question

durval avatar image
durval asked

Trying to size a Victron Phoenix for a bad power-factor load, how to proceed?

I'm trying to size a Victron Phoenix inverter to power a refrigerator. My power meter indicates it consumes around 700W peak (immediately after the compressor turns on, lasting less than 2s) then stabilizes at around 70W, *but* with a power factor of only 0.60.

I have two questions:

1) To what power should I size the inverter?

2) Would adding an appropriate capacitor in parallel to the compressor motor terminals (as explained here: https://youtu.be/qf_ZLIYT0Ro) allow me to use a smaller inverter?

Thanks in advance.

EDIT: just keeping everyone posted, I followed the instructions on the video above to calculate and add a capacitor in parallel to the refrigerator, and was able to correct its power factor from 0.60 to 0.98; as a consequence, the VA went way down and is practically identical to the Watts value now, and this made it much easier to size and buy my Victron inverter (and also allowed me to buy a much smaller one than I would have to). Thanks to everyone who contributed.

MultiPlus Quattro Inverter ChargerPhoenix Inverterpower factor
2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·
A capacitor would maybe increase the power factor but it would not lower the inrush current.
0 Likes 0 ·
durval avatar image durval Matthias Lange - DE ♦ commented ·

AFAIK reducing the power factor, in an inverter, means reducing both the starting ("inrush") current and the running current. This seems to be confirmed by the video I linked in my original post.

0 Likes 0 ·
2 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

minimum size of inverter would need to be 1200W; you calculate this as the peak load current x the voltage- i.e. the VA rating. The inverter does have some peak capacity, but stressing it repeatedly to this limit is not a good idea. I would not try to compensate the refrigerator. BTW, is the power factor 0.6 during start, or 0.6 during run?

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

durval avatar image durval commented ·

@Mike Dorsett:


> minimum size of inverter would need to be 1200W; you calculate this as the peak load current x the voltage- i.e. the VA rating.

You mean, 700 / 0.6 = ~1167, so we round it up to 1200W, correct?


> The inverter does have some peak capacity, but stressing it repeatedly to this limit is not a good idea.

I see on the datasheet the Phoenix 12/1200 has a 2000W peak power, so I think the remaining capacity should be more enough for the remaining stuff I plan on eventually powering up with it (my notebook which takes about 100W max).


> I would not try to compensate the refrigerator.

Why not?


> BTW, is the power factor 0.6 during start, or 0.6 during run?

Both. My power meter shows a starting PF of around 0.7, but it trends slowly to 0.6, reaching it after about 5 minutes running.


0 Likes 0 ·
rslifkin avatar image
rslifkin answered ·

I've got an icemaker on my boat that I've seen a brief (fraction of a second) spike to ~1800 watts, then runs at ~150 watts. I haven't checked the power factor on it though. It runs fine from my Multiplus compact 12/2000/80. Only issue is on startup. The compressor sometimes stutters slightly on startup and the AC output voltage from the inverter dips a bit (you can see a flicker in a lightbulb to go along with the stutter).

However, the issue isn't the inverter. It's the batteries. The sudden load spike is big enough that the battery voltage dips significantly, as the lightbulb test shows the stutter on the 12v side as well. If I'm underway with both engine alternators feeding power to the battery bank it starts more nicely. Solar doesn't help much, as the MPPTs can't ramp up fast enough. As battery SoC gets lower, the problem does get slightly worse, but not much.

I've been debating whether a large capacitor at the 12v input of the Multiplus might help carry the system through the compressor start better. That, or it's time to investigate a soft start for the icemaker compressor.

7 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

durval avatar image durval commented ·

> However, the issue isn't the inverter. It's the batteries. The sudden load spike is big enough that the battery voltage dips significantly, as the lightbulb test shows the stutter on the 12v side as well.

Can you please tell us what batteries (type/number/capacity) you have, as well as your other loads besides the icemaker?


> I haven't checked the power factor on it though.

It's cheap and easy to measure, shown immediately by my power meter: https://www.amazon.com/Poniie-PN2000-Electricity-Electrical-Consumption/dp/B0777H8MS8 (I believe the more common Kill-A-Watt meter would also show it, have to use the Poniie because I use 220V).


> I've been debating whether a large capacitor at the 12v input of the Multiplus might help carry the system through the compressor start better. That, or it's time to investigate a soft start for the icemaker compressor.

As instructed by the video I linked, I think it's better to try and put the capacitor directly in parallel with the icemaker motor terminals. But I wouldn't just try and guess the capacitance, as the video shows it has to be calculated (I've read elsewhere that an improper capacitance can actually make matters worse).



1 Like 1 ·
Show more comments
Mike Dorsett avatar image Mike Dorsett commented ·
This is one major problem with running large appliances on a 12V inverter - thre just isn't enough headroom to cushion the inverter against the sudden large current demand. A Capacitor on the inverter dc would be huge - not worth trying.

This problem disappears with 24 and 48V inverters - to a great extent. input current is 1/2 or 1/4, and the voltage is high enough that <1V drop does not affect the inverter performance. I'm running a 2.1kW electric kettle on my 24V solar system, and the lights hardly dim at all when the battery is hit with a 95A load.

Mike.


0 Likes 0 ·