A/C Unit draws 50% more power on 50hz vs. 60hz

[s/v Jedi]

I have learned that the subject of power factor is best avoided as only those whose education included electricity at that level understand it.

I also don’t think this is the OP’s problem, I was under the impression that their A/C units were 60Hz but their 60Hz inverter hit overload when running them longer than 30 minutes. This indicates that the inverter is either too small or it has a problem with it’s continuous rating cased by lack off cooling, or low DC battery etc.

[Cadence]

Originally Posted by Oceanride007

I'm surprised the Microwave works adequately, I would think the Magnetron frequency is a multiple of the input Hz.


Its news to me that a Isolation transformer can have its turn ration adjusted to change the output voltage, comment or what model number please.

It is a buck/boost transformer with multiple taps in all likelihood.

[Oceanride007]

^^^^ Could the Op assure us that the issue is not due to inefficiency of Transformer. Although a step down or step up transformer is also a isolating transformer. Think it description of isolation Transformer is one with the turns ratio is 1:1. Could op inform us what kind of Transformer it is.

[Cadence]

Originally Posted by Oceanride007

^^^^ Could the Op assure us that the issue is not due to inefficiency of Transformer. Although a step down or step up transformer is also a isolating transformer. Think it description of isolation Transformer is one with the turns ratio is 1:1. Could op inform us what kind of Transformer it is.

1:1 I don't believe is prerequisite for an isolation transformer as long as there is not electrical connection any ratio will work.

[manitu]

The Victron isolation transformer has a two coil input and two coil output. same numbers of turns on all coils. you connect the coils in parallel on the 115/120v side ,and in series on the 230/240v side.


.manitu

[mdsilvers]

Originally Posted by Cadence

Out of curiosity. Are you checking the voltage under load not just the amp. draw?

Yes. I am checking both.

120v/50hz draws 17 amps
119v/60hz draws 11 amps

[mdsilvers]

Originally Posted by s/v Jedi

I have learned that the subject of power factor is best avoided as only those whose education included electricity at that level understand it.

I also don’t think this is the OP’s problem, I was under the impression that their A/C units were 60Hz but their 60Hz inverter hit overload when running them longer than 30 minutes. This indicates that the inverter is either too small or it has a problem with it’s continuous rating cased by lack off cooling, or low DC battery etc.

The issue I'm trying to solve is the increased current draw on 50hz, not the inverter cutting out. The two are not related.

I found the answer. It is a power factor issue. Solved by limiting the voltage to 95-100v vs. 120v. for 50hz. With the higher current draw, I was concerned about the compressor overheating. I checked with the engineers at Dometic, and they agreed. I need to lower the voltage to get the V/f ratio closer to 1.9. Current V/f ration is 2.4 with 120v/50hz.

The shore power oscilates from 220 - 250. As the voltage increased, the current draw of course increased on my meter.

[mdsilvers]

Originally Posted by Oceanride007

Its news to me that a Isolation transformer can have its turn ration adjusted to change the output voltage, comment or what model number please.

I'm using the Victron 3600 Isolation Transformer.

[s/v Jedi]

So your compressors are rated for 50Hz?

[manitu]

Billkny is spot on!

You say your water pumps are 50/60hz rated, but what about the compressor motors?

There is an easy answer on running only 60hz rated inductive motors on 50hz: Don't do it!
The motor is probably saturating , and as it is a single phase motor there is another problem. It must have some mechanism to start in the right direction, most likely a start winding wich is usually set to disconnect at about 80% of run speed.
As you have reduced the speed by 20%, I guess you see that we may have a problem right here.

The start winding could easily be the 50% amp increase alone.

https://www.engineering.com/story/ch...en-50-and-60hz



.manitu

[Tin Tin]

Sorry I don't understand clearly, maybe missed some details



When you run the aircon - do you run it direct off the Transformer i.e. 120V at 50hz? If so the 3600W transformer should have no problem with 20Amps



If you run the Aircon off the inverter, will it not be 120V at 60 hz? What size inverter do you have in Watts.


Your battery charger may be multiple voltage, so could run off 240V on a separate pedestal and an adapter plug.

[mdsilvers]

Originally Posted by s/v Jedi

So your compressors are rated for 50Hz?

Hello Jedi. No, the compressor is rated 60hz. If you derate the voltage to get the V/f in line, from what Dometic is saying, I should be OK, with 17% less output.

The reason for the higher amps is the V/f being out of sync. Especially when the shore power spikes to 250v, and spits out 225/50.

[s/v Jedi]

Originally Posted by mdsilvers

Hello Jedi. No, the compressor is rated 60hz. If you derate the voltage to get the V/f in line, from what Dometic is saying, I should be OK, with 17% less output.

The reason for the higher amps is the V/f being out of sync. Especially when the shore power spikes to 250v, and spits out 225/50.

That’s what I thought: like others write: do not run it on 50Hz; don’t try to make it work on lower voltage etc. I can’t believe Dometic recommends that as I’m sure it voids your warranty.

You must run it on inverter and find out why the inverter overloads after 30 minutes. What is the rating of the inverter? Does it’s fan run?

[mdsilvers]

Originally Posted by s/v Jedi

That’s what I thought: like others write: do not run it on 50Hz; don’t try to make it work on lower voltage etc. I can’t believe Dometic recommends that as I’m sure it voids your warranty.

You must run it on inverter and find out why the inverter overloads after 30 minutes. What is the rating of the inverter? Does it’s fan run?

I have the MasterVolt mass-combi 2500, 120v set to 60hz. The fan runs, and it still will trip off after about 30 min (sometimes sooner). Error I get is inverter overload (E6), due to heat. It's nine years old. Fan works, and temp seems to be in the 34C range based on my gauge.

I have Lithium batteries, and the voltage drop is not the issue. I've checked this.

I will now focus on the inverter. Everyone is making me nervous about running on 50hz for the compressor. :-)

[mdsilvers]

One HUGE complaint I have with the Mastervolt unit is there is no voltage sense. It is usually off by .2 to even .4v from the actual battery voltage under load.

I doubled my wires to and from the batteries for each terminal. 2 x 2/0. The run is only about seven feet (14ft return) from the inverter to lithium. I did this because of the voltage drop on the unit, and I still see a large discrepancy. Drives me NUTS.