Chromatography Forum

Hey, I'm shopping for a UPS for my 3800 in the hopes that this will prevent the display and various other parts from blowing every once in a while. I'm deeply ignorant about electricity and I want to make sure I know what the power requirements are. The manual I found online* says the following:

Each 3800 GC requires a separate circuit with the following
characteristics:
101 Vac ± 10%, 50 or 60 Hz ± 2%, 25 Amps, 2.5 Kilowatts
120 Vac ± 10%, 60 Hz ± 2%, 20 Amps, 2.4 Kilowatts
230 Vac ± 15%, 50 Hz ± 2%, 10 Amps, 2.3 Kilowatts
Installation Category: II

The back of my instrument has a tag that says "120 V, 50/60 Hz, 2400 VA"

So... 120 volts and 20 amps is what I need?



*http://www.ecs.umass.edu/eve/facilities/equipment/Varian2200/914647.pdf

That looks right. If you look carefully at your UPS specifications you may see that it list volt-amperes instead of watts for the load. The difference is that VA includes the power factor. For your equipment, mostly heating load, assume it is 1 and take VA = watts.

I would add a bit of a margin and get a UPS that can provide 25 or 30 A, although the 20 A is maximum drain with all heaters going full blast. If your problems are caused by short-term voltage fluctuations the UPS's main role is to clean up the incoming power, so make sure you get it wired with the output side isolated from the mains.

Peter

Look for a fully regenerative UPS (also called online or double conversion). These generate the UPS output from batteries all the time. The other common UPS technologies (standby and line-interactive) supply filtered mains to the output until the mains fails when they switch to battery. https://en.wikipedia.org/wiki/Uninterru ... .2Fstandby. For most applications, this is perfectly adequate and they are cheaper than fully regenerative units.

Don't know if this applies to Varian GC's but the fast heating oven controllers in Agilent 6890's play havoc with line-interactive UPS's causing them to switch back and forth between battery and mains which is not good for the UPS and the reason we had to switch to fully regenerative. If your oven doesn't have a phase-fired controller or is run isothermally, then you can probably get away with a cheaper line-interactive UPS

Peter is right - you should add some margin when you size your UPS. It will give you a little extra backup time and some room for expansion. In my setup, the UPS load runs at about 50% when the system is ticking over and ups to about 80% when the oven is ramped or traps are being desorbed. Doing both at the same time pushes the load to over 100% so I try to avoid that

Gerry