Mitsubishi phantom loads

Polycarp

I have a Mitsubishi hyperheat multi split heat pump.  I have power metering on the HP’s branch circuit and the unit is always pulling around 220W. It used to go down to near zero, but doesn’t anymore.

 I thought it might be the crank case heater, but Mitsubishi says that should only pull 50W, and also should be turning off when the outdoor temp is higher.  This is a constant load. 

I've checked the indoor units (which are powered from the outdoor unit) and they are only pulling about 15W each.  I’d expect some off-operational load, but this just seems too high.  It accounts for 35-45% of our total energy use.

we’ve had the installer out, but they didn’t even bring the right communication cable, so I doubt their ability.

Jamie Hall

Have you electrically disconnected the Mitsubishi itself to make sure that it really is the culprit?

ratio

Yeah, chasing things like that you'll need to check the zero & calibration of your instruments, particularly if it's some comsumer-grade thing like a kill-a-watt.

What are you using?

Larry Weingarten

Hi, @Polycarp , Do you, or a friend have a thermal camera, like a Flir One? It's a very useful gadget! Use it to have a look at the equipment and see if you can find any hot-spots. That would tell you what's using the power, which will help a lot in troubleshooting.

Yours, Larry

JUGHNE

Do you have an outlet near the outdoor unit?
Is anything plugged into it?

Code requires an outlet within 25' of AC unit, I have done the outlet with the AC circuit and using 12-3 cable to get the neutral there.

The load of an outlet connected in this manner goes thru the AC CB.

What type of measuring device are you using and where is it connected?


Note: do you get the same reading if the system is in cool or heat mode?
Perhaps there is a holding coil on the reversing valve drawing power when in the opposite mode of operation.

Polycarp

ratio,

The metering system is Emporia. I double-checked with a fluke current meter and got the same answer +/- 1%.

JUGHNE,

There is nothing else on this circuit but the heat pump. The outlet for the HP does not have a receptacle, so there is no way to plug something else in.

I also get the same results whether the thermostats are in auto, heat, cool or off modes.

Larry,

I don't have a Flir or easy access to one, but maybe this is the excuse I've been waiting for.

GW

You have all the indoor units off when you are  getting 220w? What is Mitsubishi saying you should be reading? 

JUGHNE

220 watts is a lot of heat, you could not hold a 200 watt bulb in your hand very long.
You might have a power supply board/transformer etc that is cooking itself.

I got a handy FLIR camera for 350 and that might be 400 now, but it is a great toy.
I can see my heating loops thru the concrete and where the dog was laying 5 minutes after he gets up.

For instance on a 12' ceiling with diffusers from 2 systems you can tell which is heating, without a ladder.
Also for finding failed open steam traps on rads.

Jamie Hall

Kind of what I'm getting at... 220 watts is a lot of heat, indeed, and it has to be going somewhere. One of those nasties about energy is that it has a way of winding up as heat, pretty much every time.

Grits

Was there any resolution on this phantom load issue? I get pretty much the same thing - actually a bit more - about 1.26A (240V) when the breaker is closed and the unit is "OFF" (and no noises, doing nothing). That is about 7.2kW-hr a day! I have a Mitsubishi Model PUZ-HA36NKA hyper heat (36k btu).

JUGHNE

Is the unit "OFF" at the tstat or outside at the power disconnect to the unit?

Grits

Hi JUGHNE. The breaker is closed so the unit has power. It is 2 wire w/gnd (no neutral), 240VAC. I am measuring on the conductors right at the breaker; the Mitsubishi is the only thing on the circuit. There is a thermostat that connects via RF and controls the unit: it connects within 3min of power application and it is set to OFF. Neither the indoor nor outdoor parts are making any sounds. I am measuring the current monitors with a Fluke 87 (True RMS); I calibrated with 60W and 100W light bulbs and it reads just as expected. With the unit powered and in OFF mode and no evidence of activity (sure, there are control boards) it reads 1.26A, either leg of the feed. When I turn the thermostat to Cool, or Heat, the power jumps up to sensible values - something like 5kW (and then may drop back a bit and waffle as it sees fit..). So it really seems to be a "Phantom" load. I have a service visit expected 9/14/23 and they are apprised of the situation. Even if there turns out to be some explanation, this is really bad for idle power consumption.

pecmsg

Transformer(s)
crankcase heater(s)
drain pan heater(s)

Grits

pecmsg - Can you please tell me the role/function those heaters? Would they normally be active at 85F outdoor temperature? Sounds like something for -20F operation. In the unit-powered-but-off condition this load is stable and continuous. I'm having trouble imagining a modern appliance in the age of Energy Star stuff having such a high idle consumption.

Are you suggesting a "bad" transformer? That seems extremely "lossy" for a transformer. It is suspicious to me that others report very similar loads with these units and it seems like something intrinsic to the design.

pecmsg

Most Crankcase heaters are hot all the time.
Drain pan heaters also (if so equiped)
Transformers always have a small current draw.

ratio

Here's the service manual for that unit, the schematic is on page 17. It looks like the only loads that are uncontrolled are the indoor heads, although there is some kind of snubber across the contacts for the inverter board that could be leaking, and of course any of the relays or SSRs could be shorted or one of the control boards themselves could have an internal fault.

Check the current going to the head(s). An IR camera of some sort can be a real aid.

Grits

Thanks Ratio, and pecmsg. That is very helpful. It helps to have as much info as possible before the service visit (so I can "help" them ;-). I will ask about a "crankcase heater"; that wattage would be in the right range, but I would have thought that in summer and after some period of time it would start cycling (maybe) - else get very hot, and this load seems very constant. But all of the suggestions are good and worth asking about. Thanks for your suggestions. I will follow up late in the week to report what the tech tells me.

Grits

Thanks to the service manual shared by Ratio, I see that the Mitsubishi PUZ-HA36NKA does not have a crankcase heater, so that is not the issue. As I said before, I will share what I learn from the upcoming service visit within the week.

Grits

No solution yet. Service guy found the same 1.3A (240Vac) load I had seen; he seemed competent and didn't think it made sense, but didn't have a spec for IDLE power draw (unit powered but set to OFF). He said he would raise the issue with his Mitsubishi people and escalate until he has a solid answer. I will follow up when I know more.

GGross

I bet it has a pan heater that is running all the time for some reason, My understanding is that most brands only run the pan heater below certain temps, though each has their own algorithm for when and how long to run it. I am curious to find out what you learn!

109A_5

Hello @Grits,

I'm wondering if one (or more) of what appears to be Insulated Gate Bipolar Transistors (IGBT) that are in IC500 (Red annotation) are electrically leaky. Causing more of a 'Reactive' parasitic current draw. With a 'Reactive' load you won't get the heat dissipation as if it was a 'Resistive' load. DCL1, DCL2, DCL3 (Aqua annotation) are inductors for the power converter for motor power. Also even with the unknown switch or contractor contacts open just above the (Orange annotation) there is a possible current path through the unknown device (Orange annotation).

Not sure if any of this helps you, but I can see the possibility of it happening as you see it on your Ammeter. And I would venture to say it may not be what the original engineering intended.

DJDrew

Seems similar to this thread that was eventually responded to by an engineer at Mitsubishi. https://www.greenbuildingadvisor.com/question/mitsubishi-mini-split-phantom-draw

GGross

incase anyone has trouble finding the Engineers response, here they are


From Harry at Mitsubishi
"Hello Greg,

I am a controls engineer at Mitsubishi. The answer is that your energy meter doesn't take into account the power factor, and is therefore giving you incorrect readings. In reality you are only drawing 3-15 watts when the unit is off; unless the compressor heater or pan heater is active, in which case you'd be drawing between 70-120 watts. All of these numbers are perfectly acceptable for any modern appliance, and especially for an HVAC system.

Please let me know if you have any questions."
------------------------------------------------------------------------------------------
"Edward,

Actually it sounds like you're having the exact same issue as Greg, only that it's presenting itself in a different way.

In the chart on page 2 of the following link, you can see that the base pan heater for MXZ-3C24NA models only draws 80 watts, and that it is only energized when the outdoor temperature is 39°F or less. http://meus1.mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.com.s3.amazonaws.com/DAMRoot/Original/10006\M_SUBMITTAL_MXZ-3C24NAHZ2_en.pdf

In section 11-1 on page 81 of the following link, you can see that the compressor heater (labeled Pre-heat) only draws 50 watts, and although it isn't listed in this manual, it is only energized when the internal compressor temperature is 68°F or less. http://meus1.mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.com.s3.amazonaws.com/DAMRoot/Original/10006\MXZ-5C42NA_MXZ-2C20-3C24-3C30NAHZ(2)_SERVICE_OBH702H_11-20.pdf

As you can see, the system is only capable of drawing a maximum of 130 watts when the units are not operating, and that's only when the outdoor temperature is 39°F or less. In other words, the 230/260 watt reading is due to your energy meter not taking into account the power factor.

For future reference: no modern medium-large appliance draws 0 watts of standby power. If you ever see 0 watts, you can safely conclude that the meter is 'guesstimating', and probably isn't taking into account the power factor. There's a reason they're all marketed as "99% accurate" instead of "100% accurate".

Feel free to let me know if you have any other questions."
------------------------------------------------------------------------------------------
"Edward,

Let me clarify - the 260 watt reading is completely false. Your energy meter isn't detecting the power factor, and is therefore giving you a reading of roughly 90x your actual usage. In reality you're drawing closer to 2.6 watts, not 260 watts."

Grits

Thank you all for the responses. I haven't dropped my interest in this. I am a few days away from receiving a power monitor that is supposed to show true power and give power factor; I will test it on some known loads. (Ok, it's not a Fluke, but amazing things happen with mass production in China. Maybe it will really work. I treat everything as a black box and test with known loads..... )
https://www.amazon.com/Electricity-Ampermeter-Voltmeter-Frequency-Multimeter/dp/B094F85G3T

I'm trying to fix the power supply of my oscilloscope so I can actually observe the waveforms.

My heat pump manual show that it doesn't have a compressor heater. I'm not sure about a base pan heater but I'll look at the service manual again. Seems the installer would know about these and they didn't say anything.

I'm almost to the point of taking the wife camping for a week and killing all breakers except the heat pump and seeing what the utility meter reads when I return.

I will be happy if this is just an apparent power thing - as long as it doesn't show on my utility meter I'll be happy... Still, I will be shocked if these things have a standing load with such a terrible PF.

I'll be back when I have the power meter going.

Thanks again for your thoughts.

Jamie Hall

Are there any parts of the circuitry which are live when the unit is "off"? Is there, for instance, an option to turn the unit on by a remote control? If so, there is -- somewhere -- a board which is powered at all times to receive such signals. Is there an option for a wi-fi connection? Is so, that board is also powered at all times. 1 amp sounds a bit much for that, but 100 to 200 milliamps would be quite normal.

Grits

Jamie - There is control circuitry active, and a wireless thermostat, and I understand that some power consumption is necessary and expected. As you say, a small amount of current must be present. I'm going to be shocked if modern power supplies are designed with such a low power factor as to indicate 1.3A_rms. But I will have a better idea in a few days.

Grits

I got the power meter today and got readings that make sense. The meter has current, voltage, real power, kWhr, Power Factor. The current was exactly as measured before (1.3A) and voltage was about 244V. What I didn't have before was the Power Factor and real Power. I stand informed ;-) The power factor was 0.06 or below, giving real power in the 20W to 23W range. That is one heck of a poor PF, but it is a small load. As I said, as long as it isn't costing me a lot I can live with this. Still, I wouldn't just leave a 20W bulb going for months at a time so I will probably leave the unit powered off for substantial parts of the season.

Thanks for your thoughts! This is good to know and I will sleep better.

I can recommend this meter (link in a previous post; $24 from Amazon) for cost and functionality; only time will tell how it will hold up.

(I hope this URL is actually a link to the picture I uploaded; should be the meter reading.)

109A_5

Hello @Grits,
Well, I still wonder whats going on for 22.2 Watts consumed. Is there a nice display all lit up ? I would think idle or standby would be no more than a Watt or two. Now you have the meter measure other appliances in the idle or standby state. With that Power Factor the current waveform may be interesting.

Grits

109A_5 - There are control boards in both the outdoor (compressor) part and the indoor air handler part of the unit. I see LEDs. I'm sure some circuits are doing their computing and monitoring. Also, the unit is supporting the RF link to the portable wireless thermostat, even when it is not being called to actively heat/cool/fan. 22W range is acceptable. I think there may be one or more offline switchmode power supplies (like computer supplies) to power the control circuits and these typically have a large capacitor after the rectifiers on the input side (poor power factor...) and a bleeder resistor to discharge that capacitor within a few seconds when disconnected from the line (power loss, but a shock hazard otherwise). I try to be very careful to not waste power but I think this is the unavoidable overhead for a unit like this. I don't know if we can expect anything lower. There is a new generation of switchmode supplies that use a SEPIC topology and that is supposed to improve the power factor, but the need to maintain the control circuits will need some power regardless of power factor.

109A_5

Hello @Grits,
Well as long as you are happy... For as much computing and RF receiving that is going on the load should be milliWatts, not 22 Watts. Maybe the AC to DC power supply is horribly inefficient at system idle. At 22 Watts you could power a transmitter too. That is a lot of heat if it was an incandescent lamp load. That is why I was wondering if there is a display or two all lit up. Although if they used LEDs for the backlight the draw still should be minimal. I doubt there is hundreds of LEDs all lit up.

Or maybe with the power factor being that horrible your new meter does is not display real power correctly.