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  1. #21
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    Default Re: Panel Configuration

    Quote Originally Posted by mikeml View Post
    It's the voltage which kills - keep the total panel Voc voltage to less than the max rating of the controller.

    But the controller should not blow if your panels are within the voltage spec, but could deliver more current than the controller rating - the controller will only deliver the max rated amps, irrespective of what's available on tap behind it. I suppose it's similar to connecting a 6A battery charger to an Eskom source, which can deliver much more than 6A.
    What I meant if the input is a 24V setup, you will not be able to charge a 36 V battery.
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    Default Re: Panel Configuration

    Quote Originally Posted by Prof View Post
    So it is ok to do one series set with less panels as other sets?

    Wouldn't 2 five in series sets and one four in series set not be ok as well. 3 parallel strings?


    Not having equal amounts of panels per series string is a big no no, I was 50-50 on this recently and got conflicting info, so eventually confirmed this with Victron.
    And yes, higher amps is fine, the Victron controllers can handle it, just don't step over the voltage.

    Just also check on your panel specs, usually panels have a limitation on how many watts you can do per series string, I know for example on my 100W panels the limit is 1000W per series string.
    Last edited by bigboy529; 2020/07/28 at 07:29 PM.
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    Default Re: Panel Configuration

    Quote Originally Posted by bigboy529 View Post
    Not having equal amounts of panels per series string is a big no no, I was 50-50 on this recently and got conflicting info, so eventually confirmed this with Victron.
    And yes, higher amps is fine, the Victron controllers can handle it, just don't step over the voltage.
    Yes you need to have the same voltage on each set of strings. In series its not that critical as the controller will settle with the amps provided through the string, which is the lowest panel amps, if the amps do not match
    Last edited by JLK; 2020/07/28 at 07:34 PM.
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    Default Re: Panel Configuration

    Quote Originally Posted by the_terrible_triplett View Post
    .............

    Bottom line - on ALL MPPT's:
    Don't ever exceed that Maximum PV open circuit voltage.
    Don't ever exceed that Maximum PV short circuit current.

    If one does exceed either, then Phone Life Line. Find their no. in the Yellow Pages.
    Why?
    Because maybe they would care that you let the smoke out, as no-one else would.
    Yellow pages? Well that's a blast from the past......and Life Line has too much on their plate at the moment with Covid, so please do not overload them as well...

    I can't agree with your statement though concerning max current, certainly not for ALL MPPT's

    I just checked, and Victron MPPTs have current limiting, as does CTEK and Meanwell. So connecting 1000W panels at less than max Voc will not blow a controller specced at 20A with current limiting, even if the load would like more than 20A. The current limiting circuit will ensure the max current draw stays at 20A, keeping the smoke inside.

    However the Victron BlueSolar PWM controller I just checked does not have current limiting, but has an overload protection, which will shut the controller down after a certain time, based on the degree of overload.

    This might not apply to some of the cheaper brands, so yes, there could be smoke and tears.

    Here is a reply to a similar question on the Victron forum:
    DaniŽl Boekel (Victron Energy Staff) ♦♦ iostrym ∑ Mar 31 at 12:36 AM
    The energy is not 'sent somewhere else' it is just not 'taken from the solar panels'.
    If you have a panel that is not connected, the energy is also not used, that's the same.
    The MPPT is able to adjust how much power the solar panel produces by adjusting the panel's voltage. It will set the panel voltage to the optimal point for how much power the system needs.

    For a 20A MPPT, if the panel can potentially produce more, the MPPT will limit how much that panel produces to keep to the 20A battery current limit. You will not damage the controller by connecting more power than the MPPT can use.

    In fact it is recommended to install more, so you can get more power during cloudy weather.



    Mike Lauterbach

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    Default Re: Panel Configuration

    @Mikeml
    Good that we and Victron seem to be on the same page.

    This is why I mentioned it in post #18. If a cheap controller ignited the smoke bomb it does not mean all MPPTs do it. Many installs do clipping at peak sun with oversize panels in order to get more power from panels during the full day. Their MPPTs do not go up in smoke.

    It is for the same reason a 6A charger might only supply 6A even if a discharged battery would like to load it to 12A. The chargers survive and so would the MPPT.

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    Default Re: Panel Configuration

    Quote Originally Posted by mikeml View Post
    In fact it is recommended to install more, so you can get more power during cloudy weather.
    Yes, that is true BUT as I mentioned earlier in the thread, when you start with oversizing, i.e. exceeding in this case, the max watts Victron gives one as a guideline, then it is wise to keep the following in mind, right in front of your mind - as I've learnt on smaller MPPT's over time:
    1) When oversizing, do the calculation with temp coefficients in that calculation, as a ice cold sunny day with clear skies and cloud effect, can cause havoc.
    2) MPPT will start throttling when you oversize yes, but the output, not the input. You are then exceeding the design specs of the components.
    It is like that moment you faceplant, a second after your skateboard came to an abrupt stop against the curb, whilst watching that girl walk past.
    3) And it is not wise in the longterm to oversize a MPPT where daily ambient temperatures are high, unless you can keep it cool.

    I had a 150/100 on 24v, oversized array, that worked so hard that a fishtank thermometer was maxed out on over 65deg C.
    You could not keep your hand on that MPPT for long, designed to handle it, but I hated that! (...and I knew I was pushing the envelope. How else do you learn. )
    Same array 48v, cool as a cucumber.

    Oversizing must be done with care and FULL understanding of what you are doing and why, and what are the no-go limits.

    Volts, amps and temps, the death of MPPT and batteries, lead acid and lithium.


    Quote Originally Posted by mikeml View Post
    I can't agree with your statement though concerning max current, certainly not for ALL MPPT's
    O trust me, as you can have a limit on the max volts from panels to MPPT, you also have a max current from panels to MPPT - on all PWM's and MPPT's.
    It is on all the borchures.
    If you hit those hard set limits, poof, the smoke goes, as you are exceeding the components designs inside.

    That ref to 2) on Max. PV Short circuit current, the fine print:
    2) A PV array with a higher short circuit current may damage the controller.

    The 250/100 is rated at an input from the panels at max 250v and max 70amps - Note: INPUT from the PANELS, not OUTPUT from MPPT.

    So I can push my 250/100 to 7kw array, still "Accepted", and as you can see in the pic, it throttles the OUTPUT, not the INPUT.
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    Default Re: Panel Configuration

    Quote Originally Posted by the_terrible_triplett View Post
    ..................
    I had a 150/100 on 24v, oversized array, that worked so hard that a fishtank thermometer was maxed out on over 65deg C.
    You could not keep your hand on that MPPT for long, designed to handle it, but I hated that! (...and I knew I was pushing the envelope. How else do you learn. )
    Same array 48v, cool as a cucumber.

    Oversizing must be done with care and FULL understanding of what you are doing and why, and what are the no-go limits.

    Volts, amps and temps, the death of MPPT and batteries, lead acid and lithium.
    If you run your controller at near your max power, it will get hot. Just like your battery charger or power supply. The top brands are designed to run at max current at 100% duty cycle, within the recommended environment. I'm sure that they will not last as long running at max continuously than say at half the max spec.

    Quote Originally Posted by the_terrible_triplett View Post
    O trust me, as you can have a limit on the max volts from panels to MPPT, you also have a max current from panels to MPPT - on all PWM's and MPPT's.
    It is on all the borchures.
    If you hit those hard set limits, poof, the smoke goes, as you are exceeding the components designs inside.

    That ref to 2) on Max. PV Short circuit current, the fine print:
    2) A PV array with a higher short circuit current may damage the controller.

    The 250/100 is rated at an input from the panels at max 250v and max 70amps - Note: INPUT from the PANELS, not OUTPUT from MPPT.

    So I can push my 250/100 to 7kw array, still "Accepted", and as you can see in the pic, it throttles the OUTPUT, not the INPUT.
    If the controller has current limiting, or current overload protection, it is of no consequence whether you are talking of input or output current. The protection circuit prevents excess input current to protect the controller. So connecting a solar array capable of 100A to a controller rated at only 50A with current limiting, your effective current will be limited to 50A with current limiting coming into play. And this is where I disagree with you - there should be no damage.

    I do agree with you however that you should spec your equipment correctly. It makes no sense to over spec your panel array current wise if you can never use all of it. If my array was capable of producing up to 30A, I would also opt for the next size 50A controller. The recommendation of over-speccing for cloudy days was from Victron, not me.
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  13. #28
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    Default Re: Panel Configuration

    Quote Originally Posted by mikeml View Post
    The recommendation of over-speccing for cloudy days was from Victron, not me.
    Been doing that for yonks, before knowing about Victron.
    When I asked Victron years later about that over-speccing, jip, emailed them, questioning their calculations, "they said ... " it was more aimed at their big market i.e. European conditions, and not so much S/Africa / Africa / Australia, as we need to take cognizance off the heat factor on the one hand and the winter minus temps on the other, with us having a whole lot more sun than they have in Europe.

    And when I asked them if they can trace if a MPPT has had a over volt and / or too high amps, the person I spoke to said along these lines: "After decades of testing, even destructive testing, then designing equipment better, handling warranty claims, do YOU think we may have some experience on the subject matter?"

    You exceed the max Amps and/or Volts, no warranty claim, simple as that.
    The onus is on you, the user:

    • Don't ever exceed that Maximum PV open circuit voltage.
    • Don't ever exceed that Maximum PV short circuit current.


    Engineers can debate the merits of this statement, debate about clipping/throttling the incoming amps, outgoing yes, you can, for I was told incoming cannot be done as in how do you know what volts you are going to get, so how do you know what amps are coming, parts are installed in the MPPT to handle X volts and Y incoming, and all that. I'm not an engineer, just a guy taking complex situations and try and dumb them down that I can understand them.

    Me, I say: RTFM and stick to the limits written in them manuals.


    Oversizing is an art, kinda. Array position, angle towards the sun in winter, summer, cables etc.
    Once you've used an array for 12 months flat out, you will know the real peak volts, amps and if you can push the limit up a wee bit more.
    Data on ones array is so cool, it should be a must have.

    And coupled to that, the whole trick, and nothing but, is to get that balance, that sweet spot where if you want to remove more watts from Eskom, you will never make it back from the savings, the panels will disintegrate before then.
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    Default Re: Panel Configuration

    Quote Originally Posted by the_terrible_triplett View Post
    .
    Once you've used an array for 12 months flat out, you will know the real peak volts, amps and if you can push the limit up a wee bit more.
    Data on ones array is so cool, it should be a must have.
    Only thing about a year's data, is that no year is the same. You need a moving average and then a couple of year's data

    ....but a year is a fair guideline....
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    Default Re: Panel Configuration

    Quote Originally Posted by Prof View Post
    Only thing about a year's data, is that no year is the same. You need a moving average and then a couple of year's data
    Absolutely true ... with climate change going on, what is today is not so next year.

    So even with data, I still keep well away from them max volts, the amps will therefor follow.
    I use -1 as my lower benchmark, being Cpt, to be safe.
    If I was Jozi based, I would have used -4 - just in case.
    And on those values, I push the limits yes.
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    Default Re: Panel Configuration

    TTT, don't forget to add with the Don't ever exceed that Maximum PV open circuit voltage.Don't ever exceed that Maximum PV short circuit current. , get a lekker nice cold morning and add some nice high clouds in that mix to with some lekker sun and cold panels, HELLO high VOLTAGE!!! Tata MPPT!!! Al the tech guys that work and design this stuff will mention this in all there post when someone are talking about Max pv array.

    On Fb you will see all the posts popping up on the cold days of guys complaining about errors of PV high voltage on the growatt units and some other units. Because the guys are packing to the max on the PV current/voltage

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    Default Re: Panel Configuration

    Quote Originally Posted by mikeml View Post

    If the controller has current limiting, or current overload protection, it is of no consequence whether you are talking of input or output current. The protection circuit prevents excess input current to protect the controller. So connecting a solar array capable of 100A to a controller rated at only 50A with current limiting, your effective current will be limited to 50A with current limiting coming into play. And this is where I disagree with you - there should be no damage.

    If my array was capable of producing up to 30A, I would also opt for the next size 50A controller. The recommendation of over-speccing for cloudy days was from Victron, not me.
    May be this will shed some light on some bended truth answers. This answer from Victron on a question around a 250/100 Victron controller.
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    From the Victron specs you can use Isc above the I max of the controller. 35A if it is a 30A controller and 60A if it is a /50 controller.
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    A common question where it has been indicated to NEVER exceed the PV as per the spec. Victron does not agree as a fact as per this answer. Would Matthias give wrong information?
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    Smile Re: Panel Configuration

    Quote Originally Posted by Gerlach View Post
    TTT, don't forget to add with the Don't ever exceed that Maximum PV open circuit voltage.Don't ever exceed that Maximum PV short circuit current. , get a lekker nice cold morning and add some nice high clouds in that mix to with some lekker sun and cold panels, HELLO high VOLTAGE!!! Tata MPPT!!!
    My tight sailing the other winters morning! This is with frost on the panels. The weather forecast for the day was min -2degC in the morning.

    The 149.1V value is the Voc just after closing the PV panel breaker and before the MPPT does the startup V range sweep to find the Vpowermax.
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    Last edited by vlakkie; 2020/08/15 at 09:59 AM.
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    Default Re: Panel Configuration

    Quote Originally Posted by vlakkie View Post
    My tight sailing the other winters morning! This is with frost on the panels
    Knowing this what plan of action do you have?

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    Default Re: Panel Configuration

    Quote Originally Posted by ekkekan View Post
    May be this will shed some light on some bended truth answers. This answer from Victron on a question around a 250/100 Victron controller.
    Click image for larger version. 

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    From the Victron specs you can use Isc above the I max of the controller. 35A if it is a 30A controller and 60A if it is a /50 controller.
    Click image for larger version. 

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    A common question where it has been indicated to NEVER exceed the PV as per the spec. Victron does not agree as a fact as per this answer. Would Matthias give wrong information?
    Click image for larger version. 

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    Link to Victron blog where this is posted? Would like to read whole thread
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    Default Re: Panel Configuration

    Quote Originally Posted by Prof View Post
    Link to Victron blog where this is posted? Would like to read whole thread
    I will see if I can find it once I am at my PC. In the mean time just search for VICTRON as well as part of the answer I posted in the pictures. That should take you there. I saved these as screen shots some time ago.
    Last edited by ekkekan; 2020/08/15 at 08:20 AM.

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    Default Re: Panel Configuration

    Quote Originally Posted by ekkekan View Post
    I will see if I can find it once I am at my PC. In the mean time just search for VICTRON as well as part of the answer I posted in the pictures. That should take you there. I saved these as screen shots some time ago.
    Got one

    https://community.victronenergy.com/...t-current.html
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    Default Re: Panel Configuration

    .
    Last edited by vlakkie; 2020/08/15 at 10:22 AM.
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    Default Re: Panel Configuration

    Quote Originally Posted by Prof View Post
    These are good blogs and you have to filter through them as there are plenty of opinions, like the first answer, which explained correctly that max PV voltage specs must be observed, and also conservatively advises to adhere to max short circuit current.

    Like here, you will get contradictory answers. I don't think anyone is disputing exceeding max voltage array dangers, but there are different views on max short circuit current. If in doubt, size your panels under max current specs of the controller. It is in any case always a good idea to over spec your controller.

    I still maintain, like some Victron advisors on the Victron blog, that max current is not a concern for the contollers which have current limiting. Current limiting circuits are designed for this purpose.
    Mike Lauterbach

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    Default Re: Panel Configuration

    Quote Originally Posted by ekkekan View Post
    Knowing this what plan of action do you have?
    This is open circuit voltage. So there are nearly no current at these conditions. The Mppt must be able to control up to zero current conditions. So I agree that you should no go over 150V, but in my case I am right at , but at a hair’s thickness below the limit in most cases. Recently, I have in fact gone over it( 2020 is the first time since 2012) and in the process found out that this Mppt does have some protective circuitry that warns and shuts down the system..... and tries again later to switch on.

    I was thinking that some sort of zener diode arrangement that clamps terminal voltages at say 148 V over the mppt terminals might be a way to reign in the panel Voc and clip the upper voltages through some dump resistor when the mppt does the voltage range sweep while seeking the max power point. The resistor does not need to be large since the currents are very small... for my specific system.

    The Pmax point in this case sits at about 100 to 109V for a setup of 5 series connected panels In a 10 panel setup.

    That being said I am more a mechanical guy and at the moment it is easier for me to just implement some voltage nanny with an arduino. I do not want to remove a panel on each of the two series strings for a once in 8 year event.

    Should your normal Voc however sit well above 150V I am sure you will klap the holy smoke out of your MPPT rated max 150V
    Last edited by vlakkie; 2020/08/15 at 09:52 AM.
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