Various aspects of home brew inverters

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Joined: 02/02/2017
Location: Australia
Posts: 1382
Posted: 08:33am 11 Jun 2018      

Part 21: Change over from street to inverter and vice versa

My solar power system is supplying about 50% of the house's energy needs.
I arranged the inverter to switch on when the battery volts are high enough and to switch off when the battery volts reach 48.5V
This is for a SLA based 400AH 48V battery, which maintains approx 60-70% capacity when the inverter switches off.
This switching on and off of the inverter, averaging about 1 off and 1 on event per day is managed by a Latronics change over switch.

Today I show voltage and current waveforms of the change over street to inverter and inverter to street.

Some change over events occur when street AC phase is close to inverter AC phase.
Other events occurred when they were 180 deg different.

I was interested in phase matching the inverter to street AC prior to change over but my experience has shown this is not vital for inverter (&/or household equipment) health.

Yellow is inverter current
Light Blue is inverter voltage
Pink is street voltage
Dark Blue is street current
Both current and voltage scales are similar, i.e. comparable.

This is inverter -> street under light load (200W ish)
Phases are close

Street -> inverter, same light load. Close phases again

Here is a changeover, street -> inverter
180 deg phase diff.

Whoa, dude. This event was accompanied by a loud hum generated by the
inverter. This hum dies out after a minute or so.

here is inverter - street, same loads as above.
Even the street current is large for a few cycles, then it reduces to
normal. Same vertical scales, note.


So, I was always wanting to see this, and today I finally got around to it.
Maybe this feeds some reader's curiosity, if so, good.

Edited by poida 2018-06-12
wronger than a phone book full of wrong phone numbers