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Murphy's friend

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Joined: 04/10/2019
Location: Australia
Posts: 640

Posted: 08:43am 03 Jun 2024

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The 6 KW experimental inverter I'm tinkering with draws about 50W from my 55V battery bank while there is no load plugged in.

Curious to know just where that power goes, I started investigating. Standby power is important, especially for those with a smaller battery bank.

First the AC side was tackled, for that I just disconnected one choke lead from the choke.
Next, everything was disconnected from the transformer's 235V winding and 235V AC applied to it.
I used RMS reading multimeters for this testing BTW.

The winding by itself took 10.8VA of magnetising power.

Then I added a 0.22uF mains rated capacitor, this reduced the power to 10.1VA.

To this I added a 1uF cap, making a total of 1.22uF, and the result was 20.3VA.

Now, as per warpspeed's suggestion, we should resonate the secondary at 75Hz by adding capacitors in parallel. My transformer required 1.68uF to resonate at 75Hz.
This would result in even more than the 20.3VA power draw above

.
So, I will forget about that resonating idea and stick to the 0.22uF cap alone.

OK, time to connect the rest of the AC parts in the output loop.
First my 2x20A interference suppression modules:

Doing that increased the idle power to 22.8VA

The last item was the Volt/Amp/Watt/ KWH power meter. It's on all the time when the inverter is running, to keep track of the KWH used.

The total AC idle power added up to 37.6VA.

I suppose one could find a lower consumption power meter, mine was the type with different colours for the different units displayed.

The plan now is to tinker with different chokes and mosfet switching timing to see if that 50Watt draw from the battery bank could be reduced a little.

On another matter, I'm sure I'm not alone in having to swap blown multimeter fuses by forgetting the inrush current can be many times the running current of things containing transformers or capacitors

.

For the above tests I used this cheap little home made gadget:

The multimeter, set to Amps, is plugged in at one end. The 2 leads from the box then become the multimeter leads.
Switch it to 'short' to connect up and power up. When running, switch to 'measure' and read the milliamps that the meter fuse easily can handle

phil99

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Joined: 11/02/2018
Location: Australia
Posts: 2045

Posted: 09:00am 03 Jun 2024

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Quote Then I added a 0.22uF mains rated capacitor, this reduced the power to 10.1VA.

To this I added a 1uF cap, making a total of 1.22uF, and the result was 20.3VA.

The extra 10.2VA is reactive (VAR) not real power (W). It won't affect the battery current by a significant amount.

However you still don't need the extra 1µF. Extensive testing by KeepIS found the exact capacitor value is of minor importance.

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