Inverter/Charger input from Genny

AkoAko Registered Users Posts: 162 ✭✭
edited April 12 in Solar Beginners Corner #1

I have spoken to a solar dealership about buying a Victron Multiplus 1600va 24 volt inverter/charger , they tell me that my 1.8kw generator will not be big enough to charge my batteries . The charger on the Inverter/charger is 40 amps , I cant get my head around why not . At present I have a quality Battery charger and my generator is not struggling at all when charging my batteries at 35 amps while at the same time providing power into the house for appliances , lights etc at 500 watts . I am told the Inverter/charger will draw a lot more than a regular battery charger even if the unit is only charging the batteries and no load from the house it still wont be big enough . Obviously I dont understand something , to me If a battery charger is sending 40 amps to a battery at 24 or 25 volts then its drawing around 40 x 25 = 1000 watts so why wont my 2200kw ( 1800 watts constant ) Honda Inverter Generator manage it , can anyone explain what im missing ? . The dealer said its a constant problem and they have to check with Victron what size generator to tell their customers to buy before selling them an Inverter/Charger .


1050 Watt 24v Array . BP and Atersa 72 cell Panels 
Morningstar TS-60 Charge Controler
4 x 6v 400 Apm/Hr Trojan L16 AGM
Solener 1500w Pure Sinewave Inverter

Comments

  • RCinFLARCinFLA Solar Expert Posts: 1,460 ✭✭✭✭
    edited April 12 #2
    You would need to set inverter maximum allowed AC input current limit so it does not overload generator.  

    Depending on AC output load on inverter, the charging takes second priority and will automatically back down to service the AC output load from inverter first based on AC input current limit setting.

    If you don't limit max inverter AC input amp draw it can overload generator upon initial connect with generator causing it to slump in voltage or frequency causing inverter to immediately release connection to generator.  It just repeats this connect attempt and fails to maintain connection.
  • AkoAko Registered Users Posts: 162 ✭✭
    edited April 12 #3
    That aligns with what the guy said but didnt expand on , he said the Charger will look at the genny and if it cant see sufficient power it will not connect and keep trying and failing , this he said was the reason he used to have to tell clients to buy larger generator's after they have already bought and installed this inverter/charger so now he asks Victron what size genny is required for the unit to work  . From what you say he is giving poor advice , i get the impression from your explanation that all thats needed is to restrict the AC input to the charger so that its less than the genny can provide and as i will only have a small load for the house when batteries are charging its not as big a problem , I guess it comes down to what input AC i need to provide the 25 amp charging to the battery bank . 25 amp charging at 25 volts to me would be les than 700 watts plus the house max of 500 watts adds yp to a maximum of 1200 watts so 1250 watts input limit should be sufficient and genny should be happy running at only 2/3 capacity  . Have i understood everything you explained correctly or isnt it that simple ?
    1050 Watt 24v Array . BP and Atersa 72 cell Panels 
    Morningstar TS-60 Charge Controler
    4 x 6v 400 Apm/Hr Trojan L16 AGM
    Solener 1500w Pure Sinewave Inverter
  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    edited April 15 #4
    Looking at the manual and settings that affect genset interactions:

    https://www.victronenergy.com/upload/documents/Manual-MultiPlus-1600VA-EN-NL-FR-DE-ES-IT.pdf

    Page 3:

    PowerControl – Dealing with limited generator or shore side power With a Multi Control Panel a maximum generator or shore current can be set. The Multi will then take account of other AC loads and use whatever is extra for charging, thus preventing the generator or shore supply from being overloaded.

    PowerAssist – Boosting the capacity of shore or generator power This feature takes the principle of PowerControl to a further dimension allowing the MultiPlus Compact to supplement the capacity of the alternative source. Where peak power is so often required only for a limited period, it is possible to reduce the size of generator needed or conversely enable more to be achieved from the typically limited s

    Page 12:

    Input frequency range

    Input frequency range accepted by the Multi. The Multi synchronises within this range with the AC input frequency. The output frequency is then equal to the input frequency. Adjustability: 45 – 65 Hz; 45 – 55 Hz; 55 – 65 Hz

    Input voltage range

    Voltage range accepted by the Multi. The Multi synchronises within this range with the AC input voltage. The output voltage is then equal to the input voltage. Adjustability: Lower limit: 180 – 230 V Upper limit: 230 – 270 V



    Page 13:

    AC input current limit

    These are the current limit settings at which PowerControl come into operation. The factory setting is 12A.

    UPS feature

    If this setting is ‘on’ and AC on the input fails, the Multi switches to inverter operation practically without interruption. The Multi can therefore be used as an Uninterruptible Power Supply (UPS) for sensitive equipment such as computers or communication systems. The output voltage of some small generator sets is too unstable and distorted for using this setting* – the Multi would continually switch to inverter operation. For this reason, the setting can be turned off. The Multi will then respond less quickly to AC input voltage deviations. The switchover time to inverter operation is consequently slightly longer, but most equipment (most computers, clocks or household equipment) is not adversely impacted.

    Recommendation: Turn the UPS feature off if the Multi fails to synchronise, or continually switches back to inverter operation. *In general, the UPS setting can be left ‘on’ if the Multi is connected to a generator with a ‘synchronous AVR regulated alternator’. The UPS mode may have to be set to ‘off’ if the Multi is connected to a generator with a ‘synchronous capacitor regulated alternator’ or an asynchronous alternator.

    Page 14:

    Dynamic current limiter

    Intended for generators, the AC voltage being generated by means of a static inverter (socalled ‘inverter’ generators). In these generators, rpm is down-controlled if the load is low: this reduces noise, fuel consumption and pollution. A disadvantage is that the output voltage will drop severely or even completely fail in the event of a sudden load increase. More load can only be supplied after the engine is up to speed. If this setting is ‘on’, the Multi will reduce charge current until the set current limit is reached. This allows the generator engine to get up to speed. This setting is also often used for ‘classic’ generators that respond slowly to sudden load variation.

    WeakAC
     
    Strong distortion of the input voltage can result in the charger hardly operating or not operating at all. If WeakAC is set, the charger will also accept a strongly distorted voltage, at the cost of greater distortion of the input current. Recommendation: Turn WeakAC on if the charger is hardly charging or not charging at all (which is quite rare!). Also turn on the dynamic current limiter simultaneously and reduce the maximum charging current to prevent overloading the generator if necessary.

    More or less--To operate from your 1,800 Watt genset, you would change the 12 Amp @ 230 VAC 50 Hz input to:

    • 1,800 Watts / 230 VAC = 7.8 Amps max generator loading (assuming 230 VAC nominal voltage)
    And, nominally, for residential gensets, I suggest that you only run them at 80% of rated power--With battery banks, it is easy to have "hours of max battery charging current" on a non-commercial genset and possibly overheat the alternator/motor.
    • 1,800 Watts * 0.80 genset derating = 1,440 Watts suggested max genset loading
    • 1,440 Watts / 230 VAC = 6.3 amps @ 230 VAC derated genset limit (set AC inverter-charger AC max current to this as a starting point)
    Depending on how everything is setup, for example a 40 Amp @ 29.0 volt DC charging output:
    • 40 amps * 29.0 volts charging = 1,160 Watts max charging power
    More or less, the Inverter-Charger will draw power from the genset to both run the DC charging block, and your AC loads.

    If the AC loads + Charging demand exceeds AC input limit (say 6.3 amps), the charging block current (power) will be reduced to meet that 6.3 Amp AC max input current.

    If the AC loads are greater than the AC genset output, the inverter-charger will supply "missing" current and assist the generator to carry the larger loads (for short term--This is obviously draining the battery bank to supply the extra power:

    https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-5kVA-EN-.pdf

    PowerControl - Dealing with limited generator, shore side or grid power The MultiPlus is a very powerful battery charger. It will therefore draw a lot of current from the generator or shore side supply (nearly 10 A per 5 kVA Multi at 230 VAC). With the Multi Control Panel a maximum generator or shore current can be set. The MultiPlus will then take account of other AC loads and use whatever is extra for charging, thus preventing the generator or shore supply from being overloaded.

    PowerAssist - Boosting the capacity of shore or generator power This feature takes the principle of PowerControl to a further dimension. It allows the MultiPlus to supplement the capacity of the alternative source. Where peak power is so often required only for a limited period, the MultiPlus will make sure that insufficient shore or generator power is immediately compensated for by power from the battery. When the load reduces, the spare power is used to recharge the battery.

    I think for you unit, the maximum rated output current is 16 Amps @ 230 VAC (16 amp transfer switch?). I.e. 6.3 amps max genset current + 8.7 amps from inverter-charger (if needed to support AC loads--Such as for motor starting of a well pump, power tools, etc. while the genset is running).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Solar Expert Posts: 1,460 ✭✭✭✭
    Inverter has no way to tell what AC source power capability it.  It only can tell if frequency is within lock range and its AC voltage is within limits of inverter.  Distortion is not often a problem unless it causes inverter to have overload.  The inverter will fill in AC source distortion in most cases.  You have to manually setup the limit the inverter AC input is allowed to load generator by setting max allowed AC input amperage loading.

    Most common issue with synchronous generators (constant rpm that determines AC frequency output) is unstable rpm governor speed control.  Inverter phase locks to AC input and matches it rms voltage. Inverter has narrow tracking bandwidth meaning it cannot track fast changing input frequency due to wobbling generator rpm control.

    Based on inverter AC input frequency limits it will only sweep that range to find phase lock.  If generator is outside that freq range no phase lock will be achieved.  The farther off the gen frequency is from center of inverter frequency lock range the longer it take searching for phase lock.

    On initial synchronization attempt, if generator is wobbling in rpm and thus frequency too much, the inverter cannot lock to a moving target for phase of incoming AC source.

    If you overload generator, it will bog down, drop in rpm, and change frequency too fast causing inverter not to be able to track phase and causing it to release from generator. The inverter will try again from the beginning trying to establish sync to AC input before reconnecting.,  If inverter jumps on generator with too much load it will just keep releasing from generator and the process keeps repeating.
  • AkoAko Registered Users Posts: 162 ✭✭
    Thank you BB  and RCinFLA , i recognize the time you went to in order to give a comprehensive explanation and is very much appreciated .After reading everything and absorbing most of it several points have given me the confidence to go ahead and buy one of the units however after re evaluating our needs and knowing our consumption I am confident that the 1200 watt model will fit the bill .

    Our consumption in 24 hours is consistent and has been for years between 3500 to 4000 watts split fairly evenly between daylight hours and night time use . The highest peak drawing which would be the fridge or freezer cutting in at the same time as our cold wash washing machine but has never exceeded a momentary 2200 watts so the 1200 model looks like it will be ok .

    The method of calculating you demonstrated are what I did at present with my 35 amp battery charger before buying it ( 35 x 29 = 1015 + 500 = 1510 ) but the dealer made it sound like it cant be done that way , there was something about the Inverter/charger that mysteriously placed a much larger load on the genny .

    I have mentioned the numerous points your posts raised such as the Input Current Limit on the draw from the Generator but the dealer dismissed that with saying it might say that but it will never work , the generator will look for what it thinks it will need irrespective of the limit at , which is why before we sell one now we will ask Victron the minimum load that the inverter needs to draw , I am wondering if he meant that possibly only when running might the Current Limit actually do something as he is adamant that these Inverter/Chargers need far more than one would normally expect .

    I have googled the unit to see what the factory setting is for the current input but there doesnt seem to be a manual for it , shows it on google but when the links open its always the manual for a larger model . Based on the explanations given here I have now ordered a 1200 watt model so will see for myself once I get it .


    1050 Watt 24v Array . BP and Atersa 72 cell Panels 
    Morningstar TS-60 Charge Controler
    4 x 6v 400 Apm/Hr Trojan L16 AGM
    Solener 1500w Pure Sinewave Inverter
  • littleharbor2littleharbor2 Solar Expert Posts: 1,699 ✭✭✭✭
    Bear in mind that the AC current limit when charging a 24 volt bank is 1/5 the dc charging output.. If you are charging at 40 amps that should be about 8 amps @120vac.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • AkoAko Registered Users Posts: 162 ✭✭
    Bear in mind that the AC current limit when charging a 24 volt bank is 1/5 the dc charging output.. If you are charging at 40 amps that should be about 8 amps @120vac.

    Im in Spain and were 230 volts here and the model i decided to buy is the 1200 watt version with a 25 amp charger .
    1050 Watt 24v Array . BP and Atersa 72 cell Panels 
    Morningstar TS-60 Charge Controler
    4 x 6v 400 Apm/Hr Trojan L16 AGM
    Solener 1500w Pure Sinewave Inverter
  • 706jim706jim Solar Expert Posts: 476 ✭✭✭✭
    My Trace inverter manual mentions that "It takes a powerful generator to reach the rated charging current at least 2500 watts for the DR1524 or 5000 watts for the DR2524". Something to do with maintaining the 165 volts peak of the AC sine wave.

    Maybe this is what your dealer was getting at.

    I use my Honda EU1000 on occasion to charge my battery bank. It works, but it is slow.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 29th year.
  • RCinFLARCinFLA Solar Expert Posts: 1,460 ✭✭✭✭
    Old DR series modified sinewave inverters have simple transformer-rectifier battery charging.  They have poor power factor for charging so take a higher VA generator.  
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