AC Ripple?

[SVTotem]

No not the wine.

I have been having on-going trouble with our Norcold 1201 LRIM refrigerator not working on AC. The controller board was replaced twice this year, and most recently the heater elements were thought to be blowing the fuse on the latest board.

After a full day of trouble shooting yesterday, and a couple calls to Norcold, the technician is being told the probable cause is "AC ripple" getting to the DC side of the board and causing it to not work properly. Norcold suggested a direct wire to the battery for DC to the refer.

AC ripple is a new one for me. I am familiar with stray current, RFI, and other types of electronic interference. Many of which are the result of insufficient grounding or shielding. I am reluctant to start a rube goldberg fix that deviates from the original design of the electrical system and feel that the problem would be better solved at the source of the problem on the AC side. I just do not know enough about RV electrical systems to suggest a better approach.

Has anyone had experience with AC ripple, particularly in the context of the refrigerator? Perhaps known by another name? If so, what solutions have been successful.

[KIX]

I've heard of AC ripple but that's all I know or have even heard about it. It would seem that connecting directly to a dedicated battery for a test would be relatively easy. How long does it take for the symptoms to manifest?

[94-Newmar]

Bill, is the AC side of the refrig running thru the Coach's inverter? "Ripple" usually occurs with a Diode going bad or leaking AC back across. If your refrig is connected thru the Inverter then perhaps that is going south on you. If it's not then the problem must exist on the circuitry in the refrig. That is probably why they want you to test it with a direct line to the 12vdc - thus bypassing anything else that may be causing the issue. In most cases you'd need a scope of some sort to see ripple. Most digital multimeters won't be "fast" enough to see AC leakage across.

[SVTotem]

I am not sure how the AC is supplied to the refrigerator. I have not tried operating it on the inverter, just the generator and shorepower. The refrigerator is plugged into a 110 outlet, so I imagine the source for that outlet is the same as all the others. As such, the inverter is only involved if specifically selected by turning it on when shore and generator are not available.

The wiring to the battery is not meant as a test, but a fix. That is what I am concerned about.

[bigskymt]

Assuming you don't have a O-scope you can measure the DC input to the board with your DVM in AC mode. Any significant AC will register. If your DVM has a "hold" or memory feature that stores min & max measurements that would help. It's possible you're leaking some AC from your charging circuit to the DC side.
What were the symptoms you were troubleshooting for a full day that lead to the ripple diagnosis?
I'd think if AC ripple were such a potential problem to this system Norcold would install some buffers in the board to protect sensitive components, especially in a M/H environment.

[RV Wizard]

We call this dirty dc and the source is 99% of the time the charging system. You probably have a bad capacitor(s) in the charger. We usually see this problem on converter chargers; more so than with inverter/chargers. If you check the dc circuit with your digital meter on an AC volt scale you might be able to pick up this AC ripple. DC electronic control boards (some more sensitive than others) do not like this dirty DC voltage and faults out. I have not seen one that would blow the AC side fuse. What is the incoming AC voltage and how many amps total are the two heating elements drawing?

[WOODYDEL]

Quote:

Originally Posted by SVTotem No not the wine. I have been having on-going trouble with our Norcold 1201 LRIM refrigerator not working on AC. The controller board was replaced twice this year, and most recently the heater elements were thought to be blowing the fuse on the latest board. After a full day of trouble shooting yesterday, and a couple calls to Norcold, the technician is being told the probable cause is "AC ripple" getting to the DC side of the board and causing it to not work properly. Norcold suggested a direct wire to the battery for DC to the refer. AC ripple is a new one for me. I am familiar with stray current, RFI, and other types of electronic interference. Many of which are the result of insufficient grounding or shielding. I am reluctant to start a rube goldberg fix that deviates from the original design of the electrical system and feel that the problem would be better solved at the source of the problem on the AC side. I just do not know enough about RV electrical systems to suggest a better approach. Has anyone had experience with AC ripple, particularly in the context of the refrigerator? Perhaps known by another name? If so, what solutions have been successful.

The culprit was the converter. Changed it and the refrigerator returned to normal. I thought the mechanic at our local trailer dealer had made a mistake but he was told what to do by the manufacturer. I forgot to mention, we had a lightning strike just prior, not a direct hit but close.

[Gary RVRoamer]

I can see "ripple" causing problems with the controller board, but not blowing the 120vac fuse. I think you probably have two different problems, because the control board runs strictly on 12vdc, while the ac-mode heaters are strictly 120vac. The only thing the controller does for them is to switch power on/off in response to the temperature inside the fridge.

I don't see any real downside to running the fridge 12v direct to the battery. It means the fridge still has power if the battery disconnect switch is off, though. If you use the disconnect while in storage, remember the fridge is still drawing power unless physically turned off.

[SVTotem]

Thanks for the responses. Here is a summary of what took place:
The technician found 1.8 vac "ripple" in the dc circuit. At Norcold's recommendation a 12v line was run from the switched side of the Aux Battery Switch to the DC In portion of the board. All seems to be ok, but whether it is a permanent fix or not is still to be seen. The board was replaced as well. In looking at the removed board there were a couple of passive components that were obviously burned out.

I feel that there is a problem with the Dimensions Inverter/Converter that is creating this voltage issue, so there may be more to this story later.

[RV Trax]

I have had similar problems with the board issues from AC ripple on the DC line. I have installed 12 volt noise filters in line with the 12 volt power circuit (like those for CB radios) and have had great results. Noise generally is caused by a noisey converter or a fluorescent light ballast board failure. Generally the 110 Volt fuse blowing is caused by a defective 110V heating element. If your unit is a 50 amp shore power a loose nuetral (white wire) will cause excessive AC voltage into your unit causing failures.

[Ray,IN]

If I read this Ripple (electrical) - Wikipedia, the free encyclopedia correctly, a "smoothing capacitor" will solve the problem. A true RMS multimeter should be able to see the voltage variation.

[SVTotem]

RVTrax,
Can you be more descriptive of the filters you describe and where specifically you placed them? Are you speaking of the ferrite chokes seen on DC power cords? I my not have spelled that correctly, but I am speaking of the filters that clamp over the cord. Also, I have installed a Progressive Ind. EMS to protect from pedestal power problems. Would the loose neutral you speak of be somewhere else the other than at the pedestal/cord interface?

Ray,IN,
It sounds like the smoothing capacitor is something that would be designed into the refer circuit board. Is there an aftermarket approach similar to the filters RVTrax mentioned?

Thanks guys, I appreciate your help, but I am not real sharp on EE details.

[RV Wizard]

The filtering is designed into the converter/charger but at least one of the capacitors has failed. I guess you could filter the output of the charger to the battery bank with an after market rectifier and/or capacitor filters.
A loose neutral can happen at any point. Check the AC distribution panel for tight connections of all conductors; turn power off first.

[RV Trax]

The noise filter contains a capacitor and coil internally. It has a negative and positive DC input and output. The negative and positive wires at the rear of the fridge control board are to be connected to the input of the noise filter and the output filter wires connect to the fridge. It is a inline device that can be purchased from most car stereo installation facilities. It should be rated for a minimum of 10 amps DC.