Electrical Breakers and Fuses

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NOTE - Information about the fuse box under the dash which controls all of the VW wiring can be found under the menu item "VW - Fuses: Dash & Engine"





Electrical Load Center Fuse Box

Inside the fold-down cover plate of the Electrical Load Center you will find two distinct and separate electrical controls: the AC breaker side and DC fuse or breaker side. Technically, there are no AC fuses, but rather breaker switches which control the AC circuits found in the coach portion of the vehicle. The automotive DC fuses or breakers control the DC circuits in the coach portion of the vehicle.

The 12VDC configuration is slightly different depending upon which model of Rialta you have. The FD use re-settable "breakers" while the HD and QD use automotive type fuses (HD listed below, QD and FD similar but possibly in different order).

 (HD listed below, QD and FD believed to be similar)

  AC Breakers DC Fuses/Breakers
1 30 Amp Main Breaker 20A - Refrigerator
2 15A Outlets 15A - Lamps
3 15A Microwave 15A - Lamps
4 Refrigerator / Converter not used
5 Roof Air 15A - TV, VCR
6 Water Heater 15A - Furnace
7   15A - Water pump
8   5A - LP Detector
9   5A - LS Aux
10   not used
11   not used

"LS Aux" is supposed to be the Auxiliary Start button on the Rialta in which the coach batteries are connected to the vehicle's starting system when the vehicle battery is too low to crank the engine. I'm guessing LS means "Low Start"?

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"MagnaTek" Electrical Converter

The electrical load center used on the Rialta was originally a model 7400 "MagneTek" Converter/Charger. The actual MagnaTek company was bought out by Parallax Power Components.

Parallax Power no longer uses the brand name "MagnaTek" and refers to their current model as the "7400 Series Converter/Battery Charger.

This one appliance converts the 120VAC current into 12VDC for use within the coach body. It also monitors and charges the coach batteries using its built-in battery charger.

There have been messages posted in the past by others concerning the lack of the optional timer circuit on the battery charging circuit of the converter device. Some have claimed that if left connected to shore power for an extended period of time, the charger will "cook" your coach batteries by overcharging them due to a lack of a timer which shuts off the charging circuit. In reality, the optional timer merely drops the charging voltage from 14 volts to 13.5 volts but only after a 13 hour timer period has elapsed. This timer does help keep from overcharging batteries when stored for extended periods of time. Regardless of whether the optional timer is used or not, the device will deliver its maximum charge rate to the battery(s) if needed, but will always taper off to a few hundred milliamps when the battery(s) are at full charge. If your vehicle is to be stored for an extended period of time, it is always recommended to disconnect the battery(s).

The following items are available in Adobe PDF format:

  •  Series 7400 Operators Manual
  •  Series 7400 Product Brochure
  •  Series 7400 Troubleshooting Flowchart

    Additional Info:

    Typical Connections                        Series 6300 Schematic
                                                                 (For comparison purposes)
                                                                  (Still looking for a 7400 schematic)

    Click either image for a larger view


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    The following originally appeared at http://www.hayseed.net/~jpk5lad/RV Information/MagnaTek Pwr Converter/rv power converter.html and I will mirror the information here on the Rialta site just in case the original one disappears.

    Repairing the Magnatek Power Converter

    Note: This unit was in my Sierra 30 foot trailer

    When spring came and I prepared to get my RV all un-winterized and ready to take out, I discovered that my trailer battery was nearly dead. Since it was new from just the year before, I thought I wasn’t getting very good mileage on batteries, but I thought I would do some other checking before indicting the battery as defective. First, doing some various voltage checks, I found that I had good 12 volts DC to my interior lights and to the voltage monitor on the control panel. Hmmmmm….. that’s odd. That voltage was coming from the power converter 12 volt supply (although not from the converter's battery charging section).

    Checking the cigarette lighter socket, it only showed 5 volts and I determined that this was coming directly from the battery which was, by then, in a near discharged condition. Although the trailer had been plugged in all winter, the battery had not received any charge since the battery charge feature in the power converter had failed in my MagnaTek Power Converter, and I didn’t know when that had happened. The battery was OK, the MagnaTek higher current 12 volt section was OK but the battery charger section of the converter was not OK.

    Checking at the Magnatek panel in the bathroom, I found no voltage between point C (which was the positive side from the battery) and point D (which was the negative side from the battery). Now I knew where I had to concentrate my attention. NOTE:  Points C and D are actually labeled as such on the unit.

    At this point I spent several hours combing the Internet in search of a schematic for the Magnatek converter…..totally without success. I read jillions of messages from RVers, several asking for the same thing I sought. I wanted any kind of information, particularly a schematic, for this unit. I even contacted some of these people to ask if they had been successful in the search. Nope…..nada…..nothing.......no such luck.

    I found a telephone number for the factory which built the unit and even tried to call for info. Human help was available for warranty work but my unit was several years out of warranty. I was out of luck.

    I needed that schematic and since it was unavailable, it looked like I would have to generate one myself. If you’ve ever tried to do this it is akin to somewhere between trying to write down a cake recipe from only having the completed cake in front of you and unscrambling an egg. Not much fun, especially if the parts have non-standard markings or no markings at all........like my converter.

    I was ultimately successful and the schematic I have included is close enough, if not an exact rendering, of what is found in the Magnatek power converter. I hope it helps others as it helped me. Now, with schematic in hand, I returned to the project of repairing my converter.

     PIC #1: The circuit schematic is actually in two parts. The first part, shown to the left, is the main power supply part of the converter.

    PIC #2:  The schematic at the left is the battery charger part of the power converter. It will charge the RV battery but then automatically taper down to a trickle charge so as not to destroy your expensive battery. Some day I may figure out how to draw it nice and neatly. For a person who only can draw stick figures, I thought it was pretty acceptable.

    PIC #3:  I included this picture but I'm not absolutely sure of its total accuracy. I drew this out several times and I think this was the final version. Don't hold me to it, however, and if there is a discrepancy between the schematic and the underside of the PC board, you should believe the schematic first.

    CAUTION: When you decide to work on your power converter, be sure you unplug your trailer’s power cable from the 120 volt AC mains. Once that is done you can remove the screws holding the panel/cover onto the converter. This will expose the transformer, diodes, solenoid, fan and battery charge board. This solenoid is energized whenever the trailer is plugged into external AC power and it allows the converter to send charging voltage to the trailer battery. Magnatek chose to use a solenoid to activate a switch to perform this function rather than use a relay. Why? I don’t know.

    The following are steps required to remove all connections so you can pull the whole power converter out to work on it:

    1. Remove the 4 hex-head screws which hold the front board.

    2. Remove the 2 hex-head screws holding the other board.

    3. Remove the 12 volt wiring to the 12 v. distribution board – the white and red wires have screws, the blue (12v) wire is attached with a screw and nut.

    4. Open the cover to the 120v AC circuit breakers.  (You did disconnect the 120v AC didn't you?)

    5. Remove the white wire which goes to the left side vertical screw strip.

    6. Remove the black wire coming from the far right-hand circuit breaker.

    7. Carefully feed the 2 AC and 3 DC wires from the top box so they are inside the bottom power supply box. Now you can remove the power converter pieces.

    8. With the power converter box on the workbench, remove 2 hex-head screws holding the nylon posts which are holding the battery charger circuit board.

    9. NOTE: With the power converter box on the workbench, the top cover can be removed with 4 hex-head screws. This allows full access to the inside components.

    The next step is to remove the board containing several electronic parts including resistors, silicon controlled rectifier, Zener diode and a capacitor. This board, on my unit, stood vertically and was attached to the right-hand wall of the supply.  NOTE: Do NOT attempt to pop the board off the nylon posts where it is mounted. It will not come off and attempting to pop it loose will result in a cracked board, which is made of rather fragile phenolic material.  Breaking that board can separate traces on the printed circuit board and you will have additional problems.  The board can be removed but only after the whole box, holding the supply, is removed. (A word to the wise….. I hope.............. ask me how I know this...... No......... never mind.)

    It is now that you must use your electronic trouble-shooting skills to determine which component or components might be causing your problems. That is rather difficult for me to tell you what might be causing your converter to fail but, hopefully, this information and the schematic provided will allow you to find it.

    My problem turned out to be the large rectangular resistor mounted with a pop rivet to the back panel of the box. The value was obscured on mine but an ohmmeter check showed the value to be more than a mega ohm which was much, much too high. I would guess that its true value should have been less than an ohm but at a high power rating, perhaps 50–100 watts. It was here that I had to do some guessing. Since this resistor is located in the line providing charging current to the trailer battery, my guess is that its function is to drop the load a bit when first connected to a battery which is totally discharged. A fully discharged battery would place a tremendous temporary current load on the power supply components and this resistor helps to protect things during that initial surge.

    After the repair was complete, I did some checking on the converter to see just how much current was provided to a battery for charging and to see whether the higher current stayed up at the high level or if it tapered off to a trickle charge as this type of circuit should do. With a 0-3 amp meter in series with the battery charging line, and using no extra resistance in the line (the big white rectangular resistor was shorted to make zero ohms or there abouts), I placed the charging circuit across a pair of 6 volt/7.7 AHr lead-acid batteries which I had on hand. The ammeter started at just above 2 amps charging, then tapered down to around 1.25 amps.

    Then I tried it across a 12v/7 AHr lead-acid battery with was already charged.  The current started a just below an amp and within a minute, dropped to about 200 milliamps or .2 amps. I say "about" because the ammeter constantly wiggled the equivalence of .1 amp. I suspected that this might be caused by the noticeable AC ripple in the DC line. After all, there is no filtering on the rectified DC coming off the full-wave rectifier.

    I located a 2 ohm, 50 watt resistor in my junk-box to replace the defective one which had originally caused my problem. Placing the charger wires across another charged 12v/7 AHr battery it started the charge current at less than an amp. It also tapered down, within a couple of minutes, to about .2.amps…… a shaky .2 amps. The resistor did not even run warm but it had very little current through it.

    I finally found a .25 ohm/5 watt resistor and placed it in the place of the original defective white rectangular unit pop riveted to the back wall of the converter. I feared that the power rating on this resistor might be too low but I have used this one for several months and it is holding up well.

    I reassembled my converter by going in reverse with the steps taken earlier to disassemble the unit. Everything went back together as easily as it had come apart and I was a happy camper (so to speak). I hope, if you are having problems as I was, that you can use some of this information and have as much success as I did.

    One additional piece of information – the fan which you hear while the trailer is plugged into an external 120 v AC source, is actually running on 120 v AC rather than 12v DC and is thermostatically controlled. A temperature sensor is attached to the aluminum heat sink which holds the power diodes. When they are doing their job and supplying 12 volt power to your trailer (not particularly to the battery) those diodes will run hot and make the heat sink also quite hot. The sensor turns on the fan which blows across the heat sink as well as our now familiar power resistor. If you don’t hear the fan then the power converter is not having to do much work and the fan gets to rest.

    One other benefit on my converter is, I was able to clean up all the dust and "grunge" around the fan and it has become much quieter. I still hear it but nothing like it was previously.

    Just as a final encouragement for you to try to repair your own converter, when I looked up the replacement converter in a trailer accessories catalog, the replacement unit was between $200 and $300. That was enough inducement for me to attempt my own repairs.

    Jim Pickett – K5LAD

    Written June 29, 2002 ---- Updated

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    Page Updated: 5 July 2015