Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 07-11-2017, 20:41   #1
Registered User

Join Date: Mar 2017
Posts: 201
Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Now that so many solar setups seem to be able to completely recharge the battery bank, I was curious if there was value in having the option to decouple the alternator when motoring. Has anyone heard of this? What would be the expected increase in efficiency (what percentage of power does an alternator eat)?
__________________

Thalas is offline   Reply With Quote
Old 07-11-2017, 21:08   #2
Registered User
 
ErikFinn's Avatar

Join Date: Feb 2011
Location: Malaysia, Thailand
Boat: Beneteau Oceanis 430
Posts: 860
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Why would you want to do that? Alternator voltage regulator adjusts your alt charging. If your batteries are full (solar charging) the alternator makes no noticeable resistance. If you are motoring at night or when batteries are not full don't you want the alt to charge your batteries? If your batteries are overcooked you have a problem somewhere that you need to find out about.
However some peole have installed an alt on/off switch. I may recall incorrect but doesn't some Balmar regulators have one?
__________________

ErikFinn is offline   Reply With Quote
Old 07-11-2017, 21:08   #3
Registered User
 
four winds's Avatar

Join Date: Oct 2010
Location: Wandering the US Gulf Coast
Boat: 78 Pearson323 Four Winds
Posts: 2,201
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Most likely someone has done this, but I've not heard of it.

Another option would be to put a switch in the field circuit. Open the switch and the alternator has no output. Then you would be just spinning the pulley, bearings, and stator. At zero output the load would be minimal. This I have heard of people doing from time to time.
__________________
Life begins at the waters edge.
four winds is offline   Reply With Quote
Old 07-11-2017, 21:10   #4
Registered User
 
RobTryon's Avatar

Join Date: Oct 2017
Location: Channel Islands Harbor
Boat: Wauquiez Centurion 47.7
Posts: 40
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

I have two Alt's that are switched on and off from the engine panel, simple to do with external excited units.
RobTryon is offline   Reply With Quote
Old 07-11-2017, 22:01   #5
Registered User

Join Date: Mar 2017
Posts: 201
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Quote:
Originally Posted by ErikFinn View Post
Why would you want to do that? Alternator voltage regulator adjusts your alt charging. If your batteries are full (solar charging) the alternator makes no noticeable resistance.
I was not aware that there was intelligent circuitry that could reduce the alternator pull to near zero when not needed. Thanks for the information. Is this a common feature on the majority of marine diesel engines?
Thalas is offline   Reply With Quote
Old 07-11-2017, 22:12   #6
Registered User
 
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 6,981
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Quote:
Originally Posted by Thalas View Post
I was not aware that there was intelligent circuitry that could reduce the alternator pull to near zero when not needed. Thanks for the information. Is this a common feature on the majority of marine diesel engines?
It is a common feature on alternator REGULATORS. Has nothing to do with the engine.

Recommended reading: download and read an alternator regulator man ual from Balmar | Marine Charging Systems | Battery Monitors | Multi-Stage Voltage Regulators | High Power Alternators | Serpentine Pulley Conversions. MC-612 or 614

Will teach you about battery charging, too.

Good luck, happy reading.
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is offline   Reply With Quote
Old 07-11-2017, 22:25   #7
Registered User

Join Date: Apr 2017
Location: Queensland Oz
Posts: 130
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

I had a pre WW11 8 horse power Stewart Turner 2 cylinder 2 stroke petrol engine in a yacht. Stand was an 8 amp starter generator. It had a 35 amp alternator installed by a previous owner, V belt driven off the flywheel. This could stall the engine at idle, if putting out full charge.


I had an external switch installed in the exciter field wiring. With that off the alternator would not start charging. However turning it off would not always stop the alternator charging.


The saving in power was sufficient to make a knot difference to the boats speed. Without the alternator she would do 6 knots in flat calm conditions, & only 5 knots with it.


Remember the thing had only 8 horsepower when new in 1936, & god only knows how many of those had died by 1965, so the power consumption was probably not much.
Hasbeen is offline   Reply With Quote
Old 07-11-2017, 22:34   #8
Registered User
 
ErikFinn's Avatar

Join Date: Feb 2011
Location: Malaysia, Thailand
Boat: Beneteau Oceanis 430
Posts: 860
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Quote:
Originally Posted by Thalas View Post
I was not aware that there was intelligent circuitry that could reduce the alternator pull to near zero when not needed. Thanks for the information. Is this a common feature on the majority of marine diesel engines?
Actually at a basic level the "circuitry" is nothing much smart or expensive, an alt internal regulator, maybe 20 to 40 dollars, and its not "on the engine", it is in the alternator, well usually, and more often so in automobile alternators, which have an internal regulator.
A more appropriate setup in boats is to use an external regulator which you can customize to charge your larger battery bank which may be of a totally different chemistry and qualities than a standard car starting battery.
For being such a simple piece of equipment there is actually a great deal of detailed information a cruiser should know about alternators, and charging batteries, I link a good starter below.

Automotive Alternators vs. Deep Cycle Batteries Photo Gallery by Compass Marine How To at pbase.com

Edit: oh other guys beat me to replying..
ErikFinn is offline   Reply With Quote
Old 08-11-2017, 08:09   #9
Registered User
 
S/V Alchemy's Avatar

Join Date: May 2008
Location: Toronto
Boat: Custom 41' Steel Pilothouse Cutter
Posts: 4,814
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Quote:
Originally Posted by Hasbeen View Post
I had a pre WW11 8 horse power Stewart Turner 2 cylinder 2 stroke petrol engine in a yacht. Stand was an 8 amp starter generator. It had a 35 amp alternator installed by a previous owner, V belt driven off the flywheel. This could stall the engine at idle, if putting out full charge.


I had an external switch installed in the exciter field wiring. With that off the alternator would not start charging. However turning it off would not always stop the alternator charging.


The saving in power was sufficient to make a knot difference to the boats speed. Without the alternator she would do 6 knots in flat calm conditions, & only 5 knots with it.


Remember the thing had only 8 horsepower when new in 1936, & god only knows how many of those had died by 1965, so the power consumption was probably not much.
Some Atomic 4 direct-drive owners (about 17 shp instead of closer to 30 shp) who switched to the 55 amp alternator noticed the parasitic load of the bigger than stock 35 amp Delcos or Prestolite alternators had a noticeable effect on their motoring. I would suggest one approach if one has a dual PTO and the space, would be to mount two smaller alternators, one of which can be "decoupled" for use when motoring in flat seas at, say, five knots. Best of both worlds if you want to use a trip out from an anchorage to pump out beyond the limit while making ice, water or an equalization cycle.
__________________
Can't sleep? Read www.alchemy2009.blogspot.com for fast relief. Can't read? Avoid www.volumesofsalt.blogspot.com, because it's just personal reviews of sea books.
S/V Alchemy is offline   Reply With Quote
Old 08-11-2017, 08:24   #10
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 20,530
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

I had a switch on the control panel to turn the alternator off on a few of my boats. With an external regulator it's easy to do. Not sure there is a lot of reason to do it, up here in the PNW there are some strong currents to 12 knots or so, my theory was if the engine had a problem and overheating, getting rid of the alternator load might be good to make it through. But really it's a nit-pik thing...
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 08-11-2017, 08:37   #11
Registered User

Join Date: Aug 2015
Location: South Coast UK
Boat: Outremer 42
Posts: 137
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

I was thinking of setting up such a system on my cat until I read the smart charger instructions.
What it clearly says is that the smart charger adjusts the alternator output and hence workload to the battery state - the emptier the battery, the more the alternator works. It also doesn't cut in for about 30 seconds after the engine starts and then builds the charge rate up slowly over about 2 minutes to max.

When the batteries are full, the charge rate can be as low as 1 amp on a 600Ah bank, so that's 0.5 amp per alternator. Not really much need for a decoupler, I think. Given that, a smart charger may be more use to you than a switch.
out42 is offline   Reply With Quote
Old 08-11-2017, 08:45   #12
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 20,530
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Quote:
Originally Posted by out42 View Post
I was thinking of setting up such a system on my cat until I read the smart charger instructions.
What it clearly says is that the smart charger adjusts the alternator output and hence workload to the battery state - the emptier the battery, the more the alternator works. It also doesn't cut in for about 30 seconds after the engine starts and then builds the charge rate up slowly over about 2 minutes to max.

When the batteries are full, the charge rate can be as low as 1 amp on a 600Ah bank, so that's 0.5 amp per alternator. Not really much need for a decoupler, I think. Given that, a smart charger may be more use to you than a switch.
That's the function of all regulators not just a Smart Charger.
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 08-11-2017, 09:14   #13
Registered User

Join Date: Jul 2004
Posts: 146
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

It is how any voltage regulator works. Smart or otherwise.


Quote:
Originally Posted by Thalas View Post
I was not aware that there was intelligent circuitry that could reduce the alternator pull to near zero when not needed. Thanks for the information. Is this a common feature on the majority of marine diesel engines?
svJasmine is offline   Reply With Quote
Old 08-11-2017, 09:28   #14
Marine service provider
 
newhaul's Avatar

Cruisers Forum Supporter

Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 4,801
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Quote:
Originally Posted by Thalas View Post
Now that so many solar setups seem to be able to completely recharge the battery bank, I was curious if there was value in having the option to decouple the alternator when motoring. Has anyone heard of this? What would be the expected increase in efficiency (what percentage of power does an alternator eat)?
general rule of thumb for an alternator varies from 1 to 1.5 horse per 50 amp output ymmv.
__________________
Non illigitamus carborundum
newhaul is offline   Reply With Quote
Old 08-11-2017, 09:28   #15
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 14,501
Re: Do boat diesel engines ever use an alternator decoupler/clutch to disengage?

Roughly 750 watts (746~) are equal to one horsepower.
So if your alternator is putting out 14.4 volts at 50 amps, that's 720 watts, or nearly one horsepower, unless I've munged the math again. It needs to steal that one horsepower (plus some overhead and friction losses) from the engine, to make it into electricity.
Offhand I don't know how much the numbers change because of overhead and efficiency.
If you have a conventional older engine using a simple v-belt or ribbed (but not serpentine) to drive the alternator, you might want to invest in a belt tension gauge. Too little tension and you eat belts and lose efficiency. Too much tension, and you wear out the bearings with excess side-loading, and you consume more hp than you need to.
With serpentine belts that have automatic belt tensioners, in theory they take care of themselves. (Until the tensioner fails.)
__________________

hellosailor is offline   Reply With Quote
Reply

Tags
alternator, boat, clutch, diesel, engine

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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
Starter won't disengage Jasonlocke Electrical: Batteries, Generators & Solar 9 25-09-2016 08:22
Raymarine autopilot wont disengage st6002 BalideMAS Marine Electronics 1 13-07-2015 13:15
Starter won't disengage! beebopbogo Engines and Propulsion Systems 33 13-06-2014 19:10
Full Throttle Use & Diesel Engines svfinnishline Engines and Propulsion Systems 26 02-05-2011 01:01
Simrad WP30 Won't Disengage Ocean Girl Marine Electronics 3 13-08-2009 17:38



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 19:37.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.