×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

CALCULATION

CALCULATION

CALCULATION

(OP)
Could you explain the proper calulation to find volt-amps and the calculation for watts. I am trying to size a UPS to be capable of suppliying 480 watts for 5 minutes.

RE: CALCULATION

Volt-amps are watts unless you are talking inductive loads, such as motors.  If you are not running a motor, and I suspect not at 480 watts, and if you have allowed for all possible loading conditions and are sure 480 watts is adequate, then I would look for a 500 VA UPS.
The length of time it will hold up a load is supplied by the UPS manufacturer.

Lewis

RE: CALCULATION

Watts and VA's are the same for purely resistive loads, Watts=Volts x Current. For inductive loads(coils-like motors, other non-linear loads) the sizing of the UPS would have to consider, amongst others, the VA rating of the device. VA is volt-amps and is not worth typing in the formula for and trying to explain what everything means(vectors, p.f., etc) but I will if you want to see it.

RE: CALCULATION

   To complete Lewish and buzzp answers: Capacitive loads also increase VA values over watts, but in the opposite sense than inductive loads.

Julian

RE: CALCULATION

for that load, i will go for 750VA ..room for motorized load..

the back-up time selection and the corresponding size of the battery are supplied by the manufacturer...at mains failure you have the inverter plus the load running and the battery ampere-hour can only be sized accurately by a particular manufacturer..

good luck
dydt






RE: CALCULATION

Add one point, to extend the hold-up time, you can open the unit, and connect a larger battery,  as long as it is the same voltage.  Maybe car/motorcycle.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources