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Old 01-01-2019, 15:15   #1
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Regulator for 125A alternator?

I am replacing my old MD7A with a new 3YM30 which comes with a 12v 125A alternator. I assume it has an internal regulator and am wondering if that is adequate or if an external regulator should be used. The start battery is charged first through a battery combiner and then the 2 house FLAs.
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Old 01-01-2019, 15:32   #2
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Re: Regulator for 125A alternator?

Internal regulators are "adequate" if they are not the primary charge source for the house bank.

If you intend to run the engine to actually charge the house batteries, then go with a three-stage external regulator.
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Old 01-01-2019, 21:23   #3
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Re: Regulator for 125A alternator?

How big are the 2 batteries? If they are like 27 that alt will never put out much anyways. And I wouldn't be very worried. Vrs say 2 8d's. Then I would be more likly to go external reg.
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Old 02-01-2019, 09:36   #4
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Re: Regulator for 125A alternator?

1. The house bank shopuld get charged first.


2. Depends on the alternator itself that you get regardless of size:


Hitachi/Yanmar Alternators: (by Maine Sail)

Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?

Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. The battery simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.

This is from:

http://forums.sbo.sailboatowners.com...d.php?t=125392

and these, too:

Hitachi Alternator and Smart Regulator Instal Question


Most practical way to upgrade Yanmar alternator?
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Old 02-01-2019, 09:41   #5
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Re: Regulator for 125A alternator?

Quote:
Originally Posted by billknny View Post
Internal regulators are "adequate" if they are not the primary charge source for the house bank.



If you intend to run the engine to actually charge the house batteries, then go with a three-stage external regulator.


I go with this, assuming you live on shorepower and the Boat always leaves the dock fully charged and all the alternator is supposed to do is maintain the charge, then stock is fine, cause it will maintain a charge, just won’t actually do much charging.
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Old 02-01-2019, 13:37   #6
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Re: Regulator for 125A alternator?

Thanks for the replies/info!

Quote:
Originally Posted by Stu Jackson View Post
1. The house bank shopuld get charged first.


2. Depends on the alternator itself that you get regardless of size:




Most practical way to upgrade Yanmar alternator?
My original plan was all charging to House with Echo Charger to Start, but my Electrician suggested the battery combiner to the Start then House and all other sources to House.

The boat does live in a Marina with shore power mostly day-sailing with some Inter-Island. The Hybrid Grp27 Start FLA is only charged by the alternator. The House is just 2 Grp27 90AH FLAs.
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Old 02-01-2019, 13:51   #7
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Re: Regulator for 125A alternator?

this


Smart Ready Retrofit for Yanmar | Balmar


Your new motor with a valeo 120 Amp alternator that has a built in dumb regulator. i would highly recommend the Balmar upgrade.
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Old 02-01-2019, 13:58   #8
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Re: Regulator for 125A alternator?

Get a new electrician, preferably one that understands boating needs. I would suggest that you run all charging to the house bank and charge the start battery through a combiner just as you originally planned.
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Old 02-01-2019, 14:06   #9
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Re: Regulator for 125A alternator?

Quote:
Originally Posted by Thank you dad View Post
this


Smart Ready Retrofit for Yanmar | Balmar


Your new motor with a valeo 120 Amp alternator that has a built in dumb regulator. i would highly recommend the Balmar upgrade.
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Old 05-01-2019, 13:40   #10
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Re: Regulator for 125A alternator?

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Originally Posted by DeepFrz View Post
Get a new electrician, preferably one that understands boating needs. I would suggest that you run all charging to the house bank and charge the start battery through a combiner just as you originally planned.
Really? Why do you think this way is so much better?
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