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Axpert no load power consumption


Lukas

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Hi. We installed an Axpert 5kVA inverter (offgrid setup). After adding a BMV702 realized the axpert uses 65W with absolutely no load attached other than itself. This seems excessive, or is it correct? Any thoughts or similar experience

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About right. I have seen figures of 46W through to 60W quoted. Have you zeroed your BMV? I have never had to, as mine was accurate out the box. Switch your Axpert off and make sure your BMV registers 0W.

It is excessive compared to other inverters. You have a 4k inverter for about R10k and so at that price you accept the Axpert's shortcommings. More expensive inverters' quiescent current are about half to a third of that value.  

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The Victron inverters use around 35W quiescent draw... but last night I was looking at the specs of an Outback inverter... man, that thing has a quiescent draw that's half the Vicky's!

(But you should see the price...)

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Hello all,

This is my first post to this forum but i have been wanting to do so for quite some time... I am not sure whether to post my query under this particular thread or 'batteries'...

My question pertains to the operation of the Axpert inverter with respect to charging the battery bank. My display continuously shows that while utility is available, I always am 'charging' my batteries and supplying power to the house simultaneously. What has led me to this is that I am concerned about the load drawn by the inverter while I have little to no load in the house. I am using an efery power meter on my mains incomer to monitor my household power usage (not to be 100% accurate but to identify areas to reduce usage). At night when all appliances are off the draw is 0.52kW which is very high even for the phantom loads by electronic appliances... As my efergy CT is installed on the main incomer it is also reading the quiescent load of the inverter itself. Hence my concern is now two fold: 1) I am constantly pulling an unnecessary load 2) I risk overcharging my batteries.

I would expect that the inverter would monitor my battery bank to ensure that the batteries are fully charged and once this has been achieved then it will switch over to 'float mode'. i.e. I assume that no power will be directed to the batteries during float as they hold their charge... Then as the batteries gradually discharge while on standby, the inverter monitors the charge level to kick in at a predefined setting to once again top up their charge. During top up (bulk) I expect a high load draw but not during float...

Please assist? 

1 x RCT (Axpert) 5kVA MKS Inverter   |   2 x 4 -12V100Ah Renesola Gel batteries (100 cycles @ 50%DOD)   |   No battery management   |  Using as back-up battery power. Looking to install 1.3kWp of solar panels shortly...   

IMG_0029.JPG

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30 minutes ago, Trev said:

Please assist? 

Hi Trev welcome

For the most part I assume that your batteries are in float and are using very little power. Float is a battery charging state where the battery charging rate is to balance the batteries' self discharge rate. Float is the most inefficient part of the charge cycle but fortunately very little is being consumed. At such low power consumption levels I would say the Efergy readings can be ignored. One could use the Axpert reading of load +charging + about 50W quiescent draw. Last night I checked again and my Axpert draws 42-44W under no load.

 

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Thanks Chris,

So the fact that my efergy is reading an average of 520W during the night when everything is switched off (bar phantom loads and security lighting - 100W max.) should therefore be a concern right? The only device that is permanently on is the Axpert inverter. I would be happy to see my efergy read 42-44W. 

I currently have a bypass switch installed on my system that allows me to remove my Axpert should a technical fault arise without having to rewire the breakers. It is however damaged and will be replaced shortly (story for another day). When i get this changed i will test the loads that i am seeing with & without my inverter inline for  absolute confirmation that it is responsible for the high no load draw. But before i get there i was just wondering if there was anything obvious that i was doing wrong with my settings?

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14 minutes ago, Trev said:

I would be happy to see my efergy read 42-44W. 

Difficult since you seem to have a 200W base draw so I would expect round about 300W. Am I misreading this? Was the photo taken when there was a draw and not just phantom loads?

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19 minutes ago, Trev said:

efergy

Cannot make a call unless you take into account power factor, in other words, you must use something a bit more capable than the Efergy clamp meter. Your 500W measured might be a real 350, or 250... who knows. For example, my total load of LED lamps with their horrible power factor should be no more than 150W combined but measures over 350VA!

24 minutes ago, Trev said:

I would expect that the inverter would monitor my battery bank to ensure that the batteries are fully charged and once this has been achieved then it will switch over to 'float mode'. i.e. I assume that no power will be directed to the batteries during float as they hold their charge... Then as the batteries gradually discharge while on standby, the inverter monitors the charge level to kick in at a predefined setting to once again top up their charge. During top up (bulk) I expect a high load draw but not during float...

The displayed 54.6V is float as far as I know. Floating a battery means holding it at a certain voltage, to counteract the self-discharge losses in the battery. Unfortunately this voltage is high enough to cause mild gassing so it does wear the batteries down over time, but... the batteries have a so-called design-life which is usually around 10 years, so you are unlikely to commit death-by-floating on them by doing this.

The alternative is not to float them, but then they slowly lose charge and have to be recharged later, which causes about the same amount of wear. Some chargers have a 4-stage program that goes into storage mode after 24 hours, which holds the batteries at an even lower voltage (around 53V). This is enough to avoid gassing, and it avoids self-discharge to some extent, but not completely.

Also, keep in mind that sealed batteries usually have a mechanism to contain the generated gases and convert it back to water, so that prolonged floating really doesn't do much damage beyond the inescapable design life parameters.

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Thanks guys! You have jointly answered my question pertaining to the float charging of my batteries. I just need to figure out the high load shown on my efergy meter. Plonkster, point taken about the power factor! Although i cannot think of many inductive loads that would be responsible for a high amperage and this a skewed reading by the efergy which uses Amps (metered) x Voltage (constant preset) to display a 'real' power estimate. I am currently in the process of converting to LED throughout the house which started this weekend! Observations were however made prior to any LED lights at my new house as well as my old house with a similar installation presenting the same characteristics. Hence i was wondering if i got my settings wrongs somewhere for both installations? 

Just calculating quickly: Total Efergy Load: 680'W' (apparent power) with downstream Inverter load: 208W (real power). For a poor pf = 0.7 (say) the real power for the efergy would be ~475W which implies that my Axpert is drawing a quiescent load of 285W....??? The only systems that are not on the Inverter are: 1 x Geyser (solar powered with circulating pump), 5 x air conditioners (standby) and a tumble dryer (off). Could the aircons be drawing such high phantom loads? I guess during winter time they should be switched off at the CB's anyway... 

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2 minutes ago, Trev said:

many inductive loads

In the modern household it isn't the inductive loads anymore. It's all the little switch-mode power supplies, those things often have horrendous non-linear current waveforms. Right now (I'm home looking after a sick kid) my modbus meter says my power factor is 0.7!

I had to turn my inverter off for a few seconds to get that result. My inverter corrects the power factor, when the inverter runs grid-tied (offseting the grid) it corrects the power factor so that it's above 0.9 :-)

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Looking at my stats the power factor becomes worse the lower you baseload is (at 150w the power factor can get as bad as 0.52). Witch makes sense as when you are running at 150 w for the whole house there will be a couple of transformers around but I don't think it will make much of a difference at those levels. 

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2 hours ago, PaulF007 said:

power factor becomes worse the lower you baseload is

My guess would be because your baseload typically contains a lot of switch-mode type things. Transformers that are properly loaded/sized usually don't break power factor too badly, it's when they are oversized that the PF suffers. Such as my 5A transformers that used to power 50W halogen MR16s, which now powers 5W LED MR16s... combined with an SMPS on the secondary side that essentially does all the work using only half the cycle... :-)

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  • 1 month later...

i placed an efergy on my infini /axpert inverter and it always measured 400w  even when I knew it wasn't pulling any Eskom only solar. I believe its because it measures apparent power and not real power. I had the same when I had it connected to a grid tie inverter. I have since changed the power monitor an now its correct because I now pull almost zero Eskom and all solar . my inverter is set to self consumption ,so it only takes Eskom if ther is not enough solar similar to a gti

cheers

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Hi Trev,

Did you ever get to the bottom of the high power consumption?

Reason I ask is I have exactly the problem that you have explained and a similar setup to you, although I have 2 devices in parallel plus I have solar panels connected as well.

So overnight I was seeing see about 750W of power being 'lost' across the input to the inverter and the output from the inverter (basically 2-3A measured a Fluke meter).
(using efergy transmitter and Hub to Engage software online)

I changed one of the settings so that ONLY the solar panels can charge the batteries (16 -OSO), the power consumed overnight dropped by about 250W, good start. 

Last night I bypassed the inverter entirely, the power consumed was back to normal.

So these units are consuming 500W in BYPASS mode (utility to load) and the batteries are NOT being charged, where's the power going?

Idea's?

 

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Thanks for the reply Chris.

Just switched the output of the inverter off, so NO load connected (which they probably doesn't like), the current being measured on the input is now 3.12A

So they are burning up some current in this condition but also similar extra power with a load connected.

Pretty frustrating, put in the system with solar panels to save power and they use more.

Surely this is not right and there is a fix?

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Hello Dex,

Funny you should ask because today I performed a small check to test the power factor theory. My new house main DB is fitted with a power meter. Nothing fancy, just a simple single phase instrument that displays totalised power consumption in kWh (http://www.rayleigh.com/media/uploads/RI-D36-80-P_V1.00.pdf). Assuming power factor is better catered for on the DB meter than my Efergy device I obtained the following:

  • DB Meter: 105.5kWh over 115hrs (22.0kWh/day) - manual opening and closing readings
  • Efergy Meter: 191.63kWh over 115hrs (40.0kWh/day) - using efergy hourly reporting tools over the exact same period

The difference is 18.0kWh/day... If you divide this by 24hrs you get an 'error' (misreading) of 0.749kW which talks precisely to your 750W...

This crudely confirmed to me that the Axpert is in fact pulling a highly inductive load resulting in a very poor power factor which the Efergy meter does not see due to its rudimentary means of metering.

I have to concur with Chris that a tremendous amount of power is lost to heat generation. By observation, the surface and sides of the inverter are however cooler than my the 200W wall panel heater in my child's bedroom. Hence my assumption is that the unit is pulling a lot less than 200W of Real Power during no load / utility to load conditions.

I'll see if i can arrange a Fluke Power meter with logging capability that we have at work... It would be really useful to have a power & pf vs time trend during load and no load conditions for the Axpert.

Trev

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@Dex by the way, I intend conducting the same check using the readings (actual) provided by the municipality on my monthly account bill. I have to waiting for their bill because i don't have access to their locked metering board in my street. This would be the ultimate test as this meter is not only what i am billed with but also expected to be far better quality than even my simple DIN mounted power meter. 

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Hi Trev,

I agree that the efergy power reading is not providing extremely accurate measurements and I might get a meter like yours to do the comparison.

Thing is, as I mentioned to Chris, I measured over 3A being consumed with no load, which as he is rightly pointed out, must be being converted into heat.

Unless I can figure it out, or there's a setting that fixes this, probably just build a transfer switch, so switch between utility power and inverter power when the solar stops having an effect and then switch the input power to the inverter off (uses a little battery power). Thing is, the switch must be fast so power doesn't recycle.

(and this is what the Axpert is supposed to be doing...)

Dex

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Just remember @Dex that if you are measuring your current with a simple ammeter you are not considering the phase angle between the current and the voltage. That is what the efergy meter does without compensation. Therein lies the issue of power factor. It is not so much an accuracy issue as it is an 'applicability' issue... with a proper power meter we will be able to tell the severity of the the current lag/lead and therefore how 'applicable' the measured Amps are as a deduction of measuring Real Power. With zero lag/lead only then would the simple ammeter be applicable.

I have come to terms with the fact that my efergy is not accurate enough to tally consumption but rather only accurate with regards to exactly when power is drawn and a thereafter an 'indication' of how much is being drawn.

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As I recall these inverters need around 50W or so with no load. They have rather poor power factor, but since we pay for real power and not apparent power in the domestic setting it doesn't matter so much.

I'm not sure if the power factor has to do with the way the Axpert's SMPS is operated to charge the batteries, assuming that is what it is doing. I do know other manufacturers (see page 5, point 2) go to a lot of trouble to get their power factor close to 1, which at least suggests that it takes work to get this right, and in an inverter at this price point it probably didn't make sense.

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