allscott
Member
- Join Date
- Jul 2004
- Posts
- 1,332
This is slightly o.t but I know that a lot of us install UPS's in front of PLC's so I thought it was relevant.
We have a very expensive X-ray unit that has been giving us problems. We had a service tech out last week that looked at the incoming 120V supply and complained about it's quality. To be honest it was pretty ugly.
Although I didn't think that this was causing a problem with the machine I decided to install a double conversion online UPS to provide a "perfect" sine wave to his machine.
The X-ray machine was rated at 900VA max input. I put an amp clamp on the line while turning it on and observed about 8A inrush and 5A running current.
The UPS I spec'd was rated at 1000VA running and 110% overload for 3 minutes. Should be OK right??
Today I hooked up the UPS to the machine only to find that it immedeiatly went to overload when the X-ray was turned on. I phone the UPS manufacturer to find that the UPS was undersized for the application. Turns out the UPS is rated at 1000VA but only 700W because of the internal PF of the UPS and therefore could only provide 5.8A output.
Now I'm MAD.
I understand the difference between a watt, a volt amp, and a var. I understand the power triangle.
So how do these guys get away with this FALSE ADVERTISING. When you buy a transformer you spec it in volt-amps, knowing that the actual "power" developed is dependant on the power factor of your load. When you spec a motor you use horsepower or KW rating knowing that the draw of the motor is determined by the efficiency and power factor of the motor.
Now I have two problems, I look like an idiot in front of my new boss. More importantly the service rep from the X-ray manufacturer is going to be here on monday and I still have ugly power.
I'd love to slam the manufacturer but upon further investigation I found that ALL UPS manufacturers market their product this way. If this were a washing machine there would be a class action law suit against the manufacturer for false advertising. I offer this post as a warning to others so they do not get into the same situation.
Or am I an idiot and eveyone knew this?????
We have a very expensive X-ray unit that has been giving us problems. We had a service tech out last week that looked at the incoming 120V supply and complained about it's quality. To be honest it was pretty ugly.
Although I didn't think that this was causing a problem with the machine I decided to install a double conversion online UPS to provide a "perfect" sine wave to his machine.
The X-ray machine was rated at 900VA max input. I put an amp clamp on the line while turning it on and observed about 8A inrush and 5A running current.
The UPS I spec'd was rated at 1000VA running and 110% overload for 3 minutes. Should be OK right??
Today I hooked up the UPS to the machine only to find that it immedeiatly went to overload when the X-ray was turned on. I phone the UPS manufacturer to find that the UPS was undersized for the application. Turns out the UPS is rated at 1000VA but only 700W because of the internal PF of the UPS and therefore could only provide 5.8A output.
Now I'm MAD.
I understand the difference between a watt, a volt amp, and a var. I understand the power triangle.
So how do these guys get away with this FALSE ADVERTISING. When you buy a transformer you spec it in volt-amps, knowing that the actual "power" developed is dependant on the power factor of your load. When you spec a motor you use horsepower or KW rating knowing that the draw of the motor is determined by the efficiency and power factor of the motor.
Now I have two problems, I look like an idiot in front of my new boss. More importantly the service rep from the X-ray manufacturer is going to be here on monday and I still have ugly power.
I'd love to slam the manufacturer but upon further investigation I found that ALL UPS manufacturers market their product this way. If this were a washing machine there would be a class action law suit against the manufacturer for false advertising. I offer this post as a warning to others so they do not get into the same situation.
Or am I an idiot and eveyone knew this?????
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