Volt amps vs watts?

[SirBrass]

Navid, what is it you do for a living? B/c you're talking like an EE (and that's NOT a bad thing).

 

[Red Squirrel]

Wow, and I've created a circuit and added a amp meter to it to test amperage for my server. It has a 10 amp limit. LOL I guess it's not long enough to damage some equipment like that. But what you said makes sense though about the capacitors. Would not want any part of my body to be part of a circuit like that when it's turned on.

 

[JackMDS]

When a Unit is connected directly to the main (110VAC) it is usually rated it by VA (Volt Ampere).

When you rate a Unit by DC power thta is supplied by it you rate it in Watts.

Computer?s Power supplies are usually rated By Watts because it tells you the amount of DC that it can dish out to the computer.

Therefore the selection (VA or Watt) might depend on how you computed the consumption of the system.

Since most common UPS supply 110VAC it is usually rated by VA, you should compute the amount of consumption in VA and get an UPS that can supply 40% more since the rule of thumb is to use only 75% of the VA capacity.

I.e. To supply a 750VA system use 1000VA UPS.

Note* If you do not know the VA of a component the rule of thumb is DC in Watts x 1.6 = VA. I.e. 100 Watt DC needs 160VA.

Example: Monitor 100VA, Computer power supply 450Watt.

450Watt DC would need 720VA. So total consumption is 100 + 720 = 820VA

820 + 40%= 1150VA. I.e. get an UPS that is 1150VA or more.:sun:

:sun:

 

[Zepper]

Jack MDS forgot to correct for efficiency. At max output of 450 watts DC, a typical 70% efficient PSU will require about 600W from the AC side at a typical PF of 0.6 means ~1000VA. Figures are an in-my-head approximation but adequate for this purpose. Luckily, most PCs seldem require above half power from their PSUs.

.bh.

 

[OrganizedChaos]

Originally posted by: RedSquirrel
Wow, and I've created a circuit and added a amp meter to it to test amperage for my server. It has a 10 amp limit. LOL I guess it's not long enough to damage some equipment like that. But what you said makes sense though about the capacitors. Would not want any part of my body to be part of a circuit like that when it's turned on.

reminds me of back in school when we would charge an orange drop and then toss it someone

 

[JackMDS]

Originally posted by: Zepper
Jack MDS forgot to correct for efficiency. At max output of 450 watts DC, a typical 70% efficient PSU will require about 600W from the AC side at a typical PF of 0.6 means ~1000VA. Figures are an in-my-head approximation but adequate for this purpose. Luckily, most PCs seldem require above half power from their PSUs.

.bh.

Did not, the 40% more takes care of it.

70% from 1000 = 700

700 + 40% = 980

:sun:

 

[Zepper]

"450Watt DC would need 720VA. So total consumption is 100 + 720 = 820VA"

Actual will be about 1000VA as my figures showed so something hasn't been taken into consideration. Safety margin needs to be on top of 1000VA.

. Note that I recommended a 700VA UPS for the OP's 700W Zippy driven system. I did that with confidence that that humongous PSU would never come anywhere near to full output in its lifetime. The OP's choice of a 1000VA unit will have plenty of headroom.

. I also rig my battery backed up systems with a drop-out relay so that the AC doesn't get reconnected until I'm sure it is clean. More damage is done to equipment from the junk on the line immediately after the AC returns than from the power outage itself. A few high quality UPS do an adequate AC power analysis prior to reconnecting themselves, but very few... Most, if they have any self-protection at all, use a simple time delay.

.bh.

 

[sharkeeper]

Potentially long enough to damage the transistors in the UPS inverter.

There is usually protection to guard against this. Of course with the advent of really cheap offshore unit availability, who knows?

One thing for certain, as long as the unit utilises the transistor the cardinal rule still applies: The transistor is the world's fastest fuse!