Globe amperage draw - SailNet Community
 
LinkBack Thread Tools
post #1 of 8 Old 06-02-2007 Thread Starter
Tim
 
Join Date: Feb 2007
Location: Melbourne Australia
Posts: 17
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Globe amperage draw

Hi everyone can anyone please advise me of the amperage draw of
5 watt 12 volt globes / 10 watt 12 volt globes / and 15 watt 12 volt globes or can anyone advise me of the formulas to be able to calculate this problem All advise most welcome
Thanks Tim
timjf is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of 8 Old 06-02-2007
Reward for lost Kraken!
 
hellosailor's Avatar
 
Join Date: Apr 2006
Posts: 11,449
Thanks: 5
Thanked 132 Times in 129 Posts
Rep Power: 11
   
Ohm's Law:

5 watts = 12 volts x 0.41666 amps.

That is, watts divided by volts equals amps.

Ten watts? same voltage? Twice as many amps. Fifteen watts? Three times as many amps.
hellosailor is offline  
Quote Quick Reply Share with Facebook
post #3 of 8 Old 06-02-2007 Thread Starter
Tim
 
Join Date: Feb 2007
Location: Melbourne Australia
Posts: 17
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Thanks Hellosailor

Thanks Hellosailor does the same formula apply to incandesant globes as well as halogen globes I have halogen globes on my boat and that is my point of interest thanks
Tim
timjf is offline  
Quote Quick Reply Share with Facebook
post #4 of 8 Old 06-02-2007
Senior Member
 
Join Date: Aug 2006
Location: Arlington, VA
Posts: 1,853
Thanks: 0
Thanked 11 Times in 9 Posts
Rep Power: 10
   
Tim,

The formula VOLTS X AMPS = WATTS applies to all electrical circuits, ac or dc.

Bill
btrayfors is offline  
Quote Quick Reply Share with Facebook
post #5 of 8 Old 06-02-2007
Junior Member
 
Join Date: Jun 2006
Posts: 15
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
power calculation

Quote:
Originally Posted by btrayfors
Tim,

The formula VOLTS X AMPS = WATTS applies to all electrical circuits, ac or dc.

Bill

The above is true for all dc loads, and for ac resistive loads, like lighting. It isn't true, however, for inductive ac loads, like motors. (Or for ac capacitive loads either, but you shouldn't have to worry about those.) In the case of inductive or capacitive loads, P(watts)=I(amps) x E(volts) x PF(power factor).

Power factor calculation can get a little hairy, so it's best to avoid it. Fortunately, this isn't difficult. Motor nameplates should give you a value for "amps" (or "I", or "FLA") which can just be used directly. If you can't find that, there may be a power given in "VA"(volt-amps), which is "apparent power", that can be used just like dc power for calculations.

In the worst case, if you're stuck with ac watts, go ahead and calculate it like dc, then figure that the motor will really draw about 1.5-1.6 times the current you calculated.
Lurch is offline  
Quote Quick Reply Share with Facebook
post #6 of 8 Old 06-03-2007
can't re member
 
Join Date: Aug 2006
Posts: 318
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
 
please excuse the brief hijack Tim but...Lurch, does 1.5 or 1.6 describe the operating load or the startup load?
yotphix is offline  
Quote Quick Reply Share with Facebook
post #7 of 8 Old 06-03-2007
Junior Member
 
Join Date: Jun 2006
Posts: 15
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Quote:
Originally Posted by yotphix
please excuse the brief hijack Tim but...Lurch, does 1.5 or 1.6 describe the operating load or the startup load?

It doesn't really describe ANYTHING very well It's just a "fudge factor" to convert true load to apparent load for an "average" case. If you used it on "nameplate" watts, it would be a guess for operating current. Inrush can be 6 to 10 times that level, but only for a few seconds. Overload devices are already calculated to take that into consideration. It isn't significant for capacity purposes.

However, that's just a "worst case" workaround for an old piece of equipment with a worn out nameplate. You should always have a full load current (or equivalent) value to use. I just tossed it in for completeness in case Tim was figuring his system requirements, and had an ac motor in the mix.
Lurch is offline  
Quote Quick Reply Share with Facebook
post #8 of 8 Old 06-03-2007
Reward for lost Kraken!
 
hellosailor's Avatar
 
Join Date: Apr 2006
Posts: 11,449
Thanks: 5
Thanked 132 Times in 129 Posts
Rep Power: 11
   
Tim, basically yes.

Inductive loads, surge loads, AC circuits and conversion factors (VoltAmps rather than Watts) all can make it complicated but even then, using Ohm's Law gives you a reasonable ballpark for normal use. Generally, anything that makes a "boink" noise when you turn it on (like a big TV set or stereo) or has to start a motor (air conditioners and vacuum cleaners) will be an inductive load that uses a great deal more power when it first turns on. That surge can be 2x-3x as much more as it routinely uses, but you probably don't need to worry about that stuff if you are just trying to figure out your power budget on a "small" craft. The nav lights, the radio, the intruments, all can be figured by Ohm's Law. If you have any electrical winches, an anchor winch, or electrical refrigeration on board, THOSE motors all have a surge, so they need fuses/breakers which can withstand the starting pulse, and they will consume way more power for the first second of operation, than they normally consume. Because the time is so short, you can usually just use a "fudge factor" for your calculations, if the name plate on them doesn't list the surge current.
hellosailor is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Calculating Your Electrical Load Kevin Jeffrey Gear and Maintenance Articles 0 03-03-2003 07:00 PM
Help! What does my starter motor draw? namaste04 Gear & Maintenance 10 01-27-2003 12:39 AM
Vendée Globe Speed Machines Brian Hancock Racing Articles 0 11-29-2000 07:00 PM

Posting Rules  
You may post new threads
You may 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 On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome