AC Coupled- Magnum 4448 PAE & Enphase M250- help needed

calvarado · October 2016

Issue

When on grid (magnum passing thru power from main panel) the panels are producing approximately 10 amps of power @ 240 volts ac without an issue. However, when I go off grid (micro grid) the amperage from the enphase m250 inverters (coming from the solar panels) fluctuates greatly peaking at 50% of on grid power.

Initially I thought the magnum inverter was frequency shifting to 60.5 HZ to turn off enphase inverters however I monitored the frequency during the erratic behavior and it never goes above 59.9 hz and also the amperage fluctuates immediately (not after the 5 minute wait time built into the enphase inverters)

I did notice that while off grid (microgrid) the voltage fluctuates from 243 volts to 246 volts. During off grid operation the dump load ( 4 x 300 watt ceramic resistors) trigger repeatedly as the batteries are fully charged and the load in the sub panel is not significant

I have spoken to magnum energy support and they seem to believe that my batteries are undersized for the amount of power coming in from the Solar panels.

Would appreciate any help you can provide.

Solar System Setup

11 x 265 Watt Panels

11x M250 Enphase Inverters

1 x Magnum 4448 PAE Inverter (RTR remote)

8 x 6 volt interstate 205 AMP hour batteries (wired in series for 48 volts)

2 Gauge DC cables

4 x 300 watt resistors (dump load)

calvarado · October 2016

BB. · October 2016

In general, a starting recommendation would be a maximum of ~2,050 Watts of solar for a 205 AH @ 48 volt battery bank. Too small of battery bank, it is possible for a "too large" solar array to pull the battery bank into over voltage. (Some/many?) solar charge controllers do not react fast enough (or have charging algorithms that do not limit charging voltages that rise quickly) and can fault the attached devices.

Do you see any indications of battery voltage >>52-54 volts or so when the bank is full? How high does it go (your diversion load is being activated--So it is >57.6 volts)? We have had reports (not of the components in your system) that battery bank voltage was over 75 VDC.

I see that you have a diversion load--Was that recommended by Magnum folks/installation manual? Generally, I only see those for systems with Wind Turbines (you cannot disconnect the battery bank from most wind turbines as they will over-speed in moderate to high winds--They need the constant charging current load to keep the RPM in control). Nominally, the dump load would be as large as the "unthrottled" charging source (your solar array).

And you are saying that if you cold start your micro grid, that you see AC current fluctuation from the Enphase inverters before the 2 minute timeout of the GT inverters? Or is this when you have cut the AC mains to simulate the fail over to off grid?

The variation in grid voltage does not sound like a big "functional" issue (could cause some lighting to flicker which would be a pain). However, it may require an oscilloscope to measure the transient voltage--Most digital meters do not read quickly or have peak hold.

One thing to try and see if it stabilizes the AC micro grid--Plug in a portable room heater (resistance heater, or even a hair drier) and see if the AC load stabilize the grid voltage (low, medium, and high).

I have not heard of many systems configured like yours (I am not in the business--So I cannot say that I would see many)--Have you talked with anyone that has a similar installation? Has your installer/consultant worked with any similar?

-Bill

Dave Angelini · October 2016

This hurts my head! On a day without wind try testing without the wind generator/dump load.
Everything Bill said. I assume you installed this?

AC Coupled- Magnum 4448 PAE & Enphase M250- help needed

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