Midnite Solar circuit breakers buzzing

Plowman
Plowman Solar Expert Posts: 203 ✭✭✭✭✭
in Off Grid Solar & Battery Systems #1
Last month I finished expanding my little off-grid system, used four Midnite Solar 12A breakers for the combiner box and one 63A as the main battery breaker. They all seem to buzz when the sun is shining and the panels are producing. Not loud, but noticeable.

A quick Google search gives contradictory advice. Some say some buzzing is common and nothing to worry about. Others say buzzing breakers can be a sign of loose connections or an old breaker that's about to give out. I've checked the connections and they're tight (all screw compression type connections), and these breakers have only been in use for a month.

I'm hoping it's nothing to worry about? I haven't systematically tested them to tell when and when they do not buzz, under what loads, etc. None have ever tripped, but they haven't been subjected to any conditions where I'd expect them to trip.

I did measure a voltage drop when I tested one of the panel circuits, went from 14.12V to 14.06V when measured before and after the breaker in the combiner box, which is a 0.42% drop. Panel was producing 4.2 amps according to my clamp meter. I took these readings a couple weeks ago, didn't think much of them then, but upon reflection that voltage loss seems rather high.

I've also tested the battery breaker a couple times and the voltage loss is barely measurable (tested it a couple days ago, there was no measurable loss, 14.83V before and after the breaker, measured ~10 amps with my clamp meter). It also buzzes.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
    Re: Midnite Solar circuit breakers buzzing
    Plowman wrote: »
    I did measure a voltage drop when I tested one of the panel circuits, went from 14.12V to 14.06V when measured before and after the breaker in the combiner box, which is a 0.42% drop. Panel was producing 4.2 amps according to my clamp meter.

    That's 60 millivolts. Does your meter have a millivolt scale? If so, measure the voltage across the breaker and see if it agrees... your meter may be more accurate using the millivolt scale. Of course, make sure your panel is still producing 4.2 amps when you measure.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #3
    Re: Midnite Solar circuit breakers buzzing

    When you measure the voltage drop across the breaker, make sure to get right into where the wire goes into
    the connection. When you measured the voltage before, did you measure right at the breaker or was there
    wire drop as well ?

    The breakers will definitely have some kind of a voltage drop though.

    As far as the buzzing, what I suspect you are hearing is due to the closest thing there would be inside
    a breaker which would be the magnetic coil used to make it trip. Since you (probably) have an inverter
    drawing AC ripple on the battery side at 120 Hz or 100 Hz (double 50/60 Hz), that is more than likely
    the cause of the "buzz".

    As long as all of the breakers are lightly buzzing, it's probably not any issue to be concerned about.

    boB
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  • Plowman
    Plowman Solar Expert Posts: 203 ✭✭✭✭✭
    #4
    Re: Midnite Solar circuit breakers buzzing
    vtmaps wrote: »
    That's 60 millivolts. Does your meter have a millivolt scale? If so, measure the voltage across the breaker and see if it agrees... your meter may be more accurate using the millivolt scale. Of course, make sure your panel is still producing 4.2 amps when you measure.

    --vtMaps
    Yes, my meter has a millivolt scale, I'll try that next time.
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  • Plowman
    Plowman Solar Expert Posts: 203 ✭✭✭✭✭
    #5
    Re: Midnite Solar circuit breakers buzzing
    boB wrote: »
    When you measure the voltage drop across the breaker, make sure to get right into where the wire goes into
    the connection. When you measured the voltage before, did you measure right at the breaker or was there
    wire drop as well ?
    I don't recall, I took these readings a couple weeks ago. I'll check them again, but it's pouring rain right now, so will have to wait a while.
    The breakers will definitely have some kind of a voltage drop though.
    I was using an automotive type breaker (Short Stop) on my battery that had a wicked voltage drop. The Midnite is far better. The combiner box drop got me a bit worried though, I had forgotten to factor that into my system-wide voltage drop, which went up to almost exactly 3% when I factored the combiner box breakers in. Still OK, but lower is better.
    As far as the buzzing, what I suspect you are hearing is due to the closest thing there would be inside a breaker which would be the magnetic coil used to make it trip. Since you (probably) have an inverter drawing AC ripple on the battery side at 120 Hz or 100 Hz (double 50/60 Hz), that is more than likely the cause of the "buzz".

    As long as all of the breakers are lightly buzzing, it's probably not any issue to be concerned about.

    boB
    I am using a cheap MSW inverter, as well as a PWM controller. The controller buzzes sometimes, too.

    I forgot to add that I have felt the breakers on a couple occasions and they weren't warm at all.
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #6
    Re: Midnite Solar circuit breakers buzzing
    Plowman wrote: »
    I am using a cheap MSW inverter, as well as a PWM controller. The controller buzzes sometimes, too.

    I thinking those are likely to be the cause. I have lots of those breakers and none make any noise at all. But mmpt doesnt pulse width the load on the PV much or at all. Not like a PWM controller in float or aborb will. Is it a brand name controller? I ve seen reviews of some cheap controllers with really noisy waveforms, and real bad RF.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • Plowman
    Plowman Solar Expert Posts: 203 ✭✭✭✭✭
    #7
    Re: Midnite Solar circuit breakers buzzing
    zoneblue wrote: »
    I thinking those are likely to be the cause. I have lots of those breakers and none make any noise at all. But mmpt doesnt pulse width the load on the PV much or at all. Not like a PWM controller in float or aborb will. Is it a brand name controller? I ve seen reviews of some cheap controllers with really noisy waveforms, and real bad RF.
    Morningstar TS-45
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