Can you explain why an Edwards vacuum pump won't run on 60 Hz?
Can you explain why an Edwards vacuum pump won't run on 60 Hz?
(OP)
Hi,
I'm really curious to understand the following problem. I brought a vacuum pump from Switzerland to Canada. Originally the pump was obviously not designed to run in Canada. Also, the pump is pretty old but used to work flawlessly in Switzerland. I attached a picture with the few labels still present on the pump. It seems it was designed to run on single phase 220 V at 50 Hz. In Switzerland it was actually running fine on 230 V 50 Hz. I thought in Canada I would be able to make it work using a step-up converter. This is the first thing I tried. It blew the fuse on the power line where the converter was plugged in. I thought I needed more current and so I changed the plug to be able to connect the pump directly to a single phase "208 V" power outlet. In the building where I'm now it seems the mains is a little bit old. The neutral to phase is actually 115 V and the phase to phase is 200 V only. Anyway, in this configuration, that's with a single phase 200 V and 60 Hz line, the pump works for a while, about 15 seconds and then a thermal protection on the pump kicks in. When it runs, the pump doesn't seem to run correctly. The sound it makes is different from what I'm used to, it vibrates more and there is a periodic loud click. Anyway, I'm surprised that increasing the frequency from 50 Hz to 60 Hz makes such a huge effect. Because the voltage is lower and the frequency higher, I would expect the motor would run cooler not hotter. So I don't understand why the thermal switch kicks in! Before I invest 2000$ in a frequency converter and discover that the pump was actually mechanically damaged during transport, could you comment about what can possibly go wrong when trying to run a Edwards pump at 60 Hz instead of 50 Hz, in case anybody knows more about these vacuum pumps? I guess fundamentally the problem is that the motor pulls too much current but why? Is it possible that the mechanical load increases so much at 60 Hz that the motor can not drive it properly?
Thanks a lot!
Razvan
I'm really curious to understand the following problem. I brought a vacuum pump from Switzerland to Canada. Originally the pump was obviously not designed to run in Canada. Also, the pump is pretty old but used to work flawlessly in Switzerland. I attached a picture with the few labels still present on the pump. It seems it was designed to run on single phase 220 V at 50 Hz. In Switzerland it was actually running fine on 230 V 50 Hz. I thought in Canada I would be able to make it work using a step-up converter. This is the first thing I tried. It blew the fuse on the power line where the converter was plugged in. I thought I needed more current and so I changed the plug to be able to connect the pump directly to a single phase "208 V" power outlet. In the building where I'm now it seems the mains is a little bit old. The neutral to phase is actually 115 V and the phase to phase is 200 V only. Anyway, in this configuration, that's with a single phase 200 V and 60 Hz line, the pump works for a while, about 15 seconds and then a thermal protection on the pump kicks in. When it runs, the pump doesn't seem to run correctly. The sound it makes is different from what I'm used to, it vibrates more and there is a periodic loud click. Anyway, I'm surprised that increasing the frequency from 50 Hz to 60 Hz makes such a huge effect. Because the voltage is lower and the frequency higher, I would expect the motor would run cooler not hotter. So I don't understand why the thermal switch kicks in! Before I invest 2000$ in a frequency converter and discover that the pump was actually mechanically damaged during transport, could you comment about what can possibly go wrong when trying to run a Edwards pump at 60 Hz instead of 50 Hz, in case anybody knows more about these vacuum pumps? I guess fundamentally the problem is that the motor pulls too much current but why? Is it possible that the mechanical load increases so much at 60 Hz that the motor can not drive it properly?
Thanks a lot!
Razvan





RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
By the way, you cannot have 115 volts L-N and 200 volts L-L
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
B.E.
You are judged not by what you know, but by what you can do.
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
I normally would not suggest this, but from looking at vacuum pumps on Ebay I suspect that some Edwards pumps have dual rated 50/60 Hz motors. I also suspect that the motor may be slightly overpowered for the load. With the high voltage connection, each of the windings will see 200 Volts /2 or 100 Volts. Going to the low voltage connection will supply 115 Volts and that may make the difference.
Be sure to check the current at both the start and the end of the pump-down cycle.
Good luck
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
I had a look at how AC motors work. I'm still interested to find a solution if possible without using a frequency converter since indeed they are rather expensive. So I wonder if it is even possible to run reliably a motor made for 50 Hz on 60 Hz. My basic idea is that the mechanical torque required would increase proportional with the frequency, roughly 20% only. I looked where the V/freq comes in and, if I'm talking about the correct type of motor, it seems like the maximum torque generated by the motor varies with the square of this ratio. On the other hand, the position where the maximum occurs, in terms of the "slip" variable, that's s=(w-w_m)/w [that's AC freq minus shaft rotation freq over AC freq], s_max also changes and actually becomes smaller (it's inverse proportional to the AC freq). So I'm thinking that to match the torque curve in terms of s is enough to rise the voltage at ~ 240 V which would match the torque curve to that when using the motor at 50 Hz. The motor will have to work a bit harder because the mechanical torque is 20% greater so it will actually work at a larger s which will lower the efficiency and make it dissipate more heat but maybe without tripping the thermal fuse.
Right now with the voltage at 200 V and 60 Hz I get that the maximum torque is only 57% of that when operated at 220 V and 50 Hz. So clearly this is a huge problem and explains why it doesn't work properly. The s is probably very large which explains why it heats up. But at 240 V and 60 Hz I get the maximum torque at 83% of what it would be at 220 V and 50 Hz. Considering that the s_max occurs closer to s = 0 I think the torque curve as a function of s is matched to that when the motor is used at 220 V and 50 Hz. The advantage of 240 V is obviously that is more realistic to obtain it than 264 V. I'm hoping that a 240 V transformer would be a cost effective solution to power all the electric motors on my setup.
What do you think about this? Any considerations that would actually kill this idea? I haven't understood the comment about the magnetic flux density. Clearly I lack the understanding how it affects the operation of the motor but I was thinking that for a 20% mechanical torque increase there will be no saturation. Lets say somehow the motor can not deliver the torque required and the shaft rotates much slower than the AC freq. then the s is larger than at full speed and the frequency of the induced current in the rotor is larger by the same amount the mechanical frequency is smaller. Isn't this a similar configuration to when the motor starts up? It will heat more but otherwise work?
Thanks a lot!
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
You will ever get that wrong motor to run that far out of its design region for the periods demanded in vacuum service. Sometime you can get away with this type of misapplication because the load isn't continuous. For instance a hydraulic punch or press which has very cyclic loading with periods of virtually no load interspersed, with perhaps gross overloads during the end of a press cycle. In this example the motor has time to cool off regularly with no extended overheating period. But, compressors, pumps, and vacuum pumps can sit there demanding full load out of the driving motor for minutes, hours, and even days in some cases. Those type applications don't pan out in your, "I'll just tweak things and see if it works" case. It leads quickly to burnouts that sometimes cause thousands in damage, big delays, and ruined work/product.
Look what effort you're spending hoping to get this scheme to work! It isn't worth it and the results are not going to fly. You can't transport cattle on a bicycle. Replace the unit with a used one (your budget) and move on to doing things you can save on.
FAQ237-1224: Motors: Changing between a 50 and 60Hz supply.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
2 To get maximum torque at 60 Hz you will have to provide 264 Volts.
You need to gain 64 Volts.
If you use an auto-transformer with a primary of 240 Volts, you will need a secondary of 53 Volts to get a 64 Volt boost with 200 Volts on the primary. Not a standard transformer.
If you can find a transformer rated at 240:48 Volts and rated for boost, it will give you a 20% boost. Those are standard ratings even though 48 Volt secondaries may not be plentiful. That will take your 200 Volts up to 240 Volts. Now a second auto-transformer rated 240:24 Volts will take you up to 264 Volts.
After you locate and price out these transformers, check the price of a VFD to run the pump on 50 Hz. If the pump won't run on 200 Volts/50 Hz, then drop the frequency to 45 Hz. That should give you full torque at 200 Volts/50 Hz.
Bear in mind, I don't know the speed/torque characteristics of a vacuum pump. I don't know how heavily loaded the motor is.
If the motor is loaded up to the design horsepower and if the torque demand increases with speed, the pump probably won't run on 264 Volts 60 Hz without overloading anyway.
A small VFD for each pump may be more economical than one large inverter to power all the equipment.
Re torque and saturation:
The maximum torque is determined by the maximum magnetic field strength. Motors typically have a field strength close to saturation.
Slip and heat. You are correct. starting is a high slip event and the heat builds up rapidly. That is why some motors are limited to 3 or 2 or even 1 start per hour. A start only lasts for a few seconds. A few minutes at high slip conditions may destroy the motor from excess heat.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
Thanks a lot for all the tips! I experimented a little bit and finally managed to make it work with 277 V at 60 Hz. I used the neutral to phase of a 480 V line. The pump is running very smoothly and reaches an ultimate vacuum of about 15 mtorr with the motor pulling 2.4 A. The temperature on the body of the motor reaches a maximum in the middle of the distance between the fan and the pump itself. The temperature increases with time but gets flat at ~ 48.5 deg. C after a few minutes. I have never measured the temperature when it run on 50 Hz but feeling by hand it was similar. Possibly in the long run the lifetime of the motor is going to be shorter. The major remaining issue is electrical certification and maybe here I'll run out of luck! ;)
Cheers,
Razvan
RE: Can you explain why an Edwards vacuum pump won't run on 60 Hz?
Nice solution.
Thanks for the update.
Bill
--------------------
"Why not the best?"
Jimmy Carter