combiner box noise

mwilsonnm

Hello,
I just added a pv combiner box to my system and it emits a humming noise. Is this normal or should I be concerned? Thanks, Mark

Brock

Re: combiner box noise

That usually means a loose wire. I would open it up check for "hot spots" and loose connections. If it's not warm at all you’re probably ok. Be careful thought, in some pin point spots it can be dangerously hot.

crewzer

Re: combiner box noise

Is the box humming all day long, or just when your controller is in absorb- or float mode?

Regards,
Jim / crewzer

mwilsonnm

Re: combiner box noise

I installed the box 2 days ago and had my solar disconnected for 3 hours while I installed the box. When I "powered up" the charge controller went into regulation mode at 14.4 volts. The noise was loudest at that time. When in float mode it was much quieter. I double checked all of my connections and am sure they are all tight. Unfortunately I am home now and unable to check things at this time. The cabin is in a remote area 160 miles from here.

BB.

Re: combiner box noise

I think Jim maybe thinking that when the controller is regulating, the current flow in the wires is no longer "pure DC" but is "pulsing" instead...

If you have the wires just loosely set in a large box--it is possible that the magnetic fields caused by the current being rapidly turned on and off by the controller (normal operation--nothing wrong) may cause the wires (or any nearby piece of steel) to vibrate back and forth--causing your buzz.

Keeping the PLUS and MINUS wire pairs (+/- wire pairs to each device is important) close together (and twisting them a couple twists per foot or more, or taping/bundle ties) will keep the magnetic fields closer to the wires and hold them tight so that they can't move/buzz.

-Bill

mwilsonnm

Re: combiner box noise

I am using #8 and #10 tray cable in the set-up and all of the wires inside the box are cut to exact lengths to provide a clean look. I don't know if this means anything but when I turn the breaker switch off, the noise stops. Thanks for the replies....Mark :-)

crewzer

Re: combiner box noise

Bill's got it! :-) Hope you find the problems soon!

Regards,
Jim / crewzer

niel

Re: combiner box noise

hey guys, let me run this idea past you. now the controller is causing the forward current to be pulsed and is therefore pulsing the inrushing power from the pvs to the combiner box. hey, everybody here with el background knows capacitors can filter that crap if using a large enough value. maybe a large value computer electrolytic mounted in the combiner box?
if any of you try this, do know that electrolytics are polarized meaning they have a + and a -. observe this or risk the part exploding on you. also, keep the voltage rating of the cap higher than the oc voltage rating of the pvs used and that the cap's metal housing should not touch any other metal. values of mfd will be in the 10s of thousands minimumly, but could be in the hundreds of thousands as well when dealing with higher currents that pvs present.

BB.

Re: combiner box noise

Niel,

Generally, placing large distributed capacitors (and inductors) cause more problems with system/controller stability than they help... (basically, things start to ring--and those can either be at lower frequencies--audio--or higher frequencies--RF).

In the case of solar panels, you have capacitance at the panel (I would assume it to be a fairly small "Farad" value but of resonance frequency-- good at RF suppression). It probably also has a kind of low Q value (high damping factor due to the fact the dielectric is really solar cell that is trying to generate electricity)--so it would not have to much of a tendency to "Ring" at high frequencies, and its capacitance is not large enough to cause problems at low frequencies....

The distributed inductance of the system is the electrical wiring--long runs of poor coupling--when combined with the capacitance at the solar panel and, possibly filtering capacitance at the controller--could cause ringing. To reduce the distributed inductance (and increase distributed capacitance), keeping the wire pairs close together (and in the best case twisting the wires, at least several twists per inch) is good. Also, the wiring has a high "Q" as everyone is trying to reduce resistance with large wire gauges (good tendency to ring).

I would usually suggest that nobody adds any large value capacitors (especially electrolytic) as these have such low cutoff frequencies (like ~25 kWHz +/-), that they would only help in storing energy and reducing audio frequency noise.

If you have problems with a Solar Charging system creating Radio Noise (AM/FM/TV audio/picture noise), it would be nice to place several smallish capacitor right at the Solar Panel Input Connectors of the solar charger. And I would use several values--something like 1 uF, 0.01 uF, 1,000 pF to ensure that you kill the widest range of of possible RF radiation. Any large value capacitor (including electrolytic) will not be of any help for killing radio noise.

Also, if you have a PWM (non-MPPT) charge controller--I have read a few that have a "reduce Radio Noise" setting--I assume that this changes the PWM duty cycle from 100's of Hz to less than 1 Hz (instead of an audio "buzz" you would only hear an occasional "click"). Using larger electrolytic filter caps to store energy at the input to a PWM charger is not really going to help charging--because the controller is already cutting back on energy delivery (battery getting full).

For MPPT type controllers, I am sure that they have all sorts of input filtering and synchronous rectification already--placing caps on the input (of an otherwise already working system) is probably not needed. If there is an RF problem--putting both inductive and capacitive filters on the input may help--but you have to be careful... The really nice filters that we use on computers (to meet EMI rules)--from what I remember years ago--the internal inductors saturate at very low DC currents (standard filter blocks are designed for AC inputs) and probably will not work well at preventing EMI.

-Bill

niel

Re: combiner box noise

simply you are telling me that the wire and pvs have set up a reasonant circuit which is always possible. to solve it you change the reasonant frequency and a cap will do that as well as bringing the wires closer together.(this increases capacitance) properly grounding it also could possibly eliminate this problem. if you're worried of the reasonant frequency going up due to the electrolytic then don't worry as adding capacitance lowers the frequency. we are dealing with low audio frequencies and aren't dealing with rf here at all, but if we were the caps with the values you specified do come into play as ferrite cores can also do well for rf. it is just the pumping action of the pwm controller acting upon the power source as he said it's at the combiner and not the loads.(batteries) there's no definite solution without being there to see the real problem source(s), but this is my hypothesis to the solving the problem besides the obvious of being sure of the connections being good.

System2

Re: combiner box noise

There is always a buzzing sound from various areas of the circuit between the PV's, controller and the batteries in my system when the TS-60 is in PWM mode. I just ignore it, because I know that in my case, it's only the pulsing magnetic fields doing their thing. Lets me know everything is working OK. Unless it's keeping you awake at night, my advise would be to leave well enough alone, it's not a problem, just the nature of the animal. :-)
Cheers
Wayne

niel

Re: combiner box noise

i should answer his question in the first place here and say that no i don't believe this to be a big problem. it may just be more an annoyance to you hearing it in the combiner box and elsewhere. any areas that do emit sound i would periodically inspect(a few times a year) to be sure that the sound vibrations do not work loose any connections.

crewzer

Re: combiner box noise

Mark,

My recollection is that the Prostar's PWM switching frequency is ~300 Hz. You'll likely hear your Prostar "buzzing" when it's in absorb (PWM) mode, and you might hear it in float mode as well, although at a reduced volume. As indicated, this is "normal": http://www.morningstarcorp.com/products/FAQ/#4

HTH,
Jim / crewzer