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 26-05-2020, 07:04   #1
Registered User

Join Date: Mar 2015
Location: Sail out of Mahone Bay, Nova Scotia
Boat: Bayfield 29C Cutter
Posts: 10
55 Amp Alternator - Is this standard?

My new to me boat has a Yanmar 2GM20F. This is my first boat with an inboard diesel.

There's a 55 amp alternator which I think is standard. I'm doing up a power budget and will probably find this to be sufficient as my electronics and lights don't draw much.

My question is: is it common to replace an alternator with a high output version? (that is, if my power budget suggests I should). The boat is a sailboat so engine usage is minimal. Or would it make more sense to add solar panels?
__________________

and4ew is offline   Reply With Quote
Old 26-05-2020, 07:30   #2
Registered User

Join Date: Dec 2006
Location: Seattle
Boat: Cal 40
Posts: 2,613
Images: 7
Re: 55 Amp Alternator - Is this standard?

Yes it's common to upgrade alternators, but less common on your size engine/boat.
You probably don't have a large battery bank. Batteries accept less current as they become charged. Your battery will probably not accept the full output of your alternator after a short time.

It takes time to charge a battery, so running the engine for a short time will not bring the battery back to nearly full charge. Solar panels charge long term, but take a fair amount of area. You'll have to complete your power budget to get an idea of how much square footage you'll need.

I have a friend with a 100 amp alternator on an Atomic 4. He had to buy a 3 stage regulator with a time delay, which disabled the alternator for the first 30 seconds so the engine wouldn't stall when started.
__________________

cal40john is offline   Reply With Quote
Old 26-05-2020, 07:50   #3
Registered User

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 4,864
Re: 55 Amp Alternator - Is this standard?

A lot depends on how you plan to use the boat. Daysails, Weekends, or full time liveaboard?
donradcliffe is offline   Reply With Quote
Old 26-05-2020, 07:54   #4
Registered User

Join Date: Nov 2013
Location: Nice, France
Boat: Hunter Marine 38
Posts: 879
Re: 55 Amp Alternator - Is this standard?

I have installed a lot of solar capacity, but in your cruising area I don't think I would do that.
sailormed is online now   Reply With Quote
Old 26-05-2020, 07:58   #5
Senior Cruiser
 
tkeithlu's Avatar

Cruisers Forum Supporter

Join Date: Feb 2012
Location: Carrabelle, Florida
Boat: Fiberglas shattering 44' steel trawler
Posts: 2,086
Re: 55 Amp Alternator - Is this standard?

John speaks with wisdom. I'll add: Alternators that come with engines are usually sized to recharge the starting battery. If you do have much of a battery bank, you'll want to consider an upgrade. If you go to the smaller sizes of Balmar alternators, plus their programmable voltage regulator, you can have an alternator charging system that emulates a really good automatic battery charger. The combination of Balmar rig (engine running) and good marine battery charger (shore power, genset) keeps your system sweet.

When you do your energy budget, do not count on 55 amps from your exisiting alternator. If you really did that, you would (as I did) burn up your alternator pretty quickly. Think about needing half its wide open amperage.

Given a sailboat and all your lights on LED, It may just be that a bigger battery is the solution if you have enough charging power with only occasional engine use. Do be aware that (dare I say it) I've seen a lot of cruising sailboats under power offshore on what appeared to me to be really good sailing days. Whatever the cause (destination upwind?), you may use your engine longer than just getting in and out of the marina.

Solar? Got the space? Genset? Place to put it? There's been discussion on the forum on how to mount a Honda 2200 off the transom of smaller cruising boats.
__________________
Never let anything mechanical know that you are in a hurry.
tkeithlu is offline   Reply With Quote
Old 26-05-2020, 08:22   #6
Registered User
 
BlackHeron's Avatar

Join Date: Jan 2016
Location: Summering on the Chesapeake
Boat: Hallberg-Rassy Rasmus 35
Posts: 576
Images: 18
Re: 55 Amp Alternator - Is this standard?

It depends on how much power you use. We have a standard alternator but never run the diesel auxillary engine to charge batteries. We are perfectly able to keep the batteries charged and reach equalization charge every day that the sun shines with only 250w of solar panels and a very ancient wind turbine that rarely produces more than 25-30 watts. At 10 knots it barely produces 10w.

We haven't plugged into shore power in over six months and the engine has not been started in over two due to Coronavirus and basically just hunkering down on anchor.

It's all about keeping energy consumption low. Our four simple 6v lead acid flooded golf car batteries rarely see voltages under 12.6v at the end of a long still night with no sun or wind charging. If it is a sunny day we usually see 14.65v by noon again, and the charge controller shuts down happy that equalization has been completed, only putting enough power in as we are using from that point on.

If you want not use more and more power power then you are going to need to generate and store more and more power. If you are leaning on your auxiliary diesel engine to produce power on anything but very occasional exteme circumstancial uses then you have not designed your system correctly. Diesel boat engines make very poor generator sets and are a huge waste of recourses.
BlackHeron is offline   Reply With Quote
Old 26-05-2020, 08:50   #7
Registered User

Join Date: Dec 2011
Posts: 11
Re: 55 Amp Alternator - Is this standard?

I have a 2GM20F in my Island Packet 27. I used to use the 12v refrigerator when cruising and it drew down the batteries quickly. We were anchored in Marathon and there was a shop onshore that took trade ins for high cap alternators. I replaced the OEM alternator with a 110 amp model.

Yikes! Not only was there a big drop in RPM when the A/B switch was changed to a low battery for charging... I also started to destroy the 1/2" belts after only a few hours of sailing. Black rubber belt dust covered the engine compartment and belts often failed at the worst times. Overheating the engine while approaching a drawbridge, or entering a tricky inlet because a belt failed is neither safe nor fun.The reduced horsepower from the drag caused by the alternator was a serious safety issue too. Don't get greedy like me. 55 amps is fine now that I don't use the reefer, and life is more relaxing and fun after getting the alternator re-wound at an alternator shop back to stock amperage. Happy sailing!
SRQsailor is offline   Reply With Quote
Old 26-05-2020, 09:16   #8
Registered User

Join Date: Oct 2014
Location: Panama City Beach, FL
Boat: Beneteau 343
Posts: 357
Re: 55 Amp Alternator - Is this standard?

IMHO, it would be more accurate to say it is not uncommon to upgrade alternators as opposed to saying it is common. Sorry if that seems a silly distinction. I have thought about it but 220 watts of solar seems to have me a pretty good position.
EmeraldCoastSailor is offline   Reply With Quote
Old 26-05-2020, 09:29   #9
Registered User

Join Date: Aug 2016
Posts: 7
Re: 55 Amp Alternator - Is this standard?

I don't recommend a high output alternator on a 2 GM30. I switched from a 30 amp to a 100 amp alternator and blew through belts on a near monthly basis and like SRQsailor I covered my engine in belt dust and filth in the process. When I finally gave up and switched to a 50 amp alternator everything is fine. BTW there is a reason why Yanmar says you void your warranty if you put a higher amp alternator than they recommend.
Hankasail is offline   Reply With Quote
Old 26-05-2020, 09:32   #10
Registered User

Join Date: Sep 2017
Location: Langley, WA
Boat: Nordic 44
Posts: 1,222
Re: 55 Amp Alternator - Is this standard?

Quote:
Originally Posted by sailormed View Post
I have installed a lot of solar capacity, but in your cruising area I don't think I would do that.
The op did not say where he/she sails or the boat size. Obviously a smallish boat from the engine size.

Pet peeve of mine: Update your profile - you will get better answers with better supplied information.

We have very long summer days here in the Pacific northwest. Solar works very well here. My boat is at anchor in the summer and I keep a five cubic foot refer running all the time. 390 watts of solar. Batteries always full.
stormalong is offline   Reply With Quote
Old 26-05-2020, 09:36   #11
Registered User

Join Date: Sep 2013
Location: Alert Bay, Vancouver Island
Boat: 35ft classic ketch/yawl.
Posts: 1,799
Images: 4
Send a message via Skype™ to roland stockham
Re: 55 Amp Alternator - Is this standard?

The important thing with electrical systems is that they work as a complete balanced system. Simply increasing alternator output is likely to cause more problems than it solves. Start with the power budget then size the batteries to provide 24hrs to 60% DoD (regardless of battery chemistry, this is to give sufficient safety reserve). Once you have a house bank size then look at the alternator. This may depend somewhat on bett chemistry but the general range is to have an alternator capable of recharging between C5 and C7 (i.e. at max is 1/5 to 1/7 of battery amp hours). BUT, very importantly you need to look at the complete charging system. Putting a C5 alternator on without fitting a smart regulator or upgrading the wiring will not increase charging. Seams quite common for people to fit high output alternators and be disappointed in the result because the alternator is throttled down at some point in the charging system.
So overall I would say upgrading the alternator my be useful but should be the last thing in a chain of upgrades. Often the most effective changes are the cheapest such as reducing voltage drop between the alternator and battery by upgrading wiring and switches.
roland stockham is offline   Reply With Quote
Old 26-05-2020, 09:40   #12
Registered User

Join Date: Sep 2013
Location: Montreal
Boat: Dufour 39 Frers
Posts: 301
Re: 55 Amp Alternator - Is this standard?

Something you need to consider is your battery bank maximum charge rate.

For instance, lead acid charge rate is around 15% to 20% in bulk mode. Say you have 100 amp/h battery bank, maximum charge rate on the battery should be 20 amps/h to avoid damaging the cells.

In such a case a 55amps/h alternator is more than enough.
Note also the alternator is usually thermal regulated: after a few minutes at 55 amps/h output, it will become very hot, and to prevent cooking, it will reduce it amps output.

On the other end of the spectrum, if you have lithium-Ion batteries, they can take all what the alternator can deliver...
Emouchet is offline   Reply With Quote
Old 26-05-2020, 09:49   #13
cruiser

Join Date: Jan 2009
Location: Cabo Verde
Boat: Bruce Roberts Spray, 36' Steel Junk-Rigged Schooner
Posts: 1,245
Images: 26
Re: 55 Amp Alternator - Is this standard?

Quote:
Originally Posted by and4ew View Post
My new to me boat has a Yanmar 2GM20F. This is my first boat with an inboard diesel.

There's a 55 amp alternator which I think is standard. I'm doing up a power budget and will probably find this to be sufficient as my electronics and lights don't draw much.

My question is: is it common to replace an alternator with a high output version? (that is, if my power budget suggests I should). The boat is a sailboat so engine usage is minimal. Or would it make more sense to add solar panels?
Be aware that, even with a larger alternator, if you are running the engine out of gear just to generate power you will coke up your cylinders with unburnt fuel.
Captn_Black is offline   Reply With Quote
Old 26-05-2020, 09:53   #14
cruiser

Join Date: Jan 2009
Location: Cabo Verde
Boat: Bruce Roberts Spray, 36' Steel Junk-Rigged Schooner
Posts: 1,245
Images: 26
Re: 55 Amp Alternator - Is this standard?

Better off downsizing your power use or using solar or wind.
Captn_Black is offline   Reply With Quote
Old 26-05-2020, 10:09   #15
Registered User

Join Date: Nov 2010
Location: UK, Croatia
Boat: Fountaine Pajot Athena 11.6m Rapa Nui II
Posts: 587
Re: 55 Amp Alternator - Is this standard?

Fitting a larger alternator and external regulator cannot do any harm except to your wallet and belts and even may do some good if you use the engine a lot. But engine charging will never get the batteries back to 100% on a regular basis which you need to do for reasonable battery life unless you motor all day.
Solar is far more cost effective at providing power than fitting an uprated alternator and external regulator. In the UK, you can now get quality solar 250 - 300 W panels for 100-120. It's silent and carries on charging while there is daylight. The only issue is whether the is enough real estate on the boat to fit enough.

Adding a minimal amount of solar will at least allow the batteries to recharge to 100% in the idle periods when the boat is not in use. Adding more can enable you to recharge to 100% each day while in use. Our cat has 480W of solar, 360Ahr of batteries, 160 litre fridge and lots of electronic toys, heat water with electricity, and we normally get back to 100% purely by solar each day. Our engines have the stock Yanmar 80A alternator and you may see 40A charging at startup dropping back to <20A very quickly.
Basically, if you can fit any solar, do it first and then evaluate whether you need to address the alternator/regulator.
__________________

Rapanui is offline   Reply With Quote
Reply

Tags
alternator

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
Firefly (and standard AGM) alternator requirements Kevin Spacebag Electrical: Batteries, Generators & Solar 0 15-05-2020 07:20
For Sale: Cruising Guides FL, Abaco &amp;amp;amp;amp; Exumas dworkman General Classifieds (no boats) 0 12-04-2020 12:34
For Sale: Balmar Regulator, 100A Alternator & 35A alternator JimJohnston General Classifieds (no boats) 0 07-10-2018 19:36
High Rated Alternator with Alternator to Battery Charger Rumbero Electrical: Batteries, Generators & Solar 113 18-07-2014 05:29

Advertise Here


All times are GMT -7. The time now is 14:19.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.