Stand By

I’m changing out the 5kw inverter in my boat, installing a 3.5kw unit.  Do I need less power?  No, I need an inverter that runs to spec and does not melt the rubber transformer mount when you run it over 10% for a period of time.  Good electronics, but not enough transformer.  Typical Chinese math in the specifications!

I saw another Chinese inverter boldly emblazoned with a label that said “3000 WATTS”.  Read the fine print and you see “1000 w continuous” and “2000 w surge”.  So they add up the continuous and the peak power to declare this a 3000 watt inverter.  I think that is the point where you hear a loud bang, followed by a puff of smoke.  Another favorite factor in Chinese math is the use of milliwatts instead of watts.   That way they get to use a number 1000x larger.  Then they puff that up another couple of decimal places.

I did not start off to rant on fake inverter specs.  The Chinese do, in fact, make some rather good gear, but scoundrels abound.  Rather, I wanted to talk about a feature you see on some inverters, both high end and the cheapos.  This is the STANDBY position on the power switch.  An idling inverter uses a certain amount of power, even without a load.  These days the modern electronics are pretty efficient, but a load is a load and that can really matter on a small system.

What the standby mode does is mostly turn off the inverter.  There is  a little wake up pulse at intervals, say 15 seconds.  If a load is detected, then the inverter fires up and power is provided.  Two examples might be letting the inverter run only when the fridge needs to run or if you get up in the night for a bathroom run.  This feature usually requires a load of around 50 watts to get started.  In modern times when we no longer much use 60 watt incandescent light bulbs, your newfangled LED or CFL bulb is just going to flicker.  The outgoing boat inverter had this switch and was potentially useful as the switch was in an awkward place and the two ac loads I had were a microwave and coffee pot.  New, push-button microwaves might not work or they might cause the  inverter to run all the time.  Mine is an old twist knob oven.

What’s the watts math?  The new inverter says it has an idle current of 1.2 amps.  1.2X27 (the battery voltage)x 24 hours in a day comes to 778 watt hours.  Around here, a fair estimate of 5 hours is used for an effective full rating of a panel, so 778/5= a bit more than a 150 watt panel will provide in a good sunny day.  That is to do nothing.  If your standby mode uses 10% of that, then that is quite a savings.  Any time you can use less power you save money on building or maintaining your solar power system.

This could be useful on a boat or in a remote cabin with a small power system.  As a practical matter, if you are running a modern American home on solar, you’ll have some sort of load going all the time and standby would do you no benefit.  Just thought you might like to know about that switch.

As for the new boat inverter, it has a remote switch I can mount in the galley, so it will only run as needed, saving even more watts.  Oh, and I went with the 3500 watt size so I can use the boat to charge the motorcycle, two mini farm trucks and the airplane, if it is ever delivered.   That will take a big load off the home system, which is working hard to keep the a/c going in 100 degree temps.–Neal

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