Running Sanyo mini-split on MSW inverter?

Re: Running Sanyo mini-split on MSW inverter?

It is the old "how cheap can I make the voltage regulator" question...

The blocking cap is a simple way of limiting AC current to, one example being a rectifier+zener clamp diode and filter cap. The cap provides a limited amount of current through the rectifier and the zener diode just clamps the voltage to 5 volts or whatever is needed to power the electronics.

With MSW (i.e., sharp edged square/step waves), to a capacitor sharp edges have more high frequency content than the slow edge of the sine wave.

So--the capacitor not only lets through the fundamental 60 Hz (like a sine wave), it also lets through the energy of the higher frequencies too--causing much more current flow through the rectifier and the zener diode to "toss" the "extra" energy away (overheating the zener). These small devices usually do not have much thermal mass and are not significantly heat sinked (again, to save money). So when they have extra heat to dissipate, they do not survive very well.

That is just one example, another is that, again the high frequency, causes circulating currents in the iron of a power transformer--those currents do not contribute any power to the 60 Hz flowing through the transformer but instead simply just heat up the iron in the transformer.

It sound like for example in the above fridge measurements, that an extra 30 watts to dissipate out of 100 nominal is not a big deal... But remember many of these guys are 80% efficient (plus or minus). So, 20% loss of 100 watts is 20 watts of "heat" to get rid of...

Now add an extra 30 watts of waste heat do to MSW--and the design now has to dissipate 1.5x more energy than the original design.

And, it may not kill things right away... Another very handy engineering rule of thumb is the 10C rule... For every 10C (18F) increase in temperature, the life of a component will be cut by 1/2. And a 20C increase will be a 1/2*1/2=1/4 life and so on...

So extra heat can be a very serious component of reduction of life.

Another is "sharp edges" of a MSW wave form can make things buzz/rattle/etc... A 60Hz sine wave has only the fundamental frequency. It is the equivalent of "shaking" at 60 (or 120 Hz).

A MSW square wave front is almost the equivalent of hitting something with a "hammer" (in engineering, we use "impulses" to characterize a system--like hitting a bell with a hammer and measuring the resonance frequencies that result)--- Lots of high frequency energy too. Probably does not cause much of a problem for most AC devices--but the buzzing sound can be very irritating.

Again, not saying I will know what will happen to your Sanyo--Just examples of why it is so hard to "guess" what will happen without detailed knowledge of the circuits and/or using a (preferably) True RMS current meter to measure the Sine and MSW current going into the Sanyo.

If the RMS value of current is similar for both Sine and MSW--I would not be to worried about the MSW causing overheating failures of your electronics.

Of course, if there are timing circuits that use the AC power as a frequency source--MSW can run 2x faster on those devices than a TSW will (again, the fast edges can confuse a frequency detector circuit for electronic timers).

Sorry for all the hand waving... I don't have much information here and I don't want to see a $1,000 repair bill because "BB." said it "should be OK to run YOUR Sanyo on an MSW inverter".

If it was my system--I would pop for a decent (i.e., cheap:roll:) True RMS AC/DC clamp meter and do some measurements. And if the TSW vs MSW currents are close (less than 10% difference)--I probably would run it on MSW (if it makes economic sense--I.e., saving $0.10-$0.20 per day vs toasting a $1,300 A/C system + labor == ~23 year payback on risk--Ummm).

I am very much a Risk vs Reward kind of guy... Sometimes the reward is just not worth the risk. (i.e., put an AC timer on the Sanyo to turn on 1-2 hours before you return home to reduce standby heater costs instead).

-Bill

Re: Running Sanyo mini-split on MSW inverter?

JESSICA wrote: »

BILL:

Something must be wrong:

I just connected it to the msw inverter:
Kill-a-Watt readings:

Power Factor: .25
Hertz: 12
Voltage: 122
Watts: 8 - 10

What is going on? (I mean: "12" Hertz?; .25 PF?)

Regarding Hz--I am guessing it is not reading your MSW information correctly. Timing circuits from AC MSW wave forms are not aways accurate--looks like that here (I have not seen anyone else reporting this problem before--so I am at a loss).

The PF of 0.25 can be "correct"... The problem when many loads operating in "standby" have a little bit of stray/excess inductance or capacitance that becomes a major factor at low current values. (i.e., radio frequency filters on AC power lines draw a little bit of "out of phase" current too).

What is the amp reading for Grid and MSW? If nearly the same--then you may be OK to try MSW on standby). What are all the readings (volts, amps, hz, power factor, VA, etc. on Grid/MSW).

-Bill

Re: Running Sanyo mini-split on MSW inverter?

JESSICA wrote: »

Bill:

I cannot give you my opinion about your Spanish. Please, write in Spanish your next reply so that my wife (the real Jessica), who teaches this Language in the same University, may tell me !!!

I don't like to ignore things. Please, What does the kill-a-watt reading "dC" means?
Now "19" and next time "20". In fact, the first reading, early in the morning, was 24.

Got a D in Spanish 1 in high school first year, got an F in Spanish 1 the second year. Went to another high school where D was passing and never looked back (and probably would have been a very happy high school drop out if I needed more foreign language to pass). Frankly, English is not "my thing" either. As everyone can see here.

Regarding the Frequency reading. I do not know what is going on--but there are several possibilities.

One is that this use a capacitor to detect the changing voltage. Basically, a capacitor (plus diode or so) lets one or two pulses through for every sine wave:

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A MSW inverter actually looks like, upwards of 4 voltage changes for every cycle:

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  _
_/ \_   _
     \_/
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to a capacitor each of those flat spots (_) looks like a DC signal--so there may be 4 edges (AC transisitons) detected for every cycle--instead of the two expected for a sine wave.

It is also possible that they use voltage peak detection too... A sine wave has a voltage peak of around 170 volts... An MSW wave form has a peak around 150 VDC--They may just not see any peaks at all (again, an alternative to above--I don't know what they are using).

The Kill-a-Watt is designed (probably) for 40-70 Hz or so--And any number outside of a 1-100 Hz range will go to some default display (DC?).

Regarding your PF readings... Basically, PF should be:

• PF = "Useful Current" (true RMS in phase) / "Total Current" (RMS current regardless of phase)

So:

• Useful Current = Total Current * PF = 0.12 amps * 0.62 = 0.0744 amps of "useful current"
• UC = 0.34a * 0.19pf = 0.0646 amps of "useful current"

So... Both Grid and MSW inverter, the standby load is around 0.07 amps of useful current--which would be expected. The total current goes up because of losses caused by the "sharp edges" (high frequency content) of a MSW inverter--which can be wasted at heat (and the problems that causes).

Note that these are pretty small values of current and it is possible that the Kill-a-Watt does not measure them all that accurately--So you will get some variation in readings... The PF = 20-24 is could be part of that issue--or it is possible that the PF at those small loads does vary on the Sanyo that amount too--Remember we are talking about small changes turned into a ratio which can make the changes look large--even though we are talking about very small numbers (relatively speaking).

-Bill

PS: Since I am not proud about my language skills--I have no issue with answering questions using Google Translate:

hola tiene soporte en español

-Bill