4 minutes ago, PaulF007 said:

Yes but 5x spotlights is a moerse lot cheaper than 4 x inverter 

One just cannot argue with a financial guy, and then the damn spots don't last 20 years either.

In my mind... 50W at 48V is over one ampere. That just feels... wrong. I know my favourite alternative only manages about 35 on the same size, even that feels a tad high. On both inverters you have a search mode though, which uses 15W on both the large Multiplus and the 5KVA Axpert. On the Multiplus you also have AES (a kind of modified sine wave) which runs at 30W.

Perhaps something else that people tend to forget when sizing the inverter. Installing the smaller 3KVA (for both makes) means significantly less quiescent current. Without rehashing the old debate again, or making TTT unnecessarily excited, there is a case there for a smaller inverter that needs only 10W quiescent... without even resorting to AES. It's no good if you need the large one, but if you don't, you really should take this into account. 40W for 8 hours is 0.3kwh. That's about half of what my fridge needs in 24 hours... :-)

5 hours ago, PaulF007 said:

What I did was 

1. Removed all loads from inverter
2. Checked the difference between load at the inverter and load at BVM, 0-50 = 50 watt loss (Confirmed that that is about true for every one with a Axpert)
3. add a 3w load (LED Globe) 
4. Inverter showed 3 - 4 watt load  - BMV showed 73 w load 
5. I know that with no load the BMV showed 50w so when I add 3 w it adds 20 watts to the BMV
6. Confirmed it with other loads ( 20w and 30w ) with the same results 

But if there is a better way of doing it that could be used by other Axpert users , we are all ears.

Keep in mind that the LED globe has a terrible power factor and as @plonkster said, it might draw anything up to about 15VA. Now running that from the GRID is fine, because you pay for 3W, not for 15VA, but if the inverter needs to invert DC to AC and have to drive the 3W lamp, it will actually draw 15W from the DC side. (losses / efficiency ignored). Rather use a pure resistive load when you want to do these tests, e.g. a filament type globe of known wattage. A small one in a sewing machine might be in the region of 15-20W.

49 minutes ago, plonkster said:

... making TTT unnecessarily excited, there is a case there for a smaller inverter that needs only 10W quiescent ...

 Been patiently waiting for some ray of light to shine through on my rumblings of smaller may be better, T&C's apply point of view for I am not be as technical versed as most of you are, nor can I verbalize my point in such a manner that it stops most debates. but that does not mean I am not aware of the little quirks that can bite you in the end.

In time, with more data available, needs changing and the replacements drives start, this may come up again, how can we do it more efficiently. 

Thinking out aloud, if I was stuck with 50w+ used at night when we sleep, I would consider a smaller plain inverter, on same battery bank, to power the loads I deem important to be on like lights, TV, DSTV, alarm, internet and switch the main inverter off at night, or auto off / on at X times.

Next morning, main inverter comes on again, charges the batts, powers the house and all that.

1 hour ago, plonkster said:

 

In my mind... 50W at 48V is over one ampere. That just feels... wrong.

 

True in many ways but if you were running Eskom at Night as if you were on batts then it does not matter , Switch the inverter of at night. My current usage is about 3kwh per night 

@ R 2.50 per Kwh it will cost about R 7.50 per day and R7.50 x 30 = R 225.00 per month for Eskom. Now with that I can live with .. 

Then you run the batts every third day (since you already bought them) that will now give you 20x7.5 = R150 even better and those batts will last you so long that would have forgot when you bought them 

In theory that is  ....

Using AICC to post the data so I assume the data is good. 

Just for fun I plotted the "losses" excluding the 50w that we know the inverter runs on and the number varies a lot between as low as 2w and as High as 39w so I assume that is where the different types of appliances come in and there efficiency.

 

  

Sorry it will take forever to type all of this so here is a screenshot of the setup om Inputs:

As you ca see I am Omitting the Positive values as you are then generating power. I also subtracted the 50w as we all agreed that is a general loss with the Axpert. 

On my system the sweet spot seems to be at around 48w load then my losses is very low but that is on the house being on standby , when we go to bed.

 

 

I still think it might simply be because the inverter just can't measure that accurately.

Here is another link, from another project, explaining how these errors happen. I would hope that the sensor in the axpert is at least a little more sophisticated than a CT wired to 1024-bit ADC (that additionally needs several clock cycles to do a read), but I also suspect that at this price point (given that not even the expensive inverter we always discuss gets this perfectly right) it might not be significantly better.

https://openenergymonitor.org/emon/buildingblocks/measurement-implications-of-adc-resolution-at-low-current-values

2 minutes ago, plonkster said:

 

I still think it might simply be because the inverter just can't measure that accurately

 

I agree 100%.

There is so many things that could have a influence on the figures as it was pointed out in previous posts , I for one didn't know about much about it before so one lesson learned. It would be very interesting to see how another Axper inverter's data compares even if it is only to see if the measurements is consistent. 

What I would like to see is an experiment with one of those current meters @TinkerBoy uses. Then do a load test over a zero to 100W range, and plot the BMV and current meter values on one chart. Of course that means going out and buying such a sensor, then waiting 6 weeks or so for it to be shipped down here etc etc... so I suppose for now this will remain academic :-)

On 9/7/2016 at 3:02 PM, The Terrible Triplett said:

I have to agree, 20 or 50w is not a lot on 5000va ... but who uses 5000va at night constantly?

 

My Neighbor, almost, does! I think their draw is about 3KW/h!

On 9/7/2016 at 1:24 PM, plonkster said:

LED lamps often have very poor power factors and 20VA for a 5W lamp is not uncommon.

@plonkster sorry if this was asked before or discussed somewhere , but does this imply that LED are not as efficient as what I thought? (and that is by reading the BOXIE nothing else)

12 minutes ago, PaulF007 said:

@plonkster sorry if this was asked before or discussed somewhere , but does this imply that LED are not as efficient as what I thought? (and that is by reading the BOXIE nothing else)

Some LED lights are less efficient than others. Check the manufacturer's specs (if it is accurate / true), but they are generally still more energy efficient to run than energy saving lights. 

Point in case: Our living room used to have 14W energy saving globes.The light fitting takes 4 globes. Going Watt for Watt, a 10W LED light was far too bright. 5W was too bright even. So now we're using 3W globes to get the same amount of light out - in fact it's still brighter than what it used to be. The kitchen used to have 2x 6 foot tube lights - rated 36W on the tubes, but in reality it used about 110W of energy, since the balast was old. I replaced it with a single 18W LED tube light and the kitchen is much much brighter. Same in the garage. The 

So if you only work on Watts, you might be disappointed. But if you work on a value (i.e. how much light you need VS how much you get from a globe) of the complete solution you'll see LED is still much cheaper on your eskom bill / battery capacity. 

 

Someone mentioned to me yesterday, where we replaced from 400W flood lights with 20W LED flood lights that the LED flood lights give much better light than the 400W used to

Yes that was one of the first things that I noticed when I started to by these things. You can get a globe that rate 15w @ 800lm and a 9w @ 900 lm. Then even worse at these cheap shops that don't show there stats ..

Just now, PaulF007 said:

Yes that was one of the first things that I noticed when I started to by these things. You can get a globe that rate 15w @ 800lm and a 9w @ 900 lm. Then even worse at these cheap shops that don't show there stats ..

which is why you don't always buy cheap LED lights

 

As always you get what you pay for , most of the times..

Oh there is a Wikipedia article for that. In terms of how much electricity we turn into light we are still WAY below 50%.

https://en.wikipedia.org/wiki/Luminous_efficacy

Low Pressure Sodium remains king. Which is why you should laugh at people suggesting we should save power by turning off half our street lamps :-)

But more on point, don't confuse power factor with efficiency. I think @superdiy made the point earlier in this thread how the VA is what determines the current draw rather than the power (aka the apparent power rather than the real power), but I think he's wrong on that one. Well I hope he is because I used to think the same thing and someone else here changed my mind. Sort of. Thing is, the inverter can compensate to some extent for the power factor so that the real power it draws on the DC side should be pretty close to the real power being drawn on the AC side. So... I know this is confusing, but you could have a 5W lamp on the output which because of poor power factor is a 20VA lamp, but it will still draw only 5W on the DC side (ignoring efficiency here).

The real issue with poor power factor isn't battery life. It's that the inverter has a peak VA rating (not a peak watt rating), so you essentially run out of inverter capacity 4 times sooner based on your power factor. That's the issue.

LED lamps will always have a power factor below unity. I think its the space constraints: Can't get a big enough quality capacitor in there to smooth things out... :-)

Super! @plonkster it makes perfect sense and I understand , sort of , VA much better with regards to the Inverter that is. Cool always lekker to snap something ... 

This old picture of mine. That's a 12V 5W LED lamp on an old iron transformer. The smooth(ish) sine is the voltage. The saw-tooth is the current. I had the current probe the wrong way round, so it is really IN phase, not out of phase as shown. So as you can see, the power factor really isn't inductive or capacitive in the conventional sense where one waveform lags or leads the other. But it is lower than unity because it does all the work using only a small chunk of the waveform, which means the current spike you see is much higher than it would have been if the power factor was better. On a 5W incandescent lamp, for example, the current waveform would be a smooth "speed bump" at the bottom following the voltage waveform exactly, with a peak 5 times lower... :-)

Power is still the same though.

20 hours ago, plonkster said:

I think @superdiy made the point earlier in this thread how the VA is what determines the current draw rather than the power (aka the apparent power rather than the real power), but I think he's wrong on that one.

@Plonkster, you are correct it's the real power that is drawn from the batteries and not the apparent power.

Below are some measurements i performed on 3 computers of different generations.

The new computer had power factor correction built into the power supply and drew a beautiful current waveform with a crest factor of 1.9.

You can also see how much more efficient the new computer (46 watt average draw) is compared to the old (107 watt average draw).

 

On 9/9/2016 at 10:23 AM, plonkster said:

I think @superdiy made the point earlier in this thread how the VA is what determines the current draw rather than the power (aka the apparent power rather than the real power), but I think he's wrong on that one. Well I hope he is because I used to think the same thing and someone else here changed my mind. Sort of. Thing is, the inverter can compensate to some extent for the power factor so that the real power it draws on the DC side should be pretty close to the real power being drawn on the AC side.

 

On 9/9/2016 at 7:45 PM, Carl said:

@Plonkster, you are correct it's the real power that is drawn from the batteries and not the apparent power.

Below are some measurements i performed on 3 computers of different generations.

The new computer had power factor correction built into the power supply and drew a beautiful current waveform with a crest factor of 1.9.

You can also see how much more efficient the new computer (46 watt average draw) is compared to the old (107 watt average draw).

 

I stand corrected.