Inverter Idle Current

 

Now that my solar array is making more power than I use for my outdoor lighting, I decided to run some of my indoor lighting from alt-power as well.  I need only to run some wire, leave an inverter turned on, and plug the lights into the inverter.  Sounded easy.  Then I started reading the specifications on my inverters.  These things eat a lot of power in idle mode (on, with nothing connected).

My plan was to switch on the big 1800 Watt Prosine model, and use it for my lights.  By far the most expensive of my inverters, and the best output waveform, but also the most power hungry.  Idle current isn't a problem that is brand or model specific.  The high end Outback inverters also consume about 20 Watts/hr in idle mode.

If an inverter is connected to a running vehicle, or a big solar array, this parasitic load may not be a big deal.  In my case, my big inverter eats 1/2 the energy I produce in a day, doing nothing more than being switched on.

My plan after measuring all of my inverters, is to wire the living room lights to an inverter, and remotely turn the inverter on/off.  Having the inverter off when not in use will greatly reduce the parasitic load.

Take a look at the numbers.  These are actual measurements, not manufacturer's specifications, which are often inaccurate.

 

Vector 400 Watt (VEC024) OLD style MSW model.  Note the boxy shape.
1.8 Watts/hr
43.2 Watts/day
Vector 400 Watt (VEC024BCA) NEW style MSW model.  Note the rounded shape.
6.36 Watts/hr
152.64 Watts/day
Tripp-Lite 600 Watt MSW model
7.8 Watts/hr
187.2 Watts/day
Power-To-Go (Statpower) 1500 Watt MSW model
4.68 Watts/hr
112.32 Watts/day
Prosine 1800 Watt model
15.96 Watts/hr
383 Watts/day
PROwatt SW2000, 1800 Watt model
3.84 Watts/hr
92 Watts/day

Note: Xantrex claims this model has an idle current of < 0.8A.  I measured 0.32A.

 

The bigger, more expensive, PSW waveform instead of MSW, doesn't mean better.  CFL lighting works well even with an inexpensive MSW inverter.  Also note that my cheap, old model Vector inverter has the lowest idle current by far.  The next inverter with the least parasitic load is my 1500 Watt inverter, purchased back in 1995.

To put things into perspective, my Kyocera 130 Watt panel cost about $600.  130 Watts x 5 peak hours = 650 W/Hrs x 70% (derating factor) = 455 W/Hrs per day (effective).  The Prosine inverter (rated), or Outback inverter (rated) is 20 Watts x 24 hours, or 480 W/Hrs per day.  So it would take a $600 panel to have one of these inverters sit idle for a day.

My conclusion from this testing is that I will use a cheap inverter, remotely switched on/off, to operate lighting within my house.  Rather than waste energy having an inverter doing nothing more than sitting idle, it'll be left off until needed.  A 400 Watt inverter consumes 33.3 Amps, so a 40 Amp automotive relay will suffice.  I will likely only have two or three 20 Watt CFL bulbs operating on this circuit.  I'll bench test this setup before proceeding.  When completed, I'll add another link to this page showing the results.

My Prosine does have a Power Save feature.  This only consumes 1.5 Watts/hr.  Once every 2 seconds, the inverter sends out a pulse to detect if a load of 20 Watts or larger, has been applied.  If so, the inverter comes online.  When the load is removed, the inverter goes back into Power Save mode.  Very slick, and I do use this feature.  The downside is CFL bulbs don't present a resistive load, so the inverter can't detect when a light switch has been flipped.  Consequently, I only connect things like my two refrigerators to the big inverter, with an automatic transfer switch I fabricated.  If the grid goes down, the refrigerators automatically connect to the inverter.  It detects the load, comes to life, and runs them as long as the grid is down.  Very slick, but not effective for my lighting.  Inverters are cheap, and nothing says I can't have multiples to serve my needs!

This idle current issue has been an eye opener for me.  Something to think about when sizing your system.

 


*UPDATE*

Most of this data was collected when I lived at my previous house.  I've since added the Xantrex PROwatt SW2000 inverter.  I did a review at this link.  It's a rather basic, pure sine wave inverter.  It lacks a built-in charger, transfer switch, or remote display.  But I don't need any of those items in this application.  The upside is it's inexpensive ($325), puts out cleaner power than the grid, and has a rather low idle current.  Because of the low idle current, this inverter has been powered up today, and will remain on constantly.  The PROsine 1800 model has been turned off, and will be kept as a backup model.  All the MSW inverters have been removed from my system for now.  One peak hour of sun on a single panel, will supply enough power to run this inverter (at idle), all day.  Now I need to rewire portions of the house to use this power, instead of grid power.  Initially, I'll start with the lighting circuits, and go from there.

 

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Last updated 11/17/13    All rights reserved.