Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 08-01-2016, 14:53   #1
Registered User

Join Date: Apr 2011
Posts: 36
engine power consumed

ok this is probably in the realms of WTF but i'll ask anyways, would a 30 amp altenator producing say 10 amps consume anymore or less crankshaft power than say an 80 amp altenator producing 10 amps, engine is a 2QM20 yanmar in an H28
__________________
sfnz is offline   Reply With Quote
Old 08-01-2016, 15:07   #2
Registered User
 
leftbrainstuff's Avatar

Join Date: May 2011
Location: San Francisco and Australia
Boat: Liberty 458
Posts: 1,978
Re: engine power consumed

The simple answer is no. You can use the simple formula P = V*I for dc loads. Strictly speaking the alternator is producing rectified ac but for load calcs that's not a first order effect.

So P = 10 * 12 = 120 Watts

Nor including friction, bearings and belts or electrical inefficiencies. Just add 20% as a rough approximation.

So say 120 + 24 = 144 Watts

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
__________________
leftbrainstuff is offline   Reply With Quote
Old 08-01-2016, 15:45   #3
Registered User
 
Reefmagnet's Avatar

Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Nantucket Island 33
Posts: 2,734
Re: engine power consumed

Quote:
Originally Posted by leftbrainstuff View Post
The simple answer is no. You can use the simple formula P = V*I for dc loads. Strictly speaking the alternator is producing rectified ac but for load calcs that's not a first order effect.

So P = 10 * 12 = 120 Watts

Nor including friction, bearings and belts or electrical inefficiencies. Just add 20% as a rough approximation.

So say 120 + 24 = 144 Watts

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
That's the basics.

Alternators are around 60% efficient and will be generating at around 14 volts with some rectification and regulation losses as well.

This puts the output as 10 * 14 / 0.6 = approx 230 watts or around 1/3 hp.

In theory, the larger alternator will require more power if for no other reason than the fact it will have more rotating mass so differences would be marginal. Of course, different regulator and alternator designs may have differing efficiency ratings which makes it only applicable to same design comparison.
__________________
Reefmagnet is offline   Reply With Quote
Reply

Tags
engine

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Want To Buy: looking for a power cat or power boat with indo flag santelli76 Classifieds Archive 1 22-04-2013 21:13
For Sale: 2003 40' Power Catamaran w/ a Sail Rig, 20kts under Power and Sails Also $225K double exposure Classifieds Archive 3 15-07-2012 16:27
How much electric power is needed to power a 40 - 45' cat at 5 knots? KHK007 Multihull Sailboats 40 18-03-2008 07:16
Catamaran engine power Talbot Multihull Sailboats 26 15-01-2006 16:25
Outboard engine and solar power charging THamel Construction, Maintenance & Refit 2 19-05-2003 23:28



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 06:46.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.