Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 10-09-2011, 09:32   #46
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,035
Re: Alternators - What's the Difference?

Quote:
Originally Posted by ADMPRTR View Post
What are the hidden costs of replacing an alternator with higher output version in terms of engine wear, fuel, HP, etc?
Nothing hidden really. An alternator needs about 1hp from the engine for each 50A of output. If you have a 13hp engine and a 55A alternator, the alternator eats about 1hp when under full load. Increase that to a 200A alternator and it eats about 4hp (more for mechanical losses) so now it is eating almost 1/4 of oyur engine power and you've got an 9hp engine instead of the 13hp.

Take a bigger engine with 40hp, and you've still got 36hp to use, so the alternator is negligible. And because it charges faster, it releases that load and drops from consuming 4hp to consuming very little, 4x faster.

Diesels generally do better under heavy loads, i.e. 80% has been kicked about. So unless you need full power to the prop or other loads, having a heavier alternator may be better for an engine.

How long is a piece of string?
__________________

__________________
hellosailor is offline   Reply With Quote
Old 10-09-2011, 09:42   #47
Registered User

Join Date: Jul 2006
Posts: 3,949
Re: Alternators - What's the Difference ?

One of the biggest hidden costs is setting up your engine to handle the loads of a 200-amp alternator. You need at least a double belt pulley set up, and very heavy strong brackets. Plus the best belts available. Some are now going to serpentine belt set ups. There will be additional side load on the bearings on your engine too. IMHO, you are much better off going with two 100-amp alternators on opposite sides of the engine, but again there is more engineering involved setting it up. This gives you full time instant back up for the charging system.
__________________

__________________
Kettlewell Cruising
Kettlewell is offline   Reply With Quote
Old 10-09-2011, 09:43   #48
cat herder, extreme blacksheep
 
zeehag's Avatar

Cruisers Forum Supporter

Join Date: Jul 2008
Location: furycame alley , tropics, mexico for now
Boat: 1976 FORMOSA yankee clipper 41
Posts: 17,770
Images: 56
Send a message via Yahoo to zeehag Send a message via Skype™ to zeehag
Re: Alternators - What's the Difference ?

my 80 amp alternator did just fine and dandy while i was heading from ensenada to mazatlan with my autopilot and nav lights and whatever else i needed to run electrically. no sweat. but my autopilot is a hydraulic one with minimal electrical usage. i could even read at night if i wanted to so do. yes, i do have radar and gps and.....
zeehag is offline   Reply With Quote
Old 10-09-2011, 10:26   #49
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,579
Images: 240
Re: Alternators - What's the Difference?

Quote:
Originally Posted by hellosailor View Post
Nothing hidden really. An alternator needs about 1hp from the engine for each 50A of output ...
DIESEL: If you are driving your alternator with a diesel engine, and assuming adequate flywheel mass and a 3:1 engine drive pulley to alternator pulley ratio, a high efficiency, high current, 12V alternator will require about 1 hp per 30 amps of output power + about 1-2 hp for increased engine operating loads; when operating at its maximum rated output current.
Therefore, for a 150 Amp alternator, operating at full output, the expected diesel engine load would be about 7-8 hp.

GASOLINE: If using a gasoline engine instead of a diesel, with a slightly lower 2 to 2.5:1 drive ratio, figure on a requirement of about 1 hp per 15 amps of output power + about 1-3 hp for increased engine operating loads.
Hence, about 11-14 hp for a 150A alternator.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 10-09-2011, 10:30   #50
Registered User

Join Date: Apr 2010
Location: Western Australia
Boat: Boro
Posts: 87
Re: Alternators - What's the Difference?

Quote:
Originally Posted by GordMay View Post
DIESEL: If you are driving your alternator with a diesel engine, and assuming adequate flywheel mass and a 3:1 engine drive pulley to alternator pulley ratio, a high efficiency, high current, 12V alternator will require about 1 hp per 30 amps of output power + about 1-2 hp for increased engine operating loads; when operating at its maximum rated output current.
.
SO heres the question: I have the wrong pitch on my prop, and cant access the top HP of my engine anyway.

Does the alternators output come off the HP at the prop, or off the HP I cant get to the prop anyway?
__________________
billwa is offline   Reply With Quote
Old 10-09-2011, 10:59   #51
Registered User
 
ADMPRTR's Avatar

Join Date: Jan 2011
Location: Georgian Bay, Ontario, Canada
Boat: CS36 Traditional
Posts: 551
Re: Alternators - What's the Difference ?

The following is an off topic battery question but is partly relevant:

Does going with a higher than required battery capacity extend the life of the batteries because they don't discharge as much (as a percentage of their overall capacity)?

i.e. if the house required 50Ah per day I believe it would normally dictate a 200-250 reserve capacity to discharge to 25-20%. If 400Ah batteries where installed (resulting a a daily discharge of only 13%) would it be a waste of money or a strategy to extend the life of the batteries?

Essentially, does a shallow discharge help or hinder battery longevity?

If the above is true (and to bring us back on topic) would either scenario described above require the same size alternator or would the larger bank require a larger alternator even though only 50Ah are being replaced?
__________________
ADMPRTR is offline   Reply With Quote
Old 10-09-2011, 11:03   #52
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,579
Images: 240
Re: Alternators - What's the Difference?

Quote:
Originally Posted by billwa View Post
SO heres the question: I have the wrong pitch on my prop, and cant access the top HP of my engine anyway.
Does the alternators output come off the HP at the prop, or off the HP I cant get to the prop anyway?
The Alternator takes it's power from the engine, not the propeller.
At lower (than optimum) engine RPMs, the alternator will be less efficient, and will draw more
HP per Amp of output.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 10-09-2011, 11:03   #53
Registered User
 
ADMPRTR's Avatar

Join Date: Jan 2011
Location: Georgian Bay, Ontario, Canada
Boat: CS36 Traditional
Posts: 551
Re: Alternators - What's the Difference?

Quote:
Originally Posted by hellosailor View Post
Nothing hidden really. An alternator needs about 1hp from the engine for each 50A of output. If you have a 13hp engine and a 55A alternator, the alternator eats about 1hp when under full load. Increase that to a 200A alternator and it eats about 4hp (more for mechanical losses) so now it is eating almost 1/4 of oyur engine power and you've got an 9hp engine instead of the 13hp.

Take a bigger engine with 40hp, and you've still got 36hp to use, so the alternator is negligible. And because it charges faster, it releases that load and drops from consuming 4hp to consuming very little, 4x faster.

Diesels generally do better under heavy loads, i.e. 80% has been kicked about. So unless you need full power to the prop or other loads, having a heavier alternator may be better for an engine.

How long is a piece of string?
Thanks. I wasn't aware that the load from the alternator would be dependent on the amount of charge required. I thought it was just a mechanical load that would always be the same.

BTW, I once read that the price of charging up batteries quickly is that it shortens their life.
__________________
ADMPRTR is offline   Reply With Quote
Old 10-09-2011, 11:07   #54
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 19,356
Re: Alternators - What's the Difference?

Quote:
Originally Posted by donradcliffe View Post
Its not the size of the bank, its what you take out of it each day. If you are using the batteries to power the fridge, you will need some more power, be it solar panels, a trolling generator, or the Honda. LED lighting, especially for the main cabin lights and the tricolor, and a netbook instead of a laptop will significantly reduce power requirements. Be sure the the Honda will power the battery charger before you leave--it may work fine when the batteries are near full, but overload when the bank is depleted. I met a boat in Hawaii which had planned to use his 2000i on the passage from the mainland, and ended up running his main engine 8 to 10 hours per day!

Converting your 80 amp alternator to external 3-stage regulation will do more than going to 100 amps, but be sure to carry a spare alternator of some sort. If it were my boat, I would take at least 250 watts of solar panels--they are quiet, reliable, and the more variety in charging sources the better
I'm glad someone finally mentioned it's not the bank size but the daily usage. Most epople are at anchor 80% of the time. A taffrail towed generator will be useless there. Solar or wind gen will usually help. Replacing the alternatorwith a 80-100 amp shouldnt be too big a deal, but will cost some money. The honda will be quieter than the main engine, but you need to store a bunch of gas. .. and a place to do that. It's nice to have options....
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is online now   Reply With Quote
Old 10-09-2011, 11:09   #55
Registered User
 
ADMPRTR's Avatar

Join Date: Jan 2011
Location: Georgian Bay, Ontario, Canada
Boat: CS36 Traditional
Posts: 551
Re: Alternators - What's the Difference ?

Quote:
Originally Posted by Kettlewell View Post
One of the biggest hidden costs is setting up your engine to handle the loads of a 200-amp alternator. You need at least a double belt pulley set up, and very heavy strong brackets. Plus the best belts available. Some are now going to serpentine belt set ups. There will be additional side load on the bearings on your engine too. IMHO, you are much better off going with two 100-amp alternators on opposite sides of the engine, but again there is more engineering involved setting it up. This gives you full time instant back up for the charging system.
So one hidden cost would potentially be extra maintenance for the bearings and belts that are required. Thanks.

I am seriously think of going the solar route and not touching the alternator at all (thought I had a problem but my mechanic just gave it a clean bill of health).

In fact, I was thinking of separating the house circuit from the starter battery completely so that the alternator only charges the starter battery. Has anyone done that?
__________________
ADMPRTR is offline   Reply With Quote
Old 10-09-2011, 11:13   #56
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,579
Images: 240
Re: Alternators - What's the Difference ?

Battery life is directly related to how deep the battery is cycled each time.
If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD.
If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%.
However, a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film.

Typical Cycles vs Depth of Discharge chart ↓
Attached Thumbnails
Click image for larger version

Name:	Battery - Cycles vs DOD.gif
Views:	48
Size:	9.6 KB
ID:	31472  
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 10-09-2011, 11:14   #57
Registered User
 
ADMPRTR's Avatar

Join Date: Jan 2011
Location: Georgian Bay, Ontario, Canada
Boat: CS36 Traditional
Posts: 551
Re: Alternators - What's the Difference?

Quote:
Originally Posted by Cheechako View Post
I'm glad someone finally mentioned it's not the bank size but the daily usage. Most epople are at anchor 80% of the time. A taffrail towed generator will be useless there. Solar or wind gen will usually help. Replacing the alternatorwith a 80-100 amp shouldnt be too big a deal, but will cost some money. The honda will be quieter than the main engine, but you need to store a bunch of gas. .. and a place to do that. It's nice to have options....
I also understand that a taffrail towed generator optimally requires a speed of 8kt which is more than most sailboats can provide. It will work with less but the output is drastically reduced.
__________________
ADMPRTR is offline   Reply With Quote
Old 10-09-2011, 11:18   #58
Senior Cruiser
 
atoll's Avatar

Cruisers Forum Supporter

Join Date: Mar 2010
Location: gettin naughty on the beach in cornwall
Boat: 63 custom alloy sloop,macwester26,prout snowgoose 37 elite catamaran!
Posts: 9,311
Images: 75
Re: Alternators - What's the Difference?

Quote:
Originally Posted by Cheechako View Post
I'm glad someone finally mentioned it's not the bank size but the daily usage. Most epople are at anchor 80% of the time. A taffrail towed generator will be useless there. Solar or wind gen will usually help. Replacing the alternatorwith a 80-100 amp shouldnt be too big a deal, but will cost some money. The honda will be quieter than the main engine, but you need to store a bunch of gas. .. and a place to do that. It's nice to have options....
one of the problems sailing downwind on an east west axis is that solar panels are in the shade half the time due to generally having sails poled out on both sides,also in normal trade winds,10- 15 kts with a boat speed of 5-8 knots your wind gen is not putting out much power.

unless you have a wind vane your fridge and auto pilot are sucking 5+ah,thats
130+ ah in 24 that has to be replaced somehow,unless you dont mind warm beer and hand steering..............towed gens work great 24/7......downwind
__________________
my catamaran building project updates http://www.cruisersforum.com/forums/...36#post2502136
atoll is offline   Reply With Quote
Old 10-09-2011, 11:19   #59
Registered User
 
ADMPRTR's Avatar

Join Date: Jan 2011
Location: Georgian Bay, Ontario, Canada
Boat: CS36 Traditional
Posts: 551
Re: Alternators - What's the Difference ?

Quote:
Originally Posted by GordMay View Post
Battery life is directly related to how deep the battery is cycled each time.
If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD.
If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%.
However, a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film.

Typical Cycles vs Depth of Discharge chart ↓
So it is beneficial to somewhat over estimate the load requirements but not to go crazy. Good to know. Thanks.

The second part of the question is should the alternator be sized to the usage or the bank size or a combination of both?
__________________
ADMPRTR is offline   Reply With Quote
Old 10-09-2011, 11:20   #60
Registered User

Join Date: Jul 2006
Posts: 3,949
Re: Alternators - What's the Difference ?

Quote:
In fact, I was thinking of separating the house circuit from the starter battery completely so that the alternator only charges the starter battery. Has anyone done that?
I have mine set up so that all charging sources (solar and alternator) go directly to the large house bank. I have a dedicated starting battery that gets its charge via a Trik L Start from the house bank when there is excess charging going into that bank. Typically, the starter battery requires very little charging. You shouldn't be cranking your engine over for very long--if you are there is something wrong! Of course there are various switches to parallel battery banks if I need to and to shut them off too.

On your earlier question about the depth of discharge vs. life of the battery bank. I believe the current thinking is that with traditional wet deep cycle batteries you get the most amps per $ over the lifetime of the batteries if your typical discharge is about 50% of capacity.
__________________

__________________
Kettlewell Cruising
Kettlewell is offline   Reply With Quote
Reply

Tags
alternator

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
Does the colour of canvas make a difference ? plottie Construction, Maintenance & Refit 44 30-05-2012 04:28
'Distance to Waypoint' Difference janp391 OpenCPN 1 02-09-2011 09:24
Somali Cruises (with a Difference) Book Early neelie Off Topic Forum 0 20-07-2011 03:34



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 15:50.


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.