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

[mdsilvers]

I have a question. I recently installed a Victron Isolation Transformer and have my boat in Malaysia. Our boat is 120v/60hz standard. We use the transformer to step down the voltage to 120v/50hz.

Our Cruiseair AC water pumps are 120v dual 50/60hz models.

When running our AC units off the inverter, with 60hz, we draw 6amps for the smaller unit and 12 amps for the larger salon unit.

When I switch the power source to the Victron transformer, the power draw increase to 9amps for the smaller units and close to 18/19amps for the larger unit.

I get a similar increase in current when using the microwave—12amp off the inverter and 18 amps off 50hz Victron.

That is a massive increase in power. I understand that the blowers will run slower at 50hz, but I would not have expected a 50% increase in power. There must be something amiss.

Any thoughts would be greatly appreciated.

[s/v Jedi]

You need to modify your electrical system so that you can charge your batteries from shore power while running the boat on inverter.

[smac999]

How are you measuring this? On the actual wire with a clamp meter? Or trusting a gauge panel? I have seen gauge panels wired wrongly with inverters that show 2x the power off shore power... because the shore wire and inverter output both run through the same ac shunt.

[mdsilvers]

Thanks, Jedi. It's the age-old issue I supposed of 50hz vs. 60hz. My head is about to explode, reading all the threads and getting to the bottom of the right solution.

The issue is the Mastervolt inverter doesn't like running the larger AC unit 1800BTUs for more than 30 minutes before getting a fault of overheating. I read more on this issue last night. It' seems it's related to the V/f ratio being out of whack, and I would need to reduce the voltage to @90 to get the load back on track. I'm not keen on installing a high current variable transformer, so I'll need to find another solution....probably not using the larger AC unit. This will be a fun discussion with the Commodore.... ;-)

We are in Malaysia, stuck in a marina, hence the need for AC.

[mdsilvers]

Originally Posted by smac999

How are you measuring this? On the actual wire with a clamp meter? Or trusting a gauge panel? I have seen gauge panels wired wrongly with inverters that show 2x the power off shore power... because the shore wire and inverter output both run through the same ac shunt.

Yes, I used my amp clamp on this. I didn't realize with the V/f ratio being out of whack how much impact this has on current, but it's big.

[s/v Jedi]

Originally Posted by mdsilvers

Thanks, Jedi. It's the age-old issue I supposed of 50hz vs. 60hz. My head is about to explode, reading all the threads and getting to the bottom of the right solution.

The issue is the Mastervolt inverter doesn't like running the larger AC unit 1800BTUs for more than 30 minutes before getting a fault of overheating. I read more on this issue last night. It' seems it's related to the V/f ratio being out of whack, and I would need to reduce the voltage to @90 to get the load back on track. I'm not keen on installing a high current variable transformer, so I'll need to find another solution....probably not using the larger AC unit. This will be a fun discussion with the Commodore.... ;-)

We are in Malaysia, stuck in a marina, hence the need for AC.

Running both A/C’s simultaneously at 18A should not be a problem if the rating of the unit supports that load. Wouldn’t the problem happen because the battery voltage gets too low? Does the charger keep up? Does the fan still work? Stopping after 30 minutes indicates a problem with it’s continuous output rating.

Lowering voltage leads to increase of amperage because it still requires the same amount of energy to output those cooling BTU’s.

[guyrj33]

I don't know which exact pump you have. To satisfy my own curiosity I found a representative pump and it's spec sheet.
here's the link.
https://citimarinestore.com/en/march...pump-115v.html

It's definitely moves more water with 60hz power than it does with 50Hz. That leads me to believe that this particular pump probably does consume more power at 50Hz than at 60Hz.

[garychurch]

Hmmm. As far as I am aware an isolation transformer can step up or down voltage but cannot change power frequency (I.e. 60hz to 50hz). For that you need frequency converter, albeit there are units available that will do both such as convert US 120 60hz to NZ 240v 50hz.

Secondarily, I am aware inverters generally have a “high overhead” in using notable amounts of power to invert and convert long voltage DC into a pure sine wave 120v AC. You may want to check your inverter specs to determine the appropriate power draw.

[Cadence]

Originally Posted by mdsilvers

I have a question. I recently installed a Victron Isolation Transformer and have my boat in Malaysia. Our boat is 120v/60hz standard. We use the transformer to step down the voltage to 120v/50hz.

Our Cruiseair AC water pumps are 120v dual 50/60hz models.

When running our AC units off the inverter, with 60hz, we draw 6amps for the smaller unit and 12 amps for the larger salon unit.

When I switch the power source to the Victron transformer, the power draw increase to 9amps for the smaller units and close to 18/19amps for the larger unit.

I get a similar increase in current when using the microwave—12amp off the inverter and 18 amps off 50hz Victron.

That is a massive increase in power. I understand that the blowers will run slower at 50hz, but I would not have expected a 50% increase in power. There must be something amiss.

Any thoughts would be greatly appreciated.

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

[OnePapillon]

I believe you have very little wrong with your set up. Its the nature of the beast. Operating a 60Hz motor from 50 Hz the device will run at 5/6 speed, and draw more current. Lower speed, less water.
Also note where you are taking your amperage measurements from in the circuit configuration. Transformers/inverters/chargers are not as efficient at lower frequencies.
Wish I had your problem of excessive heat up here in the Pacific Northwest..

[zstine]

So the Victron iso transformer allows you to run off shore power (@50hz), but the A/C draws more current than when running on the battery via Mastervolt inverter (60hz)?



If it is running off shore power, is it a big deal that it draws more current? Are you paying the marina for usage or a flat electrical hookup fee? I guess I don't see the extra draw while connected to shore power as being a big problem.



One option is to just buy a cheap window unit locally and let it blow through a deck hatch while you are at the dock if you need A/C...

[garychurch]

Clarification... sorry I misunderstood your circumstances.

Malaysia provides 240v at 50hz. Your Victron steps that voltage down to 120v but the 50hz remains the same.

When you run off the inverter it uses battery voltage and increases it to 120v and 60hz.

Your question is why do you see such a greater power draw in amps on the 50hz source than the 60hz source.

Assuming your measuring correctly. I would guess that you have more current in the shore power circuit and less resistance (Voltage=Current x Resistance) than you should. This may indicate a fault or partial grounding in the wiring for the shore power side. Be interesting to check that both voltages are at a full 120v.

Good luck.

[valhalla360]

What's the actual voltage getting to the air/con unit?

If the inverter is putting out say 124v (within spec for a 120v appliance) vs the shore power thru a transformer running at 108v, that would increase the amperage by around 15%. Add in the 50hz vs 60hz with weak voltage, the compressor motor may be struggling compounding the issue (kind of a low grade startup draw situation).

[BillKny]

WOW... A lot of people making up answers here without getting it right, including people who claim to be electric system experts...

Let's try some REAL DATA. I know it is less fun that making stuff up, but it is a lot more nourishing.

My system is similar enough and behaves similarly enough that we can draw conclusions about the OP's question, and answer it accuratly.

My system:

• A Victron isolation transformer plugged into a nominal 120V/60Hz main, outputting nominally 240V/60Hz.
• A Victron Multiplus Inverter/charger that passes through 240V/60Hz, but inverts to 220V/50Hz
• A single 8000 BTU 50/60Hz rated A/C unit with a 50/60Hz rated cooling pump.

All data was measured by the Multiplus, and reported with a Vicrtron Cerbo GX

So let us run some experiments: First, running the A/C unit on inverter generated power of 220V/50Hz:

• Measured Voltage: 220.7 Volts
• Measured Current: 5.7 Amps
• Measured Frequency: 49.95 Hz
• Measured RMS Power: 548 Watts

Now, lets change that to Inverter generated power nominally 220V/60Hz:

• Measured Voltage: 219.6 Volts
• Measured Current: 3.7 Amps
• Measured Frequency: 59.91 Hz
• Measured RMS Power: 618 Watts

And one more, just for giggles, shore power supplied, Nominally 240V/60Hz:

• Measured Voltage: 249.8 Volts
• Measured Current: 4.0 Amps
  Measured Frequency: 60.09 Hz
• Measured RMS Power: 711 Watts

The first thing to notice is that the RMS power draw is HIGHER at 60 Hz than it is at 50 Hz. This makes perfect sense, from a mechanical standpoint because the compressor is spinning faster, and working harder, and is also a bit less efficient, and hence requires more power.

BUT WAIT... the AMPS are LOWER when the power draw is higher! How can that be? That is because a set of electrical motors (like an A/C system!) is a VERY reactive load, and is not resistive. The lower speed causes then to run at a much lower power factor. This higher current even at a lower RMS power draw, is one of the reasons that 60Hz motors burn up when run at 50Hz if they are not designed for it.

Last lesson, the Victron isolation transformers have baked into them, a voltage bump up about 10% above the nominal value. This is frequently handy because most marinas have pretty crappy power connections and excess voltage drop is not at all unusual.

So now we know...

[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.