light bulbs to the LED replacement lighting, that 18 VDC peak was destroying a lot of the LED replacements that I was installing. When I told the LED lighting vendor what was happening, he flat stated that I was running them on too high a voltage. Well, he was right. However, I also had checked the voltage on the coach 12 VDC electrical circuit, and the DVM I had used did say that it was about 13.0 VDC, so I had thought that I was OK. When I looked at the testing technique recommended for checking that circuit or the output of the "RV 12 VDC power converter," I noted that they did say to use only "a true RMS reading DVM." Then I realized what was wrong, and how I needed to check it to confirm that fact. Yes, when I put the Tektronix 475 oscilloscope on that circuit, it was very plainly obvious that it is a pulsating DC waveform from a full wave rectified AC power supply transformer secondary, and it does have the predictable 18 VDC or so peak value on the tops of that waveform.

This is why I replaced the B-W 6345 in my motor home with a Progressive Dynamics PD-4655V true 13.8 VDC power supply with "Smart Charging" regulation to allow direct connection to and keeping the coach batteries very happy. When the batteries are fully charged, the voltage drops back to a "float" charge level of 13.2 VDC to absolutely minimize gassing and loss of water in the battery electrolyte. And it bolted right into the same space and wired up with the same wires as the old B-W 6345 in my motor home.

Another factor is that the straight line smooth voltage level, just like with a battery, is much kinder to all the electronics we commonly see in our motor homes now. Not only LED lighting, but also the LCD flat screen TV, the GPS navigation systems, the "surround sound" music systems, the cellular telephones, the computers, and all the other electronics we have in our motor homes today.

In quick summary, yes, replacing the old "buzz box" with one of the new power supply type devices really is a good idea.

And, while it may sound funny to suggest that a 55 Ampere rated device can be used in place of the TU-775-2, may I also point out that Doorman has a 50 Ampere rated circuit breaker feeding what is probably a 6 AWG wire going to the coach 12 VDC electrical circuit. The power supply can be bigger and rated for more current, just as a battery can be bigger. The critical point is that the voltage must be the same. The load will determine the current drawn, and the wiring and the "Over Current Protection Device" (the circuit breaker or fuse) will be sized to carry that load current.

Go ahead and enjoy a quieter 12 VDC system. You might also notice that your music system no longer has a low level hum or buzz in it when you are plugged into "shore power."

Enjoy;

Ralph
Latté Land, Washington

I agree that the older units can still operate (the buzzing laminations in the transformer can be tamed by soaking in thin cyanoacrylate [super] glue).

But replacement of the elderly unit in the driveway with a unit from a discount house is preferable to waiting for failure, which, according to the Turd Fairy, will occur at an inopportune time and place.