MC4 connectors with built in diode ???

2Guido
2Guido Solar Expert Posts: 62 ✭✭
Hi Guys,
My system parallels all my solar mats together to feed my diversion controller. Is there any need to switch out my connectors to these new-fangled ones with built in diodes ???
Thanks

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MC4 connectors with built in diode ???
    2Guido wrote: »
    Hi Guys,
    My system parallels all my solar mats together to feed my diversion controller. Is there any need to switch out my connectors to these new-fangled ones with built in diodes ???
    Thanks

    There's no reason for a blocking diode in most any system. Simply is not necessary.

    Do you have a link to MC4 connectors with them built-in? I would like to see what they are promoting.
  • 2Guido
    2Guido Solar Expert Posts: 62 ✭✭
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: MC4 connectors with built in diode ???

    There are a lot of Chinese (and Ebay) places selling MC4 Diode connectors:

    http://www.alibaba.com/showroom/mc4-solar-connector-diode.html

    Just not sure if they have an integrated diode or not. A few are PV junction boxes+diodes+MC4 leads--Those look real enough.

    In general, you do not need blocking diodes for 12 volt battery systems.

    24 volt systems, it is a toss up (vs leakage current over night).

    For 48 volt systems, yes you should have a blocking diode (per our host's FAQ).

    Diodes are lossy devices (~0.2 to >1.0 volts depending in type/ratings). Put 8 amps through a 1 volt drop, and that is 8 watts--That should have a metal heat sink to dissipate the energy... Gets into issues with insulation vs metal heat sinks, internal heat transfer, etc.

    I would really consider a PWM or MPPT charge controller instead. They will do a much better job of charging the battery bank vs using a Dump Controller.

    You can leave the dump controller connected and set for > Vbatt-solar charging to dump any excess current when the wind turbines are pumping out current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MC4 connectors with built in diode ???

    That connection diagram shown in the link is wrong: three parallel panels with no circuit protection. Diodes do not provide this. As presented, it is a complete waste of money and incorrectly wired.

    Where you might use blocking diodes:

    1). a system with panels + turbine and only a dump controller on the battery. In such a case the turbine can push current back through the panels at night, and if it exceeds their rating it can ruin them.

    2). a system with mismatched panels where the reverse Voltage on one string is lower than another (even though the total Vmp for the strings is the same - as in one string made of more lower Voltage panels). In that case shading of the lower Voltage string can cause the higher Voltage one to push current back through it. If the Isc ratings are the same there is only a power loss. It would take a rather unusual set of specs and circumstances to damage panels this way.

    3). a system with arrays facing in quite different directions connected to the same charge controller. In some situations that can perform as #2.

    As Bill said, it really only becomes a problem at higher Voltages.

    Fuses or breakers on individual panels or strings connected in parallel is a more sensible precaution.
  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    Re: MC4 connectors with built in diode ???

    Can you recommend a good diode to solve one of the problems you listed?

    I have a system with mismatched power inputs that I need to solve. What happens when one string that is 36V is shaded and one string is 24V and not shaded? Does it hurt the 36V string?
    That connection diagram shown in the link is wrong: three parallel panels with no circuit protection. Diodes do not provide this. As presented, it is a complete waste of money and incorrectly wired.

    Where you might use blocking diodes:

    1). a system with panels + turbine and only a dump controller on the battery. In such a case the turbine can push current back through the panels at night, and if it exceeds their rating it can ruin them.

    2). a system with mismatched panels where the reverse Voltage on one string is lower than another (even though the total Vmp for the strings is the same - as in one string made of more lower Voltage panels). In that case shading of the lower Voltage string can cause the higher Voltage one to push current back through it. If the Isc ratings are the same there is only a power loss. It would take a rather unusual set of specs and circumstances to damage panels this way.

    3). a system with arrays facing in quite different directions connected to the same charge controller. In some situations that can perform as #2.

    As Bill said, it really only becomes a problem at higher Voltages.

    Fuses or breakers on individual panels or strings connected in parallel is a more sensible precaution.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MC4 connectors with built in diode ???
    Can you recommend a good diode to solve one of the problems you listed?

    I have a system with mismatched power inputs that I need to solve. What happens when one string that is 36V is shaded and one string is 24V and not shaded? Does it hurt the 36V string?

    This is not likely to be a problem. The reverse Voltage of the 36 Volt string wouldn't be achieved from a 24 Volt string.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: MC4 connectors with built in diode ???
    I have a system with mismatched power inputs that I need to solve.

    Tell us more about the array configuration... how many strings, panels per string, panel specs, etc? What controller and battery are they feeding?

    There may be other solutions... not as cheap as a diode, but you could buy another controller for as little as $30. Whether that makes any sense depends on the answer to above questions.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    Re: MC4 connectors with built in diode ???

    Can you please direct me on where to buy a quality MC-4 compatible diode? I have a special situation and I think the diode may fix the problem.

    This is for a water pumping system that has an ac-->dc power converter. The converter runs at 24V and when the panels back-feed at 36V it disrupts the power supply. I need to prevent the panels from back-feeding into the power supply so that once the sun goes down the power supply can take over. Right now I'm having to manually reset the power supply so that it will wake up. When it sees the power from the panels it somehow goes into a sleep style mode.

    I looked at the ones listed but I want to make sure I buy a quality one minimize any losses accrued through the diode.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MC4 connectors with built in diode ???

    Not sure I understand the question. If one source is 36 Volts that may 'back feed' the other that is 24 but not likely and especially not likely the other way around. Panels are basically diodes anyway, so you have to apply greater than their reverse Voltage before they will conduct the other way and become a load (that with panels shaded and not producing).

    MC4 is a type of connector, and doesn't really have anything to do with diode compatibility. It's just that some company is marketing MC4 connectors with diodes built-in, which are usually of no use.

    Otherwise for a blocking diode you are looking for a Schottky type. It has low Voltage drop on the forward bias so it doesn't reduce power significantly. Our host used to carry them and may still do so but ever since the 'upgrade' to the web site it has been more difficult and confusing to use. Here's a selection: http://ca-en.alliedelec.com/search/results.aspx?term=Schottky+Diodes&mkwid=scyVIqK8z&pcrid=28375026859&pkw=schottky%20diodes&pmt=b&gclid=CM7L_-KRkL8CFYqPfgodnrkAnA Note that the diode needs to be able to handle the current involved as well as Voltage.
  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    Re: MC4 connectors with built in diode ???

    Thank you for your answer. The panel is back-feeding the ac-->dc converter box and causing it to either trip off or sleep, I'm not sure which. It has to be manually reset to wake it up. So if I leave the power box on and the solar panels run the system the system runs on solar power during the day. At night I expected the box to take over, but since it has went to sleep it will not keep the pump running. If I put a diode in-line with the out put of the box (via MC4 cables) then it would keep the solar panels from backfeeding the box and solve the problem (hopefully).

    The amps are low, about 6amps at 24V.


    Getting one compatible with MC4 cables just facilitates the wiring for me much easier as I do not have much more space on the TOP mount. As a temporary solution I'm installing a timer that will switch the box ON at 9pm (totally dark) and then off at 6am (first light). It's a short-term fix. I would like for the converter box to take over anytime the array voltage drops below 24DC but right now it won't do that. I have 2 200watt 24V panels powering the pump and their running volts are around 36V, the converter box is always 24V and 6amps.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MC4 connectors with built in diode ???

    Okay it sounds like a diode built in to the connector won't help unless that connector is on the power supply as the block needs to be between the supply and the load, not the panels and anything.

    I'd try manually disconnecting the panels in the evening first, to be sure that will cause the power supply to take over. You may indeed need something a bit more complex than a diode. For one thing the power supply may need a 'two way' connection to the pump in order to function correctly. As such it might be necessary to use a relay powered by the panels to disconnect them when their output goes low so the power supply does not 'see' Voltage on the pump wire and think it doesn't need to run.
  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    Re: MC4 connectors with built in diode ???

    I have disconnected (actually covered the panels with a thick blanket to simulate darkness). Reading the OUTPUT of the AC/DC box it reads ~36V (panel output) and then once the panels are covered it reads about ~6V (the ACDC Box is "inactive"). If I flip it off/on it starts up and begins to supply 24VDC. The power supply will continue to run until the panels are uncovered and the voltage goes up above the 24V the box is supplying. My guess is that once the box sees a certain voltage it trips out or goes to sleep. Hence the reason for the diode. BTW: The box is not "smart" at all. It is very simple: 115VAC in and 24VDC out. There is only an on-off switch. This system that I have installed will not run above 50VDC to the pump controller or I could use other commercially available power supplies that are "smart" and know when to come on/off.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: MC4 connectors with built in diode ???

    The thing I don't like about diodes in an MC4 connector is that diodes can run hot (6 amps * 1 volt drop = 6 watts of heat).

    They do last much longer if properly cooled (heat sink). And most diodes have the metal case/tab that is electrically connected to one of the leads--So insulation/caution must be used too.

    More or less, the engineering rule of thumb (works for almost anything) is for every 10C increase in temperature, a 1/2 reduction in life. 30C increase, 1/2*1/2*1/2=1/8 life.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    Re: MC4 connectors with built in diode ???

    So if the part went bad it would just be the diode itself? I could live with that.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: MC4 connectors with built in diode ???

    Yes--Diodes can fail shorted or open--So, in this case, neither failure is a catastrophe (unless there is a battery bank involved--Then loss of charging could be an issue if nobody catches the failure in time).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset