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Thread: ((( Combiner Boxes Buzzing ! )))

  1. #1

    Default ((( Combiner Boxes Buzzing ! )))

    My installation has been running for 10 years, but is now experiencing some weird problems. Thought I would post here for some help?

    Our System:

    The system consists of an array of 40 AstroPower 120-watt, 12-volt panels.
    The system's 2 combiner boxes, 1 GFI array protection/breaker unit, 2 charge controllers, 2 SW 4048 invetrers and 2 GTI units are all Trace (Xantrex).
    A single circuit Battery bank consists of 4 Concorde 12-volt, 255Ah, series-connected (48 Volts)

    The array, combiner boxes and GFI are mounted on my house, the charge controllers, battery bank, inverters and GTI units are mounted in an enclosed storage area adjacent to my garage (35 feet away).

    The Array:

    The PVs are divided into 10 groups (or circuits), each group of 4 panels is series-connected to obtain 48 volts.

    There are (2) combiner boxes, capable of 10 circuits each. (5) PV circuits terminate in each of the combiner boxes, as the capacity of each of the charge controllers is only 40 amps (wanted some 'headroom').

    The outputs from each controller connect to the single battery bank.

    The battery bank travels through (2) 175 Amp disconnect switches (1 for each inverter).

    The Problems:

    My wife recently informed me that she heard loud 'buzzing sounds' coming from 'those boxes' at the back of the house. These would be the combiner boxes.

    The problem only happens during daylight hours. The buzzing starts off as slight pulses (intermittent), then become longer and more frequent, a short constant buzz for 10 seconds, then the buzzing stops for a while (half hour ~ a couple of hours). The period of time of the 'buzzing' starts and stops varies in length - anywhere from 5 ~ 10 minutes.

    I checked the utility meter and noticed it was not spinning backwards when this problem is occurring (not supplying power to the grid). After the 5 ~ 10 minute 'outage' the system returns to 'normal' operation and spins the meter in the correct direction (supplying power to the grid).

    This happens several times during the day, but not on any particular schedule.

    I for the life of me can't figure out why the combiner boxes 'buzz' ...

    Has anybody else had this problem? ... know what is causing it? ... and more importantly, the fix?

    Thanks in advance ...

    Last edited by Mark S.; January 23rd, 2011 at 14:53 PST. Reason: correction

  2. #2

    Default Re: ((( Combiner Boxes Buzzing ! )))

    What's inside the buzzing combiner boxes? GFI breaker? It's coils getting old and loose and starting to vibrate when the current flows at a particular rate perchance?

    Or else look out for bees!
    (Look; someone has to be the clever donkey around here!)
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  3. #3
    Join Date
    Mar 2006
    SF Bay Area (California)

    Default Re: ((( Combiner Boxes Buzzing ! )))

    My guesses... Check all of the electrical connections very closely.

    Look for hot/burned areas (changes in insulation/copper wire coloration. Many times the hot areas are the result of a loose/corroded connection next to the visible hot-spot.

    You may find that some water has gotten on them and corroded the connections (or even the breakers/fuses).

    Or you may find that one or more screws that hold down the wire have loosened up and need re-torquing.

    The "buzzing noise" is probably the solar charge controllers switching modes (bulk, MPPT, PWM) trying to figure out the solar panels that are connected and/or deciding that the batteries need less charging current (going into PWM or on/off cycling mode--probably at the frequency of the buzzing).

    Once you have "taken care of" the outside boxes--I would also check the inside connections from the charge controllers to the battery bank (and the SW inverters).

    4 kWatts of AC power requires from the battery bank/solar array:

    • 4,000 watts * 1/48 volts * 1/0.85 inverter efficiency = 98 amps

    Or upwards of 100 amps--All the 48 volt DC connections need to be clean and tight--or you can get localized heating effects that quickly cause the connections to degrade.

    You can also look for loose sheet metal, bus bar hardware, bad circuit breaker, etc... But I don't think that is the problem here.

    Also, it sounds like you have parallel connections... Those cannot be easily checked by inspection... You could have two circuits carrying current just fine, and the third carrying little to no current--and not notice the 30% reduction in power (especially if it occurs over time, during bad weather, etc.).

    You can either use a DMM (Digital Multi-Meter) set to 2.000 or 0.200 volts full scale and measure the voltage drop on a foot or so length of cable (same cable used in all three parallel circuit) and see that the voltage drop is similar in each cable set... If you find one with little to no voltage drop, it is probably not carrying any current.

    You can also use the DMM to measure the voltage drop across each run of wire and each major electric connection to look for opens/high resistance paths... It does not take much resistance to stop XX amps at 48 volts.

    If you have $60-$100+ or so, you should look at getting a DC Clamp Amp Meter (example of one here). You can simply put the clamp over a cable and instantly read the DC current flow (AC only Clamp current meters will not work with DC power systems).

    Very handy to "inspect" parallel current paths (solar panels, parallel battery strings, etc.) to ensure that each is carrying its "fair share" of the load (do the current measurements when you have lots of solar current and/or DC load current--makes the current readings much more meaningful).

    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  4. #4
    Join Date
    May 2006
    Florida, USA

    Default Re: ((( Combiner Boxes Buzzing ! )))

    Pulsing DC of relatively large current within a wire creates some strong pulsing magnetic fields. Any loosely fit metal close to the wiring, like a combiner box cover on hinges can vibrate from the magnetic fields.

    The controller is at the heart of causing the pulsing DC. At full charging rate there should not be any significant pulsing of current. In fact, PV panels must have a smooth flow of DC current to operate at peak efficiency. There are large filter caps in the controller (assuming MPPT type) that smooths out the high frequency switching going on in the controller.

    A PWM controller will just switch in and out the connection to the panels. Besides this switching, it will also expose the panels to any inverter loading AC fullwave rectified shaped current pulse profile resulting from 60 Hz AC output loads.

    When the controller detects the battery has been brought to full charge it begins backing off on the charge rate. Different controller do this slightly differently but it could produce pulsing to reduce current feed to batteries, resulting in current pulses on input feed line.

    If you are not feeding power when you think you should then check for proper controller operations.

    Check the combiner box for snuggly fit cover and any brackets within box.

  5. #5

    Default Re: ((( Combiner Boxes Buzzing ! )))

    I appreciate the replies and suggestions.

    I looked for my clamp-on amp meter last night, but was unable to locate it. I had it in my hands and checked the battery about a month ago, just forgot where I put the dang'd thing (isn't that how things go?)

    I did tighten up all the connections in the combiner boxes, the GFI breakers and the controllers before the sun came up this morning. Some of the connections were loose. The controllers are Trace C-40's (PWM, I believe).

    Happy to say that there was no evidence of overheated wiring at any of the connections.

    I will monitor the condition and report back.

    Thanks again ...


  6. #6
    Join Date
    Jul 2007
    Quetico, Ontario

    Default Re: ((( Combiner Boxes Buzzing ! )))

    After ten years,

    I would de-energize the system, and take apart each and every mechanical connection, clean and reassemble. I'm guessing some corrosion on some joint, or series of joints.

    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  7. #7
    Join Date
    Sep 2006
    Willits, CA

    Default Re: ((( Combiner Boxes Buzzing ! )))

    Wouldn't a inverter running on the system, pull DC, at a 60hz rate, and buzz ?

  8. #8
    Join Date
    Mar 2006
    SF Bay Area (California)

    Default Re: ((( Combiner Boxes Buzzing ! )))

    Usually most ac stuff vibrates at 2x the frequency-So 120 for 60 hz inverters. (Ripple current in the inverter case).

    Although, in the op's case, I believe this is the solar panel input to a charge controller, so I think the frequency is different here.

    Last edited by BB.; January 23rd, 2011 at 18:04 PST.
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  9. #9

    Default Re: ((( Combiner Boxes Buzzing ! )))

    The 'buzzing' occurred again mid-morning today. When it started, I checked the display and LEDs on the inverters and noticed that an amber LED indicated I was tied to the grid, a [normally lit] green LED indicating the FLOAT mode (where I SELL to the grid) had extinguished, and another amber LED indicated the inverters were INVERTING (not a normal condition). Again, the utility meter was not spinning in reverse, as desired.

    The displays on the charge controllers also indicated '0' (zero) amps and '0' watts.

    I changed the BULK and FLOAT charge settings as well as the BATTERY HI-CUT OUT, BATTERY LOW-CUT IN and SELL voltages on the inverters. That seemed to help and I didn't notice any additional outages this afternoon.

    I didn't have a chance to check/tighten ALL the wiring connections, still need to check connections and jumpers at the batteries, inputs to the disconnect breakers and the connections at the inverters' inputs, etc.), so I'll try to check those remaining connections after work this coming week.

    ... and yes, the 'buzzing' is occurring at the combiner boxes (solar panel input to the charge controllers) ... DC.

    I doesn't sound like its 60Hz. I'll record it with a digital audio recorder the next time I hear it happening and attempt to identify the 'actual' frequency of the buzzing with a audio signal generator.

    Not that I think this has any bearing, but I had been experiencing some RFI issues from HAM radio transmissions (40 and 75 meters) for a while. The problem only occurred at night time - when the PV array was not generating any power.

    A fellow HAM recommended installing ferrite filters on the (+) and (-) outputs from the combiner boxes, and this did eliminate the RFI problems.
    Mark S. - So. California (40) Astro Power AP-120 PV's, (2) Trace SW4048's, (4) Concorde PVX-12255, 255Ah batteries, and an Air-403 Wind Generator - Installed 2002

  10. #10
    Join Date
    Jun 2003
    pittsburgh, pa

    Default Re: ((( Combiner Boxes Buzzing ! )))

    i'm curious of what the 80 and 40 meter transmissions did to it.

    i agree it most likely would resemble 120hz so let us know for sure what it is.

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