Excessive current draw on Embraco 60HZ Compressor

[havertyp]

Hello, all
This is a strange one, the problem is on a calibration fluid bath, it is a new one, which this customer 'inherited' from the US, hence the 60Hz spec. It uses a 2 stage cascade, the first stage uses an Embraco (Aspera) hermetic compressor, type J2192GK, running on R507, the second stage uses a Copelametic semi hermetic, type KAMB-007E-CAV-800, running R508b. The Copelametic is spec'd for 208-230V (60Hz) & 200-220V (50Hz). The running current is approx 6.2 - 7A which is slightly above the spec. FLA of 5.6A (the voltage is 238V measured across the run winding). The main problem is the Embraco compressor, it is drawing between 7.7 - 9.0 A, this is way above its specified RLA of 5.4A, it also runs quite hot. The compressor spec is 208 - 230V, 60Hz with RLA = 5.4 & locked rotor A = 40. Is the 50Hz supply the sole cause of this? Again, the voltage across the run winding is 238 V. This site has quite a high supply voltage, maybe the use of a bucking transformer may help.
On a similar 50 Hz spec. appliance, (at same supply voltage), the Copelametic is drawing approx the same current and the Aspera J2212GK hermetic compressor draws approx 3.5 - 4 A, just half what the hermetic on the other machine is using. It is also much cooler to the touch. The specs of this Aspera compressor are: 220 - 240V 50Hz, FLA: 5.3 LRA: 36. Ii notice from the spec sheets that the Aspera on the older machine is rated at 1 HP, whereas the Embraco/Aspera on the new machine is rated at 0.75 HP. Any pointers would be gratefully appreciated as a compressor change would be quite drastic for a brand new machine!

[Pyr0Beast]

Such compressor won't last long on a 50Hz network, especially with such voltage. Somewhere around 180-200V should do fine for 60Hz compressor running @ 50Hz. Everything else (excessive power) turns to heat eventually.

[havertyp]

Thanks - thought that as well. I will get a transformer to buck the voltage to the appropriate amount for 50Hz, the Embraco specified voltage is 230 max @ 60 Hz, this translates to a supply voltage of 191.7 max. @ 50HZ. I will have to use it at 200V as this is the minimum spec. for the Copelametic @ 50Hz. The refrigeration load on this appliance is small, so the reduction in performance & torque should not be a problem, will keep you posted.

[Pyr0Beast]

... Something works not ..

[Pyr0Beast]

With an autotransformer you might get away pretty cheap, but be warned that the transformer must! handle enough current for the system to start properly, that's at least 5 times the operating current for a short period of time (30s).

The thing to mind is that you work within operating limits of windings eg. 5.4A, since they are designed for specific current. Voltage doesn't matter as long as the current is within limits.

I would advise to put both compressors behind a buck transformer. This won't affect their capacity, because that is only proportional to the network frequency, but will sure cut the electricity bill, excessive heat and prolong the life of this unit.

Torque is only proportional to the current and since you have the same current passing thru, the torque is the same, only thing that changes with lover network frequency is that RPM's drop, however, with each turn of the rotor, the compressor still outputs exactly the same work, but because it makes less turns in a specific time, the total power is lower.

That is why 60Hz compressors 'underpreform' on a 50Hz network
If you divide power with network frequency, you'll see results are quite the same for different powers and networks. One compressor may be rated at 0.5HP at 50Hz, 0.6HP at 60Hz, 0.7HP at 70Hz and so on

[Pyr0Beast]

190V autotransformer with taps for +5V, +10V, +15v and -5V, -10V would be perfect for job like this, allowing you to select the right voltage from. 180V to 205V.

It is worth mentioning some compressors aren't exactly suited for operating on 50Hz network ..


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[havertyp]

Thanks for useful feedback - I have sourced autotransformers which were sold as an option with an old version of a Temptronic machine I used to repair approx 10 years ago, these old machines were spec'd at 25A full load and had a compressor FLA >10A so they should do the trick. They were made by ACME Transformer Corp, if memory serves me well. Will let you know how this works out when I set them up.

[Pyr0Beast]

Good luck with that !