Moderated Discussion Areas
  ContinuousWave: Small Boat Electrical
  Computing Electrical Load In Amperes From Other Units

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Computing Electrical Load In Amperes From Other Units
ryland posted 10-17-2007 01:23 AM ET (US)   Profile for ryland   Send Email to ryland  
I have a 2005 150 Sport with 60hp Mercury Big Foot. I have recently installed new electronics and am wondering how my alternator will match up. I cannot get all the info in the same language. I have searched this website and others. My questions are: Where do I stand in terms of power? How many amps does the Garmin draw? How many amps do the nav lights draw? Does the Jensen really draw 17? Do I need to start charging my battery after use? What does the alternator put out when the engine is running? Sorry for all the questions, but I cannot figure this out. Thanks in advance.


Mercury Big Foot 60hp...18A alternator.

New Garmin 440s...power usage 15watts max at 13.8 VDC

New Uniden Solara VHF.... .6A @ 13.8 VDC at max audio output.

Jensen Marine CD Player 5112...don't know, someone on this site said 17A.

Navigation lights.

Bella con23 posted 10-17-2007 08:22 AM ET (US)     Profile for Bella con23  Send Email to Bella con23     
ryland - I looked on the Jensen website for you system. There is no listing for a model 5112 CD Player. I did find the closest model that matched your description and much to my surprise it draws 15 amps max. at 12VDC.

Your other loads are negligible at 1 amp or less. Amps = volts/ohms.

Obviously your load exceeds your alternator output with everything turned on, but there are variables to consider. Is the radio cranked from when you leave the dock until the time you get back? What is the duration of the average trip? Engine running the entire trip or a lot of drifting? You get the picture.

I think I would be more comfortable with a separate starter battery that I could always rely on. Regardless of the battery configuration, you need to have that battery or batteries on charge when you return each trip.

jimh posted 10-18-2007 10:48 PM ET (US)     Profile for jimh  Send Email to jimh     
If a load is rated in watts, you can covert to amperes according to the relationship


and thus


I would use 13.2-volts as the voltage in a "12-volt" system.

ryland posted 10-19-2007 01:17 AM ET (US)     Profile for ryland  Send Email to ryland     
No my radio is not on from start to finish. I tend to keep the motor running if i am fishing. I also today installed a battery shut off switch. I think that if I limit my use of the stereo, and be sure to have it off when returning to the harbor, i should be fine. i do not want to add a second battery. i think i will buy an emergency starter, i may also add a small solar charger, problem is i keep the boat in an insecure location, with no power.
Bella con23 posted 10-19-2007 07:58 AM ET (US)     Profile for Bella con23  Send Email to Bella con23     
The fact that you are aware of the situation will likely keep you out of trouble. I like the idea of the solar trickle charger, and even the backup power supply.

Jim, thanks I stand corrected. I don't know were that came from as I wasn't even thinking ohms.

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.