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10-19-2017, 10:24 AM
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#1
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Senior Member
City: La Conner, WA
Vessel Name: Agnus Dei
Vessel Model: 36' Shin Shing
Join Date: Sep 2014
Posts: 276
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Two Alternators
Hi All,
2 owners ago, the guy used this 36' trawler for fishing. He noticed the stock alternator didn't really charge batteries at idle, so he installed a second alternator, strictly for the purpose of trying to get the batteries some charge while trolling at idle.
Bring us up to date. I have an 8D for starting the beast and 2 sets of 6V GCB's for HOUSE 1 and HOUSE 2, shore power (of course), a generator and a monster inverter/charger. That 2nd alternator is a PAIN in the rear for trying to move around down below. If it wasn't for the fact I'm very limber and can squeeze into tight spaces, there's no way to easily get to anything in front of or on the port side of the engine.
The original alternator has a 12g Orange wire that disappears into the engine wiring harness. The second alternator has an 8g wire right to the batteries via an amp gauge.
Does anyone see an issue with me removing the second alternator and not being able to sustain electrical systems while under way?
Dave
__________________
GOD, Family, career
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10-19-2017, 10:48 AM
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#2
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,119
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Not crazy about 12ga disapperaring as your charge wire.
I prefer a heavy wire straight to your desired battery bank with appropriate fusing.
Depending on the alternater rating yes...as long as you dont draw more than 50 percent of your rating for other than charging.
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10-19-2017, 11:35 AM
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#3
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TF Site Team
City: Jacksonville
Join Date: Nov 2008
Posts: 11,670
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If your using your boat for low rpm travel such as trolling, you may not have enough pulley rpms to charge your batteries and/or keep your house 12 VDC systems alive. Here’s an alternator output curve from Balmar.
Alternator Output Curves | Balmar
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10-19-2017, 11:39 AM
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#4
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Guru
City: Brookline, NH
Vessel Name: Shalloway
Vessel Model: Defever 44, twin Perkins
Join Date: Sep 2013
Posts: 2,259
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If the "second" alternator is in your way but of higher output than the other, why not move the higher output alternator to where the first one is?
BTW - unless the alternator output is very low, 12GA is too small. Even the 8ga used on the "higher output" alternator sounds too small - and it should go straight to a battery bank and be properly fused.
Ken
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10-19-2017, 11:47 AM
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#5
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Technical Guru
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
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My Balmar alternator (100A) output can be outstripped by load when running slow at night with everything on. Volts drop from 13.8 to to around 13. If it goes into the low 12's I just crank up the gennie and use the charger to augment. Only had to do it a few times.
When trolling (daytime) I run super slow (650rpm, about 5.5-6kts but DC load is less so volts stay up.
I would consider getting rid of the second alt. If you have volt drop issues, you may be able to find a higher output alt that fits where the factory one goes.
Take the belt off the second one and see how your volts do. If ok, take the thing off.
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10-19-2017, 11:50 AM
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#6
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TF Site Team
City: Jacksonville
Join Date: Nov 2008
Posts: 11,670
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Are you sure the 12 and 8 gauge wires are the output wires from the alternator to the battery and not for gauges? 12 gauge wire rating is somewhere around 20 amps and 8 gauge wire is ~50 amps. The wire run length and temperature will affect the capacity of the wire also. What size alternators are they?
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10-19-2017, 12:11 PM
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#7
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Guru
City: Cape May, NJ
Vessel Name: Irish Lady
Vessel Model: Monk 36
Join Date: Dec 2007
Posts: 4,947
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Taking a SWAG. Do your dash instruments have an ammeter? Usually where the alternator output goes if it leaves the engine harness for parts unknown. It will come back, sometimes orange with a color stripe.
The other place the orange may show up is the starter solenoid terminal that the battery cable connects.
__________________
Archie
Irish Lady
1984 Monk 36 Hull #46
Currently in Cape May, NJ
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10-19-2017, 12:15 PM
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#8
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Senior Member
City: La Conner, WA
Vessel Name: Agnus Dei
Vessel Model: 36' Shin Shing
Join Date: Sep 2014
Posts: 276
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Quote:
Originally Posted by Larry M
Are you sure the 12 and 8 gauge wires are the output wires from the alternator to the battery and not for gauges? 12 gauge wire rating is somewhere around 20 amps and 8 gauge wire is ~50 amps. The wire run length and temperature will affect the capacity of the wire also. What size alternators are they?
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Is it possible he was charging batteries from the second and running gauges etc. from the other? Is that possible?
__________________
GOD, Family, career
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10-19-2017, 12:15 PM
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#9
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Senior Member
City: La Conner, WA
Vessel Name: Agnus Dei
Vessel Model: 36' Shin Shing
Join Date: Sep 2014
Posts: 276
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Quote:
Originally Posted by Ski in NC
My Balmar alternator (100A) output can be outstripped by load when running slow at night with everything on. Volts drop from 13.8 to to around 13. If it goes into the low 12's I just crank up the gennie and use the charger to augment. Only had to do it a few times.
When trolling (daytime) I run super slow (650rpm, about 5.5-6kts but DC load is less so volts stay up.
I would consider getting rid of the second alt. If you have volt drop issues, you may be able to find a higher output alt that fits where the factory one goes.
Take the belt off the second one and see how your volts do. If ok, take the thing off.
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I'll try that. Thanks. I will also get some specs on the primary alternator.
__________________
GOD, Family, career
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10-19-2017, 02:24 PM
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#10
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Guru
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116 2008
Join Date: Oct 2017
Posts: 10,595
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I have a second alternator. I keep it in the spare parts locker in case the installed alternator fails.
Yea, I know, not the same. LOL
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Two days out the hospital after a week in the hospital because of a significant heart attack.
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10-19-2017, 02:26 PM
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#11
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Guru
City: Adelaide
Vessel Name: Kokanee
Vessel Model: Cuddles 30 Pilot House Motor Sailer
Join Date: Jul 2012
Posts: 3,218
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Quote:
Originally Posted by Dave_E
Hi All,
Does anyone see an issue with me removing the second alternator and not being able to sustain electrical systems while under way?
Dave
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Tough to say Dave. What is your electrical load is while underway? And what is the output of your other alternator at cruising speed?
If your load is higher, it's obviously not sustainable.
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10-19-2017, 02:29 PM
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#12
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Guru
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116 2008
Join Date: Oct 2017
Posts: 10,595
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There is/was something called a cruise generator. It was mounted to the propeller shaft.
__________________
Two days out the hospital after a week in the hospital because of a significant heart attack.
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10-19-2017, 02:36 PM
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#13
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TF Site Team
City: Jacksonville
Join Date: Nov 2008
Posts: 11,670
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Quote:
Originally Posted by Dave_E
Is it possible he was charging batteries from the second and running gauges etc. from the other? Is that possible?
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One alternator could be for the starting bank and the engine gauges. The other alternator could be for House 1 and House 2.
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10-19-2017, 02:48 PM
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#14
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Guru
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116 2008
Join Date: Oct 2017
Posts: 10,595
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None of us are as rich as Rockefeller and none of us are certified marine electricians.
Before you start removing and modifying the electrical stuff, it would be worth the money to get a marine electrician out to look at the installation and trace the wires.
WE can cause more and expensive damage than necessary.
__________________
Two days out the hospital after a week in the hospital because of a significant heart attack.
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10-20-2017, 07:44 PM
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#15
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Guru
City: Fort Myers, FL... Summers in the Great Lakes
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 12,817
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Have 2 alternators on my engine. 2nd charges house batteries and has an external 3 stage regulator. If you plan 2 cruise and anchor out, it will save you countless hours of generator time. I would get an external regulator and use it for a year before making a bad mistake.
Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
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10-21-2017, 12:36 AM
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#16
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Guru
City: Seattle
Vessel Name: AZZURRA
Vessel Model: Ocean Alexander 54
Join Date: Aug 2017
Posts: 4,280
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You really should have an electrical plan for the whole boat. In order to come up with that plan you need to know how you plan to use the boat.
If you have no generator and you need to charge your batteries from a single engine, you will want a 100+ amp alternator that uses an external three stage voltage regulator. This allows charging at 14.1 volts.
If you just want to maintain while cruising then an eighty amp single wire alternator is all you will probably need. Single wire alternators have built in voltage regulators and produce 13.8 volts.
There is a lot more to this subject, this is only scratching the surface.
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10-21-2017, 05:23 AM
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#17
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,119
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It want uncommon for 80s vintage boats to have the alternator charge wire go to an ammeter as someone already posted then return to the batteries.
I had it on my last boat and fixed it on a few others. Usually an orange wire, way undersized.
Not hard to identify the batt output of an alternator and follow where the wire goes.
Not every job requires a certified anything. Thst is why box stores and libraries are filled with DIY books. All you have to be is smart enough when you are in over your head. Lacking that or not that energetic or in a rush...sure, then call a pro if the can fit you in when you need them.
Oh, and lots of "pros" arent really all that good in the marine trades so you have to ask around and then for credentials.
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