Go Back  DoItYourself.com Community Forums > Electrical, AC & DC. Electronic Equipment and Computers > Electrical - AC & DC
Reload this Page >

do i use rated output or input when determining power consumption?

do i use rated output or input when determining power consumption?

Reply

  #1  
Old 11-14-11, 06:21 AM
Member
Thread Starter
Join Date: Feb 2008
Location: New Haven, CT
Posts: 107
Received 0 Votes on 0 Posts
do i use rated output or input when determining power consumption?

A handful of our devices - laptops/xbox/wii/routers/etc - have a power cord that drops the voltage and turns the power into DC current.

I'm trying to determine rated wattage for all of my devices so I can setup a transfer switch for my new generator - i.e. i don't want to over-power the generator.

So my example is this: xbox has that converter between the socket and the machine:
input states 120v and 5amps
output states 12v 16.5 amps and 5v 1amp for a total consumption of 203watts.


Do I use the input or the output usage when determining how many watts a device will take from my generator?
 
Sponsored Links
  #2  
Old 11-14-11, 06:37 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,949
Received 33 Votes on 28 Posts
In that case you would use the input power of 5 amps.

When sizing your genny remember that motors need more power to start than when running.
 
  #3  
Old 11-14-11, 07:00 AM
Member
Thread Starter
Join Date: Feb 2008
Location: New Haven, CT
Posts: 107
Received 0 Votes on 0 Posts
great, thanks.

When sizing your genny remember that motors need more power to start than when running.

And that's another thing.

My generator says 3,000 running 4500 max.

When they say that:

does it mean that 4500 is what is seen when the generator first starts running, so that number is effectively useless, or, does it mean the generator can handle up to 4500 for a very short time in order to get a motor (like a furnace fan) running?
 
  #4  
Old 11-14-11, 10:58 AM
belgarid's Avatar
Member
Join Date: Aug 2011
Location: USA
Posts: 144
Received 0 Votes on 0 Posts
No, 4500 Max is the max surge that it can handle. This would be for starting loads like a pump or other appliance that contains a moter. They draw more current when starting then when running.
 
  #5  
Old 11-14-11, 12:03 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Originally Posted by Capslock View Post
does it mean the generator can handle up to 4500 for a very short time in order to get a motor (like a furnace fan) running?
That is correct, although it is an estimate not a firm rating.
 
  #6  
Old 11-14-11, 05:00 PM
Member
Thread Starter
Join Date: Feb 2008
Location: New Haven, CT
Posts: 107
Received 0 Votes on 0 Posts
thanks everyone, glad I am on the right track.

about calculating my needs - i went around the house and took stock of our lights and all of our electronics/appliances that are not 220v.

I still need to go back and look at starting watts, but my house comes at a little under 20a and 2300 watts running after I add up everything I'd like running on the generator (assuming all was running at once)


My breaker box is in such a hodge podge that a) to power everything I would need a 10-circuit transfer switch and b - half of the breakers in the transfer switch would have to be routed to a subpanel.



So just to be clear - I don't need the generator to handle the max amps from each circuit breaker i plan on adding to the transfer switch correct?

meaning i don't need to do 15amp * 10 breakers * 120v = 18 kW.

I instead use the list i created - with the total being 20amps * 120v = 2400 watts running.

in other words, the number of breakers on the transfer switch I would need is more dependent on my setup then it is on my generator capacity (25amp circuit breaker on my generator)


That must be right because the avg. kWh we use in a day is 14.
 
  #7  
Old 11-15-11, 10:12 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Originally Posted by Capslock View Post
So just to be clear - I don't need the generator to handle the max amps from each circuit breaker i plan on adding to the transfer switch correct?

meaning i don't need to do 15amp * 10 breakers * 120v = 18 kW.
Only if your home is a surgical operating room. Other than that, no.

I instead use the list i created - with the total being 20amps * 120v = 2400 watts running.
Right.

in other words, the number of breakers on the transfer switch I would need is more dependent on my setup then it is on my generator capacity (25amp circuit breaker on my generator)
Correct. Have you looked into a panel interlock kit instead of a transfer switch? It might be cheaper than getting a larger (10 ckt) transfer panel. The interlock kit allows you to power any circuits in the panel, but the downside is that you need to remember to flip off breakers for heavy loads like the water heater so you don't stall the generator.
 
  #8  
Old 11-15-11, 12:41 PM
Member
Thread Starter
Join Date: Feb 2008
Location: New Haven, CT
Posts: 107
Received 0 Votes on 0 Posts
Have you looked into a panel interlock kit instead of a transfer switch?
No I have not, but now that you mention it this does sound like a good idea.

The problem though is that my main panel and by sub panel are full. I would have to get a couple half-sized breakers to make this work.

Which is fine - but - the other problem is one particular circuit, my fridge, is in the sub-panel and my generator is only 120v; so I'm not sure if this would work?
 
  #9  
Old 11-15-11, 12:55 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
A 120V-only generator is possible, but not really great to use with an interlock kit. Essentially what you would have to do is jumper the hot leg to both sides of the panel. Note that you will need to do something similar even with a transfer panel. The fridge on the subpanel would still work given an interlock installed on the main panel.

Another option which is a little more hassle to hook up when the power goes out but much cheaper upfront. Put a single-circuit transfer switch on the furnace, and power everything else from a couple extension cords as needed.
 
  #10  
Old 11-15-11, 01:35 PM
Member
Thread Starter
Join Date: Feb 2008
Location: New Haven, CT
Posts: 107
Received 0 Votes on 0 Posts
Note that you will need to do something similar even with a transfer panel.
Really? what i was thinking was with the transfer panel, I would just reroute the number of transfer wires I need via conduit to the sub panel and connect them to the circuit I need then call it a day. No?

I wasn't planning on running anything 220v, it's just the subpanel has that setup.


Another option which is a little more hassle to hook up when the power goes out but much cheaper upfront. Put a single-circuit transfer switch on the furnace, and power everything else from a couple extension cords as needed.
And I actually might just do this for cost reasons; I just like having my things all nice an fancy like if I can.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: