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Old 08-02-2014, 19:42   #1
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Dual Frequency AirCon

Is anyone aware of a marine air conditioner that is rated to operate on both 50hz and 60hz power?
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Old 08-02-2014, 20:25   #2
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Re: Dual Frequency AirCon

I have seen such a thing but don't recall the exact brand. Will see if I can dig up the info. As I recall it worked on 240V 60 Hz or 230V 50 Hz and not on 125V 60 Hz.
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Old 08-02-2014, 20:38   #3
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Re: Dual Frequency AirCon

The MarineAir units I have are 120v 60hz and per the manual will operate on 50hz at lesser efficiency/output. I don't believe the newer units have this capability (after Dometic bought them).
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Old 08-02-2014, 20:51   #4
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Re: Dual Frequency AirCon

For the Marineair units I can see working on 50 or 60 Hz but how do they deal the 230V? Do you have to use a step down transformer?
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Old 08-02-2014, 21:33   #5
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Re: Dual Frequency AirCon

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For the Marineair units I can see working on 50 or 60 Hz but how do they deal the 230V? Do you have to use a step down transformer?
Yep, an isolation transformer. But an autotransformer would do it.
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Old 08-02-2014, 21:46   #6
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Re: Dual Frequency AirCon

Webasto makes 230v 50/60hz units.. both direct expansion and chilled water. Not sure about 120v systems running @ 50hz

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Old 09-02-2014, 04:13   #7
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Re: Dual Frequency AirCon

Here's one
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Old 09-02-2014, 05:10   #8
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Re: Dual Frequency AirCon

The frequency of the electricity determines the speed of the motor. A motor "wound" for 60 Hz will run at 5/6 speed at 50 Hz. At the lower speed, the performance of the compressor and any fans will be different. IF the system was sized for the lower running speed, all should be well.
I don't know enough about the engineering of such systems to know where other problems may lurk.
There is no relationship between frequency and voltage such as between a 50Hz 230V and 60Hz 120V motor. Volts are volts and frequency is frequency. (I'm not saying that there isn't a difference in power output, just V and Hz.)
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Old 09-02-2014, 07:26   #9
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Re: Dual Frequency AirCon

As Dale noted, it isn't an electrical relationship with frequency but a practical one. Appliances made for the European Market are wound to operate at 50 hz and can faster (if so engineered) at 60 with a shade higher performance. My unit seems to run less @ 60 than at 50 and was designed to do both. I haven't seen many 120v units that were rated to run at 50 but a few have popped up here; the ones I knew of were from European suppliers; that was the point I was trying to make…
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Old 10-02-2014, 09:42   #10
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Re: Dual Frequency AirCon

Yes, I am aware of all that. I am only looking for suggestions for manufacturers who specifically allow 50/60hz use at 220v.
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Old 10-02-2014, 10:06   #11
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Re: Dual Frequency AirCon

I would be interested in finding a unit that runs in 120V 60 Hz and any form of 50 Hz. Have my boat set up for 120V 60 Hz, 30 amp service and prefer to keep it that way. But would be nice to be able to run the air con on 50 Hz when I get to Europe.
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Old 10-02-2014, 21:42   #12
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Re: Dual Frequency AirCon

In general, its probably better to buy a 50hz EU unit. A 50hz unit will generally run fine at 60 hz. A 50hz motor is less stressed at 60hz, IE more efficient. If the motor is VFD rated it would be fine at 50hz for sure.

Some maybe most 60hz motors can tolerate 50hz, but it depends on winding tolerance, etc. So it might work fine but as noted at a lower output/ speed. I think generally, most small motors (<3hp) would be ok unless operated in a hot environment. YMMV
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Old 11-02-2014, 06:47   #13
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Re: Dual Frequency AirCon

The fine print on the Dometic rating plates is usually overlooked, yet is important. It has two ratings:

-230V@60hz

-200V@50hz

Yes, it can be run at 50hz, but note the reduced voltage. To be within specs, you really should use a step down transformer to reduce the typical 230V50hz shore power down to 200V. Most Charles transformers have taps that allow for this, but from what I can tell they are rarely used.

All that said, lots of people just run straight off 230V50hz and most seem to get away with it, but not all.

For anyone who is interested, what's behind this is something called Counter Electro-Motive Force, or counter EMF. I am NOT an expert on this, but have read up a bunch trying to get to the bottom of the "200V" rating on the Dometic AC units, and this is what I came to understand.

The windings in an electric motor are just wires that, if laid out straight whould be a short circuit. Counter EMF is what prevents them from being a short circuit. The magnetic field created by the motor resists current flow in what would otherwise be a short circuit. The counter EMF is related to the ratio of the voltage over frequency (V/f). If you let the V/f ratio drop, current flow increases along with internal heating of the motor. If it drops too low for too long, you burn out your motor.

Ideally you want to maintain the same V/f ratio for a motor, so when you drop the frequency, you also need to drop the voltage. That's where the somewhat cryptic nameplate rating comes from on the Dometic compressor units
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Old 11-02-2014, 21:01   #14
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Re: Dual Frequency AirCon

http://www.marinaire.com
They are fine with running their 60hz units at 50hz, will not affect the warranty. They say it's about a 17% drop in capacity. In general as long as the system is simple without fancy electronics it will operate on either 60hz or 50hz. 240v of course.
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Old 12-02-2014, 04:07   #15
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Re: Dual Frequency AirCon

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Manufacturer of quality marine air conditioning units and self contained marine air conditioners - Home
They are fine with running their 60hz units at 50hz, will not affect the warranty. They say it's about a 17% drop in capacity. In general as long as the system is simple without fancy electronics it will operate on either 60hz or 50hz. 240v of course.
Beware that MarinAire is not the same as MarineAir. The later is a well established marine AC company that is now part of Dometic.

For anyone wanting to run their 60hz AC unit on 50hz, I'd suggest first reading the nameplate on the unit(s) itself to see what it says. Then see if you can get the technical spec sheets for the product. Dometic/MarineAir's current model spec sheets have foot notes that say whether you can or cannot run at different frequencies, and what restrictions exist. This is one place where you will find a slightly less cryptic note saying you can run at 50hz provided you drop the voltage to 200V.

The danger in this is that if you just ignore it all, your AC system will likely run and seem fine, but you will be stressing it in ways it wasn't designed to be stresses. How long it lasts is anyone's guess, and if it dies, don't expect a warranty claim to be very fruitful.
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