Something seems off with Victron efficiency

[SoakedUp]

I’m running a couple fans, dorm fridge, and inverter style 10k btu Air Conditioner off my multiplus 2k (12v). VRM shows I’m using about 670 watts on the AC load. I have a victron 150/100 CC and VRM shows it’s pulling in about 920 watts to power those loads and keep my battery at its float level of 13.6v. That’s about 72% efficiency for an inverter/charger that claims 95% efficiency. The dc loads jumps around between10w to 160w which is weird because the only thing I have connected to the dc fuse block is the cerbo. The PV input doesn’t fluctuate like the dc load does. Equipment is in an air controlled room sitting at about 68F. Outside temp is 78F. Is this normal or should I start trying to figure out where the efficiency loss is? Using 2/0 cable from three 206ah SOK 12v batteries. 4AWG cable coming from the victron CC. All cables and connection points are either cool or slightly warm to the touch. Something just seems off.

 

[AntronX]

673w / (921w - 19w - 159w) = 90.6%

 

[SoakedUp]

673w / (921w - 19w - 159w) = 90.6%

The screen shot was bad timing but 99% of the time the battery is at 2-3 watts to maintain. And the dc loads jump from 10w to 160w constantly. I’m assuming the dc load is jumping that high to power the multiplus…the only other thing connected to a dc load is the cerbo gx. Does the cerbo use 160watts?

Victron says it uses 2.8w. lol.

 

[SoakedUp]

Here’s another screen shot, the suns gone down a bit but…


635w load. 556w solar input. 12w dc load. So should be 556-12-635= -91w draw on battery but I’m drawing -251w.

 

[AntronX]

If we ignore DC power reading then we get 635 / (556+251) = 78.7% eff.
That's most likely true because inverter type air conditioner may not have active power factor correction and causes high peak current on step up transformer inside the Multiplus inverter. Measure power factor of your air con using the kill-a-watt meter.

 

[SoakedUp]

If we ignore DC power reading then we get 635 / (556+251) = 78.7% eff.
That's most likely true because inverter type air conditioner may not have active power factor correction and causes high peak current on step up transformer inside the Multiplus inverter. Measure power factor of your air con using the kill-a-watt meter.

Thanks. I don’t have one but probably should get one. I figured the multiplus would just read what ever power was being drawn by the appliance. I should check if there is still a discrepancy when using a different appliance with more of a resistive load like a radiant heater.

 

[SupraSPL]

I have found it difficult to measure DC to AC inverter efficiency. Partly due to inaccuracy of clamping meters and complexities on the AC side relating to power factor. One way to simplify that is to use a purely resistive load when testing the efficiency. Or if you have a pair of inverters you want to compare, you can load them up with the exact same complex loads and compare the DC draw to see which one is more efficient.

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An engineer pointed out to me that my Midea U poor power factor was not actually going to result in an increased power draw on the battery side of the inverter and they were correct. I guess you can think of that like two jump ropes out of phase on the AC side but it nets out to zero. So that does put extra current requirement on the wires, but doesn't actually pull extra battery power so thats awesome.

My dehumidifier on the other hand, definitely had a tax on the DC side due to power factor (Watts vs VA). Then there are harmonic distortions caused by some switching power supplies that can also affect power factor if they are not corrected inside the PSU and those do increase the draw on the DC side but if there are multiple PSU or other power factor correxted devices, they interact with each other in an complex way that seems to reduce the tax overall.

 

[Q-Dog]

DC power on the VRM is an estimate, not a measurement. What that means is the system calculates the DC load from any watts that are not acounted for between the chargers and the inverter and the shunt. But, it doesn't measure all of these things at the same time, so the load estimate fluctuates based on when the values of the measured parameters are taken.

So, you can't rely on the DC Power being accurate all the time.

 

[SoakedUp]

DC power on the VRM is an estimate, not a measurement. What that means is the system calculates the DC load from any watts that are not acounted for between the chargers and the inverter and the shunt. But, it doesn't measure all of these things at the same time, so the load estimate fluctuates based on when the values of the measured parameters are taken.

So, you can't rely on the DC Power being accurate all the time.

Which leads me to think it’s just accounting for the inefficiency of the inverter because I’m not using any DC loads other than the cerbo which only uses 3 watts. I’ve now tried multiple different appliances and the efficiency definitely seems to be around 75-85% depending on the size of the load. 200 watts seems to be the sweet spot of about 92% efficiency but anything above that and it starts dropping.

It’s weird though because even when I’m not using the inverter, and only charging off solar, my charge controller will say I’m pulling in about 1000W but only 900W are going into the battery. So there is a 10% loss there also. It just seems the victron efficiency numbers are definitely over stated or numbers achieved in perfect lab settings and not real world.

 

[SoakedUp]

This just blows my mind. AC loads of 950w but discharging battery at 1250w. That’s 76% efficiency. I might need to double up on solar panels and another charge controller if I plan to run the AC through the summer. What a disappointment.