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Nickel-Iron technology Off Grid Solar Power

Q17: Testing MPPT behaviour

Notice it's 9.30 am and both Trina and Zeus are on bulk. Normal.

Since we used 100 amps yesterday, I expect at this sunshine rate to be on float by noon.

Note Trina has 30 amps coming in, and Zeus has 27 amps coming in.

Great !

In 2 hours the batteries should be fully charged at this rate.

These Hall Effect Ammeters are great, cheap, leave the back lit LED off, do not worry about settings, just hook up yellow wire to your red wire near fuse holder, red and black leads to a 5 to 9 VDC voltage supply, and things are accurate enough for visual display of the entire system, I purchased 12 of these, a total cost of $200. The current is milliamps, so wire all 12 in parallel consuming 1 amp if your lucky, hence lots of thin wires are roughly twisted together and taped over.

A switch was installed to remove heat overload from DC DC convertor, 24 V to 9V, get hots if left on 24hours per day?? Why? Dunno. So switch off when not used.

Would be nice to measure amps in and amps out of a battery bank, but this is a budget issue, and the more wires connected, voltage drops and impediance issues. So keep things simple is best.

Testing the voltage with voltmeter, is roughly same as halls effect ammeters.

27.7 Volts

OK, now lets play around with Victron data for Trina and Zeus for last few days, cut and paste and delete columns, comes in Excel format.Pictured here. Divide yield by 24 gives amps/hr coming in. Getting over 400 amp/hrs way too much for my battery bank.

It's noon, let's check the battery bank.

Both on float,, correct. :)

  • Trina on float at 3.3 amps
  • Zeus on float at 4.1 amps

    Battery voltage is 29.1 V (nearly fully charged)

    On a very sunny day, over 700W, only 104 W is coming in.

    This is normal for Zeus.

    On a very sunny day, over 700W, only 70 W is coming in.

    This is normal for Trina.

    Fridge is the only load for now, 3.9 amps.

    Now let's test the bank with a load, say 20 amps for an hour.

    My wife has got a tap water sprinkler running. Perfect timing.

    20 amps for pump + 3 amps for fridge= 23 amps/hour.

    Both MPPT's are on float with 26 amps shared, coming into battery bank.

    This is perfectly normal... 26 amps coming out and 26 amps going in, the bank floats on fully charged.

    So what went wrong with the MPPT's?

    As a computer teacher, my experience is the computer settings in the MPPT do not kick in straight away and often are ignored. So the changing back and forth, saving and resaving, causes the changes to be finally recognized. The Victron update of firmware may also have done something, a bug or two was possibly fixed. And the prayers to God may have helped too. The end result, everything is working as it should be. Shalom

    Now that everything is fine, and the user defined voltages are set:

  • Absorb is 30V
  • Float is 29V

    When your bank falls from current going out at night, the voltage drops. When the sunshine comes in next morning, there are three stages of charging:-

  • Bulk, 100% of current comes into bank.
  • Quickly the voltage rises to Absorb V.
  • Absorb stage works, holding V steady
  • Holding V steady, the current decreases
  • This happens with batteries.
  • Once current reaches 2 amps, float begins
  • Float V is set, and trickle amps maintain

    If you set ABSORB too high, the chargers might not reach this voltage, because batteries are old, chemistry does not allow, things too hot, etc.

    The absorb level is set to 30V at the moment, but with new Ni-Fe the absorb could be between 30 V and 38V. Set to 33V is typical.

    The higher the Absorb, the higher the State of Charge (SOC), or the more overcharging and water loss you get. Depends on things.

    Will hold the user define voltages here for now and test the system for a week.

    It's 2pm, time for sunshine to sink away from panels. Turn off water sprinkler.

    Some H2 pipes removed, laptop in place... Picture of system...

    Water pump using 18 amps, just before switching off. It's pressure water pump, until pressure is reached, than switches off, turning off Inverter.

    Bedroom fan and fridge going, 12 amps going out, 12 amps coming in, all still on float.

    Perfectly normal :)

    Great, the MPPT behaviour is normal and predictable.

    On second day of the new settings, overnight we had used about 100amps and during the day wife had pump and thus bore pump on, another 150 amps. So the batteries now require 150 amps to reach float. The panels have 60 amps coming in. And by 3 pm both MPTT's controllers reach absorb, which is great. The current coming in is just 12 amps, not 60 which is also great.

    Everything seems OK.

    On the second day of the new user define settings, the absorb time seems normal.

    Zeus is on Absorb with 8 amps coming in. OK

    Trina is on Absorb with 13 amps coming in. OK

    The ammeters show similar values. Great

    Everything is fine, except I may run out of sunshine to reach float.

    Its hard to get ourselves living with off grid.

    Use only the power when it's available.

    Do not go into credit, which happened today just a little.

    The biggest consumer of our power is the bore and water pumps.

    For this data for our new user defined voltages, both Trina and Zeus never get to float, so we need more sunshine from our solar panels, or more solar panels.

    Noticed as the water pump ages the watts comsumed increases, so now we get 20 amps rather than the usual 17 amps. The inverter is tripping now, nearing its 100% capacity, so I have to install a 1200VA one rather than the 800VA.

    So some advice, use a 800VA just for fridge, and 1200 VA for all other appliances.

    A long term solution is to add a third 30 amp string and MPPT.

    Next, we look at solutions to the storage battery problems.

    Ni-Fe battery technology

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