wimpy power supplies

[Guest ArielDunwright]

This is my first application with GE Fanuc. I'm required to use a 90-30. My problem is that when I load a rack with the I/O I need there isn't a power supply big enough to handle the load. What was GE thinking when they limit the P/S to 30W? Anybody have a work-around for this?

[Chris Elston 78]

Not sure what you are trying to do, (I hope you are not planning on powering your I/O from your rack power supply...) but you can check in the hardware configurator if you use Versa Pro and you'll find most applications are fine for a standard 90-30 rack power supply.

[Guest Arieldunnwright]

No, I'm not trying to power the I/O from the rack P/S. What I'm trying to do is use a 10 slot rack containing a 364 CPU, two DSM314s, two ALG220s, one APU300, one Horner Electric STG884, two Horner Electric DAC410s. Using CIMplicity ME to configure the rack, it reports that the power supply is undersized. Surely I'm not the first to load up a rack like this. For that matter, it doesn't like having seven MDL645s in one rack. The power supply is being asked to deliver 105% on the 24VDC tap. And those are simple DC inputs.

[Steve Bailey 118]

You're loading that rack with some power hogs. The CPU364 uses 7.55 watts, and each DSM314 uses 4 watts. You should be using the high capacity power supply (IC693PWR330). It's still rated for 30 watts total from all three supplies, but the 5 VDC supply can handle the full 30 watts. In the case of the MDL645s, the software is assuming that you're going to power the inputs from the PLC's power supply. The 24 VDC isolated supply refers to the terminals on the power supply module. If you don't wire the inputs to it, the module won't draw from it, and you'll be OK. The same applies to the analog modules. Personally, I don't like using the isolated 24 VDC supply to power the inputs. If the field wiring gets compromised, and you draw excessive current from the supply, the 5VDC goes down also, and the PLC shuts down.

[Chris Elston 78]

What? Really? You don't have a separate power supply for all your input/output cards? How does shorting out the power supply that is powering the I/O kill the 5VDC rack power?

[Steve Bailey 118]

What GE calls the "Isolated 24 VDC supply" is the one that's available from the terminals of the 90-30's rack power supply. That's what I was referring to. If you let the smoke out of that supply, you also lose the 5 VDC backplane supply. I prefer to use an independent DC supply for the I/O, not the one provided by the PLC.

[Chris Elston 78]

Ah...whew....I thought I was behind times or something.