Alternator questions

jim

Rear Admiral
Joined
Jan 4, 2012
Posts
1,158
Likes
1,355
Location
Rockaway NY and Stuart, Fl
Boat Make
44 John Williams (stanley)
My new(to me) boat is set up strictly as a day boat. No generator, no galley and no bright HPS or MH mast lights for raising bait. A new genset is just not in the budget for this year so I am looking for alternatives that dont involve portables and gasoline(more shit on the deck). The type of fishing I will be doing requires that I am either trolling or idling/running at night so the engine will be running 24 hours for 3-5 day trips. The boat has a 24v starting system and a seperate 12v house bank with two brand new 8ds. It has a brand new leese neville 160 amp alternator(puts out 108amps at idle). I would like to install one 1000w HPS light and two 500w HPS lights and be able to use a microwave,coffee maker or electric frying pan via a large inverter. Nothing crazy like ac or freezer just basic comforts.

With all that said I am planning on adding at least one more 8d(maybe 2) to the house bank which would give me 750ah and was wondering if a second alternator added to the engine would be needed. Or a larger alternator?All the interior lights and running lights are already LED which save alot of power. So it would be the deck lights,electronics and occasional brewing,cooking that would draw off the batteries but with the boat running. I looked at a used novi early last year that could produce over 5kw from his house bank and had a 5kw inverter. He was a lobsterman and always idling/running so had no need for a genset.

If anyone is running something similar let me know how you like it pros and cons. Is a second alternator needed or replace the 160amp with a 250amp? Ive been trying to educate myself on the subject but there is more opinion than fact in what I have read so far.Thanks. Jim
 
Last edited:

kmac

Commander
Joined
Mar 19, 2012
Posts
352
Likes
100
Location
Chesapeake Bay
What type of house batteries? Lead acid batteries should be charged at 12% of the amp hour capacity of the battery bank. i.e. 12 amps for a 100 amp hour battery. AGM batteries can be charged at a much higher amp rating. I think it is 50% but not sure. Google it.
 

Brooksie

Rear Admiral
Joined
Mar 25, 2013
Posts
2,036
Likes
1,215
Location
Cape Cod
Boat Make
Bruno-Stillman 35
No big expert here but for what it is worth...
If I understand you, 3 day trips running 24/7 2000 watts of 12v lights = 166 amps so you have a 60amp shortfall all night long (without considering the other intermitant draws) I think you need a larger alternator.

The above assumes that your alternator is 12v, if 24v, you may be OK because then you will have 2400 watts at idle.
 

jim

Rear Admiral
Joined
Jan 4, 2012
Posts
1,158
Likes
1,355
Location
Rockaway NY and Stuart, Fl
Boat Make
44 John Williams (stanley)
Brooksie the lights will only be used at night and the engine will be idling and running throughout the night and trolling during the day so the alternator should put out more than 108 most of the time. I will also have 750-1000 amp hours in reserve in the batteries. At least this is my take on it but also why I am asking. House is 12v.
KMAC...I havent taken ownership of the boat yet so Im not exactly sure the battery type but will find out tomorrow.
 

jim

Rear Admiral
Joined
Jan 4, 2012
Posts
1,158
Likes
1,355
Location
Rockaway NY and Stuart, Fl
Boat Make
44 John Williams (stanley)
Brooksie sorry I misunderstood you. Im not sure if its a 12v or 24 v alternator. All I know is the starting system is 24v and the house is 12. I will find out tomorrow.
 

Keelboater

Admiral
Joined
Oct 3, 2013
Posts
6,398
Likes
4,907
Location
Clinton Harbor
Boat Make
35' Bruno & Stillman
I'm not sure of one thing here so maybe someone can answer this for me - Are alternators rated as continuous duty? Meaning that this one can countiuously provide 160 amps without going up in flames? I'm not so sure that they are, but I could be wrong. Jim, you might want to confirm this before sizing any loads.
 

petrel

Rear Admiral
Joined
Dec 17, 2011
Posts
1,583
Likes
381
Location
NC
Boat Make
56' DMR, 31' BHM
Alternators don't charge so much at low rpms; keep that in mind.
 

petrel

Rear Admiral
Joined
Dec 17, 2011
Posts
1,583
Likes
381
Location
NC
Boat Make
56' DMR, 31' BHM
Damn, I wouldn't have figured that. I'm pretty sure mine don't come as close to capacity at idle.
 

jim

Rear Admiral
Joined
Jan 4, 2012
Posts
1,158
Likes
1,355
Location
Rockaway NY and Stuart, Fl
Boat Make
44 John Williams (stanley)
Im waiting to hear back from the current owner. Brooksie and KMAC both brought up good points. If the starting system is 24 volt Im now assuming the alternator must be 24 volt in which case there must be a converter in order for that alternator to charge the 12 volt house bank. A generator is so much easier BUT the fact that the engine will always be running it should be able to produce the small 3kw load I need. I also need to know the battery type but I believe they are AGM.
 

Keelboater

Admiral
Joined
Oct 3, 2013
Posts
6,398
Likes
4,907
Location
Clinton Harbor
Boat Make
35' Bruno & Stillman
Found this on West Marine regerding alternators FWIW:

Battery capacity

As we add electrical and electronic appliances to our boats, we notice that our battery banks have become incapable of handling the loads created by these new stereo subwoofers, floodlights, satellite TV systems, refrigerators and other thirsty power consumers. We start shopping for bigger battery banks, or consider adding a battery. Adding battery capacity requires us to take a look at our charging system.

In most cases, your alternator’s output should equal the maximum available capacity of your battery bank. In other words, if your house battery bank is made up of flooded batteries with an amp-hour capacity rating of 400Ah, the maximum acceptance rate of those batteries would be 25 percent, or 100 amps, the ideal alternator would also be rated at 100 amps.

If your house bank consisted of 400Ah capacity AGM batteries, the maximum available capacity would be 45 percent of 400, or roughly 180 Ah. To maximize charging efficiency, a 180-amp rated alternator would be required.
 

jim

Rear Admiral
Joined
Jan 4, 2012
Posts
1,158
Likes
1,355
Location
Rockaway NY and Stuart, Fl
Boat Make
44 John Williams (stanley)
Ok just heard back from the owner. The boat is set up with two alternators. The 24volt for starting system and a 12 volt 160 amp for the house batteries. The house alternator has a smaller than standard wheel which spins the alternator at a higher rpm at idle. This produces more tham 108amps and actually produces closer to 140 amps at idle. So now the question is how do I figure out how many amp output and how many 8ds I will need to run a 4kw inverter with a 3kw load without draining the house overnight. The batteries are AGM
 

samhop

Lieutenant Commander
Joined
Sep 16, 2012
Posts
136
Likes
35
The 160amp alternator on the boat now puts out 108amps at idle

(edit) ak so you have 2 alt. step down the 24v with a 12v feed to you house set. something like this http://www.powerstream.com/dc1-extreme-50A.htm

if your starting 24v than your alt would also be 24v. you might be stepped down to 12 for your electronics but 12v alt. being stepped up to 24v for a starter is something new to me.

output sounds high to me how did you determine idle output? advertised and actual are often different. goosing up output with a small drive is ok but what is your max alt. rpm at cruse.

if it really puts out that much 24v, why go to the bigger bank if your running all night. two wet d8= about 500ah that should hold up to your inverter loads. if your dc voltage starts dropping jest goose up the main to 1000 or 1200 rpm till your intermittent lode frying pan :confused: is off line.
 
Last edited:

jim

Rear Admiral
Joined
Jan 4, 2012
Posts
1,158
Likes
1,355
Location
Rockaway NY and Stuart, Fl
Boat Make
44 John Williams (stanley)
Sam there are two alternators. A 24 volt and a 12 volt. The 24v is strictly for the starting system. I dont want to mess with the starting system.So its just the house bank we are talking about. The 12 volt 160 amp alternator is for the house bank. There are currently 2 8d agm batteries in the house bank. I was thinking of adding a third(750ah) to get me thru the night with no problems. The engine will be running between idle and cruise(1400 rpm) all night long so I dont see much of a problem with the DC dropping. My original question was about adding a second alternator but I just found out from the seller it has a second alternator. My next questions are do I need a higher output alternator and will a third 8d house battery help or hurt the system. Sam the idle output is 108...the seller tested it. He gets that output because he put a smaller pulley on the alternator which makes her spin faster at idle RPM because he idles most of the day while fishing. Not sure of the max output at cruise.
 
Last edited:

Keelboater

Admiral
Joined
Oct 3, 2013
Posts
6,398
Likes
4,907
Location
Clinton Harbor
Boat Make
35' Bruno & Stillman
Jim, you didn't mention what the amp-hour rating is on the two existing house batteries. You said adding a third 750 Ah battery might be in the cards. All AGM type. If you have 750 Ah battery bank, the maximum available capacity is 45% of this, or 337 Ah. The alternator should match at 337 amps to maximize charging if I interpret the WM article correctly.

On the battery side, a 3000 watt load/12vdc = 250 amps. Yikes!
 

samhop

Lieutenant Commander
Joined
Sep 16, 2012
Posts
136
Likes
35
sounds like the setup was well planed out. at 100amp 12v your a little light to run your lights, the batteries will buffer extra intermittent lode. but adding an extra battery you would be cycling the battery, ok with agm/gel but not ideal wet. your running all the time so why not meet your base need? you have a 24v alternator that is available but doing nothing because all its has to do is charge the starting battery but your running all the time your starting bat is pretty well topped up. your 24v alt can be used to ogment your 12v charging system on an isolated cerkit without compromising your starting setup. jest an option you seen to understand what you would like to do. my experience tells me to meet my need rather than add capacity and cycle batteries. so det a bigger 12v or use your 24v its alredy there and doing much.
 

jim

Rear Admiral
Joined
Jan 4, 2012
Posts
1,158
Likes
1,355
Location
Rockaway NY and Stuart, Fl
Boat Make
44 John Williams (stanley)
Yeah Keel Im missin something here. Every big Novi i looked at last year fished 100+ miles offshore and had no generator. Just big inverters. I saw more than a few boats with 5kw inverters and 3 or four AC crab lights on the mast. The novis all have slow turnin, low HP engines. It shouldnt be too difficult to do the same here but I guess I have to get a marine electrician to figure this out. Thanks for the help. Ill let you know how it turns out.
 
Top Bottom