Running 60HZ motors at 50HZ 1

[RobSimon]

I have been presented with a situation where 110V/60Hz refrigeration equipment has been installed in a 230V/50Hz environment. A step-down transformer has been installed to reduce the input voltage to 96VAC/50Hz. From reading faq237-1224 (very good by the way) this seems to go partway to solving the V/F problems described in that FAQ. Doing the math the input voltage should be reduced to somewhere aound 91VAC/50Hz. My questions are as follows:

What is the overall impact on energy consumption?
What is the overall impact on equipment longevity?
What is the (in general) reduction in system efficiency?

These units are installed in a marine environment where energy consumption is a major consiteration.

Thanks for any info! Rob

 

[itsmoked]

Ah yes sailboats.. Wish I was on one off the coast of Chile about now.

Glad you like the FAQ.

Now to your questions.
Since refer equipment is positive displacement I would believe you'd see about a 1/6 reduction in energy consumption.

Equipment longevity would probably go up about 2/6th probably because the pistons and bearings would see the slower speed AND the maximum temperatures of the pistons, and windings, and everything related, would be lower and less stressful.

System efficiency.. Hmmm harder call. Very hard, in fact, if you take in all things like the generator, battery draw, inverter loading, cycle time, battery charging fuel consumption, generator run time, etc.

The problem is that refer equipment is designed right up to the 'edge' for cost and efficiency reasons. If you then run the system at a substantially slower speed (17%) you may find the system capacity has been reduced perhaps more than 17%. This means during that struggle to reach cutout where heat leaks in while on the other side you're trying to pump it back out you will be executing a stern chase, as it were.
The system may have to run considerably longer to achieve cutout.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

If you pay attention to the section in the FAQ regarding the motor HP capacity dropping precipitously (20% by the way), then you can surmise the rest. Unless you have a 20% drop in load requirement or it was 20% oversized to start with, you motor may end up overloaded. If you do happen to have a lower HP requirement however your efficiency may actually go up, because motors are at their most efficient when closest to their full load ratings. However, because of the lower speed, your compressor will have to run longer to move the same amount of refrigerant. The net effect (i.e. kWh) is probably close to being the same however, so as long as you are not overloading the motor, there will likely not be much of a difference at the end of a year.

I wouldn't worry too much about the 91V vs 96V by the way, the tolerance is +- 10% anyway, so that should be fine.

 

[itsmoked]

<grin>

Ahem. Ah RobSimon; One thing you didn't mention was the size equipment you are referring to. If this is single phase equipment you may well have really poor efficiency since any start switch may not achieve transition resulting in a total burnout. (= 0 eff)

Also do you already have this equipment?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[davidbeach]

110V/60Hz and 230V/50Hz both just scream single phase. About the only solution going from 60 to 50 for single phase is to buy a new motor. Yes, in theory you can do enough work to modify a 60Hz single phase motor to work at 50Hz, but if your time is worth anything it will be cheaper to buy a new motor than futz around trying to make it work and then buying a new motor after all. Three phase motors are a different ball game.

 

[RobSimon]

To answer a couple of questions above... Yes, the equipment is installed. We are looking (unfortunatly somewhat late in the process) at whether or not to have the equipment replaced with 230V/50Hz European units.

Single phase 110V/60Hz with about a 6 amp running draw sized to be handled on a 15 amp circuit. I have not been able to get more information from the manufacturer (Sub Zero)

In the FAQ noted above generated heat and loss of cooling was pointed out as a major factor. Should we be concerned about that in this application?

Finally, the manufacturer has suggested that instead of reducing the voltage to 96V as is presently installed, the voltage should be INCREASED to 115Vac. This seems to contradict everything that has been stated in the FAQ. Any suggestions on why they would feel that this is a solution?

The boat will be in tropical waters and thus will be in the worst possible environment should they already be operating on the margin. The units are air cooled. The present time is the best to implement any modifications or replacements should there be any serious concerns.

Thanks again. Rob

 

[davidbeach]

The motor won't start - er, well it will start but it won't ever make it to run. There is a speed switch that switches the motor from start to run and that happens above what would be full speed at 50Hz for a 60Hz motor. You need the right motor or some form of power converter that can take in 230V/50Hz and output 120V/60Hz.

 

[itsmoked]

Groan.. Air cooled. Another problem. The fan. The air moved goes down very rapidly with speed reduction, by the square(?).

You may need different fan blades.

Leave things at 96V that's fine. Raise it? I believe they are making a mistake.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Small hermetic compressors don't have speed switches. There are a variety of devices and techniques used to cut out the start winding. Some are current operated, some are voltage operated, and I know that there are other types of starting switches that I am not familiar with.
Speed switches, no.
We need some help from someone who is current on small hermetic units.
It may be worth considering purchasing 230V/50HZ hermetics and having a refrigeration man swap them out. Keep the "Sub-Zees" but change the compressors. If you go that far, investigate adding water cooled condensers.
I wouldn't consider using 115V/50HZ unless you get it in writing from Sub-Zee. You won't get it in writing.
respectfully